Plane on a conveyor belt

JenT · November 15, 2007

You guys need a life.

:innocent:

Edited November 15, 2007 by JenT

Ash_Koog · November 15, 2007

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

This is riddle. It was posted on another forum. Some of the answers were quite funny. I thought it could generate a good convesation, but nce again. The people on this forum are quite impressive with thinking skills. Maybe the next one will be a bit tougher.

http://britishexpats.com/forum/showthread.php?t=493959 Link to the other thread.

Edited November 15, 2007 by Ash_Koog

Ash_Koog · November 15, 2007

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.

This might be a bit easier to understand, it is an example from the other forum.

Originally Posted by Bill_S

The engines are applying thrust. So we have a thrust vector acting on the airframe. The airframe must respond to that force. The only thing that can stop the airframe from moving is an opposing force. In aircraft, the opposing force is drag, which is overcome by the thrust of the engines. The conveyor moving under the wheels is not applying an opposing force to the airframe, it is simply spinning the wheels.

Imagine holding a toy airplane with functioning wheels in your hand. Place it on a treadmill at the gym, holding the airframe with the wheels against the belt. Suppose someone starts the treadmill. Can you roll the toy towards the front of the belt? Of course you can. Your hand is applying the thrust vector. Does it matter how fast the belt is moving? Of course not. If the belt were spinning at the equivalent of 1000 mph, you could still roll the toy towards the front of the belt, because the belt is not applying an opposing force to your hand (apart from the friction of the wheel bearings).

rouguewave · November 15, 2007

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.

Thanks for restating what I'd put in earlier. I also took a look just to confirm that its not just air-flow over the wing that causes flight. Just a little more complex than that, based on my reading of this: http://travel.howstuffworks.com/airplane8.htm

GaryC · November 15, 2007

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.

Ok, I see what you mean. The jet would move just as fast as if it were on solid ground, just the wheels would be going twice as fast.

NavarreMan · November 15, 2007

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.

Thanks for restating what I'd put in earlier. I also took a look just to confirm that its not just air-flow over the wing that causes flight. Just a little more complex than that, based on my reading of this: http://travel.howstuffworks.com/airplane8.htm

I won't even get into who said what first. I assume when you said "Bearings to keep the plane from sliding along the ground," you did not mean to include the word "from".

If you are designing the wing, then the link you provided is valid info. But the wing has already been designed. The engineering work is done. Pilots do not have to design the wing, they just have to make it go fast. I could not understand your 100 foot sections of conveyor going opposite directions. While the wheels and tires (trucks is what they are called) do act as bearings allowing the plane to roll, rolling on the planes gear is not necessary if the conveyor does it for you. Landing gear configurations do have performance limitations and relative ground speed can be critical. Regardless, you could retract the gear and put the plane on matresses and hit the gas and if the conveyor was long enough you would get airborne. The neat part is that we all had good answers pretty quick. Check out the answers on the OP's link.

Next question - How much wood can a wood chuck chuck?

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.

Ok, I see what you mean. The jet would move just as fast as if it were on solid ground, just the wheels would be going twice as fast.