Originally posted by DJ Delorie
Working on a 13mm Solar Sailer (BT-5 outer), starting to think about the recovery system. Since there's an inside tube and CRs, attaching a kevlar line to that is an obvious idea. However, my current inventory only includes 8lb kevlar thread, 1/4" shock cord, and some regular rubber bands. I've got 90lb kevlar on order though. Anyone have suggestions for cobbling these together in some way to build a recover system for this little rocket, or do I need to order other sized parts?
Also, suggestions on chute/streamer too. Rocksim says 1/2 oz empty, 3/4 oz with an A10 in it. Total rocket length is about 21", with about 8" of BT5 in which to stuff stuff. On a 1/4A it only goes 100ft up, so the faster it deploys the better.
Take the kevlar you've got, roll off a piece six times longer than the length you intend for the shock cord. Tie the ends together in a knot so you have a large loop. Double the loop by folding it over, and again to make it three loops. Stick your index fingers into the loop and pull it taut. Tie knots in each end (and the middle if you want). You now have a 48 pound shock cord.
If all you have is 1/4" elastic, I suggest you double that too. Just pull off twice the length, tie the ends to make a loop, and that's enough.
The nice thing about working with loops is they hook together so easily and certainly. Just stick one end of one loop through the other loop a short way, run the other end of the first loop through the part you stuck through the second loop, and pull it tight. There's no know at the joint, so it can't untie, and they way they're connected, when there's tension, it just pulls tighter
If you want to put a drop of CyA on the knots so they don't untie, that's fine. Just put it on the ends sticking out from the knot, and on the half of the knot facing them. Don't put it on the load bearing portions of the keval or elsatic, or the half of the knots facing those portions. It can make elastic fail, and if you make a piece of kevlar stiff with glue, the part right up against the stiff part will be the only part that bends, and be more likely to wear through.
I've done this many, many times, and have even used the looped kevlar embedded in a glob of epoxy on the inside of the tube as the shock cord anchor. Bury the whole end of it, with just the cords sticking out and the knot (a couple extra knots to be sure) completely embedded, and there's no way that cord will pull loose.