"alexy" wrote in message
...
"Gary Drescher" wrote:
I think the more interesting point is to notice the implications of not
transmitting force through the wheels. Even people who know that planes
and
cars differ in that way may fail (at least at first) to draw the
appropriate
conclusion about what happens to the treadmill plane when it applies
takeoff
power.

Totally irrelevant. The answer is the same for a glider being towed to
take-off by a ground vehicle (except that you would want to change the
rear end or wheel size of the vehicle to cut the final drive ratio in
half, so that it could attain the doubled wheel speed necessary to
attain the needed forward speed.)

I don't think we're in disagreement. My point is just that (even assuming
frictionless wheels) you have to make some changes (such as the ones you
proposed) to a typical ground vehicle to imagine it running normally at
twice its usual speed (even if the relative wind is merely at the usual
speed). The airplane, in contrast, just takes off normally from the
treadmill without needing to be modified.

--Gary