"BDS" wrote in message
t...

50 kts of airspeed is by moving across the ground at 50 kts. If the
airplane is standing still because the conveyor is moving backwards at the
same speed that the airplane is moving across the ground at, then the
airspeed will still be 10 kts.

But the airplane *isn't* standing still (as others have pointed out).

Since the wheels are able to spin freely, the reverse thrust by the
conveyor belt is *not* transferred past the wheels to the plane's
fuselage, and so the only remaining applied force is the unbalanced
forward force of the thrust of the engine.

The conveyor *doesn't* "drag" the plane backwards to compensate
for the engine's thrust. All it does (as others have pointed out) is
spin the wheels faster.

If the conveyor keeps the airplane standing still relative to the ground,

It doesn't.

(Don't worry... I didn't understand it at first either.)

BDS

Jeff Shirton (PP-ASEL)