Length of shock cord

[Sterk03]

So I’m working on the 50th anniversary model if Saturn V by Estes. I feel that Estes should have done a better job of this model for what you paid but that is a different story. I do not see the length of shock cords that should be used for the two main chutes for the main body. Mia there a formula or method of length as the shock cords are quite long. I’m not sure more is better but thought someone could chime in and if there is a gauge for what they should be as they seem a little long now without being cut?
Thanks

Sterk03

 

[Antares JS]

More is better with shock cords. Use them as-is.

Most people here will tell you a shock cord should ideally be about 2-3 times the length of the rocket.

 

[Adam3836]

Agree that’s what I have been instructed as well
Being alittle on the longer side is usually better for shock cords

longer gives a buffer between the nose cone and body tube when you reach apogee and ejection takes place

sometimes a shorter shock cord can cause zippers on the body tube if your ejection is to early or to late having the shock cord longer gives some more play and room to help prevent any issues not guaranteed lol

longer shock cord also helps with shock absorption which probably is what longer shock cords do mostly

 

[Funkworks]

The shock cord of a rocket falling under a parachute is sort of like a pendulum. And like a pendulum, the longer L the shock cord is, the longer T it takes to go from side to side.

\[ T=2\pi k{\sqrt{\frac{L}{g}}}+ ... \]

If it takes a longer time T to go from side to side, that means the falling rocket is spinning down slower, so it won't hit the ground as hard when it lands. So the long L is, the safer the rocket is. Drawbacks to having too long a shock cord are its weight and volume before ejection.

(I added a k correction factor and some dots up there, because the pendulum formula isn't quite right if the top end isn't fixed to a ceiling, but a ceiling pendulum is surely a special case of a swinging parachuted rocket, i.e. if k = 1 and the dots are 0.)