Kevlar String request

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Kirk
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#1 Kevlar String request

Post by Kirk »

I am looking for a spool or supply of Kevlar string to replace elastic shockcords on my low power rockets.
Also might use it as shroud lines on parachutes that I am constructing.

Anyone got some that they would recommend?

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bernomatic
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#2 Re: Kevlar String request

Post by bernomatic »

Hmmmmm,

Might have to try adding those to the ship's store. Besides the 135 lb length I'm sending you gratis, I have some 64lb stuff that would be great for parachutes. I have been putting off really getting the ship's store running since I am too cheap to pay for the SSL to make it a secure connection. I may just have to bite the bullet and get things going.

In the mean time, shoot me a private message and I can add the thinner stuff at 10 cents per foot.
Chief Cook -n- bottle washer

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luke strawwalker
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#3 Re: Kevlar String request

Post by luke strawwalker »

Hmmm... worth a try but honestly I wouldn't use kevlar for shroud lines... I mean what are you trying to protect them from??? If the parachute is exposed to enough heat to need kevlar shroud lines, the plastic sheeting of the parachute will melt into an undeployable "plastic wad" recovery long before even cotton shroud lines would be damaged...

Kevlar is, IMHO, too abrasive and non-stretchy for shroud lines... it has ZERO stretch, period, which is why it will zipper a tube if it is yanked hard enough by a hard deployment. Now, cotton thread or "carpet thread" isn't HUGELY stretchy, but it does have SOME stretch, and it's nowhere NEAR as abrasive or prone to cutting other things as kevlar is when yanked or pulled.

Basically, every time a parachute deploys, it's trying to yank the canopy loose from the shroud lines... the shroud lines need to stretch "a little" to help absorb deployment forces... not a lot, but SOME. Kevlar doesn't stretch AT ALL that I've seen... plus it's SO strong and "abrasive" or hard that it wants to CUT other things around it when it's yanked... So it's trying to cut through the tape dots or parachute canopy every time the chute opens...

With the mylar party balloon parachutes (as well as other parachutes from kits like standard Estes chutes, Dr. Zooch "trash bag" chutes, etc) I've had the best luck with applying a small usually 1/2 by 1/2 inch square, or slightly smaller, square of duct tape or gorilla tape applied to the edge of the chute at the shroud line attach points, then using a hole punch to punch a hole through the center of the tape square and underlying parachute material, then tying a good stout cotton or "carpet thread" through the hole back to itself using a "surgeon's knot" to hold it tight. Works great from my experience. I've had too many of those stupid 'tape dots" that Estes uses on their chutes give out over the years-- the adhesive dries out and they fall off, or the lines rip out from under them... the duct tape "dots" with hole punches in them have NEVER failed yet... I DO recommend liberally dusting the chute with talcum powder a time or two to make sure that any adhesive from the tape is not gonna stick the chute together... just as insurance... Never had that problem if the chute is dusted...

Later! OL J R :)
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Kirk
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#4 Re: Kevlar String request

Post by Kirk »

Thank you for all your advice.
I will rethink the use of Kevlar in place of shroud lines.
Where do you recommend looking for Carpet thread?
Jo-Anne Fabrics?

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luke strawwalker
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#5 Re: Kevlar String request

Post by luke strawwalker »

Yeah Jo-Anns is a good place... might try HobLob... it's getting harder to find, maybe online. Basically you can use ANY good solid COTTON thread... you don't want polyester or blends or other synthetics that can easily burn if a hot particle of BP from the ejection charge hits them... sort of a million to one shot, BUT it DOES happen now and again. Cotton can withstand the close proximity of a burning BP particle for a moment or two until it disintegrates-- but thin synthetic fibers (other than aramid/kevlar) cannot-- because they're so thin they'll melt through almost instantly.

Use cotton... :) OL J R :)
My MUNIFICENCE is BOUNDLESS, Mr. Bond...

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