Estes is finally selling Aramid Cord! Aramid cord is Kevlar.
Kevlar is fire resistant, not fireproof. 100 to 150 lb. Kevlar will degrade from ejection charge exposure and eventually break through after 10 - 15 launches.
What's the advantage to using Kevlar?
In LPR smaller body tubes it is attached to the engine mount. There isn't a tri-fold shock cord mount to block the ejection of your parachute or streamer.
I prefer Kevlar tied to an elastic shock cord. That tie point should be below the lip of the body tube (unless you use a "bumper") or you can get a "Zipper" where the Kevlar can tear down and through the body tube.
I would presume that adding an ejection baffle might change things. Would you still use Kevlar in this case? Where would you place the anchor point for the shock cord in this case? If you anchor it at the engine mount, you'll have to thread it past the baffle (which could get fiddly). Anchoring the cord at the baffle might the choice -- though some baffle designs might not appear to be strong enough for use as an anchor. Anchoring the cord at the baffle brings the question of how to make the shock cord replaceable (main concern is that elastic tends to degrade on its own over time).
ReplyDeleteHi Naoto,
DeleteI could attach the Kevlar line to the top ring of a baffle. The tie point usually would require some reinforcement, maybe a small, second layer of thick cardstock.
I doubt you would ever have to replace the Kevlar line if it were attached to the upper ring. Not much heat at that point.
Mainly the concern was over replacing the elastic part of the shock cord (since elastic tends to degrade over time). Having the tie point between the Kevlar and elastic part below the front of the body tube (to avoid potential for "zippering") could make tying the two together a bit fiddly. Perhaps the solution might be to do something like this: Anchor the Kevlar line to the front of the baffle (with possible reinforcement to baffle to prevent a "pull-through" of the Kevlar line). The end of the Kevlar would end with a knot with loop (onto which we will attach the elastic) which would be formed prior to installing the baffle. Attaching the elastic would involve passing the elastic through the loop at the end of the Kevlar and tying a knot to anchor it to the Kevlar.
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