Kevlar Shock Cord Strength
- Thread starter Race58
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Race58
That is a good question, however whether you are using Kevlar, tubular Nylon, rope, bungee or anything else for a shock cord, the same basic principals apply to all.
My general "rule of thumb"
1) Shock cord should be 4 or 5 lengths of the rocket (minimum)
2) I use 9/16" Tubular Nylon for 3" and larger rockets
3) I use 11mm braided Kevlar for rockets less than 3"
4) I use 3mm braided Kevlar for Mid-powered rockets
5) When in doubt, use the next size up.
This previous thread has a lot of good information regarding G loads that can happen during deployment.
https://www.rocketryforum.com/showthread.php?t=43336
Every system at some point has a "Weakest Link" in the chain. It does not make sense to have a shock cord capable of withstanding 1800lbs if it is connected to an eye bolt that will be bent open during a hard deployment. Additionally, in my basic rule of thumb, it does not make sense to use add addtional weight of 9/16" TN if you have a 3" rocket flying on a G64.
I like to use braided Kevlar to reduce the overall weight and recovery space on smaller minimum diameter rockets.
John
That is a good question, however whether you are using Kevlar, tubular Nylon, rope, bungee or anything else for a shock cord, the same basic principals apply to all.
My general "rule of thumb"
1) Shock cord should be 4 or 5 lengths of the rocket (minimum)
2) I use 9/16" Tubular Nylon for 3" and larger rockets
3) I use 11mm braided Kevlar for rockets less than 3"
4) I use 3mm braided Kevlar for Mid-powered rockets
5) When in doubt, use the next size up.
This previous thread has a lot of good information regarding G loads that can happen during deployment.
https://www.rocketryforum.com/showthread.php?t=43336
Every system at some point has a "Weakest Link" in the chain. It does not make sense to have a shock cord capable of withstanding 1800lbs if it is connected to an eye bolt that will be bent open during a hard deployment. Additionally, in my basic rule of thumb, it does not make sense to use add addtional weight of 9/16" TN if you have a 3" rocket flying on a G64.
I like to use braided Kevlar to reduce the overall weight and recovery space on smaller minimum diameter rockets.
John
Thanks Jrcox, that helps.
Right now I'm just going to be flying low and mid power and all I knew before (70's) was elastic shockcords.
Since getting back into rocketry I see that Kevlar is used a lot in low and mid power kits but a lot smaller version of the Kevlar than with high power. (50# 150# 250#, Etc.)
What I see is the Kevlar attached to the Motor Mount and then attached to elastic cord with tape in between to prevent zippers and finally to the chute. I have been using that method in my builds and I was just wondering what strength of the Kevlar to use for various situations with low and mid power.?
Right now I'm just going to be flying low and mid power and all I knew before (70's) was elastic shockcords.
Since getting back into rocketry I see that Kevlar is used a lot in low and mid power kits but a lot smaller version of the Kevlar than with high power. (50# 150# 250#, Etc.)
What I see is the Kevlar attached to the Motor Mount and then attached to elastic cord with tape in between to prevent zippers and finally to the chute. I have been using that method in my builds and I was just wondering what strength of the Kevlar to use for various situations with low and mid power.?
Race58:
I only fly Micro to LMR (3.3lbs) Models.
Over the years I've found
Micors work fine with 27 to 50lb kevlar with lenghts from 30"to 60"
Standard Model rockets up to 1lb: 70-100lb kevlar in lengths of 36" to 72" with at least 36" elastic.
LMR's up to 3.3lbs; 100-130lb kevlar in 72" lenght with about 4feet of 1/4" elastic.
Hope this helps a little.
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