CATO of my L2 bird

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kyled921

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Figured I'd get some feedback and possible discussion of the CATO I experienced over the weekend. It was a CTI 54mm 2 grain J145-SK in a 3G casing w/ spacer. Simple motor ejection in my HyperLOC 835. 3,2,1...Poof! Attached is a photo with many pieces airborne. In my haste to recover said rocket from the pad and bring it to our local vendor for diagnosis, I did not locate the second eye bolt (first is embedded in the spacer) nor the forward closure assembly. I filed a MESS report and believe motor date was from Oct. 2015, although I had bought this on the day of the launch.

OUCH.jpg

Extent of damage:
  • Nose cone/e-bay all good. Just some scuffs.
  • Recovery harness centering ring completely shredded. This had two eyebolts and was secured below a coupler joining the upper and lower body tubes.
  • Upper body tube shredded just above coupler. Seems like an explosive separation as there is a clean break line at the top end of the coupler.
  • Motor casing forward end where the tubing is bent was straightened out from the spacer/forward closure launching skyward. Phenolic liner partially stuck. Propellant grain intact and unburnt.
  • Aeropack retainer completely stuck to casing. Sheared right off cardboard motor tube. Stayed with casing/vendor.
  • Spacer completely embedded into the steel eybolt and bent the 1/4" quick link. Needed to pry aluminum apart to get recovery harness out.
  • Jolly Logic Alt 2 LCD fractured. Would not turn on. Body case cracked. Looks like a gonner.
  • JL Chute release survived!

All in all, salvagable. Will need to cut just below old coupler and fit new body tube, coupler, CR, and eyebolts. Will need another Aeropack (have a spare for phenolic) and will reattached with JB weld. Will need new JL Alt 2, only had 5 flights on it :(. Repaint and add new vinyl.

Any ideas on what might have caused this? I had adjusted the delay using the tool, but hadn't gone too short (maybe -7s). For some reason I am thinking there is a BP charge at the top of the motor propellant grains to help with ignition. Maybe that cause over-pressure event? The damage suggests a significant amount of energy (open the motor casing with the spacer AND embed it into three pieces of steel), and the motor ejecting from the bottom would support an over-pressure event between the delay and the propellant grain. What are your thoughts TRF?
 

dixontj93060

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From the picture, somehow, as you stated the forward delay and spacer are ejected forward with the case staying behind. I'm not a CTI expert, but I would have thought this impossible the way a CTI 54mm case is made with the actual aluminum folded over to hold the load. What did the fore of the case look like after the event?

p54-1g.jpg
 

kyled921

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That curved lip was completely straightened out. The black piece in the photo is the liner for the motor grains. It, along with the spacer, was pushed through the fore end of the casing. I was just amazed as that amount of force.
Untitled.jpg
 

Steve Shannon

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Wow! The motor failed exactly as designed (lengthwise).
Definitely sounds like a very high pressure failure, but neither of the grains showed any signs of being burnt?
The pellet isn't that powerful normally. It's relatively small too. It sounds more like a crack somewhere that exposed a lot of surface area of propellant.
Did you do anything special, like use a different igniter or paint the igniter with some kind of pyrogen? I think you would have said so if you had.
Great job turning in the mess report![emoji1360]
 

dixontj93060

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I don't see how it could happen, but it almost sounds like the Pryrodex grain was instead Thermolite.
 

kyled921

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Wow! The motor failed exactly as designed (lengthwise).
Definitely sounds like a very high pressure failure, but neither of the grains showed any signs of being burnt?
The pellet isn't that powerful normally. It's relatively small too. It sounds more like a crack somewhere that exposed a lot of surface area of propellant.
Did you do anything special, like use a different igniter or paint the igniter with some kind of pyrogen? I think you would have said so if you had.
Great job turning in the mess report![emoji1360]
Didn't recover the delay element unfortunately. Too "zoned out" about seeing my bird in pieces to think about getting all of them. :facepalm: But the full propellant stack was only singed and had not ignited from what I saw. This was the LB Skidmark so I was expecting ~4 seconds of burn time. Igniter had no pyrogen on it.

Thanks on the MESS report. I saw other threads about the importance of any/all data. The vendor kept the motor casing, spacer, and packaging but I am pretty sure I had the date correct.
 

dixontj93060

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Didn't recover the delay element unfortunately. Too "zoned out" about seeing my bird in pieces to think about getting all of them. :facepalm: But the full propellant stack was only singed and had not ignited from what I saw. This was the LB Skidmark so I was expecting ~4 seconds of burn time. Igniter had no pyrogen on it.

Thanks on the MESS report. I saw other threads about the importance of any/all data. The vendor kept the motor casing, spacer, and packaging but I am pretty sure I had the date correct.
Do you have the nozzle? Maybe the throat hadn't been drilled???
 

kyled921

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Do you have the nozzle? Maybe the throat hadn't been drilled???
Unfortunately left it with the vendor when he replaced the hardware. Probably would have been a good thing to look at, but the igniter also went up without any resistance. You thinking the nozzle throat was just too narrow?
 

dixontj93060

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Unfortunately left it with the vendor when he replaced the hardware. Probably would have been a good thing to look at, but the igniter also went up without any resistance. You thinking the nozzle throat was just too narrow?
Yes, I should have said "completely drilled".
 

soopirV

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How many flights were on the casing? Don't think it's relevant, just curious!
 

Reinhard

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Do you still have the propellant grains? How do they look? Are there cracks visible on any of the grains? Does the propellant look like Skidmark? Many other propellants are faster than Skidmark, so they wouldn't play nice with a Skidmark nozzle.

Reinhard
 

cbrarick

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I wonder if the spacer was upside down..seems odd but I saw it once. Do you have any pictures of the case??
 

crossfire

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Looks like a few problems with motors made Fall of 2015
 

SpaceManMat

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How did it explode? Motor lit, stop, explode? Just explode no flame out back?
 

crossfire

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Our rocket motors don't explode. They are built so they don't explode. The ATF doesn't like the word explode.
 

grouch

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It seems like there is a rash of bad luck with the CTI stuff lately. Sorry about the CATO man.
 

manixFan

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Motor grains don't really show any sings of burning. They don't char or have soot on the surface. They generally burn very evenly along the core so upon inspection they look unburnt. You almost have to weigh them to tell they burned. I've looked at grains that were half gone but had no visible evidence of burning. The grains often extinguish when the pressure drops due to the Cato giving the impression the grains did not ignite.

Point is there is no way the igniter pellet caused that Cato. It just isn't strong enough. The propellant lit long enough to over pressurize the case and then went out.

Bummer about your flight and rocket, especially on a cert flight. Glad you can salvage some of it.


Tony
 

thomas

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Your recovery gear is attached to the spacer?
As far as I remember the attachment point in the threaded closure is motor retention.
Maybe the opening schock from a previous flight has damaged the casing, or in this flight the delay element burned trough and then the casing was ripped apart by the nosecone.
 

Steve Shannon

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Your recovery gear is attached to the spacer?
As far as I remember the attachment point in the threaded closure is motor retention.
Maybe the opening schock from a previous flight has damaged the casing, or in this flight the delay element burned trough and then the casing was ripped apart by the nosecone.
No, his recovery gear was connected to an eyebolt attached to a centering ring ahead of the motor. The spacer was ejected forward from the motor forcefully enough to be wedged onto the eyebolt and destroy the centering ring. Post 1.


[emoji1010] Steve Shannon [emoji1010]
 

thomas

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Ah, I misunderstood that, thanks for the explanation.
 

kyled921

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Motor grains don't really show any sings of burning. They don't char or have soot on the surface. They generally burn very evenly along the core so upon inspection they look unburnt. You almost have to weigh them to tell they burned. I've looked at grains that were half gone but had no visible evidence of burning. The grains often extinguish when the pressure drops due to the Cato giving the impression the grains did not ignite.

Point is there is no way the igniter pellet caused that Cato. It just isn't strong enough. The propellant lit long enough to over pressurize the case and then went out.

Bummer about your flight and rocket, especially on a cert flight. Glad you can salvage some of it.


Tony
Interesting. Well, unfortunately I had given the motor remnants to our vendor to diagnose, so maybe I'll have an answer next time I go out to launch. The flight was actually not a cert flight, just the second flight of my L2 rocket. I left it unpainted for the cert flight, in case something like this happened, so I wouldn't feel heartbroken if the rocket had a failure. Painting this bird and cutting decals took a few hours, that's what hurt most. Repairs won;t take too long, but getting that nice look/finish takes so much effort, especially in Florida humidity :)
 

kyled921

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Also for those asking about the propellant grains/type, I've never actually opened up and looked at the difference in grains between propellant types (although I may now), but the fore end of the grain appeared to have an offset core located at about 1/2 the radius of the grain. Is that typical in some of these motors? I know different core shapes change the burn rates, but I hadn't heard of an offset core. I have a video I may upload later.
 

timbucktoo

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The J-145 is a long burn & long burn motors typically have the core offset in order to achieve a longer burn.
 

Steve Shannon

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An offset core like that is referred to as a moon burner. It probably was also a single long grain in that instance.
 

kyled921

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Thanks all for the replies. Wish I had more info for a post-CATO investigation, but this was my first failure so I was mostly worried about condition of my rocket. Next time (hopefully not for a long time) I'll be sure to do a very thorough investigation and have pics for all. The MkII will rise again, with release name Phoenix ;) Hopefully will have it ready by August. Video as promised.

[video]https://youtu.be/FqImoYPVa1k[/video]
 

crossfire

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I am just trying to help you out. So this maybe a stupid question but you did use 54 spaces and not 38 space right? I did see a guy about to do this at a launch a few years ago.
Hope you find out what happened.
 

kyled921

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I am just trying to help you out. So this maybe a stupid question but you did use 54 spaces and not 38 space right? I did see a guy about to do this at a launch a few years ago.
Hope you find out what happened.
Lol. No problem. I know launch fever can take over and stupid things can happen (nearly forgot to attach the D-link to the E-bay eyebolt. . I did NOT use a 38mm spacer, I used a 54mm :) And to answer cbraric above, it was installed in the correct direction.
 
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