Paracord Mid Power Shock Cords

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ebruce1361

ebruce1361

The man with the plan. And some duct tape.
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I recently came to possess a large quantity of regular 550lb rated 4mm nylon paracord. Up until now, I have only ever used rubber and fabric elastic bands or kevlar for shock cords as I have only flown low and mid power. Providing I sufficiently protect the bottom end of the paracord from ejection heat, (baffles, nomex wraps, etc.) would this be suitable as a shock cord for mid power rockets? What about level 1 HP?
 
Unless it is somehow a huge MPR you can try pulling the core out of the paracord. You will then have a tubular webbing that will be less bulky, give a little on ejection and you can easily splice loops into the ends. I flew cords like that all weekend and they worked perfectly.

For a L1 HPR I would leave the cores in place or go to a kevlar webbing, the rockets can get pretty heavy with a H or I motor.
 
Huh. Never thought about removing material to make the cord more ideal, but that does make sense. Probably the biggest thing I would fly with the paracord would be a scratch build I'm working on made from 4" scotch bottle tubes flying on a cluster of four E15s. That particular one will have sufficient internal space to easily accommodate several yards of solid paracord, but I also have some BT80 projects in the works including my scratch-built level 1. For the lighter ones though, I might just try out that "hollowed-out" cord idea.
 
ebruce1361 said:
Huh. Never thought about removing material to make the cord more ideal, but that does make sense. Probably the biggest thing I would fly with the paracord would be a scratch build I'm working on made from 4" scotch bottle tubes flying on a cluster of four E15s. That particular one will have sufficient internal space to easily accommodate several yards of solid paracord, but I also have some BT80 projects in the works including my scratch-built level 1. For the lighter ones though, I might just try out that "hollowed-out" cord idea.
Click to expand...

The cord becomes softer when the cores are removed and this could help it not zipper a BT. When wrapped over an edge it flattens out instead of staying round so you have more surface area to disperse the load.
 
I've used paracord for LPR and HPR. It's nylon, and has reasonable stretch. Depends on the weight of the rocket. (I also use a disk or a ball to help prevent zippering). Sometimes I'll use a piece of kevlar for the lower section to keep the nylon away from ejection gases.
 
Kelly said:
I've used paracord for LPR and HPR. It's nylon, and has reasonable stretch. Depends on the weight of the rocket. (I also use a disk or a ball to help prevent zippering). Sometimes I'll use a piece of kevlar for the lower section to keep the nylon away from ejection gases.
Click to expand...

I was thinking about either having the nomex wrap or a kevlar leader before the paracord like you said. As for the ball/disk method, what does that entail exactly? Just a way to make a wide spot where the shock cord meets the edge of the body tube?
 
ebruce1361 said:
I was thinking about either having the nomex wrap or a kevlar leader before the paracord like you said. As for the ball/disk method, what does that entail exactly? Just a way to make a wide spot where the shock cord meets the edge of the body tube?
Click to expand...
What you said above would work well. Wider kevlar from MMT to out of booster tube 5-6" than go with the para cord. The cord is cheap so you can replace when needed.
 
ebruce1361 said:
As for the ball/disk method, what does that entail exactly? Just a way to make a wide spot where the shock cord meets the edge of the body tube?
Click to expand...
Yep. There's several things that can work, slipped over the line - a stiff disk of plastic cut from a container lid, a section of pool noodle, some people have used tennis balls - depends on how big your tube is. Anything to spread the force out.
 
ebruce1361 said:
I was thinking about either having the nomex wrap or a kevlar leader before the paracord like you said. As for the ball/disk method, what does that entail exactly? Just a way to make a wide spot where the shock cord meets the edge of the body tube?
Click to expand...

You got it. When I build a piston into a rocket I set it up to just reach the opening of the main tube. This way it is pretty much zipper proof
 
You can get more zippers with paracord. I avoid it with a piece of pipe insulation or foam golf ball at the point of impact with the body tube.
 
I've tried it, and thrown it out. It's no better than regular elastic, and not nearly as good as a properly-sized Kevlar shock cord. I suppose you could wrap a Kevlar sleeve around it, but for MPR why bother?
 

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