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Old 02-25-2011, 06:26 PM   #140 (permalink)
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Originally Posted by NeilBlanchard View Post
I was also thinking about the speed vs drag issue -- if a certain trailing angle works at a low speed, then it might be too steep for a higher speed? The atmospheric pressure can push air at a certain rate, and given a little longer time (i.e. at a lower speed) then wouldn't a steeper trailing angle work just as well at low(er) speeds?

In other words, is there a specific speed used to develope this ideal profile?
Neil,once the boundary layer goes over to turbulent the Cd is fixed for a body up until around 250-mph for cars,when compressibility issues come into play. Angles, good at any sub-transonic velocity will not alter drag anywhere within this velocity domain.
In fluids,the barometric pressure will affect air density,which is part of the drag equation.
The pressure drag,which is what we're going after,is ruled by separation.If you can eliminate separation you've eliminated pressure drag.
If you get an angle which will work at 25 mph,she'll still be good at 225.
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