Will a plane take off on a conveyor belt?

[w00t]

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

 

[Absane]

Yes. I cannot count how many times this question has been brought up.

Edit: oh, you added the part about the conveyor belt matching wheel speed. In that case, no.

 

[mikenostic]

Uhh, no. The plane needs airspeed. The wings need wind flowing above and below them in order to generate lift.* Now if you put it in a giant wind tunnel and had it blow the wind out at the same knots as the airspeed that the plane needs to rotate (off the runway) then yes, it would lift off the ground.

*You never had any type of aviation or aerodynamics classes did you?

 

[mikenostic]

Yes. I cannot count how many times this question has been brought up.

I took it as the OP meaning that the plane is stationary. But if he means the plane was moving, then yes. The catapult on an aircraft carrier is the same principle.

 

[w00t]

Uhh, no. The plane needs airspeed. The wings need wind flowing above and below them in order to generate lift.* Now if you put it in a giant wind tunnel and had it blow the wind out at the same knots as the airspeed that the plane needs to rotate (off the runway) then yes, it would lift off the ground.

*You never had any type of aviation or aerodynamics classes did you?

My answer would be no, the plane will not take off due to the absence of lift. Just needed some smart people to confirm it.

 

[Absane]

I took it as the OP meaning that the plane is stationary. But if he means the plane was moving, then yes. The catapult on an aircraft carrier is the same principle.

See my edit.

But usually I hear the question like this:

an airplane is on a large conveyor belt and is trying to take off by exerting the thrust needed to move it forward at 100 knots, and the conveyor belt starts moving backwards at 100 knots, will the plane be able to take off, or will it just sit stationary relative to the ground, with the backwards speed of the conveyor belt counteracting the forward thrust of the plane?

http://txfx.net/2005/12/08/airplane-on-a-conveyor-belt/

The answer to this question is YES.

But I just read here that giving the OP's orginal assumptions, then it too can lift: http://www.straightdope.com/columns/060303.html

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.

 

[Absane]

When I read that last page that I provided... it really depends on what you assume is also true of the question being asked. Depending on your own assumptions, the answer is yes or no. I answered "no" at first because I assumed a perfect system in which the conveyor exactly matches the force generated by the plane at every moment.

 

[w00t]

When I read that last page that I provided... it really depends on what you assume is also true of the question being asked. Depending on your own assumptions, the answer is yes or no. I answered "no" at first because I assumed a perfect system in which the conveyor exactly matches the force generated by the plane at every moment.

I agree with you. But this perfect system cannot be attained by experimental purposes, only in theory.

 

[D H]

This stupid topic keeps reappearing, dressed in slightly different clothes. A plane, unlike a car, does not propel itself by applying torque to the wheels. Of course it takes off.

The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

The goal is obviously is to make the plane always stationary with respect to the ground. The above does not accomplish said end. The conveyor will simply move faster and faster as the plane gains ground speed.

Suppose the conveyor were coated with ice and the plane had friction-free skates instead of wheels. What would happen? The speed of the conveyor is irrelevant. An ideal wheel operates similarly to the skate on ice.

 

[Absane]

I agree with you. But this perfect system cannot be attained by experimental purposes, only in theory.

Well even in real life, we can build a conveyor that will equally match the plane's forward force so that it won't take off. One can do this by first making the treadmill just a little too fast (so the plane is going backward) will accelerating. Then we adjust the speed ever so slightly until there is a perfect match. Then the plane never takes off.

D H, I guess I am considering that the wheels are not 100% freespining and that any friction on the ground will, in some way, affect the plane.

 

[w00t]

The goal is obviously is to make the plane always stationary with respect to the ground. The above does not accomplish said end. The conveyor will simply move faster and faster as the plane gains ground speed.

Suppose said conveyor does manage to make the plane always stationary with respect to the ground. What then?

 

[leopold]

oh shit.
another "airplane on a conveyorbelt" thread.

the answer for the umpteenth time is YES the airplane will take off.

 

[Absane]

Suppose said conveyor does manage to make the plane always stationary with respect to the ground. What then?

Maybe you mean a plane with no wheels and the plane on the ground has a coefficient of friction equal to 0.1. Then I would say it's very possible for the plane to remain stationary.

I was assuming that there was sufficient friction between the wheels and the plane. But with the conveyor going the "same speed" as the plane, I guess this isn't possible. Now it is possible if you make the conveyor go much faster than the plane.

 

[temur]

Wheels of an airplane is not active, the airplane gets its speed by pushing the air. So it does not matter what is happening with its wheels and conveyer, as long as the airplane is standing and there is not much friction, airplane will take off.

 

[Oli]

Wheels of an airplane is not active, the airplane gets its speed by pushing the air. So it does not matter what is happening with its wheels and conveyer, as long as the airplane is standing and there is not much friction, airplane will take off.

It gets lift by moving through the air.
If there is no airflow over the wing (usually caused by forward motion) then there is no pressure differential to cause lift.

 

[nietzschefan]

Wheels of an airplane is not active, the airplane gets its speed by pushing the air. So it does not matter what is happening with its wheels and conveyer, as long as the airplane is standing and there is not much friction, airplane will take off.

LMAO this thread delivers....

 

[15ofthe19]

You didn't specify if it was an African or European conveyor belt.

 

[Oli]

:roflmao:

 

[leopold]

the first post is a little confusing.
it was stated that the belt moves backwards at the same speed the wheels move forward.

now, if the are plane doesn't take off the the wheels do not move hence the belt remains stationary.

for those that say the plane doesn't take off what is it that is holding the plane stationary?

 

[nietzschefan]

I guess it could be confusing.

Basically I read it as conveyor belt acts like a frictionless surface(just moves as fast as the wheels turn no matter what speed).

With no wind(some a/c CAN take off if given enough wind), would would need a harrier jet or similar type. VTOL