The cato to end all catoes!!!

This is the one my mom and I helped your recover at LDRS right?

Damn, bummer this one blew. That was a pretty rocket :/

You have pieces left to look at. I had a hybrid motor CATO ~10 years ago. Largest piece of the rocket/motor I could find was the size of a jumbo marshmellow. The rocket was 4.5" diameter, motor 4" diameter with 9 pounds of nitrous oxide.

I'd tend to lean toward what John said - the grain faces could have squish sealed under acceleration and created a progressive burn profile.

Edward

At what part of the burn did it cato? That can rule out a few failure modes, namely burn through if it happened at ignition.

Binder Design said:

At what part of the burn did it cato? That can rule out a few failure modes, namely burn through if it happened at ignition.

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Post #13 says somewhere between 100' & 200' up

John,

Sorry for the loss of the booster on the F200.

A note that may have some of the posters reconsidering some of their statements....

Looking at the photos, from the .25" exposed casing at the rear of the rocket, I believe that case to be an AG-71 case, no? If so, let me share a recent finding of mine. I have A LOT of AG-71 hardware; love 'em....great value! Therefore this is no dig and not intended to birth fear mongering! While assembling one of nine 75mm Rx motors for Midwest Power recently, I was unable to get a forward snap ring to fully seat in the groove in one of my 3500 cases. Upon closer inspection, it became evident that the groove wasn't cut properly. It was not wide enough, deep enough, and the chamfering was a bit wonky. Had I not had trouble getting that ring into the groove, I wouldn't have looked at it closer, and the snap ring groove would have likely yielded enough to allow the ring to pass and puke the guts. Typical groove depth is about 1/2 wall thickness, this one was about 1/4 wall thickness...very shallow; not much of a lip to retain the ring with.

Point is that it may have been hardware related as John initially hypothesized. My gut reaction was also "probably something else", but if that case is what I think it is, with recent findings fresh in my mind...maybe just maybe this was indeed a hardware issue. Hard for any of us to tell without seeing the situation first hand....

ksaves2 said:

My goodness John that is pretty nasty. Folks in my prefecture were really into mixing and a ground tested 76 mm case blew aluminum shrapnel all over. I wasn't there when it happened but the prefect showed me some of the aluminum projectiles.
They say Al is the safest but that CATO left pieces that looked like they could have really sliced some one up. Thankfully it blew opposite from where they were standing.

Yours looks like it really went. Well at least you can salvage the thrust plate and the retainer. Cleaning out the retainer is a PITA but doable if one is patient. Was that the first firing of that propellant mix in that size of motor or have others flown the
same motor successfully with that propellant?

No, it's not your fault. You just had a bad test flight. Cripes, rocketry is like fishing (especially Ex/Research). If you want to catch fish you're going to lose fishing lures. If you fly rockets, "stuff" is going to happen. There are those who've had less than
nominal flights and those who are "GOING" to have less than nominal flights.
Kurt

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I was considering making a test stand for hybrids and AP. I would get a piece of thin-walled EMT conduit, and slide over the motor to contain any radial blast fragments.
If that isn't heavy enough, Shedule 80 pipe will do the trick.

I had a few fail at the snap ring. Including ripping them out with pieces of the case. Never that much damage to the rocket. Was thinking the case wall had to fail to do that much damage. Did the rocket catch fire / burn?

I had 54mm blow out BOTH snap rings with less damage to the rocket. Seeing the case might help.

Yes, the responses are all theory and speculation.

Eric, I did not want to name vendors, but you are, um, very clever.

Kevin, I, too, want to see what the motor looks like. But I just don't have the time to rush into getting it out. I am hoping that if I can remove the thrust ring, I can pull it out through the forward end. Even touching that charred mess makes me filthy, so I have to do it when I can sit down in old clothes and plan to make a mess. Once I get it out, which may not be for weeks, I will post pics.

AlphaHybrids said:

You have pieces left to look at. I had a hybrid motor CATO ~10 years ago. Largest piece of the rocket/motor I could find was the size of a jumbo marshmellow. The rocket was 4.5" diameter, motor 4" diameter with 9 pounds of nitrous oxide.

I'd tend to lean toward what John said - the grain faces could have squish sealed under acceleration and created a progressive burn profile.

Edward

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Hence the reason some motor designs use O-rings between the grain faces or folks carve the grain faces into a slight cone face or they paint with HTBP? Kurt

Brian Hastings posted this photo on the MDRA Facebook page. This is the flight at the moment just before the big CATO.

Looks a lot like my Competitor 5 on a 76-6000 White just prior to CATO. I think that the flame separation could be due to pressure runaway.


Pic by Dave Reese.

patelldp said:

Looks a lot like my Competitor 5 on a 76-6000 White just prior to CATO. I think that the flame separation could be due to pressure runaway.

Pic by Dave Reese.

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What do you mean by "flame separation?"

Nathan said:

Brian Hastings posted this photo on the MDRA Facebook page. This is the flight at the moment just before the big CATO.

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Thanks! I guess that's the last pic of my baby alive. :cry:

Bat-mite said:

What do you mean by "flame separation?"

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Separation between nozzle and the plume. Not overly common on White propellants, or at least not as pronounced as our examples.

So, Dan, here is a picture of the same rocket with the same propellant, L impulse instead of M, and it looks very similar. But this was a successful flight.

Nice rocket, bad ending. That is the most impressive outcome from a CATO I have ever seen, including some explosive hybrids. Sad for you, but that is how legends are made

The flames actually look quite different, maybe I am seeing something?. The most recent flight has more separation, wider flame and an asymmetrical plume expansion. The former flight looks to be burning a lot cleaner.

We really need to know what the failure mode is to determine possible causes. Did it torch around the seals? Did it burn through the side? Did the motor extinguish upon failure or continue to burn?

For further comparison...my Hawk Mountain Bad Attitude on 54-1400 Plain Jane's.

The happy:



The sad:

Cool. I'll be back with motor pics once I figure out how to get it out.

OverTheTop said:

Nice rocket, bad ending. That is the most impressive outcome from a CATO I have ever seen, including some explosive hybrids. Sad for you, but that is how legends are made

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When it comes to destroying rockets, Bat-mite is already a legend.

I think you already posted the picture we needed.



This picture shows that you have a jagged edge with residual burning. Looks like you experienced the exact same issue that I had with the 6000 I posted earlier in my Competitor 5.

I'm going to venture that your liner cut was wonky at the fore end or not fully engaged with the bulkhead step, and/or a very loose fitting step. I am also guessing you didn't use much, if any, grease to occupy the air spaces around the step and on the outside of the liner/bulkhead. Here's my series of events:

• Motor ignites, hopefully not with thermite as this could compound the issue.
• Gases travel past the step or through the liner at the fore end causing a localized hot spot
• Motor, now at or near Max Pc, is dealing with a motor case with a significantly decreased σt
• Case fails at localized hot spot, but it's a "soft" failure, not a resounding BAM due to the greatly decreased σt
• Propellant continues to burn outside or even inside of the case because there was never an instantaneous depressurization to extinguish it (As displayed by the scorching of your rocket).

Your case shows both melting and fracturing. I'd chalk this up to a poorly cut liner or a failed liner, compounded by not enough grease or provisions to prevent flame propagation between the case and the liner.

Bonus pad video of my Competitor CATO.

[YOUTUBE]VbPTbzfZiL4[/YOUTUBE]

It's quite possible. The liner was cut on Scott's chop saw. We did use a tone of grease, I can vouch for that. But I did not closely inspect the seating of the forward closure into the liner. I'm still questioning the roundness of the casing, though.

Thanks.

Bat-mite said:

It's quite possible. The liner was cut on Scott's chop saw. We did use a tone of grease, I can vouch for that. But I did not closely inspect the seating of the forward closure into the liner. I'm still questioning the roundness of the casing, though.

Thanks.

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Had you used that case and adapter together before? If so, how was the fit then?

Tony

You guys may be distracted but I see what is going on here, Black Friday sales. It amazes me how far some guys will go just to justify a new build.

Bat-mite said:

It's quite possible. The liner was cut on Scott's chop saw. We did use a tone of grease, I can vouch for that. But I did not closely inspect the seating of the forward closure into the liner. I'm still questioning the roundness of the casing, though.

Thanks.

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Explain why you think that was an issue? Is there evidence that it did not seal properly? It looks like you had adequate seal or else you'd have had an immediate failure. O-rings only need like 3-5% compression to effectively seal. If the case was appreciably out of round to impact the seal that bad I doubt the bulkhead would fit.

I'm guessing they're thinking blowtorch where it cuts the case below the closure. That happened to my mud puppy. Cut around, case ruptured mid-flight, propellant kept burning and caught rocket on fire.

mpitfield said:

You guys may be distracted but I see what is going on here, Black Friday sales. It amazes me how far some guys will go just to justify a new build.

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hahahahahahaha,,

cheap shot man..

Hello,, my name is _______ and I have a problem... lol..

Teddy

Sure looks to me like an over-pressure event instead of a leak.
Ripping off the end of the case doesn't happen with a leak.
Even a bad snap-ring grove usually won't show damage past the snap-ring grove.

Oh dear. Yet another reason to have onboard video. You might get lucky and get a photo like this...

Did you rocket have a recording accelerometer? Taking a look at the acceleration curve can help distinguish between an over pressurization and some other type of motor failure.