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Re: end of thread: physics, non-physics, and airplanes



On Mon, 23 Aug 1999, John Denker wrote:

I would be *delighted* if this whole degrading spectacle could have been
conducted off the list. Let me say that I didn't want it on the list, for
all the reasons Mr. Tarara cites. Indeed, back in January 1999, after
exchanging many thousands of words of private email with me, one of the
participants

(I was that participant, and I don't mind you sayig so.)

repeatedly implored me and dared me to share this discussion
with this list. I replied on Sun, 31 Jan 1999 09:05:26 -0500, saying:

Well, most of my friends are embarrassed when they make a mistake. They
*really* hate screwing up in public, and they find it painful to back down
in public. Therefore (applying the golden rule) I try to avoid telling
people "you screwed up" in public. If this discussion *had* been on the
list, I would have tried to take it off-line, so as to reduce the chance of
hurt feelings.

And my reply to this was something to the effect that I would recommend
that this sort of topic be aired in public because scientists should not
care a whit if someone discovers their embarassing mistakes. Come on, was
Feynman terrified of having someone discover flaws in his research? The
very opposite, if I understand his writings.

I then continued to exchange private messages with you about the supposed
fallacy of the "Newton/downwash" explanation of flight, and the supposed
errors in my "rotating balloons" article. I eventually gave up, seeing
that your defenses were impenetrable, and that I was totally unable to
communicate my viewpoint to you. I had hoped that a Newton/Bernoulli
discussion might start on PHYS-L. Highly public discussions keep us from
becoming blind to our own folly. They also leave a record of our behavior
for all to see, so anyone can go back and review the chains of arguments
at their leisure, and the good/bad behavior of any participants.

There's an appropriate Feynman story regarding this. In his early days on
the Manhattan project, the young unknown Feynman was in great demand among
some of the bigwigs. Why? Because he was the only one who would attack
their reasoning and point out its flaws to them. Very wise, those
bigwigs. Finding our flaws is an essential part of science. In science,
any "enemies" who are willing to direct our attention to our errors are an
extremely valuable commodity. Phys-L is full of these precious "enemies."
They quickly find holes in reasoning and help to strengthen weak
arguments.

As I said, I wasn't going to bring up the topic of the severe flaws in
your critique of the Anderson/Eberhardt paper. Then, when Dr. Cesar Levy
of that NASA education page contacted me out of the blue about the "going
on" between you and Anderson/Eberhardt, I suggested to him that the
subject be aired before a group of peers. Doing so would elevate the
level of debate to a much higher standard than any non-public personal
communications ever could. The judgement of the professional
peers/onlookers is a powerful force.

I contacted Dan MacIsaac (phys-L listowner) about this beforehand, and his
recommendation was that all involved should join PHYS-L, rather than
issuing forwarded messages to the group (and then not having the rapid
PHYS-L replies be easily available.) I did seek out advice on how to
proceed.

So here is where I will leave things:
*) The authors of the "scoop model" claim that it presents "true
physics". Alas, when applied to any single airplane, it is not true
physics. It is not science at all, for the reasons I posted earlier (Mon,
23 Aug 1999 08:55:25 -0400). In Fermi's words, it is "not even wrong".

I trust that you have encountered my rebuttal in a message entitled
"planes flying abreast: the Newtonian solution" What will your
counterargument be? I can't see any good ones, so perhaps you'll suprise
me by pointing out a gaping hole in my own reasoning.

It
purports to calculate two quantities (lift and induced drag) but does so by
the use of two fudge factors (the size of the scoop and the percentage of
the true airspeed that is converted to downwash velocity). The two
calculated quantities are not predictions but postdictions.

As I understand it, those "fudge factors" are part of the full "vortex
theory" and are not part of Anderson/Eberhardt's simplified model intended
for students and pilots. If you want the fully-detailed "Newtonian/
vortex" aerodynamics theory, ask the authors for references. (I've never
pursued any myself. My level of expertise ends at the "rotating balloons"
version of vortex theory. However, note the shape of the "wing-scoop"
implied by the "rotating balloons." That is the "invisible scoop" which
Anderson/Eberhardt have intentionally simplifed for mass-consumption.)


*) When applied to more complex situations, such as formation flight, the
scoop model can be coerced into making predictions. In such cases, it
makes grossly wrong predictions.

True. To make the correct predictions, the "scoop" must not be a
simplified model, but instead must be an extended vortex-pair crossection
whose size is related to wingspan, and whose intercepted volume/second of
air is related (I think) to the square of the area. When a slightly-
expanded "Newtonian" model is used, it predicts that planes which fly
adjacently will experience greatly reduced Induced-drag. Really now, if
you want to defeat the Newtonian explanation of flight, I think you'll
need to find out what it actually is. If you think that Anderson and
Eberhardt's paper is a full-blown and detailed aerodynamics theory like
those found in advanced textbooks, then you've made a mistake. Attacking
their theory because it lacks detail is like attacking a high-school
biology textbook and then claiming that professional biological research
is terribly flawed.


*) The paper in question also makes categorical statements about the
effect of upwash on lift and drag, and the effect of ground effect on
upwash. These statements are grossly inconsistent with well-established
experimental, analytical, and simulational results.

You say that upwash contributes lift, and downwash contributes more lift.
In other words, if upwash and downwash are equal, then the lift is
doubled. The Newtonian view says that if upwash and downwash are equal,
then the forces cancel out and lifting forc must be exactly zero. The two
predictions are opposite. We can participate in a civilized discussion
about this if you wish. However, if you cannot stand to admit to errors
in public, then you should flee from me, because I see your errors quite
clearly and am willing to spend any amount of time in explaining them to
you (if the rest of PHYS-L can stand to listen!) So, will you discuss
these issues in a civilized manner? Or should we take this to private
mail? I already attempted a private discussion in the past, but after a
huge number of messages I realized that any discussion was useless, and
you could not hear me.

The Anderson/Eberhardt paper follows Newton's laws, and your explanations
violate them. Now you apparantly wish to have 3rd-party websites remove
links to Anderson/Eberhardt's paper. Therefor I consider it worthwhile to
air these issues, and to continue the debate until its conclusion, if
PHYS-L subscribers and Dan M. will agree. When I pointed out exactly where
you violated Newton's laws, you responded that I was playing nit-picky
word games. For everyone's information, here is one violation spelled out
in detail. Judge for yourselves if this is "word games" or if it is
Newtonian Mechanics of a very simple kind, the type that any physicist
would be expected to know by heart.

If the wing applies a downwards force to the earth, the earth must
apply an upwards force to the wing. Mr. Denker is unable to tell
us how the earth can apply an upwards force to the wing. His
explanation therefor has a flaw: a missing part. It might have an
even larger flaw: there might be no force between the wing and the
earth at all (except in the special case of ground-effect flight.)

Mr. Denker uses a trampoline/baseball model to explain some of the
finer points of flight. However, he places his trampoline upon the
earth, and says that it represents the air. By contacting the earth,
the trampoline has assumend a near-infinite mass. This is a very
serious mistake. The trampoline instead should hover weightlessly
below the wing, and have only the mass of one trampoline. When this is
the case, we immediately see that as the wing is driven upwards by the
baseballs, the trampoline is simultaneously driven downwards. We
obtain a "reaction engine" where the trampoline becomes the "exhaust."
Mr. Denker's thought-experiment, when the flaw is removed, supports
the Anderson/Eberhardt paper, and does not support his own assertion
that there is a force between the airfoil and the earth. Also, his
reasoning about "upwash" now appears flawed as well. What does it
mean for "upwash" if the trampoline is being forced downwards by the
bouncing baseballs?

Mr. Denker then points out that a fly can hover in a jar, and the
weight of the jar is increased by the weight of the fly whether it
hovers or not. This is perfectly true, and is a very interesting
physics situation. I've already discussed it recently. When
a fly hovers within a jar, if it launches air downwards and then the
bottom of the jar stops this moving stream of air, then there is no
force between the fly and the jar. Why? Because the word "force" has
a very specific meaning in physics, and this meaning is not open to
opinion, or to changes of convenience. If a fly launches some air,
there is a force-pair between the fly and the air. If the air then
collides with the bottom of the jar, a SECOND INDEPENDANT force-pair
then arises. This second force-pair has the same magnitude and
direction as the first one, but if we were to say that there is a
force between the fly and the bottom of the jar, our statement would
be a blatant violation of Newton's laws. Newtonian forces are
double-ended. In the above situation we can see no force exerted
upwards upon the fly by the bottom of the jar. Not only that, there
is no need for such a force. Since the jar does not push upwards upon
the fly, we should be very suspicious of any claims that the fly
pushes downwards upon the jar. For there to be a "force", there must
be two equal and opposite forces. If the jar does not push upwards
upon the fly, then the fly does not push downwards upon the jar,
regardless of whether the jar's weight is increased by the weight of
the hovering fly. This is a fairly simple consequence of Newton's
laws. Perhaps I can make this idea clearer...

If a gun fires a bullet at a wall, *should* we say that the gun has
put "force" into the bullet, that the bullet carries "force" across
space, and then that "force" is expressed against the wall? Of
course not. This is some sort of archaic, "Aristotlean" meaning of
the word "force." Yet the gun does experience a recoil force, and the
wall is pushed sideways as the bullet strikes. Similarly, if a fly
hovers in a jar, there is no force-pair between the jar and the fly,
even though the jar does not weigh any less when the fly is hovering.
An interesting consequence: if we were to suddenly eliminate the jar,
then the fly would never know it. A hovercraft would behave
differently. If we had a hovercraft flying in our jar, and if we made
the jar go away, the hovercraft would drop like a stone. A hovercraft
DOES have a force-pair between itself and the jar.

If John Denker says that there is a force between the jar and
the fly (even an "indirect" one), then he is in direct violation of
Newton's Laws, and in violation of the concepts underlying Newtonian
Mechanics. Not a healthy spot for a physicist. This is not word
games, although I certainly do agree that it might be a subtle and
unnecessarily detailed point in many situations.

However, if this "subtle point" should form the basis of one
researcher's attack upon another's work, then it is folly of a very,
very serious kind. Physicists who see no problem in ignoring
Newton's laws are living in a very fragile glass house, and they
should not be throwing stones. Most especially they should not be
haughtily hurling stones at others, and claiming that the *others*
violate Newton's laws!!


*) I stand by the correctness of my on-line book
http://www.monmouth.com/~jsd/how/
and recommend it as suitable for student pilots, flight instructors, and
anyone else who is interested in airplanes.

On this we agree almost entirely. It certainly is an excellent book. I
have no achivements in my own life that are anything like it and it forms
the basis of my respect for you. I'm jealous. Seriously. :)


*) I stand by the correctness and fairness of
http://www.monmouth.com/~jsd/fly/lift.htm

I have nothing more to say. I will leave the last word to others.

I should have expected this I guess.

Very well. I must apologize to PHYS-L for making a grevious error. I
thought that Mr. Denker was a rational person who could participate in a
civilized debate even if there was a chance that his position would be
shown to be in error. I was wrong.

Had I known this beforehand, I would have known better than to introduce
the topic here. I certainly would never have told Mr. Denker about the
existence of PHYS-L. We don't need to attract this type of behavior to
the list.

In a civilized debate there is one tactic that cannot be defeated. That
tactic is to find an excuse to become angry, yell "you're wrong!" place
fingers firmly in ears, and run away. As long-time list moderator I have
seen people use this tactic many, many times over the years. It is very
common on the Newsgroups. In my considered opinion it is not the act of a
person of integrity. It is the act of a person who cannot admit to errors
under any circumstances, in public OR in private.


Again, PHYS-L I apologize. It was by my own actions that all of this
"Newsgroups twisted nastyness" came pouring into the pages of this
wonderful forum. It was premedititated on my part. I greatly
overestimated the the civility and rationality of the parties involved,
and I thought that the "positive forces" always exerted by PHYS-L would
lead to a rapid solution.

An event like this has never happened to me before. I certainly shall
learn from this experience. If the group wishes to dole out some sort of
punishment upon me, I will not object, even if it is severe.


((((((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))))
William J. Beaty SCIENCE HOBBYIST website
billb@eskimo.com http://www.amasci.com
EE/programmer/sci-exhibits science projects, tesla, weird science
Seattle, WA 206-781-3320 freenrg-L taoshum-L vortex-L webhead-L