Help with a CATO

[slohand]

I had my first CATO this weekend and was looking for some community input as to what went wrong. I had planned this launch for quite some time, had a seven page checklist that I followed closely and still I had this CATO. Was it the motor? Did I do something wrong?

Details:
Scratch built 4" Patriot
Launch was for my Mother-in-laws 90 birthday
it was windy but not crazy (32 kph)
rocket weighed 3 kg
Motor Ceseroni J94 (plugged)
CP and CG well within acceptable (.247 cal in Open Rocket)

From the video you can see that the motor ejected out the top. Although the Video doesn't show the aft end, there was never any smoke or flame out of the bottom of the rocket. WTF did I do wrong?????



Any comments welcome .... I'm learning.

 

[Rocketjunkie]

Did you put the reload assembly (black) into the aluminum case? Screw it in all the way? The times I've seen this type of failure was putting the reload in the rocket without the case.

 

[slohand]

It's a ceseroni. Thought it was fool proof? It was screwed in all the way. Didn't have to add any o-rings etc. Took it from it's packing tube, inserted it into the motor casing, screwed it to the stops ..... did I miss something?

 

[Rocketjunkie]

It's a ceseroni. Thought it was fool proof? It was screwed in all the way. Didn't have to add any o-rings etc. Took it from it's packing tube, inserted it into the motor casing, screwed it to the stops ..... did I miss something?

It doesn't look like it Was the cato more a boom than a pop? Do you have any pictures of the aftermath? It could be, unless you used a longer case than 5 grain without a spacer, CTI may have left out an O-ring. There should have been some resistance in the last turn screwing in the reload. If it was more like a boom, then I would suspect wrong nozzle or some other manufacturing or kitting defect. A would estimate 1-2% of commercial motors will cato through no fault of your own. I checked the J94 I have and it shows P on the ejection cap. Note that 'plugged' motors still have the smoke grain and touch hole - just no BP in the ejection well. A 'plugged' motor can still have blow by just like a motor with ejection charge. That is why I like the Aerotech plugged forward closures. I pulled out a J94 I have and it does have the longer smoke grain closure so it should stick out beyond the front of the case by about 1/4". J94 is Mellow propellant, a very slow burning propellant even in bates grains.
Nothing is fool proof, that's why I asked about using the casing

 

[Tim51]

Just running through my thoughts on two possibles here after watching your video:

Spacer omission...did the motor casing length match the motor, or did it need a spacer that you possibly forgot to include? (Easily done...,)

Front closure... was the front closure (ie resin module containing the delay grain and ejection charge well) properly seated in the liner after adjusting the delay?

 

[Steve Shannon]

Before the material problem CTI had with overpowered BP pellets, CTI had a material problem with overly slick plastic used to manufacture their forward closures. The problem resulted in delay grains and hot gases being blown out through the top of the motor. Replacement forward closures/delay grain assemblies were issued but I personally witnessed a replacement act exactly the same way.
Be sure you submit the problem to your dealer for warranty replacement and report it to motorcato.org.
Out of curiosity, what was the date on the packaging?

 

[djs]

Do you have a date code on the motor? There were some issues a few years back with a forward bulkhead failure on the CTI 38mm motors.

I had a similar failure once- with onboard video!

 

[slohand]

Thanks for the responses. 5 Grain in a 6 grain case with spacer. Here is a picture of the (un)plugged end, with a few pieces of grass stuck to it.


And here is the manufacturing date. Not sure how to interpret that? 0080 P2 18 0008

 

[boatgeek]

That looks like the bad delay grain issue from a few years ago.

 

[Steve Shannon]

That looks like the bad delay grain issue from a few years ago.

It sure does, but in a motor that’s newer production.

 

[slohand]

The date was stamped on the tube. It's June 15, 2019

 

[Speaknoevil]

The date was stamped on the tube. It's June 15, 2019

Wow, new. Kinda scary.

 

[Steve Shannon]

Wow, new. Kinda scary.

Yes, but at least the second one I’ve heard of since the problem was originally “fixed”

 

[Padseven]

Yes, but at least the second one I’ve heard of since the problem was originally “fixed”

Third one..... I had a J 145 do the same thing. Date code was March 2018.

 

[Buckeye]

I want to know what is on your checklist of 7 pages!

Even if it got off the pad, the flying conditions were sketchy:

32 kph = 20 mph = maximum allowable in the safety code. Yes, borderline crazy.

0.247 caliber margin? That is barely stable. Is that static or dynamic? With motor? With 30 kph wind?

 

[slohand]

Yeah borderline for sure but when I have, maybe if lucky, 4 good windows for a launch a year where I live I have little choice but to push the envelope. Yes simulated with motor. What was not part of the calculation for caliber margin is the 52 gram Mobius as far up the rocket as I can place it. OpenRocket doesn't deal well with the external mobius in the simulation and adding the weight internally is not very accurate. Furthermore my launch rail is 12 feet long which ensures max velocity off the rail.

The 32 kph winds were wind gusts, which were minimal at best.

The seven pages are repetition mostly but ensure that I have what I need in my field box, all the way to putting everything safely away at home. IMHO if you don't have seven pages your forgetting something or your taking shortcuts.

Obviously without having have launched, the concerns are moot. I have had many successful launch with similar conditions/parameters.

 

[WILDMANRS]

Where was the spacer in between the forward closure and case ?

 

[WILDMANRS]

Just found. The answer

 

[3stoogesrocketry]

Thanks for the responses. 5 Grain in a 6 grain case with spacer. Here is a picture of the (un)plugged end, with a few pieces of grass stuck to it.
View attachment 409382

And here is the manufacturing date. Not sure how to interpret that? 0080 P2 18 0008
View attachment 409383View attachment 409382 View attachment 409383

If you used a 5 grain motor with a spacer in a 6 grain case , why is your forward bulkhead sticking out of the end of your case ? Did you stick the spacer in between the forward bulkhead and the propellent ?

 

[WILDMANRS]

If you used a 5 grain motor with a spacer in a 6 grain case , why is your forward bulkhead sticking out of the end of your case ? Did you stick the spacer in between the forward bulkhead and the propellent ?

My thoughts also

 

[Steve Shannon]

I agree also. I didn’t realize that a spacer was used and that it was a longer case. Unless the forward closure is now inside the spacer (I think I’ve seen that happen once here on TRF in connection with a cato) something was assembled incorrectly.

 

[Ez2cDave]

I want to know what is on your checklist of 7 pages!

Even if it got off the pad, the flying conditions were sketchy:

32 kph = 20 mph = maximum allowable in the safety code. Yes, borderline crazy.

0.247 caliber margin? That is barely stable. Is that static or dynamic? With motor? With 30 kph wind?

Bottom line . . . Wind and/or stability/instability do not cause CATO's.

Dave F.

 

[slohand]

The "plug" is what's filling the spacer in the picture.

 

[wrad]

Was there any damage to the case afterwards? Bulges etc. I had a overpressure push the forward enclosure through a spacer and bulge the sidewall of the case, luckily for me the grain blew itself out unlike in this case.

 

[djs]

The "plug" is what's filling the spacer in the picture.

So what you're saying is that it shot up into the spacer as part of the CATO? Or did you put it up there when assembling the motor?

 

[TDSapp]

Sorry Slohand, you brought this upon yourself. Something bad was going to happen no matter what.

Nothing and I mean NOTHING has ever come up good when involving a Mother in law. I think that you broke some major rule of Karma by doing that and that rocket was doomed.

Tim

 

[slohand]

Too funny TD!

So what you're saying is that it shot up into the spacer as part of the CATO? Or did you put it up there when assembling the motor?

I inserted the spacer in first followed by the reload. Looked like this.

 

[crossfire]

The bottom edge of the spacer is cut square. I could see the closure getting pushed up through the space. With the spacer you have a double thickness of rounded end. That is what kept closure from going all the way out of the case. Just my thoughts anyway.

 

[slohand]

Here is the technical drawing from Cesaroni

 

[Rocketjunkie]

Too funny TD!



I inserted the spacer in first followed by the reload. Looked like this.View attachment 409640

Assembled correctly. Must have been a manufacturing defect. If a gentle cato, probably a missing O-ring or blow by around the smoke grain.