Kevlar Strings or Rubber Shock Cords?

 The Thrifty Rocketeer blog continues....

One of the biggest debates among sport rocketeers over recent years has been what glue is best...however, that's not what this entry is about.

Instead, I have heard a lot of guys insist that they hate the rubber shock cords supplied with Estes Rockets kits, and that they ALWAYS replace them with Kevlar string.

This would seem to be problematic unless you plan right from the construction, how to anchor it around either the motor mount or centering ring, or both. (Does this sound familiar?  Haven't we discussed this before?)

I bring this up again because another newby has asked  in another forum, whether he should replace his rubber shock cord, and it sparked a spirited discussion that overwhelmingly leaned toward replacing them, sight unseen, untested, and without recommendation of where to find this.

Some guys are recommending a Kevlar string that is braded, not woven.  Others suggest a shock cord that is at least three times the length of the rocket body.  And only a few have suggested a combination of both rubber shock cord AND Kevlar string, joined together OUTSIDE the body tube.

Now, having experienced more than my share of "Estes Smiles" when the nosecone bounces back and impacts the body tube lip,  I am inclined to try to replace or combine the shock cords in the future.

However, it occurs to me that there is a real benefit to having a rubber shock cord, that is bio degradable.

The major objection to the rubber shock cord these days seems to be that they snap...or that they break...and that produces a problem for the controlled recovery.

However, look at it from the point of view where a rocketeer gets their rocket snagged in a rocket-eating tree, bush, power line, telephone line, etc.  It usually is the shock cord or the parachute that hangs up and dangles the body tube out of reach.  Now, if you can't get the rocket out of the tree, your other option is to keep observing that rocket dangling over time.  Eventually, something gives, and the rocket falls.  It could be a branch. It could be a shroud line.  But more often than not, it's that same rubber shock cord that people have been complaining about snapping.

If it didn't fatigue and snap, your rocket would still be hanging up there.

Frankly, I don't know if this is Estes Rockets' thinking, but I'd like to think they've got a little planned weak link here...just for the benefit of the first-time rocketeers who may loose their rocket to a tree.

What do you think?

Post your comments below please.

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