Para cord as shock cord
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JAL3
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my guess, let me emphasize GUESS, is that you don't see it done for two reasons. I'm guessing its nylon so it will have trouble resisting the heat of ejection much more than Kevlar and therefore need and extra degree of protection. Also, nylon is less forgiving of sudden shocks. While it may have a high tensile strength, the assumption is that the load is one of long duration as opposed to the snap of an ejection event.
Actually it works well for me but you have to add zipper protection.
iter
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Thank you for your feedback John. I imagine that the shock duration is less important than the maximum force. Assuming a 10g deployment on a 3-pound rocket, the maximum force is 30 pounds, well below the cord's nominal 550 pond limit.
Heat is an issue--I remember--way back in the service--using cigarette lighters to melt the ends of para cord lengths to prevent fraying. However I imagine that the parachute itself is even more vulnerable to heat and as long as I have enough wadding to protect it, the cord may be OK.
On the other hand, as you point out, few seem to be using it, so I'm curious.
Ari.
Heat is an issue--I remember--way back in the service--using cigarette lighters to melt the ends of para cord lengths to prevent fraying. However I imagine that the parachute itself is even more vulnerable to heat and as long as I have enough wadding to protect it, the cord may be OK.
On the other hand, as you point out, few seem to be using it, so I'm curious.
Ari.
iter
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JAL3
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For heat, I am thinking of the end in the BT, not the end towards the chute. I know that nomex protectors are made of the cords as well as chutes but it seems that the nylon would have to make a personal appearance at the point of attachment.
o1d_dude
'I battle gravity'
Paracord works well for my L1 and under birds but then again I attach my shock cords just under the inserted nose cones to eliminate the heat danger.
The round shape is the only thing I can think would make it have more zippers, but in practice it holds true for me. I only use it it in mid size rockets.
MarkII
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Use a Kevlar or stainless steel cable as a leader, going from your internal mounting point up to where the cord will exit the rocket. Then tie your paracord shock line to it. Sure, a cord made from nylon is susceptible to melting from direct exposure to very high heat, but then so are the stringers on your parachute (not to mention the canopy itself). This is Basic Rocketry 101; you won't need to worry about melting your paracord shock cord if you use normal procedures to prepare your recovery system.
I absolutely would think twice about using it in a level 2 bird and beyond. I like kevlar and tubular nylon in high power birds.
qquake2k
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I used paracord in my Soothsayer and upscale Vagabond, but they're both zipperless. I think the zipper danger comes from paracord's small diameter and round cross section.
qquake2k
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I don't see why paracord wouldn't work, as long as the heat from the ejection charge doesn't damage it.
iter
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Capn', I notice on your zipperless designs, you work hard to tie the cord to the inside of the top section. I wonder about the placement of your bulkheads--I imagine if you mount the bulkhead lower, you'd still have enough room for recovery "train," but also make it easier to tie the cord.
Ari.
Ari.
qquake2k
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On my 3" zipperless builds, I can't get my arm inside the tube regardless. I usually split the difference, and put the bulkhead at 17" in 34" tubes. That gives me plenty of room for the chute and shock cord, but still reduces the volume that the ejection charge has to pressurize. I don't think moving the bulkhead a couple of inches closer would make it that much easier to thread the cord through.
