Subject: TWL: Bernoulli effect, bank effect, bottom effect, et al:
To: trawler-world-list@lists.samurai.com

the wing, and a low pressure area on top of the wing. This happens because
of the shape of the wing, which causes the air under the wing to go slower
than the air on the top of the wing. If you want to then state that the
aircraft is "sucked up" into the air, you would be correct. Or if you
wanted to say that "lift" under the wing causes the aircraft to rise, you
might be equally correct.

Actually, this is not correct.  Airplanes are not "sucked" up into the air,
as popular a misconception as this is.  Lift is the result of an equal
force in the opposite direction.  As I stated in my earlier post, a wing
develops lift by moving air down.  While the Bernouli effect is one of the
aerodynamic reasons why a wing moves air down, it is not the primary source
of lift.  Wings with symetrical airfoils develop lift, and there is no
Bernouli effect present.  As was pointed out to me in an off-line post,  a
rubber band powered, balsa wood airplane with a wing made of a flat piece
of balsa wood develops the lift needed to fly.  There is no Bernouli effect
on this wing either.

I realize this has nothing to do with trawlers, but this Bernouli thing is
a very widely held belief as to why a wing develops lift.  So I figured it
would be helpful to try to set the record straight (even if you don't want
to believe me).

I'm not making all this up on my own, by the way.  I'm repeating things
I've been told by aeronautical engineers in the miliatry and commercial
airplane industry, read in numerous books and scientific articles about
flight, and was told by, among other people, one of the top consulting
aerodynamisists at NASA who at the time was the acting head of MIT's
college of aeronautics and who was also a member of the commitee created to
investigate the Challenger accident.  So I figured he knew what he was
talking about.  I used to believe firmly in the Bernouli theory until the
evidence convinced me otherwise.

C. Marin Faure
GB36-403 "La Perouse"
Bellingham, WA

down.<<<<

Couldn't agree more. Those who are interested might like to look at these
nifty animations, which show air flow, pressure and velocity over an airfoil
at various angles of attack, and the resulting forces.

http://www.idra.unige.it/~irro/profilo_e.html

down under the wing.  In fact, much of the downward movement of air that
produces the opposite reaction -lift- is behind the wing.<<<<

Note especially the Streak Lines animation which demonstrates this effect.

Best regards, Robert Bryett,
Sydney, Australia.
mailto:rbryett@mail.com

Gregory Han
685 Curtiswood Dr
Key Biscayne FL 33149

305 361 2133
Fax: 305 437 8108

ghan@greghan.com

What a great discussion for a trawler BB.  I love the proclamations of
all the "experts". It seems that most of the posts were on the right
track except the Bernoulli defenders. So you go to the wonderful web and
seek a real expert discussion.

Take a look at:

http://www.allstar.fiu.edu/aerojava/airflylvl3.htm

Some quotes:

The second description we will call the Popular Explanation which is
based on the Bernoulli principle. The primary advantage of this
description is that it is easy to understand and has been taught for
many years. Because of it's simplicity, it is used to describe lift in
most flight training manuals. This description focuses on the shape of
the wing and prevents one from understanding such important phenomena as
inverted flight, power, ground effect, and the dependence of lift on the
angle of attack of the wing.

The third description, which we are advocating here, we will call the
Physical Description of lift. This description is based primarily on
Newton's laws. The physical description is useful for understanding
flight, and is accessible to all that are curious. Little math is needed
to yield an estimate of many phenomena associated with flight. This
description gives a clear, intuitive understanding of such phenomena as
the power curve, ground effect, and high-speed stalls. However, unlike
the mathematical aerodynamics description, the physical description has
no design or simulation capabilities.

As one can see, the popular explanation, which fixates on the shape of
the wing, may satisfy many but it does not give one the tools to really
understand flight. The physical description of lift is easy to
understand and much more powerful.