[Phys-L] Re: the plane truth

[John Denker <jsd@AV8N.COM>]

Roger Haar wrote:

>         Airplane wings are actually fairly complex.

Fluid dynamics in general is horrendously complex.

> Air
> moving faster over the top is fairly simple.
> Consider a wing that has the following
> cross-section.  A one meter long straight flat
> bottom and a half circle on top.  The air passing
> along the bottom travels a 1 meter path length.
> The air that starts at the leading edge and goes
> over the top travels a distance of pi/2.  This is
> not a very good wing, but it illustrates the
> idea.

No, that is a completely bogus wing and is completely
false and misleading with respect to what's really
going on.  For one thing, it makes a completely false
prediction about the dependence of lift on angle of
attack.

This "wing" has been re-invented many times.  Even
Albert Einstein got in on the act, proposing _multiple_
bumps on the top side.  It remains, however, completely
bogus, as Uncle Al soon realized.

> ( My favorite quick demo of this is a spoon in the
> flow of a facet the is only partially open.  Hold
> the spoon vertically by its handle. Have the water
> flow over the curved bask of the spoon. The spoon
> will be pulled into the stream, and you can see
> the deflection of the stream of water.)

Also completely bogus.
   http://www.av8n.com/how/htm/spins.html#sec-teaspoon-effect

>         Air that is split by the passing of a wing, does
> not have to rejoin at exactly the same place.  The
> upper air might lag a bit, but the amount of lag
> cannot continually increase, otherwise there would
> eventually be a huge pile of air someplace.

Diametrically false.  The air going over the top arrives
at the back substantially _earlier_ than the corresponding
air passing under the wing, as required by the Kutta-Zhukovsky
theorem.
   http://www.av8n.com/how/htm/airfoils.html#sec-k-z
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