Basically just cut off airframe just below the burnt glass, epoxy in a coupler tube and add new airframe. Haven’t really evaluated it yet but I’ve done it before on other rockets.
Small Bulge in rocket motor casing
- Thread starter mperegrinefalcon
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Basically just cut off airframe just below the burnt glass, epoxy in a coupler tube and add new airframe. Haven’t really evaluated it yet but I’ve done it before on other rockets.
BryRocket
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I’d just square cut the airframe as far forward as possible and then use an 8” piece of coupler to splice another airframe to it. Looks like 3” airframe. You could do 1.5-2 wraps of laminating carbon around the joint if you were worried (I wouldn’t I don’t think if you could get an 8” coupler). It’d hold. Will probably mess with the CG a little bit but could be managed.
I did this recently on my dads rocket that melted after a 38mm CTI FC failure (quantum tubing stinks when melted!). I was only able to get the coupler into the fincan area about 1.5” due to the forward centering ring and having to cut so much off. I did 3 wraps of CF over the joint and then sanded it down. We extended the airframe 3” from what it was to account for the extra aft weight and maintain a desirable CG. He pushed that rocket hard again at LDRS on a J to 6200+’. Nice to see them fly again.
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Thanks. Once I got your replies I realized my brain fart......for some silly reason I had though that you were talking about the CASE. Now I'm back on track!
Cory
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WELL DARN! At least it didn't blow up the Ultimate Darkstar, but what a shame about the case.I posted up about this on another thread, but it's relevant to this one too.
I spent a couple hours removing a 98mm 6XL casing from my Ultimate Darkstar today. Flew it to 21,000 ft. at LDRS 38 Sunday on an O3400.
I kinda knew what I would find, a small bubble at the top of the casing:
After I yanked and twisted it half way out, I resorted to a long piece of 2" PVC pipe and a sledge hammer. Now I have a swollen knuckle and a brand new GEN 2 casing I will never use again.
tOD
Sinking in the quicksand of HPR
Just came upon this thread after buying a Pro54 starter set. My experience with CTI so far is limited to a few 24's. I haven't purchased a motor for any of the cases yet. Are they different than the 24?
I opened up the CTI 98 6XL casing this morning while it was relatively cool in the garage. Nytrunner had some questions about this failure, and I wanted to document what I found here on this thread.
No problem removing the forward closure, which showed where the hotspot was with a slightly eaten O-ring:
No blow by evident at the seal disk, but some erosion and a small deposit of molten metal:
Not sure if that's where the damage occurred, it might be on the left.
The liner looks OK in this shot, I indexed where the damage occurred with a black line on the threads:
It took a bit of work to get the liner up to where you can see the hotspot:
I filed a MESS report and sent an email to CTI, but their contact info must be dated, because the email bounced and when I tried the phone # on their webpage I talked to some retired guy living in Quebec that had never heard of CTI.
I also sent an email to Wildman, so hopefully there will be a warranty replacement in the future.
No problem removing the forward closure, which showed where the hotspot was with a slightly eaten O-ring:
No blow by evident at the seal disk, but some erosion and a small deposit of molten metal:
Not sure if that's where the damage occurred, it might be on the left.
The liner looks OK in this shot, I indexed where the damage occurred with a black line on the threads:
It took a bit of work to get the liner up to where you can see the hotspot:
I filed a MESS report and sent an email to CTI, but their contact info must be dated, because the email bounced and when I tried the phone # on their webpage I talked to some retired guy living in Quebec that had never heard of CTI.
I also sent an email to Wildman, so hopefully there will be a warranty replacement in the future.
ECayemberg
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I wish CTI would implement the use of the forward seal disk like AT has. I use the AT disk with CTI 75 and 98 loads, as it seals better than the provided CTI fiber washer. I too have suffered the blistered case syndrome in the past (with a 75 CTI load). I'm sure they'll make good on replacement....
BryRocket
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You use the AT seal disks instead of the black fiber washer in your CTI cases? That’s interesting and seems like it could be a good idea.
Nytrunner
Pop lugs, not drugs
Which glue did y'all use when bonding the grains to the liner?
Wondering if it was liner failure for some reason, or gas escape past the bonded plastic disk.
May warrant some extra epoxy/grease application at the joint similar to the forward closure treatment for long Pro54s JimJarvis and others recommend (I use it too just in case)
ECayemberg
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Yes. Not necessarily required or endorsed by CTI (yet), but a good safety measure. Much like epoxying the forward bulkhead on the 54 loads...unwritten but a good idea.
It appears that gas escaped past the disk. You can see in Wayne's photo where the liner is A) charred on the outside...never a good thing and B), the forward edge of the liner appears to be chewed down a bit on the hotspot side...shows a very shallow V-shape where the hot gasses escaped. Plus the damaged silicone o-ring indicates the issue was at the very top of the liner/washer interface.
Regardless, great flight Wayne! Even if we had to wait out at the 80's for a while for the clouds to pass!!!
I would suggest that NO ONE use this contact info. The retired guy seemed nice enough, but if we all called him, he might not stay that way. Feel free to try the email, maybe your results will be different.
The stepped disk was already bonded at the factory, I wouldn't try to supplement it down a 4 ft. liner.
We used the supplied glue, which I think is R45 and a curative with plenty of work time.
It might have been gas escaping by the lip of the liner, hard to tell from the evidence I found. The liner was pretty charred at the site of the damage. Could have just leaked through the cracks.
We greased the liner with Superlube and slid it in from the nozzle end, so maybe next time apply more grease at the top? That might help. Not sure I will fly this load again....
My last information was that all CTI warranty claims should be filed with their dealers, not through CTI itself. I believe that’s still valid. It doesn’t necessarily have to be the dealer you bought the case or reload from. The other side of the coin is that CTI has been slow to reimburse their dealers.
Nytrunner
Pop lugs, not drugs
Interesting. Nick@Jet and his motor builder used west systems epoxy for grain bonding when he flew his Ultimate QCC
I've recently had a similar issue with a CTI Pro24 6G reload which burned through the liner at the top/fwd closure (which was fitted with an O-ring). The resulting "flaming death" caused a loss of the airframe, melted recovery gear and a brand new Jolly Logic chute release device toasted and lost in a field on it's maiden flight.
I filed a MESS report. However, when I also try to report it directly to CTI on their contacts page, the email just bounces back. The motor batch was Dec 2010.
I've since re-used the fin-can and nose cone which both survived to rebuild, but I'm disappointed to now read that there are many other fellow fliers who seem to be suffering similar issues across a range of CTI ProX reloads. I'll follow the advice and start using epoxy at the fwd enclosure.
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I filed a MESS report. However, when I also try to report it directly to CTI on their contacts page, the email just bounces back. The motor batch was Dec 2010.
I've since re-used the fin-can and nose cone which both survived to rebuild, but I'm disappointed to now read that there are many other fellow fliers who seem to be suffering similar issues across a range of CTI ProX reloads. I'll follow the advice and start using epoxy at the fwd enclosure.
.
Last two photos of the failed reload. Batch Dec 23 2010
Did a coupler repair on a Formula 54 that had a forward blowout with an H250 Mohave Green motor. The motor casing is above. The Kevlar cord was opposite the blowout and was in good shape. I knew I was in trouble when I saw two green flames coming from the rocket, one aft out the nozzle and one out the side. Didn’t have quite enough altitude for the JL chute release to get the chute out. It did its job but too low to fill the chute. Rocket and EggFinder nosecone tracker survived and I inserted an endoscope to inspect the Kevlar cord that is epoxied into the motor mount in this small rocket. It was in good shape as the flames came out at 180 degrees. Rocket has flown several times since then nominally. I had to take a brush, soap and hose to get the detritus of combustion out of the rocket so the fiberglass coupler could be slid down the tube. I masked and did a a metallic black paint job on the coupler. Always a conversation starter at the RSO table.For the rocket in message #54 above, chop it off and do a coupler repair. That will salvage it. If the harness was epoxied into the motor mount, it looks like it was burned off. In that case, there are some remedies posted here on TRF for that exact situation. I believe Jim Hendricksen had posted a technique to restore a rocket in that same situation. Kurt Savegnago
Dang this iPad does nice, detailed pictures. Never had an Apple device before. Kurt
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The last 3 CTI motors that I've burned, 1-29 and 2-38s, have all had near failures that looked JUST LIKE THAT. Time span on manufacture across all 3 motors is nearly 3 years. Something ain't right here.
mperegrinefalcon
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Yeah, I had gotten a 1 grain 38 CTI case from the dealer that came to the launches near me that was about 1/4" too short for a motor. The motor then fit into a 3 grain case with 2 spacers and worked. The other 1 grain case they had also had the same issue. It was really bizarre. The quality control seems to be slacking.
