From: "JACK L. URETSKY (C)1998; HEP DIVISION, ARGONNE NATIONAL LAB ARGONNE, IL 60439" <JLU@HEP.ANL.GOV>
Date: Sat, 16 Jan 1999 07:36:10 -0600
Hi William Beaty-
You write-
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I agree, but that's not the problem. To me it looks like the air upstream
from an ideal 2D airfoil has a net upward component which equals the
downstream downward component. At the position of the airfoil, the upward
velocity of the air changes to downward velocity, and this explains the
lift. However, the airfoil caused the oncoming air to rise to meet it,
and this subtracts from the lift. Also, the airfoil causes the descending
downstream air to deccelerate to a standstill, and this also subtracts
from lift. If we look at the entire pattern of air surrounding the
airfoil out to a fair distance, it appears that the momentum change in the
air is first upwards in the upstream section, then downwards at the
airfoil, then upwards again in the downstream section, for a net change of
zero.
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It's a quantitative question that depends upon the "angle of attack"
of the airfoil. If the angle is sufficient to give lift, then the downstream
deflection is greater than the upstream deflection, giving a net lift. This
is apparently illustrated in the Anderson-Eberhart paper.
Regards,
Jack
"I scored the next great triumph for science myself,
to wit, how the milk gets into the cow. Both of us
had marveled over that mystery a long time. We had
followed the cows around for years - that is, in the
daytime - but had never caught them drinking fluid of
that color."
Mark Twain, Extract from Eve's
Autobiography