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Old 08-01-2009, 02:57 PM   #31 (permalink)
aerohead
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Craig's brother

Quote:
Originally Posted by Rokeby View Post
This little clip rom Craig Vetters site is telling...

http://www.craigvetter.com/Movies/Streamlined_test.mov

blunt end forward, taper aft is the way to go for low drag.

I'm not sure the narrator, Craig's brother, has got the forces right. He
speaks of air pushing on the front of the car, when I think the real
issue is air pulling on the back as aerohead says.

I'm sure there are also unidentified interactions between the airflow
around the car and the tube due small clearances.

Although it is still technically "vaporware," Mitsubushi's all-electric iMiev
Sport Air concept car seems to be the best embodiment of these concepts:

Autoblog Green
In the context of a wind tunnel,the air would be impacting the body,in a positive pressure gradient up to the point of maximum cross-section,beyond which,the air would be receding away.With proper contouring,as Craig has already accomplished on his Rifle,etc.,the body could maintain attached flow all the way back,finally breaking away into a relatively turbulence-free wake.-------------- Without the proper contour,the flow would separate,and the base pressure behind the body would be that of the point of separation,acting to "pull the body back."---------- So it's the pressure differential at work here.Separated flow breeds high Delta-P,zero separation yields losses attributable only to friction,internal flow,and induced drag.------------------------------------ The Mitsubishi looks pretty good! I held a protractor up to the computer screen and measured around 22-degrees for the roofline exit profile,just at Mair's ragged-edge for attached flow.I wish they would provide an overhead plan view of the car so we could inspect that aspect of the cars architecture.I wish they'd do that for all cars!----------- Thanks for sharing that!

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