38 CTI motor fail this one is a mystery. Help

I was practicing flights on my main rocket that I was planning on using for my L1 cert March 23 I watch your videos and red the manufacturer instructions very carefully, I picked cesaroni for it simplicity but today the rocket never left the pad. G78bs 1grain took 9 secs off the delay reassembled the motor with apportate spacer, on the pad the ejection charge shot up thru the rocket the motor destroyed the areo pack retention

system and it came out of the rocket. The delay grain was not burn the delay charge was gone but does not look like it ignited. The grain was also shoved into the spacer. I guess I am just dumb founded how this happened. If you have time to let me know if there is something obvious I missed that caused this failure please let me know. I attached a picture of the pieces. I cut the case in half to attempt to recover the spacer and get the motor liner and grain and gain mor insight since case was a total loss, space is still stuck it's not coming out.

You were using a 1g reload in the 2g case, correct? And what did you use to shorten the delay element?

Did you ever see any visible flame at the nozzle? Is the throat of the fuel grain any larger / sharp grain edges rounded at all? I'm guessing not, I'm guessing the grain is just a little sooty.

At a hunch -- as the pellet ( but not reload proper ) began to pressurize, the delay gave out allowing the ejection charge to go off.

dhbarr said:

You were using a 1g reload in the 2g case, correct? And what did you use to shorten the delay element?

Did you ever see any visible flame at the nozzle? Is the throat of the fuel grain any larger / sharp grain edges rounded at all? I'm guessing not, I'm guessing the grain is just a little sooty.

At a hunch -- as the pellet ( but not reload proper ) began to pressurize, the delay gave out allowing the ejection charge to go off.

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If it was just the delay going off due to a flame out sneaking past the oring, the nose popping expected but the propellant grain was logged in first spacer and the delay grain and casing was ejected past the spacer and out of the rocket and was found 20 feet away.

dhbarr said:

You were using a 1g reload in the 2g case, correct? And what did you use to shorten the delay element?

Did you ever see any visible flame at the nozzle? Is the throat of the fuel grain any larger / sharp grain edges rounded at all? I'm guessing not, I'm guessing the grain is just a little sooty.

At a hunch -- as the pellet ( but not reload proper ) began to pressurize, the delay gave out allowing the ejection charge to go off.

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I used a 38mm cesaroni delay tool DAT set it to -9

JARED S JAYNES said:

I used a 38mm cesaroni delay tool DAT set it to -9

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It dose not look like the BP burnt at all BP well looks very clean.

CTI had quite a few defective 38mm forward closures a while back, what was the date on the reload?

Report it to your dealer and file a MESS report at https://www.motorcato.org/

I'm going to say the reload wasn't threaded into the case all the way.

This would let the liner and delay module separate enough to allow hot gasses around the outside of the delay module and ignite the BP from the top without burning the delay grain.

seth_cooper said:

I'm going to say the reload wasn't threaded into the case all the way.

This would let the liner and delay module separate enough to allow hot gasses around the outside of the delay module and ignite the BP from the top without burning the delay grain.

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BP well was clean it did not ignite, i checked the nozzle several time during pre fight. and pressure build up was large enough to force the ejection charge and delay case out thru the space and out the front of the motor case and out of the rocket, as well as yanking the aeropack motor retainer off the motor tube

mikec said:

CTI had quite a few defective 38mm forward closures a while back, what was the date on the reload?

Report it to your dealer and file a MESS report at https://www.motorcato.org/

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done and sent a email to my dealer as well. thanks

I hadn't realized that you sawed the case in half trying to get the spacer out. Probably an overpressure from a casting void in the grain. CTI will replace the case and reload. These things happen.

I read what you wrote at the beginning again and it's still a little fuzzy to me.

When you assembled the motor, where was the spacer?

Where were all of the parts after everything came to rest on the ground?

Are you saying the delay module squeezed up through the center of the spacer and out the top of the case but the spacer was left in the case with a propellant grain inside of the stuck spacer?

seth_cooper said:

I read what you wrote at the beginning again and it's still a little fuzzy to me.

When you assembled the motor, where was the spacer?

:0) infront of the the reload, per the instructions.

Where were all of the parts after everything came to rest on the ground?
rocket never left the pad nose cone, chute, shock cord were all torn from the rocket at the forward closure blasted up thru the rocket,
forward closure was 20 or so fee away after looking for it. motor case shot downwords into the blast defector on the pad bending it.

Are you saying the delay module squeezed up through the center of the spacer and out the top of the case but the spacer was left in the case with a propellant grain inside of the stuck spacer?

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exactly, yes that is what happed delay module squeezed up thru the spacer and motor case and headed for the stars.

That's odd

seth_cooper said:

That's odd

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agreed, maybe the ignitor head plugged the nozzle causing an over pressure ? no idea on this end, stumped preflight nozzle was clear before ignitor was inserted. and when examining the grain it looks intact and nothing abnormal. also how did it extinguish itself the grain is unburnt

Overpressures are supposed to blow something out and the grains usually extinguish when this happens. The only odd thing here is that typically the aft closure blows out before the forward closure can get through the front of the case, but not always. As I said, typically overpressures are caused by grain voids which increase the burn rate past normal.

show me a picture of the cardoard tube the reload came in. nice and wide with the entire label.

cbrarick said:

show me a picture of the cardoard tube the reload came in. nice and wide with the entire label.

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I agree. And please include the CTI case label so we can see exactly what case you used. That case looks larger (diameter and length) than the reload. A spacer could make up the length difference, but not the diameter. This doesn’t make any sense.

Steve Shannon said:

I agree. And please include the CTI case label so we can see exactly what case you used. That case looks larger (diameter and length) than the reload. A spacer could make up the length difference, but not the diameter. This doesn’t make any sense.

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The diameter difference is a optical illusion I believe, the aft closure is obviously plastic and those are found only on CTI 38's.

Steve Shannon said:

I agree. And please include the CTI case label so we can see exactly what case you used. That case looks larger (diameter and length) than the reload. A spacer could make up the length difference, but not the diameter. This doesn’t make any sense.

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The case is closer to the camera.

rharshberger said:

The diameter difference is a optical illusion I believe, the aft closure is obviously plastic and those are found only on CTI 38's.

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That’s true but that part comes with the reload, not the case.

Steve Shannon said:

I agree. And please include the CTI case label so we can see exactly what case you used. That case looks larger (diameter and length) than the reload. A spacer could make up the length difference, but not the diameter. This doesn’t make any sense.

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case was a pro 38 space was a 38mm and reload was a pro 38 single grain the aft closure in included in the 38mm reloads cti kinda makes it idiot proof, i am just going to get with dealer on Monday seem to me this must just be a very rare malfunction.

Steve Shannon said:

That’s true but that part comes with the reload, not the case.

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Yep, and that plastic rear closure is the one great failing of the CTI 38's IMO, too many people have cross threaded them. However not sure what the mode of failure was on this motor.

rharshberger said:

Yep, and that plastic rear closure is the one great failing of the CTI 38's IMO, too many people have cross threaded them. However not sure what the mode of failure was on this motor.

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Exactly. I have been trying to imagine a cato powerful enough to drive the entire forward closure through the turned in forward end of the case without shearing the threads on the aft closure.

rharshberger said:

Yep, and that plastic rear closure is the one great failing of the CTI 38's IMO, too many people have cross threaded them. However not sure what the mode of failure was on this motor.

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the rear closure was not cross threaded checked this closely during preflight, but really regretting my decision to switch to cti before my cert flight.

JARED S JAYNES said:

case was a pro 38 space was a 38mm and reload was a pro 38 single grain the aft closure in included in the 38mm reloads cti kinda makes it idiot proof, i am just going to get with dealer on Monday seem to me this must just be a very rare malfunction.

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You’d be surprised at the high level of idiocy that idiot proof designs reveal.
But I agree, you seem to have done it just like the instructions required. This is a strange one.

Steve Shannon said:

Exactly. I have been trying to imagine a cato powerful enough to drive the entire forward closure through the turned in forward end of the case without shearing the threads on the aft closure.

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I concur with both this post and your one following. There just doesn't appear to be a mode of failure here that's obvious, AFAIK the bad forward closures from a couple of years ago usually caused a burn through at the forward closure to liner didn't they or did they blow by the delay grain?

rharshberger said:

I concur with both this post and your one following. There just doesn't appear to be a mode of failure here that's obvious, AFAIK the bad forward closures from a couple of years ago usually caused a burn through at the forward closure to liner didn't they or did they blow by the delay grain?

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The delay grains were forced completely through the forward closures. The forward closure was still held in place by the lip on the case. Then the forward closure acted just like a burn through.

Since no one else has asked, what igniter did you use? Was it the CTI e-match? Or something else?

if the ignitor had grey and blue wires, then it's an oddity
If not, then you probably - note probably had a forward closure that should have been replaced. There are specific date stamps, which your photo doesn't show because it's too tight - to verify this.
If you buy it from me I'd have replaced the forward closure if it had the old, yellow wired ematch. Just because it's better safe then sorry. Of course, the only ones that have to be replaced is the ones in the effected date range. My problem is that I'm not that smart.....

Ive seen a similar over pressurisation issue before on a CTI 38mm, not sure which motor. I’ll try and track it down.