Paracord Mid Power Shock Cords

Discussion in 'Recovery' started by ebruce1361, Feb 18, 2020.

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  1. Feb 18, 2020 #1

    ebruce1361

    ebruce1361

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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?
     
  2. Feb 18, 2020 #2

    ThreeJsDad

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    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.
     
  3. Feb 18, 2020 #3

    ebruce1361

    ebruce1361

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    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.
     
  4. Feb 18, 2020 #4

    ThreeJsDad

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    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.
     
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  5. Feb 18, 2020 #5

    Kelly

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    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.
     
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  6. Feb 18, 2020 #6

    ebruce1361

    ebruce1361

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    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?
     
  7. Feb 18, 2020 #7

    crossfire

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    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.
     
  8. Feb 18, 2020 #8

    Kelly

    Kelly

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    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.
     
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  9. Feb 19, 2020 #9

    ThreeJsDad

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    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
     
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  10. Feb 19, 2020 #10

    cwbullet

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    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.
     
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  11. Feb 20, 2020 #11

    cerving

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    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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