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Old 06-10-2020, 01:24 PM   #41 (permalink)
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Aerohead's wind tunnel testing

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Originally Posted by JulianEdgar View Post
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.
Interesting that the curved-wall,curved-ceiling,A2 wind tunnel data went uncontested, but somehow,the curved-wall,curved-ceiling,DARKO data, a wind tunnel of which shares its design from the same Gary Eaker of the A2, is immediately called into question.
Do you also slam Pininfarina? It has a remarkably small test section cross-section and 'blockage-ratio' , yet return some of the best numbers in inter-tunnel calibration model testing.
Have you read Alan Pope's book on low-speed wind tunnel testing?
And perhaps it didn't register, that Hucho commented, that it didn't matter what tunnel one used for vehicle-specific testing,as long as you stuck with the same tunnel.
And perhaps you're unaware that people like us weren't allowed into, or couldn't compensate for all the race teams which had 'big tunnels' pre-paid for all the tunnel time spoken for,for years into the future.
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You haven't proved any theory wrong so far.

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Old 06-10-2020, 06:21 PM   #42 (permalink)
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Quote:
Originally Posted by aerohead View Post
Interesting that the curved-wall,curved-ceiling,A2 wind tunnel data went uncontested, but somehow,the curved-wall,curved-ceiling,DARKO data, a wind tunnel of which shares its design from the same Gary Eaker of the A2, is immediately called into question.
Do you also slam Pininfarina? It has a remarkably small test section cross-section and 'blockage-ratio' , yet return some of the best numbers in inter-tunnel calibration model testing.
Have you read Alan Pope's book on low-speed wind tunnel testing?
And perhaps it didn't register, that Hucho commented, that it didn't matter what tunnel one used for vehicle-specific testing,as long as you stuck with the same tunnel.
And perhaps you're unaware that people like us weren't allowed into, or couldn't compensate for all the race teams which had 'big tunnels' pre-paid for all the tunnel time spoken for,for years into the future.
So if tiny wind tunnels without moving wheels are all that's needed, car manufacturers have chosen to build huge wind tunnels just because they like spending money? I mean seriously, anyone who defends data yielded from a tiny wind tunnel with a massive blockage factor is just off in another world.

And yes, I do have the cited book on wind tunnel testing. Five of the 18 chapters are devoted to the corrections needed to gain any useful data! And a small wind tunnel just makes everything worse.

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Originally Posted by aerohead View Post
------------------------------------------------------------------------------------
You haven't proved any theory wrong so far.
I have comprehensively proved wrong many of your applications of theory to real cars. As I have said, I don't care what you believe, but when you start leading others astray with your poor advice, then I don't think that is right.
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Old 06-12-2020, 11:04 AM   #43 (permalink)
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tiny tunnels

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Originally Posted by JulianEdgar View Post
So if tiny wind tunnels without moving wheels are all that's needed, car manufacturers have chosen to build huge wind tunnels just because they like spending money? I mean seriously, anyone who defends data yielded from a tiny wind tunnel with a massive blockage factor is just off in another world.

And yes, I do have the cited book on wind tunnel testing. Five of the 18 chapters are devoted to the corrections needed to gain any useful data! And a small wind tunnel just makes everything worse.



I have comprehensively proved wrong many of your applications of theory to real cars. As I have said, I don't care what you believe, but when you start leading others astray with your poor advice, then I don't think that is right.
1) for twenty years, the maximum speed limit in the United States of America was 55- MPH.
2) at 55-MPH, the delta-mpg associated with spinning wheels constituted on the order of 0.5%.
3) in 1995, when the federal government repealed the 55 MPH National Speed Limit, and began to allow individual states to relax speed limits, by default, the impact of wheel drag would necessarily increase.
4) also, SAE requirements for 'crosswind-averaged' coefficients of aerodynamic drag, with yaw angles up to 12-degrees, would necessitate room for turntables for yaw, and in turn, necessitate larger test sections, and larger jets, larger fans, more horsepower, etc..
5) the cost of advanced wind tunnels are a legitimate corporate tax write-off, and customers will ultimately foot the bill for the expense, so why wouldn't they ?, especially during Democratic administrations, calling for 52.5-mpg CAFE standards.
6) Aerodynamic drag reduction is the cheapest way to higher fuel economy.
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* You'll remember from Hucho, that Pinifarina, while one of the world's 'smallest' wind tunnels, returned drag coefficients, some of the closest to the center of the 10-tunnel standard deviation.
* If ' the exception proves the rule', then the accuracy of Pinifarina's data must be a caveat to your claim of 'large tunnel supremacy.' That's all I'm saying.
* And as Richard Feymann admonished Cal Tech graduates, Hucho admonishes: ' ... the vehicle aerodynamicist must refer to a large amount of detail resulting from earlier development work.' ( page-1, PREFACE)
This is an example of a perspicacity failure on your part. From the very first page of the book!
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So far, you, yourself, have failed to demonstrate a failure of any material I've shared. ' Read my book' is not a scientific argument.

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