Musings of a man with lacking in self preservation

Can you do your own DIY car rear wing and what is ACTUALLY involved in doing so?

So earlier in my blog, I wrote about what is theroetically involved in DIYing a car wing. Welp, I've actually been working on it, and I figured I'd start with the a bit of a blog post on what I did and what was involved.

Step 0 Research, come up with a ballpark plan

There's the saying "you don't know what you don't know", and consequently at the start of any such endeavor you'll want to try and suss out as much unknowns as you can and come up with a ballpark plan. The plan can and should be fluid as you may learn things along the way, along with you'll want to potentially stop, reasses, and backtrack on certain parts of the plan along the way.

I wrote a lot about what is involved in this step over in my blog post on doing a DIY wing. In that research, I determined I'd need to design some components, learn some cad, and probably source a wing since making one was well beyond my means. Plus it helps to have some goals in all of this. For me the goals were simple: Learn some new things, get rear aero on my C5, release whatever I make for others to use and be able to do this for as cheap as possible.

As part of that sharing this as cheap as possible, I decided to base a lot of my design around a WingLogic 72" wing. They have CFD data confirming what they are up to, a few folks from race shops have confirmed making them work with decent enough success, and the price was very reasonable and inline with my DIY and cheap goals of the project. Added bonus points for shipping with endplates and wing mounting plates included as well.

Step 1, Approximation, and CAD (Cardboard Aided Design)

So you've got to start somewhere right? As I wrote over in another post, it helps if others have come before you, and a wide variety of folks have done rear chassis mounts on the C5 Corvette. After Dark Speed offers a mount, 9LR has a mount for sale, Tway Motorsports has a design for a wing chassis mount, and C7 carbon has an ungodly complicated and sophisticated chassis mount that is quite impressive!

Taking a gander at them, it's pretty clear where to start... with the rear crash bar structure of the C5 Corvette. Then you take a gander at the limits of the rear bumper area and the design parameters all pretty much spell out the need: You've got to mount to the rear crash bar, and there's a gap you can navigate an upright between the exists between the license plate and the tail lights. Want to go wider? You gotta shoot the very wide gap between the tail lights. Narrower isn't an option. So that's where it's going!

Now having measured everything, you gotta start with something right? So I took some cardboard, and cut in a very very approxiamte shape of what I was after. This of course is very unimpressive in it's design, but it serves the purpose of gathering some basic dimensions and scribbles on that I can then start to transfer into actual CAD drawings.

Step 2, Actual CAD Work

Having a bit of cardboard in my hand, and considering what it would take to iterate over cardboard many times, it became apparent it was likely just worth iterating in CAD instead of on multiple pieces of cardboard, especially since the final product needs to be in CAD anyways. Plus, a friend in the C5 community let me know that SendCutSend can cut your pieces in MDF, which saves me the trouble of transferring my cardboard designs to MDF myself.

So I started the process of not knowing a damn thing about CAD, to trying to learn OnShape. Now, let me just say... this process was ungodly frustrating. Running OnShape in my browser created a wide variety of headaches for me. There was a LOT of swearing and frustration fits... but I eventually got used to it all, and went from the utter garabage above to slightly better designs.

This all was coming together well enough, but then I started to get more ambitious. What about tabs to align everything? What about cutouts / skeletonizing to cut weight down? What about offsets?!?

The more ambitious the goal I set, the more opportunities I had to learn OnShape, and so after a lot of progression I was able to hit a good point with my design.

In the end I was able to put together a pretty good looking design with what I believe to be solid parameters for stiffness and strength throughout. I was also able to design tabs that would make it so as all of the pieces of the chassis mount would pop together to allow for reasonably easy assembly and welding.

Step 3 - Prototyping Round 1

So with my DWG file exports, I uploaded them to SendCutSend, selected 1/4" MDF, and placed the order. Several days later I had my parts in hand.

Much to my surprise, everything popped together right and was exactly as I designed. Now, this isn't to say I was surprised SendCutSend did such an excellent job, it was more that I was able to design something that then came out exactly as I had designed it, and on my first attempt. Not bad, not bad!

Placing the piece onto the car itself... I was able to see just how close my design was. I say close specifically though, as a few items were off. The offset of the upright from the mounting face of the crash bar wasn't quite right, placing the upright in contact with the lid of the hatchback. No worries though, with a solid piece in place I was able to bolt everything together, take some measurements, and then adjust accordingly for round 2!

Step 3 - Design the uprights, and order Prototype Round 2

So with round 1 complete and some modest success under my belt... it seemd reasonable to dive a bit more headfirst into round 2. So I began to design the next two components the design would need, mid plates and wing mounting plates!

Now the fine folks over at WingLogic sent me over their wing mounting plate DWG file. While their wing does infact come with these plates already, I wanted to be able to design my upright around it and be able to make sure I would be able to get the wing angle as desired. In the end, I did indeed revise their wing mounting plate just to have holes in it that could easily be adjusted for changing the angle of attack with the upright plate.

Now, of note is that I skeletonized the upright. Consulting with a variety of folks in a Facebook group on Aero and consulting many Youtube videos on the topic from KyleEngineers, I determined that solid plates are likely indeed better, but the losses with going skeletonized were likely okay as well. The biggest takeaway I had on this all came from Kyle's video on rear wing fins from WRC. My takeaway frome the video was that vertical flat surfaces provide yaw (rotational movement) resistance at the expense of drag. Given how much rally cars are trying to slide their rear around, they really need that help controlling yaw. I on the other hand, want a bit a of yaw potentially, especially at lower to medium speeds depending on the track. So I went skeletonized, but will be also getting some solid uprights to compare the difference as well.

Step 4 - Test Fitting Prototype Round 2 and... TBD!

Having hopefully succesfully measured everything up and came up with a slight revision to the chassis mount uprights it was now time to order a second round of prototype pieces. This time I ordered two of everything as I believe I'm at the point where I can safely assemble this all and confirm everything to be as close to accurate as possible.

Once the parts arrived from send cut send, I assembled them and start placing them on the actual Corvette to confirm fitment.

Sure enough, it all bolted up and looked pretty good!

Most importantly of all the work I did, the wing plates I made from the WingLogic provided DWG file actually matched the curvature of the wing! I'm perpetually impressed when things I worked on with such specific shapes or curvatures all come together and work. I guess I'm just that lucky?

A view of the wing on the C5 Corvette from the front.I feel pretty confident I got the height I was aiming for and it all looks pretty decent!

One thing that wasn't quite right however was the chassis mount to the deck. Here you can see the bolts are a bit off the deck of the car and a bit of the skeletonization is showing above the deck line. Reviewing this, I decided to hold off on going to aluminum right away and instead do one more round of MDF, doing just a single upright to confirm it all works properly. For this round I would lower the height of the chassis mount 10mm and further gap the top cutout another 10mm below the top. This will bring the bolts as close as I care to bring them to the deck along with creating 20mm of additional space below the current top of the chassis mount and the topmost cutout, which should in theory make it so only solid aluminum will be showing above the rear deck of the C5 corvette.

Step 5 - Yet another round of MDF Prototyping... and oh yeah what about the hatchback lid?

Welp sure enough things were better, but still not quite perfectly right. The height of the newly revised upright was great, but due to the bump not being perfect flat at this point just a smidge of one of the upper weight reduction triangles was poking above the deck lid. As that wasn't the goal, I needed to go increase the height of the upper triangle from the top edge 15mm.

While I was in there, I had considered that maybe adding some cross brace wiring under the bumper wouldn't be the worst idea. This is all likely to be very stiff since it will be built with 1/4" aluminum... but if it's not and I notice some oscillation in there... why not add in some cross bracing to stiffen it all up and eliminate that?

Then it occured to me... I had yet to try and open the hood with the wing in place. Welp, go figure... the hood makes contact with the leading edge of the wing. I'm now learning everything that everyone else who has designed wings before me seems to have figured out and I am starting to see perhaps why they ran their chassis mounts further back then I am running them. No big deal though... I'll just offset the mid plate (upright?) back two inches and it should come out alright. Oh except now it's not nearly as clear where to skeletonize to save weight so I'll go solid. Welp, now I see why everyone else goes solid there as well perhaps.

The above is the best I could figure for skeletonization, and I just may try it out. I'll probably run solid plates to start with though and if I'm feeling up to it, switch to these. I do have to admit, these are a unique and nice look on their own... I just am not so confident in their ability to resist twisting. Ideally this setup shouldn't be under much twisting load if any, but if an ascillation occurs... who knows?

Since I need to make sure the hood clears the newly revised design, I ordered another chassis mount (v4 now) and two mid plates. I should be able to reuse the most recently revised upright since the height is the same only the positioning of the cutouts shifted. If the hood clears everything and it all feels solid enough... I'll be sending it! 

Step 6 - The last of the MDF testing, hopefully. Maybe. Who the heck knows anymore though. Okay it was!

So with the newly revised uprights and the revised chasis mounts, everything finally came together! Only solid aluminum would be above the bodywork and the wing now has plenty of clearance between it and the trunk lid. This can all now go to aluminum! WOOHOO!

One thing of note at this point, is that my current estimate to complete the project will be at $1575. I could have ordered a known good product at this point for similar cost... but I wouldn't have learned anything, and I wouldn't have gotten the opportunity to design this to share with others.

Step 7 Going to Aluminum! Geting it welded up and testing initial fitment and solidness.

It took a while due to some snow and then ice storms herei n the PNW, but the aluminum parts have arrived from SendCutSend! They're going off to my friend Dave to get welded up and then onwards to get powder coated. I'm excited to get this all together and to get a general cost on welding and powder coating for folks looking to try and replicate this themselves.

The wing endplates came out AMAZING! I'm always surprised when something I design works first try, and sure enough these work out and are adjustable angle to match theadjustable wing angle. IE: If you go -10 degrees angled on the wing, you can go +10 degrees on the endplates to keep them relatively perpendicular to the ground.

Back from Welding and Powdercoating, time to assemble!

I picked the chassis mount parts and wing up direct from my friend Dave's house. He said that instead of filing to make the parts of the chassis mount fit, he simply used a press to put them together. He tallied his time to 1.5 hours to press everything together and weld it, and then $200 for powder coating. He did however mention he had an issue with the wing where the amount of welding required put a lot of heat into the wing and did result in a very modest bit of warping. So, a good note on that to take away and likely revision to the upright for a future round. Perhaps tabs that you just drill and pop rivet the wing onto? More to come, but for now I wanted to assemble what I had to work with.

Unwrapping the components, they looked pretty good. There was definitely some orange peel texture to it all, but eh... it's a race car I don't terribly care. It'll be getting covered in tire rubber in no time!

With all the pieces reviewed and looking good, it was time to do a test assembly. If everything didn't come together it wouldn't be worth putting the entire bumper assembly and what not back on the car.

The uprights went on without too much fuss. The holes I'd drilled for the MDF were slightly off as powdercoating had added just a bit of thickness, but nothing a little clearancing couldn't handle. It all came together, and I gotta say... six m10 bolts per side is major overkill. These things are insanely solid and there is surely no need for cross wiring as some folks had suggested and I'd left provision for. But eh... maybe somebody will want extra overkill?

The "skeletonized" wing uprights look positively amazing. I called them "Iccarus shoes" as they have that wing kind of look about them, and man in aluminum and powdercoated they really shine!

With everything now assembled, it looked excellent and appeared to be without any major issues. You can see the slight warping of the wing in the photo, but it's far from unbearable, and most folks won't notice it without taking a detailed look at it all. Added bonus, whenever I get another wing to fix this one, I can retire this to our lemons car as it is both bent and dinged now. Hardly a full price wing!

One last detail remained to check, and it was to check the hatch still opened and cleared the wing! Sure enough, it still does! Not sure why that would change, but eh I always am surprised when stuff I have designed just works.

Knowing everything fit, it came time to focus on getting the bumper over the chassis mounts. This necessitated removing the uprights and wing, and then modifying the original bumper foam that was in place to fit. Fortunately, the original bumper foam comes with 3 rivnuts ready to go for attaching the foam. Just cut and modify the foam to fit and let the rivnuts do the rest. As "no kill like overkill" is my motto, I decided to throw a bunch of gorilla tape on all of it to help ensure it's that much more secure.

I won't bore you with the headache that was reattaching the bumper. I had to do some yoga, but made it work. Only concerning bit for me was I had 7 bolts leftover in my magnetic dish when I completed reinstalling the bumper. I reviewed two separate videos though on reinstalling the C5 bumper, and I didn't miss a single bolt. I've got no idea where these came from, perhaps a different project? Yeah I'll just hope it's that!

With the bumper on, I began to yet again install the wing uprights and the wing itself. I figured I'd grab a quick picture though of how the clearance between the bottom bolts of the upright and the deck are just right. Other wing manufacturers put their hardware WAY above the deck and it just looks like somebody couldn't have been bothered to measure. There very well may be a great reason they did this, but visually... it just doesn't look right to me.

With everything finally attached, the car is "done". I decided to take it for a quick street shakedown, and then a few little rips in a controlled environment.

The wing held for several 130mph passes and I don't think I need to worry about going much faster than that at any tracks I frequent, so it seems safe to take it to the next step! I'll be writing about the first trackday soon with it, and then many ongoing track days. Also once it passes muster at a track, I'll be putting together a big "how to do a DIY wing" article for folks.

Takeaways from Track Use

Taking the wing out to The Ridge Motorsports Park for a track day, I was able to get some solid testing on the wing in the afternoon both when the weather cleared and the track went entirely open in format. I was able to get dozens upon dozens of laps, exceeding 120mph on the front straight and hitting 100+ between turns 9 and 10. The wing held and was without issue, and handling wise I simply couldn't get the car to oversteer other than at low speeds when intentionally inducing oversteer.

The Conclusion: A teardown to confirm everything is without issue

So I'll spare you the arduous details of tearing apart the bumper yet again and just suffice it to say... there were no issues discovered. All welds held, the bumper held, everything was as snug as before and as oversecured as before... it's good to go!

I somewhat regret going through the process of removing the bumper and everything else to get it all the way down to nothing to inspect... but I couldn't say with absolute confidence that this is robust and up to the task without having torn into it to confirm. What did work out nice is that along the way I was able to chase a few threads that were crap from likely a previous bumper removal and then rewrap all of the rear tail light wiring harness as the ancient electrical tape was coming apart.

This though, is the end. It works, it's tested, and... I did it.

I learned a new skill, developed something that looks good and works great... and now it's time to give it away!

A quick Note on Pricing and OshCut VS SendCutSend

So I've had a few people recommend OshCut over SendCutSend. I also can't deny that I am seeing advertisements for OshCut now. So I decided to price everything out and... SendCutSend was 17% cheaper, and that was before taxes and shipping. I've also been using SendCutSend up until now and had great results from the folks there so I see now reason to change that up. That said, if OshCut gives you a better price, or you can get a good price from anybody else on this, I see no reason not to run with it. Just make sure they have REALLY tight tolerances or you'll be doing a lot of filing to make this all fit together!