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Shock Cord Length
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.
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-Jonathan NAR# 88886 birminghamrocketboys.com Roger, lift-off, and the clock is started! ~Alan Shepard |
#2
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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".
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Craig McGraw BARCLONE Rocketry -- http://barclone.rocketshoppe.com BARCLONE Blogsite -- http://barclone.wordpress.com BARCLONE Forum -- BARCLONE Forum BARs helping BARs SAM 0044 AMA 352635 |
#3
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So, the only thing close to a 'General Rule" would be twice the length of the rocket?!?
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#4
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Quote:
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".
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Craig McGraw BARCLONE Rocketry -- http://barclone.rocketshoppe.com BARCLONE Blogsite -- http://barclone.wordpress.com BARCLONE Forum -- BARCLONE Forum BARs helping BARs SAM 0044 AMA 352635 |
#5
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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.
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Kit (aka Cranky Kong) I'm just a roadie for the banned... |
#6
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This recovery picture of my PDRocketry's GT-3 last flight should give an idea of how long
the shock cord should be:
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Dave, NAR # 21853 SR. |
#7
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I've never used the Kevlar before. What size is typically used?
__________________
-Jonathan NAR# 88886 birminghamrocketboys.com Roger, lift-off, and the clock is started! ~Alan Shepard |
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