This week we are comparing 3 different ones. The first one is a regular 4mm 3-ply plywood fin. This fin is very tough, but the main drawback is its weight. At 74 grams it is the heaviest. Thickness is 4.2mm.
The second one we tried making out of two 1.5mm sheets of balsa wood glued together at 90 degrees to each other with PVA glue. We then put one layer of 200gsm fiberglass on either side. Epoxy resin was used for this. The fin is quite tough and weighed in at 43 grams. The thickness is 3.9mm but the main drawback is the amount of work involved to do this and the higher cost.
The 3 fins tested. Left to right: corriflute, balsa/glass sandwich, plywood.
The last fin is made from corriflute, the material we have been using until now. It weighed in at 25 grams, but has a thickness of 5mm. It is quite tough, and has a good finish, but the main drawback is that it is made from polypropylene and hence harder to glue and paint. The leading and trailing edges are also harder to create nice and smooth.
So far the balsa sandwich is probably a good compromise, unless we can find some nice lightweight plywood.
We have also spent some time this week getting Acceleron V rebuilt and serviced so it can be launched again. We also did a 50psi leak check. We'll try to launch it again soon just for fun.
We were supposed to go out to the NSWRA launch today, but after driving half way there in pouring rain, we decided to turn back. As we got back, the weather cleared up but the wind had picked up. So we went back to the workshop and fiberglassed 3 of the spliced-quads. We are going to give them at least 5 days to fully cure before pressure testing. We are going to try to push them to 270psi for the 250psi launch pressure. We'll see how much they'll actually hold.
3 x 5.3L spliced quads wrapped in fiberglass.