If the treadmill is matching the planes forward speed then it will take off. It will reach takeoff speed and lift off as normal with the treadmill running backwards at the same speed. The wheels will be travelling at twice the takeoff speed.
If, however, the treadmill is matching the wheelspeed of the plane the plane will remain stationary and both the wheels and the treadmill will rapidly accelerate upwards to the point where the friction in the wheel bearings exactly balances the thrust of the engines, either that or the wheel bearings seize.
Last edited by NeoDude; 11th Jan 2008 at 08:58.