Screw the little fins. CUSCO 3DGT carbon wing creates 120kg of downforce at 130 mph.

 

they have them for impreza on l'aunsport.com

 

I said "seems" b/c I'm not an expert, but I did study fluid dynamics in college and I have experience testing airflow over simple objects in a wind tunnel. The poster specifically asked for opinions from a "bench racer aerodynamicist." He wasn't looking for the lead designer from mitsu or subaru to answer his question.

Your post added nothing to this thread, yet you accuse me of posting out of my ***. You must be lost this is the BAY AREA impreza forum, please go back to wherever you came from.

 

bite me. I've seen wind tunnel results from the fins, it helps reduce buildup of "dead air" because of friction with the barrier layer. as far as this being the BAY AREA forum, who gives a ****? it's the INTERNET.

 

We know that the fins work, so whats your point?

btw...its boundary layer NOT barrier layer.

 

Well ok guys I asked the stupid question to begin with, and I think we are getting someware now...

 

Motor Trend did some aerodynamics tests with the little roof fin thingies and found them effective creating turbulence (sp?) and therefore adding additional downforce to the rear wing. I'll post the artice if I can find it.

-Chris

 

none of us are "real" aero experts with access to a wind tunnel or a copy of Fluent laying around. We're hypothesizing, and it's fun dangit. take the negativity elsewhere (I hear SRIC is good for that).

 

The '06 STi thingy looks like a neat 'up-force' generating item. It will direct air "at" the rear spoiler, but the vortex generators do a lot better job and offer less drag. Lots of aircraft have vortex generators on the wings for similar reasons. You can see a few airliners that have them just ahead of the flaps - this directs air over the flaps and makes them more efficient at generating lift at low speeds, just as they would direct air down the rear window of the Mitsu and into the 'control surface' of the spoiler. The only difference is often vortex generators are mounted at a slight angle alternating fin to fin - this is to disrupt the flow of air over the wing and create more lift - since this is not the purpose on the Mitsu, they are mounted straight.

 

Haha.. +1 for sure.

 

I was under the impression that the fins on the Evo don't generate more downforce, but they reduce up force (so the end result is the same). A car is shaped like a wing that wants to take off, so if you put fins on there and make the whole car a worse wing, then you get less up force and therefore more downforce. It would surprise me if the effect is tied to the rear spoiler at all, I think the fins just mess up the low pressure area above the back of the car.

 

Here is the motortrend article

"Road Test: 2005 Lancer Evolution MR vs. Evolution VIII vs. Evolution RS (cont.)

The vortex generators act as eight tiny spoons reaching beyond the boundary layer to scoop a bit of the fast-moving freestream's momentum, spinning it down into the sluggish boundary layer to give it a kick, delaying separation. Although such devices are considered Band-Aids in the extreme in aircraft circles, here we're told they bump the rear wing's downforce by about five percent--objectively useful. Subjectively, our ribbon-watching from the rear seat suggested the vortex generators also were keeping the airflow more evenly delivered across the wing. "

http://www.motortrend.com/roadtests/...os/index4.html

Ohhh pretty colors


John

 

A wing generates lift by making the air flow faster under the bottom than over the top. If you create turbulence on top, that will slow the air thus generating more lift. If that were true, they would be lift generating devices, right?

 

wings work by creating pressure differences between the top and the bottom. The air flow faster over one surface, and thanks to Bernoulli's effect, the pressure is different. On an airplane wing, the top surface is flat and the bottom is curved. This has the effect of making air flow faster over the top, resulting in a low pressure area above the wing, creating lift. On a typical car wing, it's flipped over causing the low pressure area underneath the wing.

Overall, the car will have the same sort of effect, which is why things like air dams and splitters create downforce (less air flowing under the car than over it creates a lower pressure area under the car).

(beware i may be wrong and on crack about all this)

 

You're the man, John. That's exactly the one I was talking about. Thanks pal.

-Chris