moderated Re: Kevlar shock cord
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Great info, thanks!
From: Bob Ferrante <robert.1.ferrante@...>
To: main <email@example.com>
Sent: Mon, Sep 9, 2019 11:43 am
Subject: Re: [MTMA] Kevlar shock cord
One thing that must be considered with Kevlar is degradation. 100 pound line may work the first three flights but if the shock cord is close to the ejection charge then each time it is being exposed to the ejection charge it does degrade. After a few flights your 100 pound line is now 75 pound line, and a few more 50 pound line or less. Also Kevlar will breakdown in UV light (sunlight). The strength is significantly reduced over time exposure to sunlight. I passed on a bunch of Kevlar at NARAM this year because it had changed color on the reel from the UV breaking down the Kevlar. Several layers in had changed color because the vendor kept the reels on the back of his trailer and where constantly exposed to sunlight.
Funny thing is I purchased 150 pound and 500 pound from Emmakites right after NARAM. I have had the web address in my favorites since NARAM-53. www.emmakites.com
Experience has told many of us that it is better to overbuild the shock cord.
100 pound is good for small competition models and sport models up to B or C.
250 pound is good for models up to E or F or egglofters.
Because Kevlar is so strong you may find it breaks parts on the model. So a short section of elastic line run in parallel with the Kevlar to absorb some shock before the Kevlar line pulls tight with reduce the shock to the parts of the rocket. This is great for egglofters and TARC teams to know.
On Mon, Sep 9, 2019 at 11:14 AM Jeff Kodysz <jeffk813@...> wrote: