CTI Discussion Thread

[Bill Owens]

Yes, that's correct. #3 was the only one of the failures with an epoxied forward closure. We used Loctite 5 min. We also successfully flew a 54mm 6XL with an L265 (long burn low impulse) that we epoxied.

 

[JimJarvis50]

Yes, that's correct. #3 was the only one of the failures with an epoxied forward closure. We used Loctite 5 min. We also successfully flew a 54mm 6XL with an L265 (long burn low impulse) that we epoxied.

For what it's worth, I use better quality epoxy than 5 minute. I have heard that it softens at a pretty low temperature. Maybe an issue or maybe not.

I don't think the problem is related to the larger O-rings, whether you use one or two. How many of the motors that failed at the smaller O-ring at the overlap into the liner?

Jim

 

[OverTheTop]

We used Loctite 5 min.

For what it's worth, I use better quality epoxy than 5 minute. I have heard that it softens at a pretty low temperature. Maybe an issue or maybe not.

I so do hate 5-minute epoxies.

Has anyone had a failure of this sort when using BSI 30-minute epoxy? That's what I use when I have left preparation a bit late. Other than that my normal go-to for this task is the usual West System 105/206. Not had a failure since I started gluing forward closures, but we haven't flown much either .

 

[tim cubbedge]

Gluing the forward closure seems to work, sometimes, but not always. What really bothers me is that it says nowhere in the instructions that gluing is even needed or recommended. This is not a new problem with CTI.

 

[Banzai88]

Gluing the forward closure seems to work, sometimes, but not always. What really bothers me is that it says nowhere in the instructions that gluing is even needed or recommended. This is not a new problem with CTI.

Truth. The history goes back several years into the other CTI support threads, and there are more than a few pictures like Bill Owens posted.

There also seems to be a growing trend in the 38mm line of this type of failure happening, especially since quality control in liners (too short, not square, rough edges, inconsistent liner wall thickness, outer diameter too large) has dropped into the Laurentian Abyss.

I have yet to see CTI address it in any way, and the continued trend of seeing this type of failure ensures that I will never fly a CTI 54mm as long as there are other commercial offerings available, and I was previously a CTI fan boy. Never had a problem with their 29mms, but about half the 38s that I've burned have had some sort of issue....and I've given away all the 54s that I bought and won't buy another until the issue is addressed.

By the time you're lighting the fuse on a 54mm powered rocket, you're throwing $500+ up in the sky......and there are cheaper and less hazardous ways of playing Russian Roulette.

And unless your vendor is willing to take money out of their own pocket, a year plus turn around on warranty claims is unacceptable.

 

[tfish]

I was at the launch and camped next to Bill and his son Miles. And saw the above issues.

We had a new flyer show up to do his L2 cert flight. The new flyer had bought all his stuff from Apogee. Including his cert motor....which happened to be a CTI 54mm 5 grain motor. He was lucky to have Bill camped next to him. Bill and Miles helped him do the "field fixes" to his 54mm motor. Then we all waited to see if the field fixes worked...or did we, the vendor (knowingly or not knowing about possible motor issues) TRA and CTI just run off a new flyer?

I'm amazed at how many failures it takes to get a manufacture, NAR, TRA or who ever to step in..or step up... to do something!

Tony Alcocer

 

[Steve Shannon]

I was at the launch and camped next to Bill and his son Miles. And saw the above issues.

We had a new flyer show up to do his L2 cert flight. The new flyer had bought all his stuff from Apogee. Including his cert motor....which happened to be a CTI 54mm 5 grain motor. He was lucky to have Bill camped next to him. Bill and Miles helped him do the "field fixes" to his 54mm motor. Then we all waited to see if the field fixes worked...or did we, the vendor (knowingly or not knowing about possible motor issues) TRA and CTI just run off a new flyer?

I'm amazed at how many failures it takes to get a manufacture, NAR, TRA or who ever to step in..or step up... to do something!

Tony Alcocer

This is an issue that I have seen too frequently as well. Unfortunately, the MESS system doesn’t allow failures to be sorted according to case size. That’s nobody’s fault, just the structure of the database. I think it would be very difficult to redo.
So, some extra work is required to document that this is a problem, which is why I asked for these failures to be placed in the MESS database. I’ll send an email to the three certification committee chairs asking them to look at this. No guarantees.

 

[Bill Owens]

Thanks Jim – our 3 cases are each slightly different, but all of them appear to have failed at the smaller O ring as you suggest. While that is clearly the weak point, in one of our cases the second large O ring appears to have held and may have saved the flight.

I’m sure you are right that better epoxy would have been preferable. The bigger issue to me is we are all trying to correct apparent flaws in the field and we are guessing. Thanks for all of the comments in this thread!

 

[Johnly]

I wanted to contribute my experience this summer to the discussion of issues with CTI forward closures. I have submitted this information to CTI through my vendor, but I’m hoping this post will be helpful to those trying to understand the issues and risks. I also want to encourage CTI to provide some insight on how to avoid these problems, or even better to make product fixes to address them.

My son and I have had three CTI 54 motor/case failures this summer out of 6 attempted flights, all at AeroPac launches in the Black Rock desert. In every case the failures occurred where the motor liner meets the forward closure. The first resulted in the rocket being destroyed. The other two were successful flights however the cases bulged and are no longer usable. I have heard CTI will replace products when they fail, however I’m hesitant to continue using their products when they fail at this rate. Details follow. If anyone has advice on what we should have done differently it would be appreciated.

Issue #1 CTI 5 Grain K650 Pink launched in a CTI 6 grain 54mm case with one CTI 54mm spacer. This was the second launch with this case, which was purchased in May 2020. The seal appears to have failed before motor burnout where the forward closure meets the liner, burning through the fiberglass lower rocket body and destroying our rocket (Wildman Punisher 3). This picture shows the pieces, including the top portion of the case, the spacer and the front closure.

View attachment 479265

Issue #2 CTI 4 Grain K630 Blue Streak launched in a CTI 5 grain 54mm case with one CTI 54mm spacer. This was the first launch with this case, which was purchased in July 2021. I added an extra O-ring to the forward closure and used WD-40 Silicone lubricant. The flight was successful however the case had a bulge near the front. The failure appears to be just below where the forward closure meets the liner. The liner is burned away however the O-rings on the forward closure appear intact.

View attachment 479261

View attachment 479262

Issue #3 CTI 6 Grain K820 Blue Streak launched in a CTI 6XL 54mm case with one CTI 54mm XL spacer. This was the second launch with this case, which was purchased in July 2021. I epoxied the forward closure into the liner and added an extra O-ring to the forward closure. I also used WD-40 Silicone lubricant. The flight was successful however the case had a bulge near the front. The failure appears to be in the forward closure just above where the forward closure meets the liner. The first O-ring is burned through but the second (higher) one I added is intact. The liner does not appear burned.

View attachment 479263

View attachment 479264

Obviously all three of our failures involved spacers, but I have not ready any suggestion that creates failure risk. Again, and insights appreciated.

Just trying to get my head around this...
Was the same spacer used on all three flights?
Can you measure the length of the 54mm spacers you have as this might be the only common piece of hardware used on the flights.

John Lyngdal
NAR Standards & Testing

 

[Cesaroni Technology]

We have been looking into the P54 failures, and testing some new ideas to hopefully fix the problem in the near future. Unfortunately we've been very busy and getting results is taking longer than expected.
As a note we have never instructed customers to glue the forward closure in place, although it seems to help it doesn't always work. Sealing the forward closure to the liner causes the liner to take the pressure from the motor, the liners aren't designed to hold that much pressure. In fact the original design had no small oring between the closure and liner, so that the gasses from inside the liner could egress between the liner and forward closure. I still think this is the key to the problem, but we need to test some more to come to a conclusion.
Our thanks to the rocketry community for all their patience and support of our products.

Bob.

 

[Banzai88]

In fact the original design had no small oring between the closure and liner, so that the gasses from inside the liner could egress between the liner and forward closure.

This has been the high incidence root failure mode that an additional o-ring and/or epoxy has been trying to prevent!

 

[Rocketjunkie]

I have flown quite a few 54-6GXL loads, mostly L265 and L935. I have never glued the closure and never had any problems.

 

[Steve Shannon]

We have been looking into the P54 failures, and testing some new ideas to hopefully fix the problem in the near future. Unfortunately we've been very busy and getting results is taking longer than expected.
As a note we have never instructed customers to glue the forward closure in place, although it seems to help it doesn't always work. Sealing the forward closure to the liner causes the liner to take the pressure from the motor, the liners aren't designed to hold that much pressure. In fact the original design had no small oring between the closure and liner, so that the gasses from inside the liner could egress between the liner and forward closure. I still think this is the key to the problem, but we need to test some more to come to a conclusion.
Our thanks to the rocketry community for all their patience and support of our products.

Bob.

Bob,
We also see a similar failure mode in 38 6g xl motors.

 

[JimJarvis50]

I started gluing in the closure way back when. 2014 maybe? I fly a lot of 54mm had have not had a problem since that time. I should say, however, that the other thing I always do is to heavily grease the outside of the liner. I don't think I've ever said that with respect to this method. I put enough on such that I have to clean off a pretty heavy glob of grease that gets scrapped off by the case when the reload is inserted. Maybe this is helpful in view of Bob's comment about the liner not being intended to support the pressure (i.e., the grease makes that less of a factor by filling the space for expansion).

Jim

 

[Steve Shannon]

We have been looking into the P54 failures, and testing some new ideas to hopefully fix the problem in the near future. Unfortunately we've been very busy and getting results is taking longer than expected.
As a note we have never instructed customers to glue the forward closure in place, although it seems to help it doesn't always work. Sealing the forward closure to the liner causes the liner to take the pressure from the motor, the liners aren't designed to hold that much pressure. In fact the original design had no small oring between the closure and liner, so that the gasses from inside the liner could egress between the liner and forward closure. I still think this is the key to the problem, but we need to test some more to come to a conclusion.
Our thanks to the rocketry community for all their patience and support of our products.

Bob.

Bob
It sounds as though you are acknowledging that a problem exists. Is that fair to say? If so, I really appreciate it.
Can you tell us some numbers and possibly which reloads it has appeared in? I think it would be good to warn our members and your customers.

 

[Cesaroni Technology]

I started gluing in the closure way back when. 2014 maybe? I fly a lot of 54mm had have not had a problem since that time. I should say, however, that the other thing I always do is to heavily grease the outside of the liner. I don't think I've ever said that with respect to this method. I put enough on such that I have to clean off a pretty heavy glob of grease that gets scrapped off by the case when the reload is inserted. Maybe this is helpful in view of Bob's comment about the liner not being intended to support the pressure (i.e., the grease makes that less of a factor by filling the space for expansion).

Jim

And also I think that filling in the gap between the liner and case with grease allows less gas to seep through the closure/liner.

 

[Cesaroni Technology]

Bob
It sounds as though you are acknowledging that a problem exists. Is that fair to say? If so, I really appreciate it.
Can you tell us some numbers and possibly which reloads it has appeared in? I think it would be good to warn our members and your customers.

Most of the issues seem to be in the 5 - 6XL range, but not limited to any one propellant.

 

[Bill Owens]

Just trying to get my head around this...
Was the same spacer used on all three flights?
Can you measure the length of the 54mm spacers you have as this might be the only common piece of hardware used on the flights.

John Lyngdal
NAR Standards & Testing

John - In our cases there were three different spacers. Two were normal 54 spacers, identical in length to two others I own - roughly 3 5/16". The third spacer was a 54 XL which is about 3.0". In all cases we made sure the spacer and motor were fully seated against the front of the case, and the aft end of the motor was flush with the case.

 

[Johnly]

Excellent information. Thank You!

John

 

[Handeman]

Just thinking out loud here. I have a 6GXL case and have flown 5G, 6G, and 6GXL motors in it. The first motor I flew was a 6GXL L935. The problem I had was getting the forward closure all the way into the motor. The grease put on the o-rings are insufficient to keep them lubricated as they slide the whole length of the motor case. Lubing the whole case is essential. I now use silicon spray and liberally spray the interior of the case before assembly.

I've had 6 flights on the case with various size motors and no problems so far. Maybe I'm just lucky, or maybe the generous silicon spray in the case allows the o-rings to slide the length and seat without nicks, scraps, or any damage. I have no clue if it that makes any difference, but any scrapes, etc. on the o-rings while sliding the length of the case might contribute to gasses getting buy and burning and bulging the cases.

Just an idea.

 

[Rocketless]

Just thinking out loud here. I have a 6GXL case and have flown 5G, 6G, and 6GXL motors in it. The first motor I flew was a 6GXL L935. The problem I had was getting the forward closure all the way into the motor. The grease put on the o-rings are insufficient to keep them lubricated as they slide the whole length of the motor case. Lubing the whole case is essential. I now use silicon spray and liberally spray the interior of the case before assembly.

I've had 6 flights on the case with various size motors and no problems so far. Maybe I'm just lucky, or maybe the generous silicon spray in the case allows the o-rings to slide the length and seat without nicks, scraps, or any damage. I have no clue if it that makes any difference, but any scrapes, etc. on the o-rings while sliding the length of the case might contribute to gasses getting buy and burning and bulging the cases.

Just an idea.

you might be on to something, it is a conundrum, epoxy vs silicone is a huge difference

 

[jd2cylman]

I was told by Jeroen years ago to use silicone spray liberally inside every case before assembly. Always have since then. But I've only flown one or two 54 6XL loads.
So, basically just agreeing with Handeman...

 

[DaHabes]

I was told by Jeroen years ago to use silicone spray liberally inside every case before assembly. Always have since then. But I've only flown one or two 54 6XL loads.
So, basically just agreeing with Handeman...

Who is Jeroen? If this person is a CTI person, then why in hell isn't this a part of the standard assembly instructions? Even if this isn't a CTI person, why isn't this a part of the standard assembly instructions.

Quite candidly, on the surface, CTI seems like a better design that AT, but given the issues I see posted here in the forum, I don't want to touch CTI with a 10 foot pole...

 

[tim cubbedge]

Who is Jeroen? If this person is a CTI person, then why in hell isn't this a part of the standard assembly instructions? Even if this isn't a CTI person, why isn't this a part of the standard assembly instructions.

Quite candidly, on the surface, CTI seems like a better design that AT, but given the issues I see posted here in the forum, I don't want to touch CTI with a 10 foot pole...

Yes. Jeroen was an employee of CTI and it clearly states the use of silicon spray in the instructions for motor assembly.

 

[DaHabes]

Yes. Jeroen was an employee of CTI and it clearly states the use of silicon spray in the instructions for motor assembly.

I just read the instructions. It "recommends" using silicone spray "on the casing edge". It doesn't require the lubricant nor does it say the entire length of the case. That is a significant difference.

 

[GregC]

Hi folks, I use CTI often and find it is often hard to slide a long motor into and out of a case. I have tried a little lubricant on the o-ring as previously mentioned, however it seems to rub off before reaching the end. I was intrigued by the above discussion and the recomendation to use silicone spray. A quick search on amazon and I find one. When I zoom into the picture of the can it says: Warning - Extremely flammable. Is it OK to put a flammable material between the motor and the casing? Seems risky. Thanks for your thoughts. Have a great day.

 

[Steve Shannon]

Hi folks, I use CTI often and find it is often hard to slide a long motor into and out of a case. I have tried a little lubricant on the o-ring as previously mentioned, however it seems to rub off before reaching the end. I was intrigued by the above discussion and the recomendation to use silicone spray. A quick search on amazon and I find one. When I zoom into the picture of the can it says: Warning - Extremely flammable. Is it OK to put a flammable material between the motor and the casing? Seems risky. Thanks for your thoughts. Have a great day.
View attachment 479593

The silicone isn’t the flammable part. It’s the propellant for the spray. After you’ve sprayed it on the highly flammable part quickly evaporates.

 

[Steve Shannon]

Who is Jeroen? If this person is a CTI person, then why in hell isn't this a part of the standard assembly instructions? Even if this isn't a CTI person, why isn't this a part of the standard assembly instructions.

Quite candidly, on the surface, CTI seems like a better design that AT, but given the issues I see posted here in the forum, I don't want to touch CTI with a 10 foot pole...

Mike,
Every motor company has occasional problems. I’ve used CTI since they first came out with the Pro38s. By and large they have been absolutely excellent. When there is a problem you see a flurry of activity online until there’s some resolution but that shouldn’t lead you to believe that all CTI products have problems or that their competition is perfect. I won’t hesitate to use CTI products, but I probably will avoid the 5, 6, and 6xl reloads in 38 and 54 mm sizes until CTI issues some kind of guidance.

 

[GregC]

The silicone isn’t the flammable part. It’s the propellant for the spray. After you’ve sprayed it on the highly flammable part quickly evaporates.

Thanks Steve, good point. Appreciate your reply.

 

[OverTheTop]

The silicone isn’t the flammable part. It’s the propellant for the spray.

Yep, the propellant is typically hydrocarbons these days.

FYI, keep silicone oil away from switches. It gets in and every time the switch is opened or closed there is a little arc. This little arc turns the silicon into silicon oxide, aka sand. If you want your switches to be reliable you need to keep silicone oil away from them. That stuff used to be banned in telephone exchanges and other places. I have a can on my desk and it is amazing the number of people asking what I have it for and how bad it is. I use it as an example of what not to use when having chemicals around the workplace. If it is on my desk I know nobody else will pull it out of the cupboard and use it. About the best use I can think of for it would be as tire black. Shines up your tires really nice, but don't use it on your dashboard.