[meglamaniac]

I think I see another way to address this.

Instead of planes, lets talk cars.
Imagine you have a car on a freewheeling treadmill - i.e. the sort they have in a garage to test cars at high "speeds". Cars rely on the friction between the tires and the ground in order to accelerate - this friction allows the wheels to exert a force. If you try to apply too much force, the friction is overcome and the wheels spin.

Anyway. When on the road, the force being exerted will either move the car or it will move the world. Clearly the car is somewhat easier to move than the world, so the car moves. In actuallity the world does move because of equal and opposite reactions and all that, but the force exerted is so miniscule in comparison to the mass of the world that to all intents and purposes nothing happens. However, when the car is on a freewheeling treadmill the treadmill requires a lot less force to move than the car, so the treadmill moves instead. Got it?

Now go back to planes. Put the plane on a freewheeling treadmill. Throttle up the plane. What force do plane wheels exert on the treadmill? None*! The plane doesn't use the friction between the wheels and the ground as its method of propulsion. It uses the friction between fast air (coming out the back of the engines) and slow air (which the air coming out the back of the engines rams into) in order to propel itself. The plane would happily roll off the end of the freewheeling treadmill.

If it's still not clear after that then I'm out of ideas.



* In actual fact, as we've mentioned before, there is a small amount of friction between the wheel bearings/axel and the wheels. The only result of this would be that the treadmill might actually start moving FORWARDS slightly.