Date:	Thu, 6 Jul 1995 07:40:58 -1000
From:	sasaki@netopd.harvard.edu (Marty Sasaki)
Message-Id: <199507061740.NAA18244@netopd.harvard.edu>
Organization: Harvard University Office of Information Technology
Subject: Lift - the latest theories

I'm reposting this article from rec.models.rc (with the author's
permission). It is the most convincing article that I've seen and
explains lift in terms that almost anyone can understand.
-------------------re-post follows---------------------

Subject: Lift demons

Mary Shafer (shafer@ferhino.dfrf.nasa.gov) explains lift:

OK, here it is--the real, intuitively-obvious-even-to-the-lay-person
explanation of lift.  

People, lift is caused by lift demons.  These little, invisible demons
hold on to the leading and trailing edges of the aircraft and lift it
into the air by flapping their wings (so, in a reductionist sense,
lift is actually caused by feathers).  Some of the demons are a little
confused and they hold on backwards, causing drag.

The reason that planes stall at high alpha is that the leading edge
demons get scared and let go when they can't see the ground anymore.

Lift demons have good taste and don't like to look at ugly aircraft,
so they hold on backwards on ugly planes.  That's why gliders have
so much lift and so little drag and why F-4s have lots of drag.

John Wolter (towolt@beaker.lerc.nasa.gov) asked:

   What I would like is a simple *intuitive* explanation of what causes lift
   on a lift demon's wing.  (Here we go again... ;-)

Mary Shafer (shafer@ferhino.dfrf.nasa.gov) replied:

Feathers.  The multiple filaments on feathers trap the air molecules
and they struggle to escape, which causes the action-reaction that we
call lift.  Bat wings don't have feathers but they're hairy and that
works just about as well (air molecules are a little claustrophobic).

And Richard Winterstein (rlwinter@taco.ucdavis.edu) suggested another
mechanism:

It was originally believed smaller lift demons, who had their lift
produced by even smaller lift demons, etc., as proposed by the great
Greek philosopher/scientist Miasma.  However, with the revival of
scientific knowledge that eventually ended the Dark Ages, it was
realized that this situation was unresolvable according to Zeno's
paradox.  

Of course, the 'infinite demons' theory works in many problems of
engineering signifigance, but a real understanding requires that the
ether be introduced into the analysis at some point.  The ether
concept, of course, explains why planes fly more efficiently at higher
altitudes, and, of course, is an absolute necessity when studying
orbital and interplanetary travel, where (it is believed) many of the
lift demons are unable to breathe. Hope that settles the question.
-- 
Marty Sasaki            Harvard University           Sasaki Kite Fabrications
sasaki@noc.harvard.edu  Network Services Division    90 Melrose Street
617-496-4320            10 Ware Street               Arlington, MA 02174
                        Cambridge, MA 02138-4002     phone/fax: 617-646-1925




 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =