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#617750 - 01/01/07 11:39 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


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.

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#617751 - 02/01/07 12:57 AM Re: Know that if you do not post in this thread today the human race may cease to exist
NY Madman Offline
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Registered: 09/05/02
Posts: 5232
Loc: Florida
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?

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#617752 - 02/01/07 01:07 AM Re: Know that if you do not post in this thread today the human race may cease to exist
NY Madman Offline
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Registered: 09/05/02
Posts: 5232
Loc: Florida
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...


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#617753 - 02/01/07 01:46 AM Re: Know that if you do not post in this thread today the human race may cease to exist
Rockaholic Offline
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Registered: 18/02/02
Posts: 1632
Loc: Reading, MA
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?
_________________________
Jeffrey
I'm just trying to put my tires on the rocks of life.

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#617754 - 02/01/07 02:35 AM Re: Know that if you do not post in this thread today the human race may cease to exist
NY Madman Offline
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Registered: 09/05/02
Posts: 5232
Loc: Florida
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.

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#617755 - 02/01/07 02:58 AM Re: Know that if you do not post in this thread today the human race may cease to exist
Rockaholic Offline
Member

Registered: 18/02/02
Posts: 1632
Loc: Reading, MA
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.
_________________________
Jeffrey
I'm just trying to put my tires on the rocks of life.

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#617756 - 02/01/07 03:02 AM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


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.

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#617757 - 02/01/07 04:19 AM Re: Know that if you do not post in this thread today the human race may cease to exist
NY Madman Offline
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Registered: 09/05/02
Posts: 5232
Loc: Florida
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.

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#617758 - 02/01/07 04:54 AM Re: Know that if you do not post in this thread today the human race may cease to exist
NY Madman Offline
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Registered: 09/05/02
Posts: 5232
Loc: Florida
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.

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#617759 - 02/01/07 05:13 AM Re: Know that if you do not post in this thread today the human race may cease to exist
Rockaholic Offline
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Registered: 18/02/02
Posts: 1632
Loc: Reading, MA
_________________________
Jeffrey
I'm just trying to put my tires on the rocks of life.

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#617760 - 02/01/07 05:56 AM Re: Know that if you do not post in this thread today the human race may cease to exist
NY Madman Offline
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Registered: 09/05/02
Posts: 5232
Loc: Florida
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.

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#617761 - 02/01/07 07:29 AM Re: Know that if you do not post in this thread today the human race may cease to exist
TJ Offline
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Registered: 08/03/01
Posts: 7756
Loc: Lawrenceville, NJ, USA
"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.
_________________________
- TJ

2001 Xterra '03 VG33, SE 5 spd, 305/70/16's, Revolvers, UBSkidderz, Doubled AAL's, 3"SL/2"BL, winch/bumpers, skids, sliders, OBA, Snorkel, pine stripes....

Friends don't let friends drive stock.

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#617762 - 02/01/07 07:35 AM Re: Know that if you do not post in this thread today the human race may cease to exist
GrayHam Offline
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Registered: 17/04/01
Posts: 8849
I ate the last of the Shreddies this morning. With sliced banana.

Damn.
_________________________
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#617763 - 02/01/07 07:37 AM Re: Know that if you do not post in this thread today the human race may cease to exist
BlueSky Offline
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Registered: 17/08/00
Posts: 2286
Loc: Georgia
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.

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#617764 - 02/01/07 07:42 AM Re: Know that if you do not post in this thread today the human race may cease to exist
GrayHam Offline
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Registered: 17/04/01
Posts: 8849
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.
_________________________
Does anybody remember laughter?

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#617765 - 02/01/07 08:20 AM Re: Know that if you do not post in this thread today the human race may cease to exist
NY Madman Offline
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Registered: 09/05/02
Posts: 5232
Loc: Florida
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.

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#617766 - 02/01/07 08:25 AM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


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?

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#617767 - 02/01/07 08:27 AM Re: Know that if you do not post in this thread today the human race may cease to exist
TJ Offline
Member
*****

Registered: 08/03/01
Posts: 7756
Loc: Lawrenceville, NJ, USA
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
_________________________
- TJ

2001 Xterra '03 VG33, SE 5 spd, 305/70/16's, Revolvers, UBSkidderz, Doubled AAL's, 3"SL/2"BL, winch/bumpers, skids, sliders, OBA, Snorkel, pine stripes....

Friends don't let friends drive stock.

http://www.gifsoup.com/view/501230/tj-tackling-crawlers-ridge-o.gif

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#617768 - 02/01/07 08:28 AM Re: Know that if you do not post in this thread today the human race may cease to exist
TJ Offline
Member
*****

Registered: 08/03/01
Posts: 7756
Loc: Lawrenceville, NJ, USA
"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.
_________________________
- TJ

2001 Xterra '03 VG33, SE 5 spd, 305/70/16's, Revolvers, UBSkidderz, Doubled AAL's, 3"SL/2"BL, winch/bumpers, skids, sliders, OBA, Snorkel, pine stripes....

Friends don't let friends drive stock.

http://www.gifsoup.com/view/501230/tj-tackling-crawlers-ridge-o.gif

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#617769 - 02/01/07 08:34 AM Re: Know that if you do not post in this thread today the human race may cease to exist
GrayHam Offline
Member

Registered: 17/04/01
Posts: 8849
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.
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Does anybody remember laughter?

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#617770 - 02/01/07 08:41 AM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


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.

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#617771 - 02/01/07 08:58 AM Re: Know that if you do not post in this thread today the human race may cease to exist
TJ Offline
Member
*****

Registered: 08/03/01
Posts: 7756
Loc: Lawrenceville, NJ, USA
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
_________________________
- TJ

2001 Xterra '03 VG33, SE 5 spd, 305/70/16's, Revolvers, UBSkidderz, Doubled AAL's, 3"SL/2"BL, winch/bumpers, skids, sliders, OBA, Snorkel, pine stripes....

Friends don't let friends drive stock.

http://www.gifsoup.com/view/501230/tj-tackling-crawlers-ridge-o.gif

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#617772 - 02/01/07 09:01 AM Re: Know that if you do not post in this thread today the human race may cease to exist
XPLORx4 Offline
Member

Registered: 23/03/01
Posts: 1906
Loc: San Jose, CA
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 <--.)
_________________________
4x4 in uppercase is $X$!!!
1997 R50: VG33E/RE4R01A/TX10/3.7/R200A/ARB/4.636/H233B/ARB/4.636/321150R15

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#617773 - 02/01/07 09:14 AM Re: Know that if you do not post in this thread today the human race may cease to exist
NY Madman Offline
Member
*

Registered: 09/05/02
Posts: 5232
Loc: Florida
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.

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#617774 - 02/01/07 09:27 AM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


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

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