Small Bulge in rocket motor casing

[mperegrinefalcon]

I have a CTI 54mm 6xl grain case and I noticed that it has a small but noticeable bulge in the upper portion of the case on one side. It is approximately 1 inch long, and only 1 or 2 mm at it's highest point. I was wondering if this would be safe to launch with or if I should just get a new case. I got the case used with a large bundle that was a steal, and the guy I got it from used it 15 times.

Thanks for any help!

 

[tim cubbedge]

Funny you mention this. I had same problem about a month ago with an L730. The small oring burned thru and also created a bulge. Took it to vendor and he gave me a new one on the spot!

 

[mperegrinefalcon]

I know the vendor this casing was bought from, but as I didn't buy it from him, and with the amount it's been used I don't think it would be replaced for free, I'm just wondering if it's safe to use.

 

[MClark]

Don't use it.
See if the vendor will replace it. Even if you must buy a new one the cost is far less than incinerating your airframe.

 

[mperegrinefalcon]

okay, that's what I was thinking. Thanks for the comment!

 

[ksaves2]

Ditto,

You fly it and it might burn through. Follow the sages above advice and don't fly it. As long as you've run their commercial propellant through it, see if they'll
help you out. I've run research propellant through an AT case and the threads stripped out due to repeated heat loading. I just bought another case as
I was knew danged well I was going out of bounds on my own. Plus AT courteously publishes the plans of their motors so one can clone them with their
own propellant (and AT's parts) I go there it's my risk. Kurt

 

[G_T]

I'd go so far as to say if you try to fly it, it will most likely crack the liner at the bulge during pressurization. Followd rather quickly by a CATO.

Gerald

 

[JimJarvis50]

This is a known problem, caused by a failure of the seal where the O-ring is (just as in the picture in Post #2). The problem can cause a bulge in the case, or sometimes, a failure of the case around the circumference of the case where the bulge is. I always glue in the forward closure on Pro54 motors, just going over the O-ring if one is present, trying to create a fillet between the bottom of the closure and the top of the grains. The idea is just to buy a few tenths of a second more so that the case doesn't fail. Many people do this now. I have not seen a failure of a motor prepared this way.

Jim

 

[H_Rocket]

I wonder if you could safely use it with a spacer and keep the actual hot parts away from the weakened spot.

 

[RainierWolfcastle]

This is a known problem, caused by a failure of the seal where the O-ring is (just as in the picture in Post #2). The problem can cause a bulge in the case, or sometimes, a failure of the case around the circumference of the case where the bulge is. I always glue in the forward closure on Pro54 motors, just going over the O-ring if one is present, trying to create a fillet between the bottom of the closure and the top of the grains. The idea is just to buy a few tenths of a second more so that the case doesn't fail. Many people do this now. I have not seen a failure of a motor prepared this way.

Jim

Do you just use the same glue you would use for gluing grains normally or is something else better for this?

 

[tim cubbedge]

This is a known problem, caused by a failure of the seal where the O-ring is (just as in the picture in Post #2). The problem can cause a bulge in the case, or sometimes, a failure of the case around the circumference of the case where the bulge is. I always glue in the forward closure on Pro54 motors, just going over the O-ring if one is present, trying to create a fillet between the bottom of the closure and the top of the grains. The idea is just to buy a few tenths of a second more so that the case doesn't fail. Many people do this now. I have not seen a failure of a motor prepared this way.

Jim

Jim do you have any pics how you do this?

 

[JimJarvis50]

Jim do you have any pics how you do this?

I put together the attached pic a while back. The thing to do it to just put a layer of epoxy around the top of the tube and then the fillet gets formed when you push in the closure. In a pinch, I've seen this done with 5 minute epoxy.

Jim

 

[tim cubbedge]

I put together the attached pic a while back. The thing to do it to just put a layer of epoxy around the top of the tube and then the fillet gets formed when you push in the closure. In a pinch, I've seen this done with 5 minute epoxy.

Jim

Got it. Thanks Jim.

 

[Binder Design]

Don't use it.
See if the vendor will replace it. Even if you must buy a new one the cost is far less than incinerating your airframe.

+1 If it's bulged, it's for sure annealed (weakened). Even if you used a spacer grain to keep from further heating it, it could still tear that end of the motor off.

 

[mperegrinefalcon]

I put together the attached pic a while back. The thing to do it to just put a layer of epoxy around the top of the tube and then the fillet gets formed when you push in the closure. In a pinch, I've seen this done with 5 minute epoxy.

Jim

Couldn't you do this with using a grease like super lube?

 

[blackjack2564]

No....grease will melt and allow hot gas to escape from liner. You must seal it with epoxy, even 5 minute will do.
I have been doing this on ALL 54 CTI's 4 grain & over. I just wait till I'm gluing something in a build and do several motors with left over.

Now most , if not all [I haven't checked] forward closures have an O-ring in the lower part that fits inside liner to seal it. Much like the seal disc AT uses, CTI just builds it into closure.BUT there are a ton of reloads out there from before the "fix". You must move closure to inspect Or know the date code of change over...which I do not.

I just sleep better after putting 10 cents worth of epoxy on base of those closures, after seeing many,and being one that has lost a project.

 

[mperegrinefalcon]

No....grease will melt and allow hot gas to escape from liner. You must seal it with epoxy, even 5 minute will do.
I have been doing this on ALL 54 CTI's 4 grain & over. I just wait till I'm gluing something in a build and do several motors with left over.

Now most , if not all [I haven't checked] forward closures have an O-ring in the lower part that fits inside liner to seal it. Much like the seal disc AT uses, CTI just builds it into closure.BUT there are a ton of reloads out there from before the "fix". You must move closure to inspect Or know the date code of change over...which I do not.

I just sleep better after putting 10 cents worth of epoxy on base of those closures, after seeing many,and being one that has lost a project.

I just epoxied the FC of my L935. I used the epoxy i felt most suitable for it that i had on hand was my west systems 105/206. The rocket poxy i didnt think would be the best and neither would the JB weld.

 

[JimJarvis50]

Now most , if not all [I haven't checked] forward closures have an O-ring in the lower part that fits inside liner to seal it. Much like the seal disc AT uses, CTI just builds it into closure.

One of the failures that I had was where the closure had the O-ring. I glue them all.

Jim

 

[Steve Shannon]

In April one of our flyers had a forward closure failure on a Pro38. Not the type of failure that the recall covered (in fact the flyer was provided a new forward closure to replace the one in the package), but one I would assume was caused by the sort of o-ring seal failure mentioned above for the Pro54s. The forward end of the 6xl case was damaged, the forward end of the liner was burned off, and we didn’t find the closure. Tomorrow I’ll add a picture.


I filed the MESS report and he submitted for warranty replacement.

 

[mperegrinefalcon]

In April one of our flyers had a forward closure failure on a Pro38. Not the type of failure that the recall covered (in fact the flyer was provided a new forward closure to replace the one in the package), but one I would assume was caused by the sort of o-ring seal failure mentioned above for the Pro54s. The forward end of the 6xl case was burned off and we didn’t find the closure. Tomorrow I’ll add a picture.

I filed the MESS report and he submitted for warranty replacement.

So as i understand it the warranty with cti is through the vendor that sells the motor correct?

If a motor fails and destroys a casing would cti replace the motor and casing, just the motor or just the casing?

I find waranties on rocket motors rather confusing...

I saw a pro54 casing have the entire forward closure blow and it tore the front end of the case off. I believe it was a 5 grain casing but i couldnt tell because 1) it was in the trash bin 2) i had no idea how much of the case was ripped off. The entire front end was blown out. The flames shot through both ends of the case, so it destroyed everything in the rocket and the fiberglass itself.

 

[blackjack2564]

One of the failures that I had was where the closure had the O-ring. I glue them all.

Jim

So do I.....makes me sleep better.
Guess I should have mentioned that.

Generally manufacturer will replace BOTH cases/closures & reload, through the vendor you purchased it from.

 

[Wayco]

I had this happen at LDRS, flying an L640 dual thrust. The case didn't fail, but the bulge made it very difficult to remove from the MMT. Wildman replaced the case, but since the reload worked fine, I didn't get it replaced. The second flight was also with an L640, with some 5 minute epoxy at the top of the forward grain. Worked fine, no damage to the new case.
I haven't seen the modification that CJ talks about above, but all of my reloads are older, haven't seen any L640's for sale since the CTI incident.

 

[woferry]

I had the worse version of this happen at LDRS, K300C in the Pro54-6GXL casing. Reload was from DEC 06 2017, so pretty recent, but no O-ring in the liner section, just the single casing O-ring above. Didn't know anything about this suggestion (seems like it would be a modification to the motor and against the manufacturer's recommendations which said nothing about adding any glue), so I flew the motor like I have every other CTI Pro54 I've flown (this was my first load longer than a 4G, though, bought the 6GXL casing the same time as the load), and this was the result (after hammering the case & MMT out of the rocket):



So the rocket separated 1-2 seconds into the burn when the casing failed, thankfully the motor blew itself out at that point (you can tell by the weight that most of the propellant is still in the motor), so while it separated the rocket prematurely and broke my shock cord, the upper part of the rocket landed safely (though drifting far away) and all of my electronics were recovered, the lower part of the rocket was totally destroyed since it fell chuteless from a few thousand feet. Case was replaced on-site, load will apparently be a part of CTI's next delivery to AMW, so I'll have to see how that works.

 

[jqavins]

Don't use it.
See if the vendor will replace it. Even if you must buy a new one the cost is far less than incinerating your airframe.

And the same goes for any other damage beyond cosmetic scratches. If it's damaged, don't use it.

 

[kjkcolorado]

Well, I’m a few days too late to have seen this thread. Flew a CTI K260 long burn this past weekend. Everything looked nominal with the flight. Recovered and returned to camp only to find I couldn’t pull my 6 grain case out of the rocket. Removed the rear closure and slid it out from the top to find a substantial bulge in the case between 1-2” from the end. Sorry, no pics. Vendor swapped me out immediately on the spot.

One, I feel lucky nothing ‘blew’. Two, I’m happy this didn’t happen in the other rocket I had that can fit long 54s.... it has a zipperless coupler. Would have had to cut it out. A fellow flyer saw the bulged case and mentioned he had read about this problem on the forum and also mentioned using epoxy to glue in the forward closure. I haven’t flown many 4+ grain 54s yet. Glad I know about this now!

 

[Steve Shannon]

Well, I’m a few days too late to have seen this thread. Flew a CTI K260 long burn this past weekend. Everything looked nominal with the flight. Recovered and returned to camp only to find I couldn’t pull my 6 grain case out of the rocket. Removed the rear closure and slid it out from the top to find a substantial bulge in the case between 1-2” from the end. Sorry, no pics. Vendor swapped me out immediately on the spot.

One, I feel lucky nothing ‘blew’. Two, I’m happy this didn’t happen in the other rocket I had that can fit long 54s.... it has a zipperless coupler. Would have had to cut it out. A fellow flyer saw the bulged case and mentioned he had read about this problem on the forum and also mentioned using epoxy to glue in the forward closure. I haven’t flown many 4+ grain 54s yet. Glad I know about this now!

Please be sure to file a MESS report if you haven’t already.
www.motorcato.org

 

[Wayco]

Please be sure to file a MESS report if you haven’t already.
www.motorcato.org

I never even considered doing this, the motor performed normally. Could this be why CTI has not addressed this problem?

 

[tim cubbedge]

I never even considered doing this, the motor performed normally. Could this be why CTI has not addressed this problem?

Ummmmmm....considering the bulge was due to the seal ring burning through, I hardly consider that normal!?

 

[Steve Shannon]

I never even considered doing this, the motor performed normally. Could this be why CTI has not addressed this problem?

It should not be. The manufacturers have to replace cases; that should be a tip-off to them.
It’s unfortunate that the MESS reports are filed at “motorcato.org” because that could lead people to believe only catos should be reported, but we want to learn about problems with instructions, delays, damaged cases, etc. Anything that could be improved or that should come to the attention of the certification authorities. Even things that flyers do wrong may help us avoid a problem on a range.

 

[Wayco]

• CATO, an acronym used in rocketry, for Catastrophe At Take Off—the catastrophic failure of a rocket engine.
• The Malfunctioning Engine Statistical Survey (MESS)

There was no catastrophe, and the motor did not malfunction. It operated nominally throughout the flight.

It should not be. The manufacturers have to replace cases; that should be a tip-off to them.
It’s unfortunate that the MESS reports are filed at “motorcato.org” because that could lead people to believe only catos should be reported, but we want to learn about problems with instructions, delays, damaged cases, etc. Anything that could be improved or that should come to the attention of the certification authorities. Even things that flyers do wrong may help us avoid a problem on a range.

I went to the motorcato site and looked at what they wanted. It was all about motor malfunctions. No mention about problems with instructions. If I had a problem understanding instructions, I would post up here on TRF.
Problems with delays? Use an altimeter.
There are only six items addressed in the "Manufacture Notifications and Modification Announcements" since 2011. Maybe if everyone reported this to MESS, CTI would announce a modification? Since CTI has been aware of this problem for years now, and all they have done is add an O-ring, (Which doesn't seem to fix the problem) the only way to fix it would be to get the word out, either by word of mouth, or on the forums.
In the hope that someday, CTI will announce a modification, I filed a MESS report, but the skeptical side of me thinks that even it that happens, how many people will read about it on the motorcato site?
This thread has a much better chance of dealing with the problem.