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Re: Judgement on opposing airfoil views, pt. 1



In responding to William Beaty's comments, I've snipped quite a
bit of his original post to limit the size of this post. I apologize
in advance if I have snipped too much.

On Thu, 26 Aug 1999, William Beaty wrote:

1. What is science?

I agree that this is a big problem. If a particular concept is not
connected to the rest of science, then it might "make sense," or it might
seem like nonsense. The difference becomes purely a matter of opinion.

On the other hand, some ideas do connect to the rest of science. They
connect like puzzle-pieces into the vast concept-net which is physics.
When an idea "makes sense" in a puzzle-piece way, it provides sudden
insight.

Sometimes when obscure concepts connect together and are thereby suddenly
thrown into bright "illumination," it is a powerful personal experience.
Me, I am a kind of "aha" junkie. (I pursue the blazing insights. Is this
a bad thing?) Where the method is concerned with making sense via
"blazing insights" and "vast interconnected networks," it less resembles
"makes sense" and more resembles this:

"amazing, obvious, and NOW I understand EVVVVVEEERY THING!!!!!"

:)

In my opinion, this is what science is all about.
[snip]

I agree that it is important that science makes sense. However, the "aha"
experiences you speak of are subjective. They depend upon individual
experiences. (I suppose this is related to the constructivistic viewpoint
currently being discussed in education circles). My bet is the difference
in what "makes sense" is driving a large part of the "debate".

Bob, have you seen my "rotating balloons" paper? (Links below.) I
actually use the Newton-based lifting force concepts to make quantitative
predictions of the induced drag and power expenditure for a particular
wing. Mr. Denker is very familiar with it, and has given a detailed
critique which I recently answered. (And I fail to understand Mr.
Denker's objections to "scoop theory" as a concept, since he is well aware
that the proper "Newtonian scoop" is not a constant-height region
distributed above the wing, and that the equations that a proper "scoop"
supplies are somewhat accurate. Perhaps he wishes to avoid having you
discover the fact that there *is* a method to come up with the right
equations? It would damage his case against Anderson/Eberhardt, so it is
understandable that he would be tempted to not "supply weapons to the
enemy". I believe that this is another instance of a "debating tactic,"
and it is not appropriate to a science forum. Scientific honesty
requires that we mention any information that might show the flaws in our
ideas.)

[snip]

Also, clearly it is not the goal of Anderson/Eberhardt's paper to make
precision predictions, and that is why they did not attempt any. If you
don't believe me, then please ask them yourself.

I don't object against such "back of the envelope" calculations and thus I
don't share John's viewpoint in this regard. I am only attempting to
point out possible reasons for the disagreements.

After considering these facts above, I must respectfully disagree with
you. Mr. Denker is WRONG. He should not be attempting to censor or
silence his rivals, or to prevent people from encountering the Anderson/
Eberhardt explanation of airplanes. In particular, he should contact Dr.
Levy and withdraw his request that their link to Anderson/Eberhardt be
deleted from their website.

[snip]

If John's critique of the Anderson/Eberhardt paper is misguided, then his
position is wrong. Hence I cannot agree with your conclusion that both
are right. If both are right, then we need not object to John's ethical
violations in the "Levy" incident. I strongly object to John's ethical
violations.

I am trying to remain focused on the physics involved, rather than the
ethics. While Newton's "erred" law:

"For every action there is an emotional reaction"

or, perhaps, Newton's "word" law:

"For every viewpoint there is an opposite, but equal, viewpoint"

might apply, I do not have the expertise in psychology to come up with
possible reasons for such actions. :)

2. Upwash vs. downwash

Okay, here are two things that *everyone* can agree upon (I think):

A. When lift is occuring, there is necessarily some downward momentum
imparted to the ambient air that encounters the wing.

B. For an airplane in steady level flight, the lift force up on the wings
must be matched by a force down on the air.

The problem is in the following questions:

C. For an airplane in steady level flight, is there necessarily any *net*
upwash or downwash created at the point of the wing?

D. For an airplane in steady level flight, is there necessarily any *net*
upward or downward force exerted on the atmosphere as a whole?

At first glance, you might think that questions C and D follow from
statements A and B. It is not that simple. To me, air acts more like
water than it does like particles. Perhaps you can explain to me how an
airplane would fly under water and then I can discuss further the problem
with questions C and D.

On the other hand, I found Denker's arguments about
air/earth reaction pairs, etc., to be misguided and confusing. His first
responses on Newton's third law seemed questionable to me, but after some
thought I think I understand what he was trying to say.

Ah, then you have information that I need. What was he trying to say?

In the past he has argued that the wing pushed down on the earth and the
earth must therefor push upwards on the wing, and that the
"Newton/Reaction" viewpoint (described above) is flawed. To me this
seems totally wrong, and is an obvious violation of Newton's Laws. If it
is not, I have a great need to hear your reasoning. (I've asked John for
his, but he has not supplied it except to repeatedly assert that my
reasoning is wrong. If my reasoning is wrong, why does he not just come
out and tell me where my error lies? )

I believe his problem was with the use of "indirect". Describe the
"flight" in water and perhaps we can get down to the bottom of this.

3. Wing as reaction engine

[snip]

This does not mean that the deflected air "causes" the wing/plane to
stay up. It only means that there must be air deflected downwards.

I don't quite understand you here (but that's nothing new!)

Consider a horizontal plate falling in air (or water). As it falls, it
experiences an upward-directed resistance. Thus, it exerts a downward
force on the air. Since the air was initially stationary, you'd argue
that there must be downward-moving air as a result of the plate's motion.
My guess is that the downward moving air is in the wake of the falling
plate. Just because there is downward-moving air in the wake does not
mean that that downward-moving air *caused* the resistance.

Let me examine this. By "cause force" I think we usually mean
"acceleration is coupled to force by F=MA." Is this accurate? For
example, if I cause a force to appear against a floating rowboat, it's
because I attempt to accelerate the boat with my hand, and this causes a
force-pair to arise between myself and the surface of that boat. OK? If
not, then I need to hear your definition of the phrase "cause a force" and
hear how it should properly be used.

If mine is an acceptable meaning for "cause a force", then I conclude that
the deflected air DOES cause the wing to stay up. Here's why. The wing
deflects the air by creating a force-pair between the wing and the air.
As a result, the air is accelerated downwards and the wing is accelerated
upwards. I would describe it like so: "The force that arises between wing
and air causes the air to be deflected downwards and also causes the wing
to be pushed upwards." We could shorten this to read: "Deflecting the air
downwards causes the wing to be forced upwards." To me this appears to be
a fairly conventional way to say it. It is equivalent to saying "the
launching of a bullet causes the gun to recoil", or "the downwards
ejection of exhaust gases from the rocket engine causes the rocket to
hover above the earth." If my description is flawed, please show me my
error. I certainly hope that I'm not trying to re-define the word "cause"
as part of a debating tactic! big ironic :) !

I think we need to distinguish between the result (if the wing is forced
upwards, some air must be deflected downwards) and the cause (the
downward-deflected air causes the wing to be forced upwards). I'd agree
with the first, but I suspect some people might disagree with the second.

I'll get to part 2 in another post.

----------------------------------------------------------
| Robert Cohen Department of Physics |
| East Stroudsburg University |
| bbq@esu.edu East Stroudsburg, PA 18301 |
| http://www.esu.edu/~bbq/ (570) 422-3428 |
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