http://community.discovery.com/eve/forums/a/tpc/f/9801967776/m/5321919039/p/1

DEBATE - will the plane take off or will it stay on the ground?

I know the answer, I wonder what other people will make points either way about their opinion :) 

huh? no way... a plane requires airflow over its wings and through its jets (assuming it's a jet airplane) in order to take off. If the plane is stationary there's no way it will take off as all that's moving is the wheels. There will be no airflow over its wings, which will mean it won't get the lift required to take off.

I think if it's a jet it would just stall, but since it's a light airplane it probably won't stall but it certainly won't take off

I will be very impressed if they manage to keep the plane stationary though...

EDIT: actually, on second thoughts, what the hell am I thinking? I think I misunderstood the original scenario. Putting the damn plane on a treadmill isn't going to stop it moving forwards, it's not as if the wheels actually do the moving. Yeah it'll just go forwards and take off, Treadmill will just mean the wheels are going to move twice as fast =)

@omg:

Im not so certain about your EDIT point. Imagine the airplane standing still and being moved backwards by the threadmill. Now you would need energy in order to avoid that, meaning the engines would need to move the airplane forward.

But tough one.

yes but remember that when an airplane moves forwards on the runway, the movement is done exclusively by the jets. The wheels are just there so that as little friction as possible is slowing down the takeoff. The amount of stopping power applied by the treadmill will be negligable because of the immense power of the engines compared to the tiny wheels.

Of course, ths applies to a jet plane, which would have no trouble. A light propellor based aircraft may have some movement provided by engines on the wheels, I'm not sure, I don't know enough about light aircraft to answer.

I had to think about omg's point for a few minutes. I remember from physics that as a wheel turns against a surface, friction pushes the wheel which causes the motion. The magnitude and direction of the friction is proportional to the difference between the speed of the rim of the wheel and the wheel's forward speed (or in this case the apparent speed of the wheel). If the speed of the rim matches the forward speed then no net acceleration is experienced. All of this should apply regardless of whether the wheel is driving the motion or something else is pushing the wheel and the friction is making it turn. So it should stop the plane from moving if they can keep the treadmill matching the speed of the wheels which may be difficult since they have to make sure that the treadmill can supply sufficient power when the belt is moving at takeoff speed.

Regardless, this is a pretty stupid one to test. If they do succeed in keeping it still there's no conceivable way for it to get any lift. No motion means no apparent wind. No apparent wind means no lift.

EDIT:  I think I misstated something. If the treadmill matches the wheel's speed, the friction should be equal and opposite to the thrust. I may have messed something up above, but I'm fairly certain that's how it works out.

@non sequor:

sounds about right to me.

 That's what I was thinking at first, but now I'm thinking I may have mangled what I "learned" in freshman physics. I'm going to try to see if I can find something to confirm or deny what I think I know.

The problem with your thinking is of course "if the treadmill matches the wheel's speed". Of course, if they match then that means the plane is not moving. In my scenario, however, the speed of the wheel exceeds the speed of the treadmill, no matter how fast the treadmill moves. The deal is that the motion of the wheel is not what drives the plane, it's the jets (or propellers) that drive it. If you move the ground backwards as you push the plane forwards all that happens is the wheels spin faster. The increase in friction is minimal (the friction between the wheels and the ground remains the same, it's only the internal friction between the wheel and the bearings which is changing)

If they can match the speed of the treadmill to the speed of the wheels of course it will stop moving, that's how relative motion works. My point is that they will NOT do that, because moving the treadmill faster will simply make the wheels spin faster rather than slowing down the plane, and this is completely dependant on what is providing the force. If the wheels provide the force, then that force is applied against the treadmill, and the plane will move relative to the treadmill. However, since the engines provide the force that drives the plane forwards, and this force is applied against the air, the wheels will do nothing. Imagine you're on a flying plane, and you try to slow it down by frantically spinning its wheels. That is essentially the scenario you're depicting here. The only thing the ground is doing is providing a small amount of friction against the wheels. 

I think the main problem is that the myth is not properly defined.

"If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?"

This quote here sums up the problem with this myth. It says the plane is traveling at takeoff speed and the belt is matching the speed in the opposite direction. I assume by traveling at takeoff speed,, this is relative to the conveyor belt. In this scenario, the plane obviously can not take off, since it needs speed relative to the air around it, which it doesn't have.

The main problem is, of course, that this scenario is impossible. The conveyor belt will not slow down the plane because movement of the plane is provided by the engines, which move the plane relative to the air, and not relative to the ground. So basically if they're asking "Under this scenario that can not happen, will the plane take off?" and the answer is no. But if they're asking "If we put a conveyor belt under a plane and moved it in the opposite direction, can it take off?" the answer is yes, no matter how damn fast you move that conveyor belt.

omg got it right...

The plane will still move forward regardless of the speed of the treadmill.

Think about a few example scenario's I can give...

If you stand on a treadmill wearing roller blades and holding a rope to make sure you are in the same position - can you pull yourself forward with the rope?

If you are running on a treadmill and someone comes up from behind you and slowly pushes you forward, you maintain your running speed, do you move forward?


The myth can't be busted because it simply cannot be created, the thrust of the aircraft has absolutely nothing to do with the wheels so no matter what the wheels will just spin faster.

Of course if the plane is stationary on the ground then there is no way that it can take off, but you can't hold a plain back unless you place thrust of equal value to the thrust being created from the engines.

Myth busting = impossible.