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Old 05-28-2020, 12:36 PM   #11 (permalink)
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Originally Posted by JulianEdgar View Post
Scaled to actual lengths would be most appropriate wouldn’t it?
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Originally Posted by bobo333 View Post
"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. ...
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:

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Old 05-28-2020, 05:50 PM   #12 (permalink)
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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.



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!
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Old 05-28-2020, 07:20 PM   #13 (permalink)
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Quote:
Originally Posted by JulianEdgar View Post
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?
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.

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Originally Posted by JulianEdgar View Post
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?
Not sure I know how to answer that. Best policy in anything is never to be doctrinaire. [?]

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Originally Posted by JulianEdgar View Post
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.
Not to me, but aerohead will have to explain what else he thinks it accomplishes.

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

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Originally Posted by JulianEdgar View Post
... 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.
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.

Quote:
Originally Posted by JulianEdgar View Post
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!
C'mon man, this is not a group think environment. Plenty argument here before you showed up, and about the template, too.
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Old 05-28-2020, 07:44 PM   #14 (permalink)
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Originally Posted by California98Civic View Post
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.
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.

Quote:
Originally Posted by California98Civic View Post
Not sure I know how to answer that. Best policy in anything is never to be doctrinaire. [?]
And the template isn't doctrinaire?

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Originally Posted by California98Civic View Post
Not to me, but aerohead will have to explain what else he thinks it accomplishes.
Well if it as normal, it will be an answer full of jargon, irrelevant citations, weird theories and red herrings! Unfortunately.

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Originally Posted by California98Civic View Post

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

Quote:
Originally Posted by California98Civic View Post
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.
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.

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Originally Posted by California98Civic View Post
C'mon man, this is not a group think environment. Plenty argument here before you showed up, and about the template, too.
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.
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Old 05-29-2020, 12:24 PM   #15 (permalink)
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variety

Quote:
Originally Posted by JulianEdgar View Post
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.



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!
* 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.
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Old 05-29-2020, 03:01 PM   #16 (permalink)
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side profiles

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Originally Posted by JulianEdgar View Post
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.
* 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.
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Old 05-29-2020, 03:06 PM   #17 (permalink)
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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

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Old 05-29-2020, 03:13 PM   #18 (permalink)
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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.
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Old 05-29-2020, 05:29 PM   #19 (permalink)
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Quote:
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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?



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

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* 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.
I'll remind you then:

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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?
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.
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Old 05-29-2020, 08:28 PM   #20 (permalink)
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How on earth is showing four different shapes, all with low drag, somehow arguing for a single template?
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.

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