Thrusting or Sucking (where's Howard Stern when we need him.)

T o d d P a t t i s t wrote:
Bruce wrote:


In this regime the
contribution of upper surface lift is apparently no less than 1/3 of the total,
and at low angle of attack it may be greater than 50%.


I'm interested in where you got these figures. The numbers
I've seen put the contribution from the upper surface at
normally somewhat greater than 50%, although these were
numbers for general aviation, not laminar flow sailplane
airfoils/wings.

My personal opinion on the original question is that the
Bernoulli and Newtonian explanations are complementary.
They both explain 100% of the lift, but some people
understand one better than the other. I'm also of the
opinion that the Newtonian "air gets pushed down"
explanation is easier to misunderstand and/or misapply to
aviation than the Bernoulli form, so I prefer starting with
Bernoulli.

It's hard to explain why the contour of the upper surface is
so critical to flight if you focus on Newtonian "pushing air
down," which is usually understood as implicating only the
lower surface of the wing.

OK - I consider myself chastised on the momentum thing. I know it is transfer of
momentum, but then you have to explain momentum. "Energy" is easier for the
luddites.

The range of coeficient of lift contribution came from my (mis-)understanding of
Dr Fred Thomas's "Fundamentals of Sailplane Design" + John D Anderson's
"Fundamentals of Aerodynamics" Both of which get past my mathematical fundament
quite easily...

--
Bruce Greeff
Std Cirrus #57
I'm no-T at the address above.