RST Engineering wrote:
Let's do the old Einstein thought experiment. Let's presume a motorized
conveyor belt that is being rotated towards the departure end of the runway.
Let's also presume frictionless wheel bearings in an aircraft sitting at the
departure end of the runway on the conveyor belt.

What happens to the aircraft? Nothing. THe airplane remains motionless
because the aircraft wheels, which are rotating, do not impart any force to
the aircraft to make it move in any direction (F=ma). To a bystander
sitting on the taxi light at the end of the runway, the conveyor belt is
moving left to right, the wheels are spinning in a counterclockwise
direction, and the aircraft itself is motionless.

Actually, that isn't true. You don't need wheel bearing friction to
apply a horizontal force to the wheel at the contact point. The wheel
has inertia and accelerating the wheel will cause a reaction at the
contact point with the belt and the aircraft will begin to move along
the direction of the conveyor. This force will go to zero once the belt
reaches a steady-state speed, but the aircraft will continue to move
along with the belt.

Now if the wheels have no mass as well as no bearing friction... :-)


Matt