3 CATOs today with 1 grain 38mm CTI motors

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JimZNJ

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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
 
Try a Loki. I heard those don't Cato as much. You'll save on hazmat.
 
Try a Loki. I heard those don't Cato as much. You'll save on hazmat.

That's probably not a bad idea to explore. I also happen to have a local Loki dealer, but just never invested in new hardware to go that way.

Jim Z
 
What did you use for an igniter? CTI only needs an e-match. I'm asking because I had something kind of like what you describe happen with a 1 grain Loki 38. I used an "enhanced" igniter and it was way more than necessary.
 
What did you use for an igniter? CTI only needs an e-match. I'm asking because I had something kind of like what you describe happen with a 1 grain Loki 38. I used an "enhanced" igniter and it was way more than necessary.

I used the igniter, starter, or whatever we call them these days, that was supplied with the motors. CTI recently changed to new ones with blue and white leads. They remind me of the MJG Firewire Initiators which are non ATF regulated, and perhaps that's what they are.
 
It was just a bad day for Little Johns.
Mine separated at apogee but the JLCR didn't open. It fell 1700 feet or so, luckily the only damage appears to be a heavy crease that can likely be fixed with a coupler.
A fellow flyer had one land on the asphalt and crack a fin. Close inspection and we gave it a thumbs up to go again. He flew it again and the fin cracked even more so it now awaits it's fate.

Never flown CTI though I do have the Pro38 1G case, the loads for that particular case are way too overpriced for me. But I do have and fly the Loki 38/120, and the Little John loves it. It MAY save a few bucks in the long run as well.
 
It was just a bad day for Little Johns.
Mine separated at apogee but the JLCR didn't open. It fell 1700 feet or so, luckily the only damage appears to be a heavy crease that can likely be fixed with a coupler.
A fellow flyer had one land on the asphalt and crack a fin. Close inspection and we gave it a thumbs up to go again. He flew it again and the fin cracked even more so it now awaits it's fate.

Never flown CTI though I do have the Pro38 1G case, the loads for that particular case are way too overpriced for me. But I do have and fly the Loki 38/120, and the Little John loves it. It MAY save a few bucks in the long run as well.

Sorry to hear of the Little John mishaps. Hopefully everything can be as easily remedied as you anticipate. My Little John took a bit of abuse from the 3 motor failures, so it is also on my repair bench. The biggest part of my repair is having to re-engineer the motor retention after the Aeropack retainer and attached exposed tail of motor tube were blown off the bottom of the rocket. I have a repair I think which will work though, so my Little John should fly again soon. :)
 
It was just a bad day for Little Johns.
Mine separated at apogee but the JLCR didn't open. It fell 1700 feet or so, luckily the only damage appears to be a heavy crease that can likely be fixed with a coupler.
A fellow flyer had one land on the asphalt and crack a fin. Close inspection and we gave it a thumbs up to go again. He flew it again and the fin cracked even more so it now awaits it's fate.

Never flown CTI though I do have the Pro38 1G case, the loads for that particular case are way too overpriced for me. But I do have and fly the Loki 38/120, and the Little John loves it. It MAY save a few bucks in the long run as well.

I just looked at Wildman CTI prices and Loki prices there is very little difference. Most CTI loads were cheaper.
 
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


Three for three sounds like a statistically improbable (but certainly not impossible) reload problem, but could be easily caused by a faulty case. Did you use the same aluminum casing with all three reloads or different cases each time?
Was it a one grain case or a longer case with spacers?
Did the reload screw into the case easily?

As far as Loki vs. CTI, until the recall for bad forward closures I haven’t noted a significant number of catos with CTIs and I’ve been flying them since they first came out.
 
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Sorry to hear of the Little John mishaps. Hopefully everything can be as easily remedied as you anticipate. My Little John took a bit of abuse from the 3 motor failures, so it is also on my repair bench. The biggest part of my repair is having to re-engineer the motor retention after the Aeropack retainer and attached exposed tail of motor tube were blown off the bottom of the rocket. I have a repair I think which will work though, so my Little John should fly again soon. :)

It'll be my first repair job. Last mishap I had I cannabilized the rocket and sold it for parts. But this one is a great rocket. I'll fix it.

I just looked at Wildman CTI prices and Loki prices there is very little difference. Most CTI loads were cheaper.

Cheapest CTI I see at Chris's is $22.95 compared to the priciest Loki 2 packs at $38.95 each. Granted you have to buy two starters. :-/ Even into 2 grain, 240 loads, Loki is cheaper. Don't know what kind of prices Tim has, I am not a fan of the new site. And then of course the HAZMAT thing.
 
It'll be my first repair job. Last mishap I had I cannabilized the rocket and sold it for parts. But this one is a great rocket. I'll fix it.



Cheapest CTI I see at Chris's is $22.95 compared to the priciest Loki 2 packs at $38.95 each. Granted you have to buy two starters. :-/ Even into 2 grain, 240 loads, Loki is cheaper. Don't know what kind of prices Tim has, I am not a fan of the new site. And then of course the HAZMAT thing.

I guess I didn't see it was a 2 pack. Much better price.
 
... but could be easily caused by a faulty case. Did you use the same aluminum casing with all three reloads or different cases each time?

This is my question as well. If the case was damaged with the first CATO, and re-used, that could easily explain the subsequent failures. thread damage is not always visible. Just check some of the other threads in this section of the forum.
 
Jim, Rick Comshaw said he was notified of an issue with CTI loads failing as yours did. You might give him a call or whoever you bought yours from. They should be aware of the issue.
 
the failures with CTI were well documented by them (and many others) https://pro38.com/pdfs/Bulletin-Pro38_Forward_Clousre.pdf

So, the important question is, do you have the reload's cardboard container?
What color was the lighter?

Also, have you talked to AMW?

The bulletin from CTI is about the problem with a run of forward closures that resulted in the delay grains being blown through the forward closures. This problem appears to be completely different. Three out of three reloads had aft closures blown out the aft end.
 
The casing used was a 1 grain CTI casing used only once before about a year or two back, without incident. It had been stored in its protective plastic tube in the interim. While i can not rule out that the first of these three energetic failures impacted the threads for the two subsequent attempts, all 3 failures were equal in character. There was a boom, the aft closure and nozzle blew out and there is evidence in one instance at least of the aft closure being fragmented and not just stripping out. The delay grain and propellant grains never ignited in any of the failures. I can only assume the energetic response was from either the ignition slug in the motor, the supplied igniter, or combination there of. The igniters were all the newer ones with white and blue leads. The motors all were manufactured in the late summer of 2017. As pointed out by others, this is not the forward closure issue.
 
guys I believe these motors are from a newer batch, 2017 if I remember the date right.

Jim did save the cardboard tube w/date, it seemed the only thing that burned were the igniters, no propellant or delay gran.
 
The grains likely ignited and blew the closure when it pressurized. Once the closure was gone, it snuffed out. Grains appearing unburnt after a failure are not unheard of. I have had it happen to me and I have seen it happen to another, and that one was a Pro38, but not a 1G.
 
My Little John took a bit of abuse from the 3 motor failures, so it is also on my repair bench. The biggest part of my repair is having to re-engineer the motor retention after the Aeropack retainer and attached exposed tail of motor tube were blown off the bottom of the rocket. I have a repair I think which will work though, so my Little John should fly again soon. :)

Jim,
Sorry to hear (and witness) your CATO's.
For repairs, consider cutting off the protruding MMT stubs, and installing something along the lines of the following flat bottom retainer / thrust plate:
https://www.apogeerockets.com/Build...or-Retainers/38mm-Flat-Bottom-Rocket-Retainer



The casing used was a 1 grain CTI casing used only once before about a year or two back, without incident. It had been stored in its protective plastic tube in the interim. While i can not rule out that the first of these three energetic failures impacted the threads for the two subsequent attempts, all 3 failures were equal in character. There was a boom, the aft closure and nozzle blew out and there is evidence in one instance at least of the aft closure being fragmented and not just stripping out. The delay grain and propellant grains never ignited in any of the failures. I can only assume the energetic response was from either the ignition slug in the motor, the supplied igniter, or combination there of. The igniters were all the newer ones with white and blue leads. The motors all were manufactured in the late summer of 2017. As pointed out by others, this is not the forward closure issue.

The grains likely ignited and blew the closure when it pressurized. Once the closure was gone, it snuffed out. Grains appearing unburnt after a failure are not unheard of. I have had it happen to me and I have seen it happen to another, and that one was a Pro38, but not a 1G.

After witnessing the failures, the above description matches what I had observed.
Assuming that lighting up the igniter alone would not generate enough pressure to blow out the rear closure, the grains must have started to partially burn, then extinguished upon ejection from the case.
The only open question is why the Pro38's plastic aft closure not only blew out, but shattered (threads intact).

The aft plastic closure ring seams to be the main suspect, and the weak point in Pro38 motors. At least in the batch Jim was trying to light up the other day.


a

P.S.: I had Loki 38-120 case and motors on my "to try in 2018" list of things to do. At $0.13-18 per $/Newton, it is the only Loki motor that is marginally cheaper or similarly priced to AT and CTI (net of discounts). Hazmat is not a consideration for me. Cleaning the nozzles and messing with the snap-ring pliers will be a PITA.
P.P.S.: If you are ready to pull the trigger, we can jointly motivate Teddy to come over for one of the summer launches...
 
The only open question is why the Pro38's plastic aft closure not only blew out, but shattered (threads intact).

It struck something hard, like the blast deflector. If the aft end of the case is slightly belled from a previous Cato (or if it was manufactured oversized), those threads could appear just fine.
 
It struck something hard, like the blast deflector. If the aft end of the case is slightly belled from a previous Cato (or if it was manufactured oversized), those threads could appear just fine.

I don't know if Jim kept the shard of the plastic aft closure, but from what I remember, the threads were pristine.
My working assumption would be that plastic threads would show some damage while getting ejected from a belled casing... ?


We can't really buy motors by the Ns, so comparing them that way isnt really a good method. Never went up to my motor vendor and asked for 72 Ns of White propellant, Loki since it is cheaper. It doesn't really work that way. Since you have to buy by the motor it's best to price per motor.

I would prefer to avoid sidetracking Jim's thread by interjecting a debate over motor brand allegiances.
As is the case with automotive motor oils preferences, rocket motor brand affinities are strong, and are only occasionally fact based.

As to measuring $$/Newtons - I find that metric to be helpful when cross shopping brands and motor sizes (38 vs 54 vs 75mm).
If I am shopping for a J-motor with ~700 Newtons of total impulse to stay right under the waiver, I could stock up on a few 38mm AT J500Gs ($0.067 $/Nwtn), 54mm AT J250FJs ($0.070 $/Nwtn), 38mm Loki J320Rs ($0.076 $/Nwtn), CTI P38 J330C's ($0.071 $/Nwtn), or CTI P54 J280SS's ($0.101 $/Nwtn).
I looked at the price per Newton value props, and ordered a bunch of J500G's and J250 FJ's during BFS.

That's how I look at this motors - $$$ go in, thrust comes out.
Lowest $/Newton wins my wallet's blessing ;-).

YMMV,
a
 
My posts are acting screwy...may be from me trying to "quote" on my phone. Looks like I am hijacking this thread, not trying to. Went back and deleted all the nonsense. Sorry about that. :-/
Yes, I hate cleaning the stupid nozzles too.
 
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