Re: How Important Is Cross-section Shape Of Wing?

Date:         31 Mar 2001 16:43:24 
From:         "matt weber" <mattheww@Qwest.net>
References:   1
Next article
View raw article
  or MIME structure

At 04:05 PM 3/27/01 +0000, you wrote:
>In the April issue of Discover magazine, Robert Kunzig challanges the textbook
>explanation of the principles of flight. I have always felt the books were
>wrong on this when they say that the shape of the wing invokes Bernoulli's
>Principle to provide the lift required. Kunzig refutes the role of Bernoulli's
>Principle. He says that planes fly by pushing air down, getting lift from the
>equal and opposite reaction that pushes the plane up. I'm trying to reconcile
>that with my own thoughts on the subject - that the forces that cause an
>airplane to fly are essentially the same as those that cause a kite to fly.
>Either way you look at it, the shape of the wing is not the main element.
>Otherwise, how could a plane fly upside-down? As an old barnstormer was
>reported to have said, "Give me enough power, and I'll fly a barn door."

There are actually several different lift mechanism at work. The speed and
purpose of the aircraft largely determine which methods you want to use.

Low speed lift, very high flying subsonic aircraft like the U2/TR1, light
aircraft and gliders generally do depend upon Bernoulli for lift. This is
probably the most efficient lift. Leading edge extensions don't do much
good for anything except Bernoulli. In these aircraft,wing cross section is
key.

As the speeds go higher the lift tends to  become primarily momentum
exchange (pushing the air down).
At supersonic speeds, it is almost all momentum exchange. At very high
speeds, the shape of the wing impacts the shockwave formation, but all that
really matters is the area.  The F104 wings produced almost no aerodynamic
lift.

Upside down flight generally requires much higher speed and higher angle of
attack then right side up flight because it uses momentum exchange lift as
opposed to aerodynamic lift.

Matt Weber