Initial Modeling and Testing

After initial research on closed-wheel race car wings, such as GT3 wings, I selected a few design features to lock in: airfoil shape/sizing selection, number of elements, endplate shape/sizing, degrees of twist in the wing, and mounting.

I began with real-life testing on my car (Chevrolet Camaro). I first downloaded a track map of the Spa circuit to determine what speeds I would likely see from my car going into corners. From there, I selected 3 speeds to check for flow attachment on the rear windshield. While I drove the car, I had a friend use my camera to record the tufts on the rear windshield of my car.

Moreover, though I had a CFD model running, I wanted to try and find the true angle of twist required for my wing. The reason there is a twist in the wing is due to the downwash of the rear windshield, which increases the local angle of attack (AOA) of the wing. Thus, I would need to twist the middle portion of the wing to a lower AOA. Though, due to the relatively gradual slope of the rear windshield (especially compared to a vehicle like a Miata), I expected a small required twist.

To test this, I made the jig below.

From this jig, I then created a grid with sharpie on the Lexan endplates. After hot gluing this to my car and mounting my camera, I observed the difference in angle of attack between the outboard and inboard cardboard flaps (required some bending of the flaps to catch more air). This difference from the camera angle appeared to be approximately 4 degrees, which I reflected in my design.

Simulation

For my simulation set up, I used ANSYS Fluent. To start, however, I did basic airfoil analysis in XFOIL.

In my studies, MSHD had the highest possible downforce compared to the other profiles, but produced the most corresponding drag and had “peaky” performance. The last thing you want while driving is the car to be on the edge and lose the rear. I ended up choosing the CH-10 airfoil due to it having decent efficiency, smooth stall characteristics, and it overall performed well as a single element (my original goal was to make a single element wing).

From here, I set up a simulation with the car body and the wing together.

I first optimized vertical and longitudinal location of the wing while also making it rules-legal in GT3 terms and a few other race regulations. From there I optimized the wing angle of attack itself.

This computational study using the native ANSYS optimization function pointed me towards a 12.5 degree starting AOA for my wing for cornering.

The final area I started iteratively designing was the endplate. After optimizing sizing based off of convention and computational optimization, my final endplate sizing appeared as below.

Manufacturing

For manufacturing, I wanted to explore resin infusion. I did not get the chance to attempt it during our 1-year quick and tightly-budgeted design cycle in Formula SAE.

The first area I researched was tooling, but once I saw the costs to CNC molds, I quickly turned to 3D printing.

Though fiberglass molds from the 3D printed molds were an option, I did not plan on producing multiple wings from 1 mold, so budget-wise, a 3D printed mold would suffice.

From this general shape, I needed to prepare the surface for resin infusion. This preparation required SANDING, LOTS AND LOTS OF SANDING. Thought I was done after FSAE, NOPE. I documented my process and initial planning using Miro as shown below, but some work was subject to change as was my process.

I noted what went wrong in each attempt and updated the process accordingly.

For example, this first attempt left a pattern on the mold after I demolded the part. This leftover means the release was poor, and the part was sticking to the poorly prepared surface too much. This problem can be resolved through better sanding, clear coating (avoid orange peel), and a proper buff/polish.

I later added larger flanges to the molds in order to prevent vacuum and resin insertion creases from reaching the part. Additionally, the image above shows a much better-prepared surface, which corresponded to an easy release.

Though some of the wax transferred into the finish of the part, I was able to make it look a lot better with some sanding and clear coat. After completing these tests, my next steps are to print/assemble the big mold, space out resin insertion ports, and attempt the full span’s infusion. The mold will also serve as a jig for where to cut mounting insertion points and for where to bond the ribs (which have a carbon spar running through them).