shrockworks xterraparts
XOC Decal
Newest Members
Glim, ChossWrangler, Patman, ChargedX, Randy Howerton
10084 Registered Users
Recent Posts
The NEXTerra April Fools @ AOAA!
by Tom
12/04/18 11:46 AM
Shout Box

Who's Online
0 registered (), 65 Guests and 1 Spider online.
Key: Admin, Global Mod, Mod
Page 4 of 43 < 1 2 3 4 5 6 ... 42 43 >
Topic Options
Rate This Topic
#165787 - 28/12/06 01:19 PM Re: Know that if you do not post in this thread today the human race may cease to exist
MidnightX Offline
Member
*****

Registered: 08/03/01
Posts: 3745
Loc: Jacksonville, Florida
Everyone thank me for starting this thread! At least most of you are enjoying it.

Top
#165788 - 28/12/06 01:22 PM 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 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.

Top
#165789 - 28/12/06 01:25 PM 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 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.

Top
#165790 - 28/12/06 01:31 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 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

Top
#165791 - 28/12/06 01:34 PM 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
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.
_________________________
Does anybody remember laughter?

Top
#165792 - 28/12/06 01:39 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 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

Top
#165793 - 28/12/06 01:39 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


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.

Top
#165794 - 28/12/06 01:45 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 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).

Top
#165795 - 28/12/06 01:48 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


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

Top
#165796 - 28/12/06 01:50 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 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

Top
#165797 - 28/12/06 01:52 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 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.

Top
#165798 - 28/12/06 01:54 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


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

Top
#165799 - 28/12/06 01:55 PM 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
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.
_________________________
4x4 in uppercase is $X$!!!
1997 R50: VG33E/RE4R01A/TX10/3.7/R200A/ARB/4.636/H233B/ARB/4.636/321150R15

Top
#165800 - 28/12/06 01:56 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 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

Top
#165801 - 28/12/06 01:57 PM 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 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)?

Top
#165802 - 28/12/06 01:57 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


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!!

Top
#165803 - 28/12/06 02:01 PM 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 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.

Top
#165804 - 28/12/06 02:01 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


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.

Top
#165805 - 28/12/06 02:07 PM 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
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.
_________________________
4x4 in uppercase is $X$!!!
1997 R50: VG33E/RE4R01A/TX10/3.7/R200A/ARB/4.636/H233B/ARB/4.636/321150R15

Top
#165806 - 28/12/06 02:08 PM Re: Know that if you do not post in this thread today the human race may cease to exist
TravelingFool Offline
Member

Registered: 17/10/00
Posts: 6013
Loc: Prior Lake, MN
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.
_________________________
kjw &
the PNUTMNM

The liver is evil, and must be punished...

Top
#165807 - 28/12/06 02:29 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Anonymous
Unregistered


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

Top
#165808 - 28/12/06 02:43 PM 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 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.

Top
#165809 - 28/12/06 02:54 PM Re: Know that if you do not post in this thread today the human race may cease to exist
TravelingFool Offline
Member

Registered: 17/10/00
Posts: 6013
Loc: Prior Lake, MN
For the love of God... The plane would fly. Period.
_________________________
kjw &
the PNUTMNM

The liver is evil, and must be punished...

Top
#165810 - 28/12/06 03:18 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Smith Offline
Member

Registered: 19/07/01
Posts: 2032
Loc: Winston-Salem, NC
Is this a smoking flight or a non-smoking flight? Cause it will make a load of difference.

Top
#165811 - 28/12/06 03:19 PM Re: Know that if you do not post in this thread today the human race may cease to exist
Paul H Offline
Member

Registered: 23/08/01
Posts: 4757
Loc: Mt. Zion, IL
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?
_________________________
2001 Super Black XE R.I.P. 09/05/06
My Blog

Top
Page 4 of 43 < 1 2 3 4 5 6 ... 42 43 >


Moderator:  RedX, RiNkY 

shrockworks xterraparts
XOC Decal