APR GTC-200 wing placement project on Shelby GT350

Project objective to increase APR GTC-200 effectiveness.

First, I will make new wing risers which shift the wing rearward by 5.5" and raise the height an additional 3" from the out of box location. Next, I will make new larger endplates.

The 5.5" back and 3" raise were arrived at from the suggestions in the module. Wanting to make larger endplates also came from suggestions in the module. As a result of the module, I will also be looking for a spoiler / Gurney flap for the boot to also work in conjunction with the changes.

My question on creating a larger endplate. Would there be any benefit to having the suction side of the endplate be long enough to come down to the level of the boot? Would this give any benefit from stronger tie in with the low-pressure area behind the car? Or do I stick with the roughly twice the length of the high-pressure side?

Thank you for your time.

Jerry

Hi there Jerry,

I think the rearwards and upwards move are a good strategy as a start for powering up the wing if you're planning on adding a bit of front aero to the car. As you're probably aware, the GTC-200 isn't the most powerful wing out there, but this should help a bit. Given the high amounts of rearwards curvature on the wing element I would say adding a bootlid spoiler is definitely a good idea!

Regarding your question - going very long with endplates is always a balancing act - if you go too low the suction on the wing will draw up on the boot, so while you will get better communication with the low pressure behind the car, you may not see a big increase in downforce, especially if you don't already have a decent diffuser setup. I think given the relatively small size of this wing element that extending all the way to the boot after that proposed move might be a bit too much? Hard to be certain without images of where everything would sit. I'd say stick with the twice the length of the high pressure side. If you go somewhere around 5" up, 10" down for the endplate as a maximum on that wing you should be in the ballpark.

Hope that helps!

Hi Kyle,

Thank you for the advice. I know it is hard to visualize let alone not having dimensions. I have attached the boot spoiler now. I'm ready to design the wing risers. Before I cut them, a little more guidance. The plan is wing set-back 14 cm and raised 8 cm. If you have other suggestions, please let me know.

Spoiler dimensions: 30 degrees with height of about 8 cm above the boot at the trailing edge.

Currently the spoiler trailing edge is behind the wing trailing edge. However, I'm designing new risers so I can relocate the wing.

Should I maintain the current trailing edge correlation between wing / spoiler and just add the 8 cm height to the wing? Is 8 cm enough height?

If I move the wing back 14 cm, the spoiler trailing edge will be about in the middle of the wing. Will this be an issue? If an issue, how much distance is needed between spoiler / wing to mitigate the interactions.

The picture shows everything prior to wing raise and set-back.

Thank you for your time,

Jerry

The answers are not obvious. You need to be able to test things to see what is the best. Here is a setup I made for my Sports Racer to determine the wing position to make custom swan-neck mounts.

Hi David,

Thank you for your reply. Yes, I know ultimately that testing and data collection are the only true way to find the best solution. It is a lot harder for me to do that as a weekend warrior and on a daily driven car. I don't have the instruments to perform testing proper. I will do tuft testing and maybe try the coast down test method. I was hoping for some general guidance from Kyle's experience to point me in a direction while cutting down some things to investigate.

Your photo was very helpful. Giving me ideas. I will try to see if I can rigg something up.

Do you have a photo of where you ultimately ended up with for Swan necks and wing in relation to the rear that you can share with me? If proprietary to your race team, then I understand. Just trying to make an educated guess on where to start for my situation.

Thank you for your time,

Jerry

More than 20 years ago, we bought one of the first Stohr DSR sports racers. The car had very low drag, and with the provided wing it only made about 120 lbs for downforce total (100mph reference, using my suspension pots and math based on the spring rates). My non-winged sports 2000 made 4 times the downforce with just a spoiler. So I set about testing rear wings with different profiles and also tested a lower wing position. Attached is the report I wrote about that test.

Basically we learned that the wing location for the Stohr was critical to having it work to enhance the diffuser and improve overall downforce. What came about after that test (and is not in the report) was that I discovered the smaller cord Pennon wing increased it’s downforce in the low position (like 50% increase), but the larger wings did not. The reason was the that the trailing edges of the wings were aligned, and when I went back and moved the large-cord wings back about 2-3”, the downforce went up by like 50% (so nearly 375-400 lbs of rear downforce).

BTW - 5 years later those cars with larger diffusers where making 800 - 1000 lbs of total downforce at 100 mph.

So my adjustable mount shown previously, allows adjustments of 1/2" in both height as well as fore/aft placement. My first guess (3" behind bodywork, and 4" above bodywork) went so well, I just made the swan neck and went racing -- One day I will spend more time to find the optimum position. But this shows you how I will test it and why you might not know the answers without spending the time testing.

Hi David,

Amazing work! I wish I had the data acquisition tools and track time to perform testing. Thank you for sharing your findings and report. I will see if I can gain insight to apply to my situation.

I did perform some tuft testing. Compared to tuft testing I performed before, it looks like the spoiler has helped the air stay attached farther around the wing outer edge where it is really cranked between mount and endplate. In the center, I think I need to attach the wicker bill on the spoiler (between the two outer peaks). I think that will aid attachment in the center of the wing. Those are my observations and guesses. Thoughts?

Based on your test set-up, I have some ideas on how I can adapt something to allow me to raise and set the wing back. Again, thank you for your time.