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Date: Sun, 04 Feb 2007 09:00:16 -0500
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From: "Paul Lipps" <elippse@sbcglobal.net>
Subject: wing pressure
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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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<DIV><FONT face=3DArial>Well, at least one of you, Mark, and maybe paul =
the=20
lessor,&nbsp;was able to understand the concept! !(Actually, I hit PTL =
with the=20
concept several years ago in a hotel bar the night before an EZ =
race!)<FONT=20
size=3D1> </FONT>Guys! Think about how pressure works. It's a force =
across a=20
divider that pushes in the direction of the lesser of the two. Just =
because the=20
air is traveling along with the wing doesn't mean it no longer is a =
force to be=20
reckoned with. But since most of you failed that class, now I'm going to =
hit you=20
with my recently formulated hypothesis on how lift really takes place. I =
call it=20
the "Hose and Kite" theory of lift! (OK, HAK=20
<STRONG><EM>hypothesis</EM></STRONG> since it still hasn't been =
rigorously=20
proven). Have you seen the simple math of the force generated by water =
flowing=20
through a hose when the hose is bent? Well that is how the upper-surface =
lift=20
occurs. Except in this case, there is&nbsp;no hose bending the stream. =
That=20
bending&nbsp;takes place because of the Coanda effect (Thank you, Henri, =
you=20
cute little Rumanian). That's the effect that creates a low pressure =
when a jet=20
of fluid is forced to follow a curved surface. The smaller the radius, =
the=20
greater the pressure reduction, since the outside air must push against =
the=20
molecules in the stream to make them follow the curve, otherwise the =
curving=20
molecule&nbsp;mass would want to depart tangentially! It's the same =
reason that=20
a tornado or hurricane&nbsp;happens. The lower the pressure within the =
center,=20
the higher the speed of the rotating molecules, and the greater the =
diameter of=20
the twister. But I digress. If you look at the pressure distribution =
across a=20
wing's upper surface, you will see that the lowest pressure is at the =
smallest=20
radius at the leading edge. This gradient acts in a forward direction, =
which=20
makes the rotor of a gyrocopter turn, or creates the so-called "nacelle =
thrust"=20
on the front of a jet engine. But again, I digress. The Coanda effect is =
what is=20
responsible for turning the jet of air over the top surface to make it =
follow=20
that surface. This turning action is the same as the action in a hose, =
with the=20
resultant force acting on the wing. This force constitutes 2/3 of the =
total lift=20
acting on the wing, and is sin 4(AOA), about 0.07 / deg. The other third =
is the=20
kite-like action on the bottom surface which deflects the lower jet =
downward.=20
Taken together, they generate a lift force which is 0.105 per degree, =
which is 6=20
times sin(AOA). No circulation, no bound horshoe vortices, no Bernoulli. =
'Bet=20
most of you didn't know that the wing doesn't stop producing lift after =
the=20
stall. Most books don't show you what really takes place above the CL =
peak.=20
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=20
effect as it goes. But then the Cl drops down until it starts back up =
where the=20
"kite" effect is still climbing; that will be at an AOA of 20-25 deg.. =
It=20
describes a sinusoid that peaks at&nbsp;sin 2(AOA) or 45 degrees. Lift =
doesn't=20
go to zero until 90 degrees AOA. There now kiddies, weren't you glad you =
took=20
this class?</FONT></DIV></BODY></HTML>

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