Judgement on opposing airfoil views, pt. 1

[William Beaty <billb@ESKIMO.COM>]

On Tue, 24 Aug 1999, Robert A Cohen wrote:

<snip>
> Personally, I think I see the validity of each point of view.  Below I
> list my conclusions.  I'm bracing myself for criticism but would
> appreciate some constructive feedback.
>
> 1. What is science?
>
> "Make-sense" explanations are useful in science.  Unfortunately, one
> cannot objectively determine whether an explanation "makes sense" or not.
> Thus, "make-sense" explanations are not science per se.  For example,
> creation science may make sense to some people and evolution may make
> sense to others.  Interpreting "yom" to mean a literal day in the Bible
> may make sense to some people while others think it makes sense to
> interpret "yom" as "period of a time".  In some cases, debating which
> makes more sense is fruitless.

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.  Any ideas which
seamlessly connect themselves into the "vast network" of science will
"make sense" in an absolute way which is definitely not a matter of
opinion.  When scientists say that they prefer ideas which are
"beautiful", I think they're really referring to ideas which make
unsuspected and elegant connections between disparate sections of the
"vast network"; where those sections previously had seemed like the
opposite ends of one huge sprawling continent.  Finding such an idea is
very similar to experiencing beauty.


>    Some people think that science must "make sense".  Others think that
> science only needs to make accurate predictions.  Whichever the case, just
> because something "makes sense" does not make it science.  At the same
> time, just because an explanation does not make quantifiable predictions
> does not make it useless or misleading.

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.)

After coming up with the "disk balloons" viewpoint, I later heard from
Drs. Eberhardt and Anderson that the equations I created are correct,
except for a fudge-factor which is associated with the tapered shape of
the wingspan (my wingspan was shaped like a rectangle.)  Therefor, the
"Newton" method of explaining wings certainly can lead to accurate
numerical predictions.  It is irrelevant that this does not appear as such
in Anderson's and Eberhardt's paper.  Their paper contains a simplified
version of the "Newton" lifting-force concepts.  The full-blown "Newton"
theory has no such limitations.  My "disk balloons" article represents a
set of concepts which is half-way between the appropriately simple "wing
scoop" of the Anderson/Eberhardt paper, and the sophisticated 3D
air-entrainment equations of the Newtonian/vortex theory.

See:
   "Disk Balloons"
    http://www.amasci.com/wing/rotbal.html

    J. Denker's critique
    http://www.monmouth.com/~jsd/fly/rotbal.htm

    My response to the above
    http://www.amasci.com/wing/rotbal2.html

(as if you didn't have enough to read already!)    :)




>    I found the Anderson/Eberhardt paper to be useful because its
> explanation makes sense to me.  Even though I can't use it to make
> quantitative predictions, I can use it to make qualitative predictions
> that seem to work in most cases.
>    Verdict: both are right.

Umm...   Perhaps you missed this part below? :

Mr. Denker has sent a request to Dr. Cesar Levy that the links to the
Anderson/Eberhardt paper be removed from that NASA website, essentially
because Denker says that their paper is more harmful than useful.  If I
recall correctly, he accused them of being unable to make quantitative
predictions.  Yet when the "disk balloons" concept is added, the
quantitative predictions work just fine.  Mr. Denker already knows this.
We discussed it privately in massive communications a few months ago.

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.

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.

In addition, if Mr. Denker has contacted other webmasters in a similar
way, he should do the same as with Dr. Levy: withdraw his request that
they eliminate the Anderson/Eberhardt paper from their links.  If John's
critique of this paper is wrong, it would be the only proper thing to do.

I wonder how many other webmasters John has contacted?  If there are any
others, I hope that none of them actually removed the Anderson/Eberhardt
links without contacting Drs. Anderson and Eberhardt.  It is conceivable
that John is doing some real damage here.

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.


> 2. Upwash vs. downwash
>
> If air is accelerated, it can be accelerated because the wing is
> exerting a force on it or because the air itself is exerting a pressure
> on it (much like normal, everyday wind).
>    From what I've learned in these discussions, in many instances the wing
> compresses the air below (and toward the front) of the wing.  This
> high-pressure region not only pushes on the wing but also pushes on the
> surrounding air, leading to upwash.  The upwash, if it occurs below the
> wing, might lead to additional lift or it might not.  That is, it isn't
> clear to me whether the upwash is "pushed up *with* the wing" or the
> upwash "pushes *on* the wing".

Here's how I imagine it.

Suppose there is a parcel of air far ahead of the wing.  It hangs in the
air, bouyed up by all of the neighboring parcels.  As the wing approaches
it, that parcel of air must be accelerated upwards, and as a consequence,
some other mass must be accelerated downwards.  Important question: IS
THIS OTHER MASS THE WING?  In other words, is the Newtonian force-pair
between the air-parcel and the wing?  I do not know.  If it is, then the
wing causes the parcel to initially accelerate upwards to become upwash
and as a result, the wing must be forced downwards.  If it is the wing
which causes the initial upwash-stream to appear, then the upwash
initially creates negative lift and Mr. Denker's idea is wrong or at least
incomplete.

The upwash then partially collides with the wing, and this collision
creates positive lift as Mr. Denker has pointed out.  However, it seems
clear that the time-averaged force after both interactions are complete
must either be zero, or the net force must give a negative (downwards)
lift because the "collision" did not deliver all of the upwash momentum to
the wing.  If Mr. Denker says that "upwash creates significant lift", then
I believe that he is wrong.  Is this fairly clear?  I can explore the
details if it is not.


On the other hand, what if the wing is not the seat of forces which create
the initial upwash stream?  In that case, where can the upwash-producing
force-pair lie?  It must lie on some other parcel of air, and this parcel
is certainly part of the pattern of chordwise air circulation.  The
upwards acceleration of the "upwash" parcel must must cause a downwards
acceleration of the air somewhere else.  If this is the case, then we can
say it like this: upwash produces downwash, and the forces involved do not
touch the wing at all, instead they touch only the circulating air.  The
"upwash" forces cancel out the "downwash" forces as far as the wing is
concerned.

This seems confusing.  However, if we follow the complete path of a single
parcel of air, it becomes far less confusing.  I see that a single parcel
of air does this:


   1. The parcel of air is initially unmoving.

   2. As the wing approaches, the parcel accelerates upwards.

   3. It moves upwards and is stopped by the wing (accelerates downwards).

   4. It is accelerated downwards by the wing, and moves downwards along
      the rear half of the wing as a result.

   5. It remains moving generally downwards as it becomes part of the
      rotating system of downwards-moving wake vortices.  (no net
      acceleration.)


This describes the acceleration of the parcel.  What F=MA forces are
involved?  If we assume that the upwash is created by a force-pair
attached somewhere to the air surrounding the wing, then here are the
forces exerted over time:

   1. The parcel of air is initially unmoving.  No acceleration,
      no net forces (except bouyancy, bouyancy is ignored in this
      entire description.)

   2. As the wing approaches, the parcel accelerates upwards and
      somewhere there is a downwards force on the rest of the air.

   3. The parcel moves upwards and is stopped by the wing (parcel
      accelerates downwards). The wing is forced upwards as the upwash
      strikes its forward underside.

   4. The parcel continues horizontally across the wing and is accelerated
      downwards by the rear half of the wing, and begins moving downwards
      as a result.  The wing experiences an upwards reaction force and is
      accelerated upwards as this occurs.  It also must experience some
      downwards acceleration because of #2 above.

   5. The parcel remains moving generally downwards as it becomes part
      of the rotating system of downwards-moving wake vortices.  (no net
      acceleration, no forces applied to the wing.)

If the time-segments in the above list are roughly equal, then the net
force upon the parcel will look like this:

  1.  0
  2.  +f
  3.  -f
  4.  -f
  5.  0

... where negative indicates a downwards force upon the parcel and an
upwards force upon the wing.  Clearly there is a net lifting force.  The
upwash in #2 creates a downwards force upon the wing, but it is cancelled
when the upwash strikes the wing in #3.

Only #4 remains.  At #4, the rear half of the wing creates downwash and
the wing is lifted as a result.

If the above is correct, then a flying wing resembles a constantly-
hovering rocket engine, and the creation of downwash resembles the
downwards acceleration of the exhaust within the engine bell of the
"rocket."


>    On the one hand, I agree with Denker that the Anderson/Eberhardt
> arguments do not address this well.  Just because air is accelerated
> upwards does not mean that it is the wing that is exerting the upwards
> force on it.

True!

If it is not the wing that is initially pulling upwards upon the "upwash"
parcel, then it must be air-parcels elsewhere which do so.  In my opinion,
we have two options: either the upwash-creating acceleration pulls the
wing down, or the creation of upwash acts to create downwash elsewhere.
In either case Newton's 3rd law is satisfied, and conservation of momentum
is statisfied.

Mr. Denker does not agree with my analysis above.  Instead he says that
the upwash contributes force +f, and the downwash contributes a second
force +f, resulting in a NET UPWARDS FORCE whenever upwash and downwash
are exactly equal.  My analysis above says differently.  It says that
upwash ordinarily would cancel downwash, but because there is excess
downwash when the plane is flying, the wing experiences a net upwards
force.  Mr. Denker very definitely objects to this.

> 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? )


>    Verdict: both are right.


I'd like to believe this.  If John's violation of Newton's laws is a
mistake on my part, then I need to have my mistake pointed out to me very
clearly.  In my opinion John's "upwash lift" and his trampoline model
contain an obvious violation of Newton's laws.  He should not have placed
the trampoline upon the earth and then claimed that it represented the air
immediately below the wing.  Doing this would make the air seem infinitely
massive.  That, or it would create a mental model of an "invisible
cylinder" which constrains all of the air between the wing and the ground.

I hate to say it again, but this whole thing smacks of dishonesty, rather
than of of a desire to get to the bottom of things.  This stuff is VERY
simple physics.  It's only confusing because confusion is being created,
and because flaws are being hidden in order to defend a faulty viewpoint
against all attacks.  "Defense of assertions" sometimes is OK, but
sometimes we can lose perspective, and allow our defense of our ideas to
go far beyond the bounds of rationality.


> 3. Wing as reaction engine
>
> For the wing/plane to stay up, there must be some air deflected downwards.

If I recall, in the past John has flatly stated that your above statement
is not true.  Please ask him if I am right about this.

Instead, John asserts that in order for a plane to remain aloft in
high-altitude flight, no air need be deflected downwards whatsoever.  I
can search the archives and verify this, or perhaps John will verify this,
and perhaps he will illuminate his position in greater detail.

However, I thought that this was the whole reason for John's "upwash
causes lift" argument.  If upwash causes lift, and if downwash also causes
lift, then when upwash and downwash are perfectly equal, the result is a
positive lifting force, yet the net downwash is zero.  In my opinion, John
is clearly wrong and he is closing his eyes to an obvious violation of
Newton's 3rd law and conservation of momentum.


> 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!)

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 :)  !


>    On the one hand, I think Denker's attacks on using "reaction engine" in
> this way was inappropriate and perhaps a defensive reaction rather than
> thought-out responses.

I partially agree.  Are you aware that he has been arguing against the
"reaction engine" description for many, many months?  It's a defensive
reaction to be sure, but it is not a short-term "knee jerk" reaction.

I agree that his reaction probably isn't a thoroughly though-out response.
But think for a moment.  If he's had many months to avoid thinking about
it, then that's a problem.  If he has been discussing it on the newsgroups
for many months and has not perceived any errors in his own logic, then
that's a problem.  If he must only defend himself and never stop to listen
to criticism, and never stop to observe his own actions, then his behavior
is inappropriate for a science discussion.  This is a serious matter only
because of the "Levy incident."

(see next message)

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