G138 Cato Destroyed my rocket.

[Zyzzyva1000]

I know it happens, but this particularly bummed me out. Built a LaserLoc 163, modified it for dual deploy with a nice ebay and added GPS tracking in the nosecone. Finished it nicely and was ready for its maiden launch this past weekend. Before I tried it on a 38 mm motor I wanted to just make sure everything worked. I had a G138T reload that I had purchased on a whim during a Hazmat order and figured that would do the job. Unfortunately I was not aware of this reload's somewhat sordid history.

Rocket blew apart on launch, big hole through the side of the motor casing and trashed the booster section of the rocket (irreparable). I have emailed AT, hopefully they will stand behind their product. Luckily my electronics were undamaged. Just lots and lots of hours down the drain, and lots of disappointment. I guess I need to just stick to 38 and 54 mm, because I have never had a CATO that was a 29 mm load (this is now the third).

 

[Antares JS]

What's this about the G138T having a sordid history? I haven't heard about this.

 

[Zyzzyva1000]

Search results for query: g138 cato
Someone in my local group mentioned this after I posted on our group. Apparently this is a known problem (That I definitely was not aware of)

 

[AeroTech]

What's this about the G138T having a sordid history? I haven't heard about this.

I haven't either.

 

[Antares JS]

I haven't either.

I mean, I just flew one and it was fine. I was a little surprised at the lack of a separate liner tube, but figured Aerotech knew what they were doing.

 

[AeroTech]

I mean, I just flew one and it was fine. I was a little surprised at the lack of a separate liner tube, but figured Aerotech knew what they were doing.

Motor was designed for maximum propellant weight and performance. Karl says it’s been a year since he heard of a failure with one.

 

[Zyzzyva1000]

Well I guess I just got unlucky. I fly tons and tons of reloads through my 40-120 motors. I just thought it was strange that someone else from my group immediately knew what reload it was without me saying anything. And then when you look here, one of the first threads that comes up is 'what motors have the most CATOs'. Just frustrating because that was a lot of time and money down the drain.

 

[Zyzzyva1000]

I mean, I just flew one and it was fine. I was a little surprised at the lack of a separate liner tube, but figured Aerotech knew what they were doing.

I was surprised by this too but the instructions were clear, and no matter how many times I do this I still lay out the instructions, put the o-rings over the printed o-rings and triple check to make sure everything matches the drawings.

 

[samb]

@Zyzzyva1000 I'm agree, not a widespread well known issue. You have this from Mr. Aerotech so send them all your info and pictures. Then slap some duck tape on the Laserloc and get back on the horse.

 

[waltr]

Interesting your Cato is the only one in MESS. Which is probably why AT says they haven't heard of it.

TRF threads on G138 Cato/damage:
https://www.rocketryforum.com/threads/g138t-blistered-case.121649/https://www.rocketryforum.com/threads/motor-reloads-with-the-most-catos.147146/page-2#post-1817679https://www.rocketryforum.com/threads/g138t-claims-another-case.128085/https://www.rocketryforum.com/threads/aerotech-case-blistering.133802/#post-1577511

I have read about G138's cato'ing paticularly the upper case burn-through. There is a club news letter with a good article on this load and case and how to reliably install the G138 load.
Found the article I mentioned above. It really covers details that are missing from AT's instructions and worth a read.
Link part 1:
http://cv41.org/newsletters/V17I5.pdf
Page 8.
Part 2: http://cv41.org/newsletters/V18I1.pdf

The Failure looks to be due to the forward O-ring not sealing and combustion gases getting past the O-ring to the case.
A few things need to be check when building the motor.
1- The liner easily slides into the case. If it does not then the Fwd O-ring will not compress properly and will leak.
2- Grease the case before installing the propellant grain (liner). The grease helps to insulate the grain burn from the aluminum case. The grease also helps with #1.

 

[Zyzzyva1000]

@Zyzzyva1000 I'm agree, not a widespread well known issue. You have this from Mr. Aerotech so send them all your info and pictures. Then slap some duck tape on the Laserloc and get back on the horse.

View attachment 557486

Burned out the inside of the body tube and melted some of the fiberglass over the fins. Already sent Karl the info. Should have just thrown an I180 in there. Oh well, you live and you learn. I enjoy the building process (my wife thinks I am nuts though)

 

[Zyzzyva1000]

Interesting your Cato is the only one in MESS. Which is probably why AT says they haven't heard of it.

TRF threads on G138 Cato/damage:
https://www.rocketryforum.com/threads/g138t-blistered-case.121649/https://www.rocketryforum.com/threads/motor-reloads-with-the-most-catos.147146/page-2#post-1817679https://www.rocketryforum.com/threads/g138t-claims-another-case.128085/https://www.rocketryforum.com/threads/aerotech-case-blistering.133802/#post-1577511

I have read about G138's cato'ing paticularly the upper case burn-through. There is a club news letter with a good article on this load and case and how to reliably install the G138 load.
Found the article I mentioned above. It really covers details that are missing from AT's instructions and worth a read.
Link part 1:
http://cv41.org/newsletters/V17I5.pdf
Page 8.
Part 2: http://cv41.org/newsletters/V18I1.pdf

The Failure looks to be due to the forward O-ring not sealing and combustion gases getting past the O-ring to the case.
A few things need to be check when building the motor.
1- The liner easily slides into the case. If it does not then the Fwd O-ring will not compress properly and will leak.
2- Grease the case before installing the propellant grain (liner). The grease helps to insulate the grain burn from the aluminum case. The grease also helps with #1

 

[samb]

Whoops. Threads from 2015,16,17 and the documentation in the newsletters are something. Maybe use of the G138 has declined since then. Anyway cato's suck and I hope you get some love from Aerotech @Zyzzyva1000.

 

[green dragon]

That's a simple fix. Did same on a NCR Phantom 4000 HD that had a 54mm mount, burn through on a 38 .

Glue the 29mm adapter in, then fill the hole with a scrap piece of cardboard / tubing... fill and sand, repaint - good to go, although no longer 38mm

see photo, just at the rightside fin, where it's been patched. can't see it when on the pad

 

[waltr]

Yea, Cato's do suck and I don't like seeing them even when it is not my rocket.
I didn't try the G138 due to cato reports and can't fly it (over 80N avg thrust) at local club field and it's Hazmat shipping.
I'm now L1 so just moved to AT 29 & 38 RMS cases for HP.
I do have and fly the 29/40-120 cases a lot but with the other G reloads.

I also think the rocket is repairable.
A wax paper lined 38mm case or tube can be put into the MMT then some epoxy through the hole.
This should fix the MMT. A simple patch on the outside and some paint like Green Dragon's and it'll be good to fly.

Now that it has a patch all flights will go perfectly.

 

[Handeman]

After the first flight of a G138 I found that the case wasn't "blistered" but there was definitely a hot spot on the case near the forward end. I figured I got lucky. With the reports on here, it was the last G138 I ever flew. That was a number of years ago.

 

[Zyzzyva1000]

I have repaired burn through a before (even have some nice fiberglass tape I use). Unfortunately the cardboard 29 mm motor adapter caught fire and burned quite a bit of the tube on the inside. Whole thing doesn’t feel like it will be stable even if repaired. Luckily not a super expensive kit, and I already have the addons (extra body tubing, ebay and modified nose cone setup). So likely I will just build a new one and then use the nosecone, some 38 to 29 mm centering rings and 3d print a fin can and end up with a baby laser loc as well. The part that is most frustrating is this was probably the nicest looking rocket I had made. Oh well. Just need to get it done before planting time so I can go fly it at the other nearby club that has a 12k waiver (plan was to do that this weekend after this test flight)

 

[rharshberger]

I have seen many G138T's flown with zero issues, but every once (maybe 2 or 3 times in the last 4-5 years) in a while a case gets discolored right where your burn through was, and once one CATO'd just like yours iirc. TBH a motor with that much propellant and that little thermal protection its a wonder they are so reliable.

 

[cls]

G138s occasionally snuff the delay grain. I lost an AT Warthog, first flight, that way. But when they do work, wow, great! And good flame color, best of the 29/120s.

 

[StreuB1]

I've flown the G138T many times, I have about 7 in the motor box. Never once had an issue with them nor have I heard anything bad about them. They're one of my favorite reloads TBH.

By chance was it assembled incorrectly? Looks like it failed at the upper o-ring/disc.

 

[Zyzzyva1000]

I've flown the G138T many times, I have about 7 in the motor box. Never once had an issue with them nor have I heard anything bad about them. They're one of my favorite reloads TBH.

 

[Theory]

very sorry to hear about the issue with your flight

have flown many G138's and always assemble with the wrap of tape on the forward end of the grain. no doubt this motor takes the 29 40-120 case to the edge, however work well.

do you remember how the closures went on, was there the typical "snug fit" feeling as the closures were tighten or did the tighten very easily?

 

[Zyzzyva1000]

very sorry to hear about the issue with your flight

have flown many G138's and always assemble with the wrap of tape on the forward end of the grain. no doubt this motor takes the 29 40-120 case to the edge, however work well.

.

 

[rharshberger]

Honestly can't remember. The part that annoys me is that there is nothing in the instructions that mention this (or the extra from the newsletter that were posted above). If this is needed for a safe flight, why is it not included in the official instructions? I understand these things can be finicky, but I guess I will have to search the forum for every new reload I try since I had no idea that following the official instructions is apparently not enough (and nobody else that comes to our regular launches flys the 40-120 system regularly, so I have nobody else to get information from)

The G138 is not any more or less "finicky" than any other reload for that case.

If its not found in the reloads instructions, and AeroTech hasn't put out a PSA on it then any additional steps are someones opinion.

 

[Neutronium95]

The G138 is not any more or less "finicky" than any other reload for that case.

If its not found in the reloads instructions, and AeroTech hasn't put out a PSA on it then any additional steps are someones opinion.

Aerotech did put out an instructional video on how to assemble the G138, and it says to tape the forward end of the grain. If it isn't in the reload instructions, then that should probably be fixed.

 

[rharshberger]

Aerotech did put out an instructional video on how to assemble the G138, and it says to tape the forward end of the grain. If it isn't in the reload instructions, then that should probably be fixed.

I concur.

 

[dpower]

This is a critical part of the assembly for this particular reload:

 

[Zyzzyva1000]

Aerotech did put out an instructional video on how to assemble the G138, and it says to tape the forward end of the grain. If it isn't in the reload instructions, then that should probably be fixed.

Just checked the printed instructions that were in the reload, does not mention to tape the forward end of the grain (though apparently this has been known for 7+ years). But clearly posting anything about this was a mistake. All I found out what that I was supposed to know extra instructions that aren't included.

 

[samb]

Sorry Z not seeing any negativity directed at you here. Like I said, catos suck and I expect Aerotech to step up for you. I couldn't find any link to the instructional video anywhere. It appears to me that the tape around the grain is the missing piece.

 

[Zyzzyva1000]

It hurts to lose the rocket. But lots of replies telling me Im wrong, there's no issues with this reload, must have done something wrong. When as it turns out there is a missing piece to this that is in a video and not in the printed instructions. And I can't even delete the thread or my replies because apparently that's 'against the rules'. This is why I got out of rocketry before and looks to be where I am heading again. Feels like going to the hobby shop and having some old men look down on me again.