Was Marchaj having us on?

Marchaj's "Aero-Hydrodynamics of sailing" is widely quoted, but, I believe is a thinly disguised work of humorous fiction.
Let me explain.
In Part 2,"Basic principles of aero-hydrodynamics …", Section A "Elementary concepts…", he spends the first thirty one (31) pages developing a complex theory of lift and circulation based on fluid flow around a circular cylinder.

Then, in sub-section 5) "How lift is generated by a foil" he reminds us that the cylinder has to be rotating to generate circulation and lift and by states the bleeding obvious that a rotating cylinder is different from a foil!


He then totally abandons any conclusions from the prior 31 pages, except to hang onto this obscure concept of circulation based rotating cylinders to associate circulation with the trailing edge vortices from an aerofoil.

These first 31 pages also contain so many patent absurdities* that, in addition to the total disconnect with his arguments in sub-sect (5) I have to conclude he was providing a clue when he offers Alice's conversation with the White Queen as the epigraph to PART 2:

"Why, sometimes I've believed as much as six impossible things before breakfast"

He then goes on to offer page after page of impossible things for us to believe, culminating in this classic on P 202:


I rest my case.



* let me provide a limited sample:
P 170:

Tide...stream? what is he talking about?
P170:

I was taught that water is composed of molecules of H2O, not "schematic in nature" at all!
P170:

He quotes Isaac Newton , who certainly had no notion of water being composed of molecules!
P173-175:


The "circular cylinder" he is referring to is the mast, hardly the most obvious component of the rig to consider a a lifting surface!

That's just the first half dozen pages!
check them yourself by borrowing a free digital copy from: Aero-hydrodynamics of sailing : Marchaj, Czesław A : Free Download, Borrow, and Streaming : Internet Archive https://archive.org/details/aerohydrodynamic00marc

 

A better question would be "Are you just trolling us?"

 

No more than anyone else...
" ... all models are approximations. Essentially, all models are wrong, but some are useful. However, the approximate nature of the model must always be borne in mind....". George Box. Page 424 Empirical Model-Building and Response Surfaces (1987)

All models are wrong - Wikipedia https://en.wikipedia.org/wiki/All_models_are_wrong

 

How about addressing the message, and stop shooting the messenger?

Yes but what do you think?

 

ALL MODELS ARE APPROXIMATIONS....I can't say it clearer...
I know this, and I compensate for it. Is your mind so small that you cannot understand what it cannot comprehend? If that is the case, you are doomed. As an engineer you need to comprehend what you cannot understand, otherwise you are TRUMPed.

 

I don't know about you, but I struggled to distinguish between understand and comprehend, as did the compilers of the Concise OED:"comprehend, v.t. Grasp mentally, understand...".
So no, it's not possible for me, or anyone for that matter, to comprehend what we don't understand: that's hardly the sign of a small mind!

But anyhow, my question was what do you think (about the posted idea)?

 

A 2 or 3D model helps me understand what I can't comprehend yet even though they are only an approximation and just the beginning to knowing.

 

Only if you're using a language other than English! In English, "comprehend" and "understand" have the same meaning!
But please don't hijack my post! It's about the Marchaj book, not language!

 

Marchaj may not have been absolutely correct but it is likely that he was in the ball park with conclusions resulting from his experiments. Some of his pronouncements have been borne out by the likes of MIT, Cal Tech, even NASA.

Can we agree that Darwin, Copernicus, and Newton were not perfectly correct but their contributions have been, and remain, important ways of thought and paths to further learning?

 

Challenge: Show me where "MIT, Cal Tech, even NASA" have adopted Marchaj's theory of circulation (P 202, ref above) as the source of lift on an aerofoil.

WHAT???? You think Marchaj is in their league? Now I know you're joking!

 

Sailor AI

Are you an Artificial Intelligent Sailor ? Good to see somebody who wants "to reinvent the wheel"

Regarding the Starting Vortex as above mentionned, 25 years ago a professionnal sailor who was paid to sail 60 feet racing trimaran from one harbour to another one, told me that, at night, in some rain conditions, like they have in Brittany (West of France) the rain is so thin that it is like a spay instead of the usual teardrops.

So, in this conditions where the spray rain mimicks a fog system in a wind tunnel, the guy told me that he could observe the vortex in the wake of the mainsail.

If you look for evidences, wait for similar conditions and go sailing and check, you will then post interesting messages.

Cheers

 

UNDERSTAND and

Sailor Al,
I think it's great you are reading Marchaj aero-hydrodynamics of sail written in 1979.
I am sorry you feel I was hijack your post. I am only trying to comprehend what you are saying.
Why are you critiquing his book without setting it in the proper time. If you were to reference it’s knowledge base to the 1970’s the models would make more sense and help you comprehend them better.

comprehend stresses the process of getting there.
understand stresses the final result, an “a posteriori”
You could say hindsight is 20 20.

QVI NON INTELLIGENT, AVT TACEAT, AVT DISGAT.

 

Sailor Al, I seem you are a young people completely ignoring the history and progress of Physics, Machaj is not the Author of the theory of circulation. This theory was the first capable to assess the effect of finite span aerofoils to aeroplanes and used by the fathers of Theoretical Aeronautics e.g. Ludwig Prandl and Al , it relies on model of true physical facts (starting vortex exists and are easily seen experimentaly in wind tunnel using smoke visualisation). When You look at the Archives of NASA you will find these work was endorsed by NACA, the ancestor of NASA : NACA Rept N° 116, Ludwig Prandtl, Application of Modern Hydrodynamics to Aeronautics. This theory belongs to the first level of most course on theoretical aeronautics, but it seems you are more intelligent than most students and you can ignore it !

 

Nice try, but I had graduated and been working in the computer industry for 12 years and on my second marriage, and flown round the world twice (yes! on jet aircraft!) by the time Marchaj published the book.

Here's the report It's undated, but the latest date in his references is 1920! Is he the originator of the mad theory? It certainly doesn't meet my challenge!
[EDIT] I found the report in the original document dated 1921. A very interesting historical document.
AERONAUTICS SEVENTH ANNUAL REPORT OF THE NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 1921 INCLUDING TECHNICAL REPORTS NOS . 111 TO 132

 

Don't get me wrong, I'm not suggesting for a minute that sails don't generate vortices. Of course they do.
But they don't generate that crazy cogwheel structure I quoted from P202 above.