RH Barnard on templates

[freebeard]

I'm certain that those PhDs at I.G. Farben.... for the Third Reich were highly credentialed.

https://en.wikipedia.org/wiki/Godwin's_law

"as an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches 1"

https://img.memecdn.com/game-over-man_o_7123491.jpg

Game over, man.

[Fat Charlie]

Originally Posted by freebeard

Game over, man.

[aerohead]

Originally Posted by freebeard

I'd be careful. Critical race theory has corrupted critical thinking in all levels of education. It will take years to root that out. I'm not sure what to recommend as an alternative. Funk & Wagnalls - Wikipedia?

Why bring that up? It's not germane to fluid mechanics , perspicacity, and the type of critical thinking Carl Sagan and Michael Shermer wrote.

[JulianEdgar]

Originally Posted by aerohead

Perhaps Bernard will be better remembered for making a killing.
I'm certain that those PhDs at I.G. Farben, who succeeded in scaling up the commercial - production of Tesch und Stabenow's Zyklon-B for the Third Reich were highly credentialed.

You really are a disgusting man, aren't you?

Those people who support Aerohead, you really need to look at what this man is prepared to say.

Nothing, it seems, is too low.

[aerohead]

Originally Posted by JulianEdgar

You really are a disgusting man, aren't you?

Those people who support Aerohead, you really need to look at what this man is prepared to say.

Nothing, it seems, is too low.

I beg your pardon. I thought I was simply speaking Australian English. If you prefer I can go even lower, right into the Viper's den. I'll follow your lead.
RH Barnard will distinguish himself by his deeds, whether they be intentional,or by default. And in these times, what happens by default can easily eclipse intentional behavior, with a lasting legacy.

[freebeard]

Why bring that up

Just saying choose your mentor wisely. O'course, STEM is the last bastion of rationality.

[aerohead]

In fairness to Mr. Edgar, I slowly read through his book.
Curiously,' Modifying the AERODYNAMICS of YOUR Road Car' validates the conventional fluid dynamics of spoilers, and the 'template.'
Isn't it interesting?
I appreciate the support. Thanks.

[aerohead]

Originally Posted by Vman455

I hope he doesn't mind my excerpting his book here, but this quote, from Chapter 4 "The Aerodynamic Design of Family Cars" in Road Vehicle Aerodynamic Design: An Introduction, is salient to the discussion surrounding the 'template' on this site in recent months:



A few comments:

We know from the literature on car aerodynamics and direct measurement that the range of variation of shapes that can support attached flow (that is, that are streamlined) is large; I posted a quote from a 2010 paper by Hucho on another thread here yesterday regarding the leeway available to designers to change fastback backlight angle without increasing drag, for example, and tuft test images posted here by a handful of people show attached flow over a range of shapes.

This excerpt considers the impact of practical factors, such as occupant room, and physical parameters, such as ground clearance, on the 'ideal' form. Even if we were building cars from scratch--which most of us aren't--slavishly following a 'template' will not by default obtain the best results.

Now, consider that most of us are modifying already-existing production cars, cars that are not half-bodies of revolution, cars that may have air dams or limited underbody paneling or extensive underbody paneling from the factory, cars with narrow tires or wide tires, cars with high ground clearance or low ground clearance, cars with varying rear-body shapes that translate to varying flow fields and pressure profiles, cars with all sorts of differently-optimized (or not-optimized!) aerodynamic and styling details.

I used to think, when I didn't know any better, that extending along a 'template' was the solution--based on what I read on this site. I now realize that this an incredibly simplistic view, and one that does not take into account the facts that 1) there is no single optimum 'template', and 2) the variation in shape and thus flow over the cars we modify is in no way consistent, so a "one size fits all" approach simply cannot produce the best results possible.

For example, a few weeks ago I measured surface panel pressures and found that the flow speed down the center of the roof of a Prius is faster than at the outside edges, and that over the rear window the opposite is true. The 'template' assumes uniform pressure and thus uniform flow speed over its circular section. Given that this is not the case on a Prius, why would a person assume that extending it with a half-circular tail at a specific angle is automatically the best solution to decrease drag? Maybe it isn't. Perhaps the optimum solution doesn't involve fitting a tail at all, if doing so would increase difficulty of parking or not being able to fit in a standard garage, for instance, but looking at other areas of the car to decrease drag. Perhaps a tail that does not have a half-circular cross section would reduce drag more than one that does. How on earth would one know without testing? Without measuring, I would never have known that the flow speed over the rear body is not constant side-to-side in the first place!

'Templates' are like security blankets: someone guarantees results with a minimum of thought or effort. But after trying it, testing is infinitely more rewarding, not very expensive, and not that difficult; the hardest part is really just finding the time to do it, and that's not a huge hurdle. More importantly, testing will reveal what the air is actually doing over your car--no guessing or predicting necessary. Go try it!

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First, I want to preface what I'm going to say with an opening statement directed towards VMAN455, in hopes that he'll communicate it to Julian, whom I believe he remains in contact.
There has been 'strong' back-and-forth interplay in regards to the ASTs and 'expert' opinions.
When asked, I never received actual transcripts of conversations with the panel of experts responding to queries about the ASTs, so I've never known the actual language used in discussions, which might explain certain 'responses', including the late Dr. Barnard's.
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It appears that the language regarding the 'template' shared by R.H. Barnard is cribbed directly from SAE Paper# 2000-01-0491,'A New Aerodynamic Approach to Advanced Automobile Basic Shapes,' by Dr. Alberto Morelli, in the ABSTRACT, Introduction, page-2, and page-4.
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Professor Morelli provides artwork from Paul Jaray's patents, associated with this text.
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If, somehow, Dr. Barnard based his comments on 'these' images, rather than the ASTs, then I'd be in total agreement with his wording.
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Since neither Mr. Edgar, nor VMAN455 are mechanical engineers, aerodynamic engineers, aerodynamicists, nor aeronautical engineers ( yet in the case of VMAN ), and neither are in possession of THE THEORY OF WING SECTIONS, or Boundary-Layer Theory, then there's a possibility that some things got 'lost in translation,' and Dr. Barnard was responding to a different topic; and neither Mr. Edgar, nor VMAN would be the wiser. They wouldn't know what they don't know.
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I'll leave it to all interested individuals to compare the wording and make whatever conclusions they derive from the text.
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If Dr. Barnard 'did' base his criticisms of the ASTs on Jaray's depictions, then nothing he wrote would be germane to the AST's. They're a completely different animal. And all this gnashing of the teeth has been completely unnecessary.

[Vman455]

I don't believe you are comprehending what I wrote in this several-years-old post since you aren't addressing any of the arguments I or Barnard made or evidence I brought up. Try this: read through my post again and then summarize Barnard's and my points in full sentences in your own words. This is a good check of understanding. We can't go anywhere with a discussion if you are unwilling or unable even to understand the argument here.

[aerohead]

* I've read through Barnard's and your commentary, slowly, for the fourth time, and wrote myself a complete transcript.
* Yesterday I began to compile materials, and this morning at breakfast, I completed my 'rebuttal', short of some unknowns.
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* You mentioned a 2010 paper by Hucho, published within a day or so at a different thread, having to do with fastback backlight geometry latitude for designers which would guarantee attached flow. I went back 35-pages or so looking for it, but gave up. If you can provide a link to it, I'll give it a look, and respond.
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I only get three hours of computer time, and I don't know if that will be adequate for all the necessary typing.
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1) 'teardrop' ground proximity flow asymmetry issues are addressed in the materials which form the foundation for the ASTs. and already covered there.
2) ditto for streamlined half-bodies.
3) the 'optimum' geometry dependent upon ground clearance is going to require some 'expansion', conditions, caveats ( for the low drag of the ASTs geometry 'options' are extremely constrained, and are limited to streamlined half-bodies, Re: Hucho, page-15, 16, 18, 57, 59, 107, 114, 119, 201, 281.
4) ASTs accommodate two-people abreast.
5) Circular cross-sections are not a requirement for ASTs.
6) Semi-circular cross-sections are not a requirement for ASTs.
7) Excessive frontal area is not a requirement for ASTs.
8) the argument that there no longer exists a single 'optimum' shape, at the Cds capable of being generated by the ASTs, would have to be better argued, in light of the fact that Hucho suggests that they're the sole vehicle available for delivering these levels of drag reduction ( see 3) .
9) 'the best shape depends upon ground clearance' ( if 'best' means lowest Cd, then ASTs are not precluded from the calculus, as all vehicles will perform as a function of their mirror-image with the ground plane ).
end of Dr. Richard 'Dick' H. Barnard commentary rebuttal.
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Begin Vman455 commentary rebuttal"
10) ' (T)here is ample room for individuality even for cars with Cd 0.15...' Hucho, page-45 ( Below Cd 0.15 shapes available to designers are constrained, and recommended shapes are streamlined half-bodies [ see 3),8) ]).
11) 'Hucho's 2010 paper suggests 'leeway' available to designers to change fastback backlight angle without increasing drag' ( without this paper I'm incapable of making comment ).
12)' tuft testing images posted here by a handful of people show attached flow over a range of shapes' ( some are known to actually indicate separation-induced downwash instead of attached flow: Porsche 911 Carrera 2.7, Volkswagen New Beetle, etc., so we'd need some specificity as to what vehicles are to be excluded in the comparisons ).
13) 'Practical factors' have already been addressed with respect to the 'ideal' form.
14) 'Even if scratch-building... following a 'template' will not by default obtain the best results' ( according to Hucho, there wouldn't be any alternative to something like an AST, by default, if the 'specification' for the vehicle were the lowest drag ( see 3, 8, 10 ).
15) 'Now considering already-existing production cars... that are not half-bodies of revolution:
- airdams
- partial underbody paneling
- tire width
- ground clearance
- variability of aft-body shapes
- varying flow fields
- varying pressure profiles
- all sorts of differentiated/optimized/non-optimized aerodynamic & styling details ( all the ASTs require is attached flow from the forebody, top, sides, and underbody, as one would desire, whether or not they'd ever perform any body elongation ).
16) ' template is incredibly simplistic' ( ABSOLUTELY! that's the point of it all. Use off-the shelf aerodynamic technology which has languished for over one hundred years; pre-tested, pre-measured, a known quantity... get the vehicle streamlined, and move on to new business ).
17) the ASTs take into account, that, there is no other technology recognized, which has ever delivered lower drag, or Hucho and all the others would have never conceptually mentioned their technology in the first place.
18) as to a one-size-fits-all, as far as configuring an aft-body for fully-attached flow, and zero separation ( the entire premise of motor vehicle streamlining according to Hucho ( page 119 ), one would be hard-pressed to locate a better starting ( perhaps 'ending' ) place ( it's all in the math ).
19) Re: Vman455's panel pressures (if you had conducted the 120- sample at a time industry convention, as K. Ontani et al, SAE Paper 720100, you could construct the isobaric contour maps which would show, in detail, the entire panel pressures, including the Prius quarter windows outboard of the roof.
20) the ASTs do not assume uniform pressure and do not assume uniform flow velocity over circular section ( they're only concerned with the time-rate-of-change of flow deceleration, and its attendant pressure gradients which determine whether or not the flow will separate [ one must understand
boundary-layer theory to appreciate ] or not ( at the heart of streamlining )).
21) why one 'could' assume that an elongation along an AST profile would automatically be a 'best' solution would depend upon what 'best' means. If it has to do with the lowest Cds known, then it could be considered a 'go-to'.
( they are derived from the lowest drag forms, and also, specifically the LOWEST Cd among that family of forms, according to Hucho, via Sighard Hoerner's reporting [ Cd 0.04 for the 'parent' streamlined body of revolution, producing a Cd 0.08 streamline half-body in ground proximity ] ).
22) any notion as to the existence of a 'low drag' automobile which does not involve elongation belies a complete misunderstanding of the premise of road vehicle streamlining ( Hucho, p-119 ).
23) issues regarding 'parking, garages, and practical length have been addressed at the AST threads ( only the 'ecomodder' knows what a 'livable' length specification will be, and on one is under any mandate to elongate their vehicle ).
24) a tail which integrates to the existing vehicle point of attachment will be the requirement. From there rearwards, there may be a required morphing of the original cross-section to that of Dr. Alberto Morelli's 'fluid tail' radii minimum, or a transition into necessary tumblehome requirements, especially if converting a notchback, to a fastback, forming the basis for the modular Lay/ FKFS tail ( longitudinal 'angles' are forbidden for a streamlined aft-body ).
25) How one would know in advance if a 'template' tail would perform is like wondering if a round tire would 'roll.' The 'science' of low drag is very simple.
The shape is 'pre-tested'.
26) the ASTs are 'pre-measured' ( it's that dimensional analysis thing )
27) the ASTs performance was quantified over a hundred years ago. Minimum thought!
28 ) as to 'testing', one obvious question one may ask themselves is, when do I know that I'm 'there'?
29) Spirit of Ecomodder required no original 'thinking.' From the two trips to the wind tunnel, enough data was collected to demonstrate drag below that of Lightyear Zero, which make sense, aerodynamically. The truck will drive all day long at 108-mph. And get up to 39.9-mpg, at 65-mph, AC 'ON', with 1994 power plant and powertrain technology.
It's all about maintaining attached flow, while reducing cross-section.
That's your pressure regain.
Small wake.
High base pressure.
Pressure drag reduction ( the only reason we 'streamline').
Low overall drag
Increased fuel economy.
Increased range.
Reduced emissions.
Lower cost per mile.
Caviar instead of peanut butter.