Very interesting, I should pick up a book on race car areodynamics in order to understand the complicated nature of design and function.

Any suggestions of books to review?

 

Joseph Katz - Race Car Aerodynamics: Designing for Speed is pretty good. Not too hard to understand, goes into good detail. The topic of automobile/race car aero is also treated in Van Valkenburgh's Race Car Engineering & Mechanics and the ubiquitous Milliken/Milliken work - Race Car Vehicle Dynamics.

 

I'm willing to bet ejis has taken at least one college course in aerodynamic...

[QUOTE]Originally posted by ejis
[B]The Cd is determined mostly by what goes on BEHIND the vehicle.

 

Check out this link:

http://www.uh.edu/engines/epi1520.htm

 

The new accord coup has a CD of .29

 

Compare air to water and you can see it more easily. You are in a rowboat (blunt rear end) and stop applying forward thrust. You practically stop dead. Any similarly shaped boat, when you kill the engine, the bow heaves forward and the boat nearly stops. Do the same in a canoe (pointed rear) and you keep gliding right along. Reason: No suction at the rear from the wake. Same suction occurs with air, you just don't see it.

 

Just for reference, windtunnel testing on 3-box style cars (think typical sedan) has shown that a small rear lip spoiler will not only reduce lift/increase downforce, but will up to a certain point reduce drag as well. I believe the results were published in Forbes Aird's aerodynamics book, but it may have been another one.

Such a small spoiler could conceivably have a similar benefit on the S2000. Testing by Auto Sport (a German mag) showed 88 lbs of lift on the rear of the S2000 at 125 mph. Thus, even at 60 mph there would still be about 20 lbs of lift and probably a fair amount of drag.

UL

 

Mugen can do wounders, the full kit for the RSX decreases CD by 11%, and brings up Downforce by 169%!!!!!! That is what you get for windtunnel testing at $1k/hour, a $5.5k body kit that actually does something. I also guess they spent some odd $20K+ to make the S2k rear diffusor, and did not like the resaults and scraped the project to start over, good lord no wounder why they are so expensive. IMO as long as the quality backs up their price, it is worth it, and if anyone knows the #'s on the full mugen S2k kit, plz post

Steve
V8-What?

 

Why, so you are saying my dad's 4300lb 2000 Crown Victoria with the Handling and Performance package is just as aerodynamic as my dinky 2800lb 2 seater S2000? The Cd on the 98+ CV's is .37 or .38. The Cd on the pre 98 Crown Vic's are .32 which is as low as the Ford Taurus. I had my car parked next to the Crown Vic last week, and man my car looked so dinky! That Crown Vic used to be mine a while back, but my dad liked it so much he bought it from me.

 

Do you guys understand what the coefficient is?

I believe it's a multiplier to the frontal area of the car. Like drag force ~= Cd * A. I think it is relative, like 0 = no drag and 1 = flat plate obstructing flow. Somebody remind me!

Y'know, the frontal area of the s2000 is pretty small compared to the length of the car. Therefore, there is little hope for the s2000 to have a low Cd, compared to a stubby-nosed Civic for instance.

This is why I made the earlier comment regarding the aerodynamics inside the car being great. The upright windshield and shape of other items affecting the flow of air over the cabin lower the Cd because it's a compromise to pure aerodynamic efficiency. If I can drive all day without being beat up by the wind, I'll take that over a low Cd.