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Old 03-04-2006, 02:28 PM
timmerov2 timmerov2 is offline
Join Date: Mar 2006
Posts: 2
Originally Posted by VicSarjoo
P.S. An ordinary car with wings would *not* take off because the car is driven by wheels, which push against the runway for speed.
heh. a car with wings at a negative angle of attack could accelerate to say 400 knots. at least in this thought experiment. when the pilot pulls back on the stick the car with wings would take off. but it would not fly. because as you point out the wheels are no longer generating thrust.

as for why a plane can or cannot take off on a treadmill... the math is here

the non-math summary:
if you assume the treadmill matches the plane's airspeed then the plane clearly takes off.
if you assume the treadmill matches the planes's tire's speed then the plane clearly does not take off. but the reasons why not are usually confused. the treadmill does not apply any force to the plane. it can't. not significantly anyway. the plane is physically able to move. but if it does move then the belt speed is no longer equal to the tire speed. and a premise of the problem is violated. therefore the correct conclusion is that the premise is wrong. ie the belt speed cannot be set to the tire speed when the plane is moving relative to the air. which would be required for takeoff. the incorrect conclusion is that the treadmill holds the plane still. presumably by magic. or equivalently, closed physics models. or two. ;->