Want low drag? Don't follow a template.

[JulianEdgar]

Originally Posted by aerohead

* Your book is written for the car enthusiast and non-engineer.
* Those of us here, with an engineering background, will find certain aspects of your investigations and conclusions falling outside the bounds of scientific rigor.
* Three times already, I've attempted to direct you towards science which would provide a much deeper insight into your experiences and interpretations. And it looks like three times it was all for naught. None of your subsequent posting reveal any hint that you spent even a pico-second with the material. Had you processed it, it would be impossible for you to cling to your folk knowledge.
* I'm in doubt that your international panel of experts actually signed off on as much of your book as you claim. I'd very much like to see what your exchanges actually were, and did some things get lost in translation between an engineer-aeronautical engineer- aerodynamicist, and a sociologist-geographer.

The reality is that not only was a professional aerodynamicist (Dick Barnard) used as a technical consultant throughout the book's development (reviewing every paragraph), but the book was also reviewed in detail by another three experts as it was being written (ie I sent them each chapter in turn and they wrote extensive comments).

Since publication, the book has been reviewed by a further three professional aerodynamicists (you know, like the current head of Porsche aero) who have also given me extensive feedback.

None of the feedback from these professional car aerodynamicists would cause me to change the book sections you say are incorrect.

So I could believe what five top experts in car aerodynamics tell me - or I could believe Aerohead on Ecomodder. Hard choice, I know.

[kach22i]

Originally Posted by AeroMcAeroFace

I don't think anyone disagrees that perfectly following the template with a true half body of revolution on a plane is incorrect. That is what that drivers pod is, the perfect and correct use of the template and that shape.

What is incorrect is to say that the shape can be applied universally to non half bodies of revolution, or that a car that doesn't follow the shape is somehow wrong.

Yes and no.

Double the ratio for blisters.

See post #7 by me in link below.

Scaling the Template
https://ecomodder.com/forum/showthre...ate-25975.html

Originally Posted by aerohead View Post
If you inspect Hoerner's 'AERODYNAMIC DRAG',his treatment of canopies and blisters(pontoon fenders and separate greenhouse) actually goes in the other direction.
Instead of a 5:1 fineness ratio,he'll recommend 10:1.
It has to do with interference drag and super-velocities created by these individual elements when placed in proximity to one another.
This is a reason for keeping the aerodynamic 'singularity' of the 'Template' half-body rather than 'combination-forms.'
Since the half-body doesn't allow separation and produces minimum shear it's virtually unbeatable for a door-slammer.

More than one way to use or not use the template was my argument back in 2013. I used many specific examples but did not preface it on tuft attachment although perhaps I should have in retrospect.

Case example was NASA/Dryden truck tail treatment.

Would be interesting to examine if aggressive tail-cone angles of NASA/Dryden truck would have been better off following the template or not.


The Greyhound bus elongation images recently re-posted in one of the bus treads may serve as an example of template-style tail treatments, not sure - will review at a later time.

[aerohead]

Originally Posted by JulianEdgar

The whole idea that 'basic shapes' (let alone 'the template') can guide us in the following is just absurd:

- 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

Maybe you should read some current aero textbooks, or do some proper on-road testing, to find that out for yourself?

Even the first in the above list ("the template will show us where there is separated and attached flow on existing cars") can be disproved in a few hours of tuft testing - as I showed in the video.

Seriously, we've (I hope) moved beyond blind faith in incantations.

* If you'll re-read Hucho's 2nd- Edition, you'll realize that you're scientifically incorrect on all four counts.
* Your own book corroborates everything I've posted about the 'template.'
* No current textbook can overturn the fundamentals of fluid mechanics.
* If you'd understood Hucho's book you'd already know that you're completely mistaken about most of your conclusions from your measurements.
* You didn't show us anything of value in your video. It' s very misleading.

[aerohead]

Originally Posted by JulianEdgar

In fact, why don't we all stop stuffing around and actually go to the most recent, authoritative and up to date reference on car aero - and quote all the mentions (that it does not have) to 'the template'?

That could save a lot of time, couldn't it?



Oh, of course, it's all wrong too....

' To know and not tell makes cowards of men.' Abraham Lincoln
Okay, so what does it say specifically. Otherwise you're just name-dropping. I'm not impressed by book covers.
Perusing SAE International's website, and the PREVIEW feature for recent SAE Papers hasn't lead to any revelations in modern road vehicle aerodynamics that I can discern. Quite the contrary.

[aerohead]

Originally Posted by AeroMcAeroFace

I don't think anyone disagrees that perfectly following the template with a true half body of revolution on a plane is incorrect. That is what that drivers pod is, the perfect and correct use of the template and that shape.

What is incorrect is to say that the shape can be applied universally to non half bodies of revolution, or that a car that doesn't follow the shape is somehow wrong.

Hucho used 'optimum' and 'ideal' interchangeably in his 2nd-Edition.
All he said was that, if the design specification for a car included really low drag, then the template would be only the path to that.
We're not discussing consumer acceptance or anything else. Strictly low drag, related to something human beings could sit inside, as they do today.
Hucho provided the quanta. Hucho provided caveats and conditions. It's just technology, waiting in the wings, for 98-years now.

[aerohead]

Originally Posted by JulianEdgar

I am sorry, but now you are just making things up. There is no reference whatsoever to a template in SAE Paper Number 2011-01-0175, the development of the Audi A7 Sportback.

You sir, are mistaken.
A blueprint of the Audi A 7, and Audi's video about the A7 revealed that, on comparison to the template, the template predicted the separation on the A7 exactly as reported.
The paper goes on to discuss how Audi pushed the spoiler up level, through the separated flow to the template contour ( from the blueprint ), to first kill the separation / lift, then angled the spoiler up another 30cm higher to achieve additional direct downforce ( also from the blueprint ).
* The Audi had separation which you've claimed is impossible.
* The Audi had attached longitudinal vortices which you've claimed is impossible.
* The Audi had vortex-induced downwash which you've claimed is impossible.
* The Audi had separation-induced rear lift which you've claimed is impossible.
* By doing everything I've advocated, Audi was able to reduce rear lift as well as drag, by respecting the template, exactly as Hucho explained in his 2nd-Edition.

[aerohead]

Originally Posted by JulianEdgar

The reality is that not only was a professional aerodynamicist (Dick Barnard) used as a technical consultant throughout the book's development (reviewing every paragraph), but the book was also reviewed in detail by another three experts as it was being written (ie I sent them each chapter in turn and they wrote extensive comments).

Since publication, the book has been reviewed by a further three professional aerodynamicists (you know, like the current head of Porsche aero) who have also given me extensive feedback.

None of the feedback from these professional car aerodynamicists would cause me to change the book sections you say are incorrect.

So I could believe what five top experts in car aerodynamics tell me - or I could believe Aerohead on Ecomodder. Hard choice, I know.

Did any of them sign off on page-195 ? The reason I ask, is that, compared to page 186, you're saying the exact opposite with respect to the principles of fluid dynamics. No continuity.

[aerohead]

Originally Posted by kach22i

Yes and no.

Double the ratio for blisters.

See post #7 by me in link below.

Scaling the Template
https://ecomodder.com/forum/showthre...ate-25975.html


More than one way to use or not use the template was my argument back in 2013. I used many specific examples but did not preface it on tuft attachment although perhaps I should have in retrospect.

Case example was NASA/Dryden truck tail treatment.

Would be interesting to examine if aggressive tail-cone angles of NASA/Dryden truck would have been better off following the template or not.


The Greyhound bus elongation images recently re-posted in one of the bus treads may serve as an example of template-style tail treatments, not sure - will review at a later time.

My eyes were attracted to 'NASA', so I looked in.
There is a paper, from Norway or Sweden, discussing the interest of the US Air Force in the drag reduction of the steeply upswept tail on the Lockheed C-130 Hercules.
Within the paper, the author makes mention of NASA's truck research. He states that the stinger on the Ford Econoline test mule was attached at the separation line, and that it offered very little additional drag reduction, compared to the truncated tail. It is his belief that NASA would have seen lower drag if the sloping contour they chose, top, sides, and bottom, was less aggressive.
NASA's boat-tail, while maybe not perfect, is similar to what they designed for the Space Shuttle, which during separated free-flight from the mother 747, doubled the glide range of the spacecraft. Not too shabby!

[aerohead]

Originally Posted by Cd

Does anyone here have access to a Mercedes A class sedan ?
The car has an excellent .22 Cd, yet not only deviates from the template, but also has a short trunk / boot that you would think would keep flow from reattaching.
I seemed to recall it having quite a bit of tumblehome to the rear, and thought this maybe what helps the flow reattach, but after looking at one that my neighbpr has, I see that is not really such a big factor.

The reason I am asking is to see if someone would be willing to do a tuft test at the rear of the car to show what happens with the airflow. *

The .25 Cd LS-430 had an even steeper back window, but it has a longer trunk / boot that could help the air to reattach.

* or some CFD images of the rear of the car.

* Tufts will not necessarily allow an observer to easily distinguish between 'attached' flow and 'downwash,' whereas smoke will.
* The 'template' really shines with sub-Cd 0.15 vehicles, so Cd 0.22 is kind of a walk in the park by comparison, and doable with a notchback if the rear roof, C, or D-pillars, boot height, boot length, separation bubbles, and spoilers are all tuned to a symbiotic optimum.

[JulianEdgar]

Originally Posted by aerohead

You sir, are mistaken.
A blueprint of the Audi A 7, and Audi's video about the A7 revealed that, on comparison to the template, the template predicted the separation on the A7 exactly as reported.
The paper goes on to discuss how Audi pushed the spoiler up level, through the separated flow to the template contour ( from the blueprint ), to first kill the separation / lift, then angled the spoiler up another 30cm higher to achieve additional direct downforce ( also from the blueprint ).
* The Audi had separation which you've claimed is impossible.
* The Audi had attached longitudinal vortices which you've claimed is impossible.
* The Audi had vortex-induced downwash which you've claimed is impossible.
* The Audi had separation-induced rear lift which you've claimed is impossible.
* By doing everything I've advocated, Audi was able to reduce rear lift as well as drag, by respecting the template, exactly as Hucho explained in his 2nd-Edition.

Seriously, you are now just making up stuff.

The paper says absolutely nothing of the kind about the template or any such 'optimal shape'. Nothing at all!

And I have never said that any of the things you are quoting me as saying are impossible.

Perhaps you can find some direct quotes to support all this?