Level 1 Kevlar Shock cord length

[Jacktango22]

I am designing and scratch building a Level 1 cert. attempt rocket. It has 3 inch tube, 29 mm motor mount, and all in is about 42 inches long.

I have 1500 lb. test round Kevlar cord which will run from top centering ring ….. and here is the question: how long should Kevlar shock cord be?

Based on my experience with mid power building and what I have been reading on this forum I am thinking about 25 feet long measured from top of the tube. Would appreciate any suggestions or advice.
Thanks

 

[jbsommerfeldt]

For me flying in So Wi n No IL, use as much as possible. The only reason to go with minimal "really needed" is to save space or weight. Here is my reasoning. Land in a tall tree hopefully you have enough length hanging to grab it. Land in a pond or other lovely water hazard and maybe only your feet get wet. Nobody has any pictures of me fishing a rocket in my undies

 

[teepot]

If the nose cone is heavy, then more shock cord is better. I generally use 20' for that size rocket. 1500lb is good. Advice, put a 38mm mmt in. You can get an adapter to fly 29mm. If you use a 29mm mmt you are limited in motor choices. I put 29mm mmt in my first L1 rockets and regrated it. Now I go up one size of what I plan to fly in the rocket. Will give me some rockets with the correct mmt for L2 rockets.

 

[jmasterj]

I am designing and scratch building a Level 1 cert. attempt rocket. It has 3 inch tube, 29 mm motor mount, and all in is about 42 inches long.

I have 1500 lb. test round Kevlar cord which will run from top centering ring ….. and here is the question: how long should Kevlar shock cord be?

Based on my experience with mid power building and what I have been reading on this forum I am thinking about 25 feet long measured from top of the tube.

25ft of 1500lb Kevlar sounds perfect to me. Like @teepot, I now build with bigger mounts than I expect to use, but if you've already bought anything I wouldn't worry about it.

 

[bjphoenix]

25' seems OK to me.
However a small airframe and a heavy nose cone could act like a cannon shooting the nose cone out and it would have high momentum when it hits the end of that 25' length so watch out for that.

 

[Handeman]

25 ft. seems a little long to me. I would probably only have about one foot of Kevlar leaving the rocket and use 15 ft. of Nylon for the rest of the cord. I would also consider using a loose piston at the junction of Kevlar and Nylon. I've found that with a piston, you can use a lot less BP on the ejection charge. Usually much less than what comes with the reloads.

I absolutely agree with @teepot about using the 38mm MMT. With 38mm you can fly the full range of L1 motors. If you use a 29mm MMT, you are limited to H motors and four baby Is.