Joined: Tue Apr 07, 2009 1:36 pm
I think the pictures are pretty self-explanatory, but let me know if you have questions. Basically, the shrink wrap makes an air-tight seal with both the top cap of the booster and the sustainer nozzle, letting air pass between them. When the booster takes off the string pulls the shrink wrap out of both caps. After the booster is done thrusting the stages just fall apart.
Oh, and after you see the pictures you might wonder what stops water from the sustainer from falling into the booster. The answer is, nothing really. The shrink wrap is just small enough that water can't go down and air up at the same time. In testing, a little squirt of water did make it down from time to time, but it was nothing really. It won't take much work to add a one-way valve to the booster side of the shrink wrap either, and this might be necessary if larger diameter shrink wrap is used.
I'm also trying one out with a larger (diameter) peice of shrink wrap. The holes in the caps for that one are 9/64". I've had it up to 50 psi in the shop with only a negligible leak (tiny bubbles very slowly appearing when submerged in water) but haven't launched with it yet.
So here it is, the stupidly simple stager: