aero theory

[redvolution]

Got the Feb issue of Racecar Engineering last night and there was a very interesting column comparing various diffuser angles.

Caveats: flat-bottom 350Z in a non-moving-floor wind tunnel
Results:
Increasing the diffuser angle did little to affect drag but it did significantly change the aero balance of the car. 10deg was max overall downforce, 12deg was max forward shift of aero balance. In other words, as the diffuser angle was increased the front downforce increased faster than the rear downforce. It peaked at 12deg and then all downforce started to drop significantly (flow separation).

What does this mean to us? Adding a proper diffuser could reduce lift in the front AND the rear. It works because the diffuser allows more airflow under the car. Assuming the nose of the car is closest to the ground, this region forms a "throat" whose static pressure decreases as total airflow under the car increases. Voila, reduced front lift.

[vtluu]

Interesting. It's a shame none of us own a wind tunnel.

I hear WORKS will have one at their new facility though... ;)

[Jamie@WORKS]

Interesting. It's a shame none of us own a wind tunnel.

I hear WORKS will have one at their new facility though... ;)


Yeah, right next to our 7-post shaker rig ;)

[EVO GRIM]

I noticed a big difference in turn in since going to the cwest bumper. I think the stock 03 bumper has too much lift.

[redvolution]

The stock bumper isn't great but it certainly doesn't suck (car is remarkably stable at 150mph in a straight line). If I were to buy an aftermarket solution I would definitely go with the Voltex bumper and undertray. After that, the C-West one looks good. What undertray were you using with it?

[SpeedElement]

Voltex kit is also wind tunnel tested as well :)

[EVO GRIM]

The stock bumper isn't great but it certainly doesn't suck (car is remarkably stable at 150mph in a straight line). If I were to buy an aftermarket solution I would definitely go with the Voltex bumper and undertray. After that, the C-West one looks good. What undertray were you using with it?


None, the bumper is very rigid.

[tahoeacr]

Very good magazine. I've had a subscription for years. Got tired of it being sold out before I could get to the book store. That article is a series they do almost every month. Been goin on for years. They did one on splitters(100mm in front gave max downforce) with a diffuser style design. Quite interesting. They also found that you need four inches or less of ground clearance for any aero to work.
I could post some back issue months of good articles if anyone is interested. Don't know how easy it is to get back issues since there out of the U.K.

[redvolution]

Very good magazine. I've had a subscription for years. Got tired of it being sold out before I could get to the book store. That article is a series they do almost every month. Been goin on for years. They did one on splitters(100mm in front gave max downforce) with a diffuser style design. Quite interesting. They also found that you need four inches or less of ground clearance for any aero to work.
I could post some back issue months of good articles if anyone is interested. Don't know how easy it is to get back issues since there out of the U.K.


I'm interested in the splitter info. What did it mean 100mm? What dimension is that?

[tahoeacr]

If I can figure out my scanner, I'll e-mail you some. 100mm was the measurement extending passed the most forward part of the bumper. They tested 125, 100, 75, and I think 50mm. Also have one on spoilers/wings with graphs showing horsepower absorbed by CDA vs speed from 20 m/s up to 110 m/s. I'll dig them out tonight.