Re: Physics of Flight

[brian whatcott <inet@INTELLISYS.NET>]

At 12:48 8/17/99 -0400, Michael Edmiston wrote:
> ... Because of the tendency for a
> fluid to follow the surface of an object moving through it, a wing
> traveling in horizontal flight with positive angle of attack will
> direct the air downward.  This is true both for air passing below the
> wing and air passing above the wing....

> Michael D. Edmiston

Michael is seeking more insightful understanding of fluid flow
past an airfoil. There are two easily accessible ways which he may not
 yet have explored, which though less than perfect models are very
much better than nothing.

1) The thin film approximation.
 Take a water tray with a horizontal lip which spills water evenly
down an inclined plane. Fix an airfoil shape of interest to the incline,
 leading edge up. Place potassium permanganate crystals (or some such)
 at the head of the spillway to trace fluid streamlines.

   Notice how a parcel of water approaching the lower leading edge at
high angle of attack, first reverses direction, travels forward from
bottom to top of leading edge, then passes backwards over the top.

It is this kind of behavior that is not well suited to ping-pong ball
air molecule images, but arises almost intuitively in terms of water flow.

(I expect a determined experimentalist could arrange a pipe with small
holes across the spillway head to provide time-pulsed streamlines.)

2) Freeware 2-D airflow visualizers.
 There is at least one 2-D PC package (NVFoil) that depicts pressure
distribution over a library of several hundred airfoils including NACA,
Gottingen and RAF at Aof As which you specify.
(This is an airfoil library held at U.Illinois, Urbana-Champain, and
owes much of its variety to the gift of a computational fluid dynamics
practitioner.)

 Though the stall region is often not well handled, you can at least
see the basis for claiming that lift is maintained while drag rises
through stall.



brian whatcott <inet@intellisys.net>
Altus OK