Thursday, November 02, 2017

My Jolly Logic Chute Release issues

I have been pondering the last NARHAMS launch, specifically the flight that ended up in the trees. I decided to summarize all my JLCR issues so far. If for no other reason to reinforce what I learned.

1. Beware wind-free days. At the last launch, the ground level wind was mostly still. We had the crowd on one side, soccer fields to one side, and trees on the other two sides. Thus, we needed to angle the rods slightly towards some of the trees. There was some upper-level wind that was generally keeping the rockets away from them. My launch of the MLAS-S, between the angle and a little weathercocking, headed over the stand of trees. The ejection was on cue and the JLCR worked perfectly. Unfortunately, it fell almost straight down. In this case, not using the JLCR would have been preferable. I need to watch my angles better and, if there is no wind, consider not using the JLCR.

2. Be careful about really heavy nose cones. A lot of my rockets seem to end up needing nose weight. If the nose is heavy enough to lead the ejected rocket down, the release can let the chute open directly under the falling rocket, which means the body can fly into and snag the chute. On such rockets, I now add a leader so the chute bundle is adjacent to, or above the falling rocket.

3. Protrusions on fins look cool, but... I had one flight that had fin pods. After ejection, the body and the nose/chute bundle flopped around relative to one another and the chute ended up snagging a fin. Maybe a leader would help here too but this is harder to anticipate. This can happen even without a JLCR.

4. On the last flight of my upscale Estes Cluster Bomb, I stuffed in a huge chute protector. I decided for the first time to use a 60" chute. Afterall, if the JLCR drops it close, why not? Well, the rocket is a bit over 5" in diameter so a protector for a 4" tube seemed too small. Next up was one for an 8" rocket. I don't know if the size of the protector mattered or even why the chute snagged, but the protector went through the shroud lines after the JLCR released. The chute would almost open them the snag would deflate it. The rocket landed parallel to the ground and required a fin fix. I still can't figure out why it snagged this way much less how to avoid this failure mode.

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