While 1/4" plywood is pretty rigid I still wanted to add some cloth reinforcement because the fins are high profile and I don't want them shredding or breaking off during flight or recovery impact. Last time I used a mix of carbon fiber cloth and remnants of carbon/kevlar cloth. I also used a material-efficient stack while laminating but it's that configuration that caused the fabric bumping and layer separation difficulty:
For this mark II build I decided that carbon fiber was overkill so I reverted to 6 oz fiberglass. I also added 3/8" ply layers between the fin layups to force a smoother surface and to completely segregate each stack for easy separation ('CF fabric' below should read 'Fiberglass cloth'):
This layup worked much better although the surface still isn't as smooth as I'd like so, again, priming/sanding is the best!! Here are some pix of the layup:
Oh and I completed the motor assembly/e-bay, cut all the slots and doors, epoxied the goodies together, and this baby is ready for fins:
2 comments:
Have you calculated what PSI you get from that weight over the fin? How does this compare to vacuum which I presume gets close to 15 psi?
No I haven't calculated it but that's a good question. I do have a vacuum pump but it's tough to adjust it for an optimal resin percentage. It's also guaranteed to maximize fabric texture. I mainly used the weight on top of the 3/8" boards to minimize fabric texture and accepted the resin concentration that it yielded.
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