Shock Cord Length

[Night Tripper]

I've started a Gemini Titan (#1978). It came with the typical rubber band shock cord. I plan to replace it with an elastic one. Is there a general rule for shock cord length? If length and weight are a factor...the model will be just shy of twenty inches and weigh aprox 2.15 oz when completed.

Thanks.

[CPMcGraw]

I've started a Gemini Titan (#1978). It came with the typical rubber band shock cord. I plan to replace it with an elastic one. Is there a general rule for shock cord length? If length and weight are a factor...the model will be just shy of twenty inches and weigh aprox 2.15 oz when completed.

Thanks.

I'd suggest 18-24 inches of Kevlar, attached to the EM, and at least 36-48, maybe even 60, inches of elastic. We've been seeing too many "thermonuclear" gunshots to suggest the typical 24" elastic on a scale bird. Give that bang enough length to not become another "Estes Dent".

[mycrofte]

So, the only thing close to a 'General Rule" would be twice the length of the rocket?!?

[CPMcGraw]

So, the only thing close to a 'General Rule" would be twice the length of the rocket?!?

Yeah, I think I've heard that idea tossed around here before. I think it really depends on the power range and the type of rocket. A scale rocket, for example, needs more protection for the details. Two to three times the length is not out-of-bounds as a "general rule", though most kits tend to come with 18-24 inch "standard lengths".

[o1d_dude]

What CPM said. About 2 to 3 times the length of the rocket.

I typically make mine three times the length of the body tube and if that looks short due to a long nosecone and fin sweepback, I'll add a wee bit more.

I usually limit the length of the kevlar so that it stays inside the body tube to prevent zippering. Easily enough done by pre-measuring the kevlar and knotting the elastic to it BEFORE gluing the motor mount in place.

If you go with a longer length of kevlar, a square of masking tape on the shock cord even with the end of the motor tube probably prevents zippering just as well.

[dwmzmm]

This recovery picture of my PDRocketry's GT-3 last flight should give an idea of how long
the shock cord should be:

[Night Tripper]

I've never used the Kevlar before. What size is typically used?