Ok, time to wade through and clarify... (will try to snip tyhe unimportant)
--- William Beaty <[EMAIL PROTECTED]> wrote: > On Tue, 6 Dec 2005, Merlyn wrote: > > > I don't agree with Bernoulli, but pressure is > still > > the key. > > First see: http://amasci.com/wing/airfoil.html, and > especially the FAQ at > http://amasci.com/wing/airfoil.html#faq > Which is basically what I was saying, but explained much better. > > > As the wing pushes through the air, the leading > edge > > divides the air into roughly equivalent parts > flowing > > above and below. > > Nope, doesn't happen. When the pattern of air > flowing above and below the > wing are the same, then the lift is zero. For > example, here's a diagram > of a tilted plate at high viscosity where the > lifting force is zero: > > http://www.av8n.com//how/img48/barn20x.png > > And here's a diagram of the same plate at low > viscosity, where inertia > effects dominate, and the lift is non-zero: > > http://www.av8n.com//how/img48/barn20z.png > I meant roughly equivalent mass, I said nothing about equivalent air flow patterns. <snip explanation of diagrams> > > Here's another effect: whenever an airfoil is > creating lift, it starts > separating the upper and lower parcels permanently. > Check out the blue > band behind the airfoil in the diagram below when it > is tilted to produce > zero, medium, and high lift: > > http://www.av8n.com//how/img48/3v.png > > "Phase lag" between upper and lower parcels is > proportional to lift. > > > > > The thickest part of the wing lies > > in the front third of it's depth. > > Explanations of lift must be able to handle flat > plates, and symmetrical > thick airfoils, as well as cambered airfoils both > thin and thick. If you > start out by visualizing a thick cambered airfoil, > you're going to run > into trouble. Instead, start out by visualizing a > tilted thin plate (with > no nonlinear flow detachment, of course.) Once you > can explain the tilted > flat thin wing, then you can easily explain the > un-tilted cambered thin > wing... and both these explanations remain the same > for thick streamlined > wings. > OK, I was simplifying a typical airfoil section. The pressure dfferential explanation (which we both promote) still explains all lift. > > > As far as wingtip vortices go, I have some > > counterexamples for you. > > Airplane engineers have often over the years > sought to > > reduce or even eliminate the vortices coming off > the > > wingtips of a jet, many methods of this were > > accomplished, without reducing the wings lift. > > No, they only redistribute the flow pattern without > affecting the total > "vorticity." Because kinetic energy varies as the > square of velocity, a > flow pattern with high velocity near the "vortex > core" will have greater > net KE than a flow pattern that's distributed > differently. > > > Also, many military planes mount missiles on the > very > > tip of the wing, which would dramatically change > the > > flight capability of a plane if the vortices were > the > > primary source of lift. > > The total flow pattern, the "vorticity," is the > primary source of lift. > > Thinking in terms of the "rotating disk balloons" > analogy at this site: > http://amasci.com/wing/rotbal.html , the overall > rotary motion of the > entire "balloons" is what's important, while any > swirling of a central > core of air is unimportant (and wastes energy.) A > wing must produce a > downward-moving pair of rotating cylinders made of > air. Whether the very > center of the cylinders is spinning fast or slow is > irrelevant. It's the > downward acceleration of oncoming still air which > produces lift. > > Perhaps confusion arises because the word "vortex" > can mean "vortex core," > (where "vortex" applies only to the high speed > spinning air near the > center of the flow pattern,) **OR** the word can > apply to the entire > aircraft wake (the entire "rotating balloons" > animated in my article > above.) > > So by adding small winglets to the wing tips, we can > eliminate > the "vortex" (meaning the vortex core only,) while > having no effect on > the "vortex" (meaning the net rotation of the > overall flow pattern.) > Ah, see here is where you had me confused, because typically a "wingtip vortex" is considered to be the vortex "core". <snip electrical analogy> > > (((((((((((((((((( ( ( ( ( (O) ) ) ) ) > ))))))))))))))))))) > William J. Beaty SCIENCE > HOBBYIST website > billb at amasci com > http://amasci.com > === message truncated === BTW Bill, don't they test wing cross sections in wind tunnels with wings that extend from wall to wall, preventing the formation of the larger vortex wake pattern? Also, it would be interesting actually look at a conservation of momentum study for level flight, because there should be NO net vertical movement of air. The lift on the plane is (wholly or partially) caused by the air which the wing deflects downwards do to impact with the lower surface and Coanda effect 'stiction' on the upper surface. The air moving downwards must be balanced by something moving upwards, which would be more air (and cause your vortex wake). I suggest that the vortex is a result, not a cause. Merlyn Magickal Engineer and Technical Metaphysicist __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
