posted on Feb, 13 2006 @ 11:18 PM
As stated before "take-off" is dependent upon lift. Lift is generated by the Bernoulli Effect resulting from air moving at higher speed over the
top of the wing; thus creating an area of lower pressure Above the wing. the relatively higher pressure under the wing thus "lifts" the
plane into the air.
Thrust, provided either by a propeller or jet exhaust, serves to push the wing through the ambient air at the speed required to generate sufficient
If a sufficient volume of air does not flow around the airfoil of the wing with sufficient velocity (ie.: take-off speed), there will
not be suffiecient lift generated to allow the plane to fly.
Speed is measurement of velocity relative to another object, generally speaking, that object is the ground. Which, although the Earth (the
"ground" in this case) spins at some 3000 MPH, I believe, is generally perceived of as being stationary (Except sometimes in California!).
In the thought excercise given, the forward velocity of the plane is exactly countered by the "treadmill runway" thus negating the forward velocity
of the plane. The plane would have the same velocity, therfore , if its wheels were locked and unmoving.
Consider: A plane, when parked on the runway is still "moving" at close to 3000 MPH due solely to the spin of the planet it's parked on; yet it is
not airborn. Why not? Because it's Relative velocity to the surrounding air, which is Also moving at the same relative speed as the
ground, and therefore, to the plane parked on the ground, is 0 MPH.
Depite the vast volume of air (the entire atmosphre) available, the failure of that volume, no matter how vast, to flow about the plane's wings to
generate lift will leave the plane earth-bound.
The plane's engines do not generate lift; they generate thrust, which is translated into velocity relative to environment, which results in lift. No
matter how much thrust an engine produces (nor the means by which it produces said thrust), if there is no Velocity (or if that velocity is countered
in some way, say by a moving runway) there will be no Lift.
As a "backwards" example consider what can happen to a plane, parked on a airport tarmac, in a high wind.
A large volume of air, at sufficient velocity (no engines involved, no forward speed on the part of the plane) and yet the hapless, pilotless plane
becomes disaterously airborn.