There used to be a high power flier from the Dallas area who made some really nice recovery harnesses by putting 10 feet of bungee inside 20 feet of tubular nylon. It gave a nice spring to the recovery but had the strength to back it up. I sold a bunch of it to some people in Atlanta. They said it looks like a bucket of guts.
Okay, what if you get a bonus delay - pretty common - and the rocket is doing 75 feet a sec at deployment? Even if you have 100' of shock cord, when the chute opens, it's still gonna get a good jerk. Or if you have a good crosswind - pretty common here in Texas - and the thing weathercocks pretty badly? At top-dead-center apogee it can still be doing 100mph sideways. How long a shock cord do I need for that?
The point is that, while length may help some, absorbing the shock is a necessity. Elastic/bungee will soften the blow, but can store the energy and bring the nosecone crashing back into the airframe.
The technique I use involves wrapping masking tape around folded sections of the shock cord. When the cord is drawn tight, the tape tears thus dissipating the shock without storing it. It's worked very well for me.
HTH. Doug
You asked questions for which you evidently already know the answers, and I am no longer interested in arguing with those more knowledgeable than myself. You want to use underwear elastic in your rocket? Knock yourself out.
I have had a ~25 pound rocket deploy immediately at motor burnout while the rocket was traveling parallel to the ground, and it was "moving". I was using a cheapie 8ft. chute, and didn't even break one single shroud line. How does he do it, the crowd asks?
Deployment bag with drogue chute and the tape loops that Doug describes.
I've also seen Velcro used for this purpose.
Which brings up a question -- has anyone ever done a study as to how much force velcro requires per square inch to separate? And what the optimum sizing might be for use in a recovery system like this?
It would also seem that the method of attachment of the Velcro, as well as whether it's "fresh" or "old" Velcro. Comments from anyone who uses it???
David Erbas-White
Bob Kaplow wrote:
So far, it's not been a problem. I agree the potential is there, but I haven't been bothered by it yet. Keep in mind, of all the types of tape out there, masking tape is optimized to be low residue. So it's got that going for it.
Doug
I have to say that these various methods of shock dampening seem more attractive than using inordinate amounts of tubular nylon to create an expensive form of streamer recovery. Essentially it seems if you are willing to pack the payload with 50 feet of tubular nylon, why not just pack it with 300 feet and forget the chute. Just kidding-sort of.
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