Today we tried a method for vacuum bagging the tip-to-tip carbon fibre onto the fins of the rocket. The tip-to-tip carbon fibre has uni-directional fibres that run down one fin of the rocket, over the body tube and up the next fin. At supersonic speeds, the fins tend to flex and ‘flutter’, and can snap off the rocket. The tip-to-tip carbon fibre gives the fins a lot more flexural strength and should prevent this.
We created a vacuum bag that uses putty tape to seal on the aluminium leading edge of the fins. Because we only wanted to test the method, we covered the surface of the rocket in teflon sheet before adding the epoxy.
Although the vacuum bag gave a reasonable finish to the carbon fibre, it was quite a pain to get a good vacuum seal, and was quite an involved process. For the proper tip-to-tip carbon fibre we have decided to go for a normal wet lay-up and to manually smooth down the carbon fibre using rubber rollers. The epoxy that we are using for the lay-up is Sicomin, from Matrix Composites, which has good temperature stability without a post-cure. It is quite ‘fragrant’, however, hence some fairly hefty respirators….