Why Do My Shock Cords Get Twisted ??

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Brian Johnson

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At the moment I don't have a picture to show you. However every time I launch my rockets most of the time they come back an land Ok but the sock cord is twisted.
I have the cord connect to the nose cone and the shock cord anchor. The para chute is connected to the nose cone and the lines by a swivel.
Can some please help me to understand what I'm doing wrong?
Thank You
Brian
 

timbucktoo

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Seen it happen on a few of my rockets. Lot of times the fins will start spinning during descent and I end up with a twisted mess, usually only with duel deploy. I have added a swivel down by the booster section & that helps a lot but doesn;t eliminate the spin in its entirety.
 

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Buy a few snap swivels and attach your parachutes to them. You can find them at most sporting good stores or online. A snap swivel will allow your parachute to rotate freely without tangling and twisting your shock cords.
 

rharshberger

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The worst twisted shock cords are usually the ones attached to the fin can section of the rocket, at swivel at that point will do a lot to alleviate the issue but never totally remove it. My 5.5" Cherokee D twists the drogue harness literally into knots without a swivel at the fin can.
 

Brian Johnson

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Seen it happen on a few of my rockets. Lot of times the fins will start spinning during descent and I end up with a twisted mess, usually only with duel deploy. I have added a swivel down by the booster section & that helps a lot but doesn;t eliminate the spin in its entirety.
Tim,
I'll give it a try
Thank you
Brian
 
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Brian Johnson

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Buy a few snap swivels and attach your parachutes to them. You can find them at most sporting good stores or online. A snap swivel will allow your parachute to rotate freely without tangling and twisting your shock cords.
Afterburners
Thank you for the Idea it seems this is the soulation
Thanks
Brian
 

rklapp

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The swivel doesn't fully stop the twisting but it does make it easier to unravel, assuming your nose cone doesn't entwine with the parachute cords. I replace the plastic shock cords with elastic bands, makes it easier to attach to the swivel with a dap of glue for assurance. I attach the shock cord swivel to the cone and the parachute swivel to the top of the shock cord swivel, so if the nose cone loop were to break, I'll at least get the rocket back.

1590365441279.png
 

rharshberger

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I prefer P-Line rolling barrel swivel with crosslock snap like the one pictured, the 2/0 size is good for up to 122lbs, they are about an 1.5" long.


Rolling_Crosslock.jpg
 

jrap330

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Your not doing anything wrong. If you would think about it, logic would tell you in order to have NO twist the swivel must turn as fast, freely as the wind turns the rocket.. The swivel on the parachute helps, but as someone stated it happens more often at fin can attachment. Barrel swivels , rotate better than ordinary swivels. I wonder if 2 swivels, 1 for chute and 1-shock cord would further reduce the issue. So if you have the room in rocket and/or you don't believe it would be hard to load the nosecone with 2 swivels..try 2 and see if helps more.
 

tomsteve

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Afterburners
Thank you for the Idea it seems this is the soulation
Thanks
Brian
it would be wise to attach that swivel to the shockcord itself rather than to the NC. i make my shock cords pretty long- about 2-3 times length of rocket when possible( and usually upgrade them to kevlar) then add the swivel a few inches down from the NC.

on another note, good to see ya getting into this hobby while the band isnt doing anything.:)😂
 

rklapp

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I prefer P-Line rolling barrel swivel with crosslock snap like the one pictured, the 2/0 size is good for up to 122lbs, they are about an 1.5" long.
I try to avoid these because I fear the clasps will catch on the parachute drag lines, but they are easier to open.
 

rharshberger

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I try to avoid these because I fear the clasps will catch on the parachute drag lines, but they are easier to open.
The P-lines are not an issue, they have short hooks just like the picture shows. No snags in at least a hundred flights over the last 3 years, and the hooks are bent parrallel to the shaft they are on.
 

rklapp

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The P-lines are not an issue, they have short hooks just like the picture shows. No snags in at least a hundred flights over the last 3 years, and the hooks are bent parrallel to the shaft they are on.
Good to know. Perhaps will try them next time. They’re hella cheap at Walmart.
 

Handeman

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I haven't launched any LPR or MPR in a while, but as rharshberger said, the fin can is what causes the issues. I had 4" diameter 8 lb. rocket where the fin can would spin 100-200 RPM all the way down from apogee. I never had twisted shock cords on that rocket because the cord attached to the fin can with a ball bearing swivel.

I've tried barrel swivels, but junked some of those after one flight. I keep coming back to the more expensive ball bearing swivels because they just work.
 

n27sb

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I haven't launched any LPR or MPR in a while, but as rharshberger said, the fin can is what causes the issues. I had 4" diameter 8 lb. rocket where the fin can would spin 100-200 RPM all the way down from apogee. I never had twisted shock cords on that rocket because the cord attached to the fin can with a ball bearing swivel.

I've tried barrel swivels, but junked some of those after one flight. I keep coming back to the more expensive ball bearing swivels because they just work.
I agree. SS ball bearing swivels are the Ticket. https://www.ebay.com/i/163410354742...66500&itm=163410354742&pmt=1&noa=1&pg=238620254194E81-2D41-4BC1-9101-3197F2E80787.png
 

Brian Johnson

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I prefer P-Line rolling barrel swivel with crosslock snap like the one pictured, the 2/0 size is good for up to 122lbs, they are about an 1.5" long.


View attachment 418179
I just bought
I haven't launched any LPR or MPR in a while, but as rharshberger said, the fin can is what causes the issues. I had 4" diameter 8 lb. rocket where the fin can would spin 100-200 RPM all the way down from apogee. I never had twisted shock cords on that rocket because the cord attached to the fin can with a ball bearing swivel.

I've tried barrel swivels, but junked some of those after one flight. I keep coming back to the more expensive ball bearing swivels because they just work.
Now that's an Idea! I didn't even know there are ball bearing swivels thanks for the tip
Brian
 

Handeman

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Thanks for the link. Just ordered some #10s I have the one I used on my retired L2 Cert rocket for 10 years and 50 flight, but have 4 more rockets in process right now so will need more.
For my L3 at 48 lbs w/o motor, I use one of these.
Capture.PNG


It's a smidge over 4" long and rated at 30k Newtons. It's $17.99 on ebay
It works great. I did have a flight where the cord looped over it and prevented it from spinning. The drogue side shock cord twisted up so bad that time that the drogue was completely twisted up inside the shock cord.

It would be nice to find some ball bearing swivels in between the #10 size you showed and this climbing swivel. for those 15 - 30 lb rockets.
 

Brian Johnson

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I haven't launched any LPR or MPR in a while, but as rharshberger said, the fin can is what causes the issues. I had 4" diameter 8 lb. rocket where the fin can would spin 100-200 RPM all the way down from apogee. I never had twisted shock cords on that rocket because the cord attached to the fin can with a ball bearing swivel.

I've tried barrel swivels, but junked some of those after one flight. I keep coming back to the more expensive ball bearing swivels because they just work.
Handeman
Can you post a picture of the can swivel connected to the cord and can you please tell me how far up from the shock cord mount do you mount your swivel ?
Thank you
Brian
 

Handeman

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Handeman
Can you post a picture of the can swivel connected to the cord and can you please tell me how far up from the shock cord mount do you mount your swivel ?
Thank you
Brian
The purple nylon shock cord has the swivel tied to it. It was use for 50 fights with the purple and white fin can. It just had a quick link that held it to the u-bolt on the fin can. Now that the purple rocket is retired, its going on the new one it's attached to now.
20200528_182539.jpg


Hope that helps.
 

Brian Johnson

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Seen it happen on a few of my rockets. Lot of times the fins will start spinning during descent and I end up with a twisted mess, usually only with duel deploy. I have added a swivel down by the booster section & that helps a lot but doesn;t eliminate the spin in its entirety.
Tim thanks for idea I went to a real tackle store and bought some ball bearing swivels. I won't get to use them any time soon.
Thank you
Brian
 

Brian Johnson

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The worst twisted shock cords are usually the ones attached to the fin can section of the rocket, at swivel at that point will do a lot to alleviate the issue but never totally remove it. My 5.5" Cherokee D twists the drogue harness literally into knots without a swivel at the fin can.
Rich
I bought a pack of good ball bearing swivels. So there will be one to keep chute lines untangled and one for the can.
Thank you
Brian
 

Brian Johnson

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The swivel doesn't fully stop the twisting but it does make it easier to unravel, assuming your nose cone doesn't entwine with the parachute cords. I replace the plastic shock cords with elastic bands, makes it easier to attach to the swivel with a dap of glue for assurance. I attach the shock cord swivel to the cone and the parachute swivel to the top of the shock cord swivel, so if the nose cone loop were to break, I'll at least get the rocket back.

View attachment 418074
rklapp I bought some larger snap swivels and ball bearing swivels for the shock cord.
Thank you,
Brian
 

Brian Johnson

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Your not doing anything wrong. If you would think about it, logic would tell you in order to have NO twist the swivel must turn as fast, freely as the wind turns the rocket.. The swivel on the parachute helps, but as someone stated it happens more often at fin can attachment. Barrel swivels , rotate better than ordinary swivels. I wonder if 2 swivels, 1 for chute and 1-shock cord would further reduce the issue. So if you have the room in rocket and/or you don't believe it would be hard to load the nosecone with 2 swivels..try 2 and see if helps more.
jarp330
Your suggestion an other suggestions convinced me to use two ball bearing swivels one at the chute and on the shock cord.
Thank you,
Brian
 

Brian Johnson

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The purple nylon shock cord has the swivel tied to it. It was use for 50 fights with the purple and white fin can. It just had a quick link that held it to the u-bolt on the fin can. Now that the purple rocket is retired, its going on the new one it's attached to now.
View attachment 418565

Hope that helps.
That's what I was looking for thanks for posting the picture. I still have two more test flights and then I can test the bearing by the can.
Thank you
Brian
 

Handeman

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That's what I was looking for thanks for posting the picture. I still have two more test flights and then I can test the bearing by the can.
Thank you
Brian
Glad it helped.
BTW, I stopped using swivels on parachutes years ago. The only chutes I have with swivels are snap swivels and that's only for the snap part, not the swivel. I've found I've never had a problem with the chutes twisting anything up. If you are getting issues with shroud lines tangling, it's because nose cones are going through the lines at deployment or the chute is inverting and tangling lines before it inflates. Usually rocking is much more of an issue with flat chutes than twisting or spinning.
 
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