[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.