Composites

Formula SAE

Composites

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For the 2024 season of FSAE I am the monocoque part holder for Virginia Tech motorsports. In addition to this I have been working on developing our composite manufacturing techniques for our aerodynamics subteam.

Historically our team has issues with the quality of our wings. We have been using a positive mold and laying on top of it, resulting in the outer surface being unconstrained. A silicone surface sheet was used over the top to create a better surface finish, but without an incredible amount of tension on the sheet, wrinkles would for when vacuum was pulled or autoclave pressure was applied. Usually wrinkles formed at the leading edge causing massive ridges of resin and sometimes carbon. Additionally the surface sheet is not rigid so the texture of the carbon weave printed on the surfaces.

I spent the spring of 2023 working on prototype manufacturing to fix the issues that we had been having. The first idea that I focused on was a two part negative mold with an internal vacuum tube. I used the smallest airfoil section that we had planned on using for the car because it would save cost and it was the most difficult to pull off, so if this worked, then any size would work.

The first couple of iterations had very poor results. In the first iteration, we used a polyurethane tooling board for the mold. Also, we made and internal vacuum tube by attempting to heat seal some Stretchlon bag. This did not work. The outgassing of the board at the prepreg cure temperature prevented the cure of the part, and the internal bag was unable to distribute pressure to the center position of the mold.

Wing - Iteration 1

For the second iteration, we changed the parting line to make the machining easier and we ordered proper internal vacuum tube. This time, the part did fully cure, but the outgassing issues were still present and we had issues with release. The surface finish was awful and required a lot of sanding to bring down to an acceptable quality. Also, the tool was damaged from removing the part.

Wing - Iteration 2

I had time for one more iteration during the semester. This time I opted for a high temperature carbon tool to try to get rid of the outgassing issue.

Patterns for high temp tools

High temperature tool layup

High temp tool surface and leading edge

The high temperature tool produced much better results, but there were still some issues with the surface finish. Also, the leading edge on the tool was not consolidated well so the sharp edge was not preserved which caused a ridge similar to the original wing manufacturing method (but less prominent). I also didn't label the sides, so the leading edge of the bottom half was most likely matched up with the trailing edge of the top half.

Iteration 3 - Leading edge

Iteration 3 - Surface

At the beginning of the fall semester of 2023, I took a more methodical approach to the prototyping, and I gathered more people to delegate tasks to. I began by coming up with concepts and drawing them out. I then tasked my teammates with designing the tools in CAD. I did not come up with all the concepts at once, so I added to the board as the first few were being designed.

Final prototype

Clear coat test

Spar

(upper surface sanded after a clear coat mishap)

Weight and original surface finish

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