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The fin can fits over the motor case (at least, it's supposed to...). Since it didn't quite fit, we sanded the phenolic tube using a flapper wheel, and then overwrapped it with 3 plies of carbon fiber. The phenolic tube acts as insulation from the heat of the motor case and is not structural, so carbon fiber needed to be added to bear the structural loads. During the tube layup, the phenolic tube was held by a pole over the layup jig (much like a pig on a spit). We only had two people for the tube layup which was difficult because you need to keep turning the tube in order to keep adding more carbon fiber, so make sure you have Have at least three people helping with the tube layup.
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Sanded CF on leading edge
Lessons Learned
- Make the phenolic slot thicker to account for fit between phenolic and G10
- When doing the tube layup, make sure there are no bubbles (use heat shrink to help with this)
- Use a flapper wheel to sand the inside of the phenolic tube instead of doing it by hand
- Have at least three people to help with the tube layup
- Support the fin more securely while machining the G10 tab so that the phenolic leading edge is aligned with the fin (see "Hermes 2 Fin Design")
- Make sure the fin can jig for the root bond is properly sized so that the fins are straight/evenly spaced
- Don't make the vacuum bag too big or it will be difficult to handle and cause creases
- Taper the carbon fiber cutouts only at the trailing edge
- Make sure your laser cutter is large enough for the cutouts
- Make sure the vacuum bag is properly sized (not too big, not too small)
- Position the fin can vertically, not horizontally, so that the fins don't splay under the weight of the fin can as the epoxy softens
- Have a buddy when doing the oven cure and work in shifts