Shock cord length?

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Adam Selene

Roving Rocketeer
Jan 18, 2009
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i'm in the midst of building a LOC Stovi, which comes with underware elastic for a shock cord. i'm going to use 1/4 " tubular nylon instead. the question is how do i determine a reasonable length to use? i would guess that it should be longer than the supplied elastic but how much longer?

I don't know how long the Stovi is, but I generally use a 4:1 or 5:1 ratio. Might want to make it a bit bigger at the tube so you don't zipper it with 1/4" nylon.

Common wisdom for HPR is to use mega-lengths. For a Stovi I'd myself use 2 to 3 x the rocket length. For that width nylon, I would add several wraps of cloth tape at the point it meets the top of the airframe. Have the tape extend about 1/2" past each side of the nylon. Works for me. My 2c

BTW, I still have thick elastic on several mid power and one high power rocket. This stuff works fine and lasts a long time IF you keep it fairly far away from the ejection. All of these have either wire or nylon leaders. I use dog barf and place a portable chute protector below the nylon. Inspect it after launch just in case. The leaders I mentioned make it easy to replace. And yes, if I replace them I'll use TN or maybe the thicker Kevlar from Pratt.
After you pack the chute, wadding, and cord, If you dtill have room you haven't used enough. :)

Then there's the extreme version...

Andy Woerner reportedly once did a Bungee Thumper launch that used a long bungee cord (50 ft, or something like that). As it descended under chute, it bounced the whole way down.


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