[JulianEdgar]

Originally Posted by aerohead

1) One textbook would be, 'Aerodynamics of Road Vehicles', 2nd-Edition, page 185, Figure 4.104.
In 1973, Janssen and Hucho, working on detail optimization of the upcoming 4-door, VW Golf, deviated greatly in terms of style from Giugiaro's original design, obtaining a 33% drag reduction, to demonstrate what could be reached over and above, by departing from the stylistic concept.
Exactly what we here at EcoModder.com endeavor for.
The Golf's drag minimum was achieved when the roofline matched the 'template' profile.( Figure 4.47, page-145 )
------------------------------------------------------------------------------------

Nether of your cited diagrams have anything to do with template. Neither mentions a template, shows a template or makes any claim that a predetermined shape is applicable in any way.

So I'll say again:

What I want to see is a section in any aerodynamics textbook that applies a template as has been so often been encouraged here. Viz:

- Show where there is separated and attached flow on existing cars
- Guide the shape of rear extensions
- Show how rear spoilers on sedans should be positioned and shaped
- Allow the assessment of the ‘aerodynamic purity’ of cars

As we both know, no such textbook or paper exists - and for good reason.

2)* The 2016, Cd 0.19, Mercedes-Benz IAA extensible boat-tail section is a perfect 'template' match, according the Daimler-Benz' wind tunnel photographs and video.
* The Audi E-tron experiences a 20-count drag reduction when the 'raked' roofline is exchanged for the more template-like 'Sportback' roofline.
* The Audi SQ2, for 2019, enjoyed an 'aero improvement' by an elongation of its roof spoiler ( something the Cd 0.27, Mitsubishi Mirage takes to the limit).
* Volkswagen's 1981 Flow-Body ( long-tail ) experiences a 10-count drag reduction when the 'template' is followed to its conclusion ( Cd 0.140 ), Figure 4.120, page- 200, top of upper table.
* The Daimler-Benz, Mercedes-Benz, C-111 III demonstrates a drag reduction, from Cd 0.237, to Cd 0.178, when it's boat-tail 'template' is carried to its conclusion. Figure 4.42, page- 142
* Sunbeam utilized the 'template' for the aft-body of it's SUNBEAM 1000-HP land speed record car of the 1920s.

This is exactly the same logic as saying '225 section tyres are best' and then citing every car that uses that tyre as if it is sound evidence for the proposition that 225 section tyres are best.

--------------------------------------------------------------------------------------
3) For notchback spoilers. please see:
1965 Ford Mustang fastback (sic)
1982 Pontiac Trans AM Firebird
1990 Opel Calibra
1993 Volvo ECC
1993 Chevrolet Camaro V-6
1997 Nissan 200SX
1998 Toyota MR2
2014 Audi RS5
2014 Chevrolet Camaro SS 1LE
2015 Alfa Romeo 4C
2015 Lexus RCF
2018 KIA Stinger
2012 Toyota GR SUPRA
------------------------------------------------------------------------------------

What about them? None were developed using a template, or even a predetermined shape of any type. As for this list being evidence of anything, see my comment above about tyres.

As to assessing the aerodynamic 'purity' of a car, that's kind of subjective, and non-quantifiable.
I'd go no further than 'streamlined.'
Hucho used the terms ' optimum' and 'ideal' interchangeably in his 2nd-Edition.
Hucho explicitly described the streamline half-body as 'optimum'. The reader is free to interpret that adjective as they please.
Other than 'wings', the streamlined body of revolution-based half-body, is the only other path to ultra-low-drag according to Hucho.
The discussion of 'wings' is for it's own dedicated thread.

Hmm, so overlaying a template over cars and saying 'it would be so much better if only it matched the template' is as nonsensical as it sounds?

Without any 'testing' or 'measurements,' I've found the 'template' to be adequate for facilitating land speed records, distance records, and low-emissions records.

For amateur modifications it's shown a propensity for low drag, as a 'first' and perhaps 'last' approximation for streamlining.

Yes, and just as with the tyres, I've found that 225-section tyres give excellent results on many cars - something which proves absolutely nothing about 225 tyres.

Unfortunately the application of the template is just your weird theory - and I say 'unfortunately' because if it were as easy as that, gee, that would be good.

To others reading this, I'll say again. Don't believe me - just look in any car aero textbook and find those major sections extolling the value of a template. There aren't any.