AT I-366 R Cato

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SpartaChris

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My friend suffered a CATO last weekend when launching an I-366R that resulted in the AT casing splitting down the middle. The forward closure was still intact, the aft closure was blown off, but otherwise un-damaged. Any idea what might have caused this? I was not able to inspect the liner as I didn't build the motor so I don't know if there were any cracks or anything like that.

Thanks in advance! You guys are always most helpful! I will try and get some of the pics from that fateful day here for you morbid folk who feed off the death and destruction..

-Chris
 

JDcluster

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It sounds like a typical over pressurized & then catoed.
Which could be caused by either: the wrong nozzle size or something obstructed the nozzle /core of the motor.


A little more info. is needed:

What type of igniter was used & how big was it??
Was the nozzle recovered intact??

JD
 

Chuck Rudy

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I have an AT motor in which the nozzle orifice was never opened up. The injection molding process left a piece of plastic where the throat of the nozzle is supposed to be opened to the motor. Acting upon that, it's not enough to just get the igniter in, it seems we must inspect the nozzle openings for roundness. If they are not round and open there's a problem. Any flashing must be removed. It only takes a split second, and I'm with JD it sounds like a classic overpressurization.
 

SpartaChris

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He used the igniter that came with the motor, so probably a firstfire or whatever AT provides you with.

I don't know if the nozzle was recovered or not. I also didn't install the igniter so I don't know how clear the nozzle was. :-(

Thanks for the help, I appreciate the insight.

-Chris
 

xenon

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Splititng the casing? most commercial motors are designed to spit the nozzle or the front closure, no the side of the case. Interesting, maybe a bad casing, maybe something else funny, couldn't tell you. Just be sure to contact Aerotech about the warranty
 

Chuck Rudy

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Snap ring design fails longitudinally, screw in fails laterally. AT is screw in. AMW is snap ring as is EX. Screw in should be outlawed/
 

xenon

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I thought both failed longitudinally, guess I didn't know that. What about CTI, I've had them faillongitudinally and they are scew in
 

n3tjm

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Originally posted by Chuck Rudy
Snap ring design fails longitudinally, screw in fails laterally. AT is screw in. AMW is snap ring as is EX. Screw in should be outlawed/
Actually, screwed in has the same fail safe the snap rings have. If you notice above the threads, there is a thick grove cut into the metal. This is the failure point of the hardware. If the motor overpresurizes, and the nozzle does not blow, the case will give here (just like snap ring motors). I personally had one motor do this... a D13. Makes a nice clean cut when one end of the case severs off.

I also seen a F24 do this also, except it was the forward closure end.

If the case split its length, what probabily happened is the liner tube failed during burn. Cracked along its length, causing one of the sides to getting to hot, and the case fails. You may note cracked liners when you take them out of a case... usually, these liners crack when they were cooling off.
 

solrules

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Originally posted by n3tjm
Actually, screwed in has the same fail safe the snap rings have. If you notice above the threads, there is a thick grove cut into the metal. This is the failure point of the hardware.
...assuming that the wall thickness is the same. AT 38mm wall thickness is .054", while EX snap ring 38mm casings are usually .083"

Accoding to the calculations on Nakka's casing.xls spreadsheet, AT 38mm castings can be designed for 1263 PSI (not taking into account the groove), while snap ring cases will hold 1942 PSI with a saftey design factor of 2.
 

Ryan S.

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from personal experience i have seen AT cases fail in all kinds of weird places, I have seen them blow open, burn through split and all kinds of stuff.

Snap rings rip the end of the case off and shoot the nozzle or forward closure off.

There are some thread on cases that have a special groove for failure, never seen them fail though, but I hear the work....they werent AT cases
 

SpartaChris

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Here are the cato pics, posted with permission from Nadine Kinney, the photographer. And since I am posting her photo, let me give her website a plug: www.photosbynadine.com. She takes awesome photos, so feel free to browse her albums online and see if there is anything you like.

-Chris
 

n3tjm

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Originally posted by SpartaChris
here is a pic of the casing
That is consistant with a hot spot failure cause be a bad liner :(. I remember last time I was at AMW... they had a pile of cases that looked like that... cause... paper liners in Blue Baboon motors. That is why Blue Baboon motors require phenolic liners....
 

tallman2

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My first L2 attempt ended spectacularly at LDRS XIX in Orangeburg when my AT J350 exploded about 10' off the pad. Since it was being held on sod, we were able to recover pieces, including some chunks of propellant. Lo and behold, there was a blue thunder grain or two amongst them that I hadn't noticed when I assembled the reload. The casing looked very much like the one in the pic, but flatter.
Gary and co. were on site, so I got a new casing and reload (actually, 2) . This was pre-fire, so there was no way for me to mix up the grains with another reload
So it does happen - grain mix-ups, although I notice that Redline grains tend to all have a stripe on them.
BT will overpressurize a J-350 every time...

John
 
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