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*To*: Roland Broberg <broberg@cpg.mcw.edu>*Subject*: RE: Car Aerodynamics*From*: Alexei M Voloshin <Alexei.M.Voloshin-1@tc.umn.edu>*Date*: Fri, 9 Aug 1996 12:09:50 -0500 (CDT)*cc*: Glen Powell <gpowell@acacianet.com>, "'Paul C. Waterloo'" <74543.407@COMPUSERVE.COM>, "INTERNET:quattro@coimbra" <quattro@coimbra.ans.net>, Eric Fletcher <STEADIRIC@aol.com>*In-Reply-To*: <01I81DU8GDLU8WYGKJ@cpg.mcw.edu>*Sender*: owner-quattro@coimbra.ans.net

On Thu, 8 Aug 1996, Roland Broberg wrote: > I think there is a misunderstanding here if I remember way back to my dynamics > courses. The Cd is measured in force/area. It is not the drag, but the drag > coefficient. To do a true comparison between vehicles you'd have to multiply > the Cd x the frontal area which is where the Q is lower since it has a smaller > frontal area than the 5K. > Roland > V8 > 100 > 5KTQ former I really don't think you remember your dynamic courses very well. A simple test - compare the physical units: First of all, lets us consider the units of coefficient of drag: NO units here! (it's a ratio-> a coefficient) Then let's consider what you're saying -> force/area force is (mass * length)/(time^2). area is (length^2). devide one by the other, you get: (mass)/(time^2 * length). Somehow units of Cd and untis in you definition do not help! Booohhh.... The drag coefficient is the ration between two forces. Now another thing: Cd is dependent on speed once above about 30 MPH. Cars are optimised for different speeds. Normally the drag coefficient shoots up for any car after above 70 MPH... call non-linear turbulance. How fast it shoots up depends on the aerodynamics of the car. However when talking about the frontal area -> sure at pays a role, but I would be careful how I include it in there. Remember, frontal area is a vector in these calculations, it is not a scalar. I kind of busy right now, but if you're interested I'll tell you more. Anyway, Dick Feynman is hell of a lot better at this than I'm, that is why they gave him the Nobel Prize. Dig up his Freshman Lectures in Physics, I think you'll like it. Alex

**References**:**RE: Car Aerodynamics***From:*Roland Broberg <broberg@cpg.mcw.edu>

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