'template' in contemporary aerodynamic literature
 

Hucho discusses the 'template' in his second edition. I've already provided all the citations.
Anyone reading the book in 1987,or after would already have had access to the theory and the off-the-shelf technology.
As long as Paris Dressmakers dominate design,it doesn't matter what's published. With or without a template. All an aerodynamicist can do,is submit data to the committee that will be making the decisions and spelling out the specifications.And those folks have been concentrating on hedonic adaptation since 1926 or so.They're the ones who killed off the 'template.' I believe that they'd prefer that the 'template' remain 'killed.' Alfred P. Sloan Jr. wrote a book on it.

A book that is 33 years old is not 'contemporary aerodynamic literature'.

If the shape of the template is the best for drag, I'd have expected many references to it in current aero tech literature. I know of no such references.

That says to me that you are over-simplifying your analysis, as it applies to road cars.

To a hammer, everything looks like a nail.

contemporary use
 

Please examine:
2006 Mitsubishi i
2008 M-B Bionic Boxfish
2010 Kia Ray concept
2010 Honda FCX Clarity
2010 BMW Vision Efficient Dynamics
2010 Vauxhall/Opel Flextreme GT-E
2011 SAAB Phoenix
2011 Tata Jaguar, 75-Anniversary C-X75
2011 Ford Evos

2012 Scion/ Aston Martin iQ/ Cygnet.
2012 Prius-V
2012 Toyota FT-Bh
2012 SolarWorld GT
2012 Honda Insight-II
2012 Subaru/Scion BRZ/-F
2013 Cambrige University CUER Eco Racer
2013 Mitsubishi Concept CA-MiEV
2013 McLAREN X-1
2013 Hyundai Veloster
2013 Honda AC-X Plug-in
2014 Chevrolet Spark
2014 Renault EOLAB
2014 Cadillac CTS V sport
2015 BMW i8
2015 Mitsubishi Mirage 'G'
2015 Ford C-Max Energi
2015 Alfa Romeo 4C
2015 Buick Riviera
2015 Chevrolet Corvette
2016 Hyundai Ioniq
2016 M-B IAA
2017 Chevrolet Bolt
2017 Acura NSX
2018 Nissan-Renault Alliance Alpine A100
2018 McLAREN 720S
2018 KIA Stinger GT
2019 McLAREN Speedtail
2020 Tesla Roadster
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' If we were to design the cars 100% streamlined,following all the aerodynamic principles,would not all the cars look exactly alike and the designers have nothing to do?' H. Schmude, General Motors Corporation, to, Walter Korff,Lockheed Aircraft Company, Automobile Engineering Congress, 1963, Re. SAE Transactions, Volume 72,Page 592, 1964.
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Hucho targeted 'designers' with his textbooks. Anyone who's read his books, whom possesses any perspicacity, will be fully aware of the 'template.'
Since the existence of the 'template' threatens their very existence,do you believe that they would openly discuss it?
That we even have to discuss it here on an obscure website,underscores a complete failure on the part of public education,worldwide.
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As to Adrian Gaylord. Jaguar has produced a Cd 0.26 vehicle? Quite an accomplishment,considering that Opel had a production Cd 0.26 in 1989. And R.G.S. White gave us a free recipe for Cd 0.245 as of 1969.

You have made a long list of cars. Are you saying they all have identical side profiles?

Yes, this sort of thing was often said in the past. Even now people write how all cars look alike because of aerodynamics. It's pretty odd, because I see cars that look completely unlike and yet have low drag.

Obviously I don't have the perspicacity then. Can you quote some page numbers?

Why aren't I surprised that you've now got into conspiracy theories...

No, it (the template) represents an example of a discussion group going down a rabbit hole where a theory was developed without a lot of evidence - and then grabbed joyfully because of its simplicity.

In fact, this is becoming more than a bit ridiculous.

The last two cars on your list: 2020 Tesla Roadster and 2019 McLaren Speedtail.

And according to you, they're meant to have the same shape? And that's like your template? Well, which one is? It can't be both - let alone all the other cars on your list.

https://i.postimg.cc/PqKbsTdz/compared.png

(Happy for someone with better software skills than I to overlay them.)

I mean at some stage you need to talk about the emperor's clothes - especially in a situation when people are actually spending money, time and energy trying to implement this stuff.

Over the template and each other: (highest point to highest point)

https://ecomodder.com/forum/attachme...1&d=1590662269

Scaled to actual lengths would be most appropriate wouldn’t it?

"The template" is designed to be scaled to the height of the tallest point iirc, that's the way I used it on my F100 aero canopy and the way I've seen it applied to most other vehicles on this site.

I doubt the tesla and mclaren are anywhere near the same size but I don't think scale is relative to the shape in the context of "the template"

Wikipedia gives 5137mm for the length of the Speedtail, but for the Roadster I only found an estimate 4382mm (translated from 172.5"). That would put these images within 2% of each other relative to real size.

Yes, that's the way it has been applied here. Match the zero point on the template with the point of highest roof camber, making adjustments as needed. It has had very good effect nearly all the time, on a variety of vehicles, in a variety of tests but usually testing has been limited to somewhat longterm fuel economy tracking. bobo333's pickup and lots of other pickups on EM have gained fuel economy applying the template to bed covers (sometimes really beautifully built too).

There was also a red Gen1 Insight with an excellent, beautiful red boattail. Yes, Julian, the template was used to improve the aero of YOUR car's already slippery body shape. Wanna do some throttle stop testing? THAT would be cool, given your fabrication abilities and testing opportunities.

There were kamm backs too that applied aspects of the template... you are swimming upstream here Julian in part because many of us have watched template ideas work nearly all the time when applied well. That has certainly been what I have seen these last 9 years.

EDIT: Here is MetroMPG's Insight build, a great thread with images, video, and test results (and a link to the red Insight):
https://ecomodder.com/forum/showthre...tml#post361057

SECOND AND LAST EDIT:
http://ecomodder.com/forum/attachmen...1&d=1293910565

So if the template can be scaled in the way you describe, isn't it basically just an angle? The angle from the front the windscreen header rail to the rear of the car?

And then when we look at cars with angles that differ like the 2020 Tesla Roadster and 2019 McLaren Speedtail, isn't it just a range of that angle?

You say "It has had very good effect nearly all the time, on a variety of vehicles, in a variety of tests but usually testing has been limited to somewhat longterm fuel economy tracking."

I'd expect that to be the case if the flow remains attached - and that's great. But what I cannot see is why this is somehow regarded as the best shape.

It's like the person who says a particular airfilter gave good engine power - but hasn't compared it to any others.

I just posted this in another thread. It's from Hucho 2nd ed p.201. It shows how a variety of shapes can be used to give the same low drag.

https://i.postimg.cc/k4VTZ8Nd/IMG-0450.jpg

I think the idea that there is a 'best shape' is a bit simplistic - and especially in the real world, the thickness of the boundary layer (that in turn will depend on what is happening on the forward section of the car) will help determine if the flow remains attached.

As to swimming upstream - that's something I am very used to doing, especially in the often group-think environment of an online discussion group!

No, it is a curve. And its placement is generally indexted to the point of greatest roof camber. It has been used here to design Kamms and boat tails as well as trailer hitch storage boxes and more. As I said, kick some butt by building one on MetroMPG or Bottsaper's model for the Gen 1 Insight and throttle stop test it. Would be a great test.

Not sure I know how to answer that. Best policy in anything is never to be doctrinaire. [?]

Not to me, but aerohead will have to explain what else he thinks it accomplishes.

Oh, he and we have compared it to others... the various template threads and countless other debates here would attest to that. This EM board debates alright.

It is simple and it works, which is Pragmatism's test of truth. Simplistic is pejorative. What matters it that it is a form that DIY modders can overlay onto a lot of bodies and get results. But you make a reasonable point: there are more possibilities.

C'mon man, this is not a group think environment. Plenty argument here before you showed up, and about the template, too. :)

Why do people keep asking me to do tests? The reason I have described the testing methodology is so that everyone can do them. People write as if I have a monopoly on testing!

I actually think the boat tail looks ugly, and it would be illegal where I live.

And taking one approach that has proved to work doesn't mean it is the best approach.

And the template isn't doctrinaire?

Well if it as normal, it will be an answer full of jargon, irrelevant citations, weird theories and red herrings! Unfortunately.

There are examples where people tried different 'template style' shapes and thoroughly tested each? Can you link me to some?

Lots of things are simple and they work. But that doesn't make them the best approach. I have no issues with general guidance being that the taper angle should be around 12 degrees. In fact, my testing resulted in that figure on a wagon roof extension I made and tested (Page 134 of my book). It is also an angle used in setting EBLAs (effective backlight angles) - page 130.

But to suggest to people that here is the shape you should use, I think is simplistic and wrong. That's especially the case when building something to follow the prescribed curve is going to take quite a lot of effort.

I have seen so many statements made here that are simply wrong and yet are not challenged. (And not just on car aero - one I saw here the other day on acceptable engine oil temperatures just had my jaw dropping.) Like, stuff I'd expect anyone interested in car modification to immediately call out. But it's just accepted.

variety
 

* Below 250-mph,the bulbous nose of the 'template' is of the lowest drag, and provides for extremely good outward vision,which is lacking in some of the other VW shapes.
* The 'template' is modeled upon the lowest drag streamline body of revolution,at Cd 0.04. It's in Hucho, page 61, in Hoerner's drag table.
* In ground reflection, it actually produces Cd 0.08.
* Adding wheels raises it to Cd 0.13.
* Adding the diffuser drops it back to Cd 0.12.
* Goro Tamai's full wheel skirt package allows it to approach the Cd 0.07- 0.09 which Hucho says could be achieved,for exactly the reasoning I've shared. It's just off-the-shelf-technology.
It may not be the 'best',but it will generate Cd 0.12 and lower,depending upon how well one does with the wheels.
Since some of the folks here expressed an interest in really low drag, I thought it could help save precious time and resources.All I can say is,that it works.

* The 'template's' aft-body is modeled on the shortest streamline body of revolution, which does not violate the Mair/ Buchheim aft-body taper angle of 22-23-degrees downslope.
* Since the sides of the body are essentially the same contour as the roofline, the body is more like two wingtips joined together, with so much transverse curvature that pressures self-equalize along the path to the rear,eliminating spikes.
* Spirit of EcoModder.com is based upon it.
* Spirit is zero-lift.
You could do worse.

side profiles
 

* The emphasis is on the aft-body profile since that's where the drag is.
* All the cars listed, with the exception of the SolarWorld GT virtually fit the 'template.' The contours may deviate for some of the span, yet recover before the separation occurs.
* I devoted an entire thread to Hucho's references.
* It's extremely disrespectful calling names,when you haven't done your due diligence in investigating my line of logic.
* Your behavior does evoke the conclusion that you're devoid of perspicacity,otherwise,your reading of Hucho would have brought you to the same conclusions. Gumby 79 made an interesting observation about connecting dots.
* I've no recollection of ever suggesting or advocating for any conspiracy theory, other than illustrating with H. Schmude's comment to Walter Korff about no need of designers if all car were completely streamlined. But then we run into the perspicacity issue. Jesus taught us not to cast pearls before swine. For that, I do own guilt.
* If, presuming that you do indeed possess critical thinking skills, will go back and read my posts concerning the 'template', you'll find a complete narrative,with all the citations from Hucho, which explain it's derivation.
* I can't comprehend it for you though.
* And if you continue to attack me,I'm going to petition the moderators to give you some cool-down time, off EcoModder.com, with which you can consider the tone of your language.
* If you were a PhD mechanical engineer,with a decade of experience running a world-class wind tunnel, it'd be one thing, or self-educated to that degree of mastery, but your comments belie a deficiency in the most basic,fundamental understanding, under girding road vehicle aerodynamics.
* All I'm experiencing is fear-based, dominance rituals,from a non-alpha wannabe, perhaps terrified of losing guru status, and loss of book sales if the secret were to get out. We've tried to help you out with some science, only to have our gifts thrown back in our face and then spit on. Maybe that's the custom in Australia. ' don't know.

How about it is just the profile scaled up or down to fit. Doesn't make the profile different, look at tapered wings. Same profile same thickness %, same COP, CD, COL only thr Reynolds number changes. NACA said in their preamble that one can scale the profile to fit the application

same low drag
 

This lowest drag form in Hucho's illustration, for all intents and purposes is the 'template.' If you'll look at the preceding page, you'll see the drag table for this VW 'Flow' body Long-Tail, Cd 0.14. It's the lowest drag form tested by Buchheim et al. I posted the image many years ago, before PhotoBucket seized everyone's account for extortion.
Arguing against the 'template' with the 'template' is some sort of weird circular- logical cul de' sac.

How on earth is showing four different shapes, all with low drag, somehow arguing for a single template?

https://i.postimg.cc/VkBfFpHQ/IMG-0450.jpg

That's the point - to suggest that a single shape is "the best" is pretty silly.

I'll remind you then:

I'd call the idea that professional aerodynamacists don't discuss the template "because it threatens their existence" a pretty good example of a conspiracy theory.

It's really quite clear to me what aerohead is arguing: re-examine the previous page. There, the VW flow body longtail, the closest to the template, has the lowest drag of these four shapes (0.14). So if we argue that these are four ways to the LOWEST drag, we'd been incorrect since their Cd figures were not the same (VW flow body longtail, the template roughly, was lowest). Lowest is lowest, just like fastest is fastest.

That's not my argument. I don't have the second edition. I have the 4th.

The VW flow body longtail is only closest to the template?! Surely then we should all be using the VW flowbody long tail as the template, and not something that is only close? Then, once we are using an even more correct template, we'd all get even better results with our car modifications, no?

I just believe that, for people modifying their cars to achieve lower drag, all these templates (pick whichever one you want) are almost completely irrelevant.

That would certainly not be the case if we were developing solar race cars, or even human powered vehicles, but for people modifying their road cars, I just can't see it. But I can see people wasting a lot of time following a special curve that they're been assured will give them best results.

That's your belief? I think you mean you don't PREFER them. But they are effective. The tests of the various boat tail projects modeled on the angles and compound curves of the template that I posted and that you admitted you were not surprised would show a benefit demonstrate that one can use the template to effecctively modify road vehicles for greatly reduced drag. The Gen1 Insight projects of Botsapper and MetroMPG on this site reported 9 to 15% improvements in FE in testing. They proved its an effective approach.

Well I did ask you for links to threads where there had been proper testing of various different template style shapes for real car modification, but you didn't reply.

Yes, I think following a template in the mistaken belief that will get you a stellar outcome is wasting people's time. Far better that they do some testing and find out what is optimal on their cars.

As for your examples, as I've already said - if the extension has attached flow down to a smaller wake, I'd expect pretty good results... template or no template.

To make it categorically clear, I think posting a template for car shape on a discussion group and very strongly implying that it is the best shape for people to follow (no matter their car) is misleading and wasteful of people's time.

It might have been helpful in a past era when testing panel pressures, drag and lift were difficult, but that is not the case now.

I had already given you testing results. Exellent examples that show ways in which it works. I am not your research assistant. If you want more, you know how. Your beliefs are your own. The evidence is all there.

The template is just like any other rule of thumb in car modification.

Like, run 12.5:1 air/fuel ratio for best power.
(In fact, you'll often find that best power comes from AFRs that are not 12.5:1. It depends on the engine.)

Or, suspension natural frequency should be 1:1.3 front/rear.
(Yes, if you want to reduce pitch. But sometimes you'll find that pitch accelerations are the least of your worries.)

Or, size your turbo so that you get peak torque by 1/3rd redline rpm.
(That's one I like but for many people, it will limit top-end power too much.)

Rules of thumb are useful for people who have no idea at all, but in nearly every case, where you can do some testing on your own vehicle, you'll achieve better results than by using rules of thumb.

And the beauty of aero modification is that it's so easy to test different approaches on your car.

(And I am sorry, but citing a modification and then saying 'it worked' is not evidence that the approach is the best. I could say that about 12.5:1 AFR, 1:1.3 natural frequency, or turbo sizing. "It works!")

I already know all that Julian, as do lots of people. It takes no special training. And it's beside the point. I showed you tests of applications and not mere vivid assertion of success and what's best for all vehicles in all circumstances. You have a crappy method of of dialogue, dude. Didactic condescension like this is a real turn off. Good luck with that book you're selling.

I am sorry that you cannot see the parallels. The template is a good example of a rule of thumb being applied to car modification. People love rules of thumb in car modification because they are easy, but in every area of car modification that I know of, testing beats rules of thumb every time.

(And so far, you haven't shown me even one test where different 'template approaches' were compared. You've shown me some successful outcomes that followed one template, and said: there you are. I could equally show you an engine successfully running 12.5:1 AFR and say: there you go.)

I think that rules of thumb in all areas of car modification should be avoided, as they often deceive as much as they enhance knowledge. In my car modification books I avoid using rules of thumb as much as possible.

In fact I'd go further: as soon as you see a rule of thumb stated in any area of car modification, be very skeptical.

Sure Julian. Rules of thumb. Be skeptical. I remember my mom teaching me that when I was a teen. Thanks for the reminder. Your style of marketing here reminded me of someone: https://m.youtube.com/watch?v=xHash5takWU

I am sorry if you cannot appreciate the parallel.

Marketing? If I were here to market my book, I'd agree with every silly thing that people said. And, unfortunately, there would be a lot to agree with!

Rules of thumb abound on this group, and very few people ever challenge them. So yes, I think a warning against using rules of thumb in car modification is very apt here.

In fact I did a video on it a while ago:

https://www.youtube.com/watch?v=v_Btd0PUtjY

I am sure you'll enjoy the comments and my responses - more of my marketing!

Professor Wagstaff! Such epistemology, such methodology! Oh, benighted internet, your rule of thumb, he's against it!

the case now
 

Keep researching.:)

Well that's the thing you see.

I don't just research, I also measure on the road (lift/downforce, separated/attached flow, panel pressures) and so I can see not only what is predicted to happen, but what actually happens.

It's very illuminating.

Good point about the need to actually measure the aerodynamic effects of any modification on a particular car and its particular body design. With all the variables involved, how does one actually know what will happen with a particular modification unless its effects are actually measured?

Theory might get you in the ballpark, but it takes a lot more effort to win the game.

Yes, I agree. And when I got here in early 2011, the emphasis was on testing. Aerohead was part of that. He has done quite a bit of testing, including working at a wind tunnel. We usually did these tests on the road using a variety of measurement instrumentation. A few years ago, testing efforts fell off. Take a look at MetroMPG's guide to testing for forum members from 2009. Still useful:
https://ecomodder.com/forum/showthre...tml#post147532

I'd reject a too hard distinction between theory and empiricism. Theories are the result of empirical examination and can themselves be tested further. Darwin's theory is not an invention of his imagination. It was an empirical investigation testing somewhat different concepts. Science is not just an accumulation of measurements. The aerodynamic qualities of the so-called template and similar low-drag bodies have been investigated empirically. The only controversy about them is whether they are appealing or practical as road cars.

theory
 

The transistor was designed from theory.
Theory allows us to design aircraft and rocket ships inside a computer,within 1% accuracy.
All skyscapers are designed from theory.
All nuclear submarines are designed from theory.
The integrated circuit was designed from theory.
The upcoming Corona Virus vaccine will be derived from theory.
Theory allows capitalism to thrive.

research
 

Keep researching.Full Navier-Stokes equation would be a good one.

We must be seeing a different forum then. When I did my book, I asked people for examples of modifications that had been well-tested, so I could feature them. Lots of people contacted me but unfortunately I had to reject most of them because either:

• testing hadn't actually been carried out
• testing was done with poor methodologies (eg coastdown)
• their results were internally contradictory (eg claimed decrease in Cd didn't match actual increase in top speed)

As for Aerohead's wind tunnel testing, it was done in a such a tiny wind tunnel (with therefore such a huge blockage factor), I'd place zero credence on the results.

I can't see anything there about throttle-stop testing, lift/downforce testing or surface panel pressure testing. Or eroding clay testing or even tufting!

Who has said testing should replace theory? Not me, anyway. The actual argument is this: if test results do not match theory, then the theory (or mostly in Aerohead's case) the application of it, is wrong.

That may be your belief; it is not mine. I agree that there is controversy about them in appeal and practicality as road cars, but I also have strong doubts about they way they are applied in developing modifications to existing cars - after all, what basically 99 per cent of people here are doing.

The scary thing is that everyone is seeing a different forum.
You make a positive contribution here, hopefully everyone can coexist.

Thee Template is a Procrustean Bed. Everyone slavishly follows the longitudinal section while ignoring the lateral section. And it fails to model the underbody.

Vehicles are a collection of parts, the Template can be applied to subsets, like pickup aerocaps and the bubble top coupes. Times past we've had discussions (like tears in the rain...) about blisters and canopies.
Have you seen aerocivic?

Wouldn't normally chip in my 2 cents worth, but I think you're missing a few things from your post.

Nothing is designed from theory, things are DEVELOPED from theory. Design, production and testing, then going back to the design based on the physical testing results. It's an iterative process!

Otherwise we would never progress.

Theory AND development. Theory on it's own is useless. :)

Testing on it's own is also useless, if you don't know what to do with the results - you combine them with theory for an overall picture of what's actually happening.

Don't forget about all the failures with various buildings, nuclear reactors, transistors etc! :thumbup: because we only had a theory to go on when they were being designed.

Yes indeed.

I do a lot of electronics (been writing for electronics magazines for 25 years) and one thing is for sure - you never, ever publish an electronic project without first testing it.

(I worked for years with a top electronics engineer - a brilliant guy who had developed literally thousands of electronic projects. He used to say: "When you test the circuit, it never works exactly as you had expected!")