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Originally Posted by hat_man
So what you are saying is that if the advice is deemed as flawed it shouldn't be followed? And if it is followed, then it has no advantage? This is what I mean by something is better than nothing. A "flawed" template is better than no template at all, no?
Should this guy be shot down because his shape didn't meet your idea or Aerohead's idea of the template? I'm sure it could be improved on and needs much refining. People here at EM would share their opinions and knowledge. I have a feeling your only advice would be to buy your book.
I think the "template" we have recognized at EM was designed to be a "smidgeon more conservative" rather than a shape that is "right on the ragged edge of flow seperation."
I wish I could find the drawing of AST-II. It might be more to your liking as I believe it was a bit steeper than AST-I. I also believe someone here stated that "The AST-II is the second-most aggressive profile and fits standard rooflines with rapid descending contours. The AST-I fits more conservative contours."
According to a guy name Hucho, the most aggressive profile was by some other guy named Buchheim. I think that Hucho guy wrote a book also. Too bad he isn't around anymore. I'd bet he'd share his knowledge here in the Wiki section.
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I have seven templates that I use for the dimensional analysis. AST-I I'll use on a Mercedes-Benz GLC, due to it's 'slow' contour.
I'll use the AST-II on the Mercedes-Benz GLC 'Coupe', as it's a 'faster' contour.
Between the seven, one can get a sense of whether the carmaker is following any extant profile. It's all informational.
Both are derived from actual mirror-images of streamline bodies of revolution of L/D = 2.5, which produce Cd 0.04 in free air, and no more than Cd 0.09 as a half-body. The original is from NASA, AVA, and DVL, and is presented in Figure 5.13, page 69 of Hoerner's 'AERODYNAMIC DRAG', which also appears in Hucho's Table 2.1, Page 61, 2nd-Edition.
* Adding wheels gives Cd 0.14.
* Adding the 2.8-degree diffuser yields Cd 0.12.
* Adding the Goro Tamai full wheel fairing package nets lower drag.( Hucho says that Cd 0.09 was achievable as of 1986 ).
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The template is a 'known quantity.' Hucho talks about it all throughout his 2nd Edition. According to him, it's the only path to really low drag. He refers to it as the 'optimum', and in the context of a real passenger car. Again, I'm just the messenger.
I'm just the messenger.