Re: PHYS-L: is Circulation theory "wrong" ????

[William Beaty <billb@ESKIMO.COM>]

To everyone on the CC list:  Would you be interested if I were to
volunteer one of my listservers for use in discussing the lifting force
controversy?  This would remove the debate to a separate forum and keep
phys-L and other groups from being taken over by the "lifting force"
discussion.  I would demand civilized behavior from all participants, and
the discussion would definitely NOT descend to the level of a newsgroup
flamewar.

I have a disused list called VortexC-L (appropriate name, eh?)  The forum
would only be worthwhile if opposing sides in the controversy are both
interested.  There's no point to starting a dedicated "lifting force"
forum if it becomes a mutual-admiration society for one side of the
debate.


On Sun, 17 Jan 1999, David_Anderson wrote:

> Bill,
>
> I found your last email somewhat stimulating.  I believe that I can shed
> some light on the situation.  I will first start by giving a quote from
> Elementary Fluid Dynamics, by D.J. Acheson, Clarendon Press, Oxford:
>
>   Notwithstanding the importance of circulation, the Kutta-Joukowski
>   condition, and the theorem of [the previous section which relates lift
>   to speed and circulation], an aerofoil obtains lift essentially by
>   imparting downward momentum to the oncoming airstream.  In the case of
>   a single aerofoil, in an infinite expanse of fluid this elementary
>   truth is disguised, perhaps, by the way that the deflection of the
>   airstream tends to zero at infinity.

Hey!  Maybe all these non-mathematical "Conceptual physics" intuitions are
correct after all?   :)


> There should be no question that the net result of lift is that air is
> given vertical momentum and energy.  The confusion comes from the 2D
> simulations of the aeronautical engineers.  I think you will have an
> easier time visualizing the 2D situation if you keep in mind that a 2D
> airfoil is really an airfoil of infinite length.  This fact is often lost
> and is the cause of much of the confusion.

I agree.  However, the infinite length can be eliminated if we imagine
that the 2D world is actually 1mm deep, and is trapped between
frictionless glass walls (with the airfoil being free to move.)  This
visual image is how I eliminated my own fuzzy thinking regarding an
infinite lifting force applied to an infinitely long wing, resulting in a
finite net force.

> It is the loss of the fact that 2D simulations are of infinite wings that
> give rise to the (silly) misconceptions that lift does not require work
> (the basis for the book Stop Abusing Bernoulli! How Airplanes Really Fly,
> By Gail Craig), that if one were to look far enough back there would be no
> net momentum transfer,

I just had a brainstorm yesterday about "looking far back enough."  I
think I've found the flaw.  If we take a vertical 2D slice of the 3D air
patterns around a real aircraft, we can find a situation that resembles
the world of the 2D airfoil simulation, including the distant
starting-vortex.  However, that slice exists in a 3D world, and HENCE HAS
NO MASS.  If the same slice is made thicker and taken in a variety of
positions and orientations, it is clear that there IS a net momentum
transfer which supports the aircraft.  Only in one symmetrical position, a
position which avoids intersecting the trailing vortices, does it APPEAR
that the 2D model applies to the 3D aircraft.  In my opinion this is a
weird, nonphysical artifact, and the supporters of the 2D model are moved
to grasp it fiercely in an attempt to deny ever admitting that their
viewpoint is fundamentally flawed.  An unbiased outsider would lack the
emotional issues connected with being proved wrong, and therefor wouldn't
defend such a nonphysical distortion of reality.  In other words, our
misconceptions are strong, they are intertwined with our egos, and they
fiercely resist being cured by a dose of correct information.

> The point was brought up in the email that many textbooks and expert
> cannot possibly be wrong.  Through the years of developing the view that
> is presented in our paper, many a time I almost quit because of something
> that I read from an expert.  I would be stopped by the thought that if
> what was said were true, that I really didn't know how a wing developed
> lift.  Fortunately for me, Scott was there to explain the origin of the
> misconceptions.  This work has been more of an effort in learning where
> misconception came from than figuring out how planes really fly.

This sounds verrrrry familiar.  It took me years to realize that textbooks
as a whole are just lousy with conceptual errors.  Still, I try to confine
myself to an area of expertise I can deal with: errors in grade-school
texts.  (Obviously there are far more errors to fight in those books than
in postgraduate texts.  Yet the number of errors does not decrease to zero
as the level of study advances.  Far from it.)

Take a look at my website called SCIENCE MYTHS IN K-6 TEXTBOOKS, at

   http://www.amasci.com/miscon/miscon.html

I had to go through numerous mental "phase changes" in order to clear
these misconceptions from my worldview.  As a result, my warning bells now
go off whenever someone uses arguments from authoritiy, and insist that
the authorties confront their OWN misconceptions, no matter what the
stature of those authorities.  Fortunately, the health of my future career
does not depend on my keeping silent about the flaws of others, therefor I
have few inhibitions about speaking my mind. Also, I've been wrong so many
times in the past, that I'm no longer very embarassed about it.  The best
way to follow the process of trial and error is to pursue accuracty, yet
to unknowningly be flagrantly erroneous in front of a large group of
experts, then let them find the weak spot which shatters my flawed
reasoning.

Here's a quote which you might enjoy.  We ignore it at our peril.  It is
even MORE perilous if we apply it exclusively to our students, but not to
ourselves nor to the authors of our textbooks and reference books.

   "I know that most men, including those at ease with problems of the
    greatest complexity, can seldom accept even the simplest and most
    obvious truth if it be such as would oblige them to admit the falsity
    of conclusions which they have delighted in explaining to colleagues,
    which they have proudly taught to others, and which they have woven,
    thread by thread, into the fabric of their lives."
                                                - Tolstoy


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William J. Beaty                             SCIENCE HOBBYIST website
billb@eskimo.com                             http://www.amasci.com
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