Backwash Causes Lift?

Le Chaud Lapin wrote in
ups.com:

On Oct 3, 8:39 am, Tina wrote:
You might also want to think carefully about airfoil shapes, since
wings can provide lift when flying inverted. Any theory that does
not support inverted flight is obviously flawed.

Actually I did because every book I read about flying skimped on the
subject. I'm going to hop over to MIT's OpenCourseWare later this
week and download their most basic course on aero/astro. Benoulli's
principle is toss around as if it were facecloth, but I'm getting the
feeling that no one is really doing the physics.

Well, NASA have and they wholeheartedly support Bernoulli , as do an
Airbus engineeer and a Boeing Engineer of my acquantence. NASA used to
have a whole web page debunking the Bernoulli deniers, but it sems to be
gone now.
It's pretty simple in how it relates to how the airplane flies from one
standpoint and complex from another, but at the end of the day it's how
your knowledge makes the airplane perfomr that counts, and the only
thing tha's going to teach you that is flying an airplane guided by a
good instructor.
If you try to understand it at a molecular level, you've got a problem,
as nobody really undertands lift completely (Here's anthony's chance to
go all creationist on us now)


But the neat thing to do is to hold your hand out of a moving car's
window, and feel the impact pressure on its surfaces as you tilt it
in the airstream. It's not that the hand is being "sucked" up, you
don't feel suction on the top surface, you feel push on the bottom
one. Any theory you develop had better be consistant with those
observations. Someone with more time than I have might like to start
with the fact that air weighs about .08 pounds per square foot near
sea level, and crack some numbers to show how that deflecting that
mass can result in lift even if the lifting surface has some funny
shapes.- Hide quoted text -

Yes it is. In fact, I was having this discussion with someone who
claimed that it *was* Benoulli's principle only. I made the following
diagram to try to illustrate my point. View in fixed width


| inverted |
| table |
|--------------------|

|--------------------|
| upright |
| table |

The Bernoulli people often describe air flowing above the a table
being faster than air below a table, and therefore, pressure is
reduced. Hmmm... what happens if the horizontal velocities above and
below a table are both essentially 0?

If you place an inverted table on top of an upright table so that the
table tops are mated, then have a machine, with a tremendous amount of
force, on the order of 14.4lbs/in^2 of force, yank the inverted table
upward, in one quick jerk, I contend that the lower table will be
strongly inclined to follow by jumping updward, obviously due to
pressure beneath it. So any type of rarefication on one side of a
doubly-pressurized surface that is free to move in direction that is
perpendicular to the surface, will, indeed, move, if pressure is
reduced.

And this is why, I am pretty sure, that if I were to search the web,
one would find people who are fanatical about the leading edges of
wings, in the most minute detail, because it is not simply the length
of the top of the wing that matters, but the amount of pinching, and
the distribution of air as it flows backward from the pressure point.
IMO, that pinching results in displacement of the air above to make it
effective go backwares, causing rarefication.


That all sounds fairly sound, but it's too esoteric to relate to
handling an airplane well.

Don't forget, handling, and it's handling that is the aim of the
knowledge you seek, is primarily a right hand brain operation. If you
try to fly with too much of the left included, you are going to fly like
a chicken on crack.


Bertie