Kevlar String replacement

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Space Cadet
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#1 Kevlar String replacement

Post by Kirk »

I have heard a number of experienced Rocketeers talk about never using Estes elastic shock cords, but ALWAYS replacing them with Kevlar string, looped around centering rings and motor mounts.

How common is this?
What weight or strength of line is recommended?
Doesn't this also promote zippering of the body tube? How do you prevent that?
And how long a string do you recommend using? :mm:
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#2 Re: Kevlar String replacement

Post by bernomatic »

Copied this from your request thread.

1. If you are replacing an Estes rubber shock cord with just Kevlar, you should make the shock cord two to three times as long as the original.
2. A far better way of doing it, is to have a Kevlar Cord anchor, then change over to an elastic thread just short of the rim of the body tube joint.
3. You can anchor the Kevlar Cord in a myriad of ways to the main body tube, but one of the simplest is to cut a notch in the fore centering ring of the engine mount and slip the cord in between the engine mount and the ring. Tie the cord around the engine mount and glue in place.
4. You can drill holes in the engine mount rings and run the cord all the way to the aft portion of the engine mount tube. Then tie it around the end of the tube and put a dab of glue on the knot. This way, the cord can be somewhat easily replaced if the cord becomes damaged.
5. If you have already placed the engine mount in the body tube, there are a couple more ways to "retro fit" a Kevlar shock cord in the rocket. I use one of these methods from the getgo to easily check the cord and replace if necessary.
Chief Cook -n- bottle washer
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