Rounded forms not necessarily the most aero

[aerohead]

Originally Posted by fusion210

From the Ford Flex article.



Does that sound wrong to anyone else?

The 8.9 Bhp may reflect only the aero portion of the Road Load Horsepower @ 55 mph.I'll go on record that I'm sure of it.
The total Road Load Horsepower ( aero and rolling resistance) for Darin's Metro was 10-hp at 50 mph.I would guess the Flex to require about 17 hp at 50. Just a S.W.A.G..

[aerohead]

I don't think the author was mis-peaking although what he writes has got to be taken in context.
If your object is to build a box,well then,there are 'optimization' tricks the aero folks can do to soften the blow.
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In 1933,Walter E.Lay took a Cd 0.85 brick on wheels and got it down to Cd 0.45 just by softening the nose.
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In 1955,Moller actually did the same to create the first VW bus with Cd0.42.
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Hucho was personaly involved in the early 1970s with the detail optimization of the VW Golf/Rabbit which trimmed the 'box' to Cd 0.42.
With additional modification the Golf/Rabbit is Cd 0.29 at same length.
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I would mention that Hucho states that this 'optimization will only take you so far.
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* Kamm really proved nothing about truncated tails.His first caveat is that the car will be purposely limited in length,which precludes the longer tail.
*Second,his models were so simplistic and severely compromised in form,that they were incapable of low drag.
* Kamm's best was Cd 0.23.The car that survives has Cd 0.37.
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* The Klemperer 'brick' of 1922 achieved Cd 0.16 with generous front radius and 30 % of boat tail.
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* Jaray achieved Cd 0.13 with his 74 % Template pumpkin seed.
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* Lay achieved Cd 0.12 with his full-Template pumpkin seed.
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My opinion is that all auto makers suffer from the tyranny of unity.As in undersea engineering and aeronautics 'designers' end up with a single solution for shape efficiency.This is the most terrifying concept to auto stylists since they were invented by DuPont with the annual styling change.
-------------------------------------------------------------------------- In 1963,the beast surfaced in the form of GM's Henry Shmude(sp?) who questioned the logic of Dr.Walter Korff of Lockheed,who advocated real streamlining in automobiles at that years SAE Congress.
Shmude's remark to Korff was that " If all cars were to be designed 100% streamlined,would they not all look alike,and we stylists would have nothing to do?" [ this isn't a PROBLEM in other industries ]
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Cd 0.355 is way better than the Cd 0.55 and worse for SUVs of recent memory,so in a way we should be thankful to Ford.
And I agree that an enormous amount of latitude can be had in the vehicle fore-body,which is why I basically ignore it in the 'Template'.
And that the article even mentions the rear turbulence, can be a game-changer for the un-initiated.
So for me,the article moves the whole issue of aerodynamic drag further into the light.Thanks Frank!

[3-Wheeler]

Hi Phil,

Thanks for a nice clarification and elaboration....

I especially like this:

Originally Posted by aerohead

My opinion is that all auto makers suffer from the tyranny of unity.As in undersea engineering and aeronautics 'designers' end up with a single solution for shape efficiency.This is the most terrifying concept to auto stylists since they were invented by DuPont with the annual styling change.

It seems that we can easily lose sight of "natures engineering" in birds and sleek under-water animals.

Jim.

[slowmover]

Originally Posted by 3-Wheeler

Hi Phil,

Thanks for a nice clarification and elaboration....

I especially like this:

It seems that we can easily lose sight of "natures engineering" in birds and sleek under-water animals.

Jim.

I always think of tuna as an ideal shapr since reading a study a few years back:

[ChazInMT]

I always thought of Anne Hathaway as the ideal shape. But if yer into tuna...it takes all kinds I suppose.

[aerohead]

Originally Posted by Ryland

Am I understanding it correctly that they are not saying that the tear drop shape is bad but that boxes are not as bad as some might think.

Ryland,I think that stylists would rather that no-one discuss the teardrop.For truly low drag it's the only solution and that's the problem.As long as no-one of influence extolls the virtue of low drag,no-one is pressured to bring up the topic of the teardrop.The natural,unprecedented simplexities of the teardrop must be terrifying to stylists.
The fear of 'sameness' goes back at least as far as 1927,with duPont-GM's Director of Sales,B.G.Koether,who intimated his growing fear to GM President,Alfred P.Sloan,Jr.,that cars would 'look alike.'
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As to 'boxes',well they are highly profitable to auto makers.They're cheap to make and consumers perceive high value with them and 'a fool and his money is soon parted.'
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The 2011 Flex,at Cd 0.355,is basically a 1984 HONDA CRX of SUVs.Same Cd!
To give you an idea of where boxes have been,consider:
*1992 Suburban K1500----------------------- Cd 0.39
*1997 RAV4--------------------------------- Cd 0.40
*1991 GMC Typhoon------------------------- Cd 0.41 ( est)
*1991 Explorer------------------------------- Cd 0.42
*1991 Navajo LX----------------------------- Cd 0.43
*1993 Grand Cherokee Laredo----------------- Cd 0.44 (est)
*1995 Montero SR---------------------------- Cd 0.48
*1988 Tracker hardtop------------------------ Cd 0.50
*1988 Tracker convertible--------------------- Cd 0.53
So comparatively speaking,the Flex looks pretty good.
Keep an eye on the cross-dresser SUV offerings.They are doing some of the most aggressive 'styling.'

[aerohead]

Originally Posted by slowmover

I always think of tuna as an ideal shapr since reading a study a few years back:

I believe the bluefin tuna is the apple of at least two university's eyes.One school actually did a life cast of the bluefin for their model articulated,'swimming' submarine R&D.

[instarx]

Originally Posted by aerohead

And that the article even mentions the rear turbulence, can be a game-changer for the un-initiated. So for me,the article moves the whole issue of aerodynamic drag further into the light.Thanks Frank!

Gee, aerohaed. When I posted this exact article to EM in 2008 because I thought people might like to read about new trends in automotive edge design you thought it was useless, deceptive, poorly written and had absolutely nothing new in it (you so kindly informed me that there is nothing new in aerodynamics because it has been fully understood since 1800). It was my first original post to EM and you skewered me for being so naive to think it might be of interest.

Originally Posted by aerohead

Newspaper editors and journalists can print whatever they like without legal requirements for rebuttal space.And they can snip and paste,using industry spokesperson comments completely out of context.So far, there is no law against it.If mediocre cars are the target for carmakers,then I applaud them! They need to receive a prize! [...] As far as aerodynamics being a "black-art",I'd be happy to buy each of the carmakers a 26-Watt CFL for their windtunnel crews.Looks to me like aerodynamics has been fully understood since the day of Sir George Cayley in 1800.Newspapers.gotta love 'em!

Nice to know that you now think the article was a "game changer" and "moves the whole issue of aerodynamic drag further into the light." Although I won't go that far, I'm glad to know that I was right and the article was interesting after all.

[euromodder]

Originally Posted by aerohead

Ryland,I think that stylists would rather that no-one discuss the teardrop.For truly low drag it's the only solution and that's the problem.As long as no-one of influence extolls the virtue of low drag,no-one is pressured to bring up the topic of the teardrop.The natural,unprecedented simplexities of the teardrop must be terrifying to stylists.

The hallmark of great designers is how they design common things.
How they add their own touch to what are essentially the same objects, in order to make them stand out.

Toss thousands of laptop computers together.
They'll all have the same basic components, and will all have the same basic layout.
Yet it won't be hard to pick the Apple offerings out of that pile.

The same can be done when starting a design with the teardrop shape.
The basic teardrop layout offers plenty of scope for individual design features.

[ChazInMT]

You gotta credit Instarx on this, he has handled this much better than I'd have.

http://ecomodder.com/forum/showthrea...amic-6483.html

I particularly like post #8.