Quote:
Originally posted by TJ:
Yeah - the jets push air...and the tires are merely supporting the weight, not providing propulsion....so the tread mill would make the tires spin at double the ground speed....due to the conveyor MATCHING the plane's speed...IE: IF the plane isn't moving, the conveyor isn't moving.

Assuming that the conveyor matches the gound speed, the tires would not go backwards...as by "opposite direction", it seems to mean that its merely moving akin to a tread mill, towards the front of the plane, as the plane is trying to move forward....so the plane would never be moved backwards from a rest (No thrust) either.

The tires would just be rolling at double their normal take off speed, as the conveyor is MATCHING the speed of the PLANE...so as far as the tires are concerned, the tarmac is rolling along under them at double the plane's speed....whatever THAT is.

If "Opposite" means that it would push the plane FOWARD if it wasn't MATCHING the plane's speed...(Like a tread mill where the tread is coming from behind you, instead of the normal travel TOWARDS you, then it would not spin the tires backwards or fowards from a normal take off....but that makes no sense in this context...as its the plane's speed that is being matched, not the tire speed...IE: The tires would not roll at all. laugh

Steering/braking would of course be crazy, but, assuming the question is really to differentiate between able to move forward or not, I'd go with yes, it could take off from a propulsion standpoint...as the jets don't need tires to roll, skids or pontoons work for planes too.

laugh

IE: It would be able to take off as far as propulsion goes....the tire speed is irrelevant...but just double the airspeed.
Um, nope not really. Propulsion in this case has nothing to do with it taking off. Propulsion might as well be associated with making the wheels spin because on a treadmill that's all those jet (or prop) engines would be doing.

Flight is all about lift, and lift is all about air pressure under the wings. If the plane is effectively standing still because of the 'treadmill effect', there is not enough air mass flowing under the wing to create the necessary lift, and the plane would not move at all. The engines would move the air directly in front and directly behind the inlet and exhaust, but not enough air would be moving across the surface of the wing and that is why it wouldn't take off.

What would probably happen is this;

The wheels would just go really really fast because there would be no aerodynamic drag from the plane, and theoretically more air to push at earth level altitude for additional thrust would bring the spinning speed of the wheels to well over the planes maximum at altitude - say 700+ mph. Assuming the tires didn't melt due to the friction of spinning under all that weight, the tires would likely separate from the wheels, sending firey bits everywhere and blow up the plane.

If the treadmill was really big, like runway size, it might be able to move enough air mass on it's own to create lift - kind of like a large fan. I don't know if that would be enough to get the plain airborne, but it would be similar to the way a kite lifts into the air - the kite generates no thrust, short of resisting the wind (akin to moving in place) which allows the air mass to pile up below it (build pressure below) and push it upward (less pressure above). If the jet did get airborne this way, it would only be for a few feet before the air mass generated by the treadmill dissipated.