At the risk of getting shot by the Physics/Aerodynamic gurus, the rear trunk spoiler certaintly does have a positive effect! It adds downforce because it's slightly tilted (greater stability)
some drag for the same reason. With that said, it may reduce rear turbulence and thus the
overalldrag and maybe having a positive effect.
A simple illustration: When you put your hand out the window at 60 MPH, you probably notice that the flatter it is, the less resistance, obviously but also the easier for it to change direction erratically if you change it just a litlte bit.
However, if you can manage to, as you slowly tilt your hand, you will feel the resistance towards the top of your hand, addiwng downforce + drag and the closer you get it to 0 (? eg, TDC) degrees, the greater resistance and drag on the entire hand...
The trunk spoiler in discussion does exactly that. Adds downforce with minimal drag.
Note that however, generally speaking, the lower the CD the less high-speed stability, but easier to get there.... This is why race cars and big wings have a lot of drag (.3x+) and the Lexus LS400 as an expample, has a CD of .26sh while F1 cars have .7-1.1 :EEK: The Lexus at 140 MPH is very floaty while the F1 car has thousands of lbs of downforce that would allow it to race upside down in a tunnel! :EEK:
A balanced aero design looks to get a good bit of downforce while minimizing drag. The NSX-R attained .32 (more drag than the .30 on the 2002 wich gained a few mph (172 or 175 vs 168?) in top speed and I think it large part of the R-wing. It mitigates it by having
flatter undertray, the duct etc to get air to flow as smooth as possible over and under the car. Without those components, the drag would probably be much more, maybe .37+. This is why I have allured a number of times that the copy-cat R wings, unless they are absolutely perfect, may do more damage in drag than good. Each milimiter makes a difference imho (think hand illustration)
The post above me provides an excellent observation. One of the ways to test aerodynamic efficiency is to see how dirty the car gets at the rear (or anywhere. The smoother the air exits the vehicle, the less air and thus dirt will be pushing it.
The real question is still what SaberX stated - why didn't the NSX-R have it? I'm not sure still. Hopefully it's not because it's counterproductive but instead weight management. I would think/hope that if both produce downforce 1 + 1 downforce unit results in increased downforce, however, I haven't seen too many other cars do this
And again - the BMWs and especially the Mercedes (in the .26 range) use these in conjunction with flat undertray and small(er) frontal area to minimize drag while producing enough downforce for high speed stability.
A few couple of good links:
http://www.camaro-untoldsecrets.com/articles/rpo_d80.htm (don't diss the old school Camaros!
)
http://autospeed.com/cms/A_107773/article.html (they even mention the NSX as a
"very aero-sophisticated car!"
That's all for now.. gotta run to a meeting.:biggrin:
