From: "JACK L. URETSKY (C)1998; HEP DIVISION, ARGONNE NATIONAL LAB ARGONNE, IL 60439" <JLU@HEP.ANL.GOV>
Date: Fri, 15 Jan 1999 07:40:42 -0600
1. In subsonic flight, air is incompressible to a very good approximation.
I worked this out for phys-l a couple of years ago.
2. 2-d airfoil theory explains lift on a wing very well. Wind tunnels (the ones
I was introduced to 50 or so years ago) are set up to be 2-d and one has to
correct the measurements for wall effects, etc.
3. It is true that the ground effect is related to the wing span in 3-d. In
2-d calculations one doesn't usually introduce a ground plane. If one did, I
think the effect probably dies off either logarithmically or as 1/distance.
Airfoil theory is, after all, just the same potential theory that we came to
know and love in electrostatics - except that circulation must be introduced
in order to keep things finite.
Regards,
Jack
ps Anderson does not quarrel with conventional aerodynamics. He just thinks that
his explanation is more "physical". I think that the essential physics is contained
in the statement that the integrated pressure over the wing surface is related
to the net change in airflow (the "downwash"), but that's just a matter of taste.
"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