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Old 01-08-2021, 12:13 PM   #131 (permalink)
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many reasons, etc.

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Originally Posted by AeroMcAeroFace View Post
4) Or maybe they dismiss it due to results not being scientifically rigorous, not thought out well, not founded in science, based on flawed assumptions? Many reasons other than ignorance I can think of.

5) It is strange that you keep telling us that the template(s) (of which there are now 8) are universally applicable, but all of a sudden the windsor body is the wrong one?
6)same answer as 5)

7) do you have actual evidence for that claim? As far as I can tell, your evidence is based on a highly blocked wind tunnel, which is okay for streamlined shapes but not spirit of ecomodder. You believe it to be streamlined (streamlined means no separation) so that evidence relies on your belief.
1) Yep, Hucho's a real slacker. His PhD in mechanical engineering, running a climatic wind tunnel for a decade, spending decades around automotive aerodynamics, and working under some of the folks who literally wrote the books on aerodynamics obviously would have no credibility when recommending a pathway to low drag.
5) Would you like to offer a specific citation where I ever claimed this attribution to universality?
And have you actually looked at the Windsor body? Does it share anything even resembling a production passenger car?
7) It worked for the ITworks CRX HF. A land speed record at Bonneville. An amateur mpg record. Data from the SCTA and technical staff of CAR and DRIVER, at Bonneville and Chrysler Proving Grounds. Data reduction and results from CAR and DRIVER and General Motors Aerodynamics Laboratory.
If you'll re-visit Hucho, 2nd-Edition, chapter on wind tunnels, you'll be reacquainted with the fact that blockage ratios in excess of 30% are perfectly acceptable for zero-yaw testing. I've never made any claims for my quanta which were outside of the conditions under which they were derived.
So far, nobody's connected the dots on the blockage-ratio correction-factor Toyota Prius calibration model I used, as per Hucho's protocol.
* Spirit began at Cd 0.5016, and went to Cd 0.195 as a BEV, unibody, 'camera' truck.
* Based upon Hucho's metrics, Spirit's top speed would improve from 96-mph, to 115-mph. ( In Tucson, Arizona, I accelerated to catch, and then settle in long enough at 108-mph, to record the US GOVT license plate of a US Homeland Security, Chevy Tahoe cruising eastbound at that speed. I would have had to exceed 108- mph in order to pursue, and then catch up to the Tahoe. Think whatever you want.)
* We also need an explanation for the 957-mile range at 65-mph, for the 24-gallon tank, which I've experienced on three occasions.
* The GARMIN GPS that I use for speed, odometer, altimeter, and compass, is 'dead- on' according to the Southern California Timing Association, which is the official timing body for all FIA World Speed Records in the United States.

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Old 01-08-2021, 03:39 PM   #132 (permalink)
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Quote:
Originally Posted by aerohead View Post
1) Yep, Hucho's a real slacker. His PhD in mechanical engineering, running a climatic wind tunnel for a decade, spending decades around automotive aerodynamics, and working under some of the folks who literally wrote the books on aerodynamics obviously would have no credibility when recommending a pathway to low drag.
I've mentioned this before here, but when I emailed Hucho directly last year and asked him what he would recommend to reduce the drag of my car, he said nothing about any sort of template, tapered tail, half-body of revolution, or extension at all.

Be sure you're differentiating between what Hucho has actually recommended, and what you recommend as pathways to low drag. He is by far not the only author to treat low-drag idealized shapes--although some others do at much more length--but all of them that I have read consider streamlined half-bodies as shapes which can be, in Hucho's words, "progressively transformed into a car." (He wrote this in a section which does not appear in the 2nd edition).
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Old 01-08-2021, 04:06 PM   #133 (permalink)
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I've mentioned this before here, but when I emailed Hucho directly last year and asked him what he would recommend to reduce the drag of my car, he said nothing about any sort of template, tapered tail, half-body of revolution, or extension at all.

Be sure you're differentiating between what Hucho has actually recommended, and what you recommend as pathways to low drag. He is by far not the only author to treat low-drag idealized shapes--although some others do at much more length--but all of them that I have read consider streamlined half-bodies as shapes which can be, in Hucho's words, "progressively transformed into a car." (He wrote this in a section which does not appear in the 2nd edition).
1) ' [I]t is very important to design a rear body surface which brings the divided streamlines smoothly together. Optimum shapes are 'streamlined' bodies having a very slender rear part.' Hucho, page- 61.
2) ' [L[ow drag can only be achieved when the separation at the rear is eliminated.' Hucho, page- 16
3) ' [T]he optimum shape in terms of drag is a half-body, which forms a complete body of revolution together with its mirror image - produced through reflection from the roadway.' Hucho, page-16.
4) ' [T]he drag of the basic body is achievable. To what extent this can be approached in the development of a production vehicle is therefore more a question of the balance of the requirements of the specification, than of technical feasibility.' Hucho, page-209
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Old 01-08-2021, 04:14 PM   #134 (permalink)
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Quote:
Originally Posted by Vman455 View Post
I've mentioned this before here, but when I emailed Hucho directly last year and asked him what he would recommend to reduce the drag of my car, he said nothing about any sort of template, tapered tail, half-body of revolution, or extension at all.

Be sure you're differentiating between what Hucho has actually recommended, and what you recommend as pathways to low drag. He is by far not the only author to treat low-drag idealized shapes--although some others do at much more length--but all of them that I have read consider streamlined half-bodies as shapes which can be, in Hucho's words, "progressively transformed into a car." (He wrote this in a section which does not appear in the 2nd edition).
After reading my book, Dr Hucho wrote nothing to me about a template of any kind.

He was more concerned that I didn't have a chapter on wind tunnel testing than I'd completely missed this amazing template that Aerohead ascribes to him.

What you will find in Hucho's book is this diagram:



No less than five low drag shapes, all looking different! So which one are we to pick to help us in our modifications? Depending on that, the resulting mods will have quite different shapes! And how can that be so, when we've been told here for so long that there is only one template? (Or two, I find it hard to keep up.)
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Old 01-08-2021, 04:17 PM   #135 (permalink)
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Quote:
Originally Posted by aerohead View Post
1) ' [I]t is very important to design a rear body surface which brings the divided streamlines smoothly together. Optimum shapes are 'streamlined' bodies having a very slender rear part.' Hucho, page- 61.
2) ' [L[ow drag can only be achieved when the separation at the rear is eliminated.' Hucho, page- 16
3) ' [T]he optimum shape in terms of drag is a half-body, which forms a complete body of revolution together with its mirror image - produced through reflection from the roadway.' Hucho, page-16.
4) ' [T]he drag of the basic body is achievable. To what extent this can be approached in the development of a production vehicle is therefore more a question of the balance of the requirements of the specification, than of technical feasibility.' Hucho, page-209
All quite correct, but no evidence whatsoever for how you apply a template shape on this forum for people modifying their road cars. Viz, to purportedly do these things:

- 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
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Old 01-08-2021, 05:02 PM   #136 (permalink)
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Quote:
Originally Posted by Vman455
but all of them that I have read consider streamlined half-bodies as shapes which can be, in Hucho's words, "progressively transformed into a car."
That's the real trick isn't it. How to define and fabricate a quasi-optimal shell. This was intended as metaphorical:



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Old 01-09-2021, 01:49 PM   #137 (permalink)
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Quote:
Originally Posted by aerohead View Post
1) Yep, Hucho's a real slacker. His PhD in mechanical engineering, running a climatic wind tunnel for a decade, spending decades around automotive aerodynamics, and working under some of the folks who literally wrote the books on aerodynamics obviously would have no credibility when recommending a pathway to low drag.
5) Would you like to offer a specific citation where I ever claimed this attribution to universality?
And have you actually looked at the Windsor body? Does it share anything even resembling a production passenger car?

* Spirit began at Cd 0.5016, and went to Cd 0.195 as a BEV, unibody, 'camera' truck.

* Based upon Hucho's metrics, Spirit's top speed would improve from 96-mph, to 115-mph. ( In Tucson, Arizona, I accelerated to catch, and then settle in long enough at 108-mph, to record the US GOVT license plate of a US Homeland Security, Chevy Tahoe cruising eastbound at that speed. I would have had to exceed 108- mph in order to pursue, and then catch up to the Tahoe. Think whatever you want.)
As Vman455 so excellently wrote: "I've mentioned this before here, but when I emailed Hucho directly last year and asked him what he would recommend to reduce the drag of my car, he said nothing about any sort of template, tapered tail, half-body of revolution, or extension at all."

Mis-interpreting books written by experts and then quoting them is not evidence.

5) The fact that whenever anyone new comes on this forum, often the first thing you say is use the template. I don't remember, ever, you saying don't use the template, it won't work on your car. That is certainly implied universality.

And have you actually looked at the Windsor body? Does it share anything even resembling a production passenger car? How about, have you seen the template in 3d form, does it share anything even resembling a production passenger car? The windsor body looks more like a car than the template does. You can't suddenly change standards and claim one body to not be like a car and the other one to be like a car.

Wasn't the top speed as a claim of drag reduction to sub 0.2 shown to be not true by both Julian and R.H Barnard?
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Old 01-09-2021, 02:54 PM   #138 (permalink)
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Wasn't the top speed as a claim of drag reduction to sub 0.2 shown to be not true by both Julian and R.H Barnard?
Interesting story behind that.

First, when Aerohead offered pics/description of his truck for inclusion in my book, there was lots of back and forth emails as I kept questioning his claims. (I didn't then know Aerohead from bar of soap, but it was pretty obvious some of what he was claiming was highly doubtful.) Therefore, I didn't run any of his claimed drag coefficients in the description of his truck in my book.

One thing that raised red flags was his new/old top speeds, that didn't seem to match the claimed improvement in drag. Using Aerohead's figures, I did some calculations (page 21 - I didn't mention Aerohead, but that's the data I was using) and they showed his new claimed Cd was not right. On the basis of the top speeds he then gave me (I see Aerohead uses completely different speeds in his post above, but anyway...) it appeared to be a change in Cd from 0.44 to 0.37.

However, when Dr Wolf of Porsche read my book after publication, he said he had a much more accurate way of calculating changes in top speed with changes in Cd, and gave me a new equation to use. When I apply that equation to Aerohead's original new/old top speeds, I get 0.33 - so better than I originally calculated.

And if the correct figure is 0.33, that's an excellent reduction from the starting point (well the originally quoted one, anyway) of 0.44. Based on all I have researched about reducing drag, and looking at the pics of the truck, I'd also say that's possible.

But a claimed Cd of 0.195? That was always ridiculous.
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Old 01-09-2021, 05:31 PM   #139 (permalink)
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However, when Dr Wolf of Porsche read my book after publication, he said he had a much more accurate way of calculating changes in top speed with changes in Cd, and gave me a new equation to use. When I apply that equation....
Can the equation be expressed in ASCII or does it require LaTeX (https://www.latex-project.org/)?
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Old 01-09-2021, 06:32 PM   #140 (permalink)
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Can the equation be expressed in ASCII or does it require LaTeX (https://www.latex-project.org/)?
No, I'll save that for the next edition of my book. I don't give *everything* away here.

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