Reviewing projects for NASA SLP provides the opportunity to examine other deployment strategies. Using JLCR in high power flights with rubber band retention of the parachutes has an increased occurrence for the parachute working free during descent. One team opted to replace the rubber band with a zip tie, which worked perfectly. Lightly compressing the parachute with the zip tie allows for release of the parachute as designed, with the parachute material elastic material. A new zip tie for each use lets the flier adjust the retention compression as needed and eliminates the compression variation caused by aging rubber bands.
Most any technique will work if done properly, but I suspect that John would advise against using only a zip tie and relying on the chute to provide the elasticity, as it would encourage over tensioning . Instead, EPDM rubber bands appear to be the best solution. However, they are not as “stretchy” as a common rubber band, and have to be carefully sized. Otherwise, too much tension can be created, resulting in the JLCR NOT releasing at all. John has explained that some users are repeatedly testing their JLCRs under with hihg tension, leading to the opposite failure mode where the pin won’t clip in because the sear mechanism has been worn out.
The solution to mitigating the parachute (or its shroud lines) working free during descent is to immobilize the chute pack relative to the harness. In 2016 the “recovery sled” or chute sled was developed to do just that.
Backstory… After a failed inflation, that could not be explained, on a 72" chute at SEARS in Oct. 2016 I started investigating. Flight video from test flights showed that the shroud lines could pull out of the pack even on much smaller rockets, using much smaller chutes. Apparently, the pack thrashing about in the air stream could twist pulled lines fouling the chute. This is more of an issue on larger chutes given the JLCR’s lesser ability to compress the pack. The pack gets bigger, but of course the JLCR does not scale up with the pack.
It seemed reasonable that if the chute could be kept immobile relative to the harness that could not happen. The recovery sled does just that when properly configured, because the chute pack cannot move independent of its harness attachment point. They must move together until the JLCR releases. This can be readily inspected when packed. The chute pack is held to the sled by the JLCR, the sled is fixed along the harness at each end so where the harness moves so does the pack, and vice-a-versa.
Whether you purchase one of our sleds, heat formed from nearly indestructible polycarbonate, or fashion your own you’ll find your deployments are far more reliable even with larger chutes.
Facebook Shop (e.g. 8” x 3” pack):
https://rb.gy/zrouz