Shock cord sizing choice?

I have a scratch build that I'm about to complete, but I have one last decision to make on recovery harness. The rocket is a semi clone of a 3 inch Thor. 3 inch diameter, 38mm motor mount, 64 inches long, approximately 3.5 pounds.

I was leaning to 9/16 tubular nylon, but now I'm not so sure. What material would you use for your recovery harness/shock cord?

Banzai88 said:

I have a scratch build that I'm about to complete, but I have one last decision to make on recovery harness. The rocket is a semi clone of a 3 inch Thor. 3 inch diameter, 38mm motor mount, 64 inches long, approximately 3.5 pounds.

I was leaning to 9/16 tubular nylon, but now I'm not so sure. What material would you use for your recovery harness/shock cord?

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My usual 20'×1/4" Kevlar harnesses. They pack nice and compact and I regularly fly them in 6-8lb rockets.

If your project is cardboard, I would definitely stay with TN....less prone to zippers as its wider/softer. You should have plenty of room.

If things get tight in the payload, use the 1/4 Kevlar, but first cut off a long enough section of TN to clear the end. Then with a coat hanger/wire... fish the Kevlar through it. Small wrap of tape at junction will keep the "tube protector" in place.

If your clone is fiberglass, it really doesn't matter which you choose.

May I recommend you contact Ted Chernok/One Bad Hawk? He will know exactly what you need and cut you a great deal. And his work and his professionalism are outstanding.

There is a 'rule of thumb' floating around. Your shock cord should be at least 3x the rocket length and should be rated to 150x your total rocket weight..

So, a 64", 3.5lbs rocket would require (minimum) a 16' shock cord rated at 525lbs..

dr wogz said:

There is a 'rule of thumb' floating around. Your shock cord should be at least 3x the rocket length and should be rated to 150x your total rocket weight..

So, a 64", 3.5lbs rocket would require (minimum) a 16' shock cord rated at 525lbs..

Click to expand...

That's what I've heard and use. Last scratch I had a shorter than desired delay and utilized 14' of shock rated to 600 lbs on an 18" rocket.
Launched twice with zero signs of any stress points.