First Cato - ejection charge (but nothing else) fired at ignition - how possible?

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
No, the pressure of the motor leaked past the forward closure and pressurized the volume immediately forward of the motor. That forced the motor back (and the rocket vehicle upward) like a piston against the retainer which then failed in tension (not shear) allowing the motor to strike the blast deflector which caused the ding you noted on the aft closure.
That’s what I believe anyway.
One question: was the forward closure still screwed tightly in the case when you first examined it?

Steve Shannon

Tim, was it you who unscrewed the forward closure? Do you know the answer to Steve's question?

It was not me who removed the motor nor did I unscrew anything. All I did was help get it off the rail. You and Steve (stevethecontractor on TRF) were working on it & I really don't remember. I thought the motor came out of rocket without the FWRD closure attached but can't say for sure. You or Steve may have tried unscrewing it but can't say for sure. All I remember was that the case seemed stuck in the MMT. The threads all looked fine. Have you tried assembling the case to see if threads are still good?
 
The reason I ask is because this is exactly the behavior I’ve seen with a forward closure failure. Pressure inside the motor drives the forward closure forward and the remainder of the motor rearward. It would be pretty difficult for enough pressure to escape through the touchhole in the forward closure that quickly, but very easy if the forward closure separated from the case.


Steve Shannon
 
This is a good point by Steve - this really looks like a full forward closure failure, not just blow-by. Your grains are partly burnt, and the ejection charge alone wouldn't be enough to blow the motor out the back end. Also, don't blow-bys usually result in the motor continuing to burn? So the motor probably came to full pressure, sprung a leak around the forward closure, and blew itself backwards, losing pressure and snuffing in the process.
 
That sounds logical but I don't think that is what happened here, hopefully stevethecontractor can weigh in. I'm pretty sure he showed me the forward closure, I asked, "Where did you find that," and he replied, "I unscrewed it from the casing." The threads are fine, the closure screws in correctly, and the closure could not have blown out without damaging the threads, right? This was my first time at this launch site and I didn't know many people besides Tim, but several people helped me after the incident.

sheared retainer.jpg
 
Last edited:
Should the forward seal disk be used only when the instructions call for it or can it be used for extra protection even if not required?
 
Of course the official answer must always be follow the instructions.
I keep being drawn to the same issue pointed out in post 4 and which has been asked a couple of times. That thinnest o-ring looks too thin. Did you actually measure it? It’s the one that forms the forward seal.


Steve Shannon
 
There's a 1/16" inch O-ring and two 1/8" rings, have measured.
 
OK, Aerotech has sent me the replacement parts and this motor hopefully is ready to go. Everything look OK in the below pictures? Karl made one comment I do not fully understand: "[FONT=&amp]Make sure [/FONT][FONT=&amp]the casting tube is secure around the ends of the grains, no exposed propellant, [/FONT][FONT=&amp]if there is any [/FONT][FONT=&amp]separation, from the propellant, coat it with some epoxy.[/FONT]" What exactly does this mean?

forward closure.jpg

j800.jpg

j800 forward.jpg
 
OK, Aerotech has sent me the replacement parts and this motor hopefully is ready to go. Everything look OK in the below pictures? Karl made one comment I do not fully understand: "Make sure the casting tube is secure around the ends of the grains, no exposed propellant, if there is any separation, from the propellant, coat it with some epoxy" What exactly does this mean?

He’s just saying to inspect your propellant grains and delay grain and make sure the casting tube (the white paper covering of each grain) is still bonded tightly to the grain so excess surface area does not become exposed.
It’s really not possible to see in your pictures. You have to inspect the individual grains.

Steve Shannon
 
He’s just saying to inspect your propellant grains and delay grain and make sure the casting tube (the white paper covering of each grain) is still bonded tightly to the grain so excess surface area does not become exposed.
It’s really not possible to see in your pictures. You have to inspect the individual grains.

Steve Shannon



Man! at 95 bucks a pop a guy should not have to worry about doing that!!
 
[FONT=&amp]I finally had the opportunity on Saturday to retry the J800 with the replacement parts sent by Aerotech in December, but unfortunately the result was even worse. The first time, there was just a blow-by and the propellant did not ignite. This time, the rocket lifted a few feet off the pad, started to descend, then the motor fired and the rocket went up 176' before cocking sideways and crash landing, starting a fire.[/FONT][FONT=&amp]
[/FONT]

[FONT=&amp]There's a low quality video of the incident at https://youtu.be/UX7JREyagrs. I have filed a MESS report. This was the second of two CATOs I had on Saturday, one with a Cesaroni motor and this one with the AT motor, a sad day.

Also, the liner now seems fried to the inside of the casing, I've left it overnight in vinegar but it won't come out, any suggestions?[/FONT]


J800 remains.jpg

J800 remains 2.jpg

J800 remains 3.jpg
 
Last edited:
2 CATOS with same case? I'd toss it. I probably wouldn't have even used it a second time after first CATO.
 
Ouch, i've never seen somthing like that before, what kind of igniter did you use? Did you lube the outside of the liner? I've always lubed the outside of the liner however i recently learned from someone not to do it the heated lube can bond the liner to the case making it hard to remove. I've never had issues but the last motor i built the liner dropped out didnt stick at all and wasn't hard to clean. I wouldn't call this a cato etiher IMO.
 
Also Bill, maybe at your next launch you should ask someone to look over your shoulder to make sure you are assembling motors correctly. Can't ever hurt to have a 2nd look. How many time have you used that case in all?
 
2 CATOS with same case? I'd toss it. I probably wouldn't have even used it a second time after first CATO.

Not just with the same case, but I think it’s even with the same reload. I don’t mean the same type. I mean exactly the same reload that was involved in the first cato. The grains “appeared” reusable after the first cato. He put in new motor parts that Aerotech sent to replace damaged ones and tried it again.
I think there’s a lesson here.
 
Not just with the same case, but I think it’s even with the same reload. I don’t mean the same type. I mean exactly the same reload that was involved in the first cato. The grains “appeared” reusable after the first cato. He put in new motor parts that Aerotech sent to replace damaged ones and tried it again.
I think there’s a lesson here.


I could not believe Aerotech did not send OP a complete new reload (my post #45). I would never reuse grains from a motor that was involved in a previous cato, never seen that before. Wanted to post suggesting that a new complete reload should be provided by Aerotech, but thought well we'll see what happens.

Lesson learned is right!
 
The OP didn't say anything about damage to the case or closures, just the liner was stuck. Watching the video i'm curious what would of caused the rocket to pop up like it did, an igniter issue perhaps. Other than that the motor lit on the way down making the rocket unguided and unstable. Medusa nozzle, any of the throats blocked?
 
At LDRS, a buddies motor blew the top off. Lightly charred the grains just like in the pictures of this post. We went to the aerotech booth, and they replaced the case and said the grains should be fine. They just gave new orings and delay parts. I was kind of surprised by that. But I'll be keeping an eye out when that motor fires again.
 
I could not believe Aerotech did not send OP a complete new reload (my post #45). I would never reuse grains from a motor that was involved in a previous cato, never seen that before. Wanted to post suggesting that a new complete reload should be provided by Aerotech, but thought well we'll see what happens.

Lesson learned is right!

Under certain circumstances it’s probably just fine to reuse unconsumed grains, but a person has to be completely confident that the cause of the first problem no longer exists, which requires expertise in determining the cause of the problem.
I wouldn’t be worried if Karl from Aerotech looked it all over and said “Try it again.”, but I know that I don’t have his amount of expertise.
 
Unfortunately Karl did not personally look over my motor after the first incident, although I did send him photos and he apparently believed everything would be OK with the replacement parts he sent. With respect to this second incident, he says, "[FONT=&amp]it appears the motor over pressured and blew out the nozzle, [/FONT][FONT=&amp]almost extinguished, but came up to some pressure and tried to thrust with [/FONT][FONT=&amp]limited results.[/FONT]" He has offered to send me another J800 or another 3 grain reload. The casing and threads appear to be fine but I won't use it again, at least not unless an expert checks and clears it. It's of course possible I somehow built it wrong but if so I don't know what the error could be, in light of the first incident I was trying particularly hard to follow the instructions to the letter, and everything appeared to fit together as it should.
 
Also Bill, maybe at your next launch you should ask someone to look over your shoulder to make sure you are assembling motors correctly. Can't ever hurt to have a 2nd look. How many time have you used that case in all?

+1 to this. I would have someone experienced watch you assemble a couple motors.

I would strongly consider that hardware for retirement.
 
I would strongly consider that hardware for retirement.

+1- I've seen hardware that "looked ok". It wasn't.

On the plus side, the video was kind of a cool/weird airstart. Where did the rocket go after it flew out of the video picture?
 
+1- I've seen hardware that "looked ok". It wasn't.

On the plus side, the video was kind of a cool/weird airstart. Where did the rocket go after it flew out of the video picture?

It landed at the end of the road in culvert, maybe another 400-500 feet beyond the launch pad.
 
It looks like the first CATO may have also damaged the nozzle. If the aft enclosure had a ding in it, the nozzle may have also been hit when the rocket dropped back down on the pad.
 
If you look at the video at the 9 second mark, you can see the landing. At 14 seconds, you can see the start of the fire. I hear you guys about retiring the casing and having someone watch me assemble.
 
Back
Top