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DPChallenge Forums >> General Discussion >> Plane and a Treadmill
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12/06/2006 11:14:02 AM · #1
An interesting problem:

A plane equipped with fixed horizontal engines and wheel landing gear is placed on a huge treadmill runway. The treadmill has a clever design and always matches the speed of the plane, but runs in the opposite direction. Will the plane take off and fly or not?

Any takers?
12/06/2006 11:17:57 AM · #2
I'm guessing not. The important part is the speed of the air over and under the wing. This seems to not be affected by the treadmill design.

Even if the plane somehow did get off, I'm guessing it would stall immediately since now the wheels are not in contact with the treadmill and we are left asking ourselves if a plane just sitting there in the air can "fly"...
12/06/2006 11:19:14 AM · #3
I would postulate that it would not take off as what causes a plane to take off is the different rate of travel of the air above and below the surface of the wings. The movement of the air is caused by the engines propelling the plane through the air, so if the plane remains stationary in relationship to the surrounding air, there will be no lift.
12/06/2006 11:19:52 AM · #4
Yes it will.

The plane moves relative to the air, not the ground. Thus the planes wheels will just turn a lot faster.
12/06/2006 11:24:44 AM · #5
What LoudDog said. Yes
12/06/2006 11:33:16 AM · #6
No! because what make a jet/plane airborne is the wind going over the the wing making an updraft under the wing giving it lift. That's why most take offs are into the wind and landings with the wind.

12/06/2006 11:37:35 AM · #7
436 posts having the same argument. physorg.com what a wonderful topic. I can't wait to find out if the plane will fly or not. LOL
12/06/2006 11:38:34 AM · #8
And y'll think all that engine thrust is going no where?
12/06/2006 11:39:51 AM · #9
Originally posted by LoudDog:

Yes it will.

The plane moves relative to the air, not the ground. Thus the planes wheels will just turn a lot faster.


As the plane is on a treadmill it is stationary with respect to the ground. If you assume no wind, the air is stationary relative to the ground. Since the difference in air pressure over the top and the bottom of the wing is what generates lift, if no air is moving over and under the wings there will be no lift and hence the plane cannot take off.
12/06/2006 11:40:06 AM · #10
The original question does not say which way the treadmill is running, it only says it matches the speed of the plane. Therefore it could be turning with the plane making it propel twice as fast down the runway.
12/06/2006 11:41:14 AM · #11
The treadmill has a clever design and always matches the speed of the plane, but runs in the opposite direction
12/06/2006 11:41:29 AM · #12
No air flow, no Bernoulli's principle, no lift. No take off.

This assumes though that the treadmill moving keeps the plane stationary. The engine thrust would keep the plane traveling at the same speed as the treadmill.

When I run on a treadmill, the faster I turn up the treadmill, the more effort I expend to stay in the same place. There's never any airflow produced though.

While planes dont' take off due to driven wheels against the ground, afaik the wheels turn relative to the ground speed - otherwise planes would skid down the runway prior to take-off.


Message edited by author 2006-12-06 11:43:16.
12/06/2006 11:41:30 AM · #13
The plane will not take off - the wheels of the plane will be spinning at takeoff velocity, but thats about it - the plane itself will remain stationary, relative to the ground and the air.
12/06/2006 11:42:49 AM · #14
Originally posted by _eug:

And y'll think all that engine thrust is going no where?


The thrust is causing the plane to move relative to the surface of the treadmill, but because the treadmill itself moves at the same speed of the plane, the plane remains stationary in relationship to the surrounding air (the engines do not move the air over the wings). No air motion over the wings means no lift.
12/06/2006 11:44:09 AM · #15
eqsite, why are you assuming no wind?
12/06/2006 11:44:52 AM · #16
Originally posted by thegrandwazoo:

The treadmill has a clever design and always matches the speed of the plane, but runs in the opposite direction

I obviously need more coffee.....
12/06/2006 11:45:08 AM · #17
Originally posted by Gordon:

No air flow, no Bernoulli's principle, no lift. No take off.

This assumes though that the treadmill moving keeps the plane stationary. The engine thrust would keep the plane traveling at the same speed as the treadmill.

When I run on a treadmill, the faster I turn up the treadmill, the more effort I expend to stay in the same place. There's never any airflow produced though.

While planes dont' take off due to driven wheels against the ground, afaik the wheels turn relative to the ground speed - otherwise planes would skid down the runway prior to take-off.


Actually, I've changed my mind. It would take off.

The acceleration is against the air, behind the plane. Wheels just reduce the friction. Consider a hypothetical plane suspended from a crane, it would move forward when the engines fired. Nothing to do with being attached to the ground. The wheels just reduce friction, they don't provide drive. So the tredmill would spin and the wheels would spin faster.

The force/ reaction is against the air, not the ground, so the movement of the ground is mostly irrelevant to the question.

Message edited by author 2006-12-06 11:45:47.
12/06/2006 11:46:21 AM · #18
lol this is like the 10 forum post I have read discussing this ... it was even brought up on mythbusters
12/06/2006 11:46:34 AM · #19
You know, I change my mind.

LoudDog did it for me. I think the plane will fly but the wheels will just turn a lot faster.

Think about a prop plane instead of a jet and it may make more sense. The propeller works by "pulling" the plane through the air. That hasn't changed by having a treadmill under the plane.
12/06/2006 11:46:52 AM · #20
Originally posted by Marjo:

eqsite, why are you assuming no wind?


Fair enough. Given a strong enough breeze, even a plane with its engines off would take off, but I wouldn't want to be on it! :)
12/06/2006 11:49:06 AM · #21
Originally posted by Raziel:

Originally posted by LoudDog:

Yes it will.

The plane moves relative to the air, not the ground. Thus the planes wheels will just turn a lot faster.


As the plane is on a treadmill it is stationary with respect to the ground. If you assume no wind, the air is stationary relative to the ground. Since the difference in air pressure over the top and the bottom of the wing is what generates lift, if no air is moving over and under the wings there will be no lift and hence the plane cannot take off.


This assumes the resistance of the turning wheel is enough to counter the thrust. That's an incorrect assumption. The wheels on the plane would just turn faster.
12/06/2006 11:49:22 AM · #22
Originally posted by digitalpins:

lol this is like the 10 forum post I have read discussing this ... it was even brought up on mythbusters


I think that it is a very well formulated question - hence its popularity!
12/06/2006 11:51:46 AM · #23
Originally posted by digitalpins:

lol this is like the 10 forum post I have read discussing this ... it was even brought up on mythbusters

Okay, this is really frying my noodle....

What did mythbusters conclude?
12/06/2006 11:52:01 AM · #24
.

Aerodynamically speaking, the plane would not be able to obtain enough lift, assuming there is nothing else (no other variables) that you left out of the scenario. There would have to be something that produces a lower air pressure above the wing (as compared to higher pressure under the wing) in order to generate lift.
12/06/2006 11:52:50 AM · #25
yep I think its a great questions, makes you think..... lol.....I would love to see mythbusters try it
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