JimZNJ
Well-Known Member
- Joined
- Feb 21, 2012
- Messages
- 360
- Reaction score
- 8
I recently picked up some 1 grain 38mm CTI motors for lower flights on some of my lighter 38mm powered rockets. Today I made 3 attempts to fly my 3" Madcow Little John on the following motors, all with the same failures: G69SK, G69SK, G60 Red. Each motor ended up blowing out the rear as soon as the igniter was lit. The rocket shot partly up the rail in response before falling back down to a rest. The one grain motor casing was found in each case up inside the rocket body with the forward closure, ejection charge, and delay grain not burned at all. The plastic rear closures of the 38mm motor was blown off the bottom of the motor, and on the first failure the force blew the Aeropack retainer clean off the motor tube.
Having used a G69SK load a couple years back successfully, and having confidence in the motor casing I went looking for other clues as to the cause of the failure:
1. While I could not locate all of the ejected motor grains, the grain was never seen burning in any of these failures (no sparkies, no red). I did eventually find one of the ejected grains and it had not burned at all. The little ignition pellet was gone though.
2. I found a small fragment of the rear closure, which suggests the force of the failure shattered it. The casing threads appear fine. The shattering suggests the threads didn't just let go.
I'll be filing the motor failure reports on these events tonight. I'm posting the experience here too though just to see if anyone else has had any recent issues with CTI 38mm 1 grain loads. Mine were manufactured around August 2017. They included the new starters/igniters with the blue and white leads. I can't help but wonder if either the ignition pellet, the new igniter, or the combination of the two were behind these energetic failures. With no grains burned or ejections charges fired, there is not much else to create such a pop.
Jim Z
Having used a G69SK load a couple years back successfully, and having confidence in the motor casing I went looking for other clues as to the cause of the failure:
1. While I could not locate all of the ejected motor grains, the grain was never seen burning in any of these failures (no sparkies, no red). I did eventually find one of the ejected grains and it had not burned at all. The little ignition pellet was gone though.
2. I found a small fragment of the rear closure, which suggests the force of the failure shattered it. The casing threads appear fine. The shattering suggests the threads didn't just let go.
I'll be filing the motor failure reports on these events tonight. I'm posting the experience here too though just to see if anyone else has had any recent issues with CTI 38mm 1 grain loads. Mine were manufactured around August 2017. They included the new starters/igniters with the blue and white leads. I can't help but wonder if either the ignition pellet, the new igniter, or the combination of the two were behind these energetic failures. With no grains burned or ejections charges fired, there is not much else to create such a pop.
Jim Z