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Old 03-19-2009, 09:59 AM   #1
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Optimal Car Shape

I have read many times that the teardrop shape is the ultimate for car aerodynamics. I assume that reflects a car with two people sitting side by side, because the ultimate projectile shape is a cylinder with points on both ends. Artillery shells use a gas generator to virtually create the rear tail. Now, I can see it being pretty tough to make a car in that form. Have two wheels and outriggers that fold out only at low speeds? If you put wheels out all the time you compromise the shape. I suppose you could also approach it like a catamaran and have two connected together. Be a great way to get privacy from the kids! I apologize for my limited drawing skills. Couldn't seem to get the picture url link to work in this post.
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Old 03-19-2009, 11:54 AM   #2
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I wonder if the much lower speeds seen by cars accounts for the teardrop shape making sense?
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Old 03-19-2009, 12:01 PM   #3
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I'd like to see where someone did an aerodynamics study to show that the teardrop shape is the most efficient. The teardrop shape would create a high pressure area in front of it as opposed to cutting through like a cylinder with tapered ends.
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Old 03-19-2009, 12:03 PM   #4
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if you look at the fuselage of an airplane, it has the same shape. you have to look at it from a different angle though. tha aptera tapers from top to bottom and bottom to top. airplanes taper on the sides more than the top. of course all of this going front to back.

I have heard that the optimum angle is a 10 degree grade or slope.

*edit* also if you had to taper in the front and the back, the vehicle would have to be extemely long to have any room inside.
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Old 03-19-2009, 12:16 PM   #5
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Quote:
Originally Posted by BEEF View Post
*edit* also if you had to taper in the front and the back, the vehicle would have to be extemely long to have any room inside.
Sure would. That's why thought the catamaran arrangement would make more sense.
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Old 03-19-2009, 12:24 PM   #6
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I'm mostly just shooting the breeze. Besides, I like to think on a problem before checking out the established research. Otherwise, you can fall into the trap of not considering things that haven't come before.

Actually, what I usually do is this:

If I think the problem has a very optimal solution, I just go straight for the standard solution. If I think there's still room for improvement, I do the brainstorming first, researching second approach.

As cars are a compromise of aerodynamics with practicality, it's far from cut and dry.
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Old 03-19-2009, 12:45 PM   #7
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I once spent a week reading research for hydrogen as the ideal jet fuel. I had no possible use for it, but was living in the same city as my alma mater and had free access to their science library. Those were the days!
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Old 03-19-2009, 12:48 PM   #8
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Ever hear the joke about the difference between engineers and physicists?

A physicist will spend all day deriving a formula he could've looked up in five minutes. An engineer will spend all day looking for someone to tell him a formula he could've derived himself in five minutes.

I try to walk somewhere in the middle, but tend towards the physicist end a bit (ironic since I'm an engineer).
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Function: noun
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Old 04-18-2009, 10:18 PM   #9
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Seems like some posts have gone missing in this thread...weird.

I talked to my uncle who has a lot of wind tunnel testing knowledge and he agreed that the shape I was discussing would work pretty well (assuming the weird configuration could be made practical for the powertrain and passengers), but when I did a little measuring to see what a catamaran style car would look like it became evident pretty quickly that it's just not wide enough to warrant it, at least for four occupants. Planes and boats, sure. I once saw a race car that almost had this approach, as it just had a cockpit bubble on the driver's side. You'd have to do something similar: two people on one side, and the trunk and engine on the other or something. Very odd configuration indeed with better options (center hump, for example) particularly if you're comfortable with three wheels. If I had some 3d software I'd have done up a quick model, because the resulting vehicle is pretty amusing in its impracticality. Figuring out how to make a powertrain and balance work was fun.
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Main Entry: co de pen dence - see codependency
co de pen den cy
Pronunciation: \kō-di-ˈpen-dən(t)-sē\
Function: noun
Date: 1979

: a psychological condition or a relationship in which a person is controlled or manipulated by another who is affected with a pathological condition (as an addiction to alcohol or heroin) ; broadly : dependence on the needs of or control by another
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Old 04-19-2009, 08:11 PM   #10
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In the 1952 there was a land speed record attempt by Piero Taruffi in a twin boom vehicle (catamaran shape) called a TARF I think.

An interesting design study for those interested.

Some details and a cut away drawing here:
http://jalopnik.com/photogallery/dblbullet/1003234992

Cheers , Pete.
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