Amazing facts you're pretty sure are true

[Incognito]

The plane will take off.

[fluxquanta]

Originally Posted by Incognito

The plane will take off.

No it won't. The wings aren't producing lift.

[PoorGradStudent]

Originally Posted by fluxquanta

No it won't. The wings aren't producing lift.

Yes it will take off because the conveyer belt does not effect the propulsion of the airplane. All of the propulsion comes from the propeller or engine. The wheels are free spinning. So if the conveyer belt is moving at the same speed as the airplane in the opposite direction, the only thing that will change on the plane is the wheels will move at 2 times the speed of the plane.

[fluxquanta]

Originally Posted by PoorGradStudent

Yes it will take off because the conveyer belt does not effect the propulsion of the airplane. All of the propulsion comes from the propeller or engine. The wheels are free spinning. So if the conveyer belt is moving at the same speed as the airplane in the opposite direction, the only thing that will change on the plane is the wheels will move at 2 times the speed of the plane.

You need the relative motion of air past the wings to produce lift. The plane is not moving in the plane of the treadmill, so there is no lift. No lift, no force to counteract gravity, and it won't move upward.

[PoorGradStudent]

Originally Posted by fluxquanta

You need the relative motion of air past the wings to produce lift. The plane is not moving in the plane of the treadmill, so there is no lift. No lift, no force to counteract gravity, and it won't move upward.

But the plane IS moving forward. Like I said, the treadmill has no impact on the forward momentum because the wheels don't create the forward momentum, the engine does. There is air moving over the wings because the engine is moving the plane forward.

[fluxquanta]

Originally Posted by PoorGradStudent

But the plane IS moving forward. Like I said, the treadmill has no impact on the forward momentum because the wheels don't create the forward momentum, the engine does. There is air moving over the wings because the engine is moving the plane forward.

If the plane is moving forward, it's not staying on the treadmill, at least not in the scenario I'm picturing. If you have a really long treadmill, and the plane's forward acceleration (from the engines) is high enough to offset what amounts to drag from the treadmill (and then some), sure, it'll work.

I was thinking that the rearward force from the treadmill and forward thrust were equal, so relative to the surrounding air it stands still.

[FreydNot]

Originally Posted by fluxquanta

I was thinking that the rearward force from the treadmill and forward thrust were equal, so relative to the surrounding air it stands still.

The wheel bearings would have to have an excessive amount of friction for that to be true.

I imagine the wheel bearings have very little friction (just like they do in cars and airplanes and anywhere else there is a wheel on an axle.

[fluxquanta]

Originally Posted by FreydNot

The wheel bearings would have to have an excessive amount of friction for that to be true.

I imagine the wheel bearings have very little friction (just like they do in cars and airplanes and anywhere else there is a wheel on an axle.

If the wheel bearings have "very little" or no friction, like you're suggesting, then yeah, the force due to the treadmill on the plane would be minimal, assuming everything's already in motion. What's the point of having the treadmill at all in this case?

There will be friction, though, and it wouldn't necessarily be small. I mean, you can push a car that's in neutral, but it does require some effort.

[Spanky McDuck]

Originally Posted by fluxquanta

If the wheel bearings have "very little" or no friction, like you're suggesting, then yeah, the force due to the treadmill on the plane would be minimal, assuming everything's already in motion. What's the point of having the treadmill at all in this case?

There will be friction, though, and it wouldn't necessarily be small. I mean, you can push a car that's in neutral, but it does require some effort.

The plane would lift off. The wheels would turn as fast as the speed of the treadmill plus the forward speed of the plane. The air used by the wings and propellers for the needed lift would not be affected by the treadmill. The treadmill would only affect the very thin layer of air touching it. The treadmill would have no affect on the plane at all.

[Theremin]

Originally Posted by campy

They are also the only other mammal aside from Humans that have knees....or so i've heard

Not quite. As far as I know, elephants are the only mammals that have knees on all four of their legs.

Other species (humans, cats, dogs, etc.) tend to only have them on their hind legs.