Presented by Nine Lives Racing
JustaMiata
JustaMiata None
11/17/22 9:42 a.m.

Just got my 9LR double duece kit installed and I am looking to understand how to set the dual element setup AOA. I found a video of Johnny measuring AOA of the main element by basically laying a flat piece of whatever from the leading edge to trailing edge and that gets close enough to the actual Chord line for the AOA measurement. I couldnt find any advise or a baseline setting for the dual element from 9LR or on the interwebs. 

 

Currently, the main element is at 5*. Dual element is at roughly 42* when measured by itself. 

 

If anyone can give me a breakdown on how their 35*, 40*, 45* AOA CFD numbers are measured? Is is a measurement from leading edge of main element to trailing edge of 2nd element, or is it just the angle of the 2nd element with the main element at say a AOA of 5*? 

 

Once we get that answered, then Id like to know how other aero lovers typically tune their Dual Element setups for Autocross speeds. I am aware you dont want the gap or overlap of the 2nd element to be too small which could cause stalling. I dont know if yall are using Tafts on the bottom side of the wing to see if there is seperation and if you just max that out and adjust the total wing AOA to conrol aero balance.

stafford1500
stafford1500 GRM+ Memberand Dork
11/17/22 10:05 a.m.

The flat edge over the leading edge/trailing edge is the most repeatable measurement you can take wether at the track or in the shop. Make sure you reference it to something flat/straight/level-ish on the car, so that all of your documentation is self contained to the car. This will give you a good reference and is the correct relationship to the rest of the aerodynamically affected bodywork. My suggestion is the bottom of the rockers ar some where along the transmission tunnel that is mostly flat.

Each element should be measured and documented individually. That verifies things have not moved (in relation to the chassis. You also want to measure and document the overall assembly angle. This will be a measurement others MAY use and will give you an external reference. If your have a wicker on the second element, put our straight edge at the base of the wicker and the op surface of the wing (dont measure the wicker in the angle). The adjustment should keep nearly the same overlap and slot gap, but the positioning will probably not allow that to happen exactly.

For autocross, set the second element to the max suggested by 9-Lives, since they have done some R&D. You may need to adjust the entire assembly from there depending on the installation.

Keep in mind that the flow ahead of the first element will actually be directed down due to the impact of the wing in the airstream, so your initial setting of 5* (nose down I assume, and would be negative in aircraft) may be too much. Most multi-element wings measured the way you describe (top edges) will show level or even slightly nose up (+ve) for the first element for optimum effects. The proximity to the other body work will also matter. If the wing is over the decklid, you can set the first element more nose down (like your current measurement), if it overhangs behind the bodywork, more nose up will likely be needed.

Finally a combined 2-element angle in the 35-45* range is likely close to right.  At autocross speeds the effect of having it in stall is typically not a deal-killer. The downforce does not disappear, just reduced. Additionally, think of the drag at the high location of the wing as a force on a lever. It will still push the back of the car down, just not as efficiently as drag and max downforce. Balance is all about thinking of the levers you are pushing on.

JustaMiata
JustaMiata New Reader
11/17/22 10:29 a.m.

 

Thanks for the response Strafford. So you are thinking they have the main element at 0* and the "Wang-Dual Element @ x*" is simply the measurement on the 2nd element? 

 

Youre assumption of 5* front edge down is correct. 

The more I look at their drawings, it does seem like main element is close to 0* and they max out the 2nd. 

stafford1500
stafford1500 GRM+ Memberand Dork
11/17/22 11:20 a.m.

The drawing of the dual element assembly seems to show the first element slightly nose up as I mentioned. That profile (or at least the one it was derived from) does have a small but reasonable window for angle of attack, but 5* nose down may be a little agressive, depending on how/where it is mounted.

The callout for the second element does appear to be the element by itself.

JustaMiata
JustaMiata New Reader
11/17/22 6:45 p.m.

thanks for the advice. Have the main element at 0 and 2nd element at 40 for a starting point. 

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