Newsgroups: sci.aeronautics
Subject: Re: Aeronautical misconceptions
From: rjvictor@acs.harding.edu
Date: 6 Apr 92 17:33:14 -0500
Reply-To: rjvictor@acs.harding.edu
Organization: Harding University

In article <1992Apr4.004436.2679@tfs.com>, kudzu@tfs.com (Michael Sierchio) writes:
>In article <1992Apr03.234801.26898@bmerh2.bnr.ca> mkfeil@bcrki9.bnr.ca writes:
>
>>...
>>Myths propagated by "informed" people, who should know better:
>>
>>1. Explanation of Lift
>>
>>A wing produces lift because the top surface of the wing is longer. The air
>>flowing over the top of the wing has to travel faster to meet up with the
>>air flowing over the bottom of the wing. Lift is then created by Bernoulli's
>>principle which states that faster flowing air exerts less pressure.
>
>This is the most amazing one, isn't it?  A flat piece of cardboard
>with a positive angle-of-attack will produce lift, too.  Why do
>people believe this nonsense?  I suppose it's because flight instructors
>tell them it's so.
>-- 
>Michael Sierchio                               TRW Financial Systems
>kudzu@tfs.com                                     1947 Center Street
>                                             Berkeley, CA 94704-1105
>(MKS2)                                                  510.704.3380
  I plan on getting my degree in Aerospace Eng. and before I do so, I feel that
I should know why those long flat things on the sides of aircraft work.  Since
you have just shot down the explanation of lift that every aerodynamics book I
have ever had the pleasure of reading gives, I am left with a big question.
  But now, I present a defense of this "classic" explanation of lift, based on
some observations and theories of my own.
  I have observed: That a ping-pong ball, when placed upon an upward directed
stream of air (such as that produced by a hair dryer) will "hover" at the
approximate center of this stream.
  Now, tell me if I'm wrong.  The ball (spherical) remains at the center of
this stream , rather than "falling" off the edge, because the stream of air is 
made of concentric layers (like a cylindrical onion) of different-velocity
streams, the highest velocity being at the center of the stream and, due to
increasing friction with other air molecules, decreasing as one moves outward.
  As the hovering sphere begins to move towards the outside of the stream-
cylinder (or approximate cylinder), it crosses through these different-velocity
regions.  Consequently, the half of the sphere that is facing, and heading
toward, the outside of the stream cylinder is acted on by a lower-velocity
layer of air than is the opposite, more central side.
  And, in complete accordance with the Bernoulli principle "the faster air
exerts less pressure" and the ball is drawn to, and remains, in the center of
the stream.
  I can only conclude that, with respect to air velocity, the ball appears
not as a symmetrical sphere, but as an airfoil, "flying" to the center of the
stream.
  Does this not support the theory that it is differing air velocities over a
wing which produce lift?  Or is this even the issue in question?
  I would very much appreciate an explanation of Lift, or any criticism.
Newsgroups: sci.aeronautics