Why Do My Shock Cords Get Twisted ??

The Rocketry Forum

Help Support The Rocketry Forum:

neil_w

Hunkered down and slowly going crazy
TRF Supporter
Joined
Jul 14, 2015
Messages
8,655
Reaction score
2,101
Location
Northern NJ
One time my Deuce's Wild came down with the airframe parallel to the ground, and spinning like there was a log rolling competition taking place on top of it. Shock cord looked like a wound-up rubber motor when it came down. Would have needed a swivel somewhere between the parachute connection (about 6" below the nose cone) and the airframe to save me from that one, and I don't generally put one there. Made me consider whether I should, though I'm not sure where I'd put it.
 

Handeman

Well-Known Member
TRF Supporter
Joined
Jan 18, 2009
Messages
7,609
Reaction score
207
Location
Stafford, VA
One time my Deuce's Wild came down with the airframe parallel to the ground, and spinning like there was a log rolling competition taking place on top of it. Shock cord looked like a wound-up rubber motor when it came down. Would have needed a swivel somewhere between the parachute connection (about 6" below the nose cone) and the airframe to save me from that one, and I don't generally put one there. Made me consider whether I should, though I'm not sure where I'd put it.
A roller bearing swivel as close to the fin can as possible has worked great for me for years.
 

neil_w

Hunkered down and slowly going crazy
TRF Supporter
Joined
Jul 14, 2015
Messages
8,655
Reaction score
2,101
Location
Northern NJ
A roller bearing swivel as close to the fin can as possible has worked great for me for years.
Yeah, I guess I could embed it in the kevlar there when initially connecting everything together. Perhaps I'll do this in the future.
 

rklapp

NAR# 291223
Joined
May 8, 2020
Messages
206
Reaction score
73
Location
Oahu, Hawaii
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 a well loved rocket.

I also ordered the ball swivels from Ebay and will start using those.
 

Knuckledragger

TLAR Engineering hack
Joined
May 23, 2017
Messages
150
Reaction score
28
I ask that every time I go fly fishing. Try shaving some graphite off a pencil in to the swivel and work it around. For something designed to work in the density of water and under strain compared to a descent in air, a little dry lubricant would help. A flat ribbon, flat fins, and a twisting parachute all acting separately in the wind is going to preload and kink to some extent.
 

Handeman

Well-Known Member
TRF Supporter
Joined
Jan 18, 2009
Messages
7,609
Reaction score
207
Location
Stafford, VA
I ask that every time I go fly fishing. Try shaving some graphite off a pencil in to the swivel and work it around. For something designed to work in the density of water and under strain compared to a descent in air, a little dry lubricant would help. A flat ribbon, flat fins, and a twisting parachute all acting separately in the wind is going to preload and kink to some extent.
So far I haven't had to lube any of my swivels and they kept the shock core with almost no twists. But that is a good ball bearing swivel. I've never had an issue with the parachute twisting. I never put swivels on the chutes. Not sure where your kinking is coming from. I would suspect a swivel on the fin can that doesn't spin freely, but that's just a guess.
 
Top