2010 Audi A7/ SAE Paper/ 'Want Low Drag?'

[aerohead]

Originally Posted by JulianEdgar

Just to be clear, there is no mention whatsoever in the nominated SAE paper about a template, standardised shape, etc. There isn't in any SAE paper that I have ever seen on the aerodynamic development of a road car.

The current car aerodynamics standard reference textbook (Aerodynamics of Road Vehicles, 5th edition) gives 'template shapes' 2 pages in 1300.

If only it were as easy as using a template!

* I don't recollect ever suggesting that a template was mentioned.
* Walter E. Lay's car was generated within a 'template' environment.
* All of Kamm's, Fachsenfeld's cars were generated within a 'template' environment.
* All other references reflect 'templates' that the reader would have at their disposal.
* Perhaps the 5th-Edition presumes that the reader is already acquainted with vehicle architectures provided in previous sources.
* The two pages of your 5th-Edition would probably be of interest to the members here.

[aerohead]

Originally Posted by JulianEdgar

The SAE paper, and my book, makes no mention of a dual mode spoiler. So you certainly aren't quoting either my book or the paper.

If you wish to find other information, and build a theory from that - fine. But that makes ostensibly quoting my book and the SAE paper as your sources rather deceptive.

The premise of the SAE Paper has to do with the 'template,' as mentioned elsewhere.
We were going to discuss the association. I told you last Friday that I'd try for today.
Audi provided the video on their multi-mode spoiler. I mentioned that last week. The multi-mode spoiler is germane to the 'template' discussion.
I live in a world beyond the boundaries of your book. I will draw on all available material, as Hucho has admonished us to do so.
I am paraphrasing what you've written.
No deception. If you truly feel that way, I'll digress to your exact quotes. Cumbersome, and inefficient, but I'll do it.
No theories. Empirical science, derived from direct observation of investigators. You may be confusing 'theory' with 'hypothesis.'

[JulianEdgar]

Originally Posted by aerohead

* I don't recollect ever suggesting that a template was mentioned.

Great!

Just making it clear to others that your conflation of 'template' and 'SAE paper' is in only your mind, not the paper.

[aerohead]

Originally Posted by JulianEdgar

Great!

Just making it clear to others that your conflation of 'template' and 'SAE paper' is in only your mind, not the paper.

* Yes, the 'template' is streamlined. Incapable of generating flow separation.
* Obviously, the Audi A7 Sportback roofline is not streamlined. Had it been, then there'd be no separation.
* The 'template' is an easy Go/No Go, which can anticipate the event.
* Scientific fact in the case of the Audi A7.
* Other Volkswagen AG products which employ the AST-II roofline exhibit no separation. Easy!

[JulianEdgar]

But why stop at aerodynamics?

You can take a theory (often with a historical base), find cars that match the theory and, ipso facto, prove the theory 'true'.

We could take just this approach with optimal engine air/fuel ratios, engine ignition timing, suspension natural frequency, gearbox ratios - and so on.

And in every case, despite finding cars that apparently match our theory, our theory would likely be quite incorrect.

(Of course, you see this done all the time on car web discussion groups, not just this one.)

[aerohead]

Originally Posted by JulianEdgar

But why stop at aerodynamics?

You can take a theory (often with a historical base), find cars that match the theory and, ipso facto, prove the theory 'true'.

We could take just this approach with optimal engine air/fuel ratios, engine ignition timing, suspension natural frequency, gearbox ratios - and so on.

And in every case, despite finding cars that apparently match our theory, our theory would likely be quite incorrect.

(Of course, you see this done all the time on car web discussion groups, not just this one.)

* Streamlined profiles do exceed the threshold, adverse pressure gradient, responsible for triggering separation. It's why they're called 'streamlined.'
* It was Hucho that wrote about selecting 'streamlined bodies' for really low drag.
* The Audi began 'streamlined,' then strayed off course, triggering separation. It's real simple.
* By modifying the shape, bringing it closer to the 'streamlined' profile, some of the damage was corrected. Very simple.
* Had the profile remained faithful to the streamlined contour, we wouldn't be having this discussion.
* In America, your entitled to your opinion. I respect your's, however, I do not subscribe to your interpretations. I'll stick with fluid mechanics.

[JulianEdgar]

Originally Posted by aerohead

* In America, your entitled to your opinion. I respect your's, however, I do not subscribe to your interpretations. I'll stick with fluid mechanics.

Yes, and I'll stick with what the current textbooks, professional aerodynamicists and SAE papers say, not the weird theories of some guy on a web discussion group.

[aerohead]

Originally Posted by JulianEdgar

Yes, and I'll stick with what the current textbooks, professional aerodynamicists and SAE papers say, not the weird theories of some guy on a web discussion group.

Careful what you ask for!

[JulianEdgar]

Originally Posted by aerohead

Careful what you ask for!

As I always say to people here: don't believe me.

Go and look at the current textbooks and SAE papers, talk to professional aerodynamicists, do some measurements.

Most people here, who have been sucked-in to believing claptrap, will be astonished at what they find.

[aerohead]

Originally Posted by JulianEdgar

But why stop at aerodynamics?

You can take a theory (often with a historical base), find cars that match the theory and, ipso facto, prove the theory 'true'.

We could take just this approach with optimal engine air/fuel ratios, engine ignition timing, suspension natural frequency, gearbox ratios - and so on.

And in every case, despite finding cars that apparently match our theory, our theory would likely be quite incorrect.

(Of course, you see this done all the time on car web discussion groups, not just this one.)

1) the original hypothesis became theory after multiple, independent parties observed empirical, prima facie evidence which supported the hypothesis. Like acceleration due to gravity at sea level. Or the speed of light. No amount of testing yields alternate results.
2) no amount of testing can produce flow separation with a streamlined body.
3) by default, if a shape generates flow separation, it is, by definition, NOT streamlined.
4) your confusion may stem from the examples you've chosen for examination. They are 'complex' shapes.
5) 'complex' shapes would create special challenges for an aerodynamicist, whereas,' simple,' streamlined shapes would not.
6) a 'notchback' GOODYEAR blimp would be challenging.
7) a 'squareback' GOODYEAR blimp would be challenging.
8) a 'raked-back' GOODYEAR blimp would be a challenge.
9) GOODYEAR blimps are not a challenge, as their engineering quanta have been known and cataloged since the 1920s.
10) the 2010 Audi A7 Sportback is a 'complex' shape.