CTI 54mm motor question/concern

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VAXman

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I've purchased a 54mm CTI (1211J140) for my level 2 certification flight. I removed it from its packaging and installed it, temporarily, in the CTI 3-grain enclosure, and installed the assembled unit in my rocket to determine its CG with motor. This motor is plugged, BTW. I noticed that there is an O-ring on the delay/ejection module which mates up on the *inside* of the motor casing insulator. I'm assuming this is the same assembly also used on other 54mm CTI motors that have ejection and require adjustment. My question, however, is that there is no similar *inner* O-ring on the nozzle end module. I'm not referring to the O-rings that contact the inside of the motor casing; those exist at/on both end modules.

Is there enough pressure provided by the motor case and the retaining ring to keep gasses from leaking at the interface between the motor insulator and the nozzle? I realize the insulator will probably burn away to some extent, so this concern of mine may be moot, but I thought I'd ask here to be certain.
 

JimJarvis50

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I've purchased a 54mm CTI (1211J140) for my level 2 certification flight. I removed it from its packaging and installed it, temporarily, in the CTI 3-grain enclosure, and installed the assembled unit in my rocket to determine its CG with motor. This motor is plugged, BTW. I noticed that there is an O-ring on the delay/ejection module which mates up on the *inside* of the motor casing insulator. I'm assuming this is the same assembly also used on other 54mm CTI motors that have ejection and require adjustment. My question, however, is that there is no similar *inner* O-ring on the nozzle end module. I'm not referring to the O-rings that contact the inside of the motor casing; those exist at/on both end modules.

Is there enough pressure provided by the motor case and the retaining ring to keep gasses from leaking at the interface between the motor insulator and the nozzle? I realize the insulator will probably burn away to some extent, so this concern of mine may be moot, but I thought I'd ask here to be certain.
I have previously expressed my opinion on your question in Post #41 in this thread.

https://www.rocketryforum.com/showthread.php?134434-CTI-38mm-CATO-Report/page3

If I was flying the motor, I would glue in both the forward and rear closures, as I do on all Pro54 motors. Good luck on your cert flight.

Jim
 

mikec

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I flew one of these at LDRS last weekend. I don't recall seeing the internal O-ring on the forward closure side, which is not to say it wasn't there. Being a a little paranoid about long-burns, I glued the closure and nozzle in per Jim's advice and didn't have any problems (although the rocket weathercocked a bit and I had a 3-mile round trip for recovery.)
 

Bat-mite

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I fly CTI 29, 38, 54 and 75 mm motors almost exclusively. I use them out of the box and I've never had a cato or anything close. If you have concerns, talk to your dealer.
 

JimJarvis50

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I fly CTI 29, 38, 54 and 75 mm motors almost exclusively. I use them out of the box and I've never had a cato or anything close. If you have concerns, talk to your dealer.
My dealer is recommending gluing in the closures to whomever he sells motors to. This is based on an acknowledged QC problem and not something that is just from my personal observation. If you haven't had a problem, that's great - buy a lottery ticket.

Jim
 

VAXman

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Bat-mite

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Jim, who's your dealer? Sounds like I need to talk to them. If there is a problem, I would like to know. Feel free to PM me. Thanks.
 

watermelonman

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I've purchased a 54mm CTI (1211J140) for my level 2 certification flight. I removed it from its packaging and installed it, temporarily, in the CTI 3-grain enclosure, and installed the assembled unit in my rocket to determine its CG with motor. This motor is plugged, BTW. I noticed that there is an O-ring on the delay/ejection module which mates up on the *inside* of the motor casing insulator. I'm assuming this is the same assembly also used on other 54mm CTI motors that have ejection and require adjustment. My question, however, is that there is no similar *inner* O-ring on the nozzle end module. I'm not referring to the O-rings that contact the inside of the motor casing; those exist at/on both end modules.

Is there enough pressure provided by the motor case and the retaining ring to keep gasses from leaking at the interface between the motor insulator and the nozzle? I realize the insulator will probably burn away to some extent, so this concern of mine may be moot, but I thought I'd ask here to be certain.
J140? What are you flying it in? I had one in a rocket that simulated slightly on the good side of questionable, flew it in dead calm wind, and it went horizontal. Have plenty of margin on initial thrust!
 

JimJarvis50

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Thanks!

You glue it in with what? Due to the heat involved, I'd consider long cure JB Weld.
I have just used thickened laminating epoxy, and at a launch, 5-minute epoxy. The strategy is just to keep the gases away from the interface between the liner and closure for a second or so, just long enough to get through the burn. I try for essentially a fillet between the liner and the closure. I clean up the parts with alcohol, rough up the surfaces a little, leave on the o-ring if there is one and gluing over the top of it. This approach has been discussed with CTI, but they have never approved it, so your mileage may vary.

Jim
 

VAXman

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J140? What are you flying it in? I had one in a rocket that simulated slightly on the good side of questionable, flew it in dead calm wind, and it went horizontal. Have plenty of margin on initial thrust!
PML AIM-120 AMRAAM 4".

PML's data sheet lists 54mm motors as: J90, J180, J275, J280, J135, and J415.
 

JimJarvis50

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Jim, who's your dealer? Sounds like I need to talk to them. If there is a problem, I would like to know. Feel free to PM me. Thanks.
CTI acknowledged a problem with the size of the liners. They worked with the supplier to fix the problem and they believe they have done so. The problem typically causes the case to bulge at a point just under the forward closure, and CTI replaces cases that have that problem.

I have personally seen three flights where the case failed completely - again, at the forward closure. I suspect that this is the bulging case issue, although I can't claim to have actually proven that. Unfortunately, my records aren't such that I can say exactly what the motors were, and as this was being discussed with CTI at the time of the accident, I do not know the time frame of the problem or what dates or types of reloads were affected. Reloads hang around for a while, so I am sure they still exist in the inventories of dealers and fliers. So, until proven not to be necessary, I just take the cheap insurance of gluing on the closures to try to head off any problems.

I have been somewhat critical of CTI recently related to this issue and the VMax issue. I have always used primarily CTI motors over the years and I plan to keep doing that. They have been very responsive and helpful when I've had issues, and many times, they have gone out of their way to help me. D@mn that accident. At the same time, though, it's a problem when a rocket gets damaged, particularly when there's a simple fix. I don't believe any official action is likely on this issue and I'm not sure that we would want that. So, just allow me to pass along my advice and maybe it will save a rocket or two.

I see the issue of motor modification has been raised. Beats me. In the absence of any official guidance, I might take the opportunity to tell the RSO at any non-research launch that I am at (it's been a while) what I have done, and that the purpose of it is to avoid ballistic recovery of a burning rocket or the wide dispersion of burning grains. They can decide.

Jim
 

Steve Shannon

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CTI acknowledged a problem with the size of the liners. They worked with the supplier to fix the problem and they believe they have done so. The problem typically causes the case to bulge at a point just under the forward closure, and CTI replaces cases that have that problem.

I have personally seen three flights where the case failed completely - again, at the forward closure. I suspect that this is the bulging case issue, although I can't claim to have actually proven that. Unfortunately, my records aren't such that I can say exactly what the motors were, and as this was being discussed with CTI at the time of the accident, I do not know the time frame of the problem or what dates or types of reloads were affected. Reloads hang around for a while, so I am sure they still exist in the inventories of dealers and fliers. So, until proven not to be necessary, I just take the cheap insurance of gluing on the closures to try to head off any problems.

I have been somewhat critical of CTI recently related to this issue and the VMax issue. I have always used primarily CTI motors over the years and I plan to keep doing that. They have been very responsive and helpful when I've had issues, and many times, they have gone out of their way to help me. D@mn that accident. At the same time, though, it's a problem when a rocket gets damaged, particularly when there's a simple fix. I don't believe any official action is likely on this issue and I'm not sure that we would want that. So, just allow me to pass along my advice and maybe it will save a rocket or two.

I see the issue of motor modification has been raised. Beats me. In the absence of any official guidance, I might take the opportunity to tell the RSO at any non-research launch that I am at (it's been a while) what I have done, and that the purpose of it is to avoid ballistic recovery of a burning rocket or the wide dispersion of burning grains. They can decide.

Jim
Nothing says you can't grease the nozzle o-rings with epoxy. I don't consider that a modification.
 

VAXman

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FYI, I finally launched my PML AIM-120 AMRAAM on the CTI 1211J140LB yesterday. She was a beautiful flight; albeit, a long recovery walk. The spent motor casing shows no issues at all. I epoxied both ends with long cure JB weld which held up well. Even after the burn, I can't remove either end.
 

watermelonman

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Awesome! I was going to say, if the J90 was recommended you can certainly disregard my initial thrust warning.

Hope it was a perfect flight, I love the thought of that motor and kind of want to give it another shot. I bet 0.25-0.5lbs less would have made the difference on my flight.
 

rms

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Here's a video of my PML AIM-120 AMRAAM on the CTI 1211J140 Long Burn. I love hearing the engine roar for more than 10 seconds!

https://youtu.be/e16dfokJMDE

https://barc775.files.wordpress.com/2016/11/pml-aim-120-amraam_004.jpg
I flew this motor in Sept and set a new Canadian Association of Rocketry J impulse record. Certainly nowhere near the Tripoli J impulse record but then again not flown in the high elevation desert either. I didn't glue the closure or nozzle to the liner and experienced no issues the flight or the motor after the flight.

New J record smaller.jpg
 

JimJarvis50

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I didn't glue the closure or nozzle to the liner and experienced no issues the flight or the motor after the flight.

View attachment 305863
Another from over the weekend. Glue is good ....

This one suffered a burn-through at another point on the case. We're not sure if the two problems were related.

Jim
 

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rms

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Another from over the weekend. Glue is good ....

This one suffered a burn-through at another point on the case. We're not sure if the two problems were related.

Jim
Ouch!
If that had happened to mine, I would have never been able to get the case out of the rocket. It being carbon fibre and motor case friction fit, that bulge would have been terminal. In my case perhaps I got lucky!
My interpretation of the case photo and it's scale, it appears that the burn-through was at the forward threaded closure and liner joint? And it was glued?

Greg
 

JimJarvis50

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Ouch!
If that had happened to mine, I would have never been able to get the case out of the rocket. It being carbon fibre and motor case friction fit, that bulge would have been terminal. In my case perhaps I got lucky!
My interpretation of the case photo and it's scale, it appears that the burn-through was at the forward threaded closure and liner joint? And it was glued?

Greg
It gets a lot more terminal if the bulge fails and fire comes out. Without rehashing the issue again, let me just state that I do not fly any Pro54 motors unless I first glue the nozzle and the forward closure into the liner. I recommend that everyone do this (to avoid one or the other of the terminal outcomes). This is a relatively easy fix to a known problem.

Jim
 

mikec

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Ouch!
If that had happened to mine, I would have never been able to get the case out of the rocket.
You can push the motor forward after removing the aft closure unless you have a forward bulkhead or something. (I admit I cut a rocket in half once before realizing this, although it was trashed anyway from a burn-through.)
 

BDB

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It gets a lot more terminal if the bulge fails and fire comes out. Without rehashing the issue again, let me just state that I do not fly any Pro54 motors unless I first glue the nozzle and the forward closure into the liner. I recommend that everyone do this (to avoid one or the other of the terminal outcomes). This is a relatively easy fix to a known problem.

Jim
Any suggestions on the best glue to use?
 

rms

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You can push the motor forward after removing the aft closure unless you have a forward bulkhead or something. (I admit I cut a rocket in half once before realizing this, although it was trashed anyway from a burn-through.)
Minimum diameter and friction fitting, a bulge like that would lock the case in the rocket no matter what direction it was pushed to remove!
Greg
 

mikec

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Minimum diameter and friction fitting, a bulge like that would lock the case in the rocket no matter what direction it was pushed to remove!
You're right of course, I missed the minimum diameter part. The bulge would probably damage the airframe anyway.
 
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