kevlar fasteners

[MarkB.]

Posit the following:
1) You have not built or launched a rocket since 1977
2) You and your son are building Jr.'s first rocket;
3) Your Mom stops buy and says "Oh, I'll be right back!" and hurries out;
4) She returns a little later with a box of 30-year-old rockets you thought were long destroyed and hands them to you;
5) Inside you find Arcas, Aerobee, Nike-Smoke, Starfire, a pair of Alpha's and a partially assembled Sandhawk all in relatively good external condition;
6) Further inspection reveals parachutes melted solid and elastic rotted from 30 years of 120 degree attic storage;

So the question is: If I'm going to be born again, I understand I need to replace the rotted shock cords with Kevlar and cotton elastic. So how do I attached the kevlar to the side of the rocket (Sandhawk being the only one I can get to the engine mount on)?

Does somebody make such a retro-fit as a package?

And if not, why not?

Suggestions?

[Commanche3]

I have gone to all Kevlar shock cords and I've mounted it 2 way's. I have used epoxy and glued it where it wouldn't interfear with the nose cone. I smoothed the epoxy with a little alcohol and I hadn't had a problem with it. The other way to mount it would be when your building it to tie it around the motor tube and up thru the centering ring, it should be a couple of times longer than the rocket so when the ejection charge goes off it lets the nose cone clear everything.

[MarkB.]

Thanks,

What form does your shock cord mount take?

Is it fiberglass material with the kevlar woven through then epoxied?

Should i look for some kevlar material to make the mount out of?

Sorry for so many questions.

[mrhemi1971]

Mark,
Having done the same thing with my old kits, if you are using a thicker kevlar, you can make a mount similar to the tri-fold estes type, and it should work perfectly. The kevlar is just acting like a high tech kite thread. You'll find that the more you use it, you'll love it. BUT BEWARE- if you make the entire shock cord out of kevlar, you need to pay careful attention to your ejection delays not being too early, or you may experience a "zipper" effect, or a slice through the body tube. This happens because of the kevlars' strength and thin diameter combined with high speed ejection. But its benefits outweigh its problems for sure.

[barone]

Mark,
Having done the same thing with my old kits, if you are using a thicker kevlar, you can make a mount similar to the tri-fold estes type, and it should work perfectly. The kevlar is just acting like a high tech kite thread. You'll find that the more you use it, you'll love it. BUT BEWARE- if you make the entire shock cord out of kevlar, you need to pay careful attention to your ejection delays not being too early, or you may experience a "zipper" effect, or a slice through the body tube. This happens because of the kevlars' strength and thin diameter combined with high speed ejection. But its benefits outweigh its problems for sure.
Mark,

Ryan tells it perfectly. Of course, too late an ejection will result in a zipper also. Just wrap some tape around the cord where it would encounter the end of the body tube to help give it a little more diameter so it doesn't cut like a knife. Then again, you could just go with the thicker cotton-elastic installed the same way you would install the old style shock cord, that is, using the tri-fold method. I've only used the kevlar in kits that I am building and can wrap arond the motor mount. Otherwise, it's either 1/8 or 1/4 inch wide elastic (1/2" for the larger birds).

Great that your mom kept those rockets all those years. Good luck with the retofits.

[mrhemi1971]

That reminded me, What I like to use instead of tape is a piece of heat shrink placed on the kevlar, BUT my little secret is to take cotton off a q-tip or cotton ball and stuff it in the heat shrink first, creating a little pillow thats not too bulky, but will keep those zippers from happening. Yeah it may be a little extreme, but I have yet to have a zippered tube!

[Doug Sams]

Posit the following:
(snip list)Where's item 7 - shed tears of joy? <vbg>

As for the shock cord issue, here's my two cents worth: http://home.flash.net/~samily/MR-shock-cord/ (Actually, that's more like a buck two ninety eight's worth :D )

In your case, since you're retrofitting, you have limited options. In anchoring the kevlar in the rocket, you likely won't have the nylon ribbon described in the link, but if you use the tape wraps, that should help resist most zipper loads.

HTH.

Doug

.

[Solomoriah]

I don't bother with Kevlar on refurbishments. I just do the old folded mount with standard elastic... and I use plenty of it.

On the other hand, I use Kevlar with almost every rocket I build, scratch or kit.

[jj94]

If you don't want to mount it directly to the body tube, try attaching it via a baffle. Semroc and Fliskits both sell high quality baffles. Another advantage of a baffle, besides a sturdy attachment point, is that you won't need wadding for future flights.

[MarkB.]

Tears of joy indeed.

Thanks for all the suggestions and information. There's going to be a lot of catching up to do. I'm going to get the Arcas and Sandhawk flying first and we'll see what happens . . . .

Again, Thanks.

[LeeR]

Mark B -

I've done the wall-mount anchor like Commanche3 suggested. Here is what I do, which may differ slightly:

I take about 2-3 inches of Kevlar, and tie an overhand know in the ends, to form a small loop. I epoxy the loop on the tube wall, with the epoxy coating the knot, so a nice smooth lump is formed. I now have a loop that elastic shock cord can be fastened to. I usually do not tie the elastic onto it -- rather, I make a small loop in the shock cord, and feed this thru the Kevlar loop, place the loose end thru this loop, and then pull it snug. This makes it easy to replace once the elastic gets old/tired/scorched.

Ideally, I like to anchor to the engine mount, such as thru the top centering ring. But the loop on the wall is a good retrofit solution for older models.

[MarkB.]

Well guys,

Thanks for all the ideas! Here's what I did:

Sandhawk: The body tube was not yet attached to the plastic fins and engine mount so I tied the kevlar around the engine mount and drilled a small hole through the uppermost mounting ring.

Arcas: My favorite rocket is an Arcas. Thus, this rocket ran afoul of an AMS (Advanced Modeler Syndrome, as the plastic guys call it) flare-up. From measuring the Arcas on display at the New Mexico Space Museum , I determined that my thirty+ year old K-26 was too short by about 3.875 inches. So I ordered some kevlar thread, a piece of kevlar material, a body tube and a coupler.

Using the material, I made a mount similar to a Centuri shock cord mount with the tread woven through and epoxied to the side of the tube below the coupler. I then added the tube extension and repainted the rocket silver and black like the one at the museum . I'll launch it and Jr's first Alpha as soon as this crazy spring weather dies down.

Born Again Mark