In article ,
Jim Logajan wrote:

Alan Baker wrote:
In article ,
Jim Logajan wrote:

Alan Baker wrote:
Because the push is caused by the impact of countless air molecules
with the surface of wing. If those collisions fall to zero (i.e. in
a perfect vacuum) then there is zero push.

I don't see what a change in air density (such as taking the extreme
case of a vacuum) has to do with lift. Unless you are claiming
density change as a requirement?

I believe lift can be reasonably computed using inviscid
_incompressible_ flow theory (e.g. as far back as Kutta's 1902
dissertation,) so I don't see why any change in _density_ - much less
the vacuum edge case - needs to be invoked.

Any change in pressure is *by definition* a change in the number of
particles in the fluid that are impacting the surface.

That assertion is incorrect. You are no dummy so I'm sure you'll correct it
when you realize the errors.

Sorry, but it's not. Pressure is created by particle collisions.


I never mentioned density.

Sorry, but you used the word "vacuum." The notable characteristic of a
vacuum is that its density is zero.

That is *a* notable characteristic.

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg