JLCR advice, in no particular order…
- Read the instructions that the JLCR came with. This will still not be enough.
- Reconsider your chute folding technique from before you had a JLCR. It’s generally accepted that your chute folding technique for using a JLCR needs to be different that before. Again, read some of the TRF threads on this and consult other rocketry club members.
- Check with other rocketry club members to tap into their knowledge about using JLCR devices.
- Like packing/folding your parachutes, it is often recommended to set-up the JLCR and parachute on launch day at the site. Doing it the day before, or even earlier, can sometimes result in the chute material sticking to itself and the JLCR band binding/gripping to the chute material.
- Generally, its better to have the JLCR restraining band wrap directly around just the folded chute rather than around the outer Nomex blanket that may also being used to protect the chute bundle. This is mainly because most fliers want the Nomex blanket to be “whisked well away” from the chute attachment point so as to avoid risk of it entangling in the chute shroud lines. There is also a risk of the JLCR elastic band gripping/binding on the “rougher” texture of the Nomex cloth.
- Ground test 1 – Check that the JLCR actually releases before you finally pack it into the rocket at the launch site and before you take the rocket to the RSO. Make sure you remember to switch it back on again after the ground test.
- Ground test 2 – Do the shake test to simulate the chute bundle tumbling earthward after ejection. Ensure the JLCR holds the chute tight and that the chute shroud lines stay gripped inside your Z-folded chute bundle.
- Ground test 3 – Do the puff test or something similar. Check that the combined diameter of the folded chute + JLCR + Nomex blanket bundle will smoothly eject out of the body tube by your motor deployment charge.
- I would encourage you to have a suitably placed vent hole in your rocket body to allow equalisation of internal and external air pressure as the rocket rapidly climbs, avoiding nose cone separation, and enabling the JLCR to sense outside air pressure and hence detect launch [Note: vents are good to avoid pressure separation, but Chute Release doesn't really sense launch; it's attention is on detecting falling when it's out in the open, so in a very strict sense vents are not a hard requirement at all, but they are for altimeters and I always use them.]
- After doing your ground tests, make sure the JLCR is secured to one of the folded chute shroud lines, not the main shock chord. Attach it to a shroud line high up next to where it attaches to the chute canopy material. That way, it some of the shroud lines get pulled out during the tumble earthward, then they won’t pull on the JLCR directly.
- Also make sure the band and pin ring are nicely aligned for the tension to pull the pin straight out. Don’t have the band tension pulling the pin to one side as this can cause the pin to stick in long enough for the servo actuator rod to re-engage the pin. [Not everyone realizes that Chute Release has a swivel built into the mechanism. It's pretty sticky when new and doesn't swing easily at first. It's a good idea to put a pencil into the hole and waggle it back and forth a bit to loosen it up. In fact, in units being assembled right now we have modified the dimensions of the swivel a tiny amount to make it much more swively from now on.
That's probably the most thorough set of directions I've seen someone post all in one place. Well done. My favorites I left above, and I added a couple of comments, expand them to read.
Always delighted to hear that someone read the User Guide, btw.
I would also add a couple more notes:
1. Never use a non-elastic band like a zip-tie. Yes, it can work, but it can also ruin your Chute Release. You need elasticity to limit the tension on the band to a level below that which will strip the tiny sharp corners off of your Chute Release mechanical mechanism.
2. The most common failure (after "forgot to turn it back on") is a bundle that "didn't open in the air, but rather opened after landing."
I don't believe that ever actually happens. Rather, as
@BrendanH69 suggests here the bundle and the band were to blame.
Either the bundle was too fluffy and the band got caught up in loose folds or the folding technique wasn't adapted for Chute Release. For instance, never wrap your shround lines around the outside of the chute. Let Chute Release hold the bundle closed, not your shroud lines. You want the bundle to fall open (not to have to unroll) and your chute to snap open. Goal should be to only lose about 50 feet of altitude after release until inflation. Once inflation occurs, the rocket will quickly (in less than a second or two) slow to landing speed. I have typically used 200 or 300 feet as the release altitude, though new rockets I may add a little just due to uncertainty. But granted, my bundles are pretty optimized for Chute Release, and not at all like I used to do them. A release altitude higher than that would have no benefit to landing speed, the rocket would just drift further, and I mostly only raise the altitude in order to be able to see it on chute longer on days where the wind was really shifty and I worried I wouldn't know which direction to look to spot it.
Hope that all makes sense.
