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Summary of things to fix for Hermes 3 Fin Can:
- DESIGN
- Talk to USC about how they design their fin can (also ask for manufacturing tips)
- Reach out to MIT faculty (esp. Prof. Mark Drela for layup advice)
- Tube layup
- Overwrap the fin collar in CF (at least 3 layers). We used a fiberglass-overwrapped tube because the carbon fiber tube layup had bubbles and we ran out of time, but using carbon fiber would have been way stronger.
- Make sure there are no bubbles, and account for things going wrong
- Do a practice run so the people doing the layup have prior experience
- Root Bond
- Don't use 5-minute for the root bond. Make a jig that can support the fin/fin can so you can use a stronger epoxy. Even though most of the strength of the fins comes from the root fillet, it's still important to have the root bond as strong as possible
- Root Fillets
- Consider an inner fillet of proline and outer fillet of epoxy to add strength (and two different types of fillets might make it more difficult for a fin to come off because of fin flutter)
- Use System 3000 epoxy so that it increases in strength after the oven cure. Using West Systems saved time, but the epoxy may have become brittle after the oven cure because it has a lower glass transition temperature.
- Degas the epoxy to remove bubbles before applying it to the root.
- Make sure the fins are sanded where the epoxy will go to improve the bond (rougher surface = more surface area to bond to)
- Make the fillets larger (reference pictures below to see how large the fillets were). Larger fillets = STRONGER.
- Tip-to-tip layup
- MORE LAYERS OF CARBON FIBER
- Static load test
- Don't test the flight fin can, but make sure whatever you're testing is identical so we know for sure that the flight fin can works
- Make individual fins and test them (for example, bond a fin to a board with the same root fillet as the flight fin can, and do a CF overwrap and then test that. That way, you don't have to make a whole fin can but you can get some useful data)
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