Re: Rear Wing

[Magpie]

I have already PM'ed this info from my last lot of coast down testing, 4 times in each direction down the same road from 120 kmh down to about 60 for each AOA:

00 deg. 0.29 CDa 0.61
05 deg. 0.31 CDa 0.65
10 deg. 0.33 CDa 0.69

The only change to the car was the AOA. The frontal area of the car is 2.1 sq m.

From http://www.race-technology.com/wiki/index.php/M/Mazda
94 Miata CD 0.38, frontal area 1.71, CDa 0.65

[Lokiel]

This is what a forum thread SHOULD be like, guys giving their $0.02 worth without getting their knickers in a twist when someone challenges their assertions or calling each other a liar or troll. Questioning and valid counter arguments are good, we all benefit/learn from that.

See this thread for some additional figures on aero: http://www.miataturbo.net/race-prep-75/splitter-height-70456/

[Magpie]

Thanks Lokiel.

I will be doing more coast down testing once I have the car back from the engine change. I have changed the car's height/rake plus the car does not weight the same as when the last tests were done so it all needs to be repeated. Also I may try and find a 110 kmh zone that has a decent bitumen surface and not concrete to allow good quality measurements for the ride height sensors to kill two birds with one stone. Plan is to also put the AOA into a negative number (lift) as well as at 0, 5, 10 and 15 deg, so it will be so exciting to do a total of 40 coast down testing runs.

My last testing shows that provided I keep the wing at 00 AOC I have improved the car's drag over stock.

For the testing in my above post; the wing was a APR GTC200 with gurney flap, mounted 15" above the boot, splitter was home made (based on Charlie91's) mounted on to a GV lip with KazeSpec Engineering splitter hardware kit (however there are now 2 additional aluminum bumper support turnbuckles being used) also on the car were GV front/rear wind deflectors and a Jetstream rear diffuser with 2 vertical and 2 curved fins and a stupid air roof scoop.

[ja9]

Went and measured my AOA; it was 9.2 degrees. I'll be changing it to 0 degrees and testing to see how the understeer has changed and more importantly the lap times.

The thing that's got me baffled is when I raced at the FOSC meeting last month the wing had moved to maximum AOA (not enough tightening on my part), probably 15 degrees or so and I did not notice any understeer. I know the track does not have the overall speed of WP but the corner in front of the pit area is pretty fast and yet no understeer. Probably not going as fast as it feels.

What is the go with a wing that has stalled, what does this mean exactly?

Any thoughts.

- John

[NitroDann]

My last testing shows that provided I keep the wing at 00 AOC I have improved the car's drag over stock.

So we agree, drag can be reduced while downforce is increased

Thats good data also, thanks.

Dann

[Magpie]

So we agree, drag can be reduced while downforce is increased

Yes you can but it was not easy

What is the go with a wing that has stalled, what does this mean exactly?

from http://www.circletrack.com/ultimateracing/ctrp_1011_sprint_car_wing_aerodynamics/viewall.html
The rear wing is set at such a radical angle, that it is stalled. When an airfoil stalls, the downforce reduces dramatically and the drag increases dramatically. It still makes downforce, but it makes significantly less than it would if you reduced the angle of attack. You could test all this at a minimal cost.

Stalling on a car is the same as for a plane, however if a plane stalls it falls out of the sky we do not have those ramifications. I have tested my wing at 15 deg however have not shared that data because I think it is flawed and I need to re-run all the tests again (coast downs and timed pulls in 3rd gear to red line).

[NitroDann]

Pats car is an example similar to yours and it was pretty easy, its VERY hamfisted I'll admit but its simple, cheap, and works.

Dann

[Hellmun]

My last testing shows that provided I keep the wing at 00 AOC I have improved the car's drag over stock.

See in a straight wing Vs no-wing scenario I'd expect some extra drag for your down-force as your increasing the size of the wake and I doubt you'd get much extra flow attachment for a net improvement. How much lower is your car than stock as I'd expect that'd reduce your frontal area some and explain the improvement.

[Magpie]

Hellmun from memory the splitter was 90mm off the road, not sure of what it was at the pinch welds, rake was only a few mm's. heights were with driver weight. Also the car had its hard top on when the testing was done.