On Wed, 7 Dec 2005, Harry Veeder wrote: > > William Beaty wrote: > > But I already know the answer. It's simple: Pressure differentials > > explain 100% of the lifting force, while flow-deflection (the acceleration > > of fluid masses) also explains 100% of the lifting force. These are > > simply two independant ways of attacking the problem. There is no > > competition between a "Bernoulli" viewpoint and a "Newton" viewpoint. > > This is just another way of saying that the Bernoulli equation ends up > > obeying Newton's laws. Or in other words, if the water is deflected, > > there MUST be a pressure differential which causes a lifting force... and > > if there is a lifting force, then the water MUST be deflected. > > I don't think the two explanations are equivalent. > During level flight the Bernoulli explanation DOES NOT predict that > the fluid leaving the wing tip will be directed downwards.
On the contrary, in 3D flight the Bernoulli explanation *requires* that fluid leaving the wing tip be deflected downwards. That's the reason for sharp trailing edges, the reason that cambered airfoils give lift at zero attack, and it's the whole point of the "Kutta Condition." But there's also a wrong explanation that wormed its way into many books, and explanation which depicts the air flowing horizontally off the trailing edge of an untilted wing. The diagram is wrong, and real wings only do such a thing when adjusted to give zero lifting force. The diagrams showing undeflected air are certainly not the "Bernoulli explanation." The wrong explanation has become known as the "Popular explanation" or the "equal transit-time fallacy" in order to distinguish it from the "Bernoulli explanation." In other words... since an airfoil always deflects air downwards from its trailing edge in order to generate a lifting force, then all correct explanations of airfoil function will include the downward deflection of air as part of the explanation. (((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))) William J. Beaty SCIENCE HOBBYIST website billb at amasci com http://amasci.com EE/programmer/sci-exhibits amateur science, hobby projects, sci fair Seattle, WA 206-789-0775 unusual phenomena, tesla coils, weird sci
