Originally posted by utahrc
The swivel is 275 lbs test, that means it FAILS at 275 lbs (or thereabouts). The quick links that I have (1/8") have a working load of 220 lbs, which means they fail somewhere much higher - maybe 400+ lbs. I have tubular nylon for the shock cord, which I believe can sustain very high momentary stress (because of its elasticity) and it attaches to some mean-looking u-bolts. I don't know much about what the shroud lines or the plywood bulkheads can take.
If you know your chute and can model it open at different speeds, you can get an idea of how much pull it give.
The bulkheads are probably fine. Glued to the body, if they start to flex they'll transfer momentum to the body. Good for not breaking, but can cause whiplash and Estes dents. Someone told me their Vulcanite drove its booster into the payload section and bashed it in. I doubt that was from elastic shock. Probably from the chute slowing the payload section in front of the booster still moving at high speed.
How much give is in your shock cord? Is it going to absorb much? I know it gives some, but it does it quick and then it's tight. The chute is going to pull according to airflow for as long as it takes to get it to terminal descent velocity.
Do a simple sim on the Rocket Simulator on EMRR
https://www.rocketreviews.com/tools.shtml
and do the full table. It'll give you the speed at each 0.1 sec. Check out the range of your delay around apogee and see what speed is predicted. If your delay is longer than apogee, use the equivalent pre-apogee speed; it's all ballistic.
Once you have the speed, if it's legal to do so, try tying it to the back of a car and testing it. If you can find a spring scale, like for weighing big fish, you can get the actual pull at various speeds. If your projected opening speed is too fast to test, get some measurements at lower speeds and extrapolate. There may be a fairly simple square-inch x speed calculator somewhere for doing this; I don't know.
Did the chute come with a max rating? I'd worry about it shredding or busting a shroud.
Frankly, I'd add a small loop of strong elastic material (not necessarily elastic itself, but something with give) to absorb some of the shock from the swivel. It can have more rating than the swivel, but beling elastic it'll start to give first and absorb some.
