Goblin rear wing aero

[Indy Lonnie]

So I decided to see if my 9 Lives racing wing was truly working. I set a small experiment to check the airflow to the rear wing. I used a flexible drill bit used for fishing wiring as my measurement tool to see what height was needed to get airflow to the wing.
Let me tell you about my car. It is an extended chassis with the higher rollbar. The windshield is stock DF at 10” high and raked at 8*. The top of my roll bar is 50” high from the ground. My ride height is approx 5”. My wing stands are DF at 41.5” and the top of the wing currently sits at 47” high. I used yarn that extended to the front of the wing.

I started testing at 40-60mph. See the videos for visual evidence.
55” - complete mess. The yard flew back into the cockpit and became a tangled mess.
No video.
57” - tangled

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58” - yarn moving a lot in all planes.

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59” - yarn starting to straigten but arching downwards.

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60” - starting to straighten more.

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61” - better

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62” - better yet

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63” - Yarn straightest yet and moving mostly left to right.

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Now note, the height of my wing is 47”. This tells me my wing is functionally useless. From this quick afternoon test - I need to icrease the height of my wing stands 16”. WOW. Here is a side pic of the car and where the yarn is denoting the needed height of the wing.

 

[Desert Sasqwatch]

Good experiment and telling results. I would have to assume that angling your windshield more may help with a little less turbulence over the top of the b-pillar - maybe have straighter air an inch or two lower. But having passengers with heads and shoulders in the airstream, along with the round frame tubes top and sides, there will be turbulence within the nominal area that a rear wing will be mounted. Add to that the chaotic air in and around the engine bay and there is little airflow that can create downforce at legal street speeds. Maybe the outside 6-12 inches of your wing might be clean enough? But yes, to find clean air would raise your rear wing very high - ala Chaparral:

 

[GoblinGuyZ]

I plan to get the shorter windscreen for track use since I think alot of that turbulence comes from that (was even thinking about cutting my own one out with a style similar to the atom but larger) and I already figured that the stock wing height would be more cosmetic than functional so I have mine sitting just over the hoop. Driving below 60mph I wouldn't expect a massive difference either way.

 

[duthehustle93]

A tube or a piece of string causes a huge wake behind it. 9LR has always been a promoter to CFD in the miata community and I'm surprised that they put it in a turbulent area. Thanks for posting your testing! Keep in mind that your wing should be even higher as the wake behind your roll bar will grow. Also, as the wing gets higher, the drag generated will actually lighten the front of your vehicle at speed since your "torquing" the vehicle about the rear wheels (this can be calculated by taking the sum of the moments about your rear wheels). You can counteract this with front aero, which is extremely difficult without a body. It's really hard to do aero with a jungle gym of tubes. On our lemons miata (open top w/ cage), I mounting my wing on top of the main roll hoop of the cage.. it looks incredibly dumb but it's probably the most practical way to keep the wing up in clean air and it helps move the aero balance forward, resulting in a lesser need for front aero.

 

[Desert Sasqwatch]

Kind like this, only on a Goblin?

See @Ross for his top mount wing/spoiler.

 

[duthehustle93]

Yes very similar except we put the mounting flange on the main hoop stays ... make for a more rigid mount IMO. The wing is 3D printed for anyone wondering why it looks like that haha.

 

[Desert Sasqwatch]

That wing could benefit from adding a Gurney flap to the back edge. Only needs to be 1/8 inch, or so, to increase your downforce by 15% or more with almost no increase in drag.

 

[duthehustle93]

It's already got a gurney flap... it also doubles to help hold the 3D printed section stack together

 

[Desert Sasqwatch]

Thumbs up. Hard to see on a cell phone.