Jeff Kodysz
That could be what it’s called. I didn’t think of it myself. I read about it and tried it.
On Sep 9, 2019, at 12:41 PM, Mike Nowak < MikeMNowak@...> wrote: Sounds like a modification of the "lariat loop" which works well. On Mon, Sep 9, 2019 at 12:25 PM Jeff Kodysz < jeffk813@...> wrote: I’ve tried a method of making the Kevlar shock cord replaceable on model rockets. The method works well but is a little difficult to explain in an email. Basically, You poke a through-hole in each of the centering rings large enough to pass a carpet needle through. Then take your Kevlar and tie a small loop in one end, put the loop around the motor hook and using the needle, pass the free end from the rear up through the holes and into the body tube.
You have to make the Kevlar long enough to reach from the very aftmost portion of the rocket all the way to its final desired length, but if it gets toasted and weak, you can easily pull it out and replace it.
Jeff On Sep 9, 2019, at 12:16 PM, Tom Augustyn via Groups.Io < taugy@...> wrote:
Great info, thanks!
-----Original Message-----
From: Bob Ferrante < robert.1.ferrante@...>
To: main < main@mtma.groups.io>
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.
Bob Ferrante
On Mon, Sep 9, 2019 at 11:14 AM Jeff Kodysz < jeffk813@...> wrote:
Yes, but Kevlar is excessively strong for its diameter. 100 pound test Kevlar is like carpet thread.
On Sep 9, 2019, at 11:10 AM, Tom Augustyn via Groups.Io < taugy@...> wrote:
Okay but what about the actual size of the kevlar cord? Wouldn't heavier pound ratings have more braids and be thicker?
-----Original Message-----
From: Jeff Kodysz < jeffk813@...>
To: main < main@mtma.groups.io>
Sent: Mon, Sep 9, 2019 9:06 am
Subject: Re: [MTMA] Kevlar shock cord
Think about it this way... if it's rated to #100, you could attach a 99 pound weight to the body tube and pick the rocket up by the nosecone with the weight attached. The rocket itself would fail long before the kevlar would break.
The only thing to worry about is zippering, but if you make the cord long enough that's not a problem. You could also secure as small piece of silicone model aircraft fuel tubing to the cord where it touches the open end of the body tube.
Jeff
On Mon, Sep 9, 2019 at 9:02 AM Tom Augustyn via Groups.Io <taugy= aol.com@groups.io> wrote:
For all body tube sizes?
-----Original Message-----
From: John Ulizzi < jaulizzi@...>
To: main < main@mtma.groups.io>
Sent: Mon, Sep 9, 2019 8:49 am
Subject: Re: [MTMA] Kevlar shock cord
Just my two cents but I have used the 100# on model rockets and never had a failure of the kevlar. I have had the swivels pulled apart, which to me is an even greater testament to the strength of the 100#...
They are both very good...
John
On Sep 8, 2019, at 10:20 PM, Tom Augustyn via Groups.Io < taugy@...> wrote:
Thanks Wolf! I was actually looking for a source for this exact product!
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Jeff Kodysz
President
Mantua Township Missile Agency
NAR Section #606
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