Know that if you do not post in this thread today the human race may cease to exist

Posted by: MidnightX

Know that if you do not post in this thread today the human race may cease to exist - 27/12/06 10:35 PM

...so post something interesting by tomorrow morning.

GO!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:02 AM

here you go just for you fabuliziouis..

It is prob. a repost but its still worth a good laught.. Linky
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:12 AM

How about this.....lets see if this can get to the ALR:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?
Posted by: MidnightX

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 03:22 AM

Quote:
Originally posted by Hawk:
How about this.....lets see if this can get to the ALR:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?
Is the answer offensive? Is that why it could end up in the ALR? I say yes it can take off because it will still be able to reach maximum speed. But then again, it won't have that forward momentum it needs because it would be stuck in the same place. Does it really need that forward momentum, though? Hmm... this seems scientific. I should be a physics major to understand this, no? Too complicated.

NEXT INTERESTING POST, please!

Sincerely,
A Fan of Hootus'
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 03:27 AM

Quote:
Originally posted by Hawk:
How about this.....lets see if this can get to the ALR:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?
No there would never be any wind going over the wings. In essence the plane would be standing still?

The wheels would be going. But no wind means no lift.

God I hope that sounds right
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:07 AM

The plane would take off. It should even travel down the runway, no matter how fast the treadmill spun.

An aircraft pushes air, not pavement (or tread). The wheels would just spin at twice the normal rate.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:35 AM

yea, the jets would push it fwd, but the wheels would be spinning backwards. hope he doesnt have to use the brakes to keep it straight. i guess it also depends on the plane too. i'll have to email that to the aerospace engineers i use to work with and see what they say.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:49 AM

Yeah - the jets push air...and the tires are merely supporting the weight, not providing propulsion....so the tread mill would make the tires spin at double the ground speed....due to the conveyor MATCHING the plane's speed...IE: IF the plane isn't moving, the conveyor isn't moving.

Assuming that the conveyor matches the gound speed, the tires would not go backwards...as by "opposite direction", it seems to mean that its merely moving akin to a tread mill, towards the front of the plane, as the plane is trying to move forward....so the plane would never be moved backwards from a rest (No thrust) either.

The tires would just be rolling at double their normal take off speed, as the conveyor is MATCHING the speed of the PLANE...so as far as the tires are concerned, the tarmac is rolling along under them at double the plane's speed....whatever THAT is.

If "Opposite" means that it would push the plane FOWARD if it wasn't MATCHING the plane's speed...(Like a tread mill where the tread is coming from behind you, instead of the normal travel TOWARDS you, then it would not spin the tires backwards or fowards from a normal take off....but that makes no sense in this context...as its the plane's speed that is being matched, not the tire speed...IE: The tires would not roll at all. laugh

Steering/braking would of course be crazy, but, assuming the question is really to differentiate between able to move forward or not, I'd go with yes, it could take off from a propulsion standpoint...as the jets don't need tires to roll, skids or pontoons work for planes too.

laugh

IE: It would be able to take off as far as propulsion goes....the tire speed is irrelevant...but just double the airspeed.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:52 AM

The plane takes off.

The engines push the plane, the wheels don't.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 05:17 AM

Timmy's parents had 3 children. The first was named Quarter, the second named Dime. What was the third childs name?
Posted by: Rickster43

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 05:37 AM

Quote:
Originally posted by DBAX:
Timmy's parents had 3 children. The first was named Quarter, the second named Dime. What was the third childs name?
Nickel...
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 05:45 AM

Quote:
Originally posted by DBAX:
Timmy's parents had 3 children. The first was named Quarter, the second named Dime. What was the third childs name?
Timmy.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 05:58 AM

penny. which would make him a few cents short of a nickel.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 05:58 AM

The engines may indeed push the plane, but if the plane is on a conveyor belt moving in the opposite direction at the same speed that the engines are pushing the plane, it's still not gonna go anywhere. Unless it's a harrier jump jet - British Engineering can overcome this scenario smile

Me and my friend at work have been arguing about one of these kinda things for a few weeks now.

He says that if you fire a bullet from a gun perfectly level with the ground, then drop a bullet from the same height at the same time, both will hit the ground at the same time, as the Gravitational pull on both bullets is the same.

I call Bullshit as the aerodynamic flow over the bullet and the velocity of the bullet has to play into it somewhere.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 06:15 AM

Quote:
Originally posted by RiNkY:
The engines may indeed push the plane, but if the plane is on a conveyor belt moving in the opposite direction at the same speed that the engines are pushing the plane, it's still not gonna go anywhere. Unless it's a harrier jump jet - British Engineering can overcome this scenario smile

Me and my friend at work have been arguing about one of these kinda things for a few weeks now.

He says that if you fire a bullet from a gun perfectly level with the ground, then drop a bullet from the same height at the same time, both will hit the ground at the same time, as the Gravitational pull on both bullets is the same.

I call Bullshit as the aerodynamic flow over the bullet and the velocity of the bullet has to play into it somewhere.
The bullet that was just dropped would hit the ground first.
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 06:24 AM

I think what he meant to say is hold it horizontal to the ground not aim it at the ground.

That could make sense.

But I still hold true to the plane taking off. It is all about getting lift. If the runway is moving the plane will never gain speed even if the engines are pushing it. Speed causes air to flow over the wing causing lift etc.

My opinion anyway
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 06:31 AM

Quote:
Originally posted by Paul H:
I think what he meant to say is hold it horizontal to the ground not aim it at the ground.

That could make sense.

But I still hold true to the plane taking off. It is all about getting lift. If the runway is moving the plane will never gain speed even if the engines are pushing it. Speed causes air to flow over the wing causing lift etc.

My opinion anyway
Yea I edited my post. I also agree that the plane would not take off. If I am reading the question correctly the plane is standing still since it's going the same speed as the treadmill. The plane still needs air to flow over the wings to cause lift. The plane would have to be travelling twice as fast as the treadmill before taking off.

F1 teams that test there cars in wind tunnels usually put the car on a "treadmill" to simulate speed since aerodynamics differ between a stationary car and a car that is moving (obviously these are open wheeled cars). If you just leave the "treadmill" on and take away the wind in the tunnel you would not get any readings on the downforce of the front and rear wings since no wind is acting on the wings.
Posted by: MidnightX

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 06:41 AM

This thread got boring REALLY fast.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 06:43 AM

The plane takes off.

The engines are on the WINGS. Wheels just spin.

CO4x4.org thread
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 06:58 AM

Air Speed vs Ground Speed.

The plane is in 1 place, even if it's going 1,000mph Ground Speed because the runway is travelling at the same speed in the opposite direction. There is no lift being generated by the flow of air over the wings, because there is no flow of air over the wings - The plane with regards to the air around it is standing perfectly still. 0mph Air Speed.

That's the way my brain sees it anyway! smile

What happens when you strap a car to a Dyno - There isn't any air flowing over the car, why would anyone think the car would take off if it had wings strapped to it! lol.
Posted by: BigE515

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 06:58 AM

Quote:
Originally posted by Absolutely FabuLizz:
This thread got boring REALLY fast.
Bored? You could change your name again? [Finger]

:p
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:02 AM

lizz, hows the magnet business goin? i havent seen anything posted about it lately. can you make one with a picture of an xterra and put "if i wanted a hummer, i would have asked your girlfriend" on it?
Posted by: airbutchie

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:04 AM

Quote:
Originally posted by BigE515:
Quote:
Originally posted by Absolutely FabuLizz:
[b]This thread got boring REALLY fast.
Bored? You could change your name again? [Finger]

:p [/b]
Hehehehhehehhehe...

How 'bout "FloridaLIZZtic Gators"... Since your beloved Jaggy's failed ya this year...

Next boring thread please...

- Air B laugh
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:09 AM

There's no question that its propulsion is independant of the tires, and that as far as that goes, it will fly...

The part I'm still considering is the tire speed...the conveyor matches the PLANE'S speed...but is working as a tread mill, so the belt is rolling under the tires at the PLANE'S speed...just like a tread mill is going under your feet at YOUR speed...

Isn't that the speed the tarmac goes under the plane as it rolls down the runway anyway?

My FIRST impulse was that it would be DOUBLE the speed...but, its a given in this scenario that it MATCHES the plane's speed....so it CAN'T be double....it has to be the same.

laugh

So lets say the plane accelerates to 180 mph air speed...the belt is going 180 mph ground speed towards it under the tires...

That's the same 180 mph the tires would be rolling along at w/o the tread mill.

laugh

IE: The tires are moving at normal speed , just like for any take off...but, the plane is going forward due to engine thrust...with the belt accelerating its tread mill speed towards the plane to MATCH the plane's actual speed.

[Freak]

Here's the kicker though...the tire is obviously moving forward with the plane's air speed...so the tire is travelling at say 180 mph forward - the conveyeor is also moving at 180 mph towards it...

...if the plane is standing still in the air, with the runway rushing beneath it at 180 mph...its easy to see that the tire has to be ROLLING at 180 mph...

...but, for the air speed to also be 180 mph...the plane will at SOME POINT actually reach the end of the runway and fly off...so it has to gain on the belt's length's static starting position....

So -

As the belt speed matches the plane's speed as a given...I'm back to the tires having to ROLL at double their actual air speed.

[Freak]
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:23 AM

The plane would not fly.

Some of the others are correct when stating that a plane in that situation could not attain the lift required to fly.

Quote:
Originally posted by Absolutely FabuLizz:
This thread got boring REALLY fast.
It does seem to be quiet on the board, but then again it is a holiday week.

Is there any particular topic you wish to discuss that might ratchet things up on the board a bit?

I'd help you out, but I'm not the provocateur that I was once perceived to be. I'm the "kinder, gentler" NY Madman. [Wave] [ThumbsUp]

But then again, that statement alone could ratchet things up a bit. [Freak]
Posted by: TravelingFool

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:33 AM

Quote:
Originally posted by RiNkY:
The engines may indeed push the plane, but if the plane is on a conveyor belt moving in the opposite direction at the same speed that the engines are pushing the plane, it's still not gonna go anywhere. Unless it's a harrier jump jet - British Engineering can overcome this scenario smile

Me and my friend at work have been arguing about one of these kinda things for a few weeks now.

He says that if you fire a bullet from a gun perfectly level with the ground, then drop a bullet from the same height at the same time, both will hit the ground at the same time, as the Gravitational pull on both bullets is the same.

I call Bullshit as the aerodynamic flow over the bullet and the velocity of the bullet has to play into it somewhere.
:rolleyes:

You're one of those trailer park dudes at the racetrack who wants to know why the jet powered drag racers don't do burn-outs, huh!?
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:40 AM

Quote:
Originally posted by NY Madman:
[QB]The plane would not fly.

Some of the others are correct when stating that a plane in that situation could not attain the lift required to fly.

The lift is from air speed, which has zero to do with ground speed or tire speed.

If I left the landing gear up, so the plane is resting on its belly...and applied enough thrust, it would push the plane along the ground skittering and grinding, etc...until it had enough air speed to fly.

So its moving relative to the air, creating lift as the the air moves over the wings...the tires just hold it up.

Remember the old Road Runner Cartoons where he'd strap his ACME rocket pack on, stand on roller skates, fire it up, and chase the Road Runner?

Imagine he's on a tread mill...the rocket pack will push him forward throught the air EXACTLY the same way, even if the tread mill is making the roller skate WHEELS go faster...

...but, the roller skates themselves, and the attached Wiley Coyote, will be propelled foward, through the air, off the cliff, just like always.

laugh

Its the air speed that creates the lift...the wheel speed is not relevent.

_______

Oh, and as for the ballistics question...its a fairly well known principle that the time for the bullet, or cannon shell, etc...to hit the ground, is the same for one fired horizontally or dropped from the same starting point...to the same end elevation.

Obviously, a more powerful blast will make the END POINT further away..but, it will be going faster, and need less time to cover the distance as a less powerful blast, etc.

laugh
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:49 AM

Quote:
Originally posted by TJ:

The lift is from air speed, which has zero to do with ground speed or tire speed.
You're wrong.

In order to create lift, the plane requires air to move over the wing. The wing deflects the air downward and creates lift.

In the hypothetical situation posted here, the plane virtually stands still and there is no air moving over the wing to create the sufficient force for lift.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:50 AM

Blah blah blah. wink
Nowhere in that post does it say the 'engine' is running, just wheels spinning....

MGJ
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 08:08 AM

I agree with the ballistics thing if both bullets are fired / dropped in an airless vacuum, but only then would I believe that the friction of the bullet against the air wouldn't make one of the bullets land a fraction of a second sooner than the other.
Posted by: TravelingFool

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 08:11 AM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by TJ:

[b]The lift is from air speed, which has zero to do with ground speed or tire speed.
You're wrong.

In order to create lift, the plane requires air to move over the wing. The wing deflects the air downward and creates lift.

In the hypothetical situation posted here, the plane virtually stands still and there is no air moving over the wing to create the sufficient force for lift.[/b]
The plane gets its forward momentum from the engine thrust, NOT from the wheel spin. The plane could be sitting on a pure piece of glacial ice and it would easily take off.
Posted by: TravelingFool

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 08:15 AM

From "The Straight Dope.com"

The implicit assumption is that if the conveyor belt's speed backward exactly counteracts the airplane's "speed" (whatever that means) forward, the plane remains stationary relative to the earth and, more importantly, to the air. (We assume the winds are calm.) With no wind moving past its wings, the plane generates no lift and can't take off.

But the assumption is false. While the conveyor does exert some modest backward force on the plane, that force is easily overcome by the thrust of the engines pulling the plane ahead. The plane moves forward at roughly its usual speed relative to the ground and air, generates lift, and takes off. Many people have a hard time grasping this (although it can be easily demonstrated in the lab), but eventually they do, smack their foreheads, and move on. We'll call this Basic Realization #1.

Message-board discussions of this question tend to feature a lot of posters who haven't yet arrived at BR #1 talking right past those who have, insisting more and more loudly that the plane won't take off. Then there's a whole other breed of disputants who, whether or not they've cracked the riddle as originally posed, prefer to reframe it by proposing progressively more esoteric assumptions, refinements, analogies, etc. Often they arrive at a separate question entirely: Is there a way to set up the conveyor so that it overcomes the thrust of the engines and the plane remains stationary and doesn't take off?

The answer is yes. Understanding why is Basic Realization #2.

The conveyor doesn't exert much backward force on the plane, but it does exert some. Everyone intuitively understands this. To return to the analogy in my original column, if you're standing on a treadmill wearing rollerblades while holding a rope attached to the wall in front of you, and the treadmill is switched on, your feet will initially be tugged backwards. Partly this is due to friction in the rollerblade wheel bearings, but partly--this is key--it's because the treadmill is accelerating the rollerblade wheels and in the process imparting some angular (rotary) but some linear (backward) momentum to them. You experience the latter as backward force. Eventually the treadmill reaches a constant speed and the rollerblade wheels cease to accelerate. At this point you can easily haul in the rope and pull yourself forward.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 08:47 AM

lol....OK....First off, the bullet dropped from a height will hit the ground FAR before one shot out of a gun from the same height because of the extra force exerted on the bullet being shot.

Secondly, the 3rd child's name is Timmy.

Thirdly:
Quote:
First the obvious-but-wrong answer. The unwary tend to reason by analogy to a car on a conveyor belt--if the conveyor moves backward at the same rate that the car's wheels rotate forward, the net result is that the car remains stationary. An aircraft in the same situation, they figure, would stay planted on the ground, since there'd be no air rushing over the wings to give it lift. But of course cars and planes don't work the same way. A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane's wheels spin madly.

A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.

As you point out, one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH. Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off.
laugh [Wave]
Posted by: TravelingFool

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 08:54 AM

Quote:
Originally posted by Hawk:
lol....OK....First off, the bullet dropped from a height will hit the ground FAR before one shot out of a gun from the same height because of the extra force exerted on the bullet being shot.

Gravity works the same on all objects. IF the gun is fired while the barrel is parallel to the ground, both the bullet fired from the gun AND the bullet dropped from the same height WILL ABSOLUTELY hit the ground at the same time.

Without little "bullet wings," the fired bullet will NOT rise or gain lift. its forward thrust will propell it FAR FURTHER from the gun, but it will hit the ground when the dropped bullet does. This is one of the first things they teach you in a ballistics course and its simple 7th grade physics.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 08:58 AM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by TJ:

[b]The lift is from air speed, which has zero to do with ground speed or tire speed.
You're wrong.

In order to create lift, the plane requires air to move over the wing. The wing deflects the air downward and creates lift.

In the hypothetical situation posted here, the plane virtually stands still and there is no air moving over the wing to create the sufficient force for lift.[/b]
but as the jets push it down the runway, you adjust the leading and trailing egde flaps to obtain the lift. the air doesnt get udner the wing and blow upwards into the wing to create the lift, its the airstream over and more so under the wing. or it could be like osprey(sp?) with the vertical take off capability. take a paper air plane, trim some flaps at the rear of the wings. tilt the tabs up and throw it. and then shove it up your ass [Finger] (ALR material....no harm ment)
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:35 AM

Quote:
Originally posted by zuzuman03:
Quote:
Originally posted by NY Madman:
[b]
Quote:
Originally posted by TJ:

[b]The lift is from air speed, which has zero to do with ground speed or tire speed.
You're wrong.

In order to create lift, the plane requires air to move over the wing. The wing deflects the air downward and creates lift.

In the hypothetical situation posted here, the plane virtually stands still and there is no air moving over the wing to create the sufficient force for lift.[/b]
but as the jets push it down the runway, you adjust the leading and trailing egde flaps to obtain the lift. the air doesnt get udner the wing and blow upwards into the wing to create the lift, its the airstream over and more so under the wing. or it could be like osprey(sp?) with the vertical take off capability. take a paper air plane, trim some flaps at the rear of the wings. tilt the tabs up and throw it. and then shove it up your ass [Finger] (ALR material....no harm ment)[/b]
Who gives a damn about flaps. There's no fucking airflow going over the flaps (ALR), flaps only work when there is air traveling over them. Unless there happens to be a 200mph wind or somethin - the plane ain't going anywhere. The treadmill is pushing it backwards at the same speed the engines are pushing it forwards.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:42 AM

Quote:
Originally posted by zuzuman03:

but as the jets push it down the runway, you adjust the leading and trailing egde flaps to obtain the lift. the air doesnt get udner the wing and blow upwards into the wing to create the lift, its the airstream over and more so under the wing. or it could be like osprey(sp?) with the vertical take off capability. take a paper air plane, trim some flaps at the rear of the wings.
You are forgetting one major thing.... the plane in this hypothetical situation IS NOT moving down any runway. To an outside observer it is staying in the same place, like a stationary object.

The argument seems to be do the engines at maximum thrust have enough effect on the air behind the plane to achieve lift.

It just might lift off the ground, but it definitely isn't any plane I would want to be sitting on. [Freak]
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:45 AM

Quote:
Originally posted by RiNkY:
Unless there happens to be a 200mph wind or somethin - the plane ain't going anywhere. The treadmill is pushing it backwards at the same speed the engines are pushing it forwards.
That 200mph of wind is being created behind the engines, pushing against the air, which passes over/under the wings and creates lift, so the plane takes off. It doesn't matter how fast the wheels are rolling.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:54 AM

Quote:
A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.
Now, you on the rollerblades is the airplane, the treadmill is the conveyor belt, and you pulling the rope are the turbines. You will still move forward on the treadmill regardless of how fast the treadmill is going because of the external force moving you forward.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:57 AM

what about with a space shuttle? it sits stationary until they light those thrusters. good conditions for flight is no wind correct? have you ever stood or walked behind(at a safe distance) a prop plane when they had the engines running? i have. they would sit out there and feather them in front of the hanger to test the systems. when you go to walk out of one hanger to the other, you have to walk right through the air stream. they sit still, but they sure do push alot of air. and with a twin turbo prop for example, the engines are attatched in front of the wings.
so when the props turn, the airstream travels back over the airfoils and could potentionaly create enough lift(not sitting still;rolling) to take off. when you stand 100yds or so behind one with the props turning full speed, you can really feel it. and even more so with a jet engine. what about an f-16 taking off an aircraft carrier? they start off standing still and they dont have that much room to get up. same idea, except the with conveyor/tread mill bullshit.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 10:07 AM

OK. I don't get it... It's pretty easy to see that the plane would fly regardless.

Whoever says that the plane WOULD NOT fly is thinking of a vehicles because the speed depends on how fast the tires can spin and the tires accelerate the vehicle by coming in contact with the ground.

This is not the case with the plane. It all depends on air speed.

Think about it this way:

You take a bottle rocket. Attach some wheels to it and let it ride on the treadmill. It's attached with a rope to an end of the treadmill so it wouldn't fall of. This way it keeps riding down the belt while it's steady in proportion to the surroundings. You lite that bottle rocket and what's gonna happen? I'll fly forward no matter how fast the treadmill spins.

The engines on the plane push off against the air and not against the ground. The tires are simply supporting the weight and reducing the rolling resistance.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 10:16 AM

exactly.
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 11:25 AM

Quote:
Originally posted by NY Madman:
You're wrong.

In order to create lift, the plane requires air to move over the wing. The wing deflects the air downward and creates lift.
Lift is not created by air being directed downward towards the ground.

An airfoil, or wing, has a greater surface area on the top side of the wing as opposed to the underside.

As air rushes over the airfoil, it must move faster over the wing, as it has more distance to cover, versus the underside of the wing.

This increased velocity of airflow over the top of the wing results in a decrease in pressure on the top of the wing.
This decreased pressure generates the lift.

Greater angles of attack can therefore create greater distance differences on the top versus bottom surfaces of a wing, resulting in greater lift.
Posted by: Smith

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 11:34 AM

On a sidenote,ear wax does not taste even remotely like caramel.
Posted by: MidnightX

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 11:43 AM

Quote:
Originally posted by Smith:
On a sidenote,ear wax does not taste even remotely like caramel.
Hmm. Interesting!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 11:45 AM

well, assuming you ate some, what DOES it taste like? and no im not gona taste it.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 11:48 AM

The plane would fly. Assuming near zero friction between the plane and the wheel bearings would leave a force acting on the plane of zero. The thrust force would therefor overcome the near zero friction force, moving the plane forward to take off speed and then up and away. As someone already stated the effect on the plane would be the same if it tried to take off on a sheet of perfect ice.

The two bullets will hit the ground at the same moment. Some factors for curvature of the earth and imperfect bullet design would keep it from hitting exactly, but all things considered it would be very, very close. Wind resitance would have no effect since the force of the friction from the wind would be oriented horizontally, not vertically; this leaves only the force of gravity acting vertically, which would be exactly the same for both bullets.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 11:56 AM

You dumbasses who think a plane that is perfectly stationary to the airflow because all of the forward thrust is being canceled out by a rearward treadmill need to wake up.

This is nothing to do with wheel bearings or glaciers. Read the original question.

The plane is thrusting forward - Yes, if it weren't for the fact that the treadmill is canceling out any actual flow against the air it would take off. Planes with air flowing over their wings take off. But planes that are perfectly stationary to the airflow don't.

Are you trying to tell me that when you work out on a treadmill you actually go somewhere? Because it has nothing to do with your feet actually touching the treadmill!!!!!! eek

Stick a forward thrusting object on something that equally matches its forward thrust with rearward motion / thrust and it won't go anywhere.

Here's another example for you dumbasses who think it will fly to think about - which actually involved movement of air.

Stick the same plane on a regular runway with a constant 200mph tail wind. Accelerate the plane so it is going 200mph (Ground Speed). Will the plane fly? No - because in essence it's air speed is 0mph. The 200mph tail wind cancels out the 200mph forward speed. Airflow over the all important wings is 0mph.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 11:57 AM

Maybe here is a more real world explanation:

Imagine Plane on a river, traveling upstream, the engines have to overcome the speed of the relative resistance of the pontoons to the river flow. The only thing to stop it from taking off is the friction of the water acting on the pontoons. The plane would still be able to take off as it's airspeed increases the wings will create more lift, thereby reducing drag and friction until the plane has taken off completely.

Timmah!

And in a vacuum, without influence of air or objects the bullet fired from a gun with a trajectory parallel to the ground and one dropped in the same instance would hit the ground at the same time. Newton's law of Universal Gravitation. Both bullets will still be falling at the measured gravitational acceleration at the Earth's surface, about 980 cm/second/second. Linky

Interesting reading, kinda forgot all that stuff.
Posted by: Smith

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 11:58 AM

Quote:
Originally posted by RiNkY:


Stick a forward thrusting object on something that equally matches its forward thrust with rearward motion / thrust and it won't go anywhere.

My wife would disagree.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:09 PM

Quote:
Originally posted by GrayHam:

Lift is not created by air being directed downward towards the ground.

An airfoil, or wing, has a greater surface area on the top side of the wing as opposed to the underside.

As air rushes over the airfoil, it must move faster over the wing, as it has more distance to cover, versus the underside of the wing.

This increased velocity of airflow over the top of the wing results in a decrease in pressure on the top of the wing.
This decreased pressure generates the lift.

Greater angles of attack can therefore create greater distance differences on the top versus bottom surfaces of a wing, resulting in greater lift.
You are right.

However, getting back to the original hypothetical question posed by this thread, much of what is required for lift... or flight is not present in this hypothetical.

The only thing that exists is thrust. While this plane may achieve some lift, I tend to doubt it would achieve flight. Not any type of stable flight.

Maybe we need a mathematician, but the vector quantities that are required for flight do not seem to exist as the situation has been proposed.
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:09 PM

Quote:
Originally posted by Smith:
Quote:
Originally posted by RiNkY:
[b]

Stick a forward thrusting object on something that equally matches its forward thrust with rearward motion / thrust and it won't go anywhere.

My wife would disagree.[/b]
Yeah your wife mentioned that to me as well [Wave]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:09 PM

The Plane would only not take off in the treadmill scenario if the Pilot was throttling back the thrust to match the speed of the treadmill (initial reverse accelleration). Hence stationary no air movement, no lift, no takeoff.

If the treadmill's speed is truly infinite then ya the pilot cannot overcome the reverse accelleration and take off, but in reality the takeoff speed will be the same because the plane at full throttle will advance through the air regardless of relative ground speed.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:14 PM

Quote:
Originally posted by RiNkY:
Stick the same plane on a regular runway with a constant 200mph tail wind. Accelerate the plane so it is going 200mph (Ground Speed). Will the plane fly? No - because in essence it's air speed is 0mph. The 200mph tail wind cancels out the 200mph forward speed. Airflow over the all important wings is 0mph.
I would argue that the plane could basically hover in this condition and hence be flying. This is why you land with your nose in the wind, so you can maintain a little relative ground speed with as much as possible air speed.

There were many times flying small R/C airplanes that I experienced this, lots of fun hovering an airplane in the wind. Although when the wind changed direction quickly the lift was gone and if you didn't have the altitude to gain airspeed again you crashed.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:18 PM

Both the fired bullet and the dropped one will hit the ground at the same time. That is unless you want to get extremely technical about it. I remember this from Physics in college. Try this experiment. Grab something you don't mind dropping. It shouldn't be round or able to roll easily. Now take your object and hold it to your waist. Walk as fast as you can and let the object go in mid stride. You will find that it lands right next to you feet as you are walking. This shows that horizontal movement and vertical movement are independant. While it's hard to believe, both bullets will hit at the same time.

Now, if you want to get crazy with it, you can ponder the following. Since the earth is round, the shortest distance to the earth is right where you are standing. As you move further from that point, the distance increases. For example, if you drop a ball from right in front of your nose, it will travel a shorter distance than if you dropped the same ball from th same hight, but at arms length. Not much farther, but it is indeed a longer distance to the ground. Now considering these facts, if you want to be technical; the fired bullet will hit after the dropped one, but not by that much.

If you fire a bullet at approx 27,000KMPH it will essentially go into orbit and never land.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:22 PM

Quote:
Originally posted by PANissanX:
If you fire a bullet at approx 27,000KMPH it will essentially go into orbit and never land.
Wouldn't that mean that you fired the bullet outward (UP) and not parrallel to the ground? Hence like a rocket.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:28 PM

We don't need a mathmetician, we need someone who has a solid understanding of Newtonian physics (also called classical physics).

This is a basic question of force. Will the plane attain the force required to overcome gravity? As I stated it will.

The conveyor belt will not translate enough force to hold the plane in place. If the wheels are moving freely (indicating low friction) the force translated to the plane (through the landing gear into the main structure of the plane) will be very low. The thrust force generated is very high. The plane moves forward, the belt speeds up.

The plane will continue to gain acceleration and therefore velocity needed to attain a lift force from the wings (as stated by someone else before - it is actually the pressure differential between sides of the wing that cause lift). The conveyor belt will speed up, and will transfer more force to the plane; however, this force will be very small, and as already stated not enough to overcome the thrust). At this point the belt would be moving very fast, however the plane would continue forward relative to it's starting point. The plane will therfore reach an airspeed suitable to attain lift and take off.

I'm sorry Rinky, but you are wrong. You need to mentally disconnect the ground from the plane. Using your cue I will try it this way. If a plane is facing forward into a 200 mph wind, engines off, will it fly? Yes, straight up. The plane will attain lift and take off straight up, untill someone applies enough force to overcome the difference between lift and gravity and bring it back down.

I already tried to make a free-body diagram, but couldn't do it here. If I have to I will draw it in paint and load it into photobucket so I can link it here.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:36 PM

Quote:
Originally posted by Conundrum:
Quote:
Originally posted by PANissanX:
[b]If you fire a bullet at approx 27,000KMPH it will essentially go into orbit and never land.
Wouldn't that mean that you fired the bullet outward (UP) and not parrallel to the ground? Hence like a rocket.[/b]
No, horizontally. Because of the curvature of the earth, as the bullet drops at the normal speed the earth will have curved beneath it. It will continue to fall forever. Sounds crazy, but that's how orbits work.
Posted by: TravelingFool

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:38 PM

Rinky, you're a dumbass. You state:
Quote:
Yes, if it weren't for the fact that the treadmill is canceling out any actual flow against the air it would take off.
How can a treadmill cancel out air flow? All the treadmill is doing is spinning the wheels. The treadmill could spin the wheels on the plane up to a million rpm and it wouldn't make any difference.

1. put your car on a treadmill.
2. shift it into neutral.
3. turn on the treadmill.
4. The car's wheels will start spinning, but the car itself will realize ZERO forward motion.
5. Put the car in gear and mash on the gas.
6. the engine of the car turns the wheels which are fighting the treadmill. The car still doesn't go anywhere.

That's where YOUR brain stops. Lets do the same experiment with a jet engine strapped to the roof of your car.

1. put your car on a treadmill.
2. shift it into neutral.
3. turn on the treadmill.
4. The car's wheels will start spinning, but the car itself will realize ZERO forward motion.
5. Light the jet engine.
6. The jet engine doesn't turn the wheels like the car's engine would, it thrusts back into the air. The car will rocket forward because for every action, there is an equal and opposite reaction (Newton).
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:39 PM

Quote:
Originally posted by Branden Burden:
We don't need a mathmetician, we need someone who has a solid understanding of Newtonian physics (also called classical physics).

This is a basic question of force. Will the plane attain the force required to overcome gravity? As I stated it will.

The conveyor belt will not translate enough force to hold the plane in place. If the wheels are moving freely (indicating low friction) the force translated to the plane (through the landing gear into the main structure of the plane) will be very low. The thrust force generated is very high. The plane moves forward, the belt speeds up.

The plane will continue to gain acceleration and therefore velocity needed to attain a lift force from the wings (as stated by someone else before - it is actually the pressure differential between sides of the wing that cause lift). The conveyor belt will speed up, and will transfer more force to the plane; however, this force will be very small, and as already stated not enough to overcome the thrust). At this point the belt would be moving very fast, however the plane would continue forward relative to it's starting point. The plane will therfore reach an airspeed suitable to attain lift and take off.
You are adding into the scenario. That is NOT what was proposed in the hypothetical.

The plane would NOT move forward according to the hypothetical. The conveyor belt and the wheels would negate each other as forces. That is the scenario as it was proposed.

Hence, many of the vector quantities required for flight do not exist.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:39 PM

Consider this: If you had a powerful enough telescope, you could go to the top of mt.everest, look through...and at just the right angle, you could see yourself looking through the telescope from behind.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:40 PM

Quote:
Originally posted by PANissanX:
Quote:
Originally posted by Conundrum:
[b]
Quote:
Originally posted by PANissanX:
[b]If you fire a bullet at approx 27,000KMPH it will essentially go into orbit and never land.
Wouldn't that mean that you fired the bullet outward (UP) and not parrallel to the ground? Hence like a rocket.[/b]
No, horizontally. Because of the curvature of the earth, as the bullet drops at the normal speed the earth will have curved beneath it. It will continue to fall forever. Sounds crazy, but that's how orbits work.[/b]
Sure that's how orbits work, but it's how you get into orbit that counts. You have to first overcome the friction of the atmosphere and even if you do, orbit has to be maintained by external force or it will degrade and send you burning up in the atmosphere (Mir Space Station).

Isn't this why we still have to use the shuttle? We don't have a horizontal takeoff vehicle YET. The closest that is public is the Space Ship One by that Apple Guy?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:44 PM

man, ya'll got way to much time on your hands. when is this gona move to the ALR?
Posted by: RedX

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:46 PM

They would not negate each other. The force generated by the plane is via the air (air forced through the turbines)....the force generated by the conveyor belt is transferred to the wheels, which in the instance of take-off force play no part.

The air being forced through the turbines will be pushed through those turbines regardless of the conveyor belt's speed. And therefore, the plane will respond, as it does in take-off scenarios, to that force through the turbines. And it will react by moving forward through the airspace it is in, and the airspace that is being affected by the turbines' forcing of said air. The wheels' operations and reactions to the conveyor beneath them are unimportant in this hypothetical scenario.

The only way the conveyor could affect the plane's ability to lift off under take-off thrust was if the conveyor could also negatively (with relation to the plane's intended forward motion) affect the air through which the plane needs to move to achieve lift-off velocity.

cool
Posted by: RedX

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:51 PM

Also....think of it this way.....

Can I run forward on a treadmill and throw a balsa wood airplane forward? Will it fly. It will.....and the laws of lift apply the same to the plane on this conveyor belt.....But instead of my legs running on the treadmill, the wheels roll on the conveyor....and instead of my hand providing the propulsion for lift, the turbines move the air (independent of the conveyor remember, they are seperate forces) to provide the propulsion for lift.

smile
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:51 PM

Quote:
Originally posted by Conundrum:
Quote:
Originally posted by PANissanX:
[b]
Quote:
Originally posted by Conundrum:
[b]
quote:
Originally posted by PANissanX:
If you fire a bullet at approx 27,000KMPH it will essentially go into orbit and never land.
Wouldn't that mean that you fired the bullet outward (UP) and not parrallel to the ground? Hence like a rocket.[/b]
No, horizontally. Because of the curvature of the earth, as the bullet drops at the normal speed the earth will have curved beneath it. It will continue to fall forever. Sounds crazy, but that's how orbits work.[/b]
Sure that's how orbits work, but it's how you get into orbit that counts. You have to first overcome the friction of the atmosphere and even if you do, orbit has to be maintained by external force or it will degrade and send you burning up in the atmosphere (Mir Space Station).

Isn't this why we still have to use the shuttle? We don't have a horizontal takeoff vehicle YET. The closest that is public is the Space Ship One by that Apple Guy?

Right...at 27,000KMPH the bullet (fired horizontally) would leave our atmosphere and go into orbit. If we had a plane that would go that fast, we could fly horizontaly out of our atmosphere.
Posted by: TravelingFool

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:54 PM

Wow, this thread brings back memories. I used to work part time at Houston Raceway Park, a drag strip about 40 miles out of downtown. Some nights, they would race jet cars vs. top fuel dragsters... Lots of noise and fire, etc, to rev up the crowd.

Anyway, the Top-Fuel dragster would always do a burnout to heat up the tires and thus get better traction. Obviously, the jet car had no need... and yet; someone would ALWAYS shout out, "DO A BURN!"

Even better, people would make excuses for the jet car, "That jet car COULDN'T do a burnout cuz if'n it did, it would melt the tires!" etc.

Oh well. Its what makes America "great," I suppose...

- Thousands of Americans shot at their local water towers after Orson Wells read the story of the "War of the Worlds" on the radio...

- MILLIONS of lemmings bought thigh masters...

- Tens of thousands of people use the flash on their cameras at sporting events, even though they only illiminate about 10 feet of area in front of the camera...

We (as a nation) aren't that smart, I guess frown MAKE your kids take science classes, please?
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:56 PM

Quote:
Originally posted by RedX:
They would not negate each other. The force generated by the plane is via the air (air forced through the turbines)....the force generated by the conveyor belt is transferred to the wheels, which in the instance of take-off force play no part.

The air being forced through the turbines will be pushed through those turbines regardless of the conveyor belt's speed. And therefore, the plane will respond, as it does in take-off scenarios, to that force through the turbines. And it will react by moving forward through the airspace it is in, and the airspace that is being affected by the turbines' forcing of said air. The wheels' operations and reactions to the conveyor beneath them are unimportant in this hypothetical scenario.

The only way the conveyor could affect the plane's ability to lift off under take-off thrust was if the conveyor could also negatively (with relation to the plane's intended forward motion) affect the air through which the plane needs to move to achieve lift-off velocity.

cool
You are falsely treating the plane's jet engines as if it were moving through the air. It is NOT moving forward through the air.

The forward motion of moving through the fluid of air must be removed from your thinking regarding this hypothetical.

In the hypothetical the plane is stationary to it's relative position on the ground.

There is no air being forced through the turbines as there would be if it was moving forward through fluid air. The fuel from the plane at this point is what is moving the turbines of the jet.

There is no forward motion of this plane in the hypothetical.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 12:58 PM

someone call Mythbusters for chrissakes.. :rolleyes:
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:06 PM

NY - the question said nothing about the plane's ability/inability to move forward relative a point off of the belt.

If it was anchored and unable to move forward (again, relative to a point off of the belt), then you are right - try as you might if you don't move you won't fly.

If it is able to move relative to a point off the belt, then it would be moving thru the air, and able to attain lift. It would be moving down the conveyor belt runway away from the plane's starting point and toward the belt's "head pulley"; therefor the fluid air will be moving over the wings, and able to attain lift. This is the assumption I made, and as it was not stated otherwise, the assumption I will follow.

Edit to add: (Just thought of this) If the plane was anchored the belt would never start moving, because the plane would never start moving, because the wheels would never start turning, because they are obviously not driven by jet engines.
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:10 PM

Quote:
Originally posted by NY Madman:
The conveyor belt and the wheels would negate each other as forces. That is the scenario as it was proposed.
Agreed.

The wheels and conveyor belt would battle each other incessantly, ad nauseum.

Unfortunately, wheels on a plane play zero role in the actual forces of flight.

Even if the treadmill was able to spin the wheels backwards, against the direction of thrust, at a bazillion RPMs, the thrust propulsion is independant of the little battle the wheels are involved in.
The wheels are immaterial to the forces of flight (lift, gravity, thrust and drag).

-------------------------------------
EDIT:
That's not quite correct.
Wheels, if they are stuck, or break off, or are otherwise damaged, could generate drag by dragging against the ground or causing damage to the airframe.

But as I understand the scenario, the conveyor belt is spinning the wheels freely, creating zero drag.

I am assuming a zero-drag scenario, as the conveyor belt is not damaging the wheels, merely spinning them in an attempt to negatively affect the aircraft's groundspeed.
-----------------------------------------

In essence, the plane does not give a fuck what the wheels are doing.

So yes, the tradmill and the wheels would cancel each other out. At 100 RPM, at 1,000 RPM, and at 1,000,000 RPM.

And the thrust from the propulsion would launch the plane quite handily.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:11 PM

Well, I'd need to consider all the variables.

Such as, are there motherfuckin' snakes on this motherfuckin' plane?
Posted by: RedX

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:14 PM

Quote:
Originally posted by NY Madman:
The forward motion of moving through the fluid of air must be removed from your thinking regarding this hypothetical.

In the hypothetical the plane is stationary to it's relative position on the ground.

There is no air being forced through the turbines as there would be if it was moving forward through fluid air. The fuel from the plane at this point is what is moving the turbines of the jet.

There is no forward motion of this plane in the hypothetical.
So......how does the air interact with the turbines? The only way your scenario makes sense is if there is a mechanical bond between the conveyor and airplane.....interlocking the rearward motion of the conveyor to rearward travel by the airplane.

I think the plane will initially react as a ball will on a treadmill.....It will counter-roll to the treadmill's direction, until laws of inertia play into the equation and pull the ball back with the treadmill.....until the friction between the ball and mill overrule the law of inertia, the ball will stay in its original spot and roll backwards.

I suppose the questions are......How quickly does the conveyor get up to speed? Does it accelerate at the same rate as the plane's turbines? What is the coeficiant of friction between the wheels and conveyor (and likewise, internally in the wheels' structuring)?

I still believe the turbines' thrust will overpower the inertial and friction related actions between the wheels and conveyor.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:18 PM

Quote:
Originally posted by NY Madman:
There is no forward motion of this plane in the hypothetical.
Yes, there is. The plane is not bolted to the ground. Therefore, it moves forward because a plane's engines push against AIR, not the GROUND. Planes achieve lift via airspeed, not groundspeed.

Unless that conveyor somehow manages to prevent the engines from moving air through them, the plane is gonna take off.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:18 PM

smile I wish people added this much the the phat chicks thread! smile
Posted by: MidnightX

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:19 PM

Everyone thank me for starting this thread! At least most of you are enjoying it.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:22 PM

Quote:
Originally posted by Branden Burden:
NY - the question said nothing about the plane's ability/inability to move forward relative a point off of the belt.

If it was anchored and unable to move forward (again, relative to a point off of the belt), then you are right - try as you might if you don't move you won't fly.

If it is able to move relative to a point off the belt, then it would be moving thru the air, and able to attain lift. It would be moving down the conveyor belt runway away from the plane's starting point and toward the belt's "head pulley"; therefor the fluid air will be moving over the wings, and able to attain lift. This is the assumption I made, and as it was not stated otherwise, the assumption I will follow.
Here is the hypothetical that was proposed:

A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The conveyor matches any forward motion that would normally be created by the plane's wheels. Therefore the plane is stationary as viewed by an observer.

The plane is not moving forward relative to it's position on the ground.

It may be moving on the conveyor belt, but it is stationary relative to the ground and the surrounding atmosphere.

That removes some main vector quantities required for flight.

Thrust alone is not enough to achieve viable flight. If it were, aircraft carriers would never need their catapults. Without the additional forward motion provided by the catapults, every plane would crash leaving a carrier, regardless of the amount of thrust it's engines put out.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:25 PM

Quote:
Originally posted by ShowtimeX:
Well, I'd need to consider all the variables.

Such as, are there motherfuckin' snakes on this motherfuckin' plane?
LOL...

Damn that was funny.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:31 PM

Quote:
Originally posted by Conundrum:
Quote:
Originally posted by PANissanX:
[b]If you fire a bullet at approx 27,000KMPH it will essentially go into orbit and never land.
Wouldn't that mean that you fired the bullet outward (UP) and not parrallel to the ground? Hence like a rocket.[/b]
No, the Earth is round, therefore, the ground will drop out from beloe the bullet in this scenario wink However, you need at least 40,300kph, or escape velocity, to do that.

I knew this would turn into a huge hooplah. [LOL] The correct answer is that the plane WILL infact be able to take off though. You people are all associating the plane's movement with the wheels, and not where it's true momentum is coming from. A plane doesn't get it's forward momentum from the wheels, it gets them from the thrust of the turbines.

If you look and read and UNDERSTAND what I wrote in a reply back on page 3 (and others also said the same thing a few posts later),
Quote:
Originally posted by Hawk:
Quote:
A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.
Now, you on the rollerblades is the airplane, the treadmill is the conveyor belt, and you pulling the rope are the turbines. You will still move forward on the treadmill regardless of how fast the treadmill is going because of the external force moving you forward.
There are good examples of the exact scenario. Those that think the plane will not go anywhere, need to sit and think a bit harder and think about it with a more open mind about it laugh
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:34 PM

Quote:
Originally posted by NY Madman:

Thrust alone is not enough to achieve viable flight. If it were, aircraft carriers would never need their catapults. Without the additional forward motion provided by the catapults, every plane would crash leaving a carrier, regardless of the amount of thrust it's engines put out.
confused

Aircraft carriers use catapults because their runways are exceedingly short.

You're right; lift is as essential as thrust. Lift is created by thrust:
Thrust forces the aircraft forward, generating airflow over an airfoil. When the flow of air is fast enough, enough lift is generated, and the aircraft lifts off.

The catapult aids the F-18 in generating the airspeed necessary to get enough lift to haul the Plastic Bug into flight.
On an aircraft carrier's short flight deck, there is not enough room for the F-18's engines to generate enough thrust and airspeed over the wings to get the F-18 up on its own. So they use a catapult aid.
Same F-18 taking off from Miromar? No problem. Runways are plenty long.

Thrust from jet turbines is not instantaneous. Like any other object accelerating from a dead stop, it takes some runway to reach speed. The catapult helps shorten the time needed by magnifying the force of thrust that can be generated by the F-18's own engines.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:39 PM

Quote:
Originally posted by Absolutely FabuLizz:
Everyone thank me for starting this thread! At least most of you are enjoying it.
Hey now....you can't take all the credit! Thank you for starting it by saying it's boring here, yes, but I posted the question about the plane which is what turned this thread into what it is :p
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:39 PM

NY - now we are getting close, you have almost gotten yourself to the right answer.

As an observer standing away from the plane, what would you see, starting from the beginning?

The plane is standing still, the conveyor is not moving.

The plane starts it's engines, just like the big rev just before a takeoff. Instantly the thrust force creates an acceleration, lets say 1m/s^2.

1 second later the plane is traveling at 1m/s. The belt, which matches the plane's velocity, is now also spinning at 1m/s.

However, since there is no real force between the plane and the belt, there is no way for the belt to prevent the plane from moving down the runway. As the observer standing away from the plane, you would see it speeding down the runway, with a conveyor belt running like mad under it.

This means the plane is in fact moving down the runway, like a normal takeoff.

After say 10 sec, the plane is now at full speed, near the end of the conveyor belt, lift takes over and off it goes.

Let me ask you this Madman - starting from the beginning illustrate what you think will happen.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:45 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by NY Madman:
[b]There is no forward motion of this plane in the hypothetical.
Yes, there is. The plane is not bolted to the ground. Therefore, it moves forward because a plane's engines push against AIR, not the GROUND. Planes achieve lift via airspeed, not groundspeed.

Unless that conveyor somehow manages to prevent the engines from moving air through them, the plane is gonna take off.[/b]
The plane is pulling air through it's engines - Yes, which is making the wheels touching the ground rotate, which is being counteracted by the moving runway which is moving at exactly the same speed in the opposite direction. So for someone stood on the grass next to the moving runway parallel to the plane - the plane isn't moving backwards or forwards, it's just throttled up and rolling on the moving runway. Hense no airflow over the wings, hense no lift, hense no flight.

In affect the plane may as well be bolted to the ground either side of the runway (Not to the moving runway itself).
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:48 PM

Rinky - please explain how the belt is able to keep the aircraft from moving forward down the runway.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:50 PM

Quote:
Originally posted by Branden Burden:
NY - now we are getting close, you have almost gotten yourself to the right answer.

As an observer standing away from the plane, what would you see, starting from the beginning?

The plane is standing still, the conveyor is not moving.

The plane starts it's engines, just like the big rev just before a takeoff. Instantly the thrust force creates an acceleration, lets say 1m/s^2.

1 second later the plane is traveling at 1m/s. The belt, which matches the plane's velocity, is now also spinning at 1m/s.

However, since there is no real force between the plane and the belt, there is no way for the belt to prevent the plane from moving down the runway. As the observer standing away from the plane, you would see it speeding down the runway, with a conveyor belt running like mad under it.

This means the plane is in fact moving down the runway, like a normal takeoff.

After say 10 sec, the plane is now at full speed, near the end of the conveyor belt, lift takes over and off it goes.

Let me ask you this Madman - starting from the beginning illustrate what you think will happen.
Where are you coming from with the 'There is no force between the belt and the plane'. Did we suddenly hack the wheels off and remove Gravity or something? smile
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:52 PM

Quote:
Originally posted by Branden Burden:
Rinky - please explain how the belt is able to keep the aircraft from moving forward down the runway.
"This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction)."

The plane is moving on the runway. But the runway is moving at the same speed in the opposite direction. Hense NO AIRFLOW OVER THE WINGS.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:54 PM

Maybe my brain is just seeing this all wrong and you guys are right. But I'm sticking to my thought process! lol.

I'm gonna have to submit this thread to Mythbusters, I'll never be convinced otherwise until I see this actually done! smile
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:55 PM

Quote:
Originally posted by NY Madman:
Thrust alone is not enough to achieve viable flight. If it were, aircraft carriers would never need their catapults. Without the additional forward motion provided by the catapults, every plane would crash leaving a carrier, regardless of the amount of thrust it's engines put out.
You're right. Viable flight requires both thrust and lift. A catapult merely provides forward acceleration that adds to the thrust produced by the engines of the aircraft. And yes, because aircraft carriers aren't very long, just about any plane that does not use a catapult would just fall off the bow of the carrier because it didn't achieve enough airspeed to take off.

The hypothetical scenario only says that the conveyor has a mechanism to track the plane's speed, but it does not make any mention of whether it's airspeed or groundspeed. We assume it must be groundspeed, because a conveyor belt has no effect on air.

The only way a plane on such a conveyor would NOT take off is if it had a tailwind that equaled the thrust from the engines.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:56 PM

Quote:
Originally posted by RiNkY:
Maybe my brain is just seeing this all wrong and you guys are right. But I'm sticking to my thought process! lol.

I'm gonna have to submit this thread to Mythbusters, I'll never be convinced otherwise until I see this actually done! smile
No, I thought it the same as you did until I did some research into it. It started making more sense as to why the plane would in fact take off whens I started to research it. I posed the question to see how fast this thread will baloon into something out of the ordinary, and it did it pretty damn fast laugh

Just wanted to give Lizz a little bit of spice in the forums wink
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:57 PM

Quote:
Originally posted by GrayHam:
Quote:
Originally posted by NY Madman:
[b]
Thrust alone is not enough to achieve viable flight. If it were, aircraft carriers would never need their catapults. Without the additional forward motion provided by the catapults, every plane would crash leaving a carrier, regardless of the amount of thrust it's engines put out.
confused

Aircraft carriers use catapults because their runways are exceedingly short.

You're right; lift is as essential as thrust. Lift is created by thrust:
Thrust forces the aircraft forward, generating airflow over an airfoil. When the flow of air is fast enough, enough lift is generated, and the aircraft lifts off.

The catapult aids the F-18 in generating the airspeed necessary to get enough lift to haul the Plastic Bug into flight.
On an aircraft carrier's short flight deck, there is not enough room for the F-18's engines to generate enough thrust and airspeed over the wings to get the F-18 up on its own. So they use a catapult aid.
Same F-18 taking off from Miromar? No problem. Runways are plenty long.

Thrust from jet turbines is not instantaneous. Like any other object accelerating from a dead stop, it takes some runway to reach speed. The catapult helps shorten the time needed by magnifying the force of thrust that can be generated by the F-18's own engines.[/b]
I realize the fact of the short runways for the catapults, but if engine thrust were as intregal as being argued here, that problem could have been overcome in other ways besides the use of catapults.

As you have mentioned, the forward motion through fluid air... acceleration is also required for the lift needed for viable flight.

In the scenario proposed I doubt the plane could achieve viable flight. In such a situation I believe a conventional jet would crash.

Does anyone have any links to an actual physics web site that ponders this question? Maybe a link to a test where they did this with a plane.. on in ground rollers maybe (like those used to accelerate car wheels... only on a larger scale)?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 01:57 PM

Wrong.

Hypothetical scenario:

t = 0 :

Plane 0 mph
Conveyor 0 mph
Wheels 0 mph

t = 15 :

Plane 60 mph
Conveyor 60 mph
Wheels spin @ 120 mph

t = 55:

Plane 160 mph
Conveyor 160 mph
Wheels spin @ 320 mph

Plane takes off!!
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 02:01 PM

Quote:
Originally posted by Branden Burden:
NY - now we are getting close, you have almost gotten yourself to the right answer.

As an observer standing away from the plane, what would you see, starting from the beginning?

The plane is standing still, the conveyor is not moving.

The plane starts it's engines, just like the big rev just before a takeoff. Instantly the thrust force creates an acceleration, lets say 1m/s^2.

1 second later the plane is traveling at 1m/s. The belt, which matches the plane's velocity, is now also spinning at 1m/s.

However, since there is no real force between the plane and the belt, there is no way for the belt to prevent the plane from moving down the runway. As the observer standing away from the plane, you would see it speeding down the runway, with a conveyor belt running like mad under it.

This means the plane is in fact moving down the runway, like a normal takeoff.

After say 10 sec, the plane is now at full speed, near the end of the conveyor belt, lift takes over and off it goes.

Let me ask you this Madman - starting from the beginning illustrate what you think will happen.
I think you are making stuff up as you go along.

Of course if the plane moves down the runway, it will take off in a conventional manner.

That is not what is being discussed. The plane is NOT moving down a runway in the hypothetical.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 02:01 PM

NY and Rinky -
Quote:
Where are you coming from with the 'There is no force between the belt and the plane'. Did we suddenly hack the wheels off and remove Gravity or something?
Essentially, yes. The rolling resitance would be measurable, but that friction force will not translate to enough of a force to overcome the thrust.

So, you could treat this problem as if the wheels did not exist. A free-body diagram would show the force of gravity acting down, the force of friction acting back, the force of thrust acting forward and (given enough air speed) the force of lift acting up. The biggest forces win. Thrust will be bigger than friction, therefore it wins and the plane moves forward (again, regardless of what is happening below it). At some point lift becomes a bigger force than gravity, it wins and the plane takes off.

The only way the belt could prevent the plane from taking off is if the plane's brakes are on. Then the full force of the belt would be translated to the plane, instead of only a very small fraction of that force being translated through friction.

NY and Rinky, you have to disconnect the ground from the plane, in this problem it does not matter.

Edited to bold the part above, because that is the central arguement.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 02:07 PM

Quote:
Originally posted by RiNkY:
]The plane is pulling air through it's engines - Yes, which is making the wheels touching the ground rotate, which is being counteracted by the moving runway...
A plane pulling air through its engines in no way causes its wheels to start rotating. Let's say the pilot decides he needs lots of thrust (such as to take off on a short runway). He first sets the wheel brakes (so the plane can't move). Groundspeed=0. Conveyor speed=0. He then throttles up the engines to max power. The brakes keep the plane from moving, but the engines are just about ready to rip themselves from the wings, and woe to anyone or anything standing right behind the engine!

The pilot then releases the brakes, and the wheels start turning. The conveyor starts moving to counteract the wheelspeed. Let's call the conveyor a "groundspeed force equalizer." However, those engines are still straining against the air! (Again, woe to anyone standing behind the engine!)

Because there's nothing to counteract the force of air through the engines, the plane starts to move forward. The conveyor speeds up some more to equalize the groundspeed. But the plane keeps moving forward, since there's no "airspeed equalizer".

Eventually, the air moving through the engines would accelerate the plane enough through the air, and it would have enough lift to take off.
Posted by: TravelingFool

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 02:08 PM

RiNkY said something about the engines sucking air and then turning the wheels or something...

Nobody here actually believes there is any sort of gearing or linkage directly to the wheels from the engines of a jet plane.

Do they? [Freak]

How in the hell would a float plane take off then? They have no wheels at all!

What if the treadmill were made of ice and the plane had skates instead of wheels? The plane would still have no forward motion relative to a bystander, but if you turned on the engines... WHOOSH, it would most certainly move forward and fly.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 02:29 PM

The force of friction acting upon the plane can be determined.

Friction = (coefficient of friction) x (normal force). This means that the force of friction is a coefficiant (usually 1.0-rubber to concrete to 0.1-rubber to ice) that is multiplied times the weight of the airplane (normal force)

So if the weight of the aircraft is 150,000 kg (1,500 kN, kN = kilo Newton, measure of force) and a good guess at the friction of a wheel with no brakes applied was used - Ff=(0.25)x(1,500)= 375 kN. As long as the thrust was more than 375 KN, the plane would beat the resistance of the rolling runway.

If the friction facor was increased by a lot, the force of friction would at some point exceed the force of thrust, and the plane will not move. Essentially, the stickier the belt, the better chance it has of holding the plane back, otherwise it takes off.

Don't make me draw up a free-body diagram.

Edited to correct a spelling mistake
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 02:43 PM

Quote:
Originally posted by TravelingFool:
How in the hell would a float plane take off then? They have no wheels at all!
They accelerate (move forward) via thrust through fluid air creating lift.

Quote:
What if the treadmill were made of ice and the plane had skates instead of wheels? The plane would still have no forward motion relative to a bystander, but if you turned on the engines... WHOOSH, it would most certainly move forward and fly.
I don't believe anyone has questioned forward acceleration, lift and flight.

In this scenario there is no groundspeed. There is no forward acceleration through fluid air.

I have often used the term "viable flight". In this scenario how is viable flight possible without proper angle of attack? That requires forward motion through fluid air. It cannot be achieved in this scenario on a conveyor belt.

No one is discussing the many other factors required for flight. This hypothetical is a recipe for nothing but disaster. Flight may be achieved for a second prior to crash, but I seriously doubt any "viable flight" can be achieved via this hypothetical situation.
Posted by: TravelingFool

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 02:54 PM

For the love of God... The plane would fly. Period.
Posted by: Smith

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 03:18 PM

Is this a smoking flight or a non-smoking flight? Cause it will make a load of difference.
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 03:19 PM

Quote:
Originally posted by TravelingFool:
For the love of God... The plane would fly. Period.
Wow 7 pages and all we needed was you to answer it. Man that was easy.
:rolleyes:

An airplane requires wind speed (wings vs. wind), not ground speed (wheels turning on conveyor belt), to generate the lift. Turbines and props create thrust, which pushes the plane forward through the wind.

Without the conveyor belt, a plane generates speed through the wind as it moves forward, which means it ALSO generates it with respect to the ground.

Because (with the conveyor belt) everything remains stationary with respect to the wind (not the ground), your plane AIN'T taking off, no matter how fast the wheels turn.

If you think a plane can fly at 0 mph, think about this: A plane is moving at 500 MPH through the air, but suddenly (magically), you STOP it (to 0 mph) and, simultaneously, put a conveyor belt under it's wheels that is moving at 500 mph.

Do you think that plane is going to stay aloft at 0 mph windspeed but 500 mph wheel speed?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 03:23 PM

Madman, I fail to see how you reached the conclusion that there would be zero forward motion of the aircraft. The scenario says that the conveyor matches the speed of the plane, not the speed of the wheels. If the plane goes nowhere, the conveyor doesn't even turn. If the plane starts moving forward, the conveyor does start to turn but affects only the wheels. The plane is already moving, and is pushing air, not the surface.

Rinky, an aircraft taxis by pushing air, there is no drivetrain connected to the wheels, just steering at the nose wheel. The wheels are just there as an alternative to scraping the belly of the plane everywhere.

Madman again- the cats on a carrier are fairly irrelevant to the other discussion, but essentially they are a thrust enhancer. Perhaps the Navy could come up with a way to make jets take off of ships using thrust only, but the steam cats are fairly economical and very effective.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 03:25 PM

Quote:
Originally posted by NY Madman:
In this scenario there is no groundspeed.
And the Earth is flat.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 03:30 PM

Quote:
Originally posted by Paul H:
Quote:
Originally posted by TravelingFool:
[b]For the love of God... The plane would fly. Period.
Wow 7 pages and all we needed was you to answer it. Man that was easy.
:rolleyes:

An airplane requires wind speed (wings vs. wind), not ground speed (wheels turning on conveyor belt), to generate the lift. Turbines and props create thrust, which pushes the plane forward through the wind.

Without the conveyor belt, a plane generates speed through the wind as it moves forward, which means it ALSO generates it with respect to the ground.

Because (with the conveyor belt) everything remains stationary with respect to the wind (not the ground), your plane AIN'T taking off, no matter how fast the wheels turn.

If you think a plane can fly at 0 mph, think about this: A plane is moving at 500 MPH through the air, but suddenly (magically), you STOP it (to 0 mph) and, simultaneously, put a conveyor belt under it's wheels that is moving at 500 mph.

Do you think that plane is going to stay aloft at 0 mph windspeed but 500 mph wheel speed?[/b]
Paul, what you and so many others fail to realise is that without wind pushing the airplane itself backward at the same rate the engines push the plane forward, there will be forward motion. The airplane's engines are what are moving the airplan. NOT the wheels. You all are associating the wheels with the airplane's motion when in fact, they have nothing to do with the airplane's forward momentum. They are just moving at the rate that the engines are pulling them forward. The plane will still be pulled forward by the engines and not by the wheels.

The only way that a plane will remain stationary on the conveyor belt is if the plane was being propelled by the wheels and not the engines. The conveyor belt has no effect what-so-ever on the engines. It just moves the wheels.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 03:42 PM

OK, free body diagram it is.



Forward motion will be attained whenever the thrust force is greater than the friction force (as stated above).

The only was the plane will stay stationary is if the force of friction between the wheels and ground is greater than the thrust. Period, end of story
Posted by: Smith

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 03:43 PM

Quote:
Originally posted by Paul H:
Quote:
Originally posted by Smith:
[b]
Quote:
Originally posted by RiNkY:
[b]

Stick a forward thrusting object on something that equally matches its forward thrust with rearward motion / thrust and it won't go anywhere.

My wife would disagree.[/b]
Yeah your wife mentioned that to me as well [Wave] [/b]
I just saw this you bastard. frown
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 03:45 PM

Quote:
Originally posted by MattyX:

Rinky, an aircraft taxis by pushing air, there is no drivetrain connected to the wheels, just steering at the nose wheel. The wheels are just there as an alternative to scraping the belly of the plane everywhere.
I know that. But when an aircraft taxis the wheels rotate and the plane moves along the runway does it not. Or does the plane have that much power that it just makes long trails of rubber all over the airport without rotating the wheels? eek

What we are saying is - as the aircraft taxis and the wheels are rotating, the revolving runway / treadmill thingy is moving in the opposite direction ad the same speed. Hense the plane isn't moving anywhere with regards to anything not on the moving runway. Lets say a Tree at the side of the fucking runway. The plane may as well be sodding tied to the tree, because when it thrusts itself forward, the stupid dumbass treadmill - Which I wish wasn't there, but unfortunately is fucking there, keeps the plane static to the surrounding area. Hense no lift, hense no takeoff - regardless of if the plane is going 1mph in relation to the treadmill going backwards at 1mph or 1000mph.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 03:46 PM

Now for the bullet-

A bullet fired from gun (when the barrel is perfectly level) over tranquil ocean (for the purposes of creating the most perfect earthbound surface) will likely strike the surface of the water at exactly the same time as the bullet dropped from exactly the same height at the exact same time the other bullet was fired [huh?]. The lateral velocity of the bullet will not have any effect on or resistance to gravity, the bullet simply isn't that fast.

Now, I said "likely" not because I was unsure, but because the two bullets will encounter different conditions. The fired bullet will travel through more air than the dropped bullet and may encounter an updraft or downdraft. Were it possible to conduct this experiment in a perfect vacuum, the two bullets would strike the surface at exactly the same time, every time.

::edit to reply to Rinky::

Just because the conveyor is turning does not mean that the plane is not moving.

::ETA:: In fact if the conveyor is moving at all, it is because the plane is moving forward. The scenario calls to match the plane's speed, not its power or friction or any other imaginable thing.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:03 PM

The plane would definitely be able take off.

100% certain
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:08 PM

Quote:
Originally posted by tahoe_x:
The plane would definitely be able take off.

100% certain
I agree - But for that damn treadmill. I say we throw a spanner in the works and fuck up the treadmill, so the plane can take off and end this thread.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:10 PM

Quote:
Originally posted by Hawk:
How about this.....lets see if this can get to the ALR:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?
Let me try to break what the question is down.

Plane standing on Runway.
Runway matches speed of Plane in opposite direction.

Point of Observer outside the Plane:
Plane appears as usual and takes off.

Point of Onboard Occupants:
Feeling the sensation of acceleration (cool) and the bumpiness of the runway and the separation and weightlessness (very cool) when the plane bobs up and down as it is continually accelerating and climbing until it reaches Cruise Speed and Altitude.

No other fact is included in the question, it is what it is.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:18 PM

Quote:
Originally posted by RiNkY:
Quote:
Originally posted by tahoe_x:
[b]The plane would definitely be able take off.

100% certain
I agree - But for that damn treadmill. I say we throw a spanner in the works and fuck up the treadmill, so the plane can take off and end this thread.[/b]
Do whatever you want to the treadmill, as long as your spanner wrench doesn't FOD the engine the aircraft will take off.

If the aircraft has 0 speed, the conveyor is not moving.

In order for the aircraft to attain any speed, it must be moving.

If the aircraft MOVES forward at one mile per hour, using jet propulsion or conventional propellers, the conveyor moves in the opposite direction at one mile an hour. The result of this is not a stationairy aircraft, it is a plane moving forwards at one MPH with its wheels turning at a rate of two MPH.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:19 PM

Quote:
Originally posted by RiNkY:
Quote:
Originally posted by tahoe_x:
[b]The plane would definitely be able take off.

100% certain
I agree - But for that damn treadmill. I say we throw a spanner in the works and fuck up the treadmill, so the plane can take off and end this thread.[/b]
Think of it this way. (read slowly...) The plane is sitting still on a treadmill that isnt turned on. Try to picture that for a second. Now.... Try to imagine something holding the plane in place.

Now, turn on the treadmill. What happens? The tires on the plane turn but the plane doesnt move. Do you understand that? Now, you are inside the plane and throttling up the engines. What does the airplane want to do?

If you understand that, then you have the answer. wink
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:22 PM

To simple Adam. Why would the plane appear to take off as per normal?

What you are saying is the same as saying, if we turned on the conveyor and span it up to say 100mph, but didn't bother to do anything with the planes engines - Just the conveyor on its own. The plane would stay in 1 place!!!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:27 PM

Quoting from someone on CO 4X4 site who's quoting avweb:
Quote:
It was an interesting argument, but as things progressed, more rational heads prevailed, pointing out that the airplanes do not apply their thrust via their wheels, so the conveyor belt is irrelevant to whether the airplane will takeoff. One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:32 PM

Ok so let me get this straight....

If you belong to another forum, logically, the plane will take off ONLY if its shot out of a gun level with the ground at 27,000MPH? But on XOC, the above is BULLSHIT????

[LOL] !!!

MGJ
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:34 PM

Just emailed: mythbusters@m5industries.com

Hopefully they look into this one and give it a try smile
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 04:54 PM

RiNkY- I bet Mythbusters won't even bother wasting their time on this one.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 05:07 PM

Quote:
Originally posted by RiNkY:
To simple Adam. Why would the plane appear to take off as per normal?

What you are saying is the same as saying, if we turned on the conveyor and span it up to say 100mph, but didn't bother to do anything with the planes engines - Just the conveyor on its own. The plane would stay in 1 place!!!
Well, Exactly! confused ?

If the conveyor were turned on and doing 100MPH and the Plane were stationary upon it, then consequently the tires are rotating at 100MPH, if thrust is therefore applied to the airframe through the engines the resulting action will be an equal and opposite reaction, Ie. Newtons Third Law, the plane will move through the AIR and eventually gain the speed required for takeoff.

Rog, this will be one of those slap yourself on the forehead moments for you and with the ability to get to 8+ Pages in a day, it is worth setting up a scenario Ie. Mythbusters to quelch this thirst for knowledge. wink
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 05:12 PM

Lift is the force that directly opposes the weight of an airplane and holds the airplane in the air. Lift is generated by every part of the airplane, but most of the lift on a normal airliner is generated by the wings. Lift is a mechanical aerodynamic force produced by the motion of the airplane through the air. Lift acts through the center of pressure of the object and is directed perpendicular to the flow direction.

Lift is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid: no motion, no lift.

(too many years in the aerospace business I am afraid !!)
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 05:51 PM

Quote:
Originally posted by Scrabo:
Lift is the force that directly opposes the weight of an airplane and holds the airplane in the air. Lift is generated by every part of the airplane, but most of the lift on a normal airliner is generated by the wings. Lift is a mechanical aerodynamic force produced by the motion of the airplane through the air. Lift acts through the center of pressure of the object and is directed perpendicular to the flow direction.

Lift is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid: no motion, no lift.

(too many years in the aerospace business I am afraid !!)
I think we are in agreement regarding this hypothetical scenario.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 06:00 PM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by Scrabo:
[b]There must be motion between the object and the fluid: no motion, no lift.
I think we are in agreement regarding this hypothetical scenario.[/b]
But your hang-up is how motion through the fluid is achieved, right?

Motion through the fluid (air) is achieved by the engines pushing against the air around the plane, not by the wheels turning on the conveyor.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 06:13 PM

Another way to look at it - a plane on water.

The water is most certainly not solid. Yet the plane takes off (if it has enough power to get up to speed).

The plane may take longer to take off going against current as opposed to with the current - but it will eventually.

I think...

My brain hurts. It's been WAY too long since I bothered with this stuff.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 06:18 PM

Quote:
Originally posted by TravelingFool:
For the love of God... The plane would fly. Period.
I wouldn't bet my life on it... or your life.

Quote:
Originally posted by MattyX:
Madman, I fail to see how you reached the conclusion that there would be zero forward motion of the aircraft. The scenario says that the conveyor matches the speed of the plane, not the speed of the wheels. If the plane goes nowhere, the conveyor doesn't even turn.
You are wrong. In the scenario the conveyor speeds up and matches the thrust of the plane. As the pilot throttles down - which would normally cause the plane to move down the runway - the conveyor speeds up to match it. Thus there is no forward movement of the plane in the hypothetical scenario. The fuselage and the wings are not moving forward through fluid air. The forces of the air moving over the wings are not present in the hypothetical scenario.

If you were looking down from above (or anywhere for that matter) during this hypothetical scenario, the plane would appear to be not moving at all even though the the throttle is down and thrusters are going full blast. To an outside observer the plane would appear stationary.

Quote:
Madman again- the cats on a carrier are fairly irrelevant to the other discussion, but essentially they are a thrust enhancer. Perhaps the Navy could come up with a way to make jets take off of ships using thrust only, but the steam cats are fairly economical and very effective.
If the Navy could have done it, they probably already would have done so considering the amount of men that have died over the years by catapult accidents.

In order for a plane to achieve flight.. a flight where the pilots will not crash... the plane has to be moving in a forward direction to obtain the initial lift required to sustain the angle of attack to keep it climbing into the sky.

In the hypothetical scenario in this thread, there is no sound aerodynamics operating in which the nose can lift to obtain the proper angle.

A Harrier jet can lift itself vertically with it's technology, but if the pilot is not well experienced enough to know how to manuever the plane and the thrusters while in the air to obtain a proper angle, that plane will crash... even though it is already in the air. It will not obtain flight. Not viable flight where the occupants have a reasonable chance of living to see the next day.

Without forward motion, the lift it provides and the proper angle of attack... I would think the aircraft would stall and crash.

..............



"That's my story and I'm sticking to it...."
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 06:54 PM

Quote:
Originally posted by XPLORx4:
But your hang-up is how motion through the fluid is achieved, right?
No, not at all.

I've been discussing this hypothetical scenario. In the scenario we have NO MOTION through the fluid of air.

In the scenario we only have the thrust from the engines.

Understand? Other vital components needed for flight are absent in the scenario.

Quote:
Motion through the fluid (air) is achieved by the engines pushing against the air around the plane, not by the wheels turning on the conveyor.
Yes.. but we are not moving in the scenario. There is no motion of the plane. The plane can be at maximum thrusters, but in the scenario the conveyor matches the force created by the thrust.

We still need the plane moving forward through the air to create the lift needed for flight.

Quote:
Originally posted by Mobycat:
Another way to look at it - a plane on water.

The water is most certainly not solid. Yet the plane takes off (if it has enough power to get up to speed).
Yes... the key there is the plane on the water is moving forward through the air. It makes no difference what surface is underneath the plane, as long as the plane moves forward and can create lift and the proper angle to obtain flight.

I'm saying engine thrust against the air behind the plane is not enough for flight if the plane is not moving forward through the fluid of the air.

Am I making myself clearer now.

I think these web sites will help....

http://www.grc.nasa.gov/WWW/K-12/airplane/factors.html

http://www.grc.nasa.gov/WWW/K-12/airplane/climb.html

Remember your vectors....

http://www.grc.nasa.gov/WWW/K-12/airplane/vectors.html
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:17 PM

Quote:
Originally posted by NY Madman:
The plane can be at maximum thrusters, but in the scenario the conveyor matches the force created by the thrust.
There's where you've got force and thrust mixed up. The conveyor is only effective on the wheels of the aircraft. How can the conveyor counteract any thrust against the air around the aircraft?

As I said in an earlier post, the wheelbrakes on the aircraft could be locked on, but the engines (presumably on the wings) could be at full throttle, pushing the AIR. At this time, the aircraft has both zero airspeed and zero groundspeed. (The conveyor is also at zero).

Now imagine that you tie a big cable to the back of the aircraft so that it really can't go anywhere. Now imagine that someone walks up to the wheels of the aircraft and then tries to turn the tires by hand (simulating what the conveyor would interpret as forward motion). Let's say that they could somehow get those tires spinning at 100mph, so that the conveyor is also going 100mph, but in the opposite direction.

Now, you've got the tires spinning at 100mph, the conveyor moving at -100mph, and the aircraft, engines still at full throttle, pushing on the air, but the aircraft isn't going anywhere because it's secured by a rope.

What is counteracting the engine thrust against the air?

The answer: NOTHING is counteracting the thrust! Therefore, the aircraft moves forward through the fluid of air. As it does so, the tires accelerate, the conveyor accelerates negatively, but the surrounding air does not accelarate negatively, so the aircraft can build up enough airspeed to take off.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:18 PM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by XPLORx4:
[b]But your hang-up is how motion through the fluid is achieved, right?
No, not at all.

I've been discussing this hypothetical scenario. In the scenario we have NO MOTION through the fluid of air.

In the scenario we only have the thrust from the engines.
[/b]
Where in here does it state there is no motion?

Quote:
Originally posted by Hawk:
How about this.....lets see if this can get to the ALR:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?
NYM - You're on a tangent, take a break. :rolleyes:
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:28 PM

NYM- Here's the scenario that I think you're trying to answer:

A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). There's also a giant fan at the far end of the runway that blows a headwind at the plane in exactly the same amount of thrust the engines provide.

Will the plane be able to take off?

The answer to this is yes, but it won't have a "viable flight" because the plane won't be able to make any forward progress; the giant fan is always blowing a headwind that prevents the engine thrust from moving the plane forward.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 07:58 PM

This'll be a long post (cause I love Physics)
Let's go back to the original hypothetical situation:
Quote:
A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

Will the plane be able to take off?
A lot of people have gotten hung up on the conveyorbelt motion vs the wheels motion debate.
Howver, the hypothetical scenario doesn't what kind of plane it is, or if it has wheels or pontoons.

In any event, the type of landing gear does not matter, because the landing gear is not reponsible for any propulsion in the airplane whatsoever. The landing gear only allows for the movement and steering of the plane on land/water.

Take your old Radio Flyer Wagon, for example. The wheels of your RFW allowed you to steer the wagon, but they did not make the wagon go - either gravity or someone(thing) pulling it created the motion. The wheel rotation just allows the wagon to move easily.

The conveyor belt speed vs wheel speed is a red herring - You could easily assume the plane is a pontoon style seaplane trying to take off using a water treadmill.

I gather from what is said in the hypothetical sscenario that the plane will remain in one place relative to the ground at any engine/plane speed because of the conveyor moving in the exact same speed in an oposite direction. That means at any Plane/conveyor belt speed, the difference in velocity between the airplane's wings and the ground will always be 0 mph.
So the Plane is moving, the runway conveyor is moving, and the assumption is that the body of the plane does not move relative to the ground.

And the relative motion between an airplanes wings and the ground is irrelavent to a plane achieving lift.

What we have to remember is that we are talking about a plane, in which the thrust created by the engine is created by the engine moving the air. The airplane wing in essense does not care what the relative speed of the wing is to the ground, but rather what the relative speed of the wing is to the air. That's what is going to generate the lift required for takeoff...

Now their are other factors for an airplane to takeoff, but since we will assume that the plane would have no problems taking off under normal conditions (the "treadmill" is not what I would call a normal condition)

Lift is generated by the difference in velocity between a solid object (the wing) and a fluid (air - a gas is a fluid). There must be motion between the object and the fluid: no motion, no lift. It makes no difference whether the object moves through a static fluid, or the fluid moves past a static solid object.

Now while the airplane appears to be staying in one place relative to the ground because of the "treadmill" under the plane, we know that air movement must be taking place. We know this because the motion of an airplane is created by the engine moving the air. Without any air movement, the plane and treadmill would remain stationary.

Keep in mind we aqre dealing with velocity (directional speed).
Adding 200mph east to 200mph west = 0 mph overall movement, even though the two moving objects are moving at 200 mph be themselves.

Because the airplan wings are affixed to the airplane, the wing and plane speed are the same.

Assuming the airspeed is 0mph...

So if the treadmill is is moving at 0mph, that means the the airplane must also be moving at 0mph, and that means the difference in velocity between the wings and air are both 0 mph - no lift possible

Now if the treadmill is moving at 200mph (west), that means the the plane must also be moving at 200 mph (east) - and while the difference in velocity between the Plane and treadmill remains 0 mph, the difference in velocity between the wing and air is 200 mph.

For the treadmill to reach speeds of 200mph, the plane has to be travelling 200mph (in the opposite direction) and while the ground is not moving in relation to the plane, the air is...since the air has to be moving for an airplane to move (engines) and thus for the treadmill to move. Thus this means the assumption that the plane remains stationary on the treadmill is false.

So yes, the Plane will be able to take off on the treadmill, assuming the plane could take off under normal conditons to begin with.

As for the bullets - both bullets (ignoring air resistance) would land at the same time. Both bullets are subject to the force of gravity (~9.8 m/s^2 - with slight variances based on locations: due to differing densities of the underlying crust, that the earth is not perfectly spherical, and the centripetal force from the motion of the earth's rotation on its axis varies at different latitudes.) So at the moment of being fired or dropped, the bullet begins to fall towards the earth with an acceleration of about 9.8 m/s^2.

The fastest speed of a fired bullet is ~1500m/s (~467.3ft/s) - bullet speeds depend on the type of bullet. The time it takes a bullet to travel 32.8 meters (10 feet) at 1500m/s (476.3ft/s) is 0.021867 seconds. In that time, the bullet will have fallen towards the earth approximately 0.002344 meters (0.000714 ft)...that is pretty much inisignificant to the human eye, which makes it appear as if the bullet is defying gravity.
If the bullets are fired and dropped at a hieght of 19.6 meters (5.97ft), they will both hit the ground at the exact same time (2 seconds later), but the dropped bullet will be directly below the spot where it was dropped, while the fired bullet will be found ~3000 meters away (914.36ft) maximum (again, ignoring air resistance)
Posted by: MidnightX

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 08:28 PM

*whew!* I understood that.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 08:36 PM

Both bullets will ONLY fall at the same time if they are in a vacuum. That's the ONLY WAY POSSIBLE.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:02 PM

Quote:
Originally posted by Hawk:
Both bullets will ONLY fall at the same time if they are in a vacuum. That's the ONLY WAY POSSIBLE.
I covered that point by posting "IGNORING AIR RESISTANCE." :rolleyes:

Quote:
Originally posted by Rockaholic:
As for the bullets - both bullets (ignoring air resistance) would land at the same time.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:15 PM

this is still fuckin goin on? sheesh guys, lay off the keyboard.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:16 PM

What's MOST interesting about this thread is its been able to illustrate those able to think, and those unable to think. (Well)

laugh

It seems the major mistake is thinking a plane moves like an Xterra.

If we remove that one obstacle, maybe 90% of the "Can't Fly" camp will see the light.

The Plane = Xterra confusion renders them thinking that the foward thrust of the engine won't make the plane go forward.

All the rollerskate, skateboard, ice, etc...analogies are lost on them...

The next concept is that the tires will move foward at a different actual speed than their rotation.

What the "Can't flies" are imagining is an Xterra on this belt, trying to go forward...and its just sitting there, spinning it's tires faster and faster as the belt matches its speed.

Of course, the Xterra can ONLY move if pushed by its tires...so the X = plane crowd are dead on about the X part.

laugh

The next BIG concept is that the plane's TIRE'S ARE NOT PUSHING IT.

The Engines thrust is pushing it...and the engines have NO idea what's going on down there...they just push the plane forward.

If we say that the ground speed of the plane and the air speed of the plane are the same based upon GPS coordinates during the take off...it might help.

OK - I'm firing up the engines...we have thrust....it pushes the plane forwards, to new GPS coordinates further down the accellerating conveyor, which is rolling under the plane at the plane's speed...

So the plane is moving across the gps coordinates at say 20 mph, and the belt is going towards it at 20 mph...so the tires are spinning at 40 mph....the plane is NOT where it started by GPS...its further down the belt's length.

By the time the plane's speed across the gps coordinates reaches it's take off speed, enough lift will be created by the air rushing over the wings, and the plane will be way down the runway/end of the conveyor belt...and the plane will be able to take off.

So - Main Concepts:

1. Plane not = Xterra

2. Thrust pushes plane, doesn't care what tires are doing....plane moves forward through GPS coordinates.

3. Thrust accelerates plane, forward motion is creating airflow over the wings, as the wings don't care what the tires are doing either.

4. Plane can take off when airflow over wings is fast enough.

I can't BELIEVE how many people this doesn't make sense to.

laugh
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:23 PM

Quote:
Originally posted by TJ:
What's MOST interesting about this thread is its been able to illustrate those able to think, and those unable to think. (Well)
or, in some case *cough*Madman*cough* at all...
Quote:
Originally posted by TJ:

I can't BELIEVE how many people this doesn't make sense to.

laugh
Well, it's similar to the discussion we had at ECXC, in that you have some people who are arguing about something they really don't understand (but think they are experts in).
Of course, at some point and time, we are all guilty of that. It's realizing and admitting it which is difficult
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:30 PM

So here's another one,

Take said Xterra and strap it to a dyno.

Take a Rocket of sufficient size to propel the X without the engine and strap it to the roof.

Operate the engine to gain let's say 90MPH or near the limiter, Perfectly safe on the dyno right. Disconnect the straps and fire the rocket.

Select those that apply:
A) Will the rocket propel the X off the Dyno? (Plane will fly crowd)
B) Will the X remain stationary on the Dyno at the same 90MPH? (Plane won't fly crowd)
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:32 PM

LOL

I guess giving the brain a work out is good, even if its on a tread mill.

laugh
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:38 PM

XPLORx4 -- No, that is not the scenario I was debating.

Rock -- I understand exactly what you are saying. It was a good post...(until your next post with your obvious jab).

I do think we are not all looking at the scenario the same way. Some have made comments about the wheels and friction. I wasn't even considering that because that is irrelevant to the given scenario.

Considering that this is a hypothetical situation, I'm not sure there is a correct answer. I think we are all incorporating some assumptions into our answers.

I just did a little internet searching on this scenario and I was surprised to see that it has been discussed in many places on the web. This is the first time I've ever seen this question posed. Some sites have extremely long threads regarding this topic. I haven't found any place that seems to provide a consensus even among people who claim to be engineers and scientists.

I have seen many people start calling each other names and attacking each other over a hypothetical situation. Maybe that is why someone here thought this thread would go to the ALR. [Freak] It's good to see that this discussion has been civil for the most part.

Does the question or scenario have enough information to generate a correct answer? I don't know. Maybe not. There are very valid points to be made for and against the flight of the aircraft in this hypothetical scenario.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 09:46 PM

Madman, check out my last post on page 8. If your theory was correct and the conveyor (treadmill) could apply force to counteract the aircraft, the little balsa prop would not take off. Yet it does. Try it yourself.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 10:13 PM

Quote:
Originally posted by NY Madman:
Rock -- I understand exactly what you are saying. It was a good post...(until your next post with your obvious jab).
Aww, it's not like you've never taken a "jab" at anyone before, now is it? wink
And the "jab" doesn't discount the information or the point I was making.
I'm not sure how the quality of that post is reduced because of a joke made in another...

Quote:
Originally posted by NY Madman:
Some have made comments about the wheels and friction. I wasn't even considering that because that is irrelevant to the given scenario.
Then I'm having trouble understanding why you posted this on the second page of the thread...
Quote:
Originally posted by NY Madman:
Quote:
Originally posted by TJ:

The lift is from air speed, which has zero to do with ground speed or tire speed.
You're wrong.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 10:18 PM

Quote:
Originally posted by TJ:
LOL

I guess giving the brain a work out is good, even if its on a tread mill.

laugh
[LOL]
But will the ideas from your brain take flight, or remain on the treadmill? laugh
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 10:27 PM

Its funny - the same arguments are going on all over the web it seems...and, there's people here who read the arguments there, and here, and depite the amazing similarities, merely conclude that there's no consensus...w/o absorbing any of the concepts presented.

I'm adding a concept btw:

I CAN breath if I'm on a tread mill, it does not prevent airflow into my lungs.

___________

A jet engine can draw air into it, as can a propeller plane draw air towards the prop...

_____________________

Maybe people are thinking of the conveyor belt given as more of an entire planet, with its own atmosphere and gravity or something, rather than as the described big tread mill?

_____________________

As the conveyor matches the plane's speed...if the plane is at rest, so is the belt.

I think for the example we have to assume its as given, an exact match...not a overshoot/correct/undershoot kind of thing.

I also think some of the "CF's" just can't get past the plane not = X thing...

Why would any one think air, wind, rain, snow, hail, butterflies, etc...would not blow about even if there's a tread mill under them?

If I go outside on my tread mill, and start walking at my usual 4 mph, and its raining...I get wet.

If you push me from behind, I will fall forward...if you strap a ACME Jet Pack to my back...I will fly off the tread mill...

If the tread mill spins at 60 mph...that jet pack will still send me flying off it.

Anyway - there's a bunch of over due Eureka Moments here.

laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 10:30 PM

I can't believe you guys are still on this subject! [LOL]
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 10:35 PM

Quote:
Originally posted by AHTOXA:
I can't believe you guys are still on this subject! [LOL]
Well, you're still reading it, aren't you? [LOL]
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 10:42 PM

Quote:
Originally posted by Conundrum:
So here's another one,

Take said Xterra and strap it to a dyno.

Take a Rocket of sufficient size to propel the X without the engine and strap it to the roof.

Operate the engine to gain let's say 90MPH or near the limiter, Perfectly safe on the dyno right. Disconnect the straps and fire the rocket.
Ok, assuming the rocket goes straight and doesn't sprial our of control:
the Xterra stays on the Dyno while the trocket goes flying forward because, after disconnecting the straps, the rocket is no longer attached to the Xterra...so the Xterra is thus unaffected by the rocket propulsion.
Although the pressure from the air movement from the rocket could possibly cause the Xterra to come off the dyno, but not neccesarily.

If the rocket spirals out of control - well, what the Xterra does depends on if the rocket flys back into the Xterra. If so, I would guess the Xterra comes off the dyno.

In either case, I would want to be really, really, really far away from wherever people are planning on doing this test
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 10:43 PM

OK, I just got back from the airport...I had my buddy build a giant conveyor belt down the runway, and we rigged it to match the plane's speed exactly (We're good).

laugh

Air Canada agreed to use it for one of their Tango Economy flights if we chipped in for some potato chips for the stew.

The plane fired up, and taxi'd onto the belt...let'r rip, and the thrust from the jets pushed the plane forward, down the runway belt.

The tires were turning at double the ground speed relative to the airport, as the belt whirred by beneath them.

It reached take off velocity, and took off...so we have our answer.

laugh

(Yay!)

OK - its settled!

BTW - it was weird, the whole experiment was almost ruined when this rocket engine with loose straps hanging from it went whizzing right bye, just missing the plane...

G'night all!

laugh
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 10:44 PM

[LOL]
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 10:52 PM

Quote:
Originally posted by Rockaholic:
Quote:
Originally posted by NY Madman:
[b]Rock -- I understand exactly what you are saying. It was a good post...(until your next post with your obvious jab).
Aww, it's not like you've never taken a "jab" at anyone before, now is it? wink
And the "jab" doesn't discount the information or the point I was making.
I'm not sure how the quality of that post is reduced because of a joke made in another... [/b]
I never said the quality of the post was reduced by your jab. That's an assumption on your part. Forget about it. It makes no difference. It's just routine ball busting and you are correct that I also do it occasionally.

Quote:
Then I'm having trouble understanding why you posted this on the second page of the thread...
Quote:
Originally posted by NY Madman:
Quote:
Originally posted by TJ:

[b]The lift is from air speed, which has zero to do with ground speed or tire speed.
You're wrong.
[/b]
I wasn't referring to the tires or anything related to the wheels in that particular comment.

I also believe that I was wrong for saying definitively that the aircraft in this scenario would not obtain flight.

I do however see a problem with the scenario. I can't say it would or would not take flight at this point.

We can discuss it further tomorrow or another time.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 28/12/06 11:02 PM

Oh, I inferred that you were implying that my post quality was reduced because of the jab.I just misunderstood what you meant.

You know, as scary as this is gonna sound....

I like the "new and improved" Madman.
Posted by: Xorand

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:06 AM

OK, based on the original plane/conveyor statement, we find that the conveyor speed is dictated by the plane's speed. How is the plane's speed measured so that the conveyor can move at that speed, too?

1. The plane's speed is determined by a sensor on a wheel and the plane's speed is assumed to be based on the rotational speed of the wheel (like a car speedometer). As the forward thrust of the plane's engine(s) start moving the plane forward, the wheels start rotating.

At the first feedback cycle, the conveyor system detects a 1 mph rotational speed of the wheel, so the conveyor starts moving in the opposite direction at 1 mph. What's this? Now the wheel is rotating at 2 mph. OK, the conveyor does the same. Now the wheel appears to be moving at 4 mph, so the conveyor does the same.

Do the math. Very quickly, the conveyor speed will approach infinity. So then, the question becomes - based on the conveyor's measurement and feedback cycle, how fast will the plane's tires blow up due to rotating beyond their design limits. laugh

2. The plane's speed is determined based upon measurements against a fixed point on the ground (not on the conveyor). When the plane is moving 10 mph relative to the fixed point, the conveyor also moves 10 mph in the opposite direction. The plane is moving through the air at 10 mph and the wheels are rotating as if it were traveling at 20 mph.

Let's say the plane can rotate and lift off the ground moving at a speed of 100 mph (air speed if no wind and also ground speed compared to the imaginary fixed point). The plane will lift off. Just before leaving the conveyor, the tires will be rotating twice as fast than if it were lifting off from a fixed runway.

In summary, the moving conveyor does nothing to affect the air moving across the plane's wings, only to affect the rotational speed of the plane's tires. The plane moves from thrust imparted upon the air by the propellors or turbines to move the body of the plane forward regardless of wheel speed and will eventually take off. (Disregarding, of course, the natural physical effects of wheels potentially spinning at some speed at which they were not designed to handle).

Edited to add: Now that this problem is solved, here's another one to consider: Using common mathematical equations, prove that 1 = -1.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:22 AM

Quote:
Originally posted by Xorand:
Edited to add: Now that this problem is solved, here's another one to consider: Using common mathematical equations, prove that 1 = -1.
Easy

The square root of 1 = 1 and -1.
The square root of 1 = the square root of 1, so then 1 = -1
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 06:08 AM

Quote:
Originally posted by Rockaholic:
[QUOTE]Easy

The square root of 1 = 1 and -1.
The square root of 1 = the square root of 1, so then 1 = -1
Not really, as having the same square root does not mean its the same number...as +/- 1 does not = 1.

And the "proof" above just says the same thing twice, and then draws the conclusion.

laugh

The square root of -1 is not 1, as 1 x 1 = 1, not -1.

laugh

That's where i comes in.

i = square root of -1
Posted by: RedX

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 06:19 AM

Quote:
Originally posted by TJ:
OK, I just got back from the airport...I had my buddy build a giant conveyor belt down the runway, and we rigged it to match the plane's speed exactly (We're good).

laugh

Air Canada agreed to use it for one of their Tango Economy flights if we chipped in for some potato chips for the stew.

The plane fired up, and taxi'd onto the belt...let'r rip, and the thrust from the jets pushed the plane forward, down the runway belt.

The tires were turning at double the ground speed relative to the airport, as the belt whirred by beneath them.

It reached take off velocity, and took off...so we have our answer.

laugh

(Yay!)

OK - its settled!
The only part you left out was the pilot and co-pilot arguing about whether it would work or not.

Co-pilot was "We're just gonna sit there."

Pilot: "Naw.....we'll be fine.....Wheels are just gonna spin double-time. I saw on XOC that that would be what happens."

Co-pilot: "I don't think so."

Pilot: "Trust me......we're Canadian......What could go wrong? wink "

Guess that's why he's the pilot. laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 06:33 AM

The Dyno analogy was with the rocket attached and the straps to the X removed prior to firing said rocket due to you couldn't get up to speed without the X being affixed to the Dyno in the first place. And I agree it would be very dangerous and stupid. Perfect for XOC. laugh
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 06:46 AM

Quote:
Originally posted by TJ:
And the "proof" above just says the same thing twice, and then draws the conclusion.

laugh

The square root of -1 is not 1, as 1 x 1 = 1, not -1.

laugh

That's where i comes in.

i = square root of -1
Yeah, well, I was just hoping no one would notice laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 07:18 AM

The plane takes off.

100% positive. There is no doubt.

A plane's speed is NOT measured at the wheel. There is no speedometer hooked up the wheels. This is NOT an assumption; it's a fact. A plane's speed is measured by a tube that air passes through. In it's most basic form, wind comes into the tube, spins a little turbine, and the speed of that turbine is shown on the indicator on the dash. Now, there are other calculations that enter in, to compensate for the speed of the natural wind occuring at the time, but there's no reason to go into that for this problem.

In order for any movement to be recorded, air must come into the tube, which means the aircraft is in motion (again, not including the natural wind from the equation as it was not presented in the hypothetical problem).

The conveyor belt motion is directly proportional to the amount of speed the aircraft has at any given time. That's a given part of the problem.

The only way the conveyor belt moves is if the plane is moving. The only way the plane is "moving" is if its indicator says it's moving. The only way the indicator says it's moving is if wind is coming into the tube & turning the turbine. The only way wind enters the tube is if the aircraft is moving.

Therefore, the plane takes off, regardless of how fast the conveyor belt moves, because once the plane reaches 150+/- MPH, the wings literally get sucked up into the air, which lifts the body of the plane.

There are no "assumptions" necessary for the answer to this hypothetical problem.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 07:59 AM

I think I may have been converted to the dark side. Maybe the plane takes off! lol.

I still think the conveyor could be configured to prevent the plane from going anywhere tho, there's gotta be some way to prevent the damn thing taking off. smile
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 08:04 AM

Quote:
Originally posted by MattyX:
Quoting from someone on CO 4X4 site who's quoting avweb:
Quote:
It was an interesting argument, but as things progressed, more rational heads prevailed, pointing out that the airplanes do not apply their thrust via their wheels, so the conveyor belt is irrelevant to whether the airplane will takeoff. One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards.
Did everybody forget that the scenario has been proven with a rubber-band plane?

...

EDIT: This is not rocket science, this is not aerospace engineering. This is a 9th grade physics problem and the correct answer is that the plane takes off.

....

Besides, that "Hu's on first" video I posted is hilarious. Y'all are missin' out! [Finger]
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 08:34 AM

I just asked my boss (he's a marine engineer, though).

He thinks it will absolutely NOT take off.

The air is fluid - while it IS moving through the engines, it is NOT moving over the wings, meaning...no lift.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 09:05 AM

Quote:
Originally posted by Mobycat:
I just asked my boss (he's a marine engineer, though).

He thinks it will absolutely NOT take off.

The air is fluid - while it IS moving through the engines, it is NOT moving over the wings, meaning...no lift.
If air is moving through the engines, then it's providing thrust, which will provide forward movement of the aircraft because the wheels are FREE-SPINNING...

The problem didn't say the conveyor was moving at the same speed as the engines are rotating. It says it's moving at the same speed the aircraft will move. Again, the aircraft movement is measured by air going into a tube. If no physical movment of the aircraft, then no air going into tube, which means no movement of conveyor. If conveyor moves, then that means air is going into tube which means aircraft is physically moving (the conveyor movement is directly proportional to the aircraft physically moving), which means it will take off once it reaches the speed necessary.
Posted by: TK1

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 09:11 AM

Wow, I wonder how that plane stays in the air with the landing gear up? :rolleyes:
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 09:17 AM

But the *whole* plane has to have forward momentum to lift. It doesn't have that.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 09:18 AM

An aircraft does not push against the surface to move, it pushes against air. Once the engines are turning, whatever the surface does is irrelevant. unless of course, it creates lateral friction instead of running longitudinally.

I name myself winner for being the first on this thread to get it right. Good thing I had to work at stupid o'clock yesterday. laugh
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 09:59 AM

Based on Xorand's response, I believe it may be possible in the hypothetical scenario for the plane to not take off, so I am in agreement with NYMadman, but not because the engines don't actually move the aircraft further forward on the runway. Note: the hypothetical scenario is vague about the term "speed", and it does not provide any details about the physical environment. Most of us are filling in the blanks with what we perceive as "common knowledge" in order to arrive at our conclusion that the plane will take off.

Here's something that only Xorand hinted at (which would prevent the plane from taking off):

The conveyor is either moving at an infinite speed, if its speed-detection mechanism uses the plane's wheelspeed sensors, or it's moving opposite to the plane's groundspeed, if its mechanism is based on that. Now, we know that inifinity is a theoretical concept, and that wheel bearings and tires certainly cannot REALLY rotate at an infinite speed before self-destructing (which would then cause the conveyor to stop). So, without functional wheels, the plane can't overcome the friction of its broken landing gear sticking out beneath its belly, and it won't take off.

If the conveyor moves backwards at the same speed the plane moves forwards through space, then you would need to know the design limitations of the wheel bearings and tires to determine if they can spin at twice the take-off speed of the aircraft. If they can't handle it, again you have broken landing gear and the plane will likely careen out of control as it rolls down the runway at 180+mph. If the landing gear can handle those speeds, then the aircraft will indeed take off.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:07 AM

Damn Marine Engineers...he's wrong of course.

He made the same mistake, that the thrust won't push the plane forward for some bizarre reason.

laugh

Here's another way to test it...

Walk on a tread mill, while holding an inflated ballon at the open end...point the balloon so that when you let go...it will fly the same direction you are facing, against the direction of the tread mill belt...

It will shoot forward, it will not hover over the belt.

laugh

If some how holding it down, right at the belt surface somehow changes things for you...let the balloon go again from there....it will STILL shoot forward.

The thrust from the air rushing out of the balloon will push it forward, even if the ground or a belt, etc...is going the wrong way below it.

I personally promise that it will work.

laugh

The farting sound from the balloon is a bonus.

Enjoy.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:08 AM

Revisit the initial problem statement:

Quote:
This conveyor has a control system that tracks the plane's
speed
Notice the control system tracks the plane's speed. Not the wheel's speed, but the plane.

Nobody gives a rat's arse about the wheel speed; only the Plane's speed. So any suggestion/description that's based on what the wheels are doing at the time is irrelevent. The Plane is moving (speed) in order for the conveyor belt to move.

Whether the plane has wheels, floats, skids, or freaking hovers over top of the conveyor is of no consequence to the solution to the problem question.
Posted by: TK1

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:13 AM

Quote:
Originally posted by Mobycat:
But the *whole* plane has to have forward momentum to lift. It doesn't have that.
Yes it does, the conveyor has no effect on the air which provides the resitance to the thrust which propels the plane forward independant of what the wheels are doing with the exception of the brakes being applied. The plane doesn't care about the how fast the wheels are spinning, the wheels will just spin happily along (as the plane moves forward on or past the conveyor) until the plane takes off and then they will get tucked into their cosy little compartments until it's time to land.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:13 AM

Quote:
Originally posted by Hawk:
How about this.....lets see if this can get to the ALR:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?
The conveyor is not turning at infinite speed. It is only matching the speed of the aircraft. Hence the conveyor's speed is limited by the aircraft's speed. If the aircraft is not moving, neither is the conveyor. If the aircraft is moving, it's using the air to do so, so no matter how fast the conveyor turns the plane will continue to move relative to a fixed point.

I can't think of any aircraft that have "wheelspeed sensors". Aircraft speed is measured in KIAS, Knots Indicated Air Speed (or mach, but not in this scenario). As air flows into a tube (the pitot tube) it spins a little pinwheel.

If the conveyor spins at triple or quadruple the plane's airspeed or groundspeed, it makes no difference.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:13 AM

Quote:
Originally posted by TJ:
Damn Marine Engineers...he's wrong of course.

He made the same mistake, that the thrust won't push the plane forward for some bizarre reason.

laugh

Here's another way to test it...

Walk on a tread mill, while holding an inflated ballon at the open end...point the balloon so that when you let go...it will fly the same direction you are facing, against the direction of the tread mill belt...

It will shoot forward, it will not hover over the belt.

laugh

If some how holding it down, right at the belt surface somehow changes things for you...let the balloon go again from there....it will STILL shoot forward.

The thrust from the air rushing out of the balloon will push it forward, even if the ground or a belt, etc...is going the wrong way below it.

I personally promise that it will work.

laugh

The farting sound from the balloon is a bonus.

Enjoy.
But remember, you have to test the ballon, first, to find out how fast it'll fly all on its lonesome, so you can make sure you setup the treadmill to match the speed... And it's no excuse if you can't run that fast; that's just the "bearings of the wheels" breaking...

laugh

(BTW: Even if you're a freaking Jamaican world class sprinter, the balloon is still gonna' leave your arse from the treadmill...)
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:14 AM

Quote:
Originally posted by TJ:
Damn Marine Engineers...he's wrong of course.

He made the same mistake, that the thrust won't push the plane forward for some bizarre reason.

laugh

Here's another way to test it...

Walk on a tread mill, while holding an inflated ballon at the open end...point the balloon so that when you let go...it will fly the same direction you are facing, against the direction of the tread mill belt...

It will shoot forward, it will not hover over the belt.

laugh

If some how holding it down, right at the belt surface somehow changes things for you...let the balloon go again from there....it will STILL shoot forward.

The thrust from the air rushing out of the balloon will push it forward, even if the ground or a belt, etc...is going the wrong way below it.

I personally promise that it will work.

laugh

The farting sound from the balloon is a bonus.

Enjoy.
BUT - a heavy ass planes weight is sitting on the treadmill / runway thingy. If I stood on top of the plane and did the same thing with the balloon it would shoot forward, because the balloon isn't sitting on a set of wheels etc, which need to rotate for it to gain speed to get airborn.

The wheels may not have any power going to them, but they still have to spin for the plane to move forwards along the runway. If the treadmill is totally cancelling out the forward motion of the wheels then the plane ain't going anywhere.

I'm torn, I thought I agreed with you guys now that the plane would take off, but my brain just says no it won't! lol.
Posted by: jorge

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:14 AM

Quote:
A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed
and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).
Not wheel speed.

There is no reason why the plane won't fly.

Think of this, if the plane is just sitting there, someone straps a rope to the plane. From off the belt they pull on it for 10 feet.

Now the plane will move 10 feet. The belt would have moved backwards 10 feet, and the wheels turned a total of 20 feet.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:18 AM

Quote:
Originally posted by RiNkY:

The wheels may not have any power going to them, but they still have to spin for the plane to move forwards along the runway. If the treadmill is totally cancelling out the forward motion of the wheels then the plane ain't going anywhere.

I'm torn, I thought I agreed with you guys now that the plane would take off, but my brain just says no it won't! lol.
Dammit Rinky! Quit getting hung up on the wheels... The wheels have nothing to do with it; they FREE-SPIN, regardless of how fast the plane moves or how fast the conveyor moves.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:22 AM

Quote:
Originally posted by RiNkY:
Quote:
Originally posted by TJ:
[b]Damn Marine Engineers...he's wrong of course.

He made the same mistake, that the thrust won't push the plane forward for some bizarre reason.

laugh

Here's another way to test it...

Walk on a tread mill, while holding an inflated ballon at the open end...point the balloon so that when you let go...it will fly the same direction you are facing, against the direction of the tread mill belt...

It will shoot forward, it will not hover over the belt.

laugh

If some how holding it down, right at the belt surface somehow changes things for you...let the balloon go again from there....it will STILL shoot forward.

The thrust from the air rushing out of the balloon will push it forward, even if the ground or a belt, etc...is going the wrong way below it.

I personally promise that it will work.

laugh

The farting sound from the balloon is a bonus.

Enjoy.
BUT - a heavy ass planes weight is sitting on the treadmill / runway thingy. If I stood on top of the plane and did the same thing with the balloon it would shoot forward, because the balloon isn't sitting on a set of wheels etc, which need to rotate for it to gain speed to get airborn.

The wheels may not have any power going to them, but they still have to spin for the plane to move forwards along the runway. If the treadmill is totally cancelling out the forward motion of the wheels then the plane ain't going anywhere.

I'm torn, I thought I agreed with you guys now that the plane would take off, but my brain just says no it won't! lol.[/b]
The wheels are providing NO forward motion. The forward motion is provided by the prop/turbine blowing enough air to push the plane along. The wheels do not *have* to spin, they just do. If you greased the whole conveyor with vaseline you could conceiveably do a wheels-up takeoff, but with considerably more friction (and hence, more need for power until the friction is overcome or until lift is achieved).
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:22 AM

I hope this doesn't get to almost 500 pages like this forum on the same subject: http://forum.physorg.com/index.php?s=314...05&#entry157036

How can I not hang around on the wheels, the plane before it gains any lift from the air has to make it to 150mph or whatever speed we feel is acceptable for lift off. Which means the wheels have to get the plane to that air speed before we have lift off. If the conveyor is reversing as fast as the plane is thrusting forward, I'm still 51% convinced that it ain't going anywhere! lol.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:25 AM

The wheels don't get the plane anywhere, at any speed, ever. They just reduce friction with the ground.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:42 AM

RiNkY-

Stop thinking about the wheels. Imagine you're on a skateboard in an airport, and you're standing 20 feet from the end of one of those people-mover conveyor belts (on the side where people step off, not where you get on), but there's no people on it. Imagine that you have a jetpack attached to your back and that somehow you're able to control the jetpack so you don't kill yourself.

How do you start moving? You fire up the jetpack, right? How did you start moving? The jetpack pushed against the air.

OK, now you're moving forward because the jetpack is pushing the air, and you now jump onto the conveyor (which is moving backwards). Your roller skate wheels suddenly start spinning faster. What happens to the air that the jetpack is pushing against? Did it suddenly become very windy? No? Then you continue to move along the conveyor, although opposite to its direction of travel.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:07 AM

The plane has weight that has to be overcome. To do that, it has to move down the runway.

The air - the engines are not pushing the rest of the plane. The air is being sucked through the engines and pushing it out the other end. The air over the wings is NOT moving.

If the ground is solid, the plane is moving down the runway - THEN the air over the wings is moving in relation to the plane. Otherwise, it's not.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:10 AM

By the way - the rubber band plane would probably take off, because the propeller IS pushing air over the wings.

But we are talking about a jet engine, no?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:18 AM

A prop or turbine does not push air over wings (maybe a little, but not enough to matter). It takes air from in front and pushes it to the back. Because the air wants to keep doing what it's doing (sitting still or blowing in whatever direction it was already going) the prop/turbine meets resistance. The resistance makes the prop/turbine pull forward, and hence, pull the plane forward. Just like rowing a boat, but you're pushing water instead of air to get moving.

Because you're relying on your ability to move air to create forward motion, the surface can work against you and it won't matter, as long as you have a way to reduce friction with the surface. Something like wheels.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:25 AM

Lets invert the problem. Say you have a conveyor suspended over water, directly over your power boat. Your boat is on calm water and has a set of wheels overhead which remain in contact with the conveyor. [The conveyor in this example would work against the direction of the boat, just like the other works against the direction of the plane] If you try to accelerate the boat, and the conveyor spins against it, will you move forward?

Hint- the answer is yes.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:31 AM

The boat doesn't need lift. The propeller pushes it.

Water isn't a gas like air. The molecules are closer together.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:33 AM

Quote:
Originally posted by Mobycat:
because the propeller IS pushing air over the wings.
Moby, planes don't fly because their propellers or engines push air over the wings. There are lots of winged objects that don't have propellers. Gliders and birds, for example.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:34 AM

Sure, the boat doesn't need lift, but you said the propellor pushes it, and you're right. The plane doesn't need lift to move forward, just to fly. It can move forward, though, and increase its airspeed enough to attain lift, no matter what the conveyor does.

::edited for grammar::
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:34 AM

Right. I'm just saying a prop plane would be more likely to be able to obtain lift.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:35 AM

Quote:
Originally posted by MattyX:
It can move forward, though, and increase its airspeed enough to attain lift, no matter what the conveyor does.

::edited for grammar::
Right. But it can't move forward. Not if the conveyor is matching *exactly* the speed.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:38 AM

On a somewhat related note - jets on aircraft carriers do NOT take off with the wind. They take off against it. If they take off with the wind, they may not have enough lift.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:38 AM

Quote:
Originally posted by Mobycat:
Right. I'm just saying a prop plane would be more likely to be able to obtain lift.
And why is that?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:39 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]It can move forward, though, and increase its airspeed enough to attain lift, no matter what the conveyor does.

::edited for grammar::
Right. But it can't move forward. Not if the conveyor is matching *exactly* the speed.[/b]
Why not? You said that the boat would move forward, but the plane wouldn't? Why is that?
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:39 AM

Quote:
Originally posted by MattyX:
Sure, the boat doesn't need lift, but you said the propellor pushes it, and you're right. The plane doesn't need lift to move forward, just to fly. It can move forward, though, and increase its airspeed enough to attain lift, no matter what the conveyor does.

::edited for grammar::
Put that same boat in a river. Trying to go UPstream. If the stream is matching the speed of the propeller...no movement.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:40 AM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Mobycat:
[b]Right. I'm just saying a prop plane would be more likely to be able to obtain lift.
And why is that?[/b]
Because it's pushing air over the wings. Albeit, very little...*probably* not enough to give it lift...but if the prop were large enough, it might.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:44 AM

Think of it this way.

You have a podium connected to the wing. Stand on it. You are not going to have wind blowing on you. With no wind, there is no lift on the wings.

We are assuming the air is calm around the plane, right?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:45 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by XPLORx4:
[b]
Quote:
Originally posted by Mobycat:
[b]Right. I'm just saying a prop plane would be more likely to be able to obtain lift.
And why is that?[/b]
Because it's pushing air over the wings. Albeit, very little...*probably* not enough to give it lift[/b]
So what would be enough to give it lift?
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:46 AM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Mobycat:
[b]
Quote:
Originally posted by XPLORx4:
[b]
quote:
Originally posted by Mobycat:
Right. I'm just saying a prop plane would be more likely to be able to obtain lift.
And why is that?[/b]
Because it's pushing air over the wings. Albeit, very little...*probably* not enough to give it lift[/b]
So what would be enough to give it lift?
Beats me. Whatever the speed is needed to give that particular plane lift.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:47 AM

Quote:
Because it's pushing air over the wings. Albeit, very little...*probably* not enough to give it lift...but if the prop were large enough, it might.
In a single engine prop plane, the prop wash to which you are referring, is confined to the area where the wings are joined to the fuselage and would not produce enough lift by itself to lift the aircraft.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:48 AM

Quote:
Originally posted by Mobycat:
Whatever the speed is needed to give that particular plane lift.
And how does the plane get speed?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:49 AM

Liz- I've been noticing you've been changing the thread title. It's pretty funny. Keep it up! [ThumbsUp]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:49 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]Sure, the boat doesn't need lift, but you said the propellor pushes it, and you're right. The plane doesn't need lift to move forward, just to fly. It can move forward, though, and increase its airspeed enough to attain lift, no matter what the conveyor does.

::edited for grammar::
Put that same boat in a river. Trying to go UPstream. If the stream is matching the speed of the propeller...no movement.[/b]
Ah, but that is an erroneous analogy. The overhead conveyor plays exactly the same role as the conveyor in the first problem. You said yourself earlier (essentially) that planes like to take off into the wind (with a headwind), so assuming that there would be, say, ten knots headwind or headwater. That value being constant, any equal and opposite force would keep a craft (air or water) stationary. That would mean ten knots of airspeed or waterspeed. once the power of the craft overcomes the headwind/water, the craft moves forward, regardless of what the conveyor might do.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:49 AM

Quote:
Originally posted by Scrabo:
Quote:
Because it's pushing air over the wings. Albeit, very little...*probably* not enough to give it lift...but if the prop were large enough, it might.
In a single engine prop plane, the prop wash to which you are referring, is confined to the area where the wings are joined to the fuselage and would not produce enough lift by itself to lift the aircraft.
Exactly. For that, the prop would have to be as long as (or close) to the wingspan. Plus have enough force to put enough air over the wings.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:50 AM

Moby- how do you think a glider can become airborne?
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:51 AM

Quote:
Originally posted by MattyX:
Quote:
Originally posted by Mobycat:
[b]
Quote:
Originally posted by MattyX:
[b]Sure, the boat doesn't need lift, but you said the propellor pushes it, and you're right. The plane doesn't need lift to move forward, just to fly. It can move forward, though, and increase its airspeed enough to attain lift, no matter what the conveyor does.

::edited for grammar::
Put that same boat in a river. Trying to go UPstream. If the stream is matching the speed of the propeller...no movement.[/b]
Ah, but that is an erroneous analogy. The overhead conveyor plays exactly the same role as the conveyor in the first problem. You said yourself earlier (essentially) that planes like to take off into the wind (with a headwind), so assuming that there would be, say, ten knots headwind or headwater. That value being constant, any equal and opposite force would keep a craft (air or water) stationary. That would mean ten knots of airspeed or waterspeed. once the power of the craft overcomes the headwind/water, the craft moves forward, regardless of what the conveyor might do.[/b]
But we are not assuming a headwind. We are assuming calm air. If the plane overcomes the headwind/water (conveyor belt), then the puzzle is flawed - because that would mean the conveyor belt has NOT matched the speed of the wheels.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:52 AM

Quote:
Originally posted by XPLORx4:
Moby- how do you think a glider can become airborne?
It has to have wind over the wings.

A stationary plane on a conveyor belt in calm air does NOT have wind going over the wings.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:52 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by XPLORx4:
[b]Moby- how do you think a glider can become airborne?
It has to have wind over the wings.[/b]
And since it has no built-in means of propulsion, how does it get wind over its wings?
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:55 AM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Mobycat:
[b]
Quote:
Originally posted by XPLORx4:
[b]Moby- how do you think a glider can become airborne?
It has to have wind over the wings.[/b]
And since it has no built-in means of propulsion, how does it get wind over its wings?[/b]
Either by a windy day, or another object pulling it.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:56 AM

Quote:
Originally posted by Mobycat:
But we are not assuming a headwind. We are assuming calm air. If the plane overcomes the headwind/water (conveyor belt), then the puzzle is flawed - because that would mean the conveyor belt has NOT matched the speed of the wheels.[/QB]
For this analogy:

Headwind=headwater

Calm wind= calm water

conveyor underfoot=conveyor overhead

headwind DOES NOT = conveyor

Headwater DOES NOT = conveyor
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:56 AM

Quote:
Originally posted by MattyX:
Quote:
Originally posted by Mobycat:
But we are not assuming a headwind. We are assuming calm air. If the plane overcomes the headwind/water (conveyor belt), then the puzzle is flawed - because that would mean the conveyor belt has NOT matched the speed of the wheels.
For this analogy:

Headwind=headwater

Calm wind= calm water

conveyor underfoot=conveyor overhead

headwind DOES NOT = conveyor[/QB]
Calm wind does NOT equal calm water.

Gas does NOT equal liquid.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:57 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by XPLORx4:
[b]
Quote:
Originally posted by Mobycat:
[b]
quote:
Originally posted by XPLORx4:
Moby- how do you think a glider can become airborne?
It has to have wind over the wings.[/b]
And since it has no built-in means of propulsion, how does it get wind over its wings?[/b]
Either by a windy day, or another object pulling it.
Yes! So, let's say that this glider is being pulled by another object, possibly either a car, another airplane, or a really fast winch.

Let's say that the towing device is at the far end of the runway, not attached to the conveyor belt.

Place the glider on the conveyor belt, and start the towing device.

Does the glider take off?
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:59 AM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Mobycat:
[b]
Quote:
Originally posted by XPLORx4:
[b]
quote:
Originally posted by Mobycat:
quote:
Originally posted by XPLORx4:
Moby- how do you think a glider can become airborne?
It has to have wind over the wings.[/b]
And since it has no built-in means of propulsion, how does it get wind over its wings?[/b]
Either by a windy day, or another object pulling it.
Yes! So, let's say that this glider is being pulled by another object, possibly either a car, another airplane, or a really fast winch.

Let's say that the towing device is at the far end of the runway, not attached to the conveyor belt.

Place the glider on the conveyor belt, and start the towing device.

Does the glider take off?

That's flawed. You are now moving the glider in relation to the *calm* air - making it no longer calm to the glider.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:00 PM

Moby, it's for the sake of analogy. Are you just trolling now?

The air and the water are both the media through which their respective crafts propel themselves. The conveyor is simply there, touching an innocuous part of the craft which will have no effect on how that craft gets where it's going.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:01 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by XPLORx4:
[qbDoes the glider take off?
That's flawed. You are now moving the glider in relation to the *calm* air - making it no longer calm to the glider.[/QB]
That's right! The glider is now MOVING through *not calm* air. (Moving air is inherently *not* calm. The glider is still moving! But the conveyor belt is also moving backward! Why? Because the glider is being towed!
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:01 PM

They aren't the same craft. You really can't compare them.

Again...if the plane is standing still (it is, if the conveyor is moving), then there is NO wind to give the wings lift. The wings MUST have lift to get the plane off the ground.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:02 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Mobycat:
[b]
Quote:
Originally posted by XPLORx4:
[qbDoes the glider take off?
That's flawed. You are now moving the glider in relation to the *calm* air - making it no longer calm to the glider.[/b]
That's right! The glider is now MOVING through *not calm* air. (Moving air is inherently *not* calm. The glider is still moving! But the conveyor belt is also moving backward! Why? Because the glider is being towed![/QB]
The plane is not being towed. So it doesn't move against the calm air. No lift.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:03 PM

Quote:
Originally posted by Mobycat:
They aren't the same craft. You really can't compare them.

Again...if the plane is standing still (it is, if the conveyor is moving), then there is NO wind to give the wings lift. The wings MUST have lift to get the plane off the ground.
If the plane is standing still, then the conveyor belt isn't moving, and it may as well be a parking lot.

Moby, what part of the plane has to move in order for the plane to be moving?

For your arguement to work, you would have to say the tires. But the tires on a commercial airliner are tucked up under the body, so does the plane not move, then, if the tires aren't rotating?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:03 PM

Quote:
Originally posted by Mobycat:
That's flawed. You are now moving the glider in relation to the *calm* air - making it no longer calm to the glider.[/QB]
His example is not flawed. In it, the winch/truck/plane-not-on-a-conveyor (or on a conveyor, as it turns out) replaces a prop/turbine as a means of propulsion. None of these means are influenced by the conveyor.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:04 PM

Quote:
Originally posted by Mobycat:
The plane is not being towed. So it doesn't move against the calm air. No lift.
Forget the plane for a second. Does a glider being towed get lift?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:05 PM

The bitter taste of poor quality remains long after the sweetness of low price is forgotten.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:05 PM

I'd rather apologize once for a higher price, than over and over for poorer quality.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:06 PM

Yeah, it's better to ask forgiveness than to ask for permission.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:08 PM

Quote:
Originally posted by Mobycat:
The plane is not being towed. So it doesn't move against the calm air. No lift.[/QB]
A plane does not need lift to move forward. It needs only to push air.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:08 PM

Quote:
Originally posted by porsche996:
Quote:
Originally posted by Mobycat:
[b]They aren't the same craft. You really can't compare them.

Again...if the plane is standing still (it is, if the conveyor is moving), then there is NO wind to give the wings lift. The wings MUST have lift to get the plane off the ground.
If the plane is standing still, then the conveyor belt isn't moving, and it may as well be a parking lot.

Moby, what part of the plane has to move in order for the plane to be moving?

For your arguement to work, you would have to say the tires. But the tires on a commercial airliner are tucked up under the body, so does the plane not move, then, if the tires aren't rotating?[/b]
No, not the tires.

Assuming calm air, that means the plane has to move in relation to the air...and the ground (since it's calm). That ain't gonna happen.

Put a windsock on the tip of the wing. Start the experiment. That sock is not going to flutter at ALL. If it's not fluttering, there is no wind to provide lift for the plane.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:09 PM

Quote:
Originally posted by MattyX:
Quote:
Originally posted by Mobycat:
The plane is not being towed. So it doesn't move against the calm air. No lift.
A plane does not need lift to move forward. It needs only to push air.[/QB]
It CAN'T move forward. It's not weightless. The conveyor belt keeps it from moving foward.

If it does move forward, the conveyor belt is failing to meet the speed.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:11 PM

Dude, Moby! Forget the plane for a second. Does a glider-in-tow on a conveyor belt move forward, get wind over its wings, and take off?
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:15 PM

Not if the car is on a conveyor belt.

You're introducing an external power supply.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:16 PM

By the way...who's the fucker who started this thread?!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:17 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]
Quote:
Originally posted by Mobycat:
The plane is not being towed. So it doesn't move against the calm air. No lift.
A plane does not need lift to move forward. It needs only to push air.[/b]
It CAN'T move forward. It's not weightless. The conveyor belt keeps it from moving foward.

If it does move forward, the conveyor belt is failing to meet the speed.[/QB]
Not correct. The aircraft has weight, yet can still taxi around. It taxis by pushing air, not by turning its wheels. The conveyor cannot keep the plane from moving any more than an overhead conveyor (even with equal load-bearing, say, a weight of 500 lbs on a vessel weighing 500 lbs) can't keep a boat from moving.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:18 PM

Quote:
Originally posted by Mobycat:
Not if the car is on a conveyor belt.

You're introducing an external power supply.
The car's NOT on the conveyor belt. Yes, the power supply is EXTERNAL. But it's external to the CONVEYOR belt! The power supply is still ATTACHED TO THE GLIDER.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:18 PM

Moby... The plane doesn't power/move because it's wheels move. It's wheels moving is irrelevent. And whatever they're touching is irrelevent. They spin freely, providing NO resistance to the aircraft movement. Therefore, you can spin 'em any direction you want, sideways even, and it won't matter because the plane's overall movement is caused by its engines, not it's wheels.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:31 PM

Stolen from another forum:
Quote:
so the conveyor cant stop the plane from moving forward under its own power because it cant move the air that the plane propels itself with. plane will go forward and take off.

True the conveyor will match the speed of the plane but its only pushing against the wheels which do not propel a plane forward or measure speed of the plane.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:40 PM

Since the air is calm, the plane MUST move relative to the ground to get air flowing across it's wings.

The conveyor belt prevents it from moving in relation to the ground.

If the plane is taxiing (sp?), the conveyor belt will STILL keep it from moving.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:42 PM

No, it really won't.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:45 PM

Quote:
Originally posted by Mobycat:
The conveyor belt prevents it from moving in relation to the ground.
No, it won't. The tires on the plane spin freely.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:45 PM

It will.

Again...put a windsock on the wing. It will not flutter.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:52 PM

It is physically not possible for freely rotating wheels to prevent an airplane from moving.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:53 PM

Quote:
Originally posted by Mobycat:
Since the air is calm, the plane MUST move relative to the ground to get air flowing across it's wings.

The conveyor belt prevents it from moving in relation to the ground.

If the plane is taxiing (sp?), the conveyor belt will STILL keep it from moving.
I swear you're just trolling now. The conveyor can apply a certain amount of friction to the wheels. The prop/turbine can provide much more force (more) directly to the fuselage of the aircraft. The force applied to the bottom of the wheels/tires causes them to spin on their respective axes (axises?) but not hold the fuselage back. Greater thrust than resistance causes the plane to move forward. As the plane moves forward the conveyor speeds up, yet is only causing friction with the bottom of the spinning tires. The prop/turbine is creating greater friction with the air. The aircraft continues to move forward at a greater rate. then, of course, as air moves over the wing (because the plane is not stationary, it is moving) the effect of gravity is less and less as the plane accelerates, resulting in less friction on the tires. Eventually lift is achieved, and the plane can go look for an inverted conveyor with a boat underneath it.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:54 PM

Quote:
Originally posted by Mobycat:
It will.

Again...put a windsock on the wing. It will not flutter.
Not if the plane isn't moving.

But if the conveyor belt is moving, then the plane is moving. Period. That's in the given problem statement.

And if the plane is moving, then that windsock will be flapping like all hell.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:55 PM

Quote:
Originally posted by MattyX:
The aircraft continues to move forward at a greater rate. then, of course, as air moves over the wing (because the plane is not stationary, it is moving) the effect of gravity is less and less as the plane accelerates, resulting in less friction on the tires. Eventually lift is achieved, and the plane can go look for an inverted conveyor with a boat underneath it.
Again, you have changed it. The conveyor matches the speed in the opposite direction. The aircraft can NOT move forward at a greater rate - the conveyor will match it. It cannot move forward at ALL.

The airspeed is 0.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:56 PM

Quote:
Originally posted by porsche996:
Quote:
Originally posted by Mobycat:
[b]It will.

Again...put a windsock on the wing. It will not flutter.
Not if the plane isn't moving.

But if the conveyor belt is moving, then the plane is moving. Period. That's in the given problem statement.

And if the plane is moving, then that windsock will be flapping like all hell.[/b]
OK. Stand next to the plane on the side of the conveyor belt.

In relation to you (which is also in relation to the wind, since it's calm), the plane WILL NOT BUDGE.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 12:59 PM

If the plane moves at all, then it's by the thrust of its engines.

If the plane moves, then the conveyor moves in an opposite direction and speed.

The conveyor only applies rotational force to the wheels of the plane. The rotational force of the wheels is NOT then applied to the thrust of the engines; the two are not linked in any way.

Therefore, the plane moves independent of the wheel rotation, at all times. Hence the reason a plane can fly, yet the wheels are not rotating at all.

Don't make me go Newtonian on your ass...
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:00 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]The aircraft continues to move forward at a greater rate. then, of course, as air moves over the wing (because the plane is not stationary, it is moving) the effect of gravity is less and less as the plane accelerates, resulting in less friction on the tires. Eventually lift is achieved, and the plane can go look for an inverted conveyor with a boat underneath it.
Again, you have changed it. The conveyor matches the speed in the opposite direction. The aircraft can NOT move forward at a greater rate - the conveyor will match it. It cannot move forward at ALL.

The airspeed is 0.[/b]
Just because the conveyor matches the planes speed does not mean that the plane is stationary. I have changed nothing. No matter how fast the conveyor spins, as long as the prop is pushing air it will move forward.

::ETA:: The key is greater friction with the air (caused by the prop/jet turbine pushing air) than friction with the conveyor.
Posted by: slomatt

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:26 PM

Quote:
Originally posted by Mobycat:
Again, you have changed it. The conveyor matches the speed in the opposite direction. The aircraft can NOT move forward at a greater rate - the conveyor will match it. It cannot move forward at ALL.

The airspeed is 0.
Mobycat, please explain how the conveyor belt applies force to the aircraft. Do you agree with the following statement?

-- The force the conveyor belt applies to the aircraft is due to friction in the wheel bearings and deformation of the tires making them not perfectly circular. --

If we agree on the above statement then the aircraft needs to extert enough force (engines pushing against the atmosphere) to overcome the conveyor belt's force before the plane can move. I think it's been established that once the plane generates enough lift via. airspeed that it can take off.

So, if you agree with the above (and please post your arguments if you don't) then the critical issue is how much force the conveyor can exert on the plane.

Since the conveyor can only exert force through friction in the bearings and wheel deformation there is no way it can extert enough force to overcome the jet's engines. If it could that would mean that jet's would never take off in the first place because they wouldn't be able to get moving, which obviously is not the case. The most that could happen would be that as the jet accellerates the wheels will be spinning at 2x the normal speed, which might cause some slight additional resistance. The only way the jet won't take off is if the wheel bearings fail because they are subjected to speeds outside of their design parameters.

On a side note, when people talk about the jet's "speed" are you talking air speed or ground (wheel) speed? If we are talking air speed then the jet would need to first move relative to the air to induce movement in the conveyor. If the argument is that the conveyor can extert enough force to stop the jet then we wind up with the jet's engines on full and neither it or the conveyor moving at all, which makes absolutely no sense.

- Matt
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:30 PM

Moby, I'm afraid you're mistaken in this case. Your concept would have been correct if we were talking about a vehicle which is propelled down the runway by providing power to the wheels.

This is a completely different scenario. You must see that the wheels or the speed of the coveyor have absolutely no effect on the plane taking off.

It will fly.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:32 PM

The plane has to gain airspeed to lift off. The force of gravity keeps it on the ground when it's stationary.

For it to move forward, it would have groundspeed. The air is calm. That means the air is equal to the ground in relation to the plane. If the plane cannot move on the ground, it cannot move in the air.

It cannot move on the ground, because the conveyor is negating it's forward movement.

It wouldn't matter if the wheels had a true no-friction connection to the plane. The conveyor is STILL going to counteract it.

It WOULD matter if the wheels were locked - the jets should have enough thrust to burn the wheels off (since the conveyor then wouldn't move, since the wheels aren't moving).

The wheels move because of the jets. Which means the jets in effect move the conveyor (since it matches the speed in opposite).
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:33 PM

Quote:
Originally posted by AHTOXA:
Moby, I'm afraid you're mistaken in this case. Your concept would have been correct if we were talking about a vehicle which is propelled down the runway by providing power to the wheels.

This is a completely different scenario. You must see that the wheels or the speed of the coveyor have absolutely no effect on the plane taking off.

It will fly.
Actually it's not.

What moves the wheels? (regardless of whether they are free spinning)
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:42 PM

Quote:
Originally posted by Mobycat:


What moves the wheels? (regardless of whether they are free spinning)
The plane's motion through SPACE (both on the ground and through AIR) sets the wheels in motion.

It's a given that as something that rests on the ground moves along the ground, it also moves through the air, too. It's the air that's being pushed through the engines, not the ground.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:44 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Mobycat:
[b]

What moves the wheels? (regardless of whether they are free spinning)
The plane's motion through SPACE (both on the ground and through AIR) sets the wheels in motion.[/b]
But it's not moving through the space. The air is moving at the same speed as the plane - relative to the conveyor belt.

What moves?

Conveyor belt
Wheels

What does NOT move?

Ground
Air

Since the air is not moving, it cannot provide lift to overcome the downward force of gravity.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:46 PM

OK.

Put one plane on one end of the conveyor belt.

Put another on the opposite end.

The conveyor belt counteracts the tires of one of them.

The other plane does not start it's engines. It will go with the conveyor belt.

Which will take off?

The one that has not started it's engines. The conveyor has pushed it through the air providing the pressure to cause lift.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:47 PM

Nothing moves the wheels. The wheels are simply freespinning. Yes, when the treadmill is moving backwards there's litte friection force applied to the wheels but way not enough to overcome the force of thrust delivered by the engines.

The force of thrus is completely not dependent on the speed of ground. No matter how fast the ground moves underneath, or whether it moves fast or slower, it would play no effect.

Let's say the same plane is on the same runway, BUT the direction of the runway movement would now be the same as the direction of the plane's take off.

Let's say that when the plane guns the jet engine the runway treadmill will spin at 400 mph ground speed (example). Let's assume that it would reach that speed instanteniously. Assume that there's no friction or rolling resistance.

The plane now is standing still and not moving anywhere. Engines are off. Now turn on the engines. The plane begins to take off.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:48 PM

Quote:
Originally posted by AHTOXA:
Nothing moves the wheels.
Wrong. The propulsion of the jets move the wheels.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:51 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by AHTOXA:
[b]Nothing moves the wheels.
Wrong. The propulsion of the jets move the wheels.[/b]
Wrong. Wheels move due to plane accelerating down the runway. But the egines do NOT apply torque to the wheels thus spinning them. That's not a car. Maybe you're not really clear on how the jet engine works.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:54 PM

Quote:
Originally posted by Mobycat:
The plane has to gain airspeed to lift off. The force of gravity keeps it on the ground when it's stationary.
Correct. Gravity also keeps the plane on the ground when it's moving. If it's moving at a great enough speed, gravity is counter-acted by aerodynamic lift.
Quote:
Originally posted by Mobycat:
For it to move forward, it would have groundspeed. The air is calm. That means the air is equal to the ground in relation to the plane. If the plane cannot move on the ground, it cannot move in the air.
It means the air is stationary, even if the conveyor moves under it. Here you are assuming that the aircraft cannot move on the ground.
Quote:
Originally posted by Mobycat:
It cannot move on the ground, because the conveyor is negating it's forward movement.
Incorrect. The conveyor cannot exert enough force or friction on the tires to counteract the thrust of a jet or prop.
Quote:
Originally posted by Mobycat:
It wouldn't matter if the wheels had a true no-friction connection to the plane. The conveyor is STILL going to counteract it.
The very purpose of the wheels is to reduce friction with the ground (conveyor, in this case). The purpose of the prop/jet is to create friction with the air. The props/jets create immense power and lots of friction with the air, creating forward movement. The wheels make it easier to move the aircraft over the surface. The surface moves in the opposite direction of the plane, with the conveyor, at twice the normal rate.
Quote:
Originally posted by Mobycat:
It WOULD matter if the wheels were locked - the jets should have enough thrust to burn the wheels off (since the conveyor then wouldn't move, since the wheels aren't moving).
The wheels being locked matters in another way-it is creating more friction with the conveyor/ground. This friction can still be overcome, though it is not safe. An aircraft under full power with brakes locked will move forward.
Quote:
Originally posted by Mobycat:
The wheels move because of the jets. Which means the jets in effect move the conveyor (since it matches the speed in opposite).
The jets do not move the wheels. The jets push the plane, and the friction with the ground causes the wheels to move. The original problem says nothing about the wheels pushing the conveyor, it says the conveyor matches the plane's speed.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:57 PM

ok its going to take a blond to answer the question.. If you are in the gym and there happens to be a blond on the treadmill, she is running as fast as she can, and her hair is down.. Will her hair fly back like it would if she was running on the side of the road.. NO.. There is your answer..
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:57 PM

Quote:
Originally posted by MattyX:
The conveyor cannot exert enough force or friction on the tires to counteract the thrust of a jet or prop.
Then the question is flawed. If it cannot exert enough force, it cannot match the speed. The question said it can.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:58 PM

Well, I'm outta here. Time to go home.

I have the question sent to a couple people - 1 engineer, 1 pilot.

We'll see what their opinion is.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 01:59 PM

Quote:
Originally posted by far west X:
ok its going to take a blond to answer the question.. If you are in the gym and there happens to be a blond on the treadmill, she is running as fast as she can, and her hair is down.. Will her hair fly back like it would if she was running on the side of the road.. NO.. There is your answer..
this is assuming that the treadmill of the plane can keep up with the top speed of the jet.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 02:05 PM

Quote:
Originally posted by Mobycat:

It cannot move on the ground, because the conveyor is negating it's forward movement.

The friectional force of the conveyor belts is NOWHERE near enough to negate the Thrust force of the jet engine.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 02:14 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by AHTOXA:
[b]Nothing moves the wheels.
Wrong. The propulsion of the jets move the wheels.[/b]
If you push/pull a wagon, are you moving the wheels, or are the wheels reacting to your kinetic energy?

When you drive your rig, the engine turns the wheels directly (through the drivetrain) creating the forward motion of the truck. When you push a radio flyer, the wheels are reactive, not active. put a radio flyer on an old-fashioned treadmill (which requires you to push it to get it going). You can roll it right off and the treadmill won't turn, because you're not exerting any force on the surface.
Quote:
Then the question is flawed. If it cannot exert enough force, it cannot match the speed. The question said it can.
The speed of the aircraft and the speed of the conveyor are independant quantities. The question does not say that the plane will be kept stationary by the conveyor, it says that the conveyor will spin at the same speed in the opposite direction. Ergo- plane travels 120 KIAS, conveyor goes 120 knots, wheels spin at 240knots until liftoff.

::eta:: Speed and force are different things. The conveyor can still match the plane's speed but not be able to push the plane back. It can't push the plane back because some clever monkey put wheels on the bottom, so when the conveyor pushes against the bottom of the tire, it just spins. Meanwhile the plane is pushing air and travelling at the same speed as the conveyor, but in the opposite direction. [notice I said "travelling", not "sitting"] No matter how much the conveyor pushes, all it affects are the wheels. It cannot push on the fuselage or any other part of the plane like the prop/jet can.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 02:20 PM

Quote:
Originally posted by far west X:
Quote:
Originally posted by far west X:
[b]ok its going to take a blond to answer the question.. If you are in the gym and there happens to be a blond on the treadmill, she is running as fast as she can, and her hair is down.. Will her hair fly back like it would if she was running on the side of the road.. NO.. There is your answer..
this is assuming that the treadmill of the plane can keep up with the top speed of the jet.[/b]
Even if the conveyor spun at 100 times the speed of the aircraft, the plane would still create forward speed by pushing air the way a powerboat pushes water. The friction against the wheels is infintesmal (sp?) and is overcome by the props/jets pushing the whole plane.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 02:27 PM

OMG

OK

The Xterra on the tread mill is limited as the CF's are arguing...and could not move...the plane is not, and can move.

The engine's thrust does NOT turn the wheels...the wheels, in fact, won't move AT ALL in the given example, unless THE PLANE moves.

laugh

So, the can't fly proponents (CF'rs) are NOT saying that the wheels will spin too fast, or that the conveyor will run too fast...but, that the conveyor will not move AT all.

laugh

Pay Attention here:

If the conveyor belt rolls AT ALL...it means the plane is moving.

There is NO other way to make the conveyor move...it matches the plane's speed exactly.

Let that sink in.
_________________________________________________

laugh

OK

Now,

WHAT can make the plane move?

There's only ONE thing that makes the plane move...any guesses?

laugh

The thrust from the engines.

Can we all agree that a planes engines can make it move?

I mean...its worked for deacdes so far...that's how they do it every day at Newark Airport at least.

laugh

Fine - we have the ability to make a plane move using thrust from the engines...agreed?

(We all ALSO agree that if the plane could power its tires, that THAT would NOT make the plane move...as THAT motion is the same as the XTERRA's motion...)

Now - here's the part where all the CF's trip up on the logic...

The thrust will push the plane forward...and, the conveyor will roll along under it...

Hold that thought...

Here's the moment of truth...

Can a runway that rolls towards you, keep you from ever rolling forward?

NOT matching you...actually rolling towards you...so you would actually be carried backwards if you didn't move forward.

Could you take off then, using the same logic, it should be a lot harder, right?

Not only are you not already going forward, or accelerating from a stand still as normal, you have momentum carrying you backwards.

___________________________________-

Can thrust overcome momentum in the opposite direction?

________________________________________

I hope so, its how a retro rocket, etc, works.

_________________________________

Its also how a Jump Jet Lands, etc.

________________________________________-

OK - so we have the principle that thrust from a jet engine can over come actually travelling in the wrong direction.

_____________________________________

We also know that the runway is not going to change that....or the conveyor belt...

As, its the plane's motion relative to the planet, not the the belt, that makes a difference.

The belt is a Red Herring (A diversion for you CF'rs...) wink

The belt merely acts to support the weight of the plane....

The tires merely roll along under the plane...the landing gear supports the plane, the thrust pushes the plane...and the plane moves forward...

Now, when I say forward...I mean across the planet some distance, whatever, a foot, an inch a meter, whatever it is...

The belt just goes faster...even if it went FASTER than the plane's speed...it would be irrelevent...all THAT would do is increase the TIRE'S rotational speed...the attached landing gear would continue, as would te attached plane, to move across the planets surface, further down the belt's length.

_________________________________

One last analogy:

I kneel down next to my tread mill as it rolls along...I have a toy xterra...I put it on the tread mill...and hold it there, with its wheels spinning on the belt...I'm using one finger to hold on the back of the little X, to keep it in one spot on the belt.

Got that...?

One finger on the back of the X, holding it in position against the rolling tread mill belt...

OK...here' where I blow your CF mind...

Ready?

OK - I push my finger against the X a bit more....it can now MOVE AGAINST THE DIRECTION OF THE ROLLING BELT!!!!!!!!!!!!!!

How is that POSSIBLE you ask?

OK - its because the thrust from my finger is what's moving the little X...NOT THE LITTLE X'S TIRES.
________________________________________

Instead of a little X, I grab a toy RC plane, and do the same thing...

I use a finger to hold the plane against the on rushing belt, exactly as I did the little X...

The belt rushes along under the plane's tires...and, IT STAYS IN ONE SPOT!!!!!!!!

How is that POSSIBLE you ask?

OK - its because the thrust from my finger is what's moving the little plane...NOT THE LITTLE Plane's TIRES.

laugh

____________________________________

OK -

NOW, I still have the little plane on the tread mill, miraculously able to maintain its position through the magic of rolling tires and thrust from my finger.

I take the remote, and start the engine of the RC plane...the propeller spins, and pulls the plane forward, off of my finger and AWAY...

How is this POSSIBLE, you ask?

OK - its because the thrust from the propeller is what's moving the little plane...NOT THE LITTLE plane's TIRES.

laugh

________________________________-

So my finger can be the thrust...

There isn't a tread mill made that I could not roll my little X forward on by merely applying an external force to the X...

The tread mill CAN'T roll fast enough to keep me from doing it either...at the same speed, or at double the speed of my finger...the little X's tires will just spin faster..

...but, my FINGER will push the little X against the spinning belt.

_______________________________

As a jet engine can provide the same external force to the plane...

...perhaps even MORE force than my finger...

...the real plane will be pushed forward on the INITIALLY NOT spinning belt..MAKING it spin...

...but, just like my finger just keeps pushing the little X further along the tread mill belt...

....he real plane will ALSO be pushed IN THE SAME WAY...along the giant belt.

As the conveyor belt DOES NOT have its OWN ATMOSPHERE...the air that the plane is moving forward through, is the SAME air it would NORMALLY move forward through.

So - as the thrust independently pushes the plane like a giant finger, along the belt...through the air...eventually, the air rushing OVER THE WING, creates enough pressure differential to create lift.

(A wing does not lift the plane, or a bird, etc...by pushing air down...it creates lift by basically making the air on top of the wing take a longer path...which makes it less dense than the air below the wing...so it essentially PULLS the WING UP, rather than pushing the WIND DOWN)

I did see at least one reference to the above misconception, referred to as one reason WHY the conveyor belt would prevent air flow from creating lift...so, of course, that's not going to make any difference...because its not how a wing works, etc.

________________________________________-

sigh.

I HOPE some of this sinks in.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 02:39 PM

Quote:
Originally posted by MattyX:
Ergo- plane travels 120 KIAS, conveyor goes 120 knots, wheels spin at 240knots until liftoff.
Then it's an infinite acceleration.

The plane is not travelling at 240 knots in air speed (assuming that's what KIAS is). It's travelling at ground speed relative to the conveyor belt. It's not moving in airspeed.

At some point it WILL hit it's limit. Engines don't have an infinite speed.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 02:40 PM

Nicely done, TJ. But I know someone's not going to read the whole thing and say something like "but there's no finger holding the plane in place, stupid!" [Argue]

I thought about becoming a teacher when I retire. I'll probably think about it a little less. [LOL]
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 02:47 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]Ergo- plane travels 120 KIAS, conveyor goes 120 knots, wheels spin at 240knots until liftoff.
Then it's an infinite acceleration.

The plane is not travelling at 240 knots in air speed (assuming that's what KIAS is). It's travelling at ground speed relative to the conveyor belt. It's not moving in airspeed.

At some point it WILL hit it's limit. Engines don't have an infinite speed.[/b]
For the LOVE OF GOD! PLEASE!

The air speed has NOTHING to do with the conveyor belt...

Every one HAS to absorb this.

Ground speed of the plane is not different on a conveyor belt, any more than it would be different taking off from an aircraft carrier, or a train, or launched from a B1, etc.

Ground speed is relative to the planet...not things running about under you.

Otherwise...a plane's ground speed would be different if flew over a river ...but it ISN'T.

laugh

A Plane's AIR SPEED DOES change if there's a head wind, or a tail wind...as the AIR its flying through IS the relative baseline.

For ground speed, the relative baseline would be the planet, say by GPS coordinates.

We have GOT TO absorb this if we are to one day have every XOC member know if the damn plane can take off.

laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 02:50 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]Ergo- plane travels 120 KIAS, conveyor goes 120 knots, wheels spin at 240knots until liftoff.
Then it's an infinite acceleration.

The plane is not travelling at 240 knots in air speed (assuming that's what KIAS is). It's travelling at ground speed relative to the conveyor belt. It's not moving in airspeed.

At some point it WILL hit it's limit. Engines don't have an infinite speed.[/b]
I thought you were going home. Short commute, huh? Nice [drink]

You're partially correct, then totally wrong. The plane is travelling at 120 knots indicated arispeed. Therefore, relative to the ground (not on the conveyor) it is travelling at 120 knots (ground speed) at sea level. Relative to the surface of the conveyor, the plane IS TRAVELLING at 240 knots.

Here it is again, as the plane travels:

Airspeed-120 knots

Groundspeed (at sea level in no wind)-120 knots

Speed relative to conveyor surface- 240 knots

Read TJ's post again, thoroughly.

::eta:: Lizz, I'm glad you think so. Thanks for indirectly getting this going.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 02:52 PM

TJ, that was your damn longest post to date...
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:03 PM

Quote:
18+ Pages of FASCINATING Reading. Really. No, seriously.
Hahaha. 18+ pages of nonsense trying to convince the unconvincible that a plane on a conveyor belt can actually get off the ground.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:09 PM

I think all humans CAN apply logic...but its like playing a new sport, or writing with your other hand, for some...it just requires practice.

laugh

Sometimes...its like pointing at where you want your dog to go....trying to tell your dog to go "OVER THERE...The Ducks OVER THERE...Go get the duck!!!"

And the dog just keeps looking at your finger, not where its pointing.

laugh
Posted by: Powerguy38

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:11 PM

[Sleep] [Sleep] [Sleep] [Sleep] [Sleep] [Sleep] [Sleep] [Sleep]
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:16 PM

Quote:
Originally posted by Powerguy38:
[Sleep] [Sleep] [Sleep] [Sleep] [Sleep] [Sleep] [Sleep]
Of course, some dogs don't even get that there might be a duck, and just fall asleep.

laugh
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:19 PM

sigh...I gotta go home...someone with more time...go through the posters, and sort them by Fly or Can't Fly...I'd like to have a record of who was in which camp so if I have to explain OTHER things later, I can take it into account.

laugh

If a reader, post if you are an F'r (Fly) or a CF'r (Can't Fly).

laugh

Remember, be honest, this is for posterity.

laugh
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:22 PM

No one answered Smith's question...

Is this a smoking or a non-smoking flight?

smile
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:27 PM

Quote:
Originally posted by RiNkY:
I still think the conveyor could be configured to prevent the plane from going anywhere tho, there's gotta be some way to prevent the damn thing taking off. smile
Attach the plane to another plane with a short length of chain and have both planes attempt to take off in opposite directions....

neither plane will take off
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:27 PM

LOL

I think some people are smoking snakes.

laugh
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:28 PM

Quote:
Originally posted by NY Madman:
No one answered Smith's question...

Is this a smoking or a non-smoking flight?

smile
Neither! The plane's not flying, remember? [Laughing]
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:32 PM

If they are serving chicken for dinner, the plane will definitely fly.

If that horible airline vegetable lasagna is on the menu, it will not take off.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:43 PM

Here's another one to ponder

An airplane is on an infinately long Aircraft carrier. As this airplane attempts to take off in one direction, the aircraft carrier moves in the exact same speed in the opposite direction (so that the plane appears to be staying in the same spot to a impartial observer who is not on the aircraft carrier)....

Does the plane take off?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:43 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by NY Madman:
[b]No one answered Smith's question...

Is this a smoking or a non-smoking flight?

smile
Neither! The plane's not flying, remember? [Laughing] [/b]
Not true. The plane is flying while standing still, with snakes on board with people using treadmills on the plane in order for the frictional forces to prevent them from taking off.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 03:48 PM

Quote:
Originally posted by Rockaholic:
Here's another one to ponder

An airplane is on an infinately long Aircraft carrier. As this airplane attempts to take off in one direction, the aircraft carrier moves in the exact same speed in the opposite direction (so that the plane appears to be staying in the same spot to a impartial observer who is not on the aircraft carrier)....

Does the plane take off?
Yeah... The plane takes off.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 04:08 PM

[LOL] Man oh man!!! I posted this question not quite expecting this kind of response. It's rather funny that some of you people can't seem to get your mind off the wheels. They are not a determining factor on whether the plane can or cannot fly. Cmon people!! Think!!!

I've said it a few times now....those that said that the plane WILL take off can sleep easy tonight. It will in fact be able to take off.

It doesn't matter if the conveyor is going backwards at 1000mph. It's not pulling against the force of the engines. It's pulling at the wheels. Therefore, the engines will not be effected AT ALL by the conveyor belt causing the plane to eventually get enough speed to take off.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 04:15 PM

ok i can't be bothered to read 19 pages of stuff, but for a plane to become airborne, you need to have air moving over the wings to create lift. so if the plane has zero ground speed (engines are only making the plane keep up with the conveyor), then it doesn't fly.

aerodynamics 101 wink
Posted by: MidnightX

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 04:33 PM

Quote:
Originally posted by JayZ:
ok i can't be bothered to read 19 pages of stuff, but for a plane to become airborne, you need to have air moving over the wings to create lift. so if the plane has zero ground speed (engines are only making the plane keep up with the conveyor), then it doesn't fly.

aerodynamics 101 wink
I dunnoooooo..... people here beg to differ!!!!

Great, now this is gonna go another 10 pages.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 04:38 PM

TJ, I hope this helps you. Listed below in reverse appearing order are our "Special" XOC members:

JayZ
Mobycat
far west x
RiNky
NY Madman
Paul H
Mostly_Harmless
MarGinJoey

This doesn't include those that thought the bullet that was dropped would hit the ground first... I didn't have the patience to track 2 things at once.

[Too much XOC]
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 04:49 PM

Quote:
Originally posted by porsche996:
TJ, I hope this helps you. Listed below in reverse appearing order are our "Special" XOC members:

JayZ
Mobycat
far west x
RiNky
NY Madman
Paul H
Mostly_Harmless
MarGinJoey

This doesn't include those that thought the bullet that was dropped would hit the ground first... I didn't have the patience to track 2 things at once.

[Too much XOC]
You obviously haven't read the entire thread.

I am no longer dedicated to the position that it will not fly.
Posted by: MBFlyerfan

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 05:07 PM

It seems alot of people are stuck on the preconception that the wheels will be propelling the plane and therefore will just stand still on the treadmill.

Its been said 100 times already, but the engines do the propelling, thus negating any effect the treadmill would have.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 06:13 PM

Quote:
Originally posted by Rockaholic:
Here's another one to ponder

An airplane is on an infinately long Aircraft carrier. As this airplane attempts to take off in one direction, the aircraft carrier moves in the exact same speed in the opposite direction (so that the plane appears to be staying in the same spot to a impartial observer who is not on the aircraft carrier)....

Does the plane take off?
If the plane always appears to be in the same spot, then it's not moving through space, it's not moving through air, so it's not gonna take off. In order for the plane not to move through air, its means of propulsion must not be coming from the plane, it must come from the carrier (i.e. the infinitely long catapult).

This problem differs in that you specifically stated that the plane does not move absolutely, whereas the original scenario only mentions motion of the plane and the conveyor belt. Your plane may be in motion relative to the carrier, but in your scenario, the plane is not in motion relative to the air (or to the rest of the world).

So, again, no, your plane won't take off.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 06:17 PM

Quote:
Originally posted by NY Madman:
I am no longer dedicated to the position that it will not fly.
You don't have to recant your original position:

Quote:
Originally posted by XPLORx4 (from page 11):
Based on Xorand's response, I believe it may be possible in the hypothetical scenario for the plane to not take off, so I am in agreement with NYMadman, but not because the engines don't actually move the aircraft further forward on the runway. Note: the hypothetical scenario is vague about the term "speed", and it does not provide any details about the physical environment. Most of us are filling in the blanks with what we perceive as "common knowledge" in order to arrive at our conclusion that the plane will take off.

Here's something that only Xorand hinted at (which would prevent the plane from taking off):

The conveyor is either moving at an infinite speed, if its speed-detection mechanism uses the plane's wheelspeed sensors, or it's moving opposite to the plane's groundspeed, if its mechanism is based on that. Now, we know that inifinity is a theoretical concept, and that wheel bearings and tires certainly cannot REALLY rotate at an infinite speed before self-destructing (which would then cause the conveyor to stop). So, without functional wheels, the plane can't overcome the friction of its broken landing gear sticking out beneath its belly, and it won't take off.

If the conveyor moves backwards at the same speed the plane moves forwards through space, then you would need to know the design limitations of the wheel bearings and tires to determine if they can spin at twice the take-off speed of the aircraft. If they can't handle it, again you have broken landing gear and the plane will likely careen out of control as it rolls down the runway at 180+mph. If the landing gear can handle those speeds, then the aircraft will indeed take off.
Posted by: Southernx7

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 06:53 PM

If the Jaguars could get a few receivers and an accurate QB, we might be good next year.

Everybody sinnnnnnnggggg

The Jags still suck, the jags still suck.......

but damn can Jones-Drew run.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 08:21 PM

Quote:
Originally posted by Rockaholic:
Here's another one to ponder

An airplane is on an infinately long Aircraft carrier. As this airplane attempts to take off in one direction, the aircraft carrier moves in the exact same speed in the opposite direction (so that the plane appears to be staying in the same spot to a impartial observer who is not on the aircraft carrier)....

Does the plane take off?
Given calm winds, no. The plane does not take off. It will be at the same point relative to the air surrounding it, and thereby have attained a net of zero airspeed. However, the proposed scenario is even more unlikely than the conveyor the size of a runway. An aircraft carrier achieving speeds at which an aircraft could obtain lift would take such immense power as to be just about unthinkable. Besides which, the resulting movement of the flight deck would preclude a safe launch. But I'm just spitballin here.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 08:26 PM

ok, i might as well chime in on the bullet gun thing too.

they both hit the ground at the same time. gravity affects them equally, but the one fired from the gun also has a forward motion component to it. i could get into vectors and all the scientific crap but i wont. wink

edit: here is a link explaining lift. note the final paragraph titled 'no motion, no lift'.

http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 08:40 PM

OK, from a pilot:

Quote:
You are correct. Think of it this way. The wings provide the lift. They need a rush of air to do that. Tell your 3rd graders to think of themselves sitting on the wing of an airliner taking off from a non-conveyor-belt runway. Imagine the 150 mph winds they would feel in their face, which the wings turn into lift.
but, sitting on wing of the conveyor-belt-runway plane, they wouldn't feel any wind at all. So, all you would be doing is wasting a lot of fuel and creating unnecessary carbon dioxide.

A more realistic situation is to take a Maule aircraft (attached). It will take off at 50mph. So, if you pointed it on the runway (or anywhere else!) into a 50mph headwind, it would take off straight above of its current position. Point it into a 55 mph wind, and it will take off, and fly 5mph (relative to the ground) backwards!!
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 08:47 PM

Quote:
Originally posted by MattyX:
The plane does not take off. It will be at the same point relative to the air surrounding it, and thereby have attained a net of zero airspeed.
DING DING DING!!!

That's the EXACT same scenario as the conveyor belt!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 08:49 PM

Just because it's coming from a pilot, doesn't mean it's right. I'm an air traffic controller, I tell pilots what to do all day, but that doesn't mean a damn. Go ahead and try the balsa-plane-with-a-rubber-band-powered-prop trick on the treadmill at your local gym. See if it works, then try to figure it out.

Of course, it's been done.
Quote:
It was an interesting argument, but as things progressed, more rational heads prevailed, pointing out that the airplanes do not apply their thrust via their wheels, so the conveyor belt is irrelevant to whether the airplane will takeoff. One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards.
You've read the whole thread, right?
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 08:51 PM

Quote:
Originally posted by MattyX:
Just because it's coming from a pilot, doesn't mean it's right. I'm an air traffic controller, I tell pilots what to do all day, but that doesn't mean a damn. Go ahead and try the balsa-plane-with-a-rubber-band-powered-prop trick on the treadmill at your local gym. See if it works, then try to figure it out.

Of course, it's been done.
Quote:
It was an interesting argument, but as things progressed, more rational heads prevailed, pointing out that the airplanes do not apply their thrust via their wheels, so the conveyor belt is irrelevant to whether the airplane will takeoff. One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards.
You've read the whole thread, right?
That rubber band plane has almost no weight. It's wheels obviously moved faster than the treadmill.

If the jet is weightless, all bets are off...then yes, it could take off.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 08:58 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]The plane does not take off. It will be at the same point relative to the air surrounding it, and thereby have attained a net of zero airspeed.
DING DING DING!!!

That's the EXACT same scenario as the conveyor belt![/b]
BZZZZZZ! Sorry, you are incorrect. The scenario is not the same. Examine, if you will, scenario #1:
Quote:
A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?
Nothing in this scenario says that the plane must remain stationary. In fact, it states with certainty that the plane must move (otherwise no speed at all. Now for scenario #2:
Quote:
An airplane is on an infinately long Aircraft carrier. As this airplane attempts to take off in one direction, the aircraft carrier moves in the exact same speed in the opposite direction (so that the plane appears to be staying in the same spot to a impartial observer who is not on the aircraft carrier)....

Does the plane take off?
Given the stipulation that the aircraft remains in the same point in space (as was described in the parenthesis in the above quote), no airspeed at all could be generated, except what was necessary to counterract the minimal friction of the flight deck under the wheels. If the carrier and plane were free to move to any point in space, yet the only stipulation being that their speed must be equal in opposite directions, the aircraft would still take off.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 09:03 PM

Quote:
Originally posted by Mobycat:

If the jet is weightless, all bets are off...then yes, it could take off.
We have weightless aircraft. Blimps and hot-air balloons. But they're not relevant to this discussion.

So the balsa plane takes off because it's light. Get a bigger balsa plane, and try it again. then try it again with a larger, heavier RC plane. Then with an even larger one. If the plane's propulsion system can push enough AIR to move its own weight fast enough to achieve lift, is certainly will not sit still because something's turning its wheels.
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 09:17 PM

There is nothing that can get me to go back and read the whole thread but I would love to throw my hat into the ring:

Why is a Harrier jet able to take off from what is basically a stable position while hovering? The plane achieves flight through propultion rather than wind speed and there is no need for a runway or wheels for that matter.

I have to throw my lot in with the "it flys" crowd since a plane achieves flight through propultion at a certain level regardless of the land speed.

But I still wonder: why does it take X hundreds of feet for a plane to take off when all a pilot could do is set the throttle wide open and slingshopt the plane.

So who the hell knows....
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 09:25 PM

Welcome, SCPX. To your question-

what you've described is done frequently. The thing is, it must gain momentum to achieve airspeed. Airspeed is not created by sitting still and pushing air, you must travel through air to have airspeed.

So while a plane spools up with the brakes on, it's like a boat at 3/4ths throttle tied to a pier. Get free of the line, and it's off like a shot. If the boat is a hydrafoil, it will still need to gain momentum and speed through the water to be raised up on it's foils. Do I make any sense, ever?

::ETA:: While the engine is turning, air flows only through the turbine/prop path/both. In order to achieve lift, you must create airflow over the entire wing. This is why forward motion is required.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 09:28 PM

20 pages and still in the club house? come on, lets take this to the ALR.
Posted by: Claus

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 09:37 PM

Quote:
Originally posted by zuzuman03:
20 pages and still in the club house? come on, lets take this to the ALR.
Fuck you queer
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 09:58 PM

[Spit]
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:27 PM

Quote:
Originally posted by MattyX:

Go ahead and try the balsa-plane-with-a-rubber-band-powered-prop trick on the treadmill at your local gym. See if it works, then try to figure it out.
Matt ...

The rubber band powered balsa wood plane experiment is not a good test of the scenario that is being discussed in this thread. No where near a good test. I think you know that.

I also have a question for you....

You seem to think the plane on the aircraft carrier would not take off and you are using virtually the same argument that people are using against the plane on the conveyor belt. Why is that?
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:38 PM

Quote:
Originally posted by JayZ:
edit: here is a link explaining lift. note the final paragraph titled 'no motion, no lift'.

http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html
Maybe you should have read the paragraph and not just the title
Quote:
Lift is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid: no motion, no lift. It makes no difference whether the object moves through a static fluid, or the fluid moves past a static solid object.
One problem is that people are assuming that ground speed and air speed are one and the same, when in fact they are not.

Take my Kites, for example, which fly based on the same principles as an airplane - only they have no groundspeed...which means they rely on the air moving past the kite to generate lift.

Again, it makes no difference whether the object moves through a static fluid, or the fluid moves past a static solid object. In either case, lift is acheived.

Taht's the other problem, people are assuming that lift only occurs if the plane is moving in relation to the ground, as they assume the ground and air move together - which is compltely false.

If I run 5 mph towards the east on a calm, windless day, I will feel a 5 mph breeze coming from the west - the difference between my velocity (5mph east) and the airs velocity (omph).
That is my groundspeed is 5mph, my windspeed is 5mph.

If I run 5mph towards the east with a tailwind at 5mph, I will feel no wind - because now there is no difference between my velocity (5mph east) and the airs velocity (5 mph east)
that is my groundspeed is 5mph, but my windspeed is 0mph.

This is important, because as the NASA link states in the "no motion, no lift" paragraph
Quote:
Lift is generated by the difference in velocity between the solid object and the fluid.
Taking the conveyor belt -
Remember you have to use vector addition, and everything has to equal out.
If the plane is moving at 100mph, the Belt is also moving at 100mph in the opposite direction (add them together, you get 0 mph)
A person (impartial observer) standing off of the belt sees the plane staying in a stationary spot, and feels no windspeed (0mph). They see a person on the belt moving with the belt (away from the plane) at a speed of 100mph.

The person on the belt sees the plane moving away at a rate of 200mph (the combined speeds of the person and plane), and feels a windspeed of 100mph (the difference between speed the person is travelling on the belt and the speed of the air (omph) felt by the observer). The person on the belt sees the observer moving away from them at a rate of 100 mph.
The plane sees the person on the belt moving away at 200mph. The plane sees the observer as not moving in relation to it. The Plane also feels a windspeed of 100mph.

Now the vector addition -
The plane is moving at 100mph in one direction, the belt/person at 100mph in the opposite direction - they cancel each other out (0mph total movement)
The observer and the person on the belt see each other moving away at 100 mph (in opposite directions) so that cancels each other out. (0 mph)
The person on the belt and the airplane see each other moving away at 200 mph in opposite directions, so that cancels each other out. (0mph)
The airplane and the observer do not see any change in distance between them - they cancel out (0mph)
The person on the belt feels a windspeed of 100mph (because they are moving in relation to the wind at 100mph)- since the observer feels no windspeed, the airplane must cancel the person on the belts windspeed of 100mph out by feeling a windspeed of 100mph in the opposite direction (which would be going from head to tail on the plane).
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 10:44 PM

Oh, ands to those who think that groundspeed and airspeed are one and the same....

When the air moves (wind), does the ground move with the air?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:27 PM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by MattyX:

[b]Go ahead and try the balsa-plane-with-a-rubber-band-powered-prop trick on the treadmill at your local gym. See if it works, then try to figure it out.
Matt ...

The rubber band powered balsa wood plane experiment is not a good test of the scenario that is being discussed in this thread. No where near a good test. I think you know that.

::ETA:: Rockaholic- I'll get to your stuff tomorrow. I'm tired.

I also have a question for you....

You seem to think the plane on the aircraft carrier would not take off and you are using virtually the same argument that people are using against the plane on the conveyor belt. Why is that?[/b]
Explain to me, madman, why the balsa plane experiment is not a "good test."

There is a stipulation in the carrier scenario that the plane remain in the same point in space. There is no such stipulation in the conveyor scenario. In the conveyor scenario, the aircraft can move, regardless of what the surface does.

Once again, in the Carrier scenario, ROck stipulated that the aircraft must stay in the same position relative to the earth and the air. Of course, if you remove this stipulation, and replace the conveyor with an "infinitely ling aircraft carrier", the answers are exactly the same. The problem with Rock's question is that there's no way the motion of the aircraft carrier could affect a plane that's trying to fly off it, other than steaming downwind.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 29/12/06 11:56 PM

Quote:
Originally posted by Rockaholic:

The person on the belt feels a windspeed of 100mph (because they are moving in relation to the wind at 100mph)- since the observer feels no windspeed, the airplane must cancel the person on the belts windspeed of 100mph out by feeling a windspeed of 100mph in the opposite direction (which would be going from head to tail on the plane).
Let me play devils advocate here Rock....

Are you saying that a person sitting on the wing of the plane in your above scenario would feel 100MPH of wind hitting him in the face?

While sitting on the wing of that plane, he would look over his shoulder and see the observer standing there in the same position relative to his seat on the wing of the plane. The observer has no wind hitting him. His hair is not flowing in the wind. Is the person seated on the wing of this plane feeling his hair flowing back in the wind? Can we put a wind sock on that wing and observe a reaction to a 100MPH wind?

...........

Now take note... I am not taking a position any longer on this scenario. Those that argue that the plane would take off or rather should take off seem to be correct.

Also those that claim it may not take off have also offered some valid points and also seem to be correct. (I'm also not talking about those that bring the wheels or other matters of friction or groundspeed into the debate. The debate is beyond those aspects)

I have some further thoughts and questions on the subject, but it involves your answer to the above question I have asked. That answer would lead to further questions possibly regarding the effects of air viscosity and compressibility involved in this scenario. All of which are included in the NASA links and have a direct bearing on the entire subject.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:12 AM

Quote:
Originally posted by MattyX:

Explain to me, madman, why the balsa plane experiment is not a "good test."
Well... first of all on the balsa wood experiment it would require a lot of calculations to make it a valid experiment vs. a real world situation. You would have to calculate many things such as the torque required on the rubber band engine vs. the weight of the plane against the speed of the conveyor or treadmill, etc. ... and probably many other calculations to make it valid. You would also have to have trials of other similar experiments which would create a control group. Isn't that how scientific research is done? By doing things like that? You can't just spin up a rubber band plane and put it on any old treadmill and call it valid science.

Quote:
There is a stipulation in the carrier scenario that the plane remain in the same point in space. There is no such stipulation in the conveyor scenario. In the conveyor scenario, the aircraft can move, regardless of what the surface does.
Maybe the wording of the conveyor scenario is creating our little conundrum and the disagreements.

Quote:
Once again, in the Carrier scenario, ROck stipulated that the aircraft must stay in the same position relative to the earth and the air. Of course, if you remove this stipulation, and replace the conveyor with an "infinitely ling aircraft carrier", the answers are exactly the same. The problem with Rock's question is that there's no way the motion of the aircraft carrier could affect a plane that's trying to fly off it, other than steaming downwind.
I'll read the aircraft scenario again. I don't recall it the way you described, but you could be correct.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:18 AM

Can we first arrive at the correct answer to the original scenario, and let the aircraft carrier scenario be moved to its own thread(possibly in the ALR so that zuzuman03 will be happy)?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:39 AM

wow-that took me over an hour to read all the posts. now, what was the question?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 03:27 AM

Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:08 AM

Quote:
Originally posted by socalpunx:

Why is a Harrier jet able to take off from what is basically a stable position while hovering?
It's different.

A harrier is only needing to overcome one force - gravity. It's wings, while the engines *are forcing the air down* don't need forward momentum to create lift.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:10 AM

Quote:
Originally posted by MattyX:
In the conveyor scenario, the aircraft can move, regardless of what the surface does.
But that cannot be possible if the conveyor *matches* the speed backwards.

If the plane moves even .1 inches forward, the conveyor belt has failed.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:23 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]In the conveyor scenario, the aircraft can move, regardless of what the surface does.
But that cannot be possible if the conveyor *matches* the speed backwards.

If the plane moves even .1 inches forward, the conveyor belt has failed.[/b]
Shhhh....

You're not supposed to ask those type of questions.

Especially since you have already been named in the "enemies list" in this thread. smile
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 06:33 AM

You guys are a trip. Let me start by not even pretending to have read this entire thread, so if this is old news, forgive me.

The airplane wouldn't fly, and it doesn't matter that the engines move the plane as opposed to the wheels. In the original post, it said the belt has a control system that matches the PLANE'S speed - not the WHEELS' speed. Very important distinction because if that happens, the plane's wheels can spin at any speed but the plane's speed relative to the surrounding air remains zero.

If the plane doesn't move forward, there's no airflow (so-called relative wind) over the wings. No airflow, no lift; no lift, won't fly.

It wouldn't move forward because of the old "every action has an equal and opposite reaction" and the related laws of flight: lift must overcome gravity and thrust must overcome drag.

In our scenario, the "action" of the engines still produces the usual reaction (thrust) but not the usual result because a vital element is missing: the friction of the tires against the pavement. Take away this drag and the tires are still rolling on the conveyor belt but the result is different because the surface is not stationary.

The airplane will not move forward, so no lift will be generated and so gravity wins - the plane won't fly.

Now here's a new one for you:

Assume we're talking about a fixed-wing aircraft (i.e. not a helicopter) that is not a Harrier jet.

The plane's airspeed is 60 MPH but it is flying into a 60 MPH headwind. What is its speed over the ground?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:42 AM

Quote:
Originally posted by XPLORx4:
Can we first arrive at the correct answer to the original scenario, and let the aircraft carrier scenario be moved to its own thread(possibly in the ALR so that zuzuman03 will be happy)?
We did.....it's been stated MANY MANY times....the plane WILL TAKE OFF!

BlueSky, what would it matter if the conveyor belt reaches the speed of the plane? The plane is sitting on a set of wheels that are basically frictionless. That only means that the wheels will be spinning MUCH faster than the plane is actually moving forward. The conveyor has an acting force on the WHEELS, NOT the engine. The only thing that can act against the engine is a headwind pushing against the entire aircraft in the opposite direction and with equal speed to the plane. You people just can't grasp the fact that the wheels and the conveyor DO NOT act against the force of the airplane's engines!! WAKE UP!!!

If the airplane were to be propelled by the wheels, then yes, the plane will in fact NOT take off. BUT...that's ONLY IF it's being propelled by the wheels, and not the engines. :rolleyes:
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:49 AM

Allright, let me try to explain it this way. You're in your car on wet, perfectly level ice. You try to accelerate, but your wheels just spin and you go nowhere (for the sake of argument). Try as you might, as your tires push against the ice, they get no friction and can't get you moving. If, however, you applied an external force to the car, like a big-ass fan, then the car would move over the ice. Why is the car moving now? I mean, isn't it impossible to apply torque to the wheels to move the car? It's moving because it's NOT pushing against the ice, it's pushing against the air.

Does that convert anybody? I doubt it. [Too much XOC]

::edited for clarity::
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:55 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]In the conveyor scenario, the aircraft can move, regardless of what the surface does.
But that cannot be possible if the conveyor *matches* the speed backwards.

If the plane moves even .1 inches forward, the conveyor belt has failed.[/b]
Here's the thing, Moby. If the plane doesn't move, it has no speed. If it sits still with its wheels turning, it's not moving, and therefore, has no speed.

The conveyor matches the *speed* of the aircraft, not the movement.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:05 AM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by MattyX:

[b]Explain to me, madman, why the balsa plane experiment is not a "good test."
Well... first of all on the balsa wood experiment it would require a lot of calculations to make it a valid experiment vs. a real world situation. You would have to calculate many things such as the torque required on the rubber band engine vs. the weight of the plane against the speed of the conveyor or treadmill, etc. ... and probably many other calculations to make it valid. You would also have to have trials of other similar experiments which would create a control group. Isn't that how scientific research is done? By doing things like that? You can't just spin up a rubber band plane and put it on any old treadmill and call it valid science.

Quote:
There is a stipulation in the carrier scenario that the plane remain in the same point in space. There is no such stipulation in the conveyor scenario. In the conveyor scenario, the aircraft can move, regardless of what the surface does.
Maybe the wording of the conveyor scenario is creating our little conundrum and the disagreements.

Quote:
Once again, in the Carrier scenario, ROck stipulated that the aircraft must stay in the same position relative to the earth and the air. Of course, if you remove this stipulation, and replace the conveyor with an "infinitely ling aircraft carrier", the answers are exactly the same. The problem with Rock's question is that there's no way the motion of the aircraft carrier could affect a plane that's trying to fly off it, other than steaming downwind.
I'll read the aircraft scenario again. I don't recall it the way you described, but you could be correct.[/b]
Dude, you don't have to publish the results of the balsa plane test. There's no Nobel for re-proving basic physics. You're saying it's bad science because it isn't measured first? Accept this for any self-propelled fixed wing aircraft- balsa, canvas, aluminum or whatever- is can generate enough friction with (nothing else but) the air to move forward at a rate of speed great enough to achieve lift. Contact with the surface is incidental.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:21 AM

Quote:
Originally posted by Hawk:
The plane is sitting on a set of wheels that are basically frictionless.
But they are NOT frictionless.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:22 AM

Quote:
Originally posted by MattyX:
If, however, you applied an external force to the car, like a big-ass fan, then the car would move over the ice.
You have just added a second power source.

The plane does NOT have a second power source.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:30 AM

Quote:
Originally posted by BlueSky:
You guys are a trip. Let me start by not even pretending to have read this entire thread, so if this is old news, forgive me.

The airplane wouldn't fly, and it doesn't matter that the engines move the plane as opposed to the wheels. In the original post, it said the belt has a control system that matches the PLANE'S speed - not the WHEELS' speed. Very important distinction because if that happens, the plane's wheels can spin at any speed but the plane's speed relative to the surrounding air remains zero.
You're so very close here, until you conclude that the plane's speed is zero. If the conveyor could *magically* keep the plane in a single position, the plane would have no speed. But wait- if the plane has no speed, then the conveyor must also have no speed, as stipulated by the problem.
Quote:
Originally posted by BlueSky:

If the plane doesn't move forward, there's no airflow (so-called relative wind) over the wings. No airflow, no lift; no lift, won't fly.

It wouldn't move forward because of the old "every action has an equal and opposite reaction" and the related laws of flight: lift must overcome gravity and thrust must overcome drag.

In our scenario, the "action" of the engines still produces the usual reaction (thrust) but not the usual result because a vital element is missing: the friction of the tires against the pavement. Take away this drag and the tires are still rolling on the conveyor belt but the result is different because the surface is not stationary.
Whoa-hold up here. Wheels are a means of reducing friction while attempting to move an object-yes? The tires-on-pavement do extraordinarily little to create friction without brakes applied. The plane still moves because it moves air, and there's nothing the conveyor can do about that.
Quote:
Originally posted by BlueSky:

The airplane will not move forward, so no lift will be generated and so gravity wins - the plane won't fly.

Now here's a new one for you:

Assume we're talking about a fixed-wing aircraft (i.e. not a helicopter) that is not a Harrier jet.

The plane's airspeed is 60 MPH but it is flying into a 60 MPH headwind. What is its speed over the ground?
The plane on the conveyor will create forward motion and achieve lift, because it's using friction against something that has nothing to do with the conveyor.

Imagine roller skating on a long treadmill that matches your speed exactly. There's a taut rope directly overhead within easy reach. As you move forward, the treadmill acts to keep you in the same place. If you grab the rope and start using it to push yourself forward, hand over hand, and your wheels are just touching the treadmill, will the treadmill be able to stop you from propelling yourself forward using the rope? No, because you're applying force to the rope and your wheels are reducing friction with the treadmill.

Of course an aircraft with a 60 knot headwind and 60 KIAS will have a groundspeed of zero. I've seen a plane with a 140 knot headwind remain motionless 6000 feet over an airport for about five minutes before I asked him if he thought he was going anywhere. When he realized he wasn't, he turned around and got home in a hurry.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:33 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]If, however, you applied an external force to the car, like a big-ass fan, then the car would move over the ice.
You have just added a second power source.

The plane does NOT have a second power source.[/b]
Right, but the plane does not create its movement by pushing against the ice/ground. Put a plane on that same frictionless ice and it will still move whenever it wants to, because it moves by pushing the air, not the surface.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:33 AM

Quote:
Originally posted by MattyX:

Imagine roller skating on a long treadmill that matches your speed exactly. There's a taut rope directly overhead within easy reach. As you move forward, the treadmill acts to keep you in the same place. If you grab the rope and start using it to push yourself forward, hand over hand, and your wheels are just touching the treadmill, will the treadmill be able to stop you from propelling yourself forward using the rope? No, because you're applying force to the rope and your wheels are reducing friction with the treadmill.
Ugh.

A rope is NOT fluid. The air IS.

The rope is tied to something. The air is NOT.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:35 AM

Quote:
Originally posted by MattyX:
Put a plane on that same frictionless ice and it will still move whenever it wants to, because it moves by pushing the air, not the surface.
The wheels are NOT frictionless.

Heck, even ice has *some* friction. If it didn't, you wouldn't slow down on ice skates.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:38 AM

OH. MY. GOD.

You've been fucking with me this whole time, haven't you?
Quote:
Ugh.

A rope is NOT fluid. The air IS.

The rope is tied to something. The air is NOT.
Do you mean to say that an aircraft cannot move itself forward using fluid air?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:39 AM

Quote:
Originally posted by BlueSky:
...If the plane doesn't move forward, there's no airflow....
That's the bad assumption of everybody who thinks the plane doesn't move.

The ONLY rearward force on the system is a nominal amount of friction on the wheels (which spin FREELY!). This will NEVER be enough to prevent forward motion against thousands of pounds of thrust.

Go back in the thread and look at the free-body diagram (FBD). Also look at my t= scenario which explains how the conveyor belt will affect the system.

As I said before. This is not rocket science or an aerospace engineering problem. This is a 9th-grade Physics problem that requires the person to understand how an airplane propels itself (the wheels aren't involved in propulsion). If people don't, at least, have that background, they should refrain from comment.

There is one recognized correct answer to this problem. Look at the FBD, stop getting hung up on the conveyor belt, and disregard rockaholics invalid scenario. ONLY THEN will you be able to come to terms with the recognized correct answer.

The plane flies.

Good luck!
[ThumbsUp]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:42 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]Put a plane on that same frictionless ice and it will still move whenever it wants to, because it moves by pushing the air, not the surface.
The wheels are NOT frictionless.

Heck, even ice has *some* friction. If it didn't, you wouldn't slow down on ice skates.[/b]
Yea, it was a hypothetical. Maybe I should have said "magical frictionless surface" instead. Regardless, the plane would move on the ice, even if its brakes were locked and a car couldn't get rolling in any direction.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:56 AM

Quote:
Originally posted by MattyX:

Dude, you don't have to publish the results of the balsa plane test. There's no Nobel for re-proving basic physics. You're saying it's bad science because it isn't measured first?
I'm saying it is a bad scientific experiment to use as proof of the hypothetical scenario in this discussion of the aircraft and the conveyor belt.

With the way you are proposing the balsa wood plane experiment, you are moving away and beyond the conditions set in the original hypothetical scenario.

You keep forgetting that in the original scenario the conveyor matches the aircraft's speed. Without the numerous calculations I mentioned in my earlier post you are not duplicating the conditions for the hypothetical scenario by just spinning any rubber band plane over any treadmill.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 09:08 AM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by MattyX:

[b]Dude, you don't have to publish the results of the balsa plane test. There's no Nobel for re-proving basic physics. You're saying it's bad science because it isn't measured first?
I'm saying it is a bad scientific experiment to use as proof of the hypothetical scenario in this discussion of the aircraft and the conveyor belt.

With the way you are proposing the balsa wood plane experiment, you are moving away and beyond the conditions set in the original hypothetical scenario.

You keep forgetting that in the original scenario the conveyor matches the aircraft's speed. Without the numerous calculations I mentioned in my earlier post you are not duplicating the conditions for the hypothetical scenario by just spinning any rubber band plane over any treadmill.[/b]
So if the conveyor/treadmill had greater speed to begin with and the balsa plane still took off, the result would somehow be different if you could make the treadmill accelerate at the same rate as the plane?

I don't know how fast traditional treadmills go, but I'm fairly sure balsa planes cannot go faster than 10 MPH (being generous to the plane). So supe up a treadmill, set it for 20 MPH, and try it again. I guarantee you the balsa plane would take off.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 09:28 AM

Quote:
Originally posted by MattyX:

So if the conveyor/treadmill had greater speed to begin with and the balsa plane still took off, the result would somehow be different if you could make the treadmill accelerate at the same rate as the plane?

I don't know how fast traditional treadmills go, but I'm fairly sure balsa planes cannot go faster than 10 MPH (being generous to the plane). So supe up a treadmill, set it for 20 MPH, and try it again. I guarantee you the balsa plane would take off.
I don't care about the speed of either.

We are talking about the hypothetical scenario. If you wish to create an experiment to use as proof... you would need to calculate all of the numbers and match the speeds of each.

Otherwise we are no longer talking about the hypothetical scenario.

If this is being discussed all over the internet, why hasn't anyone tried to do a scale model experiment with a remote controlled aircraft?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 09:47 AM

People have. There are all kinds of videos on YouTube, but none of them really show much of anything. Someone needs to do this experiment with a radio controlled jetliner on a conveyor system a-la Mythbusters.....Hopefully they'll reply to the email sent to them...

I just don't understand how it is so difficult for people to understand the forces being acted upon and the forces at work here....I've said it many many times.....

The conveyor belt puts a force on the wheels, NOT the engines. The engines are completely indepentant of the conveyor. The conveyor WILL NOT provide any resistance to the engines and the engines will continue to pull the airplane forward, thus creating lift, thus allowing the plane to take off. What's so difficult about that?!?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 09:58 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by MattyX:
[b]If, however, you applied an external force to the car, like a big-ass fan, then the car would move over the ice.
You have just added a second power source.

The plane does NOT have a second power source.[/b]
Moby, you just contradicted your position, and you don't even know it...

The plane doesn't have a "second" power source. It has 1 power source. And it's not connected to the wheels. The wheels provide 0 propulsion or resistance of the plane's movement, at any time. So no matter how fast the wheels move, the plane's motion is NOT controlled by their movement.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:15 AM

Look, are we all in agreement that on the aircraft carrier, it would not take off?

Put the aircraft carrier on the conveyor belt.

The conveyor belt now moves the boat (instead of the boat's engines - they are connected, so it doesn't matter).

The exact same scenario!

The air around the wings does NOT move - there is nothing to provide lift.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:16 AM

Imagine a hamster on a wheel. The hamster runs, the wheel turns, and the hamster moves across the surface of the wheel but stays in the same relative position so like the plane, there's no airflow over the hamster.

Now on the same wheel (maybe bigger), put the hamster on "nearly frictionless" skates and strap a tiny jet engine on its back. Guess what? The wheel still turns (just faster) and the hamster still maintains a stationary position at the usual place on the wheel. It doesn't travel around the inside of the wheel.

Where Hawk seems hung up is on the relative position. Though air is moving through the engines, generating thrust, the plane itself must be moving forward to generate lift. According to the scenario, the more thrust applied, the faster the belt goes, so the moving treadmill prevents forward motion by in effect giving the wheels nowhere to go.

If the belt moves faster as the plane moves faster, the plane's RELATIVE position doesn't move forward, so again, there's no airflow over the wings. In the scenario given, even with the engines at full power, if you raise the landing gear the plane will collapse to the ground.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:16 AM

Wow-it took me over an hour late last night to read all these pages. Then I forgot what the post was about. If I have repeated any one else's post-it was not done deliberately. My two cents. Ground speed and air speed are not independent of each other. Air speed is created by thrust. Thrust in this case is created by the engines. Not the spinning wheels. If you take a balloon, and blow it up-then release it. It will essentially fly away until it has no more foreword thrust (escaping air). If that same balloon is let go into a head wind of equal thrust/speed-the balloon will stay where it is....mid air. Not counting on how un-aerodynamic a balloon is. Still flying-but going no where. If the thrust of the plane going foreword is less then the treadmills speed, then the plane will go backward. If the thrust is greater, the plane will fly away. If the thrust is equal to the tread mill-the plane will still fly. But will not take off as quickly because ground speed and air speed is the same. But the plane will fly away. Do you guys remember the old WWII Naval pictures of naval aircraft taking off from carriers? This was before catapults. The carriers would turn into the wind and go full steam ahead. Back then, they could muster maybe 20 or so knots of foreword speed. The planes would lumber into the air and would either crash into the ocean or fly away-very slowly until their air speed was much greater than ground speed. So, to all you can't fly mother fuckers, your wrong. Now, that last sentence was meant for the ALR. As you quote me and may be flame me-remember, I am a very delicate flower. Bruise easy. Have a nice New Years.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:17 AM

Quote:
Originally posted by porsche996:
Quote:
Originally posted by Mobycat:
[b]
Quote:
Originally posted by MattyX:
[b]If, however, you applied an external force to the car, like a big-ass fan, then the car would move over the ice.
You have just added a second power source.

The plane does NOT have a second power source.[/b]
Moby, you just contradicted your position, and you don't even know it...

The plane doesn't have a "second" power source. It has 1 power source.[/b]
EXACTLY. The car by itself would not have a secondary power source. It won't move.

Put the fan on it - it has a secondary power source.

Again - try the rope example. The rope is not fluid, and it is taught - meaning it's connected to something else.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:19 AM

The jet has to overcome it's weight to move forward.

So the friction of the wheels IS relevant.

If it weren't, you could walk up to a plane and push it with your own force.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:19 AM

Quote:
Originally posted by Mobycat:
Look, are we all in agreement that on the aircraft carrier, it would not take off?....
You cannot agree on anything about the Aircraft carrier scenario.

It is INVALID. It does not have anything holding the plane back yet it states the plane does not move.

That ridiculous scenario has done nothing but confuse the issue further.

Read above and please come to terms with the correct answer.

Bottom line:

Jet engines push (F = ma ==> a =F/m)

Wheels roll, and don't push back.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:20 AM

You know...

Why HASN'T someone actually gone through the trouble of a computer model of this?
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:40 AM

Quote:
Originally posted by Hawk:

People have. There are all kinds of videos on YouTube, but none of them really show much of anything. Someone needs to do this experiment with a radio controlled jetliner on a conveyor system a-la Mythbusters.....Hopefully they'll reply to the email sent to them...
I wouldn't count on Mythbusters.

Rinky linked to a physics forum with 500 pages on this topic. Someone on one of the first pages said they emailed Mythbusters and that was over a year ago. I'm sure they have received hundreds if not thousands of emails on this topic.

Quote:
The conveyor belt puts a force on the wheels, NOT the engines. The engines are completely indepentant of the conveyor. The conveyor WILL NOT provide any resistance to the engines and the engines will continue to pull the airplane forward, thus creating lift, thus allowing the plane to take off. What's so difficult about that?!?
You are correct in stating the conveyor provides no resistance to the aircraft's engines.

The conveyor is matching the speed of the plane.

Let me ask you this question.... Does a person sitting on the wing of that plane feel the wind? If the conveyor is moving 200MPH in one direction and the plane's engines are throttled down and it's instruments say it is traveling at 200MPH in the other direction -- does a person sitting on the wing of that plane feel that wind?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:43 AM

Quote:
Originally posted by BlueSky:
Imagine a hamster on a wheel. The hamster runs, the wheel turns, and the hamster moves across the surface of the wheel but stays in the same [b]relative position so like the plane, there's no airflow over the hamster.

Now on the same wheel (maybe bigger), put the hamster on "nearly frictionless" skates and strap a tiny jet engine on its back. Guess what? The wheel still turns (just faster) and the hamster still maintains a stationary position at the usual place on the wheel. It doesn't travel around the inside of the wheel.

Where Hawk seems hung up is on the relative position. Though air is moving through the engines, generating thrust, the plane itself must be moving forward to generate lift. According to the scenario, the more thrust applied, the faster the belt goes, so the moving treadmill prevents forward motion by in effect giving the wheels nowhere to go.

If the belt moves faster as the plane moves faster, the plane's RELATIVE position doesn't move forward, so again, there's no airflow over the wings. In the scenario given, even with the engines at full power, if you raise the landing gear the plane will collapse to the ground.[/b]
Bad analogy with the hamster. If the hamster were atop the wheel, it would be better. In the wheel, there is always something in front of the hamster keeping it inside the wheel, regardless of means of propulsion. However, if atop the wheel, the hamster with rockets will not be contained and will be propelled forward. Still not a good analogy, but it doesn't have the containment. Inside the wheel, depending on the thrust of the jet/rocket whatever, and the hamster's grip on the wheel, the wheel would whip around backwards like a firework pinwheel.

Hawk is not hung up, you are. The wheels cannot keep the plane from taking off, no matter how fast they spin.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:49 AM

Quote:
Originally posted by NY Madman:


Let me ask you this question.... Does a person sitting on the wing of that plane feel the wind? If the conveyor is moving 200MPH in one direction and the plane's engines are throttled down and it's instruments say it is traveling at 200MPH in the other direction -- does a person sitting on the wing of that plane feel that wind?
The plane's instruments would not indicate any speed at all if it was throttled down (no power) and the plane was stationairy. If the plane was throttled up (powered) then the plane would move forward (relative to the ground, not the conveyor) and the "wing passenger" would feel wind.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:50 AM

Quote:
Originally posted by Mobycat:
You know...

Why HASN'T someone actually gone through the trouble of a computer model of this?
Instead of trying to convince everybody that the wrong answer is right, read the UNBELIEVIABLY simple physics of the situation.

Coefficient of dynamic friction:

Force of friction:

F(f) = -uN

(negative because it opposes motion)

u = coefficient of static friction

N = weight of plane

Notice velocity is not included!

That means that the velocity of the conveyor belt is irrelevant for all practical purposes.

F(t) is force of thrust

a = (F(t)+F(f))/m

You won't find a scenario where |F(f)| is greater than |F(t)|. Therefore, in ALL cases the plane moves with respect to the atmosphere, thus achieving lift.

Please stop being so bloody indignant and pause long enough to understand why the correct answer is correct. [Huh?]
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:55 AM

Quote:
Originally posted by Mobycat:
The jet has to overcome it's weight to move forward.

So the friction of the wheels IS relevant.

If it weren't, you could walk up to a plane and push it with your own force.
Exactly. Two questions to the "plane doesn't care what the wheels are doing" group:

1. You think the wheel friction doesn't enter into it? Stick your head under one of them, since they're bearing the entire weight of the aircraft, and see what happens.

2. If what's going on with the wheels doesn't matter, try reducing their speed to zero and see what happens, even with full thrust. Trust me, you won't fly.

You guys are confusing the issue of what counteracts what to achieve flight.

Lift overcomes gravity.
Thrust overcomes drag.

BOTH must occur for flight. The wheels turning on a stationary surface allows the thrust to overcome gravity (the aircraft's weight).

Think of the law that says an object at rest tends to remain at rest unless an outside force is applied. The outside force here is engine thrust, but it's negated by the moving belt, so the object remains at rest and gravity thus is NOT overcome by lift.

The plane WILL NOT FLY.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:59 AM

Quote:
Originally posted by Mobycat:

Put the fan on it - it has a secondary power source.

Again - try the rope example. The rope is not fluid, and it is taught - meaning it's connected to something else.
Moby, the car on ice (magic frictionless surface) Is in park with the E-brake on, and you put the big-ass fan on it, it will still move.

It doesn't matter that the rope is taut, it is an external means of propulsion, just like air. Air is connected to something else-other air. For real, if you think that an aircraft cannot move by manipulating air, then I don't know if anyone will be able to make this scenario clear to you.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:01 AM

Quote:
Originally posted by MattyX:
Quote:
Originally posted by BlueSky:
[b]Imagine a hamster on a wheel. The hamster runs, the wheel turns, and the hamster moves across the surface of the wheel but stays in the same [b]relative position so like the plane, there's no airflow over the hamster.

Now on the same wheel (maybe bigger), put the hamster on "nearly frictionless" skates and strap a tiny jet engine on its back. Guess what? The wheel still turns (just faster) and the hamster still maintains a stationary position at the usual place on the wheel. It doesn't travel around the inside of the wheel.

Where Hawk seems hung up is on the relative position. Though air is moving through the engines, generating thrust, the plane itself must be moving forward to generate lift. According to the scenario, the more thrust applied, the faster the belt goes, so the moving treadmill prevents forward motion by in effect giving the wheels nowhere to go.

If the belt moves faster as the plane moves faster, the plane's RELATIVE position doesn't move forward, so again, there's no airflow over the wings. In the scenario given, even with the engines at full power, if you raise the landing gear the plane will collapse to the ground.[/b]
Bad analogy with the hamster. If the hamster were atop the wheel, it would be better. In the wheel, there is always something in front of the hamster keeping it inside the wheel, regardless of means of propulsion. However, if atop the wheel, the hamster with rockets will not be contained and will be propelled forward. Still not a good analogy, but it doesn't have the containment. Inside the wheel, depending on the thrust of the jet/rocket whatever, and the hamster's grip on the wheel, the wheel would whip around backwards like a firework pinwheel.

Hawk is not hung up, you are. The wheels cannot keep the plane from taking off, no matter how fast they spin.[/b]
I disagree about the hamster because as stated in the original post here, the wheel would keep increasing in speed.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:04 AM

Quote:
Originally posted by MattyX:

The plane's instruments would not indicate any speed at all if it was throttled down (no power) and the plane was stationairy. If the plane was throttled up (powered) then the plane would move forward (relative to the ground, not the conveyor) and the "wing passenger" would feel wind.
Throttle up/down... whatever. You knew what I was getting at.

Now -- We have already established that an outside observer viewing the plane on the conveyor belt would see it as a stationary object because of the matching speeds between the conveyor belt and the plane.

Are you absolutely sure that a person sitting on that wing would feel the rushing wind on their face... even though the observer is experiencing no wind on what is otherwise a non-windy day?

I ask because that is the key to the entire scenario and the flight of the aircraft in this hypothetical situation. None of the other peripheral issues being added to the discussion matter. That is the entire key.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:08 AM

Quote:
Originally posted by BlueSky:
Quote:
Originally posted by Mobycat:
[b]The jet has to overcome it's weight to move forward.

So the friction of the wheels IS relevant.

If it weren't, you could walk up to a plane and push it with your own force.
Exactly. Two questions to the "plane doesn't care what the wheels are doing" group:

1. You think the wheel friction doesn't enter into it? Stick your head under one of them, since they're bearing the entire weight of the aircraft, and see what happens.

2. If what's going on with the wheels doesn't matter, try reducing their speed to zero and see what happens, even with full thrust. Trust me, you won't fly.

You guys are confusing the issue of what counteracts what to achieve flight.

Lift overcomes gravity.
Thrust overcomes drag.

BOTH must occur for flight. The wheels turning on a stationary surface allows the thrust to overcome gravity (the aircraft's weight).

Think of the law that says an object at rest tends to remain at rest unless an outside force is applied. The outside force here is engine thrust, but it's negated by the moving belt, so the object remains at rest and gravity thus is NOT overcome by lift.

The plane WILL NOT FLY.[/b]
OK, I'll try again. Wheels are simple tools designed to minimize friction. Propellors and jet turbines are relatively simple machines designed to MOVE whatever vehicle they're mounted on. No matter what the surface beneath the wheels does, as long as the wheels can perform their function and reduce friction (spin freely) the prop/turbine will power the craft forward.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:10 AM

Quote:
Originally posted by MattyX:
Quote:
Originally posted by BlueSky:
[b]
Quote:
Originally posted by Mobycat:
[b]The jet has to overcome it's weight to move forward.

So the friction of the wheels IS relevant.

If it weren't, you could walk up to a plane and push it with your own force.
Exactly. Two questions to the "plane doesn't care what the wheels are doing" group:

1. You think the wheel friction doesn't enter into it? Stick your head under one of them, since they're bearing the entire weight of the aircraft, and see what happens.

2. If what's going on with the wheels doesn't matter, try reducing their speed to zero and see what happens, even with full thrust. Trust me, you won't fly.

You guys are confusing the issue of what counteracts what to achieve flight.

Lift overcomes gravity.
Thrust overcomes drag.

BOTH must occur for flight. The wheels turning on a stationary surface allows the thrust to overcome gravity (the aircraft's weight).

Think of the law that says an object at rest tends to remain at rest unless an outside force is applied. The outside force here is engine thrust, but it's negated by the moving belt, so the object remains at rest and gravity thus is NOT overcome by lift.

The plane WILL NOT FLY.[/b]
OK, I'll try again. Wheels are simple tools designed to minimize friction. Propellors and jet turbines are relatively simple machines designed to MOVE whatever vehicle they're mounted on. No matter what the surface beneath the wheels does, as long as the wheels can perform their function and reduce friction (spin freely) the prop/turbine will power the craft forward.[/b]
Unless the surface they're on is moving in the opposite direction. laugh

So by your statement, if the surface is moving sideways, the craft will go forward?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:12 AM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by MattyX:

[b]The plane's instruments would not indicate any speed at all if it was throttled down (no power) and the plane was stationairy. If the plane was throttled up (powered) then the plane would move forward (relative to the ground, not the conveyor) and the "wing passenger" would feel wind.
Throttle up/down... whatever. You knew what I was getting at.

Now -- We have already established that an outside observer viewing the plane on the conveyor belt would see it as a stationary object because of the matching speeds between the conveyor belt and the plane.[/b]
We have established no such thing. The plane will travel forward relative to the ground, relative to the air, and at twice that rate relative to the conveyor.
Quote:
Originally posted by NY Madman:

Are you absolutely sure that a person sitting on that wing would feel the rushing wind on their face... even though the observer is experiencing no wind on what is otherwise a non-windy day?

I ask because that is the [b]key to the entire scenario
and the flight of the aircraft in this hypothetical situation. None of the other peripheral issues being added to the discussion matter. That is the entire key.[/b]
The key here is what I said above. The plane is not stationary, it moves forward relative to everything around it.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:15 AM

Quote:
Originally posted by MattyX:
The plane will travel forward relative to the ground, relative to the air, and at twice that rate relative to the conveyor.
No it won't.

The WHEELS will travel at twice the rate relative to the conveyor.

The conveyor matches the PLANE'S speed.

Jet says it's doing 60knots.

Conveyor is going -60 knots.

Wheels are going 120 knots relative to the conveyor.

The original question:

Quote:
A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:20 AM

Quote:
Originally posted by MattyX:

Quote:
Originally posted by NY Madman:

Now -- We have already established that an outside observer viewing the plane on the conveyor belt would see it as a stationary object because of the matching speeds between the conveyor belt and the plane.
We have established no such thing. The plane will travel forward relative to the ground, relative to the air, and at twice that rate relative to the conveyor.
I think you need to read the thread again.

Since the conveyor is matching the speed of the plane, once those speeds have been matched, an outside observer most certainly does view the plane as being stationary.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:20 AM

Quote:
Originally posted by Mobycat:
.....The WHEELS will travel at twice the rate relative to the conveyor.....
Not exactly.

The wheels will rotate at twice their normal rate.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:20 AM

This is giving me a headache.

What if the question was a similar conveyor on a downward slope with a vehicle on it with free-spinning wheels? No matter how fast the conveyor went, gravity would pull the vehicle downhill, right?

That's causing me to rethink my position though all my previous arguments still seem valid.

Good grief.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:22 AM

Quote:
Originally posted by BlueSky:
So by your statement, if the surface is moving sideways, the craft will go forward?
No, if the surface is moving sideways it would create friction with the wheels which are designed to move longitudinally, not laterally. A plane with landing gear mounted sideways would be able to create forward motion with the props/jets, but would have a hard time overcoming the additional friction. That's why the smart fellas over at lockheed and boeing like to put the wheels on longitudinally. However, if the surface was ice (or the magical friction-free or friction-light surface) and the plane could have four sets of sideways landing gear and still move forward and take off.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:24 AM

Quote:
Originally posted by MattyX:
Quote:
Originally posted by BlueSky:
[b]So by your statement, if the surface is moving sideways, the craft will go forward?
No, if the surface is moving sideways it would create friction with the wheels which are designed to move longitudinally, not laterally. A plane with landing gear mounted sideways would be able to create forward motion with the props/jets, but would have a hard time overcoming the additional friction. That's why the smart fellas over at lockheed and boeing like to put the wheels on longitudinally. However, if the surface was ice (or the magical friction-free or friction-light surface) and the plane could have four sets of sideways landing gear and still move forward and take off.[/b]
Yeah, I know. That was a rhetorical question meant to annoy. Did it work? :p
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:24 AM

Quote:
Originally posted by JeffW:
Quote:
Originally posted by Mobycat:
[b] .....The WHEELS will travel at twice the rate relative to the conveyor.....
Not exactly.

The wheels will rotate at twice their normal rate.[/b]
Yeah, I thought about that after I typed it.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:26 AM

Quote:
Originally posted by Mobycat:
The jet has to overcome it's weight to move forward.

So the friction of the wheels IS relevant.

If it weren't, you could walk up to a plane and push it with your own force.
Guess what, Moby? You can do exactly that.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:27 AM

Quote:
Originally posted by MattyX:
Quote:
Originally posted by Mobycat:
[b]The jet has to overcome it's weight to move forward.

So the friction of the wheels IS relevant.

If it weren't, you could walk up to a plane and push it with your own force.
Guess what, Moby? You can do exactly that.[/b]
BWAHAHAHAHA.

Go try.

They do a plane pull at Dulles every year.

It takes at least 20 people to pull a plane. They have to overcome the friction.

Maybe I should be more specific - under your scenario, you could tap the plane with your finger and it would roll foward.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:46 AM

Quote:
Originally posted by BlueSky:
This is giving me a headache.

What if the question was a similar conveyor on a downward slope with a vehicle on it with free-spinning wheels? No matter how fast the conveyor went, gravity would pull the vehicle downhill, right?

That's causing me to rethink my position though all my previous arguments still seem valid.

Good grief.
If the conveyor is fast enough to overcome gravity, then yes, it would stay put, even on a downhill slope (however, it would have to travel faster than the plane at that point).

Gravity was already equalized in the horizontal position - the force pushing up on the landing assembly.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:47 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by porsche996:
[b]
Quote:
Originally posted by Mobycat:
[b]
quote:
Originally posted by MattyX:
If, however, you applied an external force to the car, like a big-ass fan, then the car would move over the ice.
You have just added a second power source.

The plane does NOT have a second power source.[/b]
Moby, you just contradicted your position, and you don't even know it...

The plane doesn't have a "second" power source. It has 1 power source.[/b]
EXACTLY. The car by itself would not have a secondary power source. It won't move.

Put the fan on it - it has a secondary power source.

Again - try the rope example. The rope is not fluid, and it is taught - meaning it's connected to something else.

Moby, you need to open your mind up a bit and take off the blinders.....The rope represents a vector. Similarly, the air also represents that same vector on a similar experiment. The two are representative of the EXACT SAME THING....
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:50 AM

Quote:
Originally posted by BlueSky:
[QUOTE]Originally posted by Mobycat:
[qb]You guys are confusing the issue of what counteracts what to achieve flight.

Lift overcomes gravity.
Thrust overcomes drag.

BOTH must occur for flight. The wheels turning on a stationary surface allows the [b]thrust to overcome gravity
(the aircraft's weight).
[/b]
Uh, you first said "Thrust overcomes drag" and then later said "thrust overcomes gravity". I think you're confused.

The way I understand it is that there is no lift (which allows the plane to overcome gravity) until there is airflow over the wings.

In order for air to flow over the wings, the plane must be in motion RELATIVE TO THE AIR. Take the example of an airborne plane flying into a very strong headwind, with its engines thrusting at 50%. Let's say that the headwind is so strong, it produces enough drag on the aircraft that the plane appears to just hover over the ground.

Remember:
thrust <> drag (horizontal forces that occur in AIR)
lift <> gravity (vertical forces that also in AIR)

The plane's airspeed may be 100mph, but the headwind is also 100mph, so its groundspeed is 0mph. The plane doesn't move over the ground but as far as the air molecules are concerned, the plane is moving through them.

Now, let's say the pilot of this plane just gets sick of not making any progress because it's so windy. He could just position the ailerons to lower the lift produced over the wing, and let gravity bring the plane to the ground. (Of course, in order to prevent the plane from moving backward because of the headwind, he'd have to keep the engines thrusting at 50%.)

But, if he wanted to actually make some forward progress (i.e. groundspeed), he could just increase the throttle to 100%, which would allow the engine thrust to overcome the drag caused by the headwind.

OK, now: let's say that directly beneath the plane is a conveyor belt that's moving backward at 100mph, exactly the speed of the headwind. The plane is still in the air, thrusting away at 50%, hovering over the conveyor belt.

The pilot looks down and sees this racing conveyor belt and wants to set the plane down on it. His plane is equipped with special wheel motors that start to spin the tires really fast so that they don't skid when they hit the ground. (You've seen how plane tires always skid when planes land, right?) Let's say he operates these motors so that the tires are spinning at 100mph, exactly the speed of the conveyor belt, then disengages them as soon as the plane touches down.

(Remember, the plane is still in the air, fighting the headwind, hovering in place over the racing conveyor belt.)

Now, the plane is flying through air molecules, the tires are spinning, and the conveyor is racing backwards at the same speed the tires are spinning (which also happens to be the same speed of the headwind).

When the pilot moves the ailerons and sets the plane down on the conveyor ,the forward-spinning tires and the backward-moving conveyor speeds cancel each other out, so the plane neither moves forward nor backward. At this point, the tires are just freewheeling along the surface of the conveyor.

OK, remember that the engine thrust is at 50%. If the engine thrust is increased to 100%, the plane can overcome the drag produced by the headwind, and move forward. At this point, the pilot could either keep the plane on the ground with the ailerons and increase thrust to move forward, or he could make the plane ascend with the ailerons and increase thrust to move forward.

Either way, it doesn't matter whether the tires are in contact with the ground or conveyor, since the engine thrust is overcoming drag and the ailerons are increasing or decreasing lift over the wing.

If there's less (or zero) headwind, 50% thrust will just move the plane forward through the air, since there's less drag.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:50 AM

Quote:
Originally posted by Hawk:
Quote:
Originally posted by Mobycat:
[b]
Quote:
Originally posted by porsche996:
[b]
quote:
Originally posted by Mobycat:
quote:
Originally posted by MattyX:
If, however, you applied an external force to the car, like a big-ass fan, then the car would move over the ice.
You have just added a second power source.

The plane does NOT have a second power source.[/b]
Moby, you just contradicted your position, and you don't even know it...

The plane doesn't have a "second" power source. It has 1 power source.[/b]
EXACTLY. The car by itself would not have a secondary power source. It won't move.

Put the fan on it - it has a secondary power source.

Again - try the rope example. The rope is not fluid, and it is taught - meaning it's connected to something else.

Moby, you need to open your mind up a bit and take off the blinders.....The rope represents a vector. Similarly, the air also represents that same vector on a similar experiment. The two are representative of the EXACT SAME THING....

No they aren't. A rope is not a gas, is not fluid. That's key.

If I put myself on skates, and pull on an "air rope", will I move forward? No. I can't overcome the friction of the wheels.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:52 AM

You people just don't get it.....If the conveyor is matching the plane's speed, the wheels will just be spinning twice as fast as the plane is actually travelling. However, the plane will still be moving forward......Forward motion will give the plane the lift required to take off. You are all STILL hung up on the wheels vs the conveyor. There is a third force at work here....the engines. And, yet again, I'll say that the conveyor is not working against the engines AT ALL! The engines are working completely independant of the conveyor....
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:54 AM

Quote:
Originally posted by Mobycat:

No they aren't. A rope is not a gas, is not fluid. That's key.

If I put myself on skates, and pull on an "air rope", will I move forward? No. I can't overcome the friction of the wheels.
Open your mind man!!! Look at an air tunnel for example....the air looks like a rope coming through the turbines. Stop thinking of the rope as the actual object it is and start thinking of it more abstractly - as a stream of air for example wink
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:54 AM

LOL

laugh

sigh

I noticed alot of people thinking the plane would appear stationary, if the conveyor went at the plane's speed towards it.

It comes down to STILL thinking that it moves like an Xterra.

I noticed a lot of people thinking that somehow if the conveyor went the same speed as the plane, that the plane was NOT MOVING.

I also noticed people thinking that the air speed would be zero, so no lift would be created...for two wrong reasons.

The first reason is because they think the plane can't move.

The second reason is they forget the wind is typically less important than the speed of the plane THROUGH the stationary air, as in calm flight, etc....

All coming down to not realizing that the plane can move, and that the conveyor ONLY moves IF the Plane MOVES...and that a plane's speed is measured along the planet, NOT across the things under them..otherwise your ground speed would be different as you crossed a river's flow, etc...which of course it isn't (The speed along the BELT IS NOT THE PLANE'S speed).

____________

Absorb this, PLEASE!!!!!!!!

______________

1. If the conveyor is moving, it is ONLY IF THE PLANE IS MOVING.

2. The Plane's speed has NOTHING TO DO WITH ITS TIRE'S SPEED. (IF the plane is in the air, and I climb out and spin the tires, does it change how fast the plane is going?)

3. If I am walking on a tread mill "at 4 mph..." measured as if I had a geared speedometer...I am REALLY GOING ZERO MPH GROUND SPEED.

4. IF I am really going ZERO MPH, THEN, THE CONVEYOR IS GOING ZERO MPH! (It matches the speed)

5. Your SPEED had NOTHING to do with your tire rotation...If I am on ice in my X, and I nail the gas, my tire rotation/speedometer SAYS I might be going 30 mph...but, I might be barely moving, maybe at ZERO, or 1-2 mph, etc....

NO MATTER HOW FAST MY TIRES ARE GOING.

6. If the Conveyor moves AT ALL, it means the plane is MOVING.

7. If the plane is moving...THEN the Conveyor belt is moving.

8. The Plane CANNOT BE STANDING STILL ON THE BELT....OR the Conveyor Belt would be NOT MOVING.

9. If the plane IS moving...it DOES NOT MATTER IF THE BELT IS MOVING, BECAUSE THE PLANE DOES NOT NEED THE BELT TO MOVE THE PLANE....IT HAS THRUST.

10. So - a guy, next to the belt, would see the plane move forward...through the air, along the belt, etc...he'd see the belt turning towards the plane like a tread mill....he's see the THRUST is pushing the plane forwards...he's see that the TIRES are merely LETTING THE BELT SLIP ALONG UNDER THE PLANE.

11. The TIRES are MOVING AT THE GROUND SPEED OF THE PLANE, and, AT THE BELT SPEED (Which matches the speed of the plane) ....and ROTATING at DOUBLE the belt speed.

12. Do NOT think that the SPEED OF THE AIR matters...its the SPEED OF THE WING THOUGH the AIR that matters, and that creates lift in this scenario.

13. The WINGS of the plane are moving forward at the same speed as the belt, because the belt matches the PLANE'S speed...as the WINGS accelerate, so does the belt, AND SO DOES THE SPEED OF THE WING THROUGH THE AIR.

14. When the speed of the wing (through the air) reaches its take off velocity...it just takes off.

laugh
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:55 AM

Quote:
Originally posted by Hawk:
And, yet again, I'll say that the conveyor is not working against the engines [b]AT ALL! The engines are working completely independant of the conveyor....[/b]
The conveyor HAS to be working against the engines if it's matching the plane's speed.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:59 AM

Quote:
Originally posted by TJ:

3. If I am walking on a tread mill "at 4 mph..." measured as if I had a geared speedometer...I am REALLY GOING ZERO MPH GROUND SPEED.
You are going zero compared to the ground AROUND the conveyor, not the conveyor. Which is also compared to the air since it is calm.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:01 PM

Dude, explain how a conveyor belt can work against engines that push air.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:02 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by Hawk:
[b]And, yet again, I'll say that the conveyor is not working against the engines [b]AT ALL! The engines are working completely independant of the conveyor....[/b]
The conveyor HAS to be working against the engines if it's matching the plane's speed.[/b]
Dude...the only thing that can work against the engines is the air flowing through them. The conveyor is working on the wheels....
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:02 PM

Quote:
Originally posted by XPLORx4:
Dude, explain how a conveyor belt can work against engines that push air.
The wheels are NOT frictionless.

The engines have to overcome that friction. But if they start to accelerate, the conveyor accelerates...cancelling out any forward movement.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:03 PM

Quote:
Originally posted by Hawk:
Quote:
Originally posted by Mobycat:
[b]
Quote:
Originally posted by Hawk:
[b]And, yet again, I'll say that the conveyor is not working against the engines [b]AT ALL! The engines are working completely independant of the conveyor....[/b]
The conveyor HAS to be working against the engines if it's matching the plane's speed.[/b]
Dude...the only thing that can work against the engines is the air flowing through them. The conveyor is working on the wheels....[/b]
FRICTION.

You guys are completely ignoring friction.

If the engines are off, and if there was NO friction, and that conveyor belt moved, the plane shouldn't budge - it will just have rolling wheels.

But it WON'T. It WILL move backwards.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:04 PM

So you think that the friction of the wheels is so great that the plane can never gain momentum. Is that it?
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:05 PM

Quote:
Originally posted by Hawk:
You people just don't get it.....If the conveyor is matching the plane's speed, the wheels will just be spinning twice as fast as the plane is actually travelling. However, the plane will still be moving forward......Forward motion will give the plane the lift required to take off. You are all STILL hung up on the wheels vs the conveyor. There is a third force at work here....the engines. And, yet again, I'll say that the conveyor is not working against the engines [b]AT ALL! The engines are working completely independant of the conveyor....[/b]
And you're hung up on thinking the plane is weightless. The wheels ARE exerting force on the conveyor - the weight of the airplane.

Your arguments only make sense if the conveyor belt has a fixed maximum speed.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:05 PM

Quote:
Originally posted by XPLORx4:
So you think that the friction of the wheels is so great that the plane can never gain momentum. Is that it?
IF the conveyor can go fast enough to match the speed of the plane, yes.

IF it can. Which in this scenario, it supposedly can.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:05 PM

Back to your "rope is rope, not wind" comments Moby....

Is it just me, or does this look like a series of ropes travelling around the wing?!?

Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:06 PM

What does the weight of the plane have anything to do with forward movement?
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:06 PM

Quote:
Originally posted by BlueSky:
Quote:
Originally posted by Hawk:
[b]You people just don't get it.....If the conveyor is matching the plane's speed, the wheels will just be spinning twice as fast as the plane is actually travelling. However, the plane will still be moving forward......Forward motion will give the plane the lift required to take off. You are all STILL hung up on the wheels vs the conveyor. There is a third force at work here....the engines. And, yet again, I'll say that the conveyor is not working against the engines [b]AT ALL! The engines are working completely independant of the conveyor....[/b]
And you're hung up on thinking the plane is weightless. The wheels ARE exerting force on the conveyor - the weight of the airplane.[/b]
Exactly. The wheels are NOT irrelevant.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:07 PM

Quote:
Originally posted by XPLORx4:
What does the weight of the plane have anything to do with forward movement?
It determines how much the engines have to work to get the thing moving forward.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:07 PM

You don't see why its an important distinction?

[Freak]

The plane's SPEED is not related to its tires rotation.

The speed of the conveyor's BELT is the speed of the plane, right?

The speed of the plane is NOT the speed of the plane along the conveyor BELT, its the speed of the PLANE.

The plane's speed is NOT the speed of its tire rotation, like on an Xterra's SPEEDOMETER.

Otherwise, my speedometer would say I was going zero mph when I'm stick in the snow and floored, and the tires spinning at 30 mph.

A Plane is NOT an Xterra.

The IMPORTANT facts are that the BELT speed matches the PLANE'S speed...

AND

That the PLANE'S speed is relative TO THE GROUND, NOT to the spinning belt.

Again...if your speedometer says you are going 50 mph while stuck in a ditch...will you REALLY be 50 miles away an hour later?

laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:07 PM

Quote:
Originally posted by BlueSky:
Quote:
Originally posted by Hawk:
[b]You people just don't get it.....If the conveyor is matching the plane's speed, the wheels will just be spinning twice as fast as the plane is actually travelling. However, the plane will still be moving forward......Forward motion will give the plane the lift required to take off. You are all STILL hung up on the wheels vs the conveyor. There is a third force at work here....the engines. And, yet again, I'll say that the conveyor is not working against the engines [b]AT ALL! The engines are working completely independant of the conveyor....[/b]
And you're hung up on thinking the plane is weightless. The wheels ARE exerting force on the conveyor - the weight of the airplane.[/b]
That's great! I'm not arguing that. The force is being exerted downward, and not forward or in reverse.... Downward force will not affect the desired end result of forward motion unless the downward force is so great that the plane won't move regardless of what's under it. We KNOW that this is not the case, otherwise there wouldn't be flight...
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:08 PM

Quote:
Originally posted by XPLORx4:
What does the weight of the plane have anything to do with forward movement?
Try pushing your Xterra up a hill in neutral and then come back and ask again.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:08 PM

Quote:
Originally posted by Hawk:
Back to your "rope is rope, not wind" comments Moby....

Is it just me, or does this look like a series of ropes travelling around the wing?!?

You're kidding, right?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:09 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by XPLORx4:
[b]What does the weight of the plane have anything to do with forward movement?
It determines how much the engines have to work to get the thing moving forward.[/b]
And there you go....it's moving forward...
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:10 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by XPLORx4:
[b]What does the weight of the plane have anything to do with forward movement?
It determines how much the engines have to work to get the thing moving forward.[/b]
So what if you just have some really huge engines?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:10 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by Hawk:
[b]Back to your "rope is rope, not wind" comments Moby....

Is it just me, or does this look like a series of ropes travelling around the wing?!?

You're kidding, right?[/b]
You need to think more abstractly wink
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:11 PM

Quote:
Originally posted by BlueSky:
Quote:
Originally posted by XPLORx4:
[b]What does the weight of the plane have anything to do with forward movement?
Try pushing your Xterra up a hill in neutral and then come back and ask again.[/b]
In the scenario you're describing, you're pushing vertically, not horizontally...
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:11 PM

Assuming there is no wind, the plane has to move relative to the surrounding ground, i.e. whatever is next to the conveyor belt, to achieve flight. It's not going to do that if the conveyor is matching the aircraft's speed.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:11 PM

Quote:
Originally posted by BlueSky:
Quote:
Originally posted by XPLORx4:
[b]What does the weight of the plane have anything to do with forward movement?
Try pushing your Xterra up a hill in neutral and then come back and ask again.[/b]
Yeah, but this scenario isn't on a hill. It's on a level runway.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:12 PM

OK. one more try. Kind of the opposite scenario posted by XPLORx4. Can we agree that one effect of the conveyor is to double the rotating speed of the wheels?

Imagine an aircraft on a long runway wtih a tailwind (FYI- a tailwind is counter-productive to the attainment of lift) of say, 120 knots. Exactly the airspeed needed by the aircraft to lift off. The aircraft begins takeoff roll, with the wind. The wheels spin faster and faster. The plane reaches 120 knots of groundspeed, and has reached zero airspeed. The aircraft continues to accelerate and reaches 180 knots groundspeed, which is 60 knots airspeed. The wheels are spinning at 180 knots now. The aircraft then reaches airspeed of 120 knots, which is 240 knots groundspeed, 240 knots of wheelspin. Lift can be achieved at 120 knots airspeed, and the plane takes off.

Those numbers in review:
At rest on the approach end:
Airspeed -120 [negative 120 knots]
Groundspeed 0
wheelspin 0

starting takeoff roll:
Airspeed 0
Groundspeed +120
wheelspin +120

Halfway to achieving lift:
Airspeed 60
groundspeed +180
wheelspin +180

at liftoff:
airspeed +120
groundspeed +240
wheelspin (before liftoff) +240

Now shouldn't the plane stay on the ground according to the "not-flyers'" logic?
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:12 PM

Quote:
Originally posted by Hawk:
Quote:
Originally posted by BlueSky:
[b]
Quote:
Originally posted by XPLORx4:
[b]What does the weight of the plane have anything to do with forward movement?
Try pushing your Xterra up a hill in neutral and then come back and ask again.[/b]
In the scenario you're describing, you're pushing vertically, not horizontally...[/b]
Fine. Try pushing your Xterra on level ground and then ponder what weight has to do with forward motion. The force of gravity must be overcome to move an object, whether it's up, down, forward, back, or sideways.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:12 PM

Quote:
Originally posted by BlueSky:
Assuming there is no wind, the plane has to move relative to the surrounding ground, i.e. whatever is next to the conveyor belt, to achieve flight. It's not going to do that if the conveyor is matching the aircraft's speed.
The conveyor matching the airplane's speed will only cause the wheels AND the conveyor to rotate at twice the speed of the aircraft. Fact of the matter is the plane will STILL be moving forward regardless...
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:12 PM

I'm becoming a PoHo thanks to this thread! [ThumbsUp]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:13 PM

Ok...how has gravity come into play now? It's not going to prevent an airplane from taking off. If that were the case, we wouldn't have flight! See my first post on page 26
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:14 PM

Quote:
Originally posted by BlueSky:
The force of gravity must be overcome to move an object, whether it's up, down, forward, back, or sideways.
Uh, dude: Gravity only affects things in the VERTICAL dimension. You don't see apples fall from trees SIDEWAYS do you?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:14 PM

Quote:
Originally posted by Mobycat:
FRICTION.

You guys are completely ignoring friction......
We are?

I guess you missed the equations:

Quote:
Originally posted by JeffW:
Instead of trying to convince everybody that the wrong answer is right, read the UNBELIEVIABLY simple physics of the situation.

Coefficient of dynamic friction:

Force of friction:

F(f) = -uN

(negative because it opposes motion)

u = coefficient of static friction

N = weight of plane

Notice velocity is not included!

That means that the velocity of the conveyor belt is irrelevant for all practical purposes.

F(t) is force of thrust

a = (F(t)+F(f))/m

You won't find a scenario where |F(f)| is greater than |F(t)|. Therefore, in ALL cases the plane moves with respect to the atmosphere, thus achieving lift.

Please stop being so bloody indignant and pause long enough to understand why the correct answer is correct. [Huh?]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:14 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by Hawk:
[b]
Quote:
Originally posted by Mobycat:
[b]
quote:
Originally posted by Hawk:
And, yet again, I'll say that the conveyor is not working against the engines [b]AT ALL! The engines are working completely independant of the conveyor....[/b]
The conveyor HAS to be working against the engines if it's matching the plane's speed.[/b]
Dude...the only thing that can work against the engines is the air flowing through them. The conveyor is working on the wheels....[/b]
FRICTION.

You guys are completely ignoring friction.

If the engines are off, and if there was NO friction, and that conveyor belt moved, the plane shouldn't budge - it will just have rolling wheels.

But it WON'T. It WILL move backwards.

What do you think a wheel is for, Moby? It's there to REDUCE FRICTION.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:15 PM

Quote:
Originally posted by MattyX:
OK. one more try. Kind of the opposite scenario posted by XPLORx4. Can we agree that one effect of the conveyor is to double the rotating speed of the wheels?

Imagine an aircraft on a long runway wtih a tailwind (FYI- a tailwind is counter-productive to the attainment of lift) of say, 120 knots. Exactly the airspeed needed by the aircraft to lift off. The aircraft begins takeoff roll, with the wind. The wheels spin faster and faster. The plane reaches 120 knots of groundspeed, and has reached zero airspeed. The aircraft continues to accelerate and reaches 180 knots groundspeed, which is 60 knots airspeed. The wheels are spinning at 180 knots now. The aircraft then reaches airspeed of 120 knots, which is 240 knots groundspeed, 240 knots of wheelspin. Lift can be achieved at 120 knots airspeed, and the plane takes off.

Those numbers in review:
At rest on the approach end:
Airspeed -120 [negative 120 knots]
Groundspeed 0
wheelspin 0

starting takeoff roll:
Airspeed 0
Groundspeed +120
wheelspin +120

Halfway to achieving lift:
Airspeed 60
groundspeed +180
wheelspin +180

at liftoff:
airspeed +120
groundspeed +240
wheelspin (before liftoff) +240

Now shouldn't the plane stay on the ground according to the "not-flyers'" logic?
See, this is what I'm saying. Your argument rides on a tailwind of fixed velocity. In the scenario, the conveyor moves faster and faster as engine thrust is increased, so the speed relative to the surrounding air remains zero.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:15 PM

Quote:
Originally posted by Hawk:
The conveyor matching the airplane's speed will only cause the wheels AND the conveyor to rotate at twice the speed of the aircraft. Fact of the matter is the plane will STILL be moving forward regardless...
If that's the case - the conveyor is no longer matching the speed of the aircraft.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:16 PM

AAARGGG!

The belt only moves if the plane moves....

Speed, or Movement, means relative to the world...not the belt.

My GPS will say I'm going 0 mph if I am on a tread mill that is turning at 4 mph.

If my tread mill MATCHES MY SPEED, it would be turning at ZERO MPH.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:17 PM

(I think Moby and BlueSky still think the earth is flat, btw...)
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:17 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by Hawk:
[b]The conveyor matching the airplane's speed will only cause the wheels AND the conveyor to rotate at twice the speed of the aircraft. Fact of the matter is the plane will STILL be moving forward regardless...
If that's the case - the conveyor is no longer matching the speed of the aircraft.[/b]
There's a new invention in town.

They call it the wheel! [Freak]

It rolls, even on conveyor belts!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:17 PM

Quote:
Originally posted by MattyX:
What do you think a wheel is for, Moby? It's there to REDUCE FRICTION.
Actually, the wheel bearings are there to make it a nearly frictionless scenario wink
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:19 PM

Quote:
Originally posted by TJ:
AAARGGG!

The belt only moves if the plane moves....

Speed, or Movement, means relative to the world...not the belt.

My GPS will say I'm going 0 mph if I am on a tread mill that is turning at 4 mph.

If my tread mill MATCHES MY SPEED, it would be turning at ZERO MPH.
We tried to explain that to them but they are two busy defending the incorrect answer to read!!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:19 PM

Quote:
Originally posted by XPLORx4:
(I think Moby and BlueSky still think the earth is flat, btw...)
[Geek] You mean it's not flat?!? Prove it!! It has to be, otherwise we wouldn't be able to see a straight line on the horizon! laugh [LOL]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:20 PM

Quote:
Originally posted by BlueSky:
See, this is what I'm saying. Your argument rides on a tailwind of fixed velocity. In the scenario, the conveyor moves faster and faster as engine thrust is increased, so the speed relative to the surrounding air remains zero.
Here's the thing, though. The tailwind does not take the place of the conveyor. It merely serves to illustrate that the wheels can meet double the friction (just like the conveyor provides) and still take off.

If the tailwind were ever-increasing to match the groundspeed of the plane, then of course the plane would not fly.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:21 PM

Quote:
Originally posted by TJ:
AAARGGG!

The belt only moves if the plane moves....

Speed, or Movement, means relative to the world...not the belt.

My GPS will say I'm going 0 mph if I am on a tread mill that is turning at 4 mph.

If my tread mill MATCHES MY SPEED, it would be turning at ZERO MPH.
You're changing the scenario.

If your moving at 4mph relative to the conveyor, the conveyor thinks you are moving 4mph, regardless of what your GPS says. Therefore, the conveyor will move at -4mph.

If there is someone controlling the conveyor and they are watching a pedometer you are wearing - you are going 4mph to them. So the conveyor stays at -4mph.

If they are WATCHING you - they will stop the conveyor (since by observation, you aren't moving relative to them). But then you will suddenly thrust forward - and they will see they were mistaken on your speed.

Basically - the question is worded poorly. It doesn't say what the speeds are relative to.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:21 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by BlueSky:
[b]The force of gravity must be overcome to move an object, whether it's up, down, forward, back, or sideways.
Uh, dude: Gravity only affects things in the VERTICAL dimension. You don't see apples fall from trees SIDEWAYS do you?[/b]
Are you serious? What the hell do you think keeps you from moving heavy objects, regardless of the direction? It's their WEIGHT which is a measure of GRAVITY.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:22 PM

Back to that image of the smoke trails around the wings Moby.....

Quote:
Showing the Airflow in a Wind Tunnel. A technique often used in wind tunnels is to introduce smoke in front of the airfoil that is being tested. The smoke comes from regularly-spaced point sources, and the wind flow in the tunnel spreads it out into parallel lines, called streamlines. The streamlines make it possible to visualize the airflow over the airfoil. When the lines continue smoothly over and past the airflow, they show that the flow remains laminar, and that the airfoil is creating very little drag. When the streamlines show more chaotic, turbulent flow, they indicate that the airfoil is creating more drag. You can do something similar with a wind tunnel by stretching thin strings across the flow path, above and below your airfoil test zone. Clip them in place so you can move them up and down to fit different airfoil shapes. Attach a ribbon (about 25 cm long) to each string. Use a stick attached to your airfoil to hold it while you place it in the flow path, between the ribbons. The ribbons will act like the smoke streamlines, so that you can visualize whether the flow over your airfoil is turbulent or laminar. Try different airfoil shapes and measure which have the most laminar and the most turbulent flow. (Parker, 2005, 18–19)
Taken from HERE

The smoke is released from a point on the wall, much in the same way that a rope is attached to a point on the wall wink Think of the rope as a representation of a streamline...
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:22 PM

Point to consider:

(Forget the belt thing for a minute)

Ordinary plane taking off from an ordinary run way...

The tires are turning at the plane's speed as it lifts off...

...the instant that the plane's tires are no longer ON the runway, they start slowing...is the plane slowing?

laugh

What if I placed some rollers on the runway EXACTLY at the POINT of lift off for the TIRES?

The plane is hurtling down the runway, its tires rotating at the plane's speed....

It hits the rollers EXACTLY AT THE POINT IT WOULD LIFT OFF...

The tires HAVE NO TRACTION on the rollers...

They JUST SPIN UNDER THE TIRES>>>>Can the plane take off?

laugh
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:22 PM

So someone answer this ignored comment:

If the engines are off, and if there was NO friction, and that conveyor belt moved, the plane shouldn't budge - it will just have rolling wheels.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:23 PM

Now I know you two are just trolling us. Ha ha, I fell for it. C'mon, quit kidding around here.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:23 PM

Quote:
Originally posted by Hawk:
Back to that image of the smoke trails around the wings Moby.....

Quote:
Showing the Airflow in a Wind Tunnel. A technique often used in wind tunnels is to introduce smoke in front of the airfoil that is being tested. The smoke comes from regularly-spaced point sources, and the wind flow in the tunnel spreads it out into parallel lines, called streamlines. The streamlines make it possible to visualize the airflow over the airfoil. When the lines continue smoothly over and past the airflow, they show that the flow remains laminar, and that the airfoil is creating very little drag. When the streamlines show more chaotic, turbulent flow, they indicate that the airfoil is creating more drag. You can do something similar with a wind tunnel by stretching thin strings across the flow path, above and below your airfoil test zone. Clip them in place so you can move them up and down to fit different airfoil shapes. Attach a ribbon (about 25 cm long) to each string. Use a stick attached to your airfoil to hold it while you place it in the flow path, between the ribbons. The ribbons will act like the smoke streamlines, so that you can visualize whether the flow over your airfoil is turbulent or laminar. Try different airfoil shapes and measure which have the most laminar and the most turbulent flow. (Parker, 2005, 18–19)
Taken from HERE

The smoke is released from a point on the wall, much in the same way that a rope is attached to a point on the wall wink
That smoke is not attached, though.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:25 PM

Quote:
Originally posted by MattyX:
Now I know you two are just trolling us. Ha ha, I fell for it. C'mon, quit kidding around here.
No. I am convinced without a shadow of a doubt - if the conveyor matches the plane's speed, it will not budge.

You guys go ahead and make a conveyor that can do it and go try and ride the plane. I'll stay on the ground, thank you.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:25 PM

The rope is a representation of the smoke streamlines....You need to open your mind. It's not that difficult to understand wink
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:25 PM

Quote:
Originally posted by Mobycat:
So someone answer this ignored comment:

If the engines are off, and if there was NO friction, and that conveyor belt moved, the plane shouldn't budge - it will just have rolling wheels.
That's a correct statement if you mean there's no friction in the wheel bearings. (You need friction between the tires and conveyor, otherwise the tires wouldn't start rolling).
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:26 PM

Quote:
Originally posted by BlueSky:
What the hell do you think keeps you from moving heavy objects, regardless of the direction? It's their WEIGHT which is a measure of GRAVITY.
Uh, no. That's called MASS, not WEIGHT.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:27 PM

Finally we agree.

Those clowns on the other side of the argument will NEVER understand! laugh

I'm done with this thread for now and will think on it some more, and if my opinion changes, I'm man enough to post it here and will. For now this is just spitting in the wind.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:27 PM

Actually, you need a forward force to overcome the downward force of gravity. Once that initial downward force is overcome, yes, the plane will theoretically role freely - barring friction of course.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:27 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Mobycat:
[b]So someone answer this ignored comment:

If the engines are off, and if there was NO friction, and that conveyor belt moved, the plane shouldn't budge - it will just have rolling wheels.
That's a correct statement if you mean there's no friction in the wheel bearings. (You need friction between the tires and conveyor, otherwise the tires wouldn't start rolling).[/b]
Yes, in the wheel bearings.

So, if there is friction, the plane will roll backwards?

Can the plane match the force with its engines?

What if it can't do anything *beyond* matching it?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:27 PM

OK, so here's what Moby's argument boils down to (if I understand it correctly):

The plane can't take off because the rolling resistance of the tires on the conveyor and the friction of the wheel bearings resists the plane's movement through the air enough to prevent it from achieving enough airspeed to take off.

Essentially, the wheel bearings and tires are acting like big parachutes behind the plane.

The plane may actually move down the runway (it would have to have some kind of forward motion because otherwise the conveyor would also stop moving) but it'll just reach the end of the runway before getting airborne.

So, the issue essentially is that we'd have to know the design limitations of the tires and wheel bearings in order to know their maximum safe RPM before self-destructing.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:29 PM

At this rate, this thread will take over the top spot for "Thread with the most pages". [LOL]

Move over Phat Chicks!! The plane is taking off!!! laugh
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:30 PM

Quote:
Originally posted by Mobycat:
So, if there is friction, the plane will roll backwards?

Can the plane match the force with its engines?

What if it can't do anything *beyond* matching it?
If there's friction in the wheel bearings, then yes, the plane will roll backwards.

Can the plane match the force with its engines!? I should hope so! Otherwise it needs bigger engines!
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:31 PM

Quote:
Originally posted by Hawk:
At this rate, this thread will take over the top spot for "Thread with the most pages". [LOL]

Move over Phat Chicks!! The plane is taking off!!! laugh
Reporter: What kind of plane is it?
Johnny: Oh, it's a big pretty white plane with red stripes, curtains in the windows and wheels and it just looks like a big Tylenol.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:32 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Mobycat:
[b]So, if there is friction, the plane will roll backwards?

Can the plane match the force with its engines?

What if it can't do anything *beyond* matching it?
If there's friction in the wheel bearings, then yes, the plane will roll backwards.

Can the plane match the force with its engines!? I should hope so! Otherwise it needs bigger engines![/b]
And the last question? What's your answer?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:33 PM

Quote:
Originally posted by Mobycat:
Reporter: What kind of plane is it?
Johnny: Oh, it's a big pretty white plane with red stripes, curtains in the windows and wheels and it just looks like a big Tylenol.
HAHAHAHAH! [LOL] [LOL] [LOL] [LOL] [LOL] [Spit]
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:33 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by TJ:
[b]AAARGGG!

The belt only moves if the plane moves....

Speed, or Movement, means relative to the world...not the belt.

My GPS will say I'm going 0 mph if I am on a tread mill that is turning at 4 mph.

If my tread mill MATCHES MY SPEED, it would be turning at ZERO MPH.
You're changing the scenario.

If your moving at 4mph relative to the conveyor, the conveyor thinks you are moving 4mph, regardless of what your GPS says. Therefore, the conveyor will move at -4mph.

If there is someone controlling the conveyor and they are watching a pedometer you are wearing - you are going 4mph to them. So the conveyor stays at -4mph.

If they are WATCHING you - they will stop the conveyor (since by observation, you aren't moving relative to them). But then you will suddenly thrust forward - and they will see they were mistaken on your speed.

Basically - the question is worded poorly. It doesn't say what the speeds are relative to.[/b]
um, relative to the planet...like what speed means.

laugh

Although...this DOES clarify WHY so many of you CAN't figure this out.

Speed is a universal term...but, the wrong answer people are confusing Speedometer speed with REAL speed.

Speed is how quickly you cover a distance, say in miles per hour.

If I am going 4 mph, I will be able to cover 4 miles in one hour.

My speed on a tread mill is zero, no mater how fast the TREAD MILL IS GOING. (Assuming I don't have a heart attack, etc...)

My pedometer/speedometer might SAY 4 mph...but it would be tricked into it...

The speed you READ while ON a tread mill is your EQUIVALENT speed, IF IT were NOT a tread mill.

Maybe that's the bone of contention...what speed means in THIS scenario?

If we agree what speed means..for THIS problem...this will all fall into place?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:35 PM

Quote:
Originally posted by Mobycat:
What if it can't do anything *beyond* matching it?
Then, again, the plane needs bigger engines.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:35 PM

I have noticed that this entire discussion keeps moving in circles. [Freak]

Please.... everyone get away from the tires...gravity...ropes...wind tunnels...pushing Xterras uphill, etc., etc.

These things are confusing some and taking the discussion in directions it doesn't need to go.

Quote:
Originally posted by TJ:

I noticed alot of people thinking the plane would appear stationary, if the conveyor went at the plane's speed towards it.

I noticed a lot of people thinking that somehow if the conveyor went the same speed as the plane, that the plane was NOT MOVING.
That is an assumption on your part.

The plane is moving. However... once the conveyor and the plane's speed are matched exactly... to an outside observer the plane would "appear" to be stationary. Remember... "appear" stationary.

Are we at least on the same page regarding that fact?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:37 PM

Quote:
Originally posted by NY Madman:
The plane is moving. However... once the conveyor and the plane's speed are matched exactly... to an outside observer the plane would "appear" to be stationary. Remember... "appear" stationary.

Are we at least on the same page regarding that fact?
I think not. The issue is how speed is measured. Is it measured in absolute speed (i.e over the earth's surface) or in relative speed (i.e. over the conveyor belt)?
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:39 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Mobycat:
[b]What if it can't do anything *beyond* matching it?
Then, again, the plane needs bigger engines.[/b]
You're avoiding the question.

Would the plane be able to keep from moving backwards due to the friction? And, because of that, stay in one place (since it's only matching, not overcoming)?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:42 PM

Quote:
Originally posted by Mobycat:
Would the plane be able to keep from moving backwards due to the friction? And, because of that, stay in one place (since it's only matching, not overcoming)?
If the plane's engines were throttled up only enough to equalize the friction produced by the wheel bearings, then, yes, you could have a plane sitting motionless on a moving conveyor belt.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:45 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Mobycat:
[b]Would the plane be able to keep from moving backwards due to the friction? And, because of that, stay in one place (since it's only matching, not overcoming)?
If the plane's engines were throttled up only enough to equalize the friction produced by the wheel bearings, then, yes, you could have a plane sitting motionless on a moving conveyor belt.[/b]
Bingo. It's the same thing.

It doesn't matter which one started the event - either way, there is an equal and opposite reaction.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:45 PM

Quote:
Originally posted by XPLORx4:
If the plane's engines were throttled up only enough to equalize the friction produced by the wheel bearings, then, yes, you could have a plane sitting motionless on a moving conveyor belt.
HOWEVER, since the original scenario specifies that the plane must have some kind of speed so that the conveyor can reverse-match it, how do you want to measure speed? In order for the conveyor to even get going, the plane would have to have some kind of ACTUAL speed...
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:45 PM

Quote:
Originally posted by NY Madman:
....The plane is moving. However... once the conveyor and the plane's speed are matched exactly... to an outside observer the plane would "appear" to be stationary. Remember... "appear" stationary.

Are we at least on the same page regarding that fact?
Heck no!

The plane moves absolutely!

It's thrusters push against the atmosphere.

Please read above!

F = ma

a = F/m
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:46 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by XPLORx4:
[b]If the plane's engines were throttled up only enough to equalize the friction produced by the wheel bearings, then, yes, you could have a plane sitting motionless on a moving conveyor belt.
HOWEVER, since the original scenario specifies that the plane must have some kind of speed so that the conveyor can reverse-match it, how do you want to measure speed? In order for the conveyor to even get going, the plane would have to have some kind of ACTUAL speed...[/b]
That's the whole crux of it, though.

What's the speed relative to?
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:48 PM

The one thing that needs more discussion and examination in this debate is the plane's relationship with the outside air in the atmosphere.

I don't see anything else that warrants attention at this point in the debate.

I'm specifically talking about the air on the wings while the plane is at full thrust and the conveyor and speed of the plane are perfectly matched. I'm not concerned with the air behind the engines at this point or the engines effect on that air behind the plane.

I've noticed that those who are proposing that the plane will take off seem to be assuming that the plane in the scenario has an identical relationship with the atmospheric air as a normal plane going down a runway in a conventional takeoff.

I believe that is a premature and most likely incorrect assumption. You are possibly looking at the problem merely in practical terms and not considering the more complex aspects.

I'm not saying you are wrong... but, as far as I can see, that should be the primary and only focus in the debate at this point.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:48 PM

If I run on a treadmill at 4mph for one hour, I don't move relative to the room I'm in.

But I don't tell someone, "I ran zero miles today!"

I DID run 4 miles.
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:48 PM

There is ZERO power being put directly to the wheels. They just spin. In fact, the plane can take off while the wheels are actually spinning backwards due to the fact that the wheels have no effect on propultion.

Ever wondered why no one has ever seen a jet on a dyno?

I also used the Harrier reference because there are two forces at work there. First it uses downword thrust to achieve lift, and then forward propultion to achieve speed.

Try to imagine a hovering Harrier. It is hovering in mid air and then when maximum thrust is applied to forward motion it reaches speed and is no longer reliant on downword thrust to defy gravity. But by "floating" it is eliminating the need for a runway, thus no need for wheels. Yet, from a standing start, mid air, it is able to achieve flight.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:50 PM

No bearing on this debate but interesting nonetheless...

On November 27, 1970, a Capitol Airways DC-8 crashed on takeoff at Anchorage, killing 47 of the 229 aboard. From the report:

PROBABLE CAUSE: "The failure of the aircraft to attain the necessary airspeed to effect lift-off during the attempted takeoff. The lack of acceleration, undetected by the crew until after the aircraft reached V1 speed, was the result of a high frictional drag which was caused by a failure of all main landing gear wheels to rotate. Although it was determined that a braking pressure sufficient to lock all of the wheels was imparted to the brake system, the source of this pressure could not be determined. Possible sources of the unwanted braking pressure were either a hydraulic/brake system malfunction or an inadvertently engaged parking brake."
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:50 PM

Quote:
Originally posted by socalpunx:

I also used the Harrier reference because there are two forces at work there. First it uses downword thrust to achieve lift, and then forward propultion to achieve speed.

Try to imagine a hovering Harrier. It is hovering in mid air and then when maximum thrust is applied to forward motion it reaches speed and is no longer reliant on downword thrust to defy gravity. But by "floating" it is eliminating the need for a runway, thus no need for wheels. Yet, from a standing start, mid air, it is able to achieve flight.
It is NOT able to achieve flight from a mid air standing start. The vents gradually turn as the plane begins moving forward.

Try taking that harrier and switching the vents instantaneously from vertical to horizontal.

It's going to drop like a rock. Because there is no lift on the wings.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:50 PM

Quote:
Originally posted by Mobycat:
It doesn't matter which one started the event - either way, there is an equal and opposite reaction.
There, you are making the assumption that the harder the engines pull, the force of friction on the wheel bearings equalizes the engine thrust. Your response assumes that the wheel bearings would have an infinite amount of friction that is opposed by an infinite amount of engine thrust. In real life, of course, we know that at some rotational speed, the tires would fly apart or the wheel bearing grease would overheat and cause the landing gear to self destruct.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:52 PM

Quote:
Originally posted by socalpunx:
There is ZERO power being put directly to the wheels. They just spin. In fact, the plane can take off while the wheels are actually spinning backwards due to the fact that the wheels have no effect on propultion.

Ever wondered why no one has ever seen a jet on a dyno?
DING DING DING DING DING!!!! It's IMPOSSIBLE to put a plane on a dyno without strapping it down so it doesn't move forward! The conveyor belt scenario is basically a theoretical dyno tester!
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:52 PM

Quote:
Originally posted by JeffW:

Heck no!

The plane moves absolutely!

It's thrusters push against the atmosphere.

Please read above!
The plane is moving.

You haven't answered the question. I'll put it another way....

If an outside observer were to look at the hypothetical experiment being discussed while it is in progress... keep in mind that the conveyor and the plane's speed are matched...

Tell me what that outside observer would see? Describe the scene from their eyes.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 12:55 PM

Quote:
Originally posted by NY Madman:
Tell me what that outside observer would see? Describe the scene from their eyes.
They would see a plane get onto a runway, jerk forward for a microsecond, then move very slowly forward until the tires and wheel bearings got too hot and self-destructed. Then they'd see some emergency vehicles and eventually an evacuation of the aircraft.
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:00 PM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by socalpunx:
[b]
I also used the Harrier reference because there are two forces at work there. First it uses downword thrust to achieve lift, and then forward propultion to achieve speed.

Try to imagine a hovering Harrier. It is hovering in mid air and then when maximum thrust is applied to forward motion it reaches speed and is no longer reliant on downword thrust to defy gravity. But by "floating" it is eliminating the need for a runway, thus no need for wheels. Yet, from a standing start, mid air, it is able to achieve flight.
Try taking that harrier and switching the vents instantaneously from vertical to horizontal.

It's going to drop like a rock. Because there is no lift on the wings.[/b]
At what moment is vertical thrust insignificant and horizontal thrust applied? Aren't we still talking about achieving maximum thrust in flight without the use of the wheels making the wheels irrelevant.

I still think it would take off in the conveyor scenario, but why is it that jet pilots appply thrust gradually as opposed to appplying full throttle and reducing runway distances? Isn't the thrust alone enough to push the plane into flight?

Does the plane on the conveyor belt also create it's own atmospheric conditions like a tornado? Althought it appears that it is not moving it of course we know that it is. Due to speed and friction of the wheel is there enough motion to create wind and simulated atmosphereic conditions of movement?
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:00 PM

It seems to me that the "will take off" crowd is right...IF the plane was already airborne. But to get airborne, it must move forward relative to the ground and surrounding air. It's not doing that on the belt, just like the runner on the treadmill doesn't advance relative to the room.

I think whoever said the question of what speed means in this instance is right. Can the belt really "match" the plane's speed, and if so, what exactly does that mean? To me it means it negates the plane's forward motion, just like a dyno does to a car or a grocery store conveyor does to an orange.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:01 PM

Quote:
Originally posted by XPLORx4:

They would see a plane get onto a runway, jerk forward for a microsecond, then move very slowly forward until the tires and wheel bearings got too hot and self-destructed. Then they'd see some emergency vehicles and eventually an evacuation of the aircraft.
[LOL] [LOL]

That's funny.

In all seriousness, the others need to answer that question. It will help us all get on the same page.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:04 PM

I have a truck
Do you give a fuck?
Maybe it needs cleaning
Maybe this has another meaning
Do you know what it is yet?
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:04 PM

Quote:
Originally posted by socalpunx:
Quote:
Originally posted by Mobycat:
[b]
Quote:
Originally posted by socalpunx:
[b]
I also used the Harrier reference because there are two forces at work there. First it uses downword thrust to achieve lift, and then forward propultion to achieve speed.

Try to imagine a hovering Harrier. It is hovering in mid air and then when maximum thrust is applied to forward motion it reaches speed and is no longer reliant on downword thrust to defy gravity. But by "floating" it is eliminating the need for a runway, thus no need for wheels. Yet, from a standing start, mid air, it is able to achieve flight.
Try taking that harrier and switching the vents instantaneously from vertical to horizontal.

It's going to drop like a rock. Because there is no lift on the wings.[/b]
At what moment is vertical thrust insignificant and horizontal thrust applied? Aren't we still talking about achieving maximum thrust in flight without the use of the wheels making the wheels irrelevant.

I still think it would take off in the conveyor scenario, but why is it that jet pilots appply thrust gradually as opposed to appplying full throttle and reducing runway distances? [/b]
That question I can answer: engine wear. Maximum thrust is not used by airliners for takeoff, "takeoff thrust" is computed using the final weight and balance figures and is usually not maximum thrust but a percentage thereof. This minimizes engine wear and allows a safety cushion of available power if needed.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:07 PM

Quote:
Originally posted by BlueSky:

Can the belt really "match" the plane's speed, and if so, what exactly does that mean? To me it means it negates the plane's forward motion, just like a dyno does to a car or a grocery store conveyor does to an orange.
You are getting VERY CLOSE.

The plane is in motion. However not in conventional terms.

We need to know the exact relationship of the plane and the atmospheric air at this point in time.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:08 PM

Quote:
Originally posted by BlueSky:
I think whoever said the question of what speed means in this instance is right. Can the belt really "match" the plane's speed, and if so, what exactly does that mean? To me it means it negates the plane's forward motion, just like a dyno does to a car or a grocery store conveyor does to an orange.
How can a conveyor belt touching wheels that have no power source negate movement caused by engines pushing against air?
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:09 PM

So if necessary, and engine life were not a factor for this excersize, you could potentially go from zero to takeoff thrust with wreckless abandon set the wing flaps for takeoff and...

Take off. Right?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:12 PM

Quote:
Originally posted by BlueSky:
That question I can answer: engine wear. Maximum thrust is not used by airliners for takeoff, "takeoff thrust" is computed using the final weight and balance figures and is usually not maximum thrust but a percentage thereof. This minimizes engine wear and allows a safety cushion of available power if needed.
It's also to make it more comfortable for passengers as well as to reduce stress on the airframe. Theoretically it could be possible for a plane to be made with engines so powerful that they could rip themselves from the wings if they were turned on full blast while the plane isn't moving.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:13 PM

Quote:
Originally posted by socalpunx:
So if necessary, and engine life were not a factor for this excersize, you could potentially go from zero to takeoff thrust with wreckless abandon set the wing flaps for takeoff and...

Take off. Right?
Not immediately. You have to have foward momentum to get wind going across the wings.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:15 PM

OK...how about this.

Regardless of whether a wheel is driven through a drivetrain or rotates freely, it covers a given distance per rotation. In this scenario, the distance covered per rotation is reduced to zero because the treadmill moves that distance back as the wheel tries to advance forward. Again, this is true regardless of what's driving the wheel forward.

So the relative forward motion is zero, the relative wind over the wing is zero, airspeed is zero, and your chances of taking off are...you guessed it...zero.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:16 PM

Socal....

You're a smart guy. If you were the outside observer looking down on the experiment in our hypothetical scenario.... (Remember plane and conveyor speed are matched)

What would you see? Describe it.... start to finish.

.......................

Now... it is not a windy day when you are observing this scenario.

Describe the wind condition on the top of the wing of the plane in the scenario. Is the wind blowing hard....

Or is the wind condition almost the same as where you are standing?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:17 PM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by JeffW:

[b]Heck no!

The plane moves absolutely!

It's thrusters push against the atmosphere.

Please read above!
The plane is moving.

You haven't answered the question. I'll put it another way....

If an outside observer were to look at the hypothetical experiment being discussed while it is in progress... keep in mind that the conveyor and the plane's speed are matched...

Tell me what that outside observer would see? Describe the scene from their eyes.[/b]
They would see the plane take off with a little extra wheelspin due to the conveyor belt.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:20 PM

Quote:
Originally posted by BlueSky:
Regardless of whether a wheel is driven through a drivetrain or rotates freely, it covers a given distance per rotation. ... Again, this is true regardless of what's driving the wheel forward.
No, it's not. In the scenario of a freewheeling wheel, what's driving it forward?
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:22 PM

Quote:
Originally posted by JeffW:

They would see the plane take off with a little extra wheelspin due to the conveyor belt.
Alright. Let me clarify.

Leading up to the hypothetical takeoff...

What do you see as the plane and conveyor are building up speed?

What is the plane's appearance relative to your position?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:22 PM

Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:25 PM

Quote:
Originally posted by Mobycat:
If I run on a treadmill at 4mph for one hour, I don't move relative to the room I'm in.

But I don't tell someone, "I ran zero miles today!"

I DID run 4 miles.
Ah HA!

No - you ran ZERO MILES.

You stayed in ONE PLACE, and, COVERED NO DISTANCE.

You moved your legs AS THOUGH you had run 4 miles...but, in fact, you did not.

laugh
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:27 PM

It's a chicken or the egg scenario though.

What we see is dependant on the result of the findings of this question.

An observer would see a large jet on a treadmill type conveyor belt. Initially the plane would not be moving as the wheel movement is being negated by the conveyor.

But as thrust is applied how that overcomes the lack of forward motion is the question here. I believe that wind speed and atmosphere are irrelevant to the plane achieving flight since propultion along with the wing design and purpose are enough to overcome the lack for forward motion.

But a vehicle moving at 200+ MPH without wings is also able to achieve flight. So again: the chicken or the egg?

I still believe that forward motion works in a symbiotic relationship to the method of thrust and wing design but they can also produce flight independant of each other.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:27 PM

Quote:
Originally posted by Alpine Spirit:
There WILL be air moving over the wing, due to the plane moving forward....the wind blowing out THE BACK OF THE ENGINE is pushing it forwards THROUGH THE AIR.

The Belt does not matter, or change the air around the plane in ay way whatso ever.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:29 PM

How does a plane move through the air? Its engines push the air through them, right?

How does a car move? Its powered wheels push the ground out from under it, right?

Now, here's a trick question: How does a car move through the air? Hint: as long as the car's tires are on the ground, it moves forward.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:30 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by BlueSky:
[b]Regardless of whether a wheel is driven through a drivetrain or rotates freely, it covers a given distance per rotation. ... Again, this is true regardless of what's driving the wheel forward.
No, it's not. In the scenario of a freewheeling wheel, what's driving it forward?[/b]
Well, if the wheel moves, something is causing that, correct? It could be a guy pulling his kid in a Radio Flyer or a soap box derby racer coasting, but if the wheel is moving, it is covering a given distance per rotation. If that distance is negated by a moving surface underneath that moves an equal distance in the opposite direction, the vehicle will not move relative to its surroundings.
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:32 PM

Quote:
Originally posted by TJ:
Quote:
Originally posted by Mobycat:
[b]If I run on a treadmill at 4mph for one hour, I don't move relative to the room I'm in.

But I don't tell someone, "I ran zero miles today!"

I DID run 4 miles.
Ah HA!

No - you ran ZERO MILES.

You stayed in ONE PLACE, and, COVERED NO DISTANCE.

You moved your legs AS THOUGH you had run 4 miles...but, in fact, you did not.

laugh [/b]
No, I covered four miles of the treadmill.

Again - what is the speed relative to in the question?

If I drive my car for four miles on a dyno - do you really think I can claim it has no miles on it if I resold it? No.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:33 PM

Quote:
Originally posted by BlueSky:
Well, if the wheel moves, something is causing that, correct? It could be a guy pulling his kid in a Radio Flyer or a soap box derby racer coasting, but if the wheel is moving, it is covering a given distance per rotation. If that distance is negated by a moving surface underneath that moves an equal distance in the opposite direction, the vehicle will not move relative to its surroundings.
So, you're saying that a guy pulling his kid in a radio flyer will be unable to keep pulling the wagon if the wagon suddenly rolls over a conveyor belt?
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:35 PM

If air speed over the wings is required for flight then why have F1 and Indy cars been airborne and why is a primary concern for land speed attempts maintaining enough downforce at speed to prevent the vehicle from achieving flight.

Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:35 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by BlueSky:
[b]Well, if the wheel moves, something is causing that, correct? It could be a guy pulling his kid in a Radio Flyer or a soap box derby racer coasting, but if the wheel is moving, it is covering a given distance per rotation. If that distance is negated by a moving surface underneath that moves an equal distance in the opposite direction, the vehicle will not move relative to its surroundings.
So, you're saying that a guy pulling his kid in a radio flyer will be unable to keep pulling the wagon if the wagon suddenly rolls over a conveyor belt?[/b]
No, I'm saying that if the conveyor belt it's on speeds up to match how hard he pulls, the wagon will not move forward, assuming it's on the belt and he isn't.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:35 PM

Quote:
Originally posted by socalpunx:

But as thrust is applied how that overcomes the lack of forward motion is the question here.
The question is whether the same amount of wind and air move over the wings as does in a conventional takeoff.

That is the key and the only thing that needs focusing.

Quote:
I still believe that forward motion works in a symbiotic relationship to the method of thrust and wing design but they can also produce flight independant of each other.
Remember the four forces required for flight.

We know we have three.

The only variable yet to be determined is the air at a certain point in time moving over the wing and body of the plane.

If it is even remotely less than that for a conventional takeoff....

Will this plane in the scenario achieve takeoff and flight?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:36 PM

The bearings in the wheels would fry and the whole thing would crash before it took off.

Or the tread mill would snap and fly through the cockpit effectively killing pilot and any chance the plane had to take off.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:36 PM

BlueSky-

Here's another scenario.

Let's say I'm riding my bike on a treadmill. No matter how fast I pedal, the treadmill keeps up, so I don't roll off the treadmill.

Now, let's say that you come long next to me and grab my arm and start pulling me forward. Will you be able to pull me off the treadmill?
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:40 PM

No because , as is the case with the plane, you are not being self propelled. (nor are the wheels) You are being propelled by an external force (the jet engines or whoever is pulling you) and the conveyor is still mathing whatever percieved forward progress you are making.

Even if a team of clydsdales were you be pulling you, you could not be pulled off of the treadmill.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:40 PM

Quote:
Originally posted by socalpunx:
If air speed over the wings is required for flight then why have F1 and Indy cars been airborne and why is a primary concern for land speed attempts maintaining enough downforce at speed to prevent the vehicle from achieving flight.

Airflow over a wing allows aircraft to achieve CONTROLLED flight. The vehicles you mentioned do not "fly" per se, they are propelled into the air by various aerodynamic forces that temporarily provide enough lift to elevate them off the ground.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:42 PM

I can see where it would take off and I can see where it would not there is just not enough information to say yes or no.

Simply because there were no limits put on the treadmill? And are the wheels totally magically not creating drag? And do the engines have enough power to overcome the weight of the plane dragging on the treadmill?

Hell if there were no limits put on the friction of the wheels on the ground and engines had insane power then yes I believe it could take off.

But this is a fictional situatoin so who is to say there are limits.

[Too much XOC] [Wave]
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:44 PM

socalpunx- whoa, that's some crazy logic.

OK, let's take this to the off-road arena.

Let's say I'm stuck on an uphill slope in my 4x4. No matter how much gas I give it, gravel/rocks/scree keep rolling under my tires so I can't move forward. (Let's assume that I'm not digging any holes and that there's an infinite supply of gravel to keep me slipping.)

I call up to you in your X and tell you I'll give you a case of beer for a winch up the hill. Can you pull my truck up?
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:49 PM

Further to the above:

Flight:



Not flight:

Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:51 PM

But your next example has definable factors. Traction, the type of along with the weight of your vehicle all come into play and we can determine the best possible way to pull you up the hill because the hill you are trying to drive up is not moving in the opposite direction as your attempt at movement.

Your treadmill is set up to negate the amound of force you apply towards forward progress therefore even if you were being pulled by that car I posted a picture of (assuming that your feet could move at three hundred MPH or you had wheels instead of feet) you would still be riding the treadmill to nowhere.

Matching exact speed is matching exact speed regardless of whether the force applied is internal or external. Remember the wheels of the plane has no source of power themselves. Their only movement is as the result of an external force.
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:54 PM

Quote:
Originally posted by BlueSky:
Not flight:

Quote:
Originally posted by Hawk:
Will the plane be able to take off?
Did Mr. Stewart "take off" though? laugh

The question is not to consider the quality of the flight or the length of flight but if or not the plane can "take off".
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 01:55 PM

Quote:
Originally posted by socalpunx:
But your next example has definable factors. Traction, the type of along with the weight of your vehicle all come into play and we can determine the best possible way to pull you up the hill because the hill you are trying to drive up is not moving in the opposite direction as your attempt at movement.
Well, since the gravel keeps rolling under my tires no matter how much gas I give them, I pretty much have zero traction. And because the gravel keeps rolling under my tires, the hill may as well me "moving in the opposite direction". The weight of my truck is only a factor in determining whether your winch can pull me up. If your winch is strong enough to pull my truck up, then I should be able to make forward progress, right?
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 02:00 PM

You are then saying that you have no relationship with the ground because if my winch is pulling you up regardless if your traction than you are basically saying that I could be winching you up the hill even if your truck was suspended or hanging off the side of a cliff. You are negating the relationship your truck has with the surface completely.

In the treadmill scenario the relative relationship beteen the surface (the belt) and you (your feet) is the most important factor because the belt is designed to match the speed to maintain the relationship. If you were to be yanked off the treadmill by an external force and your feet LEFT the surface of the treadmill then and only then could you be removed from it.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 02:07 PM

Quote:
Originally posted by socalpunx:
You are then saying that you have no relationship with the ground because if my winch is pulling you up regardless if your traction than you are basically saying that I could be winching you up the hill even if your truck was suspended or hanging off the side of a cliff. You are negating the relationship your truck has with the surface completely.
That's PRECISELY the point! We already know that the my truck's forward movement through its tires is negated by the ground's backward movement, so the net is ZERO. The only way for my truck to move FORWARD (in spite of whatever the ground is doing) is to be provided a means of forward propulsion that is not related to the tires or to the ground.

In your treadmill example, you're basically saying that if I place my treadmill on the shoulder of the freeway, and I stick a winch cable to my bike then toss it out so it catches a passing truck, I'd be able to stop that truck dead in its tracks because the treadmill would prevent my bike from leaving the treadmill. That's absurd! I'm not GLUED or BOLTED to the treadmill surface, I'm just traveling on top of it!
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 02:12 PM

I understand what you are saying and agree in your most recent example. But how would it be impacted if you WERE able to continue to maintain your relationship with the treadmill?
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 02:16 PM

It seems the plane scenario has been abandoned.

Now it's dragging treadmills with the Xterra. [Huh?]
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 02:16 PM

My relationship with the treadmill is explicitly limited to its ability to speed up and slow down according to my speed. Nothing more. It can't prevent me from exiting it. Sure, it might speed up as I start to leave it, but it can't prevent me from doing so if some force external to the treadmill surface pulls me off.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 02:18 PM

Quote:
Originally posted by NY Madman:
It seems the plane scenario has been abandoned.

Now it's dragging treadmills with the Xterra. [Huh?]
Hahah. The same principles apply.

Treadmill=conveyor belt
Xterra = external force unrelated to the conveyor belt = jet engines

Just as an Xterra can pull someone running on a treadmill, a jet engine can propel an aircraft to liftoff speed.
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 02:27 PM

Well crap. I have always maintained that. laugh
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 02:28 PM

Quote:
Originally posted by socalpunx:
Well crap. I have always maintained that. laugh
Troll. [Finger] wink
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 03:18 PM

Quote:
Originally posted by NY Madman:
It seems the plane scenario has been abandoned.

Now it's dragging treadmills with the Xterra. [Huh?]
This thread's the shit.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 03:34 PM

Quote:
Originally posted by AHTOXA:
This thread's shit.
Yep, you said it laugh
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 04:33 PM

OK - New tack -

What is making the jets tires turn?

They are not on a motor..they will ONLY turn if the jet MOVES.

The ONLY way the jet CAN move is if the engines PUSH it...

?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 04:42 PM

Im gonna try one more analogy today, then I'm gonna start drinking.

Say you've got a nice set of wheels on top of your xterra's rack. They're not geared, just free-spinning. There's a long conveyor lowered lnogitudinally atop the wheels atop your X which will match its speed. It will even put weight on the xterra, say 1000 lbs. Will you be able to drive forward?
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 04:44 PM

Quote:
Originally posted by MattyX:
Im gonna try one more analogy today, then I'm gonna start drinking.

Say you've got a nice set of wheels on top of your xterra's rack. They're not geared, just free-spinning. There's a long conveyor lowered lnogitudinally atop the wheels atop your X which will match its speed. It will even put weight on the xterra, say 1000 lbs. Will you be able to drive forward?
No, there's a tree in front of my Xterra right now, so I can't go forward laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 04:47 PM

Same analogy, inverted. Say your Xterra could run just fine upside-down. You've still got the wheels on top of the rack, but now the X is upside-down and the non-geared wheels are supporting its weight (they're well engineered). The free spinning wheels are again on a conveyor. Theres a solid, non-moving surface lowered to meet the actual drive tires atop the now-inverted Xterra with the same 1000 lbs as before. Again, this magic Xterra can run fine upside-down. Will it be able to move itself forward?
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 04:53 PM

Quote:
Originally posted by TJ:
OK - New tack -

What is making the jets tires turn?

They are not on a motor..they will ONLY turn if the jet MOVES.

The ONLY way the jet CAN move is if the engines PUSH it...

?
It's not a new tack.

It's repeating and bringing up the same things over and over again like this is the reason why this thread is 33 pages.

You are only addressing what you wish to address and are ignoring what you can't answer.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:05 PM

Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:11 PM

Quote:
Originally posted by JeffW:
Quote:
Originally posted by NY Madman:
[b]
Quote:
Originally posted by JeffW:

[b]They would see the plane take off with a little extra wheelspin due to the conveyor belt.
....What do you see as the plane and conveyor are building up speed?

What is the plane's appearance relative to your position?[/b]
Like I said. It will appear as a normal takeoff with little extra wheelspin due to the conveyor belt.

This is a Physics 101 problem. I (and others) have posted the correct answer NUMEROUS times.

Planes are not propelled by wheels! They are propelled by jet engines. The plane WILL gain the necessary airspeed, but its wheels will have to spin faster because of the treadmill.

What is it about this scenario people are having trouble understanding? How much simpler could it be?[/b]
That is part of your problem.

You are assuming it is a simple problem and that there are no complexities involved.

You are also intentionally ignoring the question I have posed to you. Are you afraid that you may find out you are wrong?

A thread doesn't go 500 pages on a physics forum if it is a simple scenario.

Answer my question and we will move along to the next level. As I said previously, you are making premature assumptions of which you may be wrong or may be right. But for some reason you are refusing to explore that possibility.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:13 PM

Madman, he answered your question. He said the plane would roll and take off with a little extra wheelspin.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:18 PM

Quote:
Originally posted by NY Madman:
.........you are making premature assumptions of which you may be wrong or may be right. But for some reason you are refusing to explore that possibility.
Let's agree on what assumptions are sensible then. All of the assumptions below apply to virtually all aircraft.

Plane is powered by engines that push air (props or jets)
Plane's speed is measured by a windspeed meter as well as GPS
Plane's wheels spin freely
Wheel friction is negligible when compared to thrust
Newtonian physics apply

If all of the above assumption are true, the plane takes off normally with just a little extra wheelspin.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:23 PM

Quote:
Originally posted by MattyX:
Madman, he answered your question. He said the plane would roll and take off with a little extra wheelspin.
The question wasn't answered.

It takes a little time to come up to take off speed.

If he or anyone is acting as the outside observer, I want to know what is seem from start to finish from the perspective of the outside observer. Namely...

-- Does the plane appear stationary from the perspective of the outside observer until takeoff

-- If so.. let's discuss the relationship of the plane in the scenario and the surrounding atmosphere (fluid air) vs. the relation to the surrounding atmosphere for the same plane in a normal conventional takeoff.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:29 PM

Quote:
Originally posted by JeffW:
Quote:
Originally posted by NY Madman:
[b].........you are making premature assumptions of which you may be wrong or may be right. But for some reason you are refusing to explore that possibility.
Let's agree on what assumptions are sensible then. All of the assumptions below apply to virtually all aircraft.

Plane is powered by engines that push air (props or jets)
Plane's speed is measured by a windspeed meter as well as GPS
Plane's wheels spin freely
Wheel friction is negligible when compared to thrust
Newtonian physics apply

If all of the above assumption are true, the plane takes off normally with just a little extra wheelspin.[/b]
So far what you have written is correct.

However it is NOT the entire picture. You are ignoring the possible difference in the fluid air and atmosphere involving the scenario vs. normal conventional takeoff.

There is more involved in flight than just the engine pushing against the air.

In the time we have been discussing this issue I feel there may be a complex problem or difference that may involve something complex called Computational Fluid Dynamics.

Just you saying the relationship of the plane to the outside air in the scenario and a conventional runway takeoff is the exact same.... doesn't make it so.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:29 PM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by MattyX:
[b]Madman, he answered your question. He said the plane would roll and take off with a little extra wheelspin.
The question wasn't answered.

It takes a little time to come up to take off speed.

If he or anyone is acting as the outside observer, I want to know what is seem from start to finish from the perspective of the outside observer. Namely...

-- Does the plane appear stationary from the perspective of the outside observer until takeoff

-- If so.. let's discuss the relationship of the plane in the scenario and the surrounding atmosphere (fluid air) vs. the relation to the surrounding atmosphere for the same plane in a normal conventional takeoff.[/b]
I have already replied to this twice.

The takeoff appears, to a bystander, completely normal but with some xtra wheelspin due to the conveyor belt.

YES! The plane still moves with respect to the air and with respect to the earth's surface.

And yes! The equation for dynamic friction still is:

F(f) = -uN

u = dynamic coefficient of friction

N = weight of plane

Notice groundspeed isn't a parameter; it's irrevelant if there's a little extra groundspeed (conveyor belt).

This has been proven many times over in this thread. A few posts ago I even quoted a Physics professor on this exact question. What is it you don't believe?

Please tell us where Isaac Newton (and common sense) failed us! [Too much XOC]

Lizz:

34 pages? I think a new name is in order. Are we over 500 posts yet? eek
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:44 PM

Quote:
Originally posted by JeffW:

The takeoff appears, to a bystander, completely normal but with some xtra wheelspin due to the conveyor belt.
Quote:
YES! The plane still moves with respect to the air and with respect to the earth's surface.
If you are saying that to an outside observer looking upon the conveyor belt scenario that it would appear like a normal takeoff from start to finish relative from their viewpoint ... then there is a big problem with your perception of this entire discussion.

Your perception of it doesn't seem to be including the fact that the conveyor and the plane's speed have been matched exactly.

Once the conveyor and the plane's speed has been matched, the outside observer will see the plane as standing still whether it is or not.

Do you understand that fact?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:51 PM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by JeffW:

[b]The takeoff appears, to a bystander, completely normal but with some xtra wheelspin due to the conveyor belt.
Quote:
YES! The plane still moves with respect to the air and with respect to the earth's surface.
If you are saying that to an outside observer looking upon the conveyor belt scenario that it would appear like a normal takeoff from start to finish relative from their viewpoint ... then there is a big problem with your perception of this entire discussion.

Your perception of it doesn't seem to be including the fact that the conveyor and the plane's speed have been matched exactly.

Once the conveyor and the plane's speed has been matched, the outside observer will see the plane as standing still whether it is or not.

Do you understand that fact?[/b]
Not true. I answered this on like page 4 or somethin'.

Searchin.....

OK, top of page 7:

Quote:
Originally posted by JeffW:
Wrong.

Hypothetical scenario:

t = 0 :

Plane 0 mph
Conveyor 0 mph
Wheels 0 mph

t = 15 :

Plane 60 mph
Conveyor 60 mph
Wheels spin @ 120 mph

t = 55:

Plane 160 mph
Conveyor 160 mph
Wheels spin @ 320 mph

Plane takes off!!
You are confusing the motion of the belt with force. It exerts virtually no force on the plane due to the wheels, which spin freely.

EDIT:

Please take a really close look at wheelspeed before you reply...
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 05:58 PM

Quote:
Originally posted by JeffW:

You are confusing the motion of the belt with force. It exerts virtually no force on the plane due to the wheels, which spin freely.
It is you my friend who is confused.

Stop bringing the wheels and all the other peripheral garbage back into the discussion. You are confusing yourself.

If you are running on a treadmill with the treadmill's speed and your running pace matched exactly, your relative position to the earth will not change.

It is no different for the plane. Once you get over that fact, we can move on. Where's your "open mind"?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 06:02 PM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by JeffW:

[b]You are confusing the motion of the belt with force. It exerts virtually no force on the plane due to the wheels, which spin freely.
....If you are running on a treadmill with the treadmill's speed and your running pace matched exactly, your relative position to the earth will not change.

It is no different for the plane. Once you get over that fact, we can move on. Where's your "open mind"?[/b]
Roller skate on your treadmill, you won't go anywhere.

Strap a jet engine to your a$$ and turn it on. We'll see how long you stay put.

50 tons of thrust will EASILY overcome the friction of your lil roller skates, with or without a treadmill!! [Finger]
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 06:03 PM

They have none.

I like cornflakes.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 06:12 PM

Quote:
Originally posted by JeffW:

Roller skate on your treadmill, you won't go anywhere.

Strap a jet engine to your a$$ and turn it on. We'll see how long you stay put.

50 tons of thrust will EASILY overcome the friction of your lil roller skates, with or without a treadmill!! [Finger]
That is exactly what I was stating earlier. You have no desire to discuss the scenario. Not in a reasonable manner.

You are projecting your own arrogance into the debate.

If I strapped a jet engine to myself and was on a conveyor that matched my speed as in the original scenario, an outside observer would view my position as stationary.

The original scenario obviously means nothing anymore in your contributions to the discussion.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 06:38 PM

NYMadman-

Please explain how a backwards-moving treadmill or conveyor belt that contacts the WHEELS of an airplane can negate the thrust of engines pushing against air that is not backwards-moving. Remember: the wheels aren't GLUED to the treadmill, they're just rolling along its surface.
Posted by: MBFlyerfan

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 06:40 PM

I am now starting to believe that madman is correct. The treadmill speed will consistantly increase to match the opposing velocity, so therefore you will stay in one place. The jets are basically working to keep you from flying off in the opposite direction.

Stand on a treadmill in a pair of roller blades. If you aint holding on, you fly off the back. Strapping jets to your back will counter that momentum, but if you are on some super sonic treadmill that can continually exert the opposing force to the jets, you will never reach forward motion, you will contantly be stationary.

It would be the same with the plane. You would never get airflow over the wings. BECAUSE THE TREADMILL WILL CONTINUALLY SPIN FASTER. (since that is the whole premise of the question.)

If the treadmill reached a maximum velocity that does not match the output of the jets then perhaps enough forward motion would be reached to provide enough airflow for lift.

But since hypothetically the treadmill will always match the output of the engines, it will reamin stationary.

Look at it this way. If you shut down the engines, you would fbe thrown through the wall behind you wheels or not.

Thats how I see it.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 06:47 PM

MBFlyerfan-

You, my friend, are also mistaken about thrust.

Think about how ground-based vehicles move. They basically force the ground beneath them to move backwards, relative to the vehicle. How do they do this? By applying power to the wheels in contact with the ground.

If there's a really strong headwind, can the vehicle still move forward? The answer, of course, is yes, until the drag on the vehicle is so great that the engine can no longer move the vehicle forward. Unfortunately, on ground-based vehicles, the forces of both friction (traction) and drag affect forward motion.

In an airplane, drag is the only thing that can prevent forward motion. (When an airplane is in the air, it's not touching the ground. The plane doesn't care what the ground is doing, it only cares about the air it's traveling through is doing.)
Posted by: MBFlyerfan

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 06:53 PM

I see what you are saying. If the plane is exerting no thrust, in the scenario, the treadmill is also still.

I can see why this was such a connundrum. Even a few guys on that link someone posted disputed the conclusion.

Would it get to a point where the wheels cant spin any faster due to friction? Yet the treadmill would continue to increase speed to infiniti. That is where my brain starts to twist up. And if the wheels couldnt turn fast enough eventually it would counter the thrust of the engines through friction alone?

Im just asking questions, no need to get insulting.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 06:56 PM

no way in hell the plane will take off. and just like forrest gump, "that's all i have to say about that."
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:11 PM

Quote:
Originally posted by XPLORx4:
NYMadman-

Please explain how a backwards-moving treadmill or conveyor belt that contacts the WHEELS of an airplane can negate the thrust of engines pushing against air that is not backwards-moving. Remember: the wheels aren't GLUED to the treadmill, they're just rolling along its surface.
Why don't you please explain to me why you are even bothering bringing the wheels into this discussion.

The wheels ARE NOT part of the discussion. If the wheels were intended to be part of the discussion the original scenario would have stipulated something about the wheels. It would have done that because in the real world the wheels will blow or some other thing would happen due to the increased rotation.

The hypothetical scenario said the conveyor belt matches the plane's speed.

The discussion is supposed to be about the parameters laid out in the hypothetical scenario. Not about wheels, bearings or anything else along those lines. The plane could be held up on the shoulders of a bunch of illegal immigrants running for the border on the conveyor belt for all we care regarding the scenario parameters. It's an irrelevant aspect of the scenario.

People are bringing things into the debate that really shouldn't be part of the discussion.

...PLANE--CONVEYOR BELT MATCHING SPEED OF PLANE--AERODYNAMICS....

That is all that should be discussed according to the original scenario. It is not asking for any more.

Are we in agreement on that fact?
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:13 PM

Quote:
Originally posted by socalpunx:
If air speed over the wings is required for flight then why have F1 and Indy cars been airborne
F1 and Indy cars have wings.

HOWEVER. As the case with Johnny Rutherford a number of years ago flipping his car after it took off - the bottom of an Indy car is completely flat. It already had forward momentum. The car was NOT at a right angle - it was at an acute angle to the ground. The car's bottom pushed against the wind - the opposite force of the air pushed the car UP and over.

Quote:
and why is a primary concern for land speed attempts maintaining enough downforce at speed to prevent the vehicle from achieving flight.
Look at the shape of it. The air is forced into a smaller area underneath. It will force the car up.

If that car was on a conveyor belt, and that conveyor belt didn't move ANY air underneath - it would not lift.
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:14 PM

Quote:
Originally posted by MBFlyerfan:
I see what you are saying. If the plane is exerting no thrust, in the scenario, the treadmill is also still.

I can see why this was such a connundrum. Even a few guys on that link someone posted disputed the conclusion.

Would it get to a point where the wheels cant spin any faster due to friction? Yet the treadmill would continue to increase speed to infiniti. That is where my brain starts to twist up. And if the wheels couldnt turn fast enough eventually it would counter the thrust of the engines through friction alone?

Im just asking questions, no need to get insulting.
This has been my point all along. I have no doubt in my mind if the speed of the conveyor was limited the plane would take off. However, in this scenario the conveyor is not. What it does not state is if the planes engines (thrust) is limited i.e. maximum throttle. If they are not either then I say the plane would blow up or the wheels would fly off.

The best one yet was turn the engines off as the wheels are flying along and they engines were at max thrust. Eventually the plane will move backwards. So there is some friction there. If the conveyor can continually meet that it will never gain enough speed to take off. Some yes but in my mind not enough.

What is really funny is the ones who think it will fly are the only ones so far who have said we are closed minded and resorted to name calling. Not all of them but some.

For those fuck off.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:28 PM

Quote:
Originally posted by XPLORx4:

The plane doesn't care what the ground is doing, it only cares about the air it's traveling through is doing.)
And I have said it NUMEROUS times, that is what the primary discussion should be about.

Think about it for a second...

The only difference between what we have to work with in the scenario and a normal conventional takeoff is the effects of the fluid air and the differences or similarities between the scenario and a normal conventional runway takeoff.

People are not staying within the paramenters of the scenario.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:41 PM

Hmm...the fact that MadMan thinks the wheels are unimportant explains why he doesn't understand that they are the single MOST important point...

MadMan thinks (As do many others...not just him...) that somehow that the tires rotating is because of the belt.

He even thinks that a person next to the belt would see it spinning, but see the plane standing still.

What he DOESN'T see is WHY WE KEEP BRINGING UP THE FREEKIN WHEELS.

laugh

Its GOT to be the speed thing...its the ONLY way for this many people to look at this, and come to this many conceptions of it.

We have a physic professer giving a perfectly reasonable exaplaination that makes perfect sense...and, we STILL have people (Who just did not understand the physics...) arguing that the plane can't take off.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:50 PM

The "parameters of the scenario" are that the plane is on a conveyor belt, and that the belt matches the plane's speed.

We have a logical point, that as the belt MATCHES the plane's speed, the plane has to MOVE for the belt to move.

__________________________________________________

The Plane CANNOT MOVE BY TURNING ITS TIRES.

__________________________________________________

IE: A PLANE, in the context of this "can it take off" scenario...CAN NOT MOVE BY ROTATING ITS TIRES.

THE PLANE CAN NOT TURN ITS TIRES....the tires can ONLY turn, IF the plane rolls forward....by engine thrust PUSHING IT...and the tires JUST ROLL, PASSIVELY.

____________

Its a conyeyor belt...it does not change fluid dynamics, physics, wind speed, air density, or any of the odd suggestions that it might.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:52 PM

So -

CF's are in essence, saying that the belt never moves...as, of course, the plane can not move.

_____________

They say this indirectly, because the belt only moves if the plane does...and there is no way for the plane to make its tires turn w/o moving.

________________________
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:54 PM

The CF'r say: (Indirectly)

There are NO forces that are making the tires spin faster...or at all...so the plane sits there on a still conveyor belt.

Agreed?
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:57 PM

No I don't think it sits still. I just think there will not be enough speed gained before running out of runway or the tires blow up.

I think it will move.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:59 PM

I put a toy car (no motor, like a Hot Wheel...) on the floor.

If the car moves, I will move the floor at the EXACT SAME SPEED AS THE CAR.

Will I EVER need to move the floor?

laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 07:59 PM

Ya know, it has just occurred to me that this thread has been a huge boost to the post count of a select few XOC members laugh
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:02 PM

Quote:
Originally posted by TJ:

Hmm...the fact that MadMan thinks the wheels are unimportant explains why he doesn't understand that they are the single MOST important point...

MadMan thinks (As do many others...not just him...) that somehow that the tires rotating is because of the belt.

He even thinks that a person next to the belt would see it spinning, but see the plane standing still.
I don't know who is worse, you or Jeff.

You don't bother to read what is written, and when you seemingly claim to read what is written your comprehension is the same as the groundspeed in the scenario, which is zero.

The wheels ARE NOT the single most important point. When are you going to face that fact? They are completely irrelevant to the discussion.

Since the hypothetical scenario tells us that the conveyor matches the plane's speed ... that is all we need to know. The hypothethical doesn't give a damn how the plane got it's speed or how it is maintaining it's speed. All the hypothetical gives a damn about is that the conveyor matches the speed of the plane. Nothing else is important at this point.

In a nutshell... all we care about is aerodynamic principles. We are concerned with the relative velocity of the plane in the scenario vs. the relative velocity of the same plane in a conventional runway takeoff.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:06 PM

As explained in the physics professor's explaination, and a few others...

The tires needing to rotate faster is not a problem as far as take off goes...

Planes LAND at much higher loads, and the tires are designed to take quite a lot of extra load, in case of blowout of other tires, etc.

So - IF the plane CAN move...it is travelleing DOWN the CONVEYOR BELT>>>as to turn a tire, the tire HAS TO ROLL OVER THE BELT, AND because the belt matches the speed of the PLANE, but

THE TIRES ARE TRAVERSING THE SURFACE OF THE BELT AT TWICE THE SPEED OF THE BELT.

THAT means that the plane is moving at normal take off speed, and travelling down the belt.

Period.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:07 PM

Fine - just answer this:

Will the belt EVER turn?
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:27 PM

Quote:
Originally posted by TJ:

So - IF the plane CAN move...it is travelleing DOWN the CONVEYOR BELT
The plane IS NOT traveling down the conveyor belt.

The conveyor belt has matched the speed of the plane. Once this occurs.. the plane is moving ON the conveyor belt. It is not traveling anywhere. Not in relation to the ground.

You are not comprehending the basic statement from the scenario regarding the conveyor matching the plane's speed. Whatever speed the plane happens to decide to operate.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:34 PM

OMFG!

Who cares about the bloody belt???

Chrike!!!

Refute the equations, if you can.

Otherwise you should endeavor to learn why the correct answer is correct.

Being indignant and obstinate will never make the incorrect answer correct.

One assumption I forgot to mention:

the airplane is capable of flying (with airspeed).

........

Quote:
Originally posted by TJ:
Fine - just answer this:

Will the belt EVER turn?
Not unless the plane is MOVING (airspeed?)!!
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 08:38 PM

Quote:
Originally posted by JeffW:
OMFG!

Who cares about the bloody belt???

Chrike!!!

Refute the equations, if you can.

Otherwise you should endeavor to learn why the correct answer is correct.

Being indignant and obstinate will never make the incorrect answer correct.

One assumption I forgot to mention:

the airplane is capable of flying (with airspeed).

........

Quote:
Originally posted by TJ:
[b]Fine - just answer this:

Will the belt EVER turn?
Not unless the plane is MOVING (airspeed?)!![/b]
You are the biggest prick I know
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 09:01 PM

Relavent information:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?

Let's agree on what assumptions are sensible then. All of the assumptions below apply to virtually all aircraft.

Plane is powered by engines that push air (props or jets)
Plane's speed is measured by a windspeed meter as well as GPS
Plane's wheels spin freely
Wheel friction is negligible when compared to thrust
Newtonian physics apply



Coefficient of dynamic friction:

Force of friction:

F(f) = -uN

(negative because it opposes motion)

u = coefficient of static friction

N = weight of plane

Notice velocity is not included!

That means that the velocity of the conveyor belt is irrelevant for all practical purposes.

F(t) is force of thrust

a = (F(t)+F(f))/m

You won't find a scenario where |F(f)| is greater than |F(t)|. Therefore, in ALL cases the plane moves with respect to the atmosphere, thus achieving lift.

Possible scenario:

t = 0 :

Plane 0 mph
Conveyor 0 mph
Wheels 0 mph

t = 15 :

Plane 60 mph
Conveyor 60 mph
Wheels spin @ 120 mph

t = 55:

Plane 160 mph
Conveyor 160 mph
Wheels spin @ 320 mph

....

The plane takes off.

Either learn why it is correct or refute it....

..scientifically.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 09:02 PM

Quote:
Originally posted by JeffW:

Otherwise you should endeavor to learn why the correct answer is correct.
Whatever you say Jeff.

Just because you say the answer is correct it must be correct. [Freak]

Regardless of the fact that you have added absolutely nothing other than your claim that you are correct.

I'll try to keep that in mind.

Quote:
Being indignant and obstinate will never make the incorrect answer correct.
Considering we do not know the correct answer, who is being indignant and obstinate.

Quote:
One assumption I forgot to mention:

the airplane is capable of flying (with airspeed).
No shit.

That is once it has first obtained lift. There has been no evidence provided so far to support the assumption that this aircraft in the scenario will obtain the proper lift to achieve takeoff.

I'm still not committed to either argument. I just see flaws and lack of anything concrete here to support the claim that this aircraft will takeoff. That includes your posts.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 09:08 PM

Quote:
Originally posted by JeffW:

Therefore, in ALL cases the plane moves with respect to the atmosphere, thus achieving lift.
You and others keep repeating the same exact FLAW.

The plane DOES NOT move in relation to either the atmosphere or the ground. It's engines are ONLY pushing air behind it.

You can't seem to get your arms around that fact. (You can stop posting Branden's drawing. How man times is that now?)
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 09:45 PM

Quote:
Originally posted by Alpine Spirit:
I can see where it would take off and I can see where it would not there is just not enough information to say yes or no.

Simply because there were no limits put on the treadmill? And are the wheels totally magically not creating drag? And do the engines have enough power to overcome the weight of the plane dragging on the treadmill?

Hell if there were no limits put on the friction of the wheels on the ground and engines had insane power then yes I believe it could take off.

But this is a fictional situatoin so who is to say there are limits.

[Too much XOC] [Wave]
[drink]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:32 PM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by JeffW:

[b]Therefore, in ALL cases the plane moves with respect to the atmosphere, thus achieving lift.
You and others keep repeating the same exact FLAW.

The plane DOES NOT move in relation to either the atmosphere or the ground. It's engines are ONLY pushing air behind it.

You can't seem to get your arms around that fact. (You can stop posting Branden's drawing. How man times is that now?)[/b]
Holy shit. I'm gone most of the day and you CF'rs still can't grasp that the aircraft is not stationary and that the belt can't make it stationary.

You, Madman, are making an assumption when you state that the plane will not be travelling through the air. The conveyor is said to match the plane's speed, not keep the plane stationary. A plane's speed is measured either through the air or over the ground, not over the surface directly beneath it (if the last were the case, then an aircraft's groundspeed would change when it flew over running water or ocean currents).

Let's try it the other way. The aircraft is already airborne and on approach to the conveyor/runway for a touch-and-go. The runway is spinning at exactly the same speed in the opposite direction, just like when it took off. laugh Now, when the aircraft touches down (no brakes, remember, doing a touch-and-go) will it immediatly come to a complete stop and be unable to take off again (do the "go" part)?
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:39 PM

a) I can't belive how I'm getting my ass whipped over on Full Tilt Poker right now.

b) I can't believe this fucking argument is still going on.

Damn.
Posted by: MidnightX

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 10:47 PM

Quote:
Originally posted by GrayHam:
a) I can't belive how I'm getting my ass whipped over on Full Tilt Poker right now.

b) I can't believe this fucking argument is still going on.

Damn.
a) Get a life.

b) Me either, man. Me either...
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:07 PM

Quote:
Originally posted by NY Madman:
The wheels ARE NOT the single most important point. When are you going to face that fact? They are completely irrelevant to the discussion.
Do you really mean to say that the wheels are irrelevant? Because if that's true, then the next logical conclusion you should come to is that anything touching the wheels (such as the CONVEYOR BELT) is also irrelevant.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:11 PM

Quote:
Originally posted by MattyX:

You, Madman, are making an assumption when you state that the plane will not be travelling through the air. The conveyor is said to match the plane's speed, not keep the plane stationary.
I'm not making any assumptions. You are failing to grasp the concept.

Let's go by your assumption for a minute. How far is this plane traveling through the air? Are you talking distance? Please tell me what distance and at what rate the plane is moving through the atmosphere? (We will assume for the question posed to you that the atmosphere is mostly static with no wind conditions).

If you are so sure of yourself, tell me the rate at which the air is flowing over the fuselage and wings if your plane is traveling through the atmosphere?

Also, the conveyor is not keeping the plane stationary. Once it's speed is matched with the plane, the plane is virtually stationary in relation to the surrounding atmosphere, the ground, and to an outside observer. It is not stationary on the conveyor.

Why is that such a difficult concept for you?

The concept of the plane's status in relation to the atmosphere and ground comes into play in aerodynamic principles.

I'll attempt to show that in my next post.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:15 PM

Quote:
Originally posted by XPLORx4:

Do you really mean to say that the wheels are irrelevant?
As far as the aerodynamic forces involved with the plane in this scenario, yes, they are.

People are making calcualtions based on wheel rotation and such and that is flawed.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:20 PM

I have to rest up for New Years... so I will leave you with some things to ponder.

These are some facts regarding the plane in this scenario.

-- The plane becomes a static object in relation to the atmosphere once it's speed is matched with the conveyor.

-- The atmosphere, or air, is the fluid required for aerodynamics in this case which is airplane flight.

-- Since the plane became a static object in relation to the atmosphere, there is either none or little air flowing toward and over the wings and fuselage. This basically brings the difference in velocity between the solid object(plane) and the fluid(air) to almost ZERO.

-- The plane has ZERO groundspeed once it's speed has been matched by the conveyor.




As you can see above - NO FLUID, NO LIFT.

...Lift is a mechanical force. It is generated by the interaction and contact of a solid body with a fluid (liquid or gas)...

Since the plane in our scenario matched it's speed with the conveyor, some of the forces required for lift either no longer exist, or have been significantly reduced and/or compromised.

Since the plane is not speeding down an actual runway and pushing itself forward at a rapid rate of speed ...we have lost these forces and they can no longer be used to factor in lift for the aircraft in our scenario.

We have also lost DRAG, or at least a sizeable and signficant portion. We have lost enough to the point that we now basically only have two other forces involved, WEIGHT and THRUST.

Now would be a good time to explore Relative Velocity.



As you can see, we will also have a problem with our airplane's Relative Velocity.

...A fixed object in a static fluid does not generate aerodynamic forces. Hot air balloons "lift" because of buoyancy forces and some aircraft like the Harrier use thrust to "lift" the vehicle, but these are not examples of aerodynamic lift. To generate lift, an object must move through the air, or air must move past the object...

We know that there is little or no air moving past the body and wings of our aircraft in the scenario. We know that a key factor in generating lift is calculationg the Relative Velocity.

Let's take a closer look....



Is it looking good for our plane in the scenario?

Here are some examples...





As we already know, our hypothetical scenario is about as far from a wind tunnel type situation as you can get without being parked in a hangar.

Some things to consider once everyone comes to the realization that once the plane and the conveyor match speeds, our plane is virtually stationary in relation to the atmosphere.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 30/12/06 11:27 PM

Post whatever you like about the forces on an aero-plane, though I noticed that nowhere on your post did you illustrate any negative force on aircraft wheels or wheels being able to overcome a certain amount of friction.

Madman, answer my question now-
The aircraft is already airborne and on approach to the conveyor/runway for a touch-and-go. The runway is spinning at exactly the same speed in the opposite direction, just like when it took off. laugh Now, when the aircraft touches down (no brakes, remember, doing a touch-and-go) will it immediatly come to a complete stop and be unable to take off again (do the "go" part)?
Posted by: Claus

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 12:42 AM

Shut the fuck up Donniem you are out of your element,,,,
Posted by: Xterrian

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 02:40 AM

I really can't believe this argument is still going on. I went shooting with some friends, went to the casino and won $400 playing black jack and celebrated my wife's birthday since this was at 18 pages.

I worked on aircraft for 1 1/2 years and can tell you with absolute certainty that the plane in this scenario would develop forward movement in relation to the air even if the conveyor belt moved at an infinite speed. The drag caused by the wheels could never overcome the forward thrust of the engines if they were capable of turning. The only way to keep the plane from taking off would be to attach it to something static or the conveyor belt itself if the wheels are not locked. Oddly enough, a car would stay in one spot in this same scenario, but then the car doesn't have an external motive force like a prop. You must think of it in these terms, the plane doesn't pull itself along the runway, it pulls itself through the air, and it just appears to move along the runway. If the plane wouldn't move then a lot of bush pilots would have a hell of a hard time taking off upstream off of rivers, but they usually do it that way unless there is a severe tailwind.(Easier to steer with the rudders on the floats upstream.)

Now if the bush pilot throttles back so that the reistance to the floats was the same as the forward thrust of the engine they would stand still in relation to the river, but even if the river(conveyor belt)were moving at an infinite speed it couldn't cause enough resistance to stop the plane from moving forward once the floats were on plane.

Madman's argument would be valid if the plane never moved in relation to the air around it, but the plane would move in relation to the air no matter how fast the conveyor belt runs. The wheels would just spin up to match the conveyor belt speed until the plane left the ground while moving forward in relation to the air around it.

If you still think the plane won't take off, PM me and I'll give you my phone number and we can discuss it. Please don't post any more arguments against it here. I think you're smarter than this one thread is making you look. Rinky can post anything he wants, I don't agree with anything he ever posts anyway. wink
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 02:55 AM

The wheels spin as a result of friction with the ground and are independent of the thrust being provided by the engines. A conveyor can't stop the forward motion of the plane.

The hypothetical is flawed. The conveyor can't stop a planes forward motion. Speeding it up only slows it down by the amount of friction that is being created between the wheels, bearings and ground.

The only way it works would be to in some way increase friction to counter thrust. Only then would forward motion be stopped.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 03:11 AM

The key is forward motion, which has everything to do with the tires because that's how the airplane - REGARDLESS OF HOW PROPELLED - moves across the ground.

Let go of how the tires are being propelled (moved forward) and think of it this way: a tire rolling over a fixed surface results in forward motion. A non-VTOL (Vertical Take-Off/Landing) fixed-wing aircraft MUST have forward motion to achieve flight from a standing start.

On a runway, imagine the plane is sitting at point A on a straight line, with points B through Z representing the takeoff roll, Z being rotation (when the nose is lifted for takeoff).

Power is applied and that power - engine thrust - is converted into forward motion that takes the plane through points B to Z because again, a tire on the ground, regardless of HOW it is moved forward, covers a given distance for each revolution (i.e. forward motion). So if NYMadman's observer was standing alongside point A, the plane would leave him/her behind as it accelerated.

Distance traveled equals 2πR, where R is the wheel's radius. Let's just say the answer to that equation in our scenario is 12 feet. But the treadmill moves 12 feet in the opposite direction. The tires are attached to the plane, we can all agree on that, right? So if:

2πR = 12 feet but treadmill motion = -12 feet then the resulting forward motion is ZERO.

For the plane to move forward, 2πR MUST be greater than the distance the treadmill moves backward, but the scenario says the belt matches the plane's speed, so the result can't be greater than zero.

On a runway of course, there's no counter-motion backwards so 2πR is always greater than zero, resulting in forward motion.

In the scenario presented, points B through Z are on the treadmill, so as engine thrust is applied, it is NOT converted into forward motion because the treadmill accelerates as the thrust does. Points A-Z simply pass under the plane, and it remains relatively stationary beside the observer, NOT leaving him/her behind.

No relative wind (airflow over the wings), no lift, no takeoff.

For the "what if it was on perfect ice" argument, that doesn't fly (ha!) because even though the tires might not rotate, there is still forward motion when thrust is applied because the tires' purpose (reducing friction to allow relatively easy forward motion) has been eliminated by the ice's absence of friction. The plane would still cover points A to Z on the takeoff roll.

BTW, asked my wife so as to get an independent opinion, and hers was profound: "Don't know, don't care. You guys need to get a life." Yes, dear. laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 03:40 AM

The thrust provided by the engines is independent of the wheels. It doesn't even have to be wheels most of you guys are caught up on that. What if the plane was floating on a pocket of air like an airboat. What does thrust care what the ground is doing? The ground/conveyor could be traveling at a 100 MPH and it would not affect the floating plane right? OK so lets start the engines and create some thrust. What happens to the plane then? It moves forward at a gradually increasing speeed, generates lift and takes off.

If you think about it the planet is a big ass conveyor traveling/spinning at thousands of miles per hour. According to you guys we would never be able to take off.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 03:50 AM

Quote:
Originally posted by Timmah:
The thrust provided by the engines is independent of the wheels. It doesn't even have to be wheels most of you guys are caught up on that. What if the plane was floating on a pocket of air like an airboat. What does thrust care what the ground is doing? The ground/conveyor could be traveling at a 100 MPH and it would not affect the floating plane right? OK so lets start the engines and create some thrust. What happens to the plane then? It moves forward at a gradually increasing speeed, generates lift and takes off.

If you think about it the planet is a big ass conveyor traveling/spinning at thousands of miles per hour. According to you guys we would never be able to take off.
I just added something to my post above so you missed it. It DOES matter what the tires do because they're attached to the plane. Here's my addition:

Distance traveled equals 2πR, where R is the wheel's radius. Let's just say the answer to that equation in our scenario is 12 feet. But the treadmill moves 12 feet in the opposite direction. The tires are attached to the plane, we can all agree on that, right? So if:

2πR = 12 feet but treadmill motion = -12 feet then the resulting forward motion is ZERO.

For the plane to move forward, 2πR MUST be greater than the distance the treadmill moves backward, but the scenario says the belt matches the plane's speed, so the result can't be greater than zero.

On a runway of course, there's no counter-motion backwards so 2πR is always greater than zero, resulting in forward motion.

------------------------

And you didn't do what I asked - FORGET the method of propulsion because it DOESN'T MATTER.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 05:18 AM

The tires are just rolling. They are just there. Heck, they don't have to turn at all given enough wind to have the plane take flight. It doesn't matter what they are doing.

Until the friction being created by them rolling overcomes the thrust provided by the jet engines the plane will be able to get enough speed to take off.

You're caught up on the wheels and for some reason you keep thinking they are propelling the plane.

Lets say your on rollerskates standing on a moving sidewalk. For arguements sake lets say your stationary to the rest of us and the walkway is moving underneath you without you having to do anything to brace yourself to stay in place.

I walk up behind you and push you forward. Do you move? Lets say I pass you a tow rope and walk along side the moving walkway and pull you against the traving sidewalk direction. Do you move in the direction I pull or do you stay still?
Would you still move if in my direction if the sidewalk was going 2x faster than I was walking?

Just think of the jet engines as a tow rope.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 05:24 AM

You folks are silly.

The plane will not move (or it will if you add the element of time).

Break it down and simplify it, we just need to know if an object on the treadmill would move forward. If it can, then with wings, it can fly.
Let's remove the wings from the plane and the type of thrust from the plane, hell, do it in a vacuum. Now we have an object on a treadmill, it can be a box with 4 wheels, maybe a Hummer.

Apply a force to that box with 4 wheels, maybe with your hand, or maybe with a jet engine like in the scenario. If the treadmill matches the rotation of the wheels exactly, our object, box with no wings, Hummer, whatever, will remain in the same spot.

By matching the speed of the wheel rotation exactly, you have basically created 100% resistance, just like a wall. Park a plane against a wall, and see how far it gets.

Let's turn off the engine. Now, spin that treadmill up to 150 mph, roughly takeoff speed. The wheels on the plane are turning at 150mph as well. The plane is stationary.

Walk up a down escalator and match it's speed. Imagine that the escalator would speed up if you started running, keeping you in the same spot. Imagine a friend giving you a push from behind, making you run faster, but at the exact moment, the escalator speeds up again. Still can't get upstairs to Starbucks.

The only way it could actually move forward is from latency of the treadmill system adjusting to each increment in rotational speed and falling just a tiny bit behind. That was not part of the equation though.

PS: More pictures of Evangeline Lily please.
Posted by: Southernx7

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 05:27 AM

The Jags still suck, the Jags still suck.....everybody....

Sorry to interupt this debate....but Kansas is going to whip our asses today, you know how I knkow this? It's easy.......The Jags still suck, the Jags still suck...
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 05:57 AM

Quote:
Originally posted by Mobycat:
Quote:
Originally posted by XPLORx4:
[b]
Quote:
Originally posted by Mobycat:
[b]So someone answer this ignored comment:

If the engines are off, and if there was NO friction, and that conveyor belt moved, the plane shouldn't budge - it will just have rolling wheels.
That's a correct statement if you mean there's no friction in the wheel bearings. (You need friction between the tires and conveyor, otherwise the tires wouldn't start rolling).[/b]
Yes, in the wheel bearings.

So, if there is friction, the plane will roll backwards?

Can the plane match the force with its engines?

What if it can't do anything *beyond* matching it?[/b]
Why is it that this scenario seems to be possible UNTIL you get to the last question?

What magic appears to make the plane suddenly overcome the friction? When it can ONLY match it? (Which is what the conveyor belt is doing?)
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 06:35 AM

Quote:
Originally posted by Timmah:
The tires are just rolling. They are just there. Heck, they don't have to turn at all given enough wind to have the plane take flight. It doesn't matter what they are doing.
Yes, I'm afraid it does matter because they're attached to the plane and represent the means by which the plane moves forward, whether it's being towed by a tractor or propelled by its engines.

Quote:
Originally posted by Timmah:
You're caught up on the wheels and for some reason you keep thinking they are propelling the plane.
I spent 20 years in the airline industry and have a very thorough knowledge of aircraft and the theory of flight. I assure you that I DO know that aircraft wheels are not powered, and spin freely except for being slowed by brakes.

Quote:
Originally posted by Timmah:
Lets say your on rollerskates standing on a moving sidewalk. For arguements sake lets say your stationary to the rest of us and the walkway is moving underneath you without you having to do anything to brace yourself to stay in place.

I walk up behind you and push you forward. Do you move? Lets say I pass you a tow rope and walk along side the moving walkway and pull you against the traving sidewalk direction. Do you move in the direction I pull or do you stay still?
I stay still, IF the treadmill matches my speed, which it does in this scenario.

Believe it or not, you're the one who doesn't get it. :rolleyes:
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 07:07 AM

Ok, I screwed up in my last posts with respect to the 3rd party - so ignore those - I ended up confusing myself when people began mention 3rd party observers to the scenario - and made a mistake. If the plane is not moving in relation to the 3rd party observer Like in my aircraft scenario) then the plane does not fly. However my aircraft scenario is flawed because there is nothing to prevent the airplane from moving with respect to the gound. Thus the plane to a 3rd party observer could not appear to stay in one spot.

The assumption that the airplane on a conveyor remains staionary with respect to the ground is wrong.

Think about this - carefully.

The conveyor is set up to match the airplanes speed, so if the airplane is moving at 10 mph, so is the conveyor in the exact opposite direction.

The originally scenario does not say that the planes causes the conveyor to move, but that the conveyor is moved by some other control to match speed of the plane.

So if the plane is off of the conveyor on hard ground moving towards the conveyor at 10mph, then the conveyor is still going to move at 10mph in the opposite direction...

Now replace the Airplane with a car (make it a Front wheel driven car) and with the same setup as above, but this time the car drives onto the conveyor.
Once the front wheels of this car touch the conveyor the car stops it's forward motion with respect to the ground - with the front wheels on the conveyor spinning at 10 mph on the conveyor and the rear wheels (which were only spinning because the front wheels were moving along the ground and the rear wheels have to follow) are on the ground stationary.

Now replace the Airplane with another car (make it a 2wd Xterra) and with the same setup as above, what happens when the Xterra drives onto the conveyor? When the front wheels contact the conveyor they (being free spinng) double their speed as they contiune to move up the conveyor until the rear wheels get onto the conveyor. At that point, all 4 sets of wheels are spinning at 10 mph and the Xterra stays in one spot with respect to the ground.

Now, an Airplane has front wheels and rear wheels, so what happens when the airplane moves onto the conveyor?
Does the plane stop it's forward motion when the front wheels touch the conveyor belt? No, the front wheels, which are free spinning, begin to move at 2x the belts speed and the plane continues to move with respect to the ground...
Does the plane stop when all of the wheel are on the conveyor? No, all of the wheels are free spinning so all of the wheels double their speed, the plane continues to move with respect to the ground.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 08:21 AM

Wow. Up to 37 pages, and there's still a handful of morons that think the wheels on an airplane control the airplane's motion...

Guys, it's pretty simple. The original statement says the belt goes the same speed as the plane, but in an opposite direction.

If the plane has no forward motion (speed), then the belt does not move.

If the plane goes forward at 10 mph, then the belt goes in reverse at 10 mph.

If the plane goes forward at 150 mph, then the belt goes in reverse at 150 mph.

But what does that mean to an outside observer, for Madman's benefit? It means that the person, standing still, sees a plane moving forward at 10mph, then accelerating up to 150 mph, and then taking off.

Nowhere in the original problem statement does it say the belt matches the speed of the tires. The belt matches the speed of the AIRPLANE. The speed of the tires are relative to the forward motion of the plane, and the reverse motion of the belt.

In this scenario, the plane's movement forward makes the tires rotate forward. The conveyor belt moving backwards makes the tires rotate forward as well (think of it like two gears in contact with each other; turn one, and the other moves in the opposite direction). The actual rotational speed of the tires is the sum of both inputs, airplane speed plus conveyor speed. So if the plane is moving at 10 mph, and the conveyor belt is moving at 10mph the opposite direction, the tires are rotating at 20 mph.

The thing is, there are two completely independent forces acting on the tires. There is the force from the engines of the plane, pushing air and not directly in contact w/ the tires. Then there's the force of the conveyor belt acting directly on the tires. The tires move based on the two inputs.

The problem that everyone that thinks the plane won't take off is the external power source of the engines. The force of the engines acts on the body of the plane. The tires only spin by the plane if the plane is moving forward and the tires are in contact with the ground. The force of the belt acts directly on the tires, causing them to do nothing more than spin in the forward direction. But again, the tires spinning in the forward direction do not cause the body of the aircraft to move, as they are only free spinning along the axle shaft, with no mechanical linkage to force the aircraft forward.

Guys, the plane has not only taken off on the original page, but it already landed at it's destination, and all the passengers have been sitting at home reading this thread, knowing PERSONALLY that the "won't take off" group are out of their minds...
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 08:31 AM

I disagree, but respectfully. I know the wheels don't control the plane's motion, but I also know they are the means by which engine power is converted to forward motion over the ground when the aircraft isn't flying.

Calling people morons because they don't share your point of view - which very well may be wrong, Einstein - makes you a gold-plated asshat. IMHO of course. [Finger]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 08:41 AM

Quote:
Originally posted by BlueSky:
I disagree, but respectfully. I know the wheels don't control the plane's motion, but I also know they are the means by which engine power is converted to forward motion over the ground when the aircraft isn't flying.

Calling people morons because they don't share your point of view - which very well may be wrong, Einstein - makes you a gold-plated asshat. IMHO of course. [Finger]
Yes, I am an asshat. I have no problems admitting that.

But if you think the force of motion of an airplane is magically created by the tires when a plane is on the ground, but created by the engines when it's in the air, then frankly, yes, you are a moron.

Forward motion of the plane is caused by the engines pushing the plane forward, whether it's in the air, on the ground, on the water, or wherever. Never, ever, is forward motion either caused or restricted by the tires on the ground.

I'm no einstein, but I'm evidently smart enough to know where the force for the motion comes from for a plane, and that it doesn't magically shift from one thing to another based on the plane's position... [Finger]

Blue, the tires DIRECT the motion of the plane on the ground; the same as the ailerons and rudder DIRECT the motion of the plane in the air. NONE of those things either cause or prevent motion that is originated by the force applied by the ENGINES.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 09:08 AM

Quote:
Originally posted by BlueSky:
I disagree, but respectfully. I know the wheels don't control the plane's motion, but I also know they are the means by which engine power is converted to forward motion over the ground when the aircraft isn't flying.
And the wheels don't care if the ground is moving under the plane, if the plane is moving over the ground, or both at the same time...

The wheel rotational speed does not have to equal the plane speed.
Quote:
Calling people morons because they don't share your point of view - which very well may be wrong
See my last post -cars/plane moving onto the moving conveyor- to understand why the plane moves and thus takes off...
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 09:18 AM

Quote:
Originally posted by porsche996:
Quote:
Originally posted by BlueSky:
[b]I disagree, but respectfully. I know the wheels don't control the plane's motion, but I also know they are the means by which engine power is converted to forward motion over the ground when the aircraft isn't flying.

Calling people morons because they don't share your point of view - which very well may be wrong, Einstein - makes you a gold-plated asshat. IMHO of course. [Finger]
Yes, I am an asshat. I have no problems admitting that.

But if you think the force of motion of an airplane is magically created by the tires when a plane is on the ground, but created by the engines when it's in the air, then frankly, yes, you are a moron.

Forward motion of the plane is caused by the engines pushing the plane forward, whether it's in the air, on the ground, on the water, or wherever. Never, ever, is forward motion either caused or restricted by the tires on the ground.

I'm no einstein, but I'm evidently smart enough to know where the force for the motion comes from for a plane, and that it doesn't magically shift from one thing to another based on the plane's position... [Finger]

Blue, the tires DIRECT the motion of the plane on the ground; the same as the ailerons and rudder DIRECT the motion of the plane in the air. NONE of those things either cause or prevent motion that is originated by the force applied by the ENGINES.[/b]
I didn't say the tires CREATED the plane's motion, I said they are the instrument through which forward motion occurs. Don't believe that? Retract the gear and see how far you go.

Apply thrust, what happens? The tires roll and the plane moves over the ground. The thrust provides the power but the tires rolling results in the plane moving.

Now apply the brakes. The tires stop and so does the plane (assuming there's not enough thrust to overcome the braking action). The tires didn't stop the plane, the brakes did, but the tires were the catalyst through which the braking action caused a RESULT - the plane stopping.

We'll apparently agree to disagree. I'm a moron and you're an asshat. Do those cancel each other out? laugh

P.S. Did you read my post 2nd from the top on this page?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 09:25 AM

Rockaholic, I'm glad you got it right. It's easy to get hung up on something, in fact, that's what the question's designed for.

For Bluesky, Madman, Mobycat and any other CF-rs, answer my earlier question please.

The aircraft is already airborne and on approach to the conveyor/runway for a touch-and-go. The runway is spinning at exactly the same speed in the opposite direction, just like when it took off. laugh Now, when the aircraft touches down (no brakes, remember, doing a touch-and-go) will it immediatly come to a complete stop and be unable to take off again (do the "go" part)?
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 09:30 AM

Quote:
Originally posted by MattyX:
Rockaholic, I'm glad you got it right. It's easy to get hung up on something, in fact, that's what the question's designed for.

For Bluesky, Madman, Mobycat and any other CF-rs, answer my earlier question please.

The aircraft is already airborne and on approach to the conveyor/runway for a touch-and-go. The runway is spinning at exactly the same speed in the opposite direction, just like when it took off. laugh Now, when the aircraft touches down (no brakes, remember, doing a touch-and-go) will it immediatly come to a complete stop and be unable to take off again (do the "go" part)?
It *ALREADY HAS* foward momentum in the air.

The conveyor belt scenario - it does not start with forward momentum. It cannot attain it, because the conveyor keeps it from gaining it.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 09:34 AM

Sure, but if what you're saying is correct, once the wheels are on the conveyor (full weight, just like every touch-and-go), the forces applied to the tires should stop the aircraft flat.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 09:36 AM

Quote:
Originally posted by BlueSky:
For the plane to move forward, 2πR MUST be greater than the distance the treadmill moves backward, but the scenario says the belt matches the plane's speed, so the result can't be greater than zero.

On a runway of course, there's no counter-motion backwards so 2πR is always greater than zero, resulting in forward motion.
Now you have a serious problem...See this scenario I posted and you've been ignoring...
Quote:
The conveyor is set up to match the airplanes speed, so if the airplane is moving at 10 mph, so is the conveyor in the exact opposite direction.

The originally scenario does not say that the planes causes the conveyor to move, but that the conveyor is moved by some other control to match speed of the plane.

So if the plane is off of the conveyor on hard ground moving towards the conveyor at 10mph, then the conveyor is still going to move at 10mph in the opposite direction...Now, an Airplane has front wheels and rear wheels, so what happens when the airplane moves onto the conveyor?
Now revisiting what you said - the wheels of the plane on the conveyor have a counter motion from the conveyor, so the result is always zero (no motion) whearea the wheels of the plane on a runway have no counter motion, and thus always have a result of greater than zero (forward motion)

Now the problem is that the length of the plane and the distance bewteen the wheels remains a constant, and based on what you posted: The the front wheels of the plane on the treadmill have a counter motion and so the result can't be greater than zero, so there is no forward motion; yet the rear wheels (on the solid ground) have no counter motion, so those wheels are moving forward...

How can the rear wheels be moving forward if the front wheels are not moving forward when the distance between the wheels remains constant? That is physically impossible!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 10:01 AM

Obviously people who have never taken a physics class find this tuff hard to grasp.

Please prove this answer wrong:
(since you claim it is incorrect)

Quote:
Originally posted by JeffW:
Relavent information:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?

Let's agree on what assumptions are sensible then. All of the assumptions below apply to virtually all aircraft.

Plane is powered by engines that push air (props or jets)
Plane's speed is measured by a windspeed meter as well as GPS
Plane's wheels spin freely
Wheel friction is negligible when compared to thrust
Newtonian physics apply



Coefficient of dynamic friction:

Force of friction:

F(f) = -uN

(negative because it opposes motion)

u = coefficient of static friction

N = weight of plane

Notice velocity is not included!

That means that the velocity of the conveyor belt is irrelevant for all practical purposes.

F(t) is force of thrust

a = (F(t)+F(f))/m

You won't find a scenario where |F(f)| is greater than |F(t)|. Therefore, in ALL cases the plane moves with respect to the atmosphere, thus achieving lift.

Possible scenario:

t = 0 :

Plane 0 mph
Conveyor 0 mph
Wheels 0 mph

t = 15 :

Plane 60 mph
Conveyor 60 mph
Wheels spin @ 120 mph

t = 55:

Plane 160 mph
Conveyor 160 mph
Wheels spin @ 320 mph

....

The plane takes off.

Either learn why it is correct or refute it....

..scientifically.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 10:19 AM

Quote:
Originally posted by Mobycat:
It *ALREADY HAS* foward momentum in the air.

The conveyor belt scenario - it does not start with forward momentum. It cannot attain it, because the conveyor keeps it from gaining it.
You agree then that the plane continues to move over the conveyor belt....
So what you are saying is the conveyor belt stops the object on the belt from gaining momentum, yet it doesn't stop and object in motion before being on the conveyor from losing it's momentum once it is on the conveyor.

So then why doesn't the front wheel drive car pull the rear wheels up onto the conveyor? It also has it's momentum throug the air before getting onto the conveyor belt.
Is it because the front wheels would have to be moving forward when they are experiencing a counter motion, which would have to be impossible in order for the plane to remain in the exact same spot on the conveyor....and then the rear wheel would have to be moving forward without any motion from the ground(because the ground doesn't move and the engine doesn't provide any motion to the free spinng rear wheels) and thus would have to move without a counter motion of the ground...

So how is this conveyor belt magically stopping the cars but not stopping the plane?

You've agreed the pane keeps moving after all, so why not the cars? (Beause their method of forward propulsion is different)

Or how is this plane magically moving it's rear wheels, while not moving it's front wheels, while at the same time the wheels remain a constant distance apart?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 10:56 AM

I think that the "can't fly" folks have this in common: short attention span. If any post is longer than about 5 lines, they stop reading and immediately post their reply to the first 5 lines of the previous post.

All the scenarios countering their arguments are summarily ignored because the CF'ers never read them.

As a result, this thread is never gonna take off.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 10:57 AM

Quote:
Originally posted by XPLORx4:
I think that the "can't fly" folks have this in common: short attention span. If any post is longer than about 5 lines, they stop reading and immediately post their reply to the first 5 lines of the previous post.

All the scenarios countering their arguments are summarily ignored because the CF'ers never read them.

As a result, this thread is never gonna take off.
Nice job editing your post to take out the part indicating that you hadn't read all of my post. You're funny...not to mention full of s***.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 11:02 AM

Quote:
Originally posted by JeffW:
Obviously people who have never taken a physics class find this tuff hard to grasp.

Please prove this answer wrong:
(since you claim it is incorrect)

Quote:
Originally posted by JeffW:
[b]Relavent information:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?

Let's agree on what assumptions are sensible then. All of the assumptions below apply to virtually all aircraft.

Plane is powered by engines that push air (props or jets)
Plane's speed is measured by a windspeed meter as well as GPS
Plane's wheels spin freely
Wheel friction is negligible when compared to thrust
Newtonian physics apply



Coefficient of dynamic friction:

Force of friction:

F(f) = -uN

(negative because it opposes motion)

u = coefficient of static friction

N = weight of plane

Notice velocity is not included!

That means that the velocity of the conveyor belt is irrelevant for all practical purposes.

F(t) is force of thrust

a = (F(t)+F(f))/m

You won't find a scenario where |F(f)| is greater than |F(t)|. Therefore, in ALL cases the plane moves with respect to the atmosphere, thus achieving lift.

Possible scenario:

t = 0 :

Plane 0 mph
Conveyor 0 mph
Wheels 0 mph

t = 15 :

Plane 60 mph
Conveyor 60 mph
Wheels spin @ 120 mph

t = 55:

Plane 160 mph
Conveyor 160 mph
Wheels spin @ 320 mph

....

The plane takes off.

Either learn why it is correct or refute it....

..scientifically.
[/b]
While I work on refuting yours, can you refute my distance traveled equation? Or did you bother to read the post?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 11:02 AM

Blue, I did read all of your post (2nd from the top on p37), and it's flawed.

Without responding to all of your 2piR references, the major flaw is you (and other CF'ers) fail to see that motion through air and motion over ground are two different things. Do you understand that you can have motion over ground without motion through air (i.e. tailwind)? Do you understand that you can have motion through air without motion over ground (headwind)?

Answer those two questions for me.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 11:10 AM

Better yet, read --> this <-- .
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 11:16 AM

Quote:
Originally posted by XPLORx4:
Blue, I did read all of your post (2nd from the top on p37), and it's flawed.

Without responding to all of your 2piR references, the major flaw is you (and other CF'ers) fail to see that motion through air and motion over ground are two different things. Do you understand that you can have motion over ground without motion through air (i.e. tailwind)? Do you understand that you can have motion through air without motion over ground (headwind)?

Answer those two questions for me.
Uh, yeah, I understand those things. Like why it can take 15.5 hours to fly LAX-HKG and only 12 hours to fly the same route back? Winds.

Do YOU understand that those two things are irrelevant if the plane is stationary on the ground and has not achieved flight?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 11:36 AM

Quote:
Originally posted by BlueSky:
Do YOU understand that those two things are irrelevant if the plane is stationary on the ground and has not achieved flight?
No, I do not, because airspeed and groundspeed are relevant at all times. A moving car has both airspeed and groundspeed, do you agree? (If you don't think a car has airspeed, stick your hand out the window. But cars don't care about airspeed, since it's the motion over the ground that we care about). Additionally, a STATIONARY car can have airspeed without groundspeed on a windy day. Again, stick your hand out the window. Feel the air moving past the car? That's airspeed. Notice the ground isn't moving, but the air is!

The same things apply to aircraft, whether in the air or on the ground. Do you agree?
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 11:38 AM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by BlueSky:
[b]Do YOU understand that those two things are irrelevant if the plane is stationary on the ground and has not achieved flight?
No, I do not, because airspeed and groundspeed are relevant at all times. A moving car has both airspeed and groundspeed, do you agree? (If you don't think a car has airspeed, stick your hand out the window). Additionally, a STATIONARY car can have airspeed without groundspeed on a windy day.

The same things apply to aircraft, whether in the air or on the ground.

Do you agree?[/b]
Yes, but I said the aircraft is STATIONARY. Assuming no wind, it has no airspeed.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 11:42 AM

Great. On a windless day, if the engines are off the aircraft has neither airspeed nor groundspeed.

OK, now, let's place a conveyor belt under the aircraft's wheels, and bolt the plane to the ground by its nose, tail,and wingtips. Now, let's fire up the conveyor belt to 30mph.

It's still a windless day.
Answer these questions:
1) What's the aircraft airspeed?
2) What's the aircraft groundspeed?
3) What's the aircraft's wheelspeed on the conveyor?
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 11:53 AM

Quote:
Originally posted by XPLORx4:
Great. On a windless day, if the engines are off the aircraft has neither airspeed nor groundspeed.

OK, now, let's place a conveyor belt under the aircraft's wheels, and bolt the plane to the ground by its nose, tail,and wingtips. Now, let's fire up the conveyor belt to 100mph.

It's still a windless day.
Answer these questions:
1) What's the aircraft airspeed?
2) What's the aircraft groundspeed?
3) What's the aircraft's wheelspeed on the conveyor?
1) Zero
2) Zero
3) I'm not sure what you mean. All over this thread, people have said "the wheels are turning at X MPH." But speed is a measure of movement, and the wheels aren't moving (except for rotation), so it should really be measured in RPM, right? Can you clarify please?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 12:06 PM

Quote:
The key is forward motion, which has everything to do with the tires because that's how the airplane - REGARDLESS OF HOW PROPELLED - moves across the ground.
Yes, the tires reduce the friction between the plane & the ground. But they do NOT propel, aka, cause the airplane's motion. They are only there to reduce friction w/ the ground.

Quote:

Let go of how the tires are being propelled (moved forward) and think of it this way: a tire rolling over a fixed surface results in forward motion. A non-VTOL (Vertical Take-Off/Landing) fixed-wing aircraft MUST have forward motion to achieve flight from a standing start.
You are correct. Except that an airplanes tire will not roll unless there is an outside force exerted, because they are not powered tires.

Quote:
On a runway, imagine the plane is sitting at point A on a straight line, with points B through Z representing the takeoff roll, Z being rotation (when the nose is lifted for takeoff).

Power is applied and that power - engine thrust - is converted into forward motion that takes the plane through points B to Z because again, a tire on the ground, regardless of HOW it is moved forward, covers a given distance for each revolution (i.e. forward motion). So if NYMadman's observer was standing alongside point A, the plane would leave him/her behind as it accelerated.
Yes. But listen carefully. The tires roll because the plane moves. The tires do not cause the movement. The tires could be fixed in place, with absolutely no rotation, and the plane can still move, aka, a float plane or a skid plane. The rolling tires only reduce the normal friction against the ground. They do not cause the plane to move.

Quote:
Distance traveled equals 2πR, where R is the wheel's radius. Let's just say the answer to that equation in our scenario is 12 feet. But the treadmill moves 12 feet in the opposite direction. The tires are attached to the plane, we can all agree on that, right? So if:

2πR = 12 feet but treadmill motion = -12 feet then the resulting forward motion is ZERO.
Wrong. If a treadmill moves 12 feet in REVERSE, the tires that are sitting on top of the treadmill move 12 feet FORWARD. Look at a simple gear setup. Place two gears in contact with each other. Now turn one gear. The other turns in the OPPOSITE direction.

So for your math problem, if the plane moved 12', that caused the wheels to move 12' FORWARD. If the conveyor moved 12' in REVERSE, it moves the wheels 12' FORWARD. The total distance the circumference of the tires have traveled is 24'.

Quote:
For the plane to move forward, 2πR MUST be greater than the distance the treadmill moves backward, but the scenario says the belt matches the plane's speed, so the result can't be greater than zero.

On a runway of course, there's no counter-motion backwards so 2πR is always greater than zero, resulting in forward motion.
Your math is wrong. See previous paragraph.

Quote:
In the scenario presented, points B through Z are on the treadmill, so as engine thrust is applied, it is NOT converted into forward motion because the treadmill accelerates as the thrust does.
No. The scenario states the treadmill accelerates as the PLANE accelerates. It does not say the treadmill matches the thrust. It says the conveyor matches the plane's speed. Thrust is not speed. Thrust is a force. Speed is a distance per unit of time. They are not the same thing. That's in the given initial conditions of the problem statement.

Quote:
Points A-Z simply pass under the plane, and it remains relatively stationary beside the observer, NOT leaving him/her behind.
Your visualiztion of the points means nothing. The plane has to move in order for the conveyor to move. If the plane is moving, then it's moving. There is no stationary plane that's also moving at the same time. There are only 3 dimensions in our physical world; if the plane is moving on a horizontal plane, it's either moving or its not. There is no possible way it can be moving and not moving at the same time...

Quote:
No relative wind (airflow over the wings), no lift, no takeoff.
There is airflow over the wings as the plane moves down the runway...

Quote:
For the "what if it was on perfect ice" argument, that doesn't fly (ha!) because even though the tires might not rotate, there is still forward motion when thrust is applied because the tires' purpose (reducing friction to allow relatively easy forward motion) has been eliminated by the ice's absence of friction. The plane would still cover points A to Z on the takeoff roll.
How can you possibly realize that the tires are only there to reduce friction to allow relatively easy forward motion in one sentence, yet still hold onto your belief that they propel the plane forward??? There are only two lines of thought here:

1) The engines provide horizontal force to propel the plane. The tires are there to reduce friction between the plane and the ground. (plane takes off)

or

2) The engines provide horizontal force to propel the plane through the air. The tires are there to propel the plane on the ground. (plane doesn't take off)

There is no other viewpoint for the solution. And if you believe #2, that the tires propel the plane on the ground, then you don't have a clue how an airplane works.

Remove the wings. Remove everything except the body, the engine attached to the body that provides the horizontal moving force, and the wheels that reduce friction. When that's the case, it doesn't matter what the ground is doing; whether it's moving or not doesn't matter, because the wheels are only reducing the friction between the ground and the main body of the vehicle.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 12:15 PM

Once and for bloody all, I KNOW THAT AIRCRAFT WHEELS ARE NOT POWERED.

You're wrong when you say the belt causes the tires to "move" forward 12 feet. It causes the tires to ROTATE, not MOVE. And that's why the plane DOESN'T MOVE.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 12:19 PM

Bluesky, think about what you just posted.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 12:23 PM

Quote:
Originally posted by BlueSky:
It causes the tires to ROTATE, not MOVE.
EXACTLY!!!!!!!!!

The belt causes the wheels to ROTATE, not MOVE!!! And if it can't CAUSE the wheels to MOVE, then it CAN'T keep the wheels from moving, either!!!

So there is nothing the conveyor can do to prevent the aircraft from MOVING based on the force from the engines.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 12:27 PM

You guys are smoking something. If the wheels don't move, and they're attached to the plane, I have news for you. The plane isn't moving either. As thrust is applied, the wheels will just rotate faster because the belt accelerates to keep up.

At least that's the way it works in my world. If it's different in yours, so be it. cool
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 12:28 PM

lol, 39 pages
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 12:32 PM

Quote:
Originally posted by BlueSky:
You guys are smoking something. If the wheels don't move, and they're attached to the plane, I have news for you. The plane isn't moving either. As thrust is applied, the wheels will just rotate faster because the belt accelerates to keep up.

At least that's the way it works in my world. If it's different in yours, so be it. cool
Hell, man, the original problem statement didn't even say the plane HAS wheels... It could be sitting on skids or floats... So then what happens? The plane still takes off... There's just more friction between the plane & the conveyor belt.
Posted by: slomatt

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 12:35 PM

Quote:
Originally posted by BlueSky:
You guys are smoking something. If the wheels don't move, and they're attached to the plane, I have news for you. The plane isn't moving either. As thrust is applied, the wheels will just rotate faster because the belt accelerates to keep up.

At least that's the way it works in my world. If it's different in yours, so be it. cool
Except that this isn't a difference of opinion, people have posted proof that the plane will take off using valid physics.

Perhaps the only way to prove this to everybody is to call up the Myth Busters? smile

- Matt
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 12:46 PM

Quote:
Originally posted by slomatt:
Quote:
Originally posted by BlueSky:
[b]You guys are smoking something. If the wheels don't move, and they're attached to the plane, I have news for you. The plane isn't moving either. As thrust is applied, the wheels will just rotate faster because the belt accelerates to keep up.

At least that's the way it works in my world. If it's different in yours, so be it. cool
Except that this isn't a difference of opinion, people have posted proof that the plane will take off using valid physics.

Perhaps the only way to prove this to everybody is to call up the Myth Busters? smile

- Matt[/b]
They SAY it's valid physics and post an impressive looking formula. Well, I'll be the first to admit that I personally can't refute it because I don't have the knowledge of physics or mathematics. But that doesn't make it right.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 12:48 PM

Quote:
Originally posted by porsche996:
Quote:
Originally posted by BlueSky:
[b]You guys are smoking something. If the wheels don't move, and they're attached to the plane, I have news for you. The plane isn't moving either. As thrust is applied, the wheels will just rotate faster because the belt accelerates to keep up.

At least that's the way it works in my world. If it's different in yours, so be it. cool
Hell, man, the original problem statement didn't even say the plane HAS wheels... It could be sitting on skids or floats... So then what happens? The plane still takes off... There's just more friction between the plane & the conveyor belt.[/b]
You're most amusing. If you applied thrust with the plane on skids or floats, the plane would nose over just like somebody going downhill on a bike who locks up the front brakes. That pesky friction again.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 01:16 PM

Quote:
Originally posted by BlueSky:
Quote:
Originally posted by XPLORx4:
[b]Great. On a windless day, if the engines are off the aircraft has neither airspeed nor groundspeed.

OK, now, let's place a conveyor belt under the aircraft's wheels, and bolt the plane to the ground by its nose, tail,and wingtips. Now, let's fire up the conveyor belt to 100mph.

It's still a windless day.
Answer these questions:
1) What's the aircraft airspeed?
2) What's the aircraft groundspeed?
3) What's the aircraft's wheelspeed on the conveyor?
1) Zero
2) Zero
3) I'm not sure what you mean. All over this thread, people have said "the wheels are turning at X MPH." But speed is a measure of movement, and the wheels aren't moving (except for rotation), so it should really be measured in RPM, right? Can you clarify please?[/b]
The conveyor belt has a surface speed of 100mph, right? The RPM of the tires over the conveyor belt is determined by the size of the tire, but we don't care about the tire RPM, we care about the speed at which the tread of the tire is moving, which is... 100mph! Right?
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 01:21 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by BlueSky:
[b]
Quote:
Originally posted by XPLORx4:
[b]Great. On a windless day, if the engines are off the aircraft has neither airspeed nor groundspeed.

OK, now, let's place a conveyor belt under the aircraft's wheels, and bolt the plane to the ground by its nose, tail,and wingtips. Now, let's fire up the conveyor belt to 100mph.

It's still a windless day.
Answer these questions:
1) What's the aircraft airspeed?
2) What's the aircraft groundspeed?
3) What's the aircraft's wheelspeed on the conveyor?
1) Zero
2) Zero
3) I'm not sure what you mean. All over this thread, people have said "the wheels are turning at X MPH." But speed is a measure of movement, and the wheels aren't moving (except for rotation), so it should really be measured in RPM, right? Can you clarify please?[/b]
The conveyor belt has a surface speed of 100mph, right? The RPM of the tires over the conveyor belt is determined by the size of the tire, but we don't care about the tire RPM, we care about the speed at which the tread of the tire is moving, which is... 100mph! Right?[/b]
How are you calculating that?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 01:28 PM

Quote:
Originally posted by BlueSky:
How are you calculating that?
Look, you should know that tire size and forward speed are irrelevant to each other. An Xterra with 35" tires and an Xterra with 31" tires can both keep up with each other, right? They both can use GPS to travel at 60mph, right? But their speedometers are different because their tires are rotating at different RPM. Cars use rotational sensors, multiplied by the differential gear ratios, multiplied by the stock OEM tire diameter to provide accurate speed.

So, in our plane's tires, if the tires are really big or really small, their tread is still moving at the surface speed of the conveyor belt, right? So, if the conveyor belt is going 100mph, and the plane is bolted to the ground on a windless day:

1) What's the airspeed? 0 mph
2) What's the groundspeed? 0 mph
3) What's the tire tread speed? 100 mph

Do you agree?
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 01:32 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by BlueSky:
[b]How are you calculating that?
Look, you should know that tire size and forward speed are irrelevant to each other. An Xterra with 35" tires and an Xterra with 31" tires can both keep up with each other, right? They both can use GPS to travel at 60mph, right? But their speedometers are different because their tires are rotating at different RPM. Cars use rotational sensors, multiplied by the differential gear ratios, multiplied by the stock OEM tire diameter to provide accurate speed.

So, in our plane's tires, if the tires are really big or really small, their tread is still moving at the surface speed of the conveyor belt, right? So, if the conveyor belt is going 100mph, and the plane is bolted to the ground on a windless day:

1) What's the airspeed? 0 mph
2) What's the groundspeed? 0 mph
3) What's the tire tread speed? 100 mph

Do you agree?[/b]
Yes, I know all that. So answer my question.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 01:34 PM

I dunno...

Most of the people did a pretty good job explaing why exactly the plane WOULD move, and how it will be achieve. I guess it's hard for some to visualize. You're still imagining a scenario when the wheels would be delivering power to ground but they are not.

I like the "plane on ice" analogy. On perfect ice, the plane wheels would not spin, but simply slide along the ice with the plane moving forward once the engines are fired, resulting in the plane taking off.

In this scenario, ice is what eliminated the friction and allowed the place to move and take off.

With out original given scenario, it's the tires that are eliminating friction (perfect world with no rolling resistance, for the same of my point). Since there's no friction, it doesn't matter how fast the conveyor belt moves. It can move at 200 mph, BUT THE PLANE WOULD BE STILL WITH ENGINES OFF. I hope you're with me.

Now add the thrust of the engine. Bam! The plane takes off because the engine THRUST offsets the equilibrium of forces (again, keep in mind, we are not taking into consideration the rolling resistnace of tires and bearings).

If after 39 pages it's still not clear, I give up. [Laughing]
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 01:38 PM

Quote:
Originally posted by BlueSky:
Yes, I know all that. So answer my question.
So what's your question? How I'm calculating the speed of the tire tread?

The speed of the tire tread that's in contact with the conveyor belt, relative to the plane that's bolted to the ground is equal to the speed of the conveyor belt, assuming that the tire isn't skidding.

The speed of the tire tread that's on the TOP of the tire is traveling at the negative speed of the conveyor belt.

So, if the conveyor is going 100mph towards the rear, the bottom of the tire tread is also going 100mph towards the rear, but the top of the tire tread is going 100mph towards the front.

But none of this matters anyway, because the wheel axle isn't moving. It's still bolted to the aircraft, which is bolted to the ground.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 01:44 PM

Quote:
Originally posted by BlueSky:
[QUOTE]Originally posted by XPLORx4:
[qb] Yes, I know all that. So answer my
question.
You stil haven't answered mine, so why should he answer yours?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 01:45 PM

I'm trying to establish that the "tire tread" speed has no relevance to the plane's groundspeed or airspeed. You already accepted that the airspeed and groundspeed are both ZERO, in spite of the fact that the tires are turning beneath the plane.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 02:12 PM

Quote:
Originally posted by Rockaholic:
Quote:
Originally posted by BlueSky:
[b][QUOTE]Originally posted by XPLORx4:
[qb] Yes, I know all that. So answer my
question.
You stil haven't answered mine, so why should he answer yours?[/b]
Go back in your corner. He can handle his own conversation.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 02:15 PM

Quote:
Originally posted by XPLORx4:
I'm trying to establish that the "tire tread" speed has no relevance to the plane's groundspeed or airspeed.
If you're saying the rotation speed of the tire is irrelevant to the forward movement of the plane, I'd agree because as thrust is applied, if the plane starts to move forward the belt accelerates. The tires spin faster but the plane still doesn't move.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 02:27 PM

The answer is the conveyor can never stop the plane from moving. Forward motion is provided by an external force outside the conveyors control. What does the plane care how fast the conveyor is moving? It's relative motion to a stationary object is unaffected by the conveyor.

I thought the walkway and tow rope explaination worked but some of you guys ignored it.

Take a toy car and stick it on a treadmill... Hold it in your hand and turn the treadmill on. The wheels spin matching the speed of the conveyor. Move your arm forward and backward relative to the conveyor. Does the conveyor speed affect your ability to move the car faster or slower on the conveyor?

Turn the speed up on the treadmill. Standing off to the side, can you still push the car towards the front of the conveyor? Was there enough resistance to make it impossible to move the car forward?

The wheel speed is independent of motion of the car on the treadmill because it's means of propulsion (your hand/arm) is independent of the treadmill.

Now a normal car being driven by the wheels on the same conveyor would go no where relative to objects not on the conveyor.

Man I hope this helps.

I'm starting to think you're just jerking us around to see how long we'll try to explain it before we get frustrated to the point of exhaustion.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 02:45 PM

Who knows, maybe you guys are right. I see your point about the toy car, but in that example, the treadmill's speed is constant.

In answer to your question, I'm not jerking anybody's chain. It seems to me you can use maximum thrust and if the belt speeds up also, it's not going to move.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 02:55 PM

Even if the treadmill speed varies, would it affect the car as long as you are providing the motion? The motion is provided by you not the treadmill.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 03:12 PM

laugh

Damn

We're still on this?

Its the speed thing...

the ONLY thing KEEPING the last to see the light is the Speed issue.

EVERYONE else knows that the speed of the plane is how fast IT IS MOVING, and

NOT

How fast its tires are SPINNING.

If you think that the SPEED of the plane is the speed of its tires' rotation (Like off a speedometer of a truck doing a burn-out)..

THEN

you come to the wrong conclusion...and think the plane is not moving.

Of course, if its not moving...there's no conveyor speed to match.

So - One camp is saying the plane sits there on a stationary/non-rotating conveyor belt.

(Because there's nothing to make the plane turn its tires, except it moving)

AND

It can't move unless the engine pushes it

AND

The engine can ONLY push the plane like the finger pushing the toy truck.

_______

In the world of the CF'r:

The finger pushes the truck...but, some how, it does not move forward.
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 05:20 PM

Quote:
Originally posted by Timmah:
Even if the treadmill speed varies, would it affect the car as long as you are providing the motion? The motion is provided by you not the treadmill.
Yes.

Same as the rope with guy on treadmill on skates. Sure you can pull yourself forward. But increase the speed of the treadmill as you do so. It will become harder to pull yourself forward. Just as with the toy car. Sure you can push it. But it will be harder as you increase the speed. Eventually the engines will reach max thrust and will go forwad no more.

I am not confused thinking the wheels deliver power.
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 05:23 PM

Quote:
Originally posted by JeffW:
Obviously people who have never taken a physics class find this tuff hard to grasp.

Please prove this answer wrong:
(since you claim it is incorrect)

Quote:
Originally posted by JeffW:
Relavent information:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?

Let's agree on what assumptions are sensible then. All of the assumptions below apply to virtually all aircraft.

Plane is powered by engines that push air (props or jets)
Plane's speed is measured by a windspeed meter as well as GPS
Plane's wheels spin freely
Wheel friction is negligible when compared to thrust
Newtonian physics apply



Coefficient of dynamic friction:

Force of friction:

F(f) = -uN

(negative because it opposes motion)

u = coefficient of static friction

N = weight of plane

Notice velocity is not included!

That means that the velocity of the conveyor belt is irrelevant for all practical purposes.

F(t) is force of thrust

a = (F(t)+F(f))/m

You won't find a scenario where |F(f)| is greater than |F(t)|. Therefore, in ALL cases the plane moves with respect to the atmosphere, thus achieving lift.

Possible scenario:

t = 0 :

Plane 0 mph
Conveyor 0 mph
Wheels 0 mph

t = 15 :

Plane 60 mph
Conveyor 60 mph
Wheels spin @ 120 mph

t = 55:

Plane 160 mph
Conveyor 160 mph
Wheels spin @ 320 mph

....

The plane takes off.

Either learn why it is correct or refute it....

..scientifically.
Guess those who took physics didn't take spelling.

And in your formula wait someone else posted that. It their formula it clearly states as long as the thrust is enough to overcome the friction then the plane takes off. I agree.

I just don't think the engines will with the counter action of the belt. That’s me and my opinion.

Now come up with your own.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 06:20 PM

yes, ever so slightly more difficult to move forward but not enough to stop you from moving the car forward.

That is friction. Other than the minute friction from the wheels rolling along it won't stop the toy car/plane from moving forward.
Posted by: Xorand

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 06:25 PM

I've figured it out:

42
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 06:28 PM

[LOL] 40 pages!!! The plane is moving down the runway to take-off as the top page holder!! WOO HOO!!!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 07:03 PM

Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 07:22 PM

Uh I believe I just did. They are free wheeling but there is friction. If the belt can match the speed it can go fast enough to keep it from moving.

Now you are just refusing to listen.

But I am used to that with you and our many gps debates.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 07:56 PM

For the friction to stop the forward motion of the plane it would not be able to do so by just matching the speed of the plane. It would have to speed up to the point to where the friction would counter the thrust provided by the engines. By then it isn't matching the speed of the plane it is vastly surpassing it.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 31/12/06 08:48 PM

At this rate, this thread is going to last until next year! [LOL]

The CF'ers believe that the friction of the tires and wheel bearings will counteract the thrust from the plane's engines, so the plane won't take off. However, the CF'ers also believe that the plane does NOT have any ground speed or airspeed, but this is not true. We have already established that conveyor belt and tire speed are UNRELATED to groundspeed/airspeed, since for a plane bolted to the ground, the tires can turn at any rate they want, but the plane won't move.

In the scenario, the plane MUST be moving down the runway/conveyor belt, otherwise the plane has ZERO speed. The conveyor matches the PLANE's speed, not the plane's TIRE speed.

So, given enough friction to prevent the plane from achieving sufficient airspeed before it reaches the end of the conveyor belt/runway, a plane could be prevented from taking off. However, that plane would be very poorly designed indeed.
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 03:36 AM

Quote:
Originally posted by Timmah:
For the friction to stop the forward motion of the plane it would not be able to do so by just matching the speed of the plane. It would have to speed up to the point to where the friction would counter the thrust provided by the engines. By then it isn't matching the speed of the plane it is vastly surpassing it.
I disagree. The belt will do whatever it takes to match the speed. Doesn't say it is equal just says it can go fast enough to match. If that is far faster than the speed of the wheels to create enough resistance then I see that as what the question states.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 05:06 AM

Will-flyers, I challenge you. Read this entire post and tell me why it's wrong.

It's a given that the tires are mounted on freewheeling, unpowered wheels. Still, something has to happen for any wheeled craft or vehicle to move.

For our purposes, let's define "roll" as rotation over stationary ground, resulting in movement. "Movement" means covering a given distance. Agree? Good.

For an aircraft at rest on the ground with the landing gear down, how does any kind of propelling force - a tow tractor, people pushing, engine power, or a downhill slope as examples - become forward motion? How does the plane itself accelerate forward? Move from point A to point B? How does ANY FORCE applied to the plane result in forward movement?

One thing must happen for the plane to move. The tires must roll. It doesn't matter how that propelling force is applied but for that aircraft to move forward, the tires, mounted on their freewheeling, unpowered wheels, must roll. That's why we need brakes and wheel chocks, right?

What happens when the tires, mounted on their freewheeling, unpowered wheels, roll? The plane moves along the ground. This is, IMHO, one missing link for the WFers - the rolling tires only travel forward because the ground is stationary. That distance, as we know, is a certain amount per tire rotation depending on their size.

But when the belt is added, the ground under the plane is in effect moving in the opposite direction. Forward movement is no longer the result of applying any kind of propelling force because...why?

The tires are no longer rolling along the stationary ground, they're rotating in place. And since the freewheeling, unpowered wheels they're mounted upon are on an axle attached to the plane, if the tires are not moving forward, neither is the plane.

And guess what? That pesky friction? It's WFer missing link #2. You don't need enough to stop the plane, you only need enough to make the tires rotate. That's why the "perfect frictionless ice" scenario works, because the need for the tires to roll is effectively removed because there's not enough friction to make them rotate.

The plane would fly IF the belt was a constant speed less than the plane can attain or IF the belt did not speed up as power was applied to the aircraft's engines. In the scenario as presented, the aircraft's tires, mounted on their freewheeling, unpowered wheels, will merely rotate faster in place as thrust is applied but the plane will not move forward.

That's as simply as I can state my opinion. If it works for you, great. If not, that's great too.

Happy New Year!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 05:11 AM

it mentioned...

"conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction)."

hmm exact same... must not me fast enough to counter thrust. 1000 MPH conveyor to counter a 10 MPH thrust does to mean equal speed does it? Doesn't say anything about stopping movement just matching speeds.

If you change the senerio, no the plane doesn't fly if thrust is negated by friction as stated numerous times before.

If you follow the scenerio then the plane flys without much additional effort.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 05:28 AM

Quote:
Originally posted by BlueSky:


But when the belt is added, the ground under the plane is in effect moving in the opposite direction. Forward movement is no longer the result of applying any kind of propelling force because...why?

The tires are no longer rolling along the stationary ground, they're rotating in place. And since the freewheeling, unpowered wheels they're mounted upon are on an axle attached to the plane, if the tires are not moving forward, neither is the plane.
You're logic is flawed here. The wheels rotating would stop nothing. The thrust provided by the engine is not countered by the conveyor because the air isn't being affected by the conveyor's motion.


The plane would fly IF the belt was a constant speed less than the plane can attain or IF the belt did not speed up as power was applied to the aircraft's engines. In the scenario as presented, the aircraft's tires, mounted on their freewheeling, unpowered wheels, will merely rotate faster [b]in place
as thrust is applied but the plane will not move forward.[/b]

Flawed as well. As long as thrust is greater than friction the plane flys.

The engines are providing an external force outside of the conveyors control. The wheels spinning (as long as they are spinning) would not affect the thrust provided by the engine. As long as thrust > friction.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 06:45 AM

You must have missed the part about it not mattering where the propelling force comes from. If the tires don't roll ALONG the ground, just rotate over the belt, the plane won't move. If you don't get that, forget it.

You're never going to agree with my logic and I sure don't agree with yours.
Posted by: Smith

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 06:58 AM

Who's the asshole who started this thread? mad
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 08:10 AM

Blue, in your "challenge" post you seem to be hung up on creating some number of wheel revolutions being the key to forward movement of an aircraft.

Actually, if you get in a plane and lock the wheels up (create more friction with the ground) and power up enough (not all that difficult) the thrust will still overcome the friction of the tires on plavement and the plane will move forward. Not very smoothly, but it will move forward.

It does matter where the propelling force comes from, because the propelling force (air) is not affected at all by the conveyor.

OK, some punk kid threw their skateboard at you. How much pressure must you apply longitudinally to the BOTTOM OF THE WHEELS to stop it?

Well, golly, Wilbur. If I can only touch the bottom of the wheels then the wheels are just gonna spin and the skateberd's gonna hit me smack 'tween the eyes.

Please, blue. Open your mind a little and accept that aircraft can use the force of air to overcome minimal friction (as the wheels' friction is minimal, even on a conveyor) to move forward and create lift. They do it every day, and if they didn't I'd be out of work.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 08:38 AM

Now, Blue, you made me read your entire post. I ask the same of you and all you non-believers...

Quote:
Originally posted by BlueSky:
For our purposes, let's define "roll" as rotation over stationary ground, resulting in movement. "Movement" means covering a given distance. Agree? Good.
You're WRONG! Roll is defined as moving along a surface by revolving or turning over. That surface doesn't have to be stationary as described in the convyor belt scenario.

Quote:
Originally posted by BlueSky:
For an aircraft at rest on the ground with the landing gear down, how does [b]any kind of propelling force - a tow tractor, people pushing, engine power, or a downhill slope as examples - become forward motion? How does the plane itself accelerate forward? Move from point A to point B? How does ANY FORCE applied to the plane result in forward movement?[/b]
Are you serious? Have you taken ANY kind of physics classes at all?!?

To ALL of your questions here...There is a force being applied to propell the airplane forward. It is an outside source, but that source is great enough to be able to move the airplane from point A to point B.

Let's review Newton's three laws of physics. They will disprove your entire statement:

I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

II. The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors (as indicated by their symbols being displayed in slant bold font); in this law the direction of the force vector is the same as the direction of the acceleration vector.

III. For every action there is an equal and opposite reaction.

Quote:
Originally posted by BlueSky:
One thing must happen for the plane to move. The tires must roll. It doesn't matter how that propelling force is applied but for that aircraft to move forward, the tires, mounted on their freewheeling, unpowered wheels, [b]must roll. That's why we need brakes and wheel chocks, right?[/b]
You don't seem to understand...it DOES matter what the propelling force is. There are two forces at action here....the force that the conveyor is putting on the wheels, and the force the engine is creating. The ONLY THING that will work against the engines is the air itself. UNLESS the engine is resting on the conveyor belt with no wheels below it. Then, the conveyor is acting on the engine itself because of the downward force of gravity applied to the engine to push it directly into the conveyor belt. The wheels are there to take that force off of the engine so the engine will work independantly of the wheels.

Quote:
Originally posted by BlueSky:
What happens when the tires, mounted on their freewheeling, unpowered wheels, roll? The plane moves along the ground. This is, IMHO, one missing link for the WFers - the rolling tires only travel forward because [b]the ground is stationary. That distance, as we know, is a certain amount per tire rotation depending on their size.

But when the belt is added, the ground under the plane is in effect moving in the opposite direction. Forward movement is no longer the result of applying any kind of propelling force because...why?
/[qb]

Because the wheels are not the propelling force...the ENGINES are!!! Simple physics!!!

Quote:
Originally posted by BlueSky:
[QB]The tires are no longer rolling along the stationary ground, they're rotating in place. And since the freewheeling, unpowered wheels they're mounted upon are on an axle attached to the plane, if the tires are not moving forward, neither is the plane.[/b]
See, THIS is where all you that say it can't fly are being hung up. The wheels and tires are not doing the propelling. The original statement states that the conveyor is matching the plane's speed. Now, for it to match the plane's speed, it's going to make the wheels spin at twice the plane's speed in the opposite direction. Thing is, the wheels are assumed to be nearly frictionless due to the ball bearings. How in the hell is a conveyor belt going to stop the wheels if they can ALWAYS travel MUCH faster than what the plane can travel? If the wheels are travelling at 10x the speed of the airplane, the airplane will STILL MOVE FORWARD because the ENGINES DON'T HAVE ANY FORCE ACTING ON THEM!!! THE WHEELS HAVE FORCE ACTING ON THEM.

Quote:
Originally posted by BlueSky:
And guess what? That pesky friction? It's WFer missing link #2. [b]You don't need enough to stop the plane, you only need enough to make the tires rotate. That's why the "perfect frictionless ice" scenario works, because the need for the tires to roll is effectively removed because there's not enough friction to make them rotate.[/b]
The bearings are there to provide a nearly frictionless surface. Similar to what the ice would produce.

Think of this.....the friction created by the wheels is also being created by the conveyor if we presume that the conveyor is on a similar system of wheels and bearings. If this is the case, how will the conveyor get enough speed in the opposite direction to stop the forward momentum of the airplane? By focusing so much on the friction between the wheels and the conveyor, all you "Can't Flyers" are digging yourselves deeper into this hole....

The friction is something that needs to be taken out of this entire discussion, or it can open an entirely new can of worms because it wouldn't matter then....the belt's bearings would seize and burn up causing the conveyor belt to stop allowing the plane to take off wink

Quote:
Originally posted by BlueSky:
The plane would fly IF the belt was a constant speed less than the plane can attain or IF the belt did not speed up as power was applied to the aircraft's engines. In the scenario as presented, the aircraft's tires, mounted on their freewheeling, unpowered wheels, will merely rotate faster [b]in place as thrust is applied but the plane will not move forward.[/b]
You just stated it right here why the plane WOULD fly. The wheels can travel infinately faster than what the engines can produce. They only travel as fast as the plane is moving. HOWEVER, they can travel at 1000000000x faster than what the thrust can produce. so, it really doesn't matter how fast the conveyor is moving. The engines are still pulling the plane forward causing the wheels to just travel that much faster.

In this scenario, the wheels will travel as fast as the conveyor will make them, not as the engines will. That's because there are multiple forces at work here (GOD, I'm starting to sound like a broken record!!!) The forces applied between the conveyor belt and the wheels are comp[letely independant of the forces applied between the engine and the air!!!

Quote:
Originally posted by BlueSky:
Happy New Year!
Right back at ya!!!

Also, do me a favor. Do a Google search for "airplane on conveyor belt" 99% of the returned hits are going to chastise all the non believers because they are associating the airplane to a car because of the wheels. In just about all the hits, they will describe exactly what the "flyers" have been trying to describe to you guys....The conveyor is working on the wheels, not on the engines. [Wave]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 08:39 AM

Quote:
Originally posted by BlueSky:
You must have missed the part about it not mattering where the propelling force comes from. If the tires don't roll ALONG the ground, just rotate over the belt, the plane won't move. If you don't get that, forget it.

You're never going to agree with my logic and I sure don't agree with yours.
This only works if the wheels are what are doing the propelling. If there is another force acting on the object sitting on the wheels, the conveyor won't affect that at all!! See my above post ^^^^
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 08:43 AM

Quote:
Originally posted by BlueSky:
You must have missed the part about it not mattering where the propelling force comes from. If the tires don't roll ALONG the ground, just rotate over the belt, the plane won't move. If you don't get that, forget it.

You're never going to agree with my logic and I sure don't agree with yours.
This isn't about agreeing.

This is about whether or not you folks have the cognitive abilities to understand why the correct answer is correct.

If the wheels roll, what is holding the plane back? Nothing! The wheels just spin faster if there's a belt. The plane still moves with respect to the earth as well as the atmosphere. Please explain how you are refuting the physics above. [Freak]

Quote:
Originally posted by Smith:
Who's the asshole who started this thread? mad
It's not Lizz's fault, it's Hawk's fault!!!

Happy new year, Hawk! [Finger] [Finger] [Too much XOC]

...

How is it that people who can't understand a high-school physics free-body diagram have deemed themselves more qualified than this guy:

Quote:
If I properly understand your travelator, the travelator moves at
exactly the speed of the airplane, but in the opposite
direction. This means the wheels rotate twice as fast as they would
on a normal runway and nothing else is different. Right?

In that case, I claim the plane would take off normally except that
the wheels would be rotating twice as fast as normally. Since the
frictional force is, as you say, f=uR, the frictional force will be
exactly the same in the two cases since v does not appear in the
equation for the frictional force. In other words, the frictional
force is independent of the speed. In that case the forces on the
plane are exactly the same whether the travelator is operating or
not and so the plane takes off the same way in the two cases.

-Dick Plano, Professor of Physics emeritus, Rutgers University
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 08:49 AM

Quote:
Originally posted by JeffW:

Quote:
Originally posted by Smith:
[b]Who's the asshole who started this thread? mad
It's not Lizz's fault, it's Hawk's fault!!!

Happy new year, Hawk! [Finger] [Finger] [Too much XOC] [/b]
And it's also me that's trying to put an end to it [Finger] Not my fault we have a bunch of people here that can't seem to grasp the basic concepts of physics :rolleyes:
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 09:54 AM

Hey -

CF argument:

Me and my freind are wearing roller skates...

I lay on my back, stick my feet up, and my freind climbs up, and stands on my skate wheels with her skate wheels.

Now - my skate wheels, and hers, will ROTATE at EXACTLY the same speed, if they roll at all...as they are in essence interacting like contact gears, or a tread mill, etc.

No matter HOW FAST my wheels rotate, hers will rotate EXACTLY at the same speed, MATCHING my wheel's speed....AND mine will match HERS.

OK, she's up there...and, CAN NOT move...because, if she rolls forward, mine will roll backwards the EXACT SAME AMOUNT.

My OTHER freind, named Jet, comes up behind her, and pushes her from behind.

eek

She of course DOES NOT MOVE, because, no mater how fast he pushes her...my wheels will rotate just as fast as her's will.

laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 10:27 AM

Sorry TJ-I think that your thoughts are wrong. Unless you guys are in a vacuum. You are for getting about friction. I think? LOL. Happy New Years.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 10:30 AM

TJ, that made no sense at all....
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 10:56 AM

OF COURSE IT MAKES NO SENSE!!!!!!!!!!!

I was calling this the CF Argument.

:rolleyes:

Because...its what they are saying would be the case.

laugh

And

It NOT wrong because I forgot about friction...

...its wrong because it doesn't recognize that the important thing about moving forward , was that it was NOT limited by the wheels' rotational speed, and was in fact entirely due to the thrust from behind.

laugh

I was trying for a visual that illustrated the difference between MOVING and wheel speed/rotational speed.

The CF's keep thinking that as long as the tread mill speed up...you could not move....for getting that the tread mill speed was irrelevent (A red herring).

laugh
Posted by: Rickster43

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 11:01 AM

Hey Absolutely FabuLizz, Why do you keep on changing the name of the Topic so many times....makes no sense...I think this Topic needs to be Deleted completly, Moderators !!!
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 11:05 AM

Quote:
Originally posted by Rickster43:
Hey Absolutely FabuLizz, Why do you keep on changing the name of the Topic so many times....makes no sense
Actually, I think it's kinda funny. It's her contribution to this thread. laugh

PS. Happy New Year, everyone! Anyone hung over? :p
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 11:05 AM

I think this thread is one of the best off topic threads ever.

We had a civil discussion that went on for days, w/o getting out of hand, and w/o hurting anyone.

We disagreed on things...and kept going, until it seems, finally, all saw the light, slapped their foreheads, and came to a decision.

That's very rare on XOC...but, this is proof that it can happen.

Its a testament to hope for humanity...for if a 40+ page thread on XOC can exist w/o a fight...we may one day have peace in the middle east.

laugh

Happy New Year Every One!!!!

laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 11:35 AM

I've enjoyed this thread. The responses-some wrong, have been very interesting to read. I've spoken to a couple aviators and they give different responses as well.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 12:10 PM

Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 12:18 PM

Hmmm...we CFers seem to be in the minority.

At this point I'm going to let go of this. Perhaps I'm wrong, I'm open-minded enough to consider the possibility and to think on it some more. It still doesn't make sense to me, and despite what some of you seem to think, I'm a fairly intelligent person with a long background in aviation.

In the end, being hypothetical and meaningless in the big picture of life, it doesn't matter anyway, and if I'm wrong...well, again despite what some people seem to think, being wrong isn't the end of the world.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 12:23 PM

You all know that the real answer is that EVERYONE'S right! The plane can either NOT fly or it CAN fly! [LOL] Hahahaha!
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 12:37 PM

Quote:
Originally posted by BlueSky:
Go back in your corner. He can handle his own conversation.
OK - I asked you a question, and you've chosen to ignore it... I wasn;'t jumping into "your" conversation, as much as I've been waiting for an answer from you to mine.
So let me show you the problem with your argument...and pay atention this time. I understand you claim to be a "a fairly intelligent person with a long background in aviation." So why don't you prove that and read thorugh this and show me where I'm wrong.

Quote:
Originally posted by BlueSky:
It's a given that the tires are mounted on freewheeling, unpowered wheels. Still, something has to happen for any wheeled craft or vehicle to move.

For our purposes, let's define "roll" as rotation over stationary ground, resulting in movement. "Movement" means covering a given distance. Agree? Good.
Ok, so based on that statrement a plane moving at 100mph with it's wheels on solid ground must have the wheels rolling over the ground at 100mph.

Quote:
For an aircraft at rest on the ground with the landing gear down, how does [b]any kind of propelling force - a tow tractor, people pushing, engine power, or a downhill slope as examples - become forward motion? How does the plane itself accelerate forward? Move from point A to point B? How does ANY FORCE applied to the plane result in forward movement?

One thing must happen for the plane to move. The tires must roll. It doesn't matter how that propelling force is applied but for that aircraft to move forward, the tires, mounted on their freewheeling, unpowered wheels, must roll. That's why we need brakes and wheel chocks, right?
[/b]
OK, I'm going to give you that one....

Quote:

What happens when the tires, mounted on their freewheeling, unpowered wheels, roll? The plane moves along the ground. This is, IMHO, one missing link for the WFers - the rolling tires only travel forward because [b]the ground is stationary
. That distance, as we know, is a certain amount per tire rotation depending on their size.

But when the belt is added, the ground under the plane is in effect moving in the opposite direction. Forward movement is no longer the result of applying any kind of propelling force because...why?

The tires are no longer rolling along the stationary ground, they're rotating in place. And since the freewheeling, unpowered wheels they're mounted upon are on an axle attached to the plane, if the tires are not moving forward, neither is the plane.[/b]
Ok, now you have a problem with your argument- it's flawed - badly.
Here's why:

If the plane has the front wheels on the conveyor belt and the rear wheels on solid ground - you now have a contradiction.

According to you the plane will not move because the front wheels are on the conveyor and "the ground under the plane is in effect moving in the opposite direction. Forward movement is no longer the result of applying any kind of propelling force because the tires are no longer rolling along the stationary ground, they're rotating in place. And since the freewheeling, unpowered wheels they're mounted upon are on an axle attached to the plane, if the tires are not moving forward, neither is the plane."

But the rear wheels are on solid ground and since the plane is moving at 100mph, "One thing must happen for the plane to move. The tires must roll. It doesn't matter how that propelling force is applied but for that aircraft to move forward, the tires, mounted on their freewheeling, unpowered wheels, must roll."

Now the problem is that the front and rear wheels are mounted to the exact same plane. Now based on what you claim, the planes wheels on the conveyor do not move in relation to the ground (no rolling) because that counteracts the planes speed of 100mph, yet the rear wheels must roll because the plane is moving at 100mph (otherwise the conveyor isn't moving at all), and since they roll that means they move in relation to the ground...

So now I ask you again:
[b]How do the front wheels remain stationary while the rear wheels are moving when the distance between the wheels remains a constant?[/b}
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 12:48 PM

-----------------
SCENARIO: A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

Will the plane be able to take off?

-----------------

Here's my position:

The plane CAN FLY if.... see below.
The plane CAN NOT FLY if.... see below.

Here are the facts, which both CF and CNF folks agree on (I hope!)

FACT #1: Airspeed is an essential element to flight of a fixed-wing aircraft.
FACT #2: Groundspeed is irrrelevant to flight. It's only relevant if you actually hope for a plane to do anything except hover in mid-air.
FACT #3: AIrcraft use a Pitot tube , usually mounted on the wing, to measure airspeed.
FACT #3: Aircraft use GPS and radio-based distance measuring equipment to measure groundspeed.
FACT #4: In the absence of wind, airspeed and groundspeed are equal.
FACT #5: On an aircraft, wheel RPM, or wheelspeed, is irrelevant to both groundspeed and airspeed.
FACT #6: Airplane engines apply thrust against air.
FACT #7: Drag resists motion through air.
FACT #8: Friction resists motion on the ground.

-----------------

ASSUMPTION #1: The pilot knows how to operate the aircraft and can successfully take off on a normal runway.
ASSUMPTION #2: Windspeed = 0mph
ASSUMPTION #3: The plane has wheels.
ASSUMPTION #4: The wheels are the only part of the plane in contact with the conveyor belt.
ASSUMPTION #5: The moving conveyor belt does not create wind that has a significant impact on the plane.
ASSUMPTION #6: The tires and wheel bearings on the airplane are NOT frictionless.
ASSUMPTION #7: There is a physical limit to the maximum RPM that the plane tires and wheel bearings can rotate before failure.
ASSUMPTION #8: Based on the question, "Will the plane be able to take off?" we only care about FLIGHT. By association to FACT #1, we therefore only care about AIRSPEED.

-----------------

CONCLUSION #1: Based on ASSUMPTION #8, "plane's speed" means AIRSPEED.
CONCLUSION #2: Based on ASSUMPTION #2 and FACT #4, groundspeed = airspeed.
CONCLUSION #3: Based on CONCLUSION #2, "speed of the conveyor" means "negative GROUNDSPEED".
CONCLUSION #4: Based on CONCLUSION #2, the plane MUST ALWAYS HAVE a measurable groundspeed and airspeed or the conveyor would stop moving.
CONCLUSION #5: Based on CONCLUSION #4 and ASSUMPTION #5, the conveyor MUST ALWAYS HAVE a measurable negative groundspeed, but NEVER HAS a measurable negative airspeed.
CONCLUSION #6: Based on CONCLUSION #3, ASSUMPTIONS #4 and #5, and FACT #5, the conveyor does not negate airspeed.
CONCLUSION #7: Based on CONCLUSION #4 and CONCLUSION #6, the plane moves forward.

THEREFORE... the ANSWER to the question is:
Yes, the plane takes off if the thrust from the engine can overcome the wheel bearing friction and propel the aircraft to liftoff airspeed before the runway ends or before the tires and wheel bearings fail.
No, the plane does not take off if the engine thrust is insufficient to overcome wheel bearing friction before the runway ends or before the tires or wheel bearings fail.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 12:51 PM

CONCLUSION #3: Based on CONCLUSION #2, "speed of the conveyor" means "negative GROUNDSPEED".
CONCLUSION #4: Based on CONCLUSION #2, the plane MUST ALWAYS HAVE a measurable groundspeed and airspeed.
CONCLUSION #5: Based on CONCLUSION #4 and ASSUMPTION #5, the conveyor MUST ALWAYS HAVE a measurable negative groundspeed, but NEVER HAS a measurable negative airspeed.

Hmm...damn...I THOUGHT we all got it.

The conveyor DOES NOT change your ground speed.

If ground speed is the same as air speed in zero mph wind...and I fly over a river flowing towards me...I am covering the same ground...but the "ground" is flowing water.

A flowing conveyor belt is as much a part of my ground speed as a flowing river...or a highrway with cars under me...even if my tires are rolling on the car's roofs...the car roofs do not change my ground speed either.

laugh

Actually, we might be done.

I don't think there's any one left who doesn't get it.

laugh

The last key seemed to be "SPEED".

The CF camp confused OR misinterpreted SPEED as the speed of the conveyor being MATCHED to the speed of the PLANE - as meaning more than it did.

That's why all the seemingly odd references to the plane going at some speed, and the conveyor matching it...so it was standing still, etc.

As soon as each one realized that the conveyor's speed - while NUMERICALLY the same as the PLANE's speed (like a tread mill), was not in fact ACTUALLY the plane's speed.

As soon as they realized that your SPEED on a tread mill is zero, but your ROTATIONAL SPEED was what ever the belt speed was going around at...it became clear.

UNTIL the concept that your SPEED is zero when staying in place on a tread mill, even if the speedometer SAYS 4 mph...is absorbed, no further progress could be made.

I think we're all onboard now though.

laugh
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 01:05 PM

Quote:
Originally posted by TJ:
Hmm...damn...I THOUGHT we all got it.

I think we're all onboard now though.

laugh
TJ, you missed FACT#1, ASSUMPTION#8, and CONCLUSION#6.

You're right, we don't care about "negative groundspeed" at all. All we care about is airspeed.

However, if the plane's wheel bearings impart sufficient friction to the aircraft, then it won't ever develop enough airspeed to take off. But, IMO, that would be a very poorly designed aircraft.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 01:15 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by TJ:
[b]Hmm...damn...I THOUGHT we all got it.

I think we're all onboard now though.

laugh
TJ, you missed FACT#1, ASSUMPTION#8, and CONCLUSION#6.

You're right, we don't care about "negative groundspeed" at all. All we care about is airspeed.[/b]
Yes, except for one problem - there is no fact or assumption that the plane remains in one spot relative to the ground. That would be a false assumption

Let me take my "front wheels on coneyor, rear wheel on ground" one step farther.

The planes starts with no speed with the front wheels on the conveyor and the rear rears off the conveyor.

The conveyor is set to match the speed of the plane, so whatever the plane's speed is at any exact moment the conveyors speed is.

As the planes speed increases, does the plane move (not neccessairly take flight) with repect to the ground?

If the plane moves, then the plane on a conveyor flies.

If the plane does not move, then the plane on the conveyor does not fly

Since it would be impossible for the rear wheel to be on solid ground and not moving when the plane has a speed of anything greater than 0mph, then of course the plane moves, and thus the plane on the conveyor must fly.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 01:20 PM

Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 01:20 PM

Quote:
Originally posted by Rockaholic:
Yes, except for one problem - there is no fact or assumption that the plane remains in one spot relative to the ground.
You missed conclusion #4.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 01:24 PM

Quote:
Originally posted by BlueSky:
IF you WFers are correct, is the distance needed for takeoff more, less, or the same as needed on a runway?

How did you reach your answer?
Distance needed for takeoff is greater on a conveyor belt than on a conventional runway.

Why? Because the friction of wheel bearings spinning at twice their normal speed creates an opposing force to the engine thrust. As my previous posts have indicated, if the wheel bearing friction is so great that the engines can't overpower that force, then that's either a poorly designed or poorly maintained aircraft.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 01:33 PM

Quote:
Originally posted by BlueSky:
To answer your question:

My hypothesis is based on the scenario given, that all aircraft tires are on the belt.

In yours, it seems to me the front tires would rotate faster than the rear ones but the aircraft would continue moving forward until all tires were on the belt, at which time the aircraft's forward motion would cease and all tires would rotate in place.

Does that answer your question?
No, you create a new problem -

You have the plane moving at 100 mph, and the front wheels moving at 100 mph going forward on a conveyor belt moving -100mph and then just stopping.

What force is being applied that stops the forward motion of the plane?
You can't say the motion of the conveyor belt, because if that were true the front wheels of the plane would not be able to move forward in relation to the ground on the belt.

Quote:
Originally posted by BlueSky:
IF you WFers are correct, is the distance needed for takeoff more, less, or the same as needed on a runway?

How did you reach your answer?
The distance the plane travels on the ground for takeoff is the same for either the gorund or the conveyor. The distance the wheels "travel" (that is based on rational speed) on the conveyor belt is twice the distance the wheels travel on the ground becuase their rotaional speed is double.

2 tires of the same size, one turning at 1rpm and theother turning at 2rpm travel different lenghts of ground in the same time. The tire turning 2rpm travels twice the distance of the tire turing 1rpm in the same time amount.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 01:36 PM

Quote:
Originally posted by Rockaholic:
Quote:
Originally posted by BlueSky:
[b]To answer your question:

My hypothesis is based on the scenario given, that all aircraft tires are on the belt.

In yours, it seems to me the front tires would rotate faster than the rear ones but the aircraft would continue moving forward until all tires were on the belt, at which time the aircraft's forward motion would cease and all tires would rotate in place.

Does that answer your question?
No, you create a new problem -

You have the plane moving at 100 mph, and the front wheels moving at 100 mph going forward on a conveyor belt moving -100mph and then just stopping.

What force is being applied that stops the forward motion of the plane?
You can't say the motion of the conveyor belt, because if that were true the front wheels of the plane would not be able to move forward in relation to the ground on the belt.[/b]
BlueSky answered the question as if the plane were a RWD car.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 01:41 PM

Quote:
Originally posted by XPLORx4:
BlueSky answered the question as if the plane were a RWD car.
Again - that is a problem
A plane is not a RWD car, becasue a rear wheel drive cars wheels are not all free spinning (only the front tires are free spiining, the rear wheels are not, hence rear wheel drive), whereas an airplanes wheels are all free spinning.

If the free spinng wheels of the airplane are going to be stopped by the conveyor, then the RWD car should implode on itself, and not climb up onto the conveyor with the front wheels moving forward on the conveyor.

So now you've said that free spinning wheels can be stopped moving forward by the conveyor belt, and contradicted yourself by saying they can not be stopped moving forward by the conveyor belt - which is it?
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 01:47 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Rockaholic:
[b]Yes, except for one problem - there is no fact or assumption that the plane remains in one spot relative to the ground.
You missed conclusion #4.[/b]
That conclusion does not say the plane remains in one spot - only that the conveyor matches the measerued airspeed and groundspeed of the plane

Thus if the plane is on the conveyor and not moving in relation to the ground (Groundspeed thus =0 mph) then the conveyor is moving at 0 mph...

Based on that conclusion if the conveyor has a speed, the plane must be moving in relation to the ground.

Since the plane is moving in relation to the ground, it will fly based on Conclusion #2 (airspeed = groundspeed)

The assumption that the plane remains stationary to one spot on the ground is faulty and incorrect
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 01:57 PM

Quote:
Originally posted by Rockaholic:
The assumption that the plane remains stationary to one spot on the ground is faulty and incorrect
Which assumption or conclusion makes that claim? Certainly not me.

Quote:
CONCLUSION #4: Based on CONCLUSION #2, the plane MUST ALWAYS HAVE a measurable groundspeed and airspeed.
CONCLUSION #6: Based on CONCLUSION #3, ASSUMPTIONS #4 and #5, and FACT #5, the conveyor does not negate airspeed.
I never said the plane remains stationary, it just may not take off if it can't develop sufficient airspeed by the end of the runway.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:03 PM

Quote:
Originally posted by XPLORx4:
Quote:
Originally posted by Rockaholic:
[b]The assumption that the plane remains stationary to one spot on the ground is faulty and incorrect
Which assumption or conclusion makes that claim? Certainly not me.
[/b]
See Bluesky's posts...
Bluesky's assuming the plane remains stationary.

Itr's an assumption not included in the list, but one that people are making.

The only way the plane does not take off is if the plane remains stationary - which is the heart of the question about will a plane on a conveyor take off.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:08 PM

Quote:
Originally posted by Rockaholic:
It's an assumption not included in the list, but one that people are making.
Yes, they are making an incorrect FALSE assumption. The scenario specifically states that the conveyor matches the plane's speed, and by inference, its airspeed, since that's how planes measure whether they can fly or not. If there's no wind, the plane must ALWAYS continue to move in order for the conveyor to have any kind of speed to react negatively to.

Quote:
The only way the plane does not take off is if the plane remains stationary - which is the heart of the question about will a plane on a conveyor take off.
That's actually not true. The plane could move all the way down the runway and still not take off if the wheel bearing friction was high enough to prevent the plane from acquiring enough airspeed.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:11 PM

BTW - Bluesky does contracdict "him"self...

Quote:
Originally posted by BlueSky:
That pesky friction? It's WFer missing link #2. [b]You don't need enough to stop the plane, you only need enough to make the tires rotate. That's why the "perfect frictionless ice" scenario works, because the need for the tires to roll is effectively removed because there's not enough friction to make them rotate.

The plane would fly IF the belt was a constant speed less than the plane can attain or IF the belt did not speed up as power was applied to the aircraft's engines. In the scenario as presented, the aircraft's tires, mounted on their freewheeling, unpowered wheels, will merely rotate faster in place as thrust is applied but the plane will not move forward.[/b]
Quote:
Orignally posted by Blue Sky:
In yours, it seems to me the front tires would rotate faster than the rear ones but the aircraft would continue moving forward until all tires were on the belt, at which time the aircraft's forward motion would cease and all tires would rotate in place.
There's enough friction from the conveyor to roate the tires, but not enough to stop the plane from moving forward(quote#1)
Yet Bluesky seems to believe the friction of the conveyor will stop the forward motion of the plane on the conveyor (quote #2)
Which is it?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:11 PM

Ok, if what's below you moving is all you have to overcome, how does the stewardess walk up and down the aisle if the plane is moving 500 mph?
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:13 PM

Quote:
Originally posted by XPLORx4:
That's actually not true. The plane could move all the way down the runway and still not take off if the wheel bearing friction was high enough to prevent the plane from acquiring enough airspeed.
Since the coeffecient of friction between 2 objects is constant, if the wheel bearing friciton is high enough to prevent the plane from taking off on the conveyor, it's high enough to prevent the plane from taking off on a runway - which violates the assumption that the plane would take off on a normal runway
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:14 PM

Quote:
Originally posted by Rockaholic:
BTW - Bluesky does contracdict "him"self...
Which is it?
Hahaha, maybe last night's festivities have had some consequences on his thinking ability this morning. [LOL]
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:20 PM

Quote:
Originally posted by Rockaholic:
Since the coeffecient of friction between 2 objects is constant, if the wheel bearing friciton is high enough to prevent the plane from taking off on the conveyor, it's high enough to prevent the plane from taking off on a runway - which violates the assumption that the plane would take off on a normal runway
But the coefficient of friction on the wheel bearings isn't constant. As the bearing grease heats up, its lubricating ability changes. And the ability of the tires to stay in one piece depends on how fast they can rotate. Let's say that a particular model of aircraft achieves liftoff speed at 120mph. For cost purposes, they install tires with a speed rating of 180mph, well above the speed the airplane might ever need when taking off or landing.

However, on the conveyor belt, the tire speed would be 240mph, exceeding the speed rating of the tire, and.... KABOOM! Blowout!
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:26 PM

If the bearings and tires were to fail, then "yes" the plane probably wouldn't fly...again assuming the plane has wheels

However, you are the only one here that seems to be making that particular argument.

If you assume upgraded bearings/tires to deal with those new stresses (like a stock Xterra being given a Body lift and larger, more aggressive tires to handle tougher offroad trails) for the scenario - then the plane flies.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:28 PM

You people are unreal and digging too deep. Friction is negligible and therefore not an issue in this particular problem. If there were an issue with friction and the possibility of exploding the bearings/wheels/tires of the plane, then the same can be said for the wheel system on the conveyor belt. Therefore, the friction is a negligible and moot part of this experiment.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:29 PM

Just want to add that with this post, we tie Phat Chick Fridays in post count [Wave]
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:35 PM

Yes, in the real world, friction is a neglible force to counteract engine thrust. So, practically speaking, the average well-maintained would take off, whether on a conveyor belt or not.

It would, however, be interesting to find out what the speed rating of aircraft tires is, and whether they have >200% safety margin over takeoff speed.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:36 PM

Quote:
Originally posted by Hawk:
Just want to add that with this post, we tie Phat Chick Fridays in post count [Wave]
Unfortunately, no Hot chick pictures in this tread.....
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 02:47 PM

Just to make it relevant to both (and a beer thread, if there was one this long)...

Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 03:46 PM

The plane takes off in approximately the same distance necessary on a conveyor belt as it does on a regular runway.

Since Blue-Sky is mentioning his 20 years "aviation" experience, I guess I'll throw mine into the hat, even though it too has no bearing on the problem... I'm an airport designer. Civil Engineer. I design Runways, Taxiways, Aprons, and all things associated except the electrical & navigational equipment. I've been doing this for 6 years, now.

I assure you, the friction of the wheel bearings does not matter to the plane taking off. How's that? Because different surfaces have different coefficients of friction already. Asphalt runways have different coeff. than concrete. Significantly different on paper; absolutely no difference in the real world. Why's that? Because both numbers are so small in relationship to the take-off thrust of any aircraft that it doesn't matter.

READ BELOW COMPLETELY FOR AS SIMPLE AN EXPLANATION AS YOU CAN GET ON WHY THE AIRPLANE WILL TAKE OFF

An aircraft's engine PUSHES (jet) / PULLS (prop) the aircraft along the ground. This results in a horizontal force on the axles of the aircarft because they are fixed rigidly to the aircraft. The by-product of this force is it causes ROTATION of the tires around the axles. The tires do nothing more than rotate around the axle; they do not cause any horizontal movement.

If a conveyor belt were under the tires, it too would cause rotation of the tires around the axles. But, it can not cause any movement and/or restriction of movement of the axles, as the tires do nothing but free-spin around them. Again, the conveyor belt spins the tires, but does not exert any horizontal force on the axle. You can test this "theory" by jacking up your truck (get a whole axle up in the air), and spinning a free-wheeled tire from below. The tire will spin, but the truck will NOT move. This is not because you aren't spinning the tire fast enough; spin it as fast as you want, and the truck still will not move. The truck can't move, because all the force you apply goes into spinning the tire; none of it is a horizontal force on the axle.

Summing the forces in the horizontal direction gives you a positive force from the engines, and 0 negative force, as the conveyor belt can not move the axles of the plane regardless of how fast it spins.

From Newton, Force = Mass x Acceleration. So divide the sum of the Forces (the engine force only as shown in the above paragraph) and divide by the Mass of the plane. What you get is the Acceleration of the aircraft. The friction is negligable, as it is an extremely small number compared to the Force.

The net result is the aircraft accelerates down the runway, and eventually obtains flight once there's enough lift provided by the air passing over the wings.

END EXPLANATION

And, it will reach its takeoff speed at the same distance down the runway as it would without the conveyor belt. The additional friction of the tires as they spin twice as fast is not enough to make a significant difference. Dynamic friction levels off at a certain point, and for all practical purposes remains a constant level whether the tire spins at 150 mph or 300 mph.

Editorial Comments...:
While this is a physics, it's also a Statics & Dynamics problem. A problem like this would be taught in a 200 level Engineering Dynamics course, and any Engineer that can't answer it with only a fleeting glance ought to take some continuing education classes in a hurry...
Posted by: Mobycat

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 04:05 PM

Quote:
Originally posted by porsche996:
The plane takes off in approximately the same distance necessary on a conveyor belt as it does on a regular runway.

Since Blue-Sky is mentioning his 20 years "aviation" experience, I guess I'll throw mine into the hat, even though it too has no bearing on the problem... I'm an airport designer. Civil Engineer. I design Runways, Taxiways, Aprons, and all things associated except the electrical & navigational equipment. I've been doing this for 6 years, now.
Interestingly enough, my brother is a civil engineer (with about the 20 years experience).

His take was that there would be no wind over the wings. BUT...he also made it a point to say it's a trick question.

Edit to add - if the plane is going 20 mph, does the conveyor think it's going 20mph to the ground or to itself?

If the conveyor thinks it's to itself, shouldn't it be impossible for the conveyor belt to match it? That is, if the conveyor think's the plane is going 20 mph to the conveyor belt, the conveyor belt goes to 20mph...but then the plane is going 40 mph to the belt - and so on and so on?

Which brings back the question - what's the speed in relation to?

If it's to the ground away from the plane - then the plane should take off. If it's to the ground underneath - the conveyor - it's an impossible scenario.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 04:12 PM

Quote:
Originally posted by Mobycat:
Interestingly enough, my brother is a civil engineer (with about the 20 years experience).

His take was that there would be no wind over the wings. BUT...he also made it a point to say it's a trick question.

Edit to add - if the plane is going 20 mph, does the conveyor think it's going 20mph to the ground or to itself?

If the conveyor thinks it's to itself, shouldn't it be impossible for the conveyor belt to match it? That is, if the conveyor think's the plane is going 20 mph to the conveyor belt, the conveyor belt goes to 20mph...but then the plane is going 40 mph to the belt - and so on and so on?

Which brings back the question - what's the speed in relation to?

If it's to the ground away from the plane - then the plane should take off. If it's to the ground underneath - the conveyor - it's an impossible scenario.
Speed isn't revolutions per second, which is what any measurement of the tires would give you. That's "angular speed", and not "speed". In a car, angular speed is translated into speed by the speedo, gears, and in newer ones, electronics. But the angular speed of the tires and the speed of the vehicle are never coinciding.

Moby, run my explanation by your brother and see what he has to say. Don't paraphrase; copy that last post directly and ask him about it. I'm betting a little light-bulb will go off over his head (maybe even a good palm-smacking of the forehead if he's that kinda' person) and he'll tell you the plane takes off...
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 04:58 PM

Quote:
Originally posted by porsche996:

I'm an airport designer. Civil Engineer. I design Runways, Taxiways, Aprons, and all things associated except the electrical & navigational equipment. I've been doing this for 6 years, now.
What does potassium acetate mean to you on a concrete runway?
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 05:24 PM

An aircraft's ability to leave a conveyor-belt runway is influenced PREDOMINANTLY by the speed rating of its tires.

I briefly searched google, and found that a common speed rating of many aircraft tires is 160knots . There are some tires with speed ratings as high as 225knots.

Most people in this discussion believe that the aircraft will take off on a conveyor belt. A few still hold onto the fact that the plane never moves relative to its surroundings, which has been disproved many times.

The plane DOES move towards the end of the runway, which moves backwards at the same rate, making only the tires spin faster (but the plane still moves forwards). Wheel bearing friction is negligible, provided proper bearing maintenance. However, if the tire speed exceeds 160knots, which means the plane's groundspeed/airspeed can only be 80knots, the tire is at risk of failure while it's on the conveyor belt. Most planes require airspeeds of approx 80-90knots to acquire lift. On the scenario's conveyor belt, the tires would have to spin at an effective speed at 180knots, which is a little faster than the speed rating of the tire.

As long as the tire can hold together before the plane takes off, the plane will fly away. But if the tire fails before then, the plane is probably going to lose control near the end of the runway and probably crash.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 05:36 PM

Quote:
Originally posted by Eric P.:
Quote:
Originally posted by porsche996:
[b]
I'm an airport designer. Civil Engineer. I design Runways, Taxiways, Aprons, and all things associated except the electrical & navigational equipment. I've been doing this for 6 years, now.
What does potassium acetate mean to you on a concrete runway?[/b]
Means nothing to me. My airports don't use potassium acetate in their deicing ops. I'm in Louisville for cripes sake... We don't need extreme cold temperature deicing.

Only airport I've done work for that has extensive deicing operations was Denver, and I only worked on the design of a Frontier apron that never got built, so far as I know. That was almost 2 years ago.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 05:48 PM

Quote:
Originally posted by XPLORx4:
An aircraft's ability to leave a conveyor-belt runway is influenced PREDOMINANTLY by the speed rating of its tires.

I briefly searched google, and found that a common speed rating of many aircraft tires is 160mph . There are some tires with speed ratings as high as 225mph.

Most people in this discussion believe that the aircraft will take off on a conveyor belt. A few still hold onto the fact that the plane never moves relative to its surroundings, which has been disproved many times.

The plane DOES move towards the end of the runway, which moves backwards at the same rate, making only the tires spin faster (but the plane still moves forwards). Wheel bearing friction is negligible, provided proper bearing maintenance. However, if the tire speed exceeds 160mph, which means the plane's airspeed can only be 80mph, the tire is at risk of failure while it's on the conveyor belt. Most planes require airspeeds over 100mph to acquire lift. On the scenario's conveyor belt, the tires would have to spin at an effective speed at over 200mph, more than 25% faster than the speed rating of the tire.

As long as the tire can hold together before the plane takes off, the plane will fly away. But if the tire fails before then, the plane is probably going to lose control near the end of the runway and probably crash.
Wow. You're reading way too much into the problem...

If it makes you feel any better, nobody ever said the airplane had tires to begin with. The original problem statement never said either way. For all we know, the plane is sitting on skids, and the conveyor belt is covered in butter to reduce friction...

But...
Goodyear Airplane tires

According to Good Year, they have tires rated up to 230 MPH.

So if it's a small plane w/ takeoff of 60 knots (indicated air speed) such as the Cessna 172R, then not only does it take off, but the wheels don't even come close to their max speed...
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 05:57 PM

Wow this is some intense shit... Seriously thou.. Can't we all just get along and just say who gives a rip if the plane takes off.. Who the hell puts a plane on treadmill anyways??
Posted by: MidnightX

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 06:29 PM

smile
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 06:32 PM

Yes-how about Britney's twat.
Posted by: spalind

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 06:38 PM

Quote:
Originally posted by Joe Kanter:
Yes-how about Britney's twat.
I thought she was referring to nudie pictures of herself....
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 06:59 PM

Ok, in just 5 days this thread has already exceeded the page count of the Phat Chicks thread.
That's really really sad. I'm disappointed in all of you. eek

Except Lizz. Never shoot the messenger. Or the person who helps with your Clearcoat Quest.
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 07:40 PM

Lizz,

Feel free to PM more nude pics of yourself to me.

I lost the last set.

Thanks, doll.

-Graham
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 07:43 PM

If you could CC me on those pics I would really appreciate it Liz, darling....
Posted by: Lightning

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 07:48 PM

I've avoided this thread for 5 days now... and then you lure me here with nudie shots and it's just a tease! Drat! Hmm, is it really worth my while I'm here to read 45 pages to see what this thread is all about and to get caught up?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 08:17 PM

Quote:
Originally posted by Lightning:
I've avoided this thread for 5 days now... and then you lure me here with nudie shots and it's just a tease! Drat! Hmm, is it really worth my while I'm here to read 45 pages to see what this thread is all about and to get caught up?
WTF? More pages than the Phat chicks thread and no pics? mad
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 08:44 PM

This might be more your speed:

Words and Pictures laugh
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 10:06 PM

This thread has grown a lot in the last couple of days.

I'll give my assessment so far....

The people who say that the plane will fly have offered some good arguments but every single one is completely flawed.

Some arguments are more flawed than others, but there are flaws in all of them.

Some are even claiming now that the plane is moving down the conveyor just like it would on a regular runway. If that were true, there would be no question or hypothetical scenario.

Many people claim their arguments are based on physics. That may be so, but they certainly are not based on aerodynamics.

Some have even posted a comment from a physics professor. It makes no difference what he says because there are people arguing all aspects of this scenario on the internet who are also college professors and scientists. Many of those scientists say the plane will not fly.

I've noticed many people have gotten very far away from the original scenario. Most of those are in the camp that the plane will fly. Many are completely ignoring the original scenario.

It's both surprising and shocking at the amount of extraneous stuff that has been brought into the debate.

I think people need to focus purely on the original scenario and aerodynamic principles.
Posted by: Xterrian

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 10:24 PM

Ny Madman, I specifically asked you not to reply to this thread without PM'ing me and yet here is a post from you continuing to debate this scenario without a PM in my box. I was trying to protect you, but you seem to be more interested in proving to me that I was wrong all this time and that there is no intelligence there, just ego. I'm very disapointed and will never believe any argument you post from this point forward on any topic as it is obvious that you are interested in being right no matter how wrong you are and will gladly wear a blindfold and earplugs if that is what it takes to believe you are right.

My statement at the 45 page mark is that anyone that still does not understand that the plane will fly is a complete fucking idiot. It can not be explained any simpler or in a more complex manner than it has been so far in this thread. My 12 year old son understood it without any explanation at all.

Please post a reference to any proffesor that states that the plane will not fly so I wiil know where not to send my kids to school.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 10:34 PM

Quote:
Originally posted by Xterrian:

Ny Madman, I specifically asked you not to reply to this thread without PM'ing me and yet here is a post from you continuing to debate this scenario without a PM in my box.
And who are you? My boss.

Quote:
I was trying to protect you, but you seem to be more interested in proving to me that I was wrong all this time and that there is no intelligence there, just ego.
You were wrong. You include "assumptions" in your argument.

And since when did this discussion become about ego?

Quote:
I'm very disapointed and will never believe any argument you post from this point forward on any topic as it is obvious that you are interested in being right no matter how wrong you are and will gladly wear a blindfold and earplugs if that is what it takes to believe you are right.
So now I am wrong for pointing out flaws in other people's arguments. [Freak]

You need to remove emotion from your arguments.

Quote:
My statement at the 45 page mark is that anyone that still does not understand that the plane will fly is a complete fucking idiot. It can not be explained any simpler or in a more complex manner than it has been so far in this thread. My 12 year old son understood it without any explanation at all.


You are a fucking idiot for making what was and should be a rational debate into your own personal forum and for taking things personally.

Quote:
Please post a reference to any proffesor that states that the plane will not fly so I wiil know where not to send my kids to school.
A couple of people have already provided links to people much smarter than you who say you are wrong.

Rinky also provided a link to a thread that is 500 pages long. There are engineers and scientists in that thread. Good Luck with your reading.
Posted by: socalpunx

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 10:35 PM

Quote:
Originally posted by Xterrian:
Ny Madman, I specifically asked you not to reply to this thread without PM'ing me and yet here is a post from you continuing to debate this scenario without a PM in my box. I was trying to protect you, but you seem to be more interested in proving to me that I was wrong all this time and that there is no intelligence there, just ego. I'm very disapointed and will never believe any argument you post from this point forward on any topic as it is obvious that you are interested in being right no matter how wrong you are and will gladly wear a blindfold and earplugs if that is what it takes to believe you are right.

My statement at the 45 page mark is that anyone that still does not understand that the plane will fly is a complete fucking idiot. It can not be explained any simpler or in a more complex manner than it has been so far in this thread. My 12 year old son understood it without any explanation at all.

Please post a reference to any proffesor that states that the plane will not fly so I wiil know where not to send my kids to school.
To be honest, there is something very juvinile and sophmoric about the whole "I'm right and anyone who doesn't agree with me is a fucking idiot" mentality.

A) Madman is under no obligation to PM you merely because you deem it to be necessary.

B)Your resume based on what you stated is that you are/were an airplane mechanic which while the determination can be made that you understand the mechanics of the systems involved in airplanes, it does not make you the finite expert on the physics, engineering and other issues being debated in this question.

C)A lot of other people that are a hell of a lot smarter than you have discussed and debated both sides of this question for a lot longer and in terms that you likely will never comprehend. So instead of claiming to be the be all and end all of the argument just enjoy the warm fuzzy feeling that you obviously think you know the answer.

So please. If the guy wants to argue with whoever wants to argue with him by all means, either argue away at your leisure or feel content that you stated your case, believe you are correct, and move on to something more worthy of your expertise.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 11:17 PM

Still waiting for that twat shot of Britney.
Posted by: Xterrian

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 11:29 PM

Thanks for commenting on my intelligence, but if it's a comment coming from one of the CF crowd, please don't take offense if it doesn't bother me.

I've always felt NYMM got a bad wrap here and felt sorry for him and was a bit aggravated that he continues to prove himself a fool despite my desire to help him out.

I can guarantee that no one smarter than me believes the plane won't fly.

We make the ALR yet? laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 01/01/07 11:39 PM

Quote:
Originally posted by TJ:
Yeah - the jets push air...and the tires are merely supporting the weight, not providing propulsion....so the tread mill would make the tires spin at double the ground speed....due to the conveyor MATCHING the plane's speed...IE: IF the plane isn't moving, the conveyor isn't moving.

Assuming that the conveyor matches the gound speed, the tires would not go backwards...as by "opposite direction", it seems to mean that its merely moving akin to a tread mill, towards the front of the plane, as the plane is trying to move forward....so the plane would never be moved backwards from a rest (No thrust) either.

The tires would just be rolling at double their normal take off speed, as the conveyor is MATCHING the speed of the PLANE...so as far as the tires are concerned, the tarmac is rolling along under them at double the plane's speed....whatever THAT is.

If "Opposite" means that it would push the plane FOWARD if it wasn't MATCHING the plane's speed...(Like a tread mill where the tread is coming from behind you, instead of the normal travel TOWARDS you, then it would not spin the tires backwards or fowards from a normal take off....but that makes no sense in this context...as its the plane's speed that is being matched, not the tire speed...IE: The tires would not roll at all. laugh

Steering/braking would of course be crazy, but, assuming the question is really to differentiate between able to move forward or not, I'd go with yes, it could take off from a propulsion standpoint...as the jets don't need tires to roll, skids or pontoons work for planes too.

laugh

IE: It would be able to take off as far as propulsion goes....the tire speed is irrelevant...but just double the airspeed.
Um, nope not really. Propulsion in this case has nothing to do with it taking off. Propulsion might as well be associated with making the wheels spin because on a treadmill that's all those jet (or prop) engines would be doing.

Flight is all about lift, and lift is all about air pressure under the wings. If the plane is effectively standing still because of the 'treadmill effect', there is not enough air mass flowing under the wing to create the necessary lift, and the plane would not move at all. The engines would move the air directly in front and directly behind the inlet and exhaust, but not enough air would be moving across the surface of the wing and that is why it wouldn't take off.

What would probably happen is this;

The wheels would just go really really fast because there would be no aerodynamic drag from the plane, and theoretically more air to push at earth level altitude for additional thrust would bring the spinning speed of the wheels to well over the planes maximum at altitude - say 700+ mph. Assuming the tires didn't melt due to the friction of spinning under all that weight, the tires would likely separate from the wheels, sending firey bits everywhere and blow up the plane.

If the treadmill was really big, like runway size, it might be able to move enough air mass on it's own to create lift - kind of like a large fan. I don't know if that would be enough to get the plain airborne, but it would be similar to the way a kite lifts into the air - the kite generates no thrust, short of resisting the wind (akin to moving in place) which allows the air mass to pile up below it (build pressure below) and push it upward (less pressure above). If the jet did get airborne this way, it would only be for a few feet before the air mass generated by the treadmill dissipated.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:57 AM

Quote:
Originally posted by Xterrian:
Thanks for commenting on my intelligence, but if it's a comment coming from one of the CF crowd, please don't take offense if it doesn't bother me.

I've always felt NYMM got a bad wrap here and felt sorry for him and was a bit aggravated that he continues to prove himself a fool despite my desire to help him out.

I can guarantee that no one smarter than me believes the plane won't fly.

We make the ALR yet? laugh
You really do think highly of yourself.

I can guarantee that many people smarter than you say the plane will not fly. Also many people who are not as smart as you claim to be.

I've said a number of times in this thread, I don't know the answer to this question. I don't think any one does. You don't either.

The fools in this thread are those making the claim they are absolutely right and then proceed to start name calling those who oppose them. Now who would that be?
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:07 AM

Quote:
Originally posted by Mike in NRH:

Um, nope not really. Propulsion in this case has nothing to do with it taking off. Propulsion might as well be associated with making the wheels spin because on a treadmill that's all those jet (or prop) engines would be doing.

Flight is all about lift, and lift is all about air pressure under the wings. If the plane is effectively standing still because of the 'treadmill effect', there is not enough air mass flowing under the wing to create the necessary lift, and the plane would not move at all. The engines would move the air directly in front and directly behind the inlet and exhaust, but not enough air would be moving across the surface of the wing and that is why it wouldn't take off.
That's the major problem with many of the "does fly" arguments. Many completely fail to show that an acceptable amount of lift will be generated.

Here is an explanation from a NY Times blog thread on this subject (Note - the wording of the scenario in that thread is slightly different than our scenario).

Link to thread...

Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:46 AM

Quote:
Originally posted by NY Madman:
[So now I am wrong for pointing out flaws in other people's arguments. [Freak]
I read your posts Madman...

Please tell me where you pointed out the flaw in my argument (from page 37 on). I don't see that flaw in my argument pointed out anywhere.

I see where you claim the arguments for flight are flawed, but not actually pointing out the specific flaw in my argument.

Just saying the argument is flawed doesn't make it so.

Oh, by the way...
Your "aerospce engineer" has a flaw in his/her explanation.
The engineer says that the ground is moving in relation to the wing, but that the air is not moving in relation to the wing.
Either the plane is moving up the conveyor relative to the ground (flaw - airplane moving forward relative to the ground is moivng forward relative to the air creating airspeed and thus lift)
or the aerospace engineer is now calling the conveyor the ground...qand assuming the airplane remains stationary to a point on the ground next to the conveyor...to which I bring back the point the plane can not be stationary on the conveyor relative to the ground. For proof, re-read the argument I make from page 37 on...

So I'll ask you a second time in this post: Where exactly is my argument flawed?
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:35 AM

Quote:
Originally posted by Rockaholic:

Please tell me where you pointed out the flaw in my argument (from page 37 on). I don't see that flaw in my argument pointed out anywhere.
Are you talking about this statement?...

Quote:
Rockaholic wrote:

Ok, I screwed up in my last posts with respect to the 3rd party - so ignore those - I ended up confusing myself when people began mention 3rd party observers to the scenario - and made a mistake. If the plane is not moving in relation to the 3rd party observer Like in my aircraft scenario) then the plane does not fly. However my aircraft scenario is flawed because there is nothing to prevent the airplane from moving with respect to the gound. Thus the plane to a 3rd party observer could not appear to stay in one spot.
In that statement your flaw is making the assumption that the aircraft in our scenario is moving forward relative to the ground or an outside observer.

There is nothing in the original scenario that could generate such an assumption. Let's take a look at the original scenario again:



In the original scenario the conveyor and the plane's speed effectively cancel each other out in the equation.

Even if we were to allow an assumption of some forward movement on this conveyor ... relative to the ground and the atmosphere ... that forward movement would have to be enough to allow conditions for lift to occur.

Seeing that the conveyor exactly matches the plane's speed, how much forward motion do you envision?

Quote:
Oh, by the way...
Your "aerospce engineer" has a flaw in his/her explanation.
The engineer says that the ground is moving in relation to the wing, but that the air is not moving in relation to the wing.
I don't see him saying the ground is moving. He makes a statement referring to the "motion of the ground". That is most likely referring to the conveyor. The conveyor is afterall underneath the wheels of the plane, is it not?

Quote:
to which I bring back the point the plane can not be stationary on the conveyor relative to the ground. For proof, re-read the argument I make from page 37 on...
If you are claiming that the plane is moving forward on the conveyor relative to a point on the ground, then you are no longer arguing the parameters of the original scenario.

If the plane were moving forward on the conveyor relative to a point on the ground or an outside observer, then the conveyor is not matching the speed of the plane.

I thought it was interesting that on the NY Times blog thread there are more people who claim the plane would not fly.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:58 AM

Yes, Madman - I posted on page 37 at the start of the post that I made an error in the previos 3 posts.... :rolleyes:

Um, you can't say you pointed that out, because I pointed it out for you by posting that I made a mistake...

Then, after saying ignore those previous posts (that statement is in in the part you quoted), I made the argument about why the plane has to move on the conveyor.

Where is the flaw in the argument I make after I admit I made a mistake in my previous posts.... the ones I say to ignore because they I screwed them up and created a totally different scenario than the original one. :rolleyes:

You haven't shown where that argument is flawed - but let me tackle your argument becuase it is flawed...

This is the flaw in your argument, NYMaman and BlueskyIn the original scenario you are assuming the airplane remains in one spot relative to the ground.That is the flaw in your argument

However, the original scenario does not say that the plane remains in one spot relative to the ground, only that the conveyor and the airplane have the same speeds in the opposite directions.


The original scenario does not say that the plane causes the conveyor to move, but that the conveyor is moved by some other control to match speed of the plane.

So in that scenario, if the plane is taken off of the conveyor and placed onto hard ground and then beings moving towards the conveyor at 10mph, then the conveyor is still going to move at 10mph in the opposite direction of the planes motion...

Now, if you want to claim the plane remains stationary to a 3rd person observer on the conveyor, but not on solid ground, I bring you back to the argument I make after the admission of making an error in the previous posts. (read just below the part you quoted)

Show me the flaw in that argument:
Repeating myself a bit here:
Going back to the scenario of the plane with the front wheels on the conveyor and the rear wheels on solid ground, because it is related to the plane having all of its wheels on the conveyor.

The wheels on solid ground have to move in relation to the ground and the wheels on the conveyor are argued by you to remain stationary in relation to the ground, if that is true then when the airplane has the front wheels on the conveyor and the rear wheels on the ground how do the rear wheels move forward while the front wheels remain stationary since the distance between the front and rear wheels remains a constant?

I'll answer this question for you (and Bluesky) - The answer is that the front wheels do not remain stationary in relation to the ground, they move in relation to the ground.

Why?

That is because the rear wheels are moving in relation to the ground (otherwise planes wouldn't be able to take off of a normal runway) and because the distance between the wheels remains constant the front wheels would have to move forward in relation to the ground on the conveyor to maintain the constant distance. Now (this is important)unlike a car, the front and rear wheels of a plane are all the same in that they are free spinning and do not create the forward motion of the plane, they mearly react to the forward motion of the plane. Since the free spinning front wheels move in relation to the ground on the conveyor this means the rear wheels (being constructed identically) will also move forward in relation to the ground on the conveyor. That means the conveyor does not cancel out the forward motion of the plane! That means with all the wheels on the conveyor the plane will move forward in relation to the ground, even if the plane starts with all of the wheels on the conveyor.

Since the plane is moving in relation to the ground on the conveyor, then the plane has a groundspeed and a windspeed, and does in fact take off.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 03:02 AM

Quote:
Originally posted by NY Madman:
....In the original scenario the conveyor and the plane's speed effectively cancel each other out in the equation.....
"Speed" doesn't cancel.

Forces may cancel, but don't in this case.

This is not an aerospace engineering problem. An assumption is that the plane is already properly engineered. So we are back to Physics 101. Regardless, I wouldn't trust an aerospace engineer who has no grasp of basic physics (like the one you quoted).Please refer him to the physics professor quoted earlier.

It is disappointing that you have chosen to fanatically support the incorrect answer instead of taking a few minutes to understand this high-school level problem.

Please read the basic physics:

Quote:
Originally posted by JeffW:
Relavent information:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?

Let's agree on what assumptions are sensible then. All of the assumptions below apply to virtually all aircraft.

Plane is powered by engines that push air (props or jets)
Plane's speed is measured by a windspeed meter as well as GPS
Plane's wheels spin freely
Wheel friction is negligible when compared to thrust
Newtonian physics apply



Coefficient of dynamic friction:

Force of friction:

F(f) = -uN

(negative because it opposes motion)

u = coefficient of static friction

N = weight of plane

Notice velocity is not included!

That means that the velocity of the conveyor belt is irrelevant for all practical purposes.

F(t) is force of thrust

a = (F(t)+F(f))/m

You won't find a scenario where |F(f)| is greater than |F(t)|. Therefore, in ALL cases the plane moves with respect to the atmosphere, thus achieving lift.

Possible scenario:

t = 0 :

Plane 0 mph
Conveyor 0 mph
Wheels 0 mph

t = 15 :

Plane 60 mph
Conveyor 60 mph
Wheels spin @ 120 mph

t = 55:

Plane 160 mph
Conveyor 160 mph
Wheels spin @ 320 mph

....

The plane takes off.

Either learn why it is correct or refute it....

..scientifically.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 04:19 AM

Quote:
Originally posted by Rockaholic:

Yes, Madman - I posted on page 37 at the start of the post that I made an error in the previos 3 posts.... :rolleyes:

Um, you can't say you pointed that out, because I pointed it out for you by [b]posting
that I made a mistake...[/b]
Did I ever say I pointed out your specific argument?

There are many people posting in this thread. It is not a conversation between just you and I.

In the future if you want me to comment on something specific that you wrote, just quote yourself and reprint the specific point instead of just saying "back on page whatever". The thread is growing too fast.

Quote:
That is because the rear wheels are moving in relation to the ground (otherwise planes wouldn't be able to take off of a normal runway) and because the distance between the wheels remains constant the front wheels would have to move forward in relation to the ground on the conveyor to maintain the constant distance. Now (this is important)unlike a car, the front and rear wheels of a plane are all the same in that they are free spinning and do not create the forward motion of the plane, they mearly react to the forward motion of the plane. Since the free spinning front wheels move in relation to the ground on the conveyor this means the rear wheels (being constructed identically) will also move forward in relation to the ground on the conveyor. That means the conveyor does not cancel out the forward motion of the plane! That means with all the wheels on the conveyor the plane will move forward in relation to the ground, even if the plane starts with all of the wheels on the conveyor.

Since the plane is moving in relation to the ground on the conveyor, then the plane has a groundspeed and a windspeed, and does in fact take off.
I have to say, your scenario with some wheels on the conveyor and some wheels not on the conveyor is ridiculous. It has nothing to do with what we are discussing. It actually is creating more of a problem because once you do things like that, we are no longer discussiong the original scenario. In the scenario being discussed the plane starts off on the conveyor belt runway. Remember it is "standing on a runway that can move".

You are also making a huge assumption in what you wrote above. You are assuming forward motion of the plane. I don't think anyone disputes the fact that if forward motion exists, the plane will take off. But, the problem with your argument is that you are assuming said forward motion.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 04:54 AM

Quote:
Originally posted by JeffW:

Forces may cancel, but don't in this case.

This is not an aerospace engineering problem. An assumption is that the plane is already properly engineered. So we are back to Physics 101. Regardless, I wouldn't trust an aerospace engineer who has no grasp of basic physics (like the one you quoted).Please refer him to the physics professor quoted earlier.

It is disappointing that you have chosen to fanatically support the incorrect answer instead of taking a few minutes to understand this high-school level problem.
Yes, forces can cancel each other out and for the sake of our scenario, the thrust of the plane's engines is virtually cancelled out by the fact that the conveyor is matching any speed that can be generated by our plane's engines.

You are also looking at the situation from a Physics 101 viewpoint. You are not considering the principles of aerodynamics that are required for lift.

You also completely ignore the speed of the conveyor belt. Your argument is not even based on the hypothetical scenario. You made up your own scenario and are arguing based on your own scenario.

Until you can show or prove that there is enough air moving over this plane's wings, then you do not have the correct answer.

That is if there is even a correct answer. You certainly have not provided it. Arrogance IS NOT the correct answer.
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 05:13 AM

Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 05:56 AM

Quote:
Originally posted by Rockaholic:

read it again - scroll back up and read my argument - you'll see my argument does not violate the original scenario in any way unless you are assuming the plane remains stationary, in whcih case you have created a contradiction (see the previous bolded section of post above tis one- you can scroll up, I hope)

to which I bring back the point the plane can not be stationary on the conveyor relative to the ground. For proof, re-read the argument I make from page 37 on...

[b] False - the scenario does not say the planes remains in one spot and has no forward motion in relation to the ground - that is an assumption you are making because you do not understand the physics involved with the problem.


False - the conveyor matches the speed of the plane, but it doesn not stop the plane from moving - if it does you have the wheel problem I mentioned before
[/b]

Your idea of the plane with some wheels on and some wheels off the conveyor is NOT the original scenario.

In our scenario the plane is already on the conveyor runway. The scenario does not start off with our plane "halfway" on the runway.

It is pointless to argue and bring in totally different scenarios. It is also pointless to make comparisons to cars.

The scenario doesn't say the plane remains in one spot. By using your logic, the scenario also doesn't say the plane will have any foward motion either.



The scenario says the conveyor matches the plane's speed. That is all it says on that subject. If the plane attempts to do 100MPH the conveyor will be going 100MPH in the opposite direction. That does not equate to forward motion in relation to a point on the ground off of the conveyor.

The scenario doesn't say a lot of things. It doesn't tell us the length of the conveyor. Should we all start making assumptions regarding that too? Does this matter? For the sake of the scenario, most likely not.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 07:29 AM

"Um, nope not really. Propulsion in this case has nothing to do with it taking off. Propulsion might as well be associated with making the wheels spin because on a treadmill that's all those jet (or prop) engines would be doing. "

I think sums up the flawed logic in the CF argument.

laugh

For some bizarre reason...they seem to think that the thrust from the engines is turning the wheels of the plane, WITHOUT THE PLANE MOVING FORWARD.

They seem oblivious to the fact that UNLESS the plane moves forward, the wheels WON'T turn.

FOrward in THIS case has NOTHING to do with the speed of the belt, as FORWARD is, and CAN ONLY be, relative to the absolute postion of the plane...say, at a GPS coordinate.

The REASON for this - Is that the tires CANNOT turn from the belt alone (Which only MATCHES the plane's speed)....They can ONLY turn

IF THE THRUST PUSHES THE PLANE FORWARD...regardless of if the tires are on a belt, a river, a runway, a roller skate, etc.
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 07:35 AM

I ate the last of the Shreddies this morning. With sliced banana.

Damn.
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 07:37 AM

I'm sticking to my guns. If that makes me an idiot in some peoples' minds, so be it. If this was as cut and dried as the WFers make it out to be, there wouldn't be such a debate about it.

The WFers see the debate as them (superior) and the rest of us (too dumb to understand). It's not that simple.

Tell me this...how would this scenario be different than a seaplane trying to take off against a current? If the current accelerates to match the plane's speed, the plane will remain stationary and not take off, correct?

BTW, speed is a tricky word in the scenario. I take "matching the plane's speed" to mean exactly counteracting the speed the plane would attain under normal conditions. The "belt wouldn't move if the plane stayed in place" crowd obviously doesn't see it that way.
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 07:42 AM

Quote:
Originally posted by BlueSky:
Tell me this...how would this scenario be different than a seaplane trying to take off against a current? If the current accelerates to match the planes speed, the plane will remain in place, correct?
On a seaplane, the pontoons are fixed to the airframe.

The force of the current acts through the pontoons onto the airframe.

On an airplane on a runway, with wheels, the wheels are free-turning. Forces enacted on the wheels do not get transferred to the airframe.

The seaplane is a single airframe.

The airplane is an airframe with independent rolling gear.

They are two different animals in this scenario.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 08:20 AM

Quote:
Originally posted by BlueSky:

BTW, speed is a tricky word in the scenario. I take "matching the plane's speed" to mean exactly counteracting the speed the plane would attain under normal conditions. The "belt wouldn't move if the plane stayed in place" crowd obviously doesn't see it that way.
There is no correct answer because of the way the question is worded.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 08:25 AM

Quote:
Originally posted by JeffW:


This is not an aerospace engineering problem. An assumption is that the plane is already properly engineered. So we are back to Physics 101. Regardless, I wouldn't trust an aerospace engineer who has no grasp of basic physics (like the one you quoted).Please refer him to the physics professor quoted earlier.

It is disappointing that you have chosen to fanatically support the incorrect answer instead of taking a few minutes to understand this high-school level problem.

Please read the basic physics:

[QUOTE]Originally posted by JeffW:
[qb]Relavent information:

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?

Let's agree on what assumptions are sensible then. All of the assumptions below apply to virtually all aircraft.

Plane is powered by engines that push air (props or jets)
Plane's speed is measured by a windspeed meter as well as GPS
Plane's wheels spin freely
Wheel friction is negligible when compared to thrust
Newtonian physics apply



Coefficient of dynamic friction:

Force of friction:

F(f) = -uN

(negative because it opposes motion)

u = coefficient of static friction

N = weight of plane

Notice velocity is not included!

That means that the velocity of the conveyor belt is irrelevant for all practical purposes.

F(t) is force of thrust

a = (F(t)+F(f))/m

You won't find a scenario where |F(f)| is greater than |F(t)|. Therefore, in ALL cases the plane moves with respect to the atmosphere, thus achieving lift.

Possible scenario:

t = 0 :

Plane 0 mph
Conveyor 0 mph
Wheels 0 mph

t = 15 :

Plane 60 mph
Conveyor 60 mph
Wheels spin @ 120 mph

t = 55:

Plane 160 mph
Conveyor 160 mph
Wheels spin @ 320 mph

....

The plane takes off.

Either learn why it is correct or refute it....

..scientifically.
how do assume that thrust is 20% of the normal force? yes your simple fbd shows that f(t) is greater than the f(f), but you also need the f(l) to be greater than the f(g) for the plane to become ariborne, correct? how do we obtain a f(l) greater than f(g)? there needs to be a forward speed great enough to create the f(l) to overcome the f(g). you said that velocity does not factor into this problem, but i think it does.

lets take a practical example. forget the conveyor for a minute. a plane moves at 20mph down the runway. the f(t) is greater than the f(f). will the plane take off? it is moving forward, so by your reasoning it will fly, but it will not fly. why is that? because there is not eoungh lift created f(l) to overcome the f(g).

so back to the original problem, any thrust created by the plane to move it forward is counteracted by the conveyor, therefore there is no forward motion, therefore the plane does not fly.

jeffw, just out of curiosity, why wouldn't you trust the aerospace engineer? i'm sure that he has taken several physics courses past the grade 9 level. are you an engineer yourself?
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 08:27 AM

However...even though different scenarios...

A seaplane takes off either with the current, or against the current, it doesn't matter, as the friction of the water on the pontoons is not enough to overcome the thrust of the engines...regardless of flow direction.

Obviously, a tire rolls more easily than a pontoon floats, etc...especially initially, as the pontoon starts out sitting deeper, and is designed to plane up closer to the surface as speed increases.

So - until the CF's SEE that the tires don't turn UNLESS the plane moves forward...

....and that (AS the conveyor only MATCHES the speed of the plane) there is no such thing as rolling forward on the belt w/o forward motion RELATIVE TO THE BELT...

...as the ONLY thing that CAN make the tires TURN is a SPEED difference between the tire bottom, and the belt top.

laugh
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 08:28 AM

"so back to the original problem, any thrust created by the plane to move it forward is counteracted by the conveyor, therefore there is no forward motion, therefore the plane does not fly."

This is incorrect.

laugh

See above post.
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 08:34 AM

Does this help?

Think of an airplane as two independent entities:

The airframe, and the rolling gear.

Any and all forces generated by a conveyor in an attempt to affect the perceived forward progress of the airframe will instead be enacted upon the rolling gear only.

The force the conveyor is trying to enact upon the airframe is lost due to the free-flowing wheels. The force is dissipated through the wheels, and never reaches the airframe.

The airframe, in essence, does not know what the conveyor belt is trying to do, and doesn't care.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 08:41 AM

Quote:
so back to the original problem, any thrust created by the plane to move it forward is counteracted by the conveyor, therefore there is no forward motion, therefore the plane does not fly.
The thrust of the engines causes the wheel axles to move forward. This axle movement causes the wheels to spin.

The conveyor belt causes the wheels to spin about the axles.

The conveyor belt can not resist movement of the wheel axles. In order for the plane to NOT take off, the conveyor belt MUST prevent movement of the wheel axles. It can not, as the tires free-spin about the axles; they do not cause the axles themselves to move. The tires can ONLY push the axles IF they are powered at the wheel (like on a car). On a car, the axles move because the tires move. On an airplane, the tires move because the airplane moves. It's simple cause & effect... THINK ABOUT IT!!!

Therefore the plane will still accelerate as normal, and will take off upon reaching takeoff velocity.

There is nothing "flawed" about this logic. And I actually challenge any of the "can't fly" crowd to refute this post with proof. Good luck...

PS: You're going to need to prove that the conveyor belt CAN move the axles of an aircraft in order for your conclustion that it can't take off to be correct. There is no way the conveyor belt can move the axle as long as the tires are allowed to spin freely about the axle. None. No way. It's not physically possible. Not in theory, not in a lab, and not in the real world.

And once you realize the conveyor belt can not move the axles, then you *should* be able to realize that means the plane can take off, becaues the motion of the conveyor can not counteract the motion caused by the aircraft engines. Only 1 force in the example has any effect on the axles of the plane, and that's the engines of the plane. There is no counter-force to prevent the movement of the aircraft. The plane takes off.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 08:58 AM

PS - I am OPPOSED to just taking someone's word for this...I really think its more meaningful if the brain gets to wrap itself around this concept...and actually understand.

In the meantime...the school of aerodynamic Red Herrings swimming here seem to be quite abundant.

laugh
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 09:01 AM

CF crowd (apparently only Madman + BlueSky + Mike in NRH):

Please answer the following questions:

1) How is an airplane's speed measured?

a. Groundspeed
b. Airspeed
c. Other (specify)

2) What measurement devices are used to determine an airplane's speed? (Hint: --> click here <--.)
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 09:14 AM

Quote:
Originally posted by XPLORx4:
CF crowd (apparently only Madman + BlueSky + Mike in NRH):

Please answer the following questions:

1) How is an airplane's speed measured?

a. Groundspeed
b. Airspeed
c. Other (specify)
The hypothetical scenario does not specify the type of speed. Hence, a large reason the scenario is a conundrum.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 09:27 AM

Quote:
Originally posted by NY Madman:
The hypothetical scenario does not specify the type of speed. Hence, a large reason the scenario is a conundrum.
Answer my post you damn yankee.

:p
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 09:31 AM

JayZ - I was actually the one that originally assumed about a 20% thrust vs. normal force. It seemed about right when taking a quick look at thrusts of several large aircraft. That said, I could be totally wrong.

I said what I needed to say and posted a FBD back on page 8, and was done, but came back to make sure to clarify that I said it was 20%, not JeffW. Jeff just happens to be using the FBD in his arquement as well.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 09:32 AM

Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 09:38 AM

Again...the aerodynamics issues are Red Herring.

laugh

The ONLY thing that really matters here is that the tires can't roll w/o moving along the conveyor belt...as in getting closer to one end of the belt....

...Because the conveyor belt only moves when the plane moves...and the tires only turn when the belt slips/rolls beneath them...

...making them turn.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 09:39 AM

PS- The above seems irrelevant UNTIL you understand it.

laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 09:47 AM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by XPLORx4:
[b]CF crowd (apparently only Madman + BlueSky + Mike in NRH):

Please answer the following questions:

1) How is an airplane's speed measured?

a. Groundspeed
b. Airspeed
c. Other (specify)
The hypothetical scenario does not specify the type of speed. Hence, a large reason the scenario is a conundrum.[/b]
In the event something is not specified, a logical assumption should be made. Speed means speed and is not dictated by wheelspin, it is dictated by movement with respect to the earth's surface. I have listed two methods of measurement that make sense.
So far, nobody has been able to explain why they think Isaac Newton was wrong and the plane can't move.

All I hear is people going back and forth over sidenotes instead of coming to terms with the physical realities here.

There is only one correct answer to the problem. I recommend trying to understand the simple solution instead of wandering around in a fog of superstition.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 09:49 AM

A fog of Sugar Free Red Bull maybe?

laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 09:55 AM

Quote:
Originally posted by JayZ:
....

so back to the original problem, any thrust created by the plane to move it forward is counteracted by the conveyor, therefore there is no forward motion, therefore the plane does not fly.

jeffw, just out of curiosity, why wouldn't you trust the aerospace engineer? i'm sure that he has taken several physics courses past the grade 9 level. are you an engineer yourself?
That's not my fbd, it's Branden's. I posted it becaise I deemed it useful.

But a 3D fbd isn't even necessary in this case. We have a certain airspeed required for takeoff. So the question is simply whether the wheels roll and whether there is thrust. As long as the wheels roll and we have thrust, the plane will achieve the required airspeed for take-off.

This should be simple enough to understand once you thoroughly read the post you are commenting on.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 10:12 AM

Quote:
Originally posted by porsche996:

Answer my post you damn yankee.
I'll give it a shot rebel. [Freak]

Quote:
Originally posted by porsche996:

The thrust of the engines causes the wheel axles to move forward. This axle movement causes the wheels to spin.

The conveyor belt causes the wheels to spin about the axles.

The conveyor belt can not resist movement of the wheel axles. In order for the plane to NOT take off, the conveyor belt MUST prevent movement of the wheel axles.
In order for the plane to NOT take off, all that is required is an insufficient amount of air moving over the wings. Our scenario doesn't include atmospheric conditions such as headwinds.

Quote:
Therefore the plane will still accelerate as normal, and will take off upon reaching takeoff velocity.

There is nothing "flawed" about this logic. And I actually challenge any of the "can't fly" crowd to refute this post with proof. Good luck...

PS: You're going to need to prove that the conveyor belt CAN move the axles of an aircraft in order for your conclustion that it can't take off to be correct. There is no way the conveyor belt can move the axle as long as the tires are allowed to spin freely about the axle. None. No way. It's not physically possible. Not in theory, not in a lab, and not in the real world.

And once you realize the conveyor belt can not move the axles, then you *should* be able to realize that means the plane can take off, becaues the motion of the conveyor can not counteract the motion caused by the aircraft engines. Only 1 force in the example has any effect on the axles of the plane, and that's the engines of the plane. There is no counter-force to prevent the movement of the aircraft. The plane takes off.
So now instead of talking about the wheels it's the axles. I don't even know why you are now focusing on the axles because we already know the wheels are free spinning.

You are also asking other people for proof of this and that, yet you have provided no proof that the plane in this scenario will move forward in relation to the atmosphere fast enough to gain lift.

Moving forward is one thing. Moving forward fast enough in relation to the atmosphere is what is required for lift.

On both sides of the argument, assumptions are being made. That is why I say it is a conundrum the way it is worded.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 10:18 AM

Quote:
Originally posted by GrayHam:
Does this help?

Think of an airplane as two independant entities:

The airframe, and the rolling gear.

Any and all forces generated by a conveyor in an attempt to affect the perceived forward progress of the airframe will instead be enacted upon the rolling gear only.

The force the conveyor is trying to enact upon the airframe is lost due to the free-flowing wheels. The force is dissipated through the wheels, and never reaches the airframe.

The airframe, in essence, does not know what the conveyor belt is trying to do, and doesn't care.
I've been trying to get this point across, but the "CF" people can't seem to grasp it.

The conveyor belt exerts ALL of it's force on the wheels, NOT the engines. The only thing exerting a horizontal force on the engines is the air. Therefore, the conveyor will have 0 effect on the engines thus causing the engines to pull the airplane forward while the wheels spin at an unGodly rate of speed. This forward momentum will eventually give the airplane the needed lift to be able to take off.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 10:19 AM

I think people don't have time to read all this...they just think they've solved it, read a few of the posts, and post their reply.

Its hard to imagine taking the time to absorb the important concepts...and missing it.

My wife and kids got it figured out in about 30 seconds.

I asked the receptionist, (1 minute 23 seconds to solve) who replied she had NO idea what made a jet move...I told her it sucked air in one end, added fuel, and blew hot exhaust out the back to push the plane forward...

She said..."I guess it would go forward like a balloon, when you let go of a ballon knot".

I said "What would the conveyor do to it?"

She said "Nothing I guess, the conveyor would just spin the tires - how would that stop the plane from moving?"

laugh
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 10:36 AM

Quote:
Originally posted by Hawk:

The conveyor belt exerts ALL of it's force on the wheels, NOT the engines. The only thing exerting a horizontal force on the engines is the air. Therefore, the conveyor will have 0 effect on the engines thus causing the engines to pull the airplane forward while the wheels spin at an unGodly rate of speed. This forward momentum will eventually give the airplane the needed lift to be able to take off.
The way the scenario is worded, it can easily be said you are making an assumption.

Let me ask you a further question.....

The scenario does not specify the length of our conveyor belt runway. How long would such a runway have to be in order for the plane to gain enough forward motion needed for lift?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 10:49 AM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by Hawk:

[b]The conveyor belt exerts ALL of it's force on the wheels, NOT the engines. The only thing exerting a horizontal force on the engines is the air. Therefore, the conveyor will have 0 effect on the engines thus causing the engines to pull the airplane forward while the wheels spin at an unGodly rate of speed. This forward momentum will eventually give the airplane the needed lift to be able to take off.
The way the scenario is worded, it can easily be said you are making an assumption.

Let me ask you a further question.....

The scenario does not specify the length of our conveyor belt runway. How long would such a runway have to be in order for the plane to gain enough forward motion needed for lift?[/b]
Huh?!? That's the basic physics of flight. How is it an assumption?

The runway wouldn't have to be much longer than a standard runway. Once the initial friction between the wheels and the belt is overcome, the plane will accelerate down the "runway" normally.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 10:50 AM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by XPLORx4:
[b]CF crowd (apparently only Madman + BlueSky + Mike in NRH):

Please answer the following questions:

1) How is an airplane's speed measured?

a. Groundspeed
b. Airspeed
c. Other (specify)
The hypothetical scenario does not specify the type of speed. Hence, a large reason the scenario is a conundrum.[/b]
NYM- The hypothetical scenario also doesn't say what type of plane it is, what the runway is made of, or whether there's any type of wind. For all we know, the plane is a Harrier Jump Jet, there's a 100mph headwind, and the runway is made of glass!

Your response completely avoids the question.

Please tell me the assumptions you are making about the scenario, then answer the question: How is an airplane's speed measured? (You may use google to find your answer.)
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 10:56 AM

Mad -

I think that the context of the scenario is to see if people could determine the relevance of the concept of the tread mill as a runway...not to nit pick over "What if a terrorist were to fire a RPG, or what if the conveyor belt was too short, or what if the conveyor frightened the pilot", etc.

laugh

Reading the given scenario...it seems perfectly reasonable to assume that if the conveyor is the runway, that it is, other than being a tread mill, ....it is normal...

IE: Straight and flat, as opposed to ski slope shaped, or mountain road shaped, too short, with a giant wall across the end, etc.

The ONLY variable from a normal runway seems to be that it is a conveyor belt.

laugh

Same with the plane...it should be assumed that it is not a helicopter, or a thing used to shave wood, etc.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 10:58 AM

A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

Quote:
Originally posted by TJ:
Mad -

I think that the context of the scenario is to see if people could determine the relevance of the concept of the tread mill as a runway...not to nit pick over "What if a terrorist were to fire a RPG, or what if the conveyor belt was too short, or what if the conveyor frightened the pilot", etc.

laugh

Reading the given scenario...it seems perfectly reasonable to assume that if the conveyor is the runway, that it is, other than being a tread mill, ....it is normal...

IE: Straight and flat, as opposed to ski slope shaped, or mountain road shaped, too short, with a giant wall across the end, etc.

The ONLY variable from a normal runway seems to be that it is a conveyor belt.

laugh

Same with the plane...it should be assumed that it is not a helicopter, or a thing used to shave wood, etc.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 11:37 AM

Quote:
Originally posted by XPLORx4:

NYM- The hypothetical scenario also doesn't say what type of plane it is, what the runway is made of, or whether there's any type of wind. For all we know, the plane is a Harrier Jump Jet, there's a 100mph headwind, and the runway is made of glass!

Your response completely avoids the question.

Please tell me the assumptions you are making about the scenario, then answer the question: How is an airplane's speed measured? (You may use google to find your answer.)
I'm trying to avoid making any assumptions. That is why I say there is no correct answer the way the scenario is worded. There isn't enough information given, so it is almost impossible to not make some assumptions.

I've already discussed airspeed and relative velocity on page 36. Here is the link....

Link to post...

The scenario says the belt matches the plane's speed. It doesn't say whether it is the groundspeed or airspeed.

The one assumption I think we all can make is that the wind speed is zero.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 11:41 AM

Quote:
Originally posted by NY Madman:
[QB]
Moving forward is one thing. Moving forward fast enough in relation to the atmosphere is what is required for lift.[QB]
Once you realize the plane can move forward, then surely you can realize that it will accelerate as more throttle is added, as it would in a normal takeoff, and once it reaches its takeoff speed, it WILL takeoff.

What you're arguing is that the conveyor belt will prevent the axles (and in effect, the aircraft since they're attached rigidly to the axles) from moving. If the wheels spin freely, as you admit to realizing, then the belt in no way, shape, or form, can have ANY force on the axles, and in effect, in no way, shape, or form can have ANY effect on the plane that's rigidly attached to the axles. So the force of the engines is NEVER counteracted by the conveyor belt, and the plane acclerates right on down the runway and takes off...

If the plane can move an inch, then it WILL take off once it reaches the speed necessary. Your whole theory that the plane won't take off means you think the plane CAN NOT MOVE AT ALL... But it can. The belt spins the tires about the axle; it does not generate any horizontal force on the axles. Therefore, the belt does not counteract the horizontal force being supplied by the engines which are rigidly attached to the plane which is rigidly attached the axles... I only brought up the axles because the CF'ers obviously can't grasp the fact that the axles/plane/engine are 1 rigid object.

I was trying to pick something close to the tires that the weaker minds could get a grasp on. Evidently, I can't make this any easier for you to understand, so you WILL be going through life without grasping the concept. In a way, I felt sorry for you. But then I realized you're from New York, and frankly, I don't give a damn.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 11:50 AM

Quote:
Originally posted by NY Madman:
The scenario says the belt matches the plane's speed. It doesn't say whether it is the groundspeed or airspeed.

The one assumption I think we all can make is that the wind speed is zero.
NYM- OK, we can all agree that windspeed = 0.

Do you make any assumptions about what kind of plane we're talking about? Is it a Harrier? Is it a 737? A Cessna? How about a WWI biplane?

If you can't make any assumptions, then your answer to the question "Can the plane take off" must be: "I cannot answer without more information," and not "The plane won't take off."
Posted by: PartsPeddler

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 11:59 AM

If the conveyor belt negates the forward movement of the aircraft you'll be unable to produce air speed for lift.

Without appropriate air speed an aircraft can not acheive enough lift to take off.

What am I missing?
Posted by: Samueul

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:02 PM

If the wind speed is 0 the plane cannot take off as there will be no lift, but a plane doesn't really need it's wheels to generate wind speed or lift. The THRUST of it's propeller or jets and the plane's weight to wing span ratio determines it's minimum lift. If you have a plane that is parked on a runway and you put a big enough fan in front of it, it will "lift" even if it's not moving "forward" on its wheels. If the plane is powerful enough to break the friction barrier of the belt it will fly no matter how fast backwards the belt moves. The only way to keep it down would be to weigh it down enough so that the weight to wing span ratio is off.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:03 PM

Quote:
Originally posted by NY Madman:
The scenario says the belt matches the plane's speed. It doesn't say whether it is the groundspeed or airspeed.

The one assumption I think we all can make is that the wind speed is zero.
Umm, if you're saying we can make the assumption that wind speed is zero, then when the plane is on the ground, GROUND SPEED = AIR SPEED... So there is no reason to "assume" what we're talking about...

Wheel spinning is NOT a measurement of speed. The speed of any vehicle on wheels is a FUNCTION OF THE WHEEL SPIN, and NOT the wheel spin. For proof, how do you convert wheel spin into speed? You have to take the radius of the wheel, do some math, and you can convert the spinning revolutions per second into miles per hour of horizontal movement. The revs per second are NOT speed!!! The CF'ers do not realize this... If tires spinning always equaled the speed of movement of the vehicle, then a) you could never get stuck in mud because if your tires were spinning, you'd be moving, and b) there would be no need to adjust for larger/smaller tire sizes for your speedo...

Here's the math for those that can actually follow along. For those that can't, please keep believing the plane won't take off...

A wheel's axle moves 1 ft/s horizontally. What is the radius & revolution per second required to match?

You've got two unknowns. Let's simplify by saying the Circumference of the wheel is 1', so the revolutions per second = 1 rev/s, as the full circumfernce would travel the 1' horizontal distance the axle moves.

So, C=2*pi*r. C is 1 rev/s. Solving for r and you've got a wheel radius of 0.5pi, or 1.57'.

Ok, so now this tire is spinning at the EXACT same speed as the axle/tire combination is moving horizonatally.

But what if we don't want a 1.57' tire. What if we want a 2' tire? Then what happens.

Back-solving for C=2*pi*r, and you have a circumference of 4pi, or 12.57'.

For each revolution of the tire, the axle would move horizonatlly 12.57', so, if the axle moves only 1', the tire rotated only 1/12.57 = .08 revolutions.

So, the axle is moving at 1 ft/s. The tire is rotating at only 0.08 rev/s.

Oops. The tire's rotation speed and the horizontal movement are NOT the same... Which proves that unless a couple initial conditions are absolutely met, the wheel does NOT spin around an axle at the same rate the axle moves horizontally... That makes since, considering when you're doing a burn-out, stuck in mud, etc., your tires are spinning like mad, but the axles are only moving a little, if at all.

So what's this all mean to the CF'ers? It means 1) they got lost a long time ago as soon as reason entered the conversation, and 2) even with the math in front of their face, they still aren't going to believe a tire can rotate independent of the axle movement.

Which is a shame, 'cause I did a pretty cool burnout on my motorcycle yesterday, and yet the bike didn't move an inch.... If I lived in the CF'ers world, that wouldn't have been possible.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:05 PM

Quote:
Originally posted by PartsPeddler:
If the conveyor belt negates the forward movement of the aircraft you'll be unable to produce air speed for lift.

Without appropriate air speed an aircraft can not acheive enough lift to take off.

What am I missing?
You're missing that the belt can only spin the tires. It can not effect the motion of what the tires are attached to. Therefore it can not keep the plane from moving down the runway as originally scheduled, acheiving the lift it needs, and flying its merry little way to Vegas, feeling lucky 'cause he beat the odds...
Posted by: Samueul

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:05 PM

http://www.straightdope.com/columns/060203.html
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:05 PM

Yeah, Mad, we're pointing at the duck, and you are looking at our fingers.

laugh

I know that once the real issue sinks in, and you get it...you'll wonder how you missed it...but, you are missing the point of the question.

Its a runway, and a plane...in a problem such as this...the variables mentioned are the one's to consider.

Saying there is not enough information is a cop out...as there IS enough information, as long as you follow the presented given.

Otherwise, if the quesiton were re-worded to read:

There is a plane on the runway, a girl in the plane blows her nose, can the plane take off?

If you do it your way...the answer is ALWAYS that there is insufficient information...as what if her blowing was a signal for terrorists to blow up the plane? What if the plane had no gas?

etc.

Is 2=2 equal to 4?

Well, what if its 2 elephants, plus 2 lions, equal 4 zebras?

etc.

The problem assumes that we understand that we're testing the concept of the tread mill preventing the take off......

Let's say you just can not answer that type of brain teaser...as you must say things like:

"What if the plane could not fly any way, they didn't say if it has wings, or it does, but maybe they were not designed right, or maybe the pilot is dead, or maybe the stewardess is having trouble inflating the autopilot..."

etc.

OK, fine...no question ever posed has an answer, as there will never be eough information.

You can stop if that's the case, as there are no scenarios that will ever work for you.

For people who CAN solve problems like this...its STILL all about FINALLY understanding that the speed is the speed...as in gps coordinate to gps coordinate, in a given time....because that's what speed IS.

The conveyor belt is designed to confuse you...its a red herring.

Your speed on a tread mill is zero...your EQUIVALENT speed is what ever the speedometer says.

If you are on a tread mill, and I yank you forward with a rope...NO MATTER HOW FAST THE TREAD MILL BELT GOES...you WILL move forward....by the distance the rope pulled you.

If that's unclear...you may NEVER get it.
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:11 PM

Damn.

Lizz, I accidentally deleted the pics you sent me last night.

Could you resend?

By the way: was that thing acrylic or glass?

Either way, applause applause applause!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:19 PM

I know my response will be buried deep within the hundreds of pages this thread will accumulate, but here's the rub.

Aircraft will take off.
You can accelerate the hell out of the 'treadmill runway' and all will impart on the aircraft is a negligible amount of angular momentum in the -x direction (opposite thrust) about the wheels causing the nose to dip (easily countered with elevator angle). Aicraft will move forward, generate flow over the airfoils, generate lift per Bernoulli's equation, airborne.

Bullets will fall at the exact same moment unless you were able to achieve orbital velocity with the fired bullet (ignoring wind resistence). This bullet would be traveling traveling across the surface of the earth (provided you fired it above any mountains in the path) so that gravity would pull the bullet into an arc therby achieving an orbit of Re+drop height. As for the argument of air resistence causing the fired bullet to land faster than the dropped one, the air resistence would limit the distance traveled, but not the hangtime with regards to the dropped bullet (remember both bullets are experiencing resistence proportional to their speed).

Don't believe me, look at my profile to see what I do for a living.
Posted by: KJ_dragon

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:27 PM

Did someone email this question to these guys? I want to see them build a model to test it.

Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:27 PM

Quote:
Originally posted by RocketX:
Don't believe me, look at my profile to see what I do for a living.
Excellent, despite being a janitor, you have a better grasp of this than the remaining hold outs.

laugh
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:29 PM

Quote:
Originally posted by KJ_dragon:
Did someone email this question to these guys? I want to see them build a model to test it.

You mean like the 23 posts before yours suggested?

laugh

It was already agreed that they would not have to test it...simple logic solves it.

No experiment is required.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:31 PM

The conveyor belt is designed to confuse you...its a red herring.

Your speed on a tread mill is zero...your EQUIVALENT speed is what ever the speedometer says.

If you are on a tread mill, and I yank you forward with a rope...NO MATTER HOW FAST THE TREAD MILL BELT GOES...you WILL move forward....by the distance the rope pulled you.

If that's unclear...you may NEVER get it.
Posted by: MidnightX

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:46 PM

Graham, you're funny.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:50 PM

you know, this is sad. there are more posts here then the phat chick friday thread. if everyone who posted here posted one good picture in the other thread, we would be set.
Posted by: Xterrian

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 12:51 PM

I would like to apologize to everyone I insulted last night. I was frustrated and took it out on the people here. It does seem to me now that the people that don't get it are just pretending to not get it in order to get people like me irritated. I get the joke now and feel much better. I just feel that people that I have so much in common with should be smarter than the average bear and when it seems to be otherwise, it tends to get me pissed. Kind of the way I feel when somebody in the Army does something stupid. I feel it reflects on me personally. I will try in the future to not let that happen. frown
Posted by: TravelingFool

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:04 PM

So... Here's a new question!

Lets say you're on a train moving along the tracks at 12mph. Let's also say that all of the exit doors on the train are open. The doors between the train cars are open too. It has become apparent to you that the train is headed for a ravine and the bridge is out. Your only options are A and B. Which option is safest?

A) Jump out of a side exit door, hit the ground and roll, keeping your momentum rolling forward in the direction of the train.

B) Sprint toward the rear of the train, trying your best to approximate 12mph, and jump out of the back.
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:06 PM

Quote:
Originally posted by TravelingFool:
So... Here's a new question!

Lets say you're on a train moving along the tracks at 12mph. Let's also say that all of the exit doors on the train are open. The doors between the train cars are open too. It has become apparent to you that the train is headed for a ravine and the bridge is out. Your only options are A and B. Which option is safest?

A) Jump out of a side exit door, hit the ground and roll, keeping your momentum rolling forward in the direction of the train.

B) Sprint toward the rear of the train, trying your best to approximate 12mph, and jump out of the back.
confused

Where's the treadmill?
Posted by: Trihead

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:09 PM

Half nudie girl on treadmill

Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:20 PM

Quote:
Originally posted by Xterrian:
I would like to apologize to everyone I insulted last night. I was frustrated and took it out on the people here. It does seem to me now that the people that don't get it are just pretending to not get it in order to get people like me irritated. I get the joke now and feel much better. I just feel that people that I have so much in common with should be smarter than the average bear and when it seems to be otherwise, it tends to get me pissed. Kind of the way I feel when somebody in the Army does something stupid. I feel it reflects on me personally. I will try in the future to not let that happen. frown
I wouldn't say I was arguing any side to piss you off or anyone else.

It is amazing that regardless of how civil one conducts themselves in any debate on here, there are those that instantly sink to nothing but insults. (I don't mean you either. You have also came back and apologized like a gentleman).

As far as this subject goes, I clearly stated early on that I was wrong in my initial responses and that I was going to play devil's advocate.

You shouldn't feel that anyone else's responses are a reflection on you.

I'll continue to play the devil's advocate. So, does the plane actually fly? smile
Posted by: Xterrian

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:25 PM

I read every response in this thread and can't find the devil's advocate reference. Could you point me towards the page number it is on?
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:29 PM

Actually, I did see that...but I thought he just went back to the dark side...as I thought on this one, the Devil was well represented already.

Coals to New Castle so to speak.

laugh
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:33 PM

"Lets say you're on a train moving along the tracks at 12mph. Let's also say that all of the exit doors on the train are open. The doors between the train cars are open too. It has become apparent to you that the train is headed for a ravine and the bridge is out. Your only options are A and B. Which option is safest?

A) Jump out of a side exit door, hit the ground and roll, keeping your momentum rolling forward in the direction of the train.

B) Sprint toward the rear of the train, trying your best to approximate 12mph, and jump out of the back.
"

Well, for this one, its more like the the train is the tread mill.

laugh

You are comparing your impact with stationary ground in two scenarios...one leaping sideways to your direction of travel...one leaping backwards opposite your direction of travel.

laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:39 PM

Quote:
Originally posted by TravelingFool:
Lets say you're on a train moving along the tracks at 12mph. Let's also say that all of the exit doors on the train are open. The doors between the train cars are open too. It has become apparent to you that the train is headed for a ravine and the bridge is out. Your only options are A and B. Which option is safest?

A) Jump out of a side exit door, hit the ground and roll, keeping your momentum rolling forward in the direction of the train.

B) Sprint toward the rear of the train, trying your best to approximate 12mph, and jump out of the back.
This one's easy for me... Jump out the side door. Why? Because there's less distance to it, and frankly, I want to reduce the risk of falling down when I'm trying to "approximate" 12 mph, and end up riding the damn thing to the bottom of the cliff.

Besides, it's 12 mph.. I've crashed on a mountain bike going faster than that! Avg. human walks at 5 mph, so 12 isn't really any big deal at all...

[Finger]
Posted by: Trihead

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:49 PM

12mph is what 5 min per mile, I am guessing there isn't anyone on the this board running sub 5's.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:50 PM

Quote:
Originally posted by Xterrian:
I read every response in this thread and can't find the devil's advocate reference. Could you point me towards the page number it is on?
A brief summary of some things I have said....

Page 10...
I wasn't referring to the tires or anything related to the wheels in that particular comment.

I also believe that I was wrong for saying definitively that the aircraft in this scenario would not obtain flight.

I do however see a problem with the scenario. I can't say it would or would not take flight at this point.

We can discuss it further tomorrow or another time.


Page 19...
If they are serving chicken for dinner, the plane will definitely fly.

If that horrible airline vegetable lasagna is on the menu, it will not take off.


Page 19...
You obviously haven't read the entire thread.

I am no longer dedicated to the position that it will not fly.


Page 21...
Let me play devils advocate here Rock....

I was out of the thread for a number of pages and people were beating on a few other users.

I'm neutral on the plane scenario. Will that piss some people off?
Posted by: TravelingFool

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 01:56 PM

Quote:
Originally posted by Trihead:
12mph is what 5 min per mile, I am guessing there isn't anyone on the this board running sub 5's.
there's a TON of people on this board who could run that fast for a short distance.

I was curious how many people would think it would be a bad idea to run out the back. If I could sprint 12mph out the back door, I'd essentially "plop" down in place on the tracks since my relative speed to the ground would be zero.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:02 PM

Quote:
Originally posted by Trihead:
12mph is what 5 min per mile, I am guessing there isn't anyone on the this board running sub 5's.
Except that this would be a sprint, not a marathon where 12mph equates to a 6.8 40 time (ver attainable). Even if you didn't achieve that speed, you would only experience the difference between your sprint and the 12mph which would be at worst similar to stepping off a moving sidewalk.
Now, if proximity is an issue (ravine is coming up quick) then maybe a sprint down the train won't work and at worst you get some rock burns and such from a dive out the side (sprinters can maintain 20mph speeds so a fall wouldn't be too severe from 12mph).

This situation needs worse consequences than 12mph to be a viable debate.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:05 PM

My thought is that even if I match the 12 mph - I will be falling straight down.

The trick of course would be how to DO that...as, if it were going to work that way....I'd see the exact same thing outside through the train car window as I ran, and the train ran out from under me.

laugh

I have NO idea how I'd run in place as the train went out from under me, especially considering I only have one leg, etc.

OK - So even if I DID manage to stay in place as the train rolled out from under me...I'd fall straight down...maybe 4'? Onto a rail road track...

If I went out the side and rolled, I would contact the ground at around 12 mph...but, rolling would absorb most of the impact.

laugh
Posted by: Trihead

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:06 PM

Smart people scare me.

Yeah a sub 5 sprint would be pretty easy and I realized that...just stirring the pot to avoid work.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:10 PM

Another (probably futile) attempt at an analogy.

There's a car in a northbound lane traveling at 60 mph, and a car in the southbound lane traveling at 60 mph. They have no effect on each other.

Now suppose the highway is perfectly straight and the southbound car has an enormous vertical board attached to the left side, miles long. The northbound car has a set of non-geared, free-spinning wheels on its left side. Supposing that both cars drive straight and the wheels remain in constant contact with the board, what happens

Each car travels at 60 mph, the wheels on the side travel at a rate of 120 mph. If they have a standing start and accelerate at the same rate, they still would be able to move in opposite directions and the free-spinning wheels would spin at twice the rate of the drive tires.

Hence, the cars are not "equal and opposite forces" because they are not opposing, just like the conveyor is not opposing the plane.
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:10 PM

Quote:
Originally posted by Trihead:
Smart people scare me.
You feel fairly safe here, don'tcha?
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:16 PM

Quote:
Originally posted by NY Madman:
[QUOTE]
I'm neutral on the plane scenario. Will that piss some people off?
Neutral?

You mean you STILL don't know it would fly, but are just trying to avoid pissing people off?

By pretending to think it would NOT fly?

[Freak]

Still, somehow, that's endearing.

laugh
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:20 PM

Side note...

I do spin control for some clients, and one of the things I advise is to NOT throw charts at people, as despite their factual weight and clearness of case, etc...the average person perceives them as chicken scratch, or a foreign language...

Typically, analogies work most of the time, avoiding technobabble.

On this thread...we have analogy after analogy, equation after equation...and the dog is still looking at the finger instead of where its pointing to.

laugh
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:26 PM

Oops. Forgot to add another reason I'd go out the side door instead of the rear.

Railroad ties aren't very good on ankles... I'd rather scratch up my leg on the brush than twist and/or break an ankle on a railroad tie... No thank you. Not to mention the very real possibility of hopping off the back, stepping down ackward, and smacking my face on an extremely hot and extremely hard railroad track!
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:36 PM

Who said there was brush along the sides of the tracks? [Finger]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:37 PM

Quote:
Originally posted by Trihead:
12mph is what 5 min per mile, I am guessing there isn't anyone on the this board running sub 5's.
I used to be able to run a 5 minute mile. I can still run a 7 minute mile though. But this is for a short burst. I was a sprinter in high school. Used to be able to run 200m in 23 seconds. That's what....1600m in 184 seconds or a mile in 3 minutes 4 seconds which is approximately 19 mph... Granted, I couldn't keep that pace for a whole mile if I had to, but for short distances I could do it with no problem...

That being said, I'd hang out the side, get up to speed with the train and slow at my own pace once I let go of the train....
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:44 PM

TJ, JeffW and porsche996 all agree on this one....

S-C-A-R-Y

[Uh Oh !]

Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:44 PM

I don't suppose anyone tried the emergency brakes?

laugh
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:46 PM

Quote:
Originally posted by JeffW:
TJ, JeffW and porsche996 all agree on this one....

S-C-A-R-Y

[Uh Oh !]

[Shudder] Urban sprawl [/Shudder]
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 02:59 PM

Quote:
Originally posted by JeffW:
TJ, JeffW and porsche996 all agree on this one....

S-C-A-R-Y

[Uh Oh !]

Yet Jeff still was the only dick about it until Randall came in. [Huh?]

I am still of the middle. No one here has absolutely convinced me it will 100% every time take off. To much variables not explained in the scenario. I am not 100% convinced it would stay on the ground either.

I am of the wheels blow up or wheel bearing melts runway run out of room type of guy. I know the plane will move but will the conveyor give enough counter friction to mess up the flight. Depends on me the size of plane and runway which is not laid out.

Small plane long runway I am of the fly theory.

Big plane small runway (small yet large enough for the big plane to take off under normal circumstances) no fly.

That is my opinion.

Jeff you cannot prove you are 100% right. I agree the plane moves. So shut up about how it moves. I am tired of seeing someone else's work in your argument.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 04:14 PM

Interesting...so the only remaining reservations come down to:

1. If the plane's wheels can freely rotate against nothing but the normal resistance of their own bearings at double the minimal take off speed w/o over heating and shear welding, etc...before the plane can take off..

and

2. The plane's tires will similarly survive long enough to allow take off, despite double the minimum take off speed.

While beyond the apparent scope of the problem's given...its at least something that is potentially able to be confirmed....if we knew the weight of the plane, its minimum take off speed, its appropriate take off distance, and the specs for its tires, and so forth....

I'm pretty sure that these parameters are well beyond the scope of the simple logic test...and, I'm sure...NOT intended to be part of the question...as, if it were, they could simply say its a Boing Boing 69 E or whatever, and expect us to research its specs, etc.

laugh

So - With the given that the question is intended to evaluate our ability to realize that the conveyor belt would not prevent the plane from taking off, (Or at least to evaluate our ability to evaluate IF the conveyor belt would prevent take off), rather than our ability to research tire speed ratings and take off specs for every known tire and every known plane combination....

Can you therefore conceed that, assuming the above given, that the plane would therefore take off?

(And I will conceed that I have not researched every known tire/plane combination, and then determined WHICH one was on the belt, etc...)
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 05:01 PM

Quote:
Originally posted by Paul H:
...Jeff you cannot prove you are 100% right. I agree the plane moves. So shut up about how it moves.....
Stop being a schmuck.

Go take High School Physics.

or:

Disprove F=ma

or:

[Save the fine unicorns]

...

Over and out.

Quote:
Originally posted by TJ:
Interesting...so the only remaining reservations come down to:....
I agree 100%.

Interesting but out of scope.

Quote:
Originally posted by TJ:
[QB.....[Shudder] Urban sprawl [/Shudder]....[/QB]
Not everybody can afford to live in Mercer County! [Finger]

....

Damn, this thread has been a helluva post-whoring opp!!! [LOL]

I'll try to make this my last post!

[Too much XOC]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 05:10 PM

i choose option B on the train. tuck n roll. instead of jumping out the back and landing on the tracks, i would roll out the train and keep the same speed and slow down. if you run out the back, you will leap and probably fall anyway since you cant be like wile coyote and run off a clif, stop and fall straight down. and how can you know you're running exactly 12mph? what if the train has no windows? how can you judge your speed? if it had windows, you could look outside and find something stationary to keep up with. and you only said the side doors were open, what if the back one was locked? there's alot to consider.
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 05:24 PM

Quote:
Originally posted by JeffW:
Damn, this thread has been a helluva post-whoring opp!!!
x2. I think I added 50 posts to my count. [Sleep]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 02/01/07 08:20 PM

ok, the plane will fly. finally there were a couple of explanations that made sense. i got too hung up in finding flaws in the 'can fly' group. almost everyone who said it can fly, said it for the wrong reasons. it is a 50/50 guess....and no i couldn't be bothered to read all the pages of dribble either. lol

i am man enough to admit when i am wrong. [Finger]

what's really sad is that in just one week there are more posts in this thread than the phat chick friday thread. [Freak]
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 04:14 AM

I think its because people lingered over each post longer in the Phat Thread...and were more interested in absorbing the information other's posted, than they were in presenting new information.

laugh
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 05:46 AM

Quote:
Originally posted by Paul H:

I am still of the middle. No one here has absolutely convinced me it will 100% every time take off. To much variables not explained in the scenario. I am not 100% convinced it would stay on the ground either.

I am of the wheels blow up or wheel bearing melts runway run out of room type of guy. I know the plane will move but will the conveyor give enough counter friction to mess up the flight. Depends on me the size of plane and runway which is not laid out.

Small plane long runway I am of the fly theory.

Big plane small runway (small yet large enough for the big plane to take off under normal circumstances) no fly.

That is my opinion.

Jeff you cannot prove you are 100% right. I agree the plane moves. So shut up about how it moves. I am tired of seeing someone else's work in your argument.
Don't worry about what side of the debate you were on. The question itself is intentional designed to immediately confuse people.

Plus some on the board have seen the question before.

Jayz is also correct when he says many of us spent a lot of time trying to prove the theories of others wrong.

This question has confused people with some of the most advanced scientific degrees. What I was amazed about was the amount of pilots who claim that the plane could not take off....and still do.

It probably all comes down to whether you immediately look at things in practical terms or theoretical terms.

You are correct though when you say there will be problems with the wheels. While looking at another site that claimed to have a lot of pilots, there were guys who gave data regarding the amount of stress and abuse the wheels could take. A standard passenger airliner couldn't take the abuse and stress placed on the wheels. They would come apart and the plane would crash... hence no takeoff.

So there was a certain amount of suspension of disbelief involved with the scenario.

The scenario was also good at something else. It kind of proved who here on XOC is capable of civil and reasonable debate and who is not.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 05:50 AM

Quote:
Originally posted by NY Madman:
The scenario was also good at something else. It kind of proved who here on XOC is capable of civil and reasonable debate and who is not.
I would say that all of those involved in the actual debate itself handled themselves quite well. It never really got out of hand to the point of being moved to the ALR. Tempers may have flared, but all-in-all, everyone remained civil.
Posted by: airbutchie

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 06:47 AM

Quote:
Originally posted by Hawk:
Quote:
Originally posted by NY Madman:
[b]The scenario was also good at something else. It kind of proved who here on XOC is capable of civil and reasonable debate and who is not.
I would say that all of those involved in the actual debate itself handled themselves quite well. It never really got out of hand to the point of being moved to the ALR. Tempers may have flared, but all-in-all, everyone remained civil.[/b]
Fuck that shit... I can't believe this thread has overtaken the same amount of input (in less time) as the "Phat" thread!!! frown

Hhehehehehhe... Now go post on the Phat thread and... and.... and... Aw shit, never mind... Hehheheehehe...

- Air B wink
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 12:07 PM

Yeah, that is kinda pathetic to see how fast this thread grew as opposed to the "phat chicks friday". frown
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 01:46 PM

Quote:
Originally posted by JeffW:
Quote:
Originally posted by Paul H:
[b] ...Jeff you cannot prove you are 100% right. I agree the plane moves. So shut up about how it moves.....
Stop being a schmuck.

Go take High School Physics.

or:

Disprove F=ma

or:

[Save the fine unicorns]

...

Over and out.

Quote:
Originally posted by TJ:
Interesting...so the only remaining reservations come down to:....
I agree 100%.

Interesting but out of scope.

Quote:
Originally posted by TJ:
[QB.....[Shudder] Urban sprawl [/Shudder]....[/b]
Not everybody can afford to live in Mercer County! [Finger]

....

Damn, this thread has been a helluva post-whoring opp!!! [LOL]

I'll try to make this my last post!

[Too much XOC] [/QB]
I am not trying to disprove how the plane moves jackass. Get your head outta your ass and take a reading class or something.
Posted by: Paul H

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 01:47 PM

Quote:
Originally posted by AHTOXA:
Yeah, that is kinda pathetic to see how fast this thread grew as opposed to the "phat chicks friday". frown
Not really. Was a good debate that remained civil. Good points made by all. You can only look at so many titties [Laughing]
Posted by: GrayHam

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 02:00 PM

Quote:
Originally posted by Paul H:
You can only look at so many titties [Laughing]
You know how I know you're gay?

Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 02:05 PM

Holy shit. 52+ pages. I feel dumber for actually having read the bulk of this.

The plane question is designed to confuse based on anyone's interpretation of the word speed.

If the plane's speed relative to the treadmill was equal, the plan would appear to not be moving and would not take off.

If the plane's speed relative to the air and the stable ground was equal to the treadmill's speed, aside from having to overcome minimal friction at the wheels spinning twice the speed of the plane, it takes off.

Not that all that hasn't been said about 700 times....

Now...in order to maintain airspeed velocity, an African swallow has to beat its wings 37 times a second....Am I right?
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 02:16 PM

BTW, I never understood the hamster references. Hamsters can't fly unless chucked across the room in a fit of rage.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 02:53 PM

Quote:
Originally posted by Desert_Rat:
Holy shit. 52+ pages. I feel dumber for actually having read the bulk of this.

The plane question is designed to confuse based on anyone's interpretation of the word speed.

If the plane's speed relative to the treadmill was equal, the plan would appear to not be moving and would not take off.

If the plane's speed relative to the air and the stable ground was equal to the treadmill's speed, aside from having to overcome minimal friction at the wheels spinning twice the speed of the plane, it takes off.

Not that all that hasn't been said about 700 times....

Now...in order to maintain airspeed velocity, an African swallow has to beat its wings 37 times a second....Am I right?
Laden, or unladen?

laugh

The problem is not KNOWING what speed means in the context...as how quickly you are moving your wheels or legs around, unless you are moving proportionally, is not your speed.

Moving AS IF you are going a speed, is not your speed....yet, some people could not get their head's around that.

(I'm stuck in a ditch, spinning my tires...the speedometer SAYS I'm going 40 mph....my tires are turning AS IF I'm going 40 mph....what's my speed?)

The other impediment was the addition of details obviously not part of the posed problem...like tire speed ratings, etc....while missing the fundamental issue.

Its as if the people hear a simple concept based brain teaser, such as ...."If a tree falls in the woods, but there's nobody around to hear it, does it make a noise?"

...And focus on how soft the surrounding trees might be, what time of year it is, how tall the tree might be, the slope of the terrain, wind direction, speed and weather conditions, the type of wood, its density, what made it fall, how old is it, could it have been dropped from a plane into a lake which held a flooded forest, etc...instead of on what noise is, and its relation to observation.

laugh

IE: Instead of using logic to solve the presented question, they focus upon unanswerable and irrelevant potential complications.
Posted by: Chris Mc

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 03:16 PM

Where are Lizz's nudie pics? I was stranded in a snowstorm outside Albuquerque on I-40 for a few days and missed this thread...
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 03:28 PM

Quote:
Originally posted by NY Madman:
Quote:
Originally posted by Paul H:

[b]I am still of the middle. No one here has absolutely convinced me......
Don't worry about what side of the debate you were on. The question itself is intentional designed to immediately confuse people....[/b]
That is 100% true. The first time I pondered this question I momentarily thought "no". But as I thought deeper, I realized the irrelevance of the belt.

I posed this question to both of my brothers and they both gave the correct answer. One is a music teacher and the other is not degreed but lightly technical. TJ asked some non-technical people who were able to come up with the correct answer, also.

Some people can reject their initial hangups and swallow the pride of being initially wrong to reach the sensible conclusion.

Anybody who claims to be an engineer who does not understand this question should be ashamed of themselves. This is a very simple problem which requires very little technical knowledge, but (apparently) plenty of common sense.

Quote:
Originally posted by NY Madman:

...You are correct though when you say there will be problems with the wheels. While looking at another site that claimed to have a lot of pilots, there were guys who gave data regarding the amount of stress and abuse the wheels could take. A standard passenger airliner couldn't take the abuse and stress placed on the wheels. They would come apart and the plane would crash... hence no takeoff........
That is not true.

Aircraft tires and landing gears are required (by the FAA) to be tested to a factor of safety of 1.5 for 200 cycles. So that means a 200 mph tire and bearing should easily be able to withstand some extra wheelspin. Additionally, taking off is much less stressful than landing due to the lack of impact. The plane is also achieving lift as it achieves airspeed, thus lessening the load on the landing gear, wheel and tire. Tires being tested do not have this advantage because they are tested under full load by a machine.

Regardless, that's just a copout by somebody who doesn't want to embrace the a different answer because they feel they'll lose face by admitting it.

.....

It sounds like most people have taken the time to read what has been posted and come to terms with the simple answer.

[ThumbsUp]

.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 03:34 PM

Quote:
Originally posted by Chris Mc:
Where are Lizz's nudie pics? I was stranded in a snowstorm outside Albuquerque on I-40 for a few days and missed this thread...
There in there somewhere. I forget which page though. Just read through the entire thread I'm sure you'll find them.
wink
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 03:56 PM

I like the one with the pony.

laugh
Posted by: MidnightX

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 05:59 PM

Oh you like that one, huh? Wait 'til you see the one with the hot pink feather boa!
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 06:02 PM

I admit I didn't read all 52 pages, just 15, so maybe it was mentioned in the remaining pages, but I just want to add a few things.

Definitions
  • wind speed: speed of the air relative to the plane, 100mph wind speed means the wind is moving 100mph across the wings.
  • Global Perspective: This is the perspective being observed from the outside world, an example would be some one not standing on the tread mill watching the plane try to take off
  • Scenario perspective: Perspective from the plane, relative to the treadmill
  • Relative speed: speed of the treadmill as observed from the Scenario perspective, aka the plane
  • Absolute speed: speed of the treadmill as observed from the Global perspective.

Assumptions
  1. conveyor belt only moves the ground below the plane, not the air around the plane, and moves in the opposite direction the plane is trying to move.
  2. weather is ideal and wind is calm (0MPH).
  3. group speed = air speed since the plane is on the ground.
  4. wheels are freewheeling, ie there is little if any rotational friction between the wheel and the object it is attached to.
  5. plane would be able to take off if the tread mill was kept stationary.

Facts
  1. lift if determined by the wind speed over the wings.
  2. Thrust produced by the engines (prop or turbine) applies a force against the air.
  3. Thrust is dependent on wind speed, the higher the wind speed the lower the thrust, and vice versa.
  4. Force from the thrusters is what propels the plane and not the wheels.
  5. air is a fluid

ProofThe tread mill doesn't effect the speed of the wind:
Lets just say for the sake of argument that the tread mill does move the air around the plane at the same rate as the treadmill. If the plane is trying to go down the run way and is stationary from the global perspective the the wind will increase in speed as it passes over the wings. This equivalent wind speed will cause enough lift for the plane to take off, this scenario is essentially the same as if it was going down a normal run way. So we know that the tread mill does not effect the planes air speed because if it did it would be able to lift off.

If we look at a force diagram, the engines produces thrust forward by "throwing" air backwards and pushes against the air already present which produces a force pointing in the forward direction, this is because of newtons third law, equal and opposite reaction. So a force backwards produces a force forwards. The ONLY way for the plane to stand still from the global perspective is to have another force applied to the plane that would counter act this forward force, other wise the plane will move forward since F=ma (Force = mass X acceleration). Here are some possible options that could produce the required force to prevent:
  1. Air resistance, which is determiend by surface area and wind speed
  2. Excessive friction between the plane and the ground, for example Wheel Brakes are applied, or wheels are not present wheels.
  3. Plane is chained to a solid anchor

As seen by the fact that a high enough wind speed would creates lift and allow the plane to take off we can rule out wind, as enough wind the keep the plane stationary would surely allow it to take off.

Now if we make the assumption that the plane would be able to take off if the treadmill is kept still like a normal run way we can safely assume that plane has little resistance relative to the force generated by the thrusters. And that there is nothing nothing else binding the plane such as it being anchored. So we are safe to assume the airplane is not held by any external constraints.

Plus we know the wheel brakes are not applied because otherwise the plane would not be able to move anyways and the question is a trick question smile

So without any kind of constraints it is impossible for a plane to not move from a global perspective when it is at full throttle because there is no resistance to the forward force and because thrust and wind speed are inversely proportional therefor there will be a force acting on the plane moving it forward increasing the wind speed over the wing allowing for take off.

... In summary
The planes method of propulsion acts on the global perspective and not on the relative perspective allowing it to move in the global perspective as well, even if the wind was acted form a relative perspective it would be able to take off since it would have a high enough wind speed.

so yeah, the plane can take off regardless...
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 06:32 PM

Quote:
Originally posted by Chris Ritchey:

... In summary
The planes method of propulsion acts on the global perspective and not on the relative perspective allowing it to move in the global perspective as well, even if the wind was acted form a relative perspective it would be able to take off since it would have a high enough wind speed.

so yeah, the plane can take off regardless...
Cool, five trucks to you! Love the format, it must have taken you a while to punch that out. [Laughing]

Another for the Flies Club. Lord of the flies Kill the PIG! [Too much XOC]

ETA - Whoo Who, 53 and counting! [Argue]
Posted by: XPLORx4

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 06:55 PM

How many days do you think it will take before this thread is no longer on the first page of "The Club House"? [Laughing]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 07:01 PM

With all the CF'ers either enlightened or chased out, this is probably as far at this thread goes, maybe one more page.

I'm still not sure where Madman stands, though. His posts mentioned something about "neutrality" and being a "devil's advocate," and I never heard him say (since he proclaimed "neutrality") that the plane would fly. Maybe he did, but I've missed it. Bluesky, I think, is still "sticking to his guns".

But honestly, how much farther does this thread need to go? I mean, there's probably a dozen or two different analogies and tons of redundancy.
Posted by: TJ

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 07:16 PM

Most likely, as each hold-out gets his Eureka Moment, slaps his forehead...realizing the real factors...he will probably just clam up, and not post again.

Mad may be an exception, because I believe he really feels a need to show open mindedness....the kindler, gentler Madman, etc.

laugh

Otherwise....mor mumbling about tire ratings and so forth, to act like OTHER THAN THAT, they got it...etc.

laugh
Posted by: Rockaholic

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 07:22 PM

I'm not sure that madman doesn't actually get it.

After reading his post about playing Devil's advocate (and then rereading the posts after he posted that) I think he might understand but have been posting just for the sake of argument.

Initially when I read that "devil's advocate" I thought it was just about my "carrier" scenario - which in and of itself was flawed.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 10:00 PM

I was disappointed that this thread was not at the top of the page. So, do I get a present for being with the "will fly crowd." LOL.
Posted by: NY Madman

Re: Know that if you do not post in this thread today the human race may cease to exist - 03/01/07 10:35 PM

People are back to talking about the plane? [Huh?]

It should fly.



............



"The flight of Mr. Robert Wilson has ended now, a flight not only from point A to point B, but also from the fear of recurring mental breakdown. Mr. Wilson has that fear no longer, though, for the moment, he is, as he has said, alone in this assurance. Happily, his conviction will not remain isolated too much longer, for happily, tangible manifestation is very often left as evidence of trespass, even from so intangible a quarter as the Twilight Zone."
Posted by: Origami Gangsta

Re: Know that if you do not post in this thread today the human race may cease to exist - 04/01/07 02:46 AM

Jebus, I'm gone for a few days, and this entire place goes to shit with lame ass threads.

Christ on a stick. [Finger]
Posted by: BlueSky

Re: Know that if you do not post in this thread today the human race may cease to exist - 04/01/07 05:44 AM

Quote:
Originally posted by Fried Rice Mofo:
Jebus, I'm gone for a few days, and this entire place goes to shit with lame ass threads.

Christ on a stick. [Finger]
How did that happen without you ?? [LOL]
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 04/01/07 06:17 AM

if you tie a rope to the tail of the plane and to a phone pole, and the treadmill turns the wheels of the plane above the stall speed of the plane, will it fly?

wink
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 04/01/07 06:45 AM

If the treadmill is the one moving the plane wheels, you need to attach the rope to the nose, not the tail, otherwise the plane will just back up in the phone pole.
Posted by: Anonymous

Re: Know that if you do not post in this thread today the human race may cease to exist - 04/01/07 07:13 AM

Quote:
Originally posted by XterraAdam:
if you tie a rope to the tail of the plane and to a phone pole, and the treadmill turns the wheels of the plane above the stall speed of the plane, will it fly?

wink