Re: Judgement on opposing airfoil views, pt. 1

[William Beaty <billb@ESKIMO.COM>]

On Thu, 26 Aug 1999, Richard Tarara wrote:

> There is NO upwash without the wing (in motion) being present.

Obviously!

> The upwash
> HAS to be caused by the wing doing  _something_ to the air.

Hi Rich!  Right.  However, if the wing created the chordwise circulation
in the distant past, then, in a nonviscous simplified model, that
circulation continues conceivably forever. That circulation is similar to
a coasting wheel.  It inherently contains this idea: equal amounts of
upwash and downwash.  If we think of the region of the chordwise
circulation as being a flywheel, we would state it like this: "one bit of
the flywheel accelerates another bit of the flywheel, and the forces
between them sum to zero and do not produce a net force upon the axel of
the flywheel."  If we describe the air surrounding the wing, we would say
"one air-parcel in the pattern of chordwise circulation accelerates
another parcel of the same pattern of circulation, but the forces between
them sum to zero and do not produce a net lifting force upon the airfoil
as a whole."

>  Define this
> process _exactly_ and perhaps some of the conflicts will be resolved.

That's the problem because the definition is different in a 2D model than
in a 3D model.  In a 3D model, those darned wake-vortices behind the wing
make the downwash NOT behave as part of a spinning flywheel of chordwise
circulating air.  As a result, a 2D crossection of a 3D airflow does NOT
resemble the air-flow surrounding a traditional "infinite wing" 2D flow
simulation.  This issue causes Bernoulli-ists and Newton-ists to
constantly be at each other's throats.

To me it looks simple:  dump the 2D model, and declare that it's just too
simple to explain the flight of a 3D craft.  Use a 3D fluid flow
simulator, and maybe simplify things by investigating 2D flow-pattern
crossections of the complete 3D flow pattern.  The staunch Bernoulli-ists
say "No, we will not do this", but they do not give any good reason for
their stance, and do not show me why my assertion is flawed.  I say this:
(and have said it for years): "By simplifying the 3D airflow and placing
it into a 2D world, the loss of degrees-of-freedom has profoundly changed
the physics of flight, and as a result, a 2D flow simulation does not at
all describe the physics of a 3D wing in level flight at high altitude."

The Bernoulli-ists say "No, you're wrong", but do not show me why my
assertion is faulty.

I'm happy to go into more detail regarding the above so that any holes in
my argument can be exposed.

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William J. Beaty                                  SCIENCE HOBBYIST website
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