Paracord anti-zipper idea

[qquake2k]

I use 550 paracord for shock cords on a lot of my MPR's. The problem with it is, because of its narrow width, it's prone to zippering. I've heard of some people using tape or Nerf darts as padding where the paracord meets the top edge of the body tube. But I got to thinking, what about a length of chain stitch? It would make the paracord thicker, and I hope, less zipper prone. It's certainly worth a try. You wouldn't have to worry about it slipping. I know it could still zipper, but maybe not as easily. Can anyone think of a reason not to try it?

 

[DizWolf]

I think it would work well.

Your idea got me thinking, we used to loop ropes back on themselves over and over again to shorten them, but still allow you to rapidly pull it to full length. Wonder if it'd slow the force enough

 

[awseiger]

I think it would work well.

Your idea got me thinking, we used to loop ropes back on themselves over and over again to shorten them, but still allow you to rapidly pull it to full length. Wonder if it'd slow the force enough

I *ALWAYS* use the crochet method shown on Apogee components. It acts as a great shock absorber, and helps keep everything tidy inside the tube. With paracord, one can easily crochet a 20 foot shock cord in under a minute using just a finger.

I like the idea of the knot you have here. I'll try it on my next build that uses paracord.

 

[cwbullet]

I used a foam golf ball or a nerf dart as a zipper preventer.

 

[qquake2k]

I think it would work well.

Your idea got me thinking, we used to loop ropes back on themselves over and over again to shorten them, but still allow you to rapidly pull it to full length. Wonder if it'd slow the force enough

I bet it would slow it at least as much as rubber bands do.

I *ALWAYS* use the crochet method shown on Apogee components. It acts as a great shock absorber, and helps keep everything tidy inside the tube. With paracord, one can easily crochet a 20 foot shock cord in under a minute using just a finger.

I like the idea of the knot you have here. I'll try it on my next build that uses paracord.

The chain stitch (and that may not be the proper term) that I make will pull apart like that as long as you don't pull the cord through at the end of it. And it doesn't require a crochet hook.

 

[qquake2k]

The chain stitch (and that may not be the proper term) that I make will pull apart like that as long as you don't pull the cord through at the end of it. And it doesn't require a crochet hook.

Like this.

 

[BrAdam]

This is the same thing I have been doing. Finger crochet the entire exposed length of shock cord from booster to parachute attachment. First saw it on Apogee's video, tested in the living room several times with my son pulling the nose cone off and has worked each time I have launched. Always comes completely undone and very easy to pack.

 

[rbelknap]

yep, I chain-stitch (single crochet) my shock cords. Got the idea from apogee as well. On my lpr birds with thin kevlar, I use a hook. On my larger rockets I just finger crochet. I haven't thought about "locking" part of the chain to help prevent zippers. I'll have to try that.

One concern I have with crocheting the shock cord is the possibility that it could lead to additional wear and tear of the kevlar/paracord/whatever as the chain undoes itself. But that hasn't really been an issue for me yet.

 

[qquake2k]

Here's how I set up the Kevlar and paracord harness in my Patriot Goony.

 

[scsager]

I like it ! - It seems reasonable that the "chain stitch" should at least reduce the tendency to zipper. Besides - that is one awesome looking knot!

 

[CarVac]

I have seen this discouraged because it causes intense heating that reduces the breaking strength of the line, sometimes dramatically.

 

[qquake2k]

I have seen this discouraged because it causes intense heating that reduces the breaking strength of the line, sometimes dramatically.

What exactly causes the "intense heating"?

 

[cwbullet]

Knots and bends can decrease cord strength - especially in kevlar.

 

[qquake2k]

Knots and bends can decrease cord strength - especially in kevlar.

I know that knots can reduce the strength of a rope, but I've never heard of a knot causing intense heat.

 

[cwbullet]

Me neither, but I am sure it could over time.

 

[DizWolf]

The way the stitch works , the only friction would be as it pulled itself out of a single loop. Even at speed I don't see that generating enough heat to reduce strength significantly. It's not like the cord is constantly running over the same point and building heat.

 

[CarVac]

I know that knots can reduce the strength of a rope, but I've never heard of a knot causing intense heat.

It's not the knot itself, but the fact that it gets pulled out very rapidly, rubbing the rope against itself.

 

[troj]

I have seen this discouraged because it causes intense heating that reduces the breaking strength of the line, sometimes dramatically.

Yep. As the nylon pulls past itself, it rubs against itself generating friction, which means heat. Because there's tension, it will also tend to tighten the loops a bit, generating even more friction. It may not do enough damage the first time, it may not by 5 times, but at some point that cord is going to break because it has finally degraded enough.

I would never recommend someone chain-stitch a recovery system when packing it for a flight. For storage? Sure. For a flight? No way. Use a light-weight rubber band, or a single wrap of masking tape, if you need to control it while packing.

Something to keep in mind is how professional riggers pack canopies for use. If chain-stitching was a good idea, don't you think they'd use it, since it's so easy to do?

-Kevin

 

[1tree]

Something to keep in mind is how professional riggers pack canopies for use. If chain-stitching was a good idea, don't you think they'd use it, since it's so easy to do?

If we take this to the logical conclusion, our rockets will easily triple in cost. Sorry, but it just doesn't follow here given that most don't even pack their chute into a deployment bag.

What one could realize though is that a good deal of engineering has gone into controlling the inflation rate of the chute to prevent damage to the load.

If a person chains their cord, they should watch for failure. And realize that a good controlled study to determine how much damage is time consuming. In the meantime, the method will absorb some of the shock in a somewhat controlled manner at the cost of degrading the amount if load the cord can deal with.

 

[qquake2k]

According to what I've been able to find out, mil spec paracord has a melting point of 244C (471F). I'm not too worried about it melting from friction.

 

[chadrog]

Small size tennis ballz for small size doggz. Crocheting is for grannies...