Plane on a conveyor belt

[Ash_Koog 0]

Imagine a plane is sitting on a massive hypothetical conveyor belt, as wide and as long as a runway. The conveyor belt is designed to match the speed of the plane exactly but moves in the opposite direction. The engines are running at take-off thrust, the brakes are off, etc. Everything is normal save for the fact the plane is on a treadmill.

Can the plane take off?

Discuss

[GaryC 7]

No, because the only way a plane can fly is if there is enough air flow over the wings to provide lift. The only thing that matters is the air speed. In your scenario there would be 0 mph air speed.

[Mr. Big Dog 10,747]

Imagine a plane is sitting on a massive hypothetical conveyor belt, as wide and as long as a runway. The conveyor belt is designed to match the speed of the plane exactly but moves in the opposite direction. The engines are running at take-off thrust, the brakes are off, etc. Everything is normal save for the fact the plane is on a treadmill.

Can the plane take off?

Discuss

If the purpose of the hypothetical conveyor belt is to keep the plane from moving, then why would it have to be as long as a runway? Besides, unlike a road vehicle, a plane doesn't accelerate via it's wheels but via it's jets (or props). Hence, all your simulation would need would be a mechanism to hold said plane in place while the engines run full throttle. A conveyor bet wouldn't really work here - no matter how fast it runs against the speed of the plane, the plane would still be moving forward. The wheels would just spin faster.

How'd you figure that your "treadmill for an airplane" idea makes any sense?

Explain

Edited November 15, 2007 by Mr. Big Dog

[NavarreMan 10]

Try the same thing but instead of the planes wheels being on a treadmill you are blowing wind over the wings at 150+/-mph while the plane is tied to or affixed to the ground somehow so that it is stationary. Then, as Gary pointed out, you generate lift and the plane (dependent on the lift charateristics) would become airborne.

Why the interest? Is there a point to this hypothetical?

[NavarreMan 10]

Imagine a plane is sitting on a massive hypothetical conveyor belt, as wide and as long as a runway. The conveyor belt is designed to match the speed of the plane exactly but moves in the opposite direction. The engines are running at take-off thrust, the brakes are off, etc. Everything is normal save for the fact the plane is on a treadmill.

Can the plane take off?

Discuss

I have re-read very carefully what you have asked. I think I might have missed something the first time around. Let's have another look at it:

Start with plane on treadmill @ 0mph. Treadmill not moving, plane not moving. Increase thrust to take-off power; plane starts to roll forward but treadmill increases speed moving opposite the direction of the planes travel. I believe the effect this would have would be to allow the plane to continue forward and ultimately reach take-off velocity but the wheels would be turning twice as fast as they would be if there were no treadmill. The treadmill and its effect is only pertinent to the wheel speed. The speed of the wheels over the runway does not provide the lift required to get the plane airborne. That is strictly a function of airflow over the wings augmented somewhat by the thrust of the engine(s). You can get a stationary plane in the air regardless of wheel speed or relative ground speed simply by flowing enough air over the wings. That is exactly what wind tunnel tests do.

If the planes airspeed necessary for take-off is 150mph then the wheels would be turning at 300mph relative to the treadmills artificial groundspeed.

The only concern I can see is a possible failure of the landing gear/tires due to excessive rotational speed.

Edited November 15, 2007 by NavarreMan

[NavarreMan 10]

Another interesting way to look at this is to visualize a non-powered conveyor that is free to move with any applied force. You could actually park the plane and lock the brakes, then increase power and the plane would move opposite to the thrust of the engines until take-off speed is acheived or the plane comes to the end of the conveyor at which time some very bad things will happen.

If the plane reached take-off speed and did get into the air it would do so with the wheels stationary.

[Ban Hammer 15,140]

No, because the only way a plane can fly is if there is enough air flow over the wings to provide lift. The only thing that matters is the air speed. In your scenario there would be 0 mph air speed.

that's the way i read it too.

[Mr. Big Dog 10,747]

No, because the only way a plane can fly is if there is enough air flow over the wings to provide lift. The only thing that matters is the air speed. In your scenario there would be 0 mph air speed.

that's the way i read it too.

You are both missing the point that a treadmill-like device won't work to hold the plane in place. Hence, the plane certainly would take off even if said treadmill was running under it's wheels at the opposite speed of the plane.

[Ban Hammer 15,140]

No, because the only way a plane can fly is if there is enough air flow over the wings to provide lift. The only thing that matters is the air speed. In your scenario there would be 0 mph air speed.

that's the way i read it too.

You are both missing the point that a treadmill-like device won't work to hold the plane in place. Hence, the plane certainly would take off even if said treadmill was running under it's wheels at the opposite speed of the plane.

mkay........

[Mr. Big Dog 10,747]

No, because the only way a plane can fly is if there is enough air flow over the wings to provide lift. The only thing that matters is the air speed. In your scenario there would be 0 mph air speed.

that's the way i read it too.

You are both missing the point that a treadmill-like device won't work to hold the plane in place. Hence, the plane certainly would take off even if said treadmill was running under it's wheels at the opposite speed of the plane.

mkay........

So, you disagree? Why? How do you figure that a conveyor belt would be suitable to hold a plane with engines in full throttle in place to prevent it from developing the lift necessary for take-off?

[Sister Fracas 5]

[GaryC 7]

No, because the only way a plane can fly is if there is enough air flow over the wings to provide lift. The only thing that matters is the air speed. In your scenario there would be 0 mph air speed.

that's the way i read it too.

You are both missing the point that a treadmill-like device won't work to hold the plane in place. Hence, the plane certainly would take off even if said treadmill was running under it's wheels at the opposite speed of the plane.

mkay........

So, you disagree? Why? How do you figure that a conveyor belt would be suitable to hold a plane with engines in full throttle in place to prevent it from developing the lift necessary for take-off?

If you run on a treadmill and the belt is matching your speed in the other direction do you go anywhere? Neither would the plane.

[Mr. Big Dog 10,747]

No, because the only way a plane can fly is if there is enough air flow over the wings to provide lift. The only thing that matters is the air speed. In your scenario there would be 0 mph air speed.

that's the way i read it too.

You are both missing the point that a treadmill-like device won't work to hold the plane in place. Hence, the plane certainly would take off even if said treadmill was running under it's wheels at the opposite speed of the plane.

mkay........

So, you disagree? Why? How do you figure that a conveyor belt would be suitable to hold a plane with engines in full throttle in place to prevent it from developing the lift necessary for take-off?

If you run on a treadmill and the belt is matching your speed in the other direction do you go anywhere? Neither would the plane.

That is because my traction is generated against the ground. As is the traction for a road vehicle. For a plane, though, that's not the case.

[rouguewave 7]

Imagine a plane is sitting on a massive hypothetical conveyor belt, as wide and as long as a runway. The conveyor belt is designed to match the speed of the plane exactly but moves in the opposite direction. The engines are running at take-off thrust, the brakes are off, etc. Everything is normal save for the fact the plane is on a treadmill.

Can the plane take off?

Discuss

I have re-read very carefully what you have asked. I think I might have missed something the first time around. Let's have another look at it:

Start with plane on treadmill @ 0mph. Treadmill not moving, plane not moving. Increase thrust to take-off power; plane starts to roll forward but treadmill increases speed moving opposite the direction of the planes travel. I believe the effect this would have would be to allow the plane to continue forward and ultimately reach take-off velocity but the wheels would be turning twice as fast as they would be if there were no treadmill. The treadmill and its effect is only pertinent to the wheel speed. The speed of the wheels over the runway does not provide the lift required to get the plane airborne. That is strictly a function of airflow over the wings augmented somewhat by the thrust of the engine(s). You can get a stationary plane in the air regardless of wheel speed or relative ground speed simply by flowing enough air over the wings. That is exactly what wind tunnel tests do.

If the planes airspeed necessary for take-off is 150mph then the wheels would be turning at 300mph relative to the treadmills artificial groundspeed.

The only concern I can see is a possible failure of the landing gear/tires due to excessive rotational speed.

Actually, I disagree with much of this and the rest of the thread, but I'm not an aeronautical engineer so please excuse my lay-person explanation.

The actions of the treadmill are irrelevant, because the forward motion of the plane is due to jet propulsion against air. The jet propulsion will "push" the plane forward regardless of whether the treadmill moves forward, backward, or changes rate of speed. That DOES make the length of the theoretical conveyor belt relevant, but not imperitive. What's more important is what is beyond the conveyor belt if it isn't as long as a runway. The plane still needs the runway length clear, but in 2 other dimensions (height & width) as well as length.

Lets not start an argument about what would happen if the plane rolled off the end of a too short runway conveyor onto various things. I don't think that's the point. Imagine the conveyor was built of 100 foot (seemless) segments that alternately were moving forward and backward. The plane would still take off because the wheels are then portraying their actual role. Bearings to keep the plane from sliding along the ground, not a means of propulsion.

[NavarreMan 10]

OK, that one completely lost me. A driven treadmill, like an exercising type only huge, makes no difference because the forward motion is not from driven wheels but from thrust against air. The treadmill could be stationary or moving, it does not matter. The plane will accelerate due to the thrust. The joke I made about running aground at the end of the conveyor only applies to my idea of parking the brakes and using a conveyor rather than a powered treadmill. There would be a disastrous stop at the end of the conveyor. Again it does not matter. It is only a joke. We should assume there was enough conveyor for the plane to achieve take-off speed. Whatever the case, all the plane has to do is to get enough air-flow over the wings to achieve enough lift to achieve flight. This has nothing to do with ground speed.

This is not aeronautical engineering. We are not designing the wing that has been done. All we are doing is accelerating airflow over the wing. Doesn't take an astronaut to drive a car. Speed the air up over the wing, it flies.