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  #1  
Old 07-28-2009, 11:36 PM
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dbryantphoto dbryantphoto is offline
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Default Securing the shock cord to the body tube dilema

I just finished building a beautiful Estes Executioner. After having nearly completed everything I decided that I would like to install a better shock cord.. maybe some sort of nylon cord instead of the rubber band thing.

There's really no way for me to dig out the installed rubber band cord which is secured deep inside the rocket tube.

What is the best way to install a shock cord to the inside of the tube other than folding a piece of paper and gluing it inside? I was thinking of drilling a hole in the tube, tying a new and better piece of shock cord and securing it with a nice knot. The remaining knot that would be protruding outside the body of the tube... i was thinking of designing some sort of smooth cowl that would be placed over the knot... gluing it neatly and then painting to match.

Is there a better way?
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Old 07-28-2009, 11:44 PM
stefanj stefanj is offline
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LOC used a simple and effective method:

Tie a loop in the nylon shock cord . . . a circle maybe 2" wide.

Mix up a batch of epoxy.

Lay the body tube flat.

Use a tongue depressor taped to a dowel as a spoon to transfer a nice pool of epoxy down the inside of the body tube a ways. Smear it around a little.

Lay the loop of cord right in the pool of epoxy. Use a dowel with waxed paper wrapped around it to press it firmly against the body tube. Pour on a little more epoxy so the cord is encased.

Let dry, keeping the model horizontal.
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Old 07-28-2009, 11:50 PM
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dbryantphoto dbryantphoto is offline
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That sounds like a great idea. So basically the cord will be attached to the inside of the body tube encased in a little pool of epoxy. I will try to get the pool of epoxy deep inside. Thanks so much. Are there any pics of this online anywhere just so I can compare my mental visual with pictures?
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Old 07-28-2009, 11:59 PM
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dbryantphoto dbryantphoto is offline
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Is it necessary to use the rubber band type shock cord or can I just use a nice long piece of nylon cord? Does a portion of the cord need to be eleastic?
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  #5  
Old 07-29-2009, 01:31 AM
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Night Tripper Night Tripper is offline
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I use elastic on all of my low-power builds. You can pick up a small roll in the fabric section of most any Walmart.

And btw, Welcome to YORF, Don!
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  #6  
Old 07-29-2009, 05:00 AM
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mycrofte mycrofte is offline
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After ordering a shock cord, just to find out they use elastic bands, I went to Wal-Mart too. I started with the same width as the old rubber bands. But they tend to give out faster. Until my supply runs out (18 feet) I started doubling them up...

But I still use the old folded paper to mount them. Some of these guys post about them giving out but mine never have. But, I use so much Elmer's on them they are hard to conform to a round tube...
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Old 07-29-2009, 07:23 AM
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GregGleason GregGleason is offline
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I do a modified pool of epoxy, in that I take fiberglass cloth, about a 2" x 2" section, sometimes bigger or smaller as the airframe dictates. I make a "U" in the cord, then tack it to the cloth with some CA. I then mix epoxy laminate resin and wet it out, then place some wax or parchment paper over the cloth. Lastly, I either lay on the side or inflate a balloon in the airframe press to press the airframe. After the epoxy cures, remove the balloon and/or paper. Using this method I have never had a failure at this area of the rocket.

CAVEAT: watch that the place you attach your cord gives sufficient room for the nose cone shoulder so that there is no interference.

Also, you may want to consider braided Kevlar. It is strong, and heat resistant and will likely be the last part of the recovery train to fail. I know that Gus (a.k.a, Steve) had a post a few months back on where to get it.

Greg
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Old 07-29-2009, 11:33 AM
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jeffyjeep jeffyjeep is offline
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I nearly always attach a kevlar leader to the engine mount (Quest style) to serve as the shock cord mount. I just tie a loop in the forward end of the kevlar and make sure it's long enough to extend past the forward end of the body tube to facilitate replacement of the elastic shock cord itself. Jeff
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Old 07-29-2009, 11:55 AM
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dbryantphoto dbryantphoto is offline
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Not sure what you mean.. sort of... you're saying that you attach a length of kevlar shock cord to the engine mount on and then run said cord all the way through the entire length of the body tube? then at the top end connect your elastic cord? easy access to the elastic cord for replacement if need be? i think i got it. however my entire body tube is complete. i'll do that on my next build.
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  #10  
Old 07-29-2009, 12:33 PM
stefanj stefanj is offline
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Use a barrel swivel to attach the kevlar to the shock cord.

The kevlar should NOT extend past the front end of the body tube.

Feed it out the rear of the model when the time comes to attached the barrel swivel and shock cord.
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