Quote:
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Originally Posted by NASA Website
NO MOTION, NO LIFT
Lift is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid: no motion, no lift. It makes no difference whether the object moves through a static fluid, or the fluid moves past a static solid object. Lift acts perpendicular to the motion.
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What this doesn't say is that lift is also potential, in that just because an object as a whole exhibits zero lift in any direction perpendicular to motion, doesn't mean that individual parts of the same object would not be subject to lift. If each part of a whole would be subject to lift in every possible direction perpendicular to motion, the net effect is zero lift, but the potential for lift is still there.
The principal of zero lift on a tear drop profile also assumes that the tear drop shape is traveling in dead air. Active airspace directly affects the way flow negotiates the surface of a shape, and thus, even a teardrop would act as an airfoil in normal conditions, except in an unpredictable direction based on the low-pressure area it contacted.
Lift doesn't only go up, it can go in any direction perpendicular to the direction of motion. The concept that lift means up is caused by thinking 2 dimensionally.
This forum is making me wish I hadn't sold all my books years ago when I quit high school. I knew it was a bad idea back then.
