Update from Aerotech..was Need help..My first truly catastrophic CATO

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jhein

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R.I.P. Mega Der RedMax 6/20/14

Today was a beautiful morning to fly my Mega RM! First flight was on a AT G76-4 Green motor. Beautiful flight to 800ft, according to Altimeter 2. The second flight was on a G64-7 White Lightning drilled out to a 4 second delay. Little did I know that this would be its last.

The motor ignited and the rocket lifted off the pad about two inches and then BOOM!. The nose cone ejected on the pad and the motor casing (what was left of it) shot out the bottom with a shotgun blast. Thankfully both grains self extinguished The force was so great my AT Mantis pad broke one of its plastic leg mounts and the entire pad fell over.

I attached some pictures to see if the TRF hive collective can help me analyze what went wrong. I gathered up the debris to do a post mortem. The case failed immediately below the forward closure. The failure is so perfect, you would think it was cut off with a hack saw. I suspect black powder leakage but I am not sure. The red cap is still on and most of the BP seems to be there. The outside of RM is intact but the motor mount tube is totally shot, only about 3 inches of it left.

I have filed a MESS report already. The case is less than a year old so AT should warranty it and the reload. What about the rocket and the pad? Do I add them to the spare parts pile?

Thanks
Jim
Cato-3.jpgCato-2.jpgCato-1.jpgCato-5.jpgCato-8.jpgCato-9.jpg
 
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did you have the grain slots lined up and the igniter all the way up to the top of the motor ?
 
Well, the delay didn't even really get burning so I don't think it's a BP issue. Looks like the grains didn't burn much either.

It overpressurized, and fast. What ignitor did you use, did you vent the cap on the nozzle, and whats the nozzle look like right now? Is anything plugging it/did you cut out all the flashing?

That's some crazy destruction to the liner for as little of the grains that are burned. If you pull the remaining grain out of the liner, what's it look like? I'm suspecting a clogged nozzle, but not sure.

The case is designed to fail like that, rather than shreading itself, hence the clean cut look.

edit: oh and that DRM is totally fixable :)
 
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Have you contacted AeroTech support? Also, have you filed a motor failure report?

There are numerous things that could be the cause, from a plugged nozzle, to an incorrect nozzle, to a bad grain....the ones best equipped to help you are at AeroTech, as they know their motors the best.

-Kevin
 
Aerotech will (eventually) warranty the case and reload, assuming that there was no obvious user error (which there doesn't seem to be). The rocket is a loss - they will NOT warranty an Estes rocket but as David said, that is totally repairable. The pad....they might, they might not. I am leaning towards not, but you never know.

Hopefully Aerotech has improved their customer service. I have had 2 failures (2 completely separate 24/40 incidents) and it took a lot of nagging for them to send the promised warrantied part. In fact, with one of them I just gave up because they became non-responsive. I can say that this encouraged me to look elsewhere for my motor needs, but I do enjoy torturing 24mm rockets with some White Lightning (that is, when I can get it to light up).

Sorry for the loss. I hope that your experience is far better than mine.
 
Was the forward O-ring installed / seated? Looks like a blow torch cut right where that O ring would be?
 
With that kind of perfect failure of the metal casing i wouold suspect a manufacturing (machining) defect where it was cut a bit too deep where the threads run-out or a small crack developed that grew with pressure cycles and eventually failed.

Generally, if the closures are threaded on properly, and there is an overpressurization, you blow out the aft closure/nozzle or sometimes fail the casing out the side, but that would be a lengthwise split.


jhein said:
R.I.P. Mega Der RedMax 6/20/14

Today was a beautiful morning to fly my Mega RM! First flight was on a AT G76-4 Green motor. Beautiful flight to 800ft, according to Altimeter 2. The second flight was on a G64-7 White Lightning drilled out to a 4 second delay. Little did I know that this would be its last.

The motor ignited and the rocket lifted off the pad about two inches and then BOOM!. The nose cone ejected on the pad and the motor casing (what was left of it) shot out the bottom with a shotgun blast. Thankfully both grains self extinguished The force was so great my AT Mantis pad broke one of its plastic leg mounts and the entire pad fell over.

I attached some pictures to see if the TRF hive collective can help me analyze what went wrong. I gathered up the debris to do a post mortem. The case failed immediately below the forward closure. The failure is so perfect, you would think it was cut off with a hack saw. I suspect black powder leakage but I am not sure. The red cap is still on and most of the BP seems to be there. The outside of RM is intact but the motor mount tube is totally shot, only about 3 inches of it left.

I have filed a MESS report already. The case is less than a year old so AT should warranty it and the reload. What about the rocket and the pad? Do I add them to the spare parts pile?

Thanks
Jim
View attachment 175378View attachment 175377View attachment 175376View attachment 175379View attachment 175380View attachment 175381
Click to expand...
 
DizWolf said:
Well, the delay didn't even really get burning so I don't think it's a BP issue. Looks like the grains didn't burn much either.

It overpressurized, and fast. What ignitor did you use, did you vent the cap on the nozzle, and whats the nozzle look like right now? Is anything plugging it/did you cut out all the flashing?

That's some crazy destruction to the liner for as little of the grains that are burned. If you pull the remaining grain out of the liner, what's it look like? I'm suspecting a clogged nozzle, but not sure.

The case is designed to fail like that, rather than shreading itself, hence the clean cut look.

edit: oh and that DRM is totally fixable :)
Click to expand...

Agreed. The DRM appears to be repairable. The hardware; well, not so much...:(
 
To all:
Thanks for the info! It is your helpful replies that make TRF the place for all things rockets! In reading the comments I omitted one fact that now seems relevant. The reload came with a FFjr igniter. Normally I insert the igniter into the fully assembled motor just prior to launch. This time the pyrogen blob was much bigger than normal and would not fit through the nozzle (it wasn't even close). I had to remove the aft closure and nozzle to insert the igniter and then reassemble. Could this cause an overpressure event?

Upon further reflection I too have determined that the rocket is repairable. I am looking for suggestions on the best way to repair the MMT. My arm/hand can just fit inside the tube and reach the damage.

thanks again
Jim
 
Well, if it just blew out the top of the motor mount and front CR, I'd just beef up the internal fillets on the fin tabs and fly as is. Only possible issue is the higher volume for ejection charges to pressurize.
 
Please keep this in mind before responding to my post... I don't have one of those launch pads, and have never seen one up close, nor at a distance.

I think the launch pad is repairable... That is, if the legs stick into the hole below the cracked portion. If that's the case, I'd cut a piece of wood that fits between the vanes of the cracked piece. I'd drill, glue, and screw that piece of wood in place. I'd then mount additional wood reinforcements to the outside of the launcher that would sandwich that assemblage between them. Drilled, screwed together, and glued so that the wood is taking the strain, rather than the plastic, it should be able to last for a long time. It may not be as light, or as pretty as before, but it should be safe and strong.

attachment.php
 
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I had the whole top part of a "leg holder" snap off on mine. I used med. vis. CA to fix it and after a couple hundred or so launches on it since it is still holding together just fine. With yours breaking do to a cato, Aerotech might send you a new base for it.

Mantis Pad 2.JPG Mantis Pad.JPG
 
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Contact Aerotech and get a hold of Karl in the warranty section. I have had nothing but good luck on two occasions..
 
Something similar happened to me last weekend. Flying a G-69 in a 38-120 case. Case split at the top of the threads of the aft closure. Could not have cut it off cleaner if I had tried.
Steve
 
SDramstad said:
Something similar happened to me last weekend. Flying a G-69 in a 38-120 case. Case split at the top of the threads of the aft closure. Could not have cut it off cleaner if I had tried.
Steve
Click to expand...

Just curious, did this CATO happen at ignition or at or right near motor burnout???

If it was the latter, you might have forgotten to apply grease to the end of the grain. I've flown a few of these and they all worked perfectly - a very unique motor to say the least.
 
Donaldsrockets said:
Just curious, did this CATO happen at ignition or at or right near motor burnout???

If it was the latter, you might have forgotten to apply grease to the end of the grain. I've flown a few of these and they all worked perfectly - a very unique motor to say the least.
Click to expand...

Right at ignition. It never made it off the rail.
Steve
 
Heard from Aerotech about my CATO:

Quote:
Our motors are not designed to be that close to the edge that a little extra pyrogen on an igniter head would
result in a over pressurization.

The failure of your case was a defect in the manufacturing process in which the machinist cut the thread relief
much deeper than required. Your flight on the G76 motor stretched the case and the G64 finished
the job. These cases can handle close to 800 + psi, but we normally run them at +- 500 psi for reliability.

You will receive a motor case from an entirely different lot that did not have the thread relief issue......K

Thank you for choosing Aerotech for your rocketry endeavors

Karl Baumann


Once again AT has done right by me:cool:

Jim
 
Exactly what I said in my earlier post. Over pressure failures do not look like that.
 

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