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Well, at least one of you, Mark, and maybe paul the
lessor, was able to understand the concept! !(Actually, I hit PTL with the
concept several years ago in a hotel bar the night before an EZ race!) Guys! Think about how pressure works. It's a force across a
divider that pushes in the direction of the lesser of the two. Just because the
air is traveling along with the wing doesn't mean it no longer is a force to be
reckoned with. But since most of you failed that class, now I'm going to hit you
with my recently formulated hypothesis on how lift really takes place. I call it
the "Hose and Kite" theory of lift! (OK, HAK
hypothesis since it still hasn't been rigorously
proven). Have you seen the simple math of the force generated by water flowing
through a hose when the hose is bent? Well that is how the upper-surface lift
occurs. Except in this case, there is no hose bending the stream. That
bending takes place because of the Coanda effect (Thank you, Henri, you
cute little Rumanian). That's the effect that creates a low pressure when a jet
of fluid is forced to follow a curved surface. The smaller the radius, the
greater the pressure reduction, since the outside air must push against the
molecules in the stream to make them follow the curve, otherwise the curving
molecule mass would want to depart tangentially! It's the same reason that
a tornado or hurricane happens. The lower the pressure within the center,
the higher the speed of the rotating molecules, and the greater the diameter of
the twister. But I digress. If you look at the pressure distribution across a
wing's upper surface, you will see that the lowest pressure is at the smallest
radius at the leading edge. This gradient acts in a forward direction, which
makes the rotor of a gyrocopter turn, or creates the so-called "nacelle thrust"
on the front of a jet engine. But again, I digress. The Coanda effect is what is
responsible for turning the jet of air over the top surface to make it follow
that surface. This turning action is the same as the action in a hose, with the
resultant force acting on the wing. This force constitutes 2/3 of the total lift
acting on the wing, and is sin 4(AOA), about 0.07 / deg. The other third is the
kite-like action on the bottom surface which deflects the lower jet downward.
Taken together, they generate a lift force which is 0.105 per degree, which is 6
times sin(AOA). No circulation, no bound horshoe vortices, no Bernoulli. 'Bet
most of you didn't know that the wing doesn't stop producing lift after the
stall. Most books don't show you what really takes place above the CL peak.
That's where the "hose" deflection drops off due to the adverse pressure
gradient where the air flows back up the upper surface, destroying the Coanda
effect as it goes. But then the Cl drops down until it starts back up where the
"kite" effect is still climbing; that will be at an AOA of 20-25 deg.. It
describes a sinusoid that peaks at sin 2(AOA) or 45 degrees. Lift doesn't
go to zero until 90 degrees AOA. There now kiddies, weren't you glad you took
this class?
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