Travis Marlatte wrote:
The propulsion system is irrelevant as long as it is independant of the
treadmill.

No, it doesn't even have to be "independant of the treadmill." Even
if the wheels of the plane were providing the thrust, all that would
happen is that the wheels would be spinning twice as fast by the time
the plane lifted off.

The key is in the wording of the question. The people here who have
gotten it wrong have misinterpreted the riddle to imply that it means
the aircraft is being held stationary. But that's not true. That's
not what it said. It simply said the belt is moving backwards at the
same speed the plane is moving forward. If the belt were moving
backwards fast enough to keep the plane motionless, then you've just
violated the fundamental rule of the riddle. Vbelt != -(Vplane) in
that case.

Picture it this way:


--- Plane @ 100 mph
Treadmill @ 100 mph ---

Now, what is the TAS of that aircraft? 100 mph. I assure you, it
will fly.

The only braintwister is that one must realize that the WHEELS are
turning at 200 mph, rather than 100 mph.

Kevin.