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- Jun 4, 2019
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I will make it brief. I saw a few threads where the use of Kevlar line for shock cord was discussed.
In those discussions it was stated that the cord can be used without any 'stretchy' shock cord as long as it is at least 3 times the body tube length.
I had built the now demised HF XL with a Kevlar shock cord a little more than 4x the body tube length.
It flew great however at deployment the plastic parachute ripped right off leaving the shroud lines with the knots still intact attached to the nose cone.
I believe the failure was due to too short of a delay of 4 seconds and the system deployed while it was still doing around 80mph. The resulting stress ripped off the parachute, and zippered the tube about an inch. Also the snap swivel holding the altimeter was bent.
If the bent swivel was from the landing or the ejection impact is un known. But it musta been one hell of a jerk!
I 'think' that if a section of elastic cord had been included it may have been enough to avoid the catastrophic failure.
Yes choosing a longer delay would also have probably averted the event. But the elastic gives some backup in case of such a thing. Delay charges are notoriously erratic from what I understand.
I will be including some stretchy part to my shock cords from now on.
Thanks for bearing with me
In those discussions it was stated that the cord can be used without any 'stretchy' shock cord as long as it is at least 3 times the body tube length.
I had built the now demised HF XL with a Kevlar shock cord a little more than 4x the body tube length.
It flew great however at deployment the plastic parachute ripped right off leaving the shroud lines with the knots still intact attached to the nose cone.
I believe the failure was due to too short of a delay of 4 seconds and the system deployed while it was still doing around 80mph. The resulting stress ripped off the parachute, and zippered the tube about an inch. Also the snap swivel holding the altimeter was bent.
If the bent swivel was from the landing or the ejection impact is un known. But it musta been one hell of a jerk!
I 'think' that if a section of elastic cord had been included it may have been enough to avoid the catastrophic failure.
Yes choosing a longer delay would also have probably averted the event. But the elastic gives some backup in case of such a thing. Delay charges are notoriously erratic from what I understand.
I will be including some stretchy part to my shock cords from now on.
Thanks for bearing with me