Strange cable cutter failure

[T34zac]

Over the last weekend at LDRS, I flew a 54mm min diameter rocket that used a cable cutter for main deployment. Main altitude was set for 500’, but when I got the rocket back I noticed two fins broken off and the parachute still neatly folded next to the rocket. Both cable cutters had fired and done their job, but the parachute never unfurled. Does anyone know how to prevent this in the future?

I plan on doing some tests using a rocket that is normally drogueless at apogee, but including a second main parachute that’s held by cable cutters.

 

[dhbarr]

Are the shroudlines wrapped around the canopy? I could be mistaken, but I thought failing to unfurl is a known failure mode of that technique.

 

[rfjustin]

You need a much higher main deployment altitude, 500' is way too low IMO.

 

[Cl(VII)]

You need a much higher main deployment altitude, 500' is way too low IMO.

This. I have always set my main alt at 1000 when using cable cutter (as opposed to 600 in traditional DD). Chute almost always opens by 500, but has opened as low as "last possible moment" before. Never went splat though.

Also, I never wrap the lines around the chute. I lay the chute flat, and Z-fold the lines inside, then nomex burrito around the whole thing.

 

[tfish]

attach the fins better.
how long had that chute been balled up for..or loaded into the rocket?
Dont wrap the shroud lines..
go with a much higher main deployment setting.

Tony

 

[T34zac]

Are the shroudlines wrapped around the canopy? I could be mistaken, but I thought failing to unfurl is a known failure mode of that technique.

Yes they were. I’ve never had an issue when using this with traditional DD so I figured I’d use it here too

 

[T34zac]

You need a much higher main deployment altitude, 500' is way too low IMO.

That’s one of the thing I was going to test

 

[T34zac]

This. I have always set my main alt at 1000 when using cable cutter (as opposed to 600 in traditional DD). Chute almost always opens by 500, but has opened as low as "last possible moment" before. Never went splat though.

Also, I never wrap the lines around the chute. I lay the chute flat, and Z-fold the lines inside, then nomex burrito around the whole thing.

noted for the folding technique. I plan to change my packing methodology in the future as well as deployment altitude

 

[T34zac]

attach the fins better.
how long had that chute been balled up for..or loaded into the rocket?
Dont wrap the shroud lines..
go with a much higher main deployment setting.

Tony

Yeah it’s an old rocket of mine that never got to fly before. Not up to my current standards of construction so I have it gentle motor with the intent of not flying it again. The chute was wrapped up for a few days which I know isn’t ideal, but I’m taking all this advice into consideration. Thanks for the help everyone!