L3 Project Construction Tips

[Doug GerrardParticipant]

Yes, I have zippered fiberglass G10 tubing with kevlar shock cord. However, it was a very long rocket and I was trying to pop the nose cone off first (at apogee) instead of breaking it in the middle.

Doug

[Bruce R. Schaefer]

Funny, I’m using 1/2″ Kevlar harnesses… I’ll have the booster at 4′, next section holding the chute at 3′, that would stay together at 7′, and the payload section with the main at 3′ with a 2′ nosecone, at 5′. So it’s about divided in half. Still that bothers me. Doug, does glassing the top help at all? Sounds like it would, but, man, if the stress is there, it’s going to slice and dice the G10 or break the Kevlar cord, something’s gotta give. 🙄 [/quote]

[Anonymous]

Bruce, I’m 3 for 3 in warning people about 1/2″ Kevlar. Maybe it is me giving them the kiss of death… but all three times I told guys it would NOT hold, and it did not. Is this the MW stuff? I love it, but would never use it for more than a 54mm rocket. I’ve seen it used for bigger rockets and it just won’t hold.

I have 3 shock cords that are 5/8″ tubular Kevlar (lengths of ~25′, 25′, and 30′). You, and for that matter ANYONE in the club can use them whenever you wish. They have flown many, many times.

The 1/2″ flat Kevlar is wonderful stuff, but not for a rocket that is over a few lbs, as your L3 most certainly will be…

JW

[Conway StevensParticipant]

JW please elaborte.. As far as wont hold. 1/2 inch tubular kevlar should easily hold a 75lb and under project without a hitch according to the ratings of it. In fact its also what I am using. Got mine from Giant leap infact. Like 100 feet of it. I also tie knots in my stuff and I avoid the pre-sewn loops myself. The correct knot will not weaken the shock cord and will not come apart.

But in the issue of the 1/2 tubular kevlar. Bruces project will probably be lighter then mine (mine with the empty case after the motor burns out will be 50 to 60 lbs max) SO you say its not strong enough? curious.

I to have seen shock cord zipper fiberglass tube.. but its a lot less comon then phenolic or cardboards.

He is a tip. Be sure to find the spot where you harnes will rub on the rim of the body tube as it deploys and is under chute and wrap it in duct or masking tape. I have seen that lip cut even Tubular Kevlar harness.

[Anonymous]

For some reason, I thought Bruce was refering to FLAT Kevlar. Tubular stuff is another matter. Tubular = good for L3, flat stuff is wonderful but not for a project of this size. I’ve seen flat stuff break three times… as noted, I was suspicious (and voiced those concerns) to all three fliers.

The 1/2″ or 5/8″ tubular stuff will do fine. I use it all the time…

JW

[Bruce R. Schaefer]

Sorry! For the record I’m using GLR’s Tubular KEVLAR® 1/2″, and I think it’s rated at 7k-8k lbs. I trust the loops. But haven’t stressed them past K’s. I don’t trust tubular nylon, had it break–though I believe the Event Horizon uses tubular nylon quite successfully. I WILL make an L3 version of GLR’s Fireball, which is Kevlar rolled up into a ball that hits the BT instead of the tubular harness. Man, I’m glad I ask these questions… 😉

[Anonymous]

My bad, Bruce! For some reason, I was thinking you were using flat stuff… You will do superb with the tubular Kevlar. It is wonderful stuff.

FWIW, I failed an L3 attempt because my sewn loops failed. It was on a piston strap. It was a perfect boost, perfect day, perfect everything — until the main opened and the loop tore, dropping Mr. Booster from 1000′. Approximately 3 hours after that heartbreak, all my shock cords had KNOTS instead of sewn loops. I used a knot called a “turle” knot, which is sometimes used by flyfishing enthusiasts. Never a problem since.

After a very rocky start to my L3 (I blew it twice) I have had 7 great M or N flights on the knotted Kevlar, all without a hitch, some on really heavy birds. I’m going to try to make it 8 straight if it ever rains again :-O

JW

[Bruce R. Schaefer]

You have to show me that “turle” knot. Not using a piston, just Kev pad. The sewn loops WERE to be used to hold Quikllinks that attached to the U-bolts, etc. Not anymore though. Thanks! 😉

Found this knot site: http://shoreangling4u.tripod.com/knotguide/index.html

There are WAY too many knots in the world…

[Conway StevensParticipant]

John and I both use about the same kind of knot. Ive seen to many of the loops fail and wont use them either. Its kinda like this deployment bag im not gonna use. All sewn with loops, Flat Nylon shock cord and its all kevlar but sewn together with nylon/polyester thread. As far as I am concerned all strikes against it for anything good to use. Should be using tubular kevlar, able to tie knots, and kevlar thread. So I will just have to do it with a large chute protector pad or 2 from kevlar. A properly tied knot should cinch down on itself and not weaken the fabric as well as not come loose.

[Bruce R. Schaefer]

All the loops in GLR’s tubular Kevlar cords use Nomex thread and say the loops are stronger than the cord itself. I thought about using a deployment bad, but as you did, decided against it.

From GLR’s site:

Laboratory tested. The loops are stronger than the cords!

Loops are sewn with fire-resistant NOMEX®!

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