On Apr 15, 9:20*pm, Mike the Strike wrote:
On Apr 15, 5:14*pm, brian whatcott wrote:

Mike the Strike wrote:
You might want to check on the accuracy of the oft-repeated /myth/ that
wings develop lift because of the pressure difference between the
upper and lower surfaces. *My understanding of the physics is that
this component is negligible compared to the second mechanism you
mention of the downward deflection of the airflow.

If you think I am mistaken, then please explain how symmetrical
airfoils develop lift!

Mike

Amusing how partisans grow zealous for their chosen explanation! :-)

Brian W

Actually, we physicists get annoyed when people get the science wrong.

Mike

Mike,

You might want to check your own physics, before making comments like
this.
Because us aerodynamicists get annoyed when people get the science
wrong :-)

Symetrical airfoils work the same way asymetric foils work. The air
is pushing up on the bottom, stronger than the air is pushing down on
the top. If the pressure was the same on the top and bottom surfaces,
there would be no lift.

Please, don't confuse pressure differential with the incorrect "equal
transit time" theory.

I have lost my favorite link to a well presented and complete theory
of lift, so I can't post it here. But the short version is:

angle of attack makes the air flow change direction
that change of direction makes
air pressure rise on the bottom ( but not by much )
air pressure drop on the bottom ( most of the change)

And it all happens because of the Kutta Condtion.
http://en.wikipedia.org/wiki/Kutta_condition

If you are going to berate people for their own incorrect knowledge,
you should be able to improve on that knowledge.

The original posters slides look like a pretty good explanantion. I
think that it is more information than a pilot really needs, but some
people won't relax and actually learn until they think they understand
"why" it works.

Todd Smith
Masters of Science Aerospace Engineering 1990