Second CATO w/Cesaroni J595 6XL 38mm

Discussion in 'Propulsion' started by billdz, May 5, 2019.

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  1. May 5, 2019 #1

    billdz

    billdz

    billdz

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    Almost one year ago, I had a CATO with a Cesaroni J595 motor, see https://www.rocketryforum.com/threads/cesaroni-j595-6xl-38mm-plastic-aft-closure-failure.146262/

    Cesaroni's warranty service is not great, I did not get a replacement motor until March. Today I tried to launch it. It was another CATO, very similar to last year. Apparently the plastic rear closure blew out again. There was a loud boom right at ignition, and the grains fell out the bottom. Unlike last year, when the casing flew forward inside the rocket and damaged the av-bay, this time the casing came out the back. The chute ejected, although the ejection charge did not go off.

    The CATO did more damage than it originally seemed. The rocket itself is undamaged. However, the 54mm to 38mm Aeropack adapter is damaged, don't think it can be used again. The Cesaroni 6XL casing looks OK but I'm not sure if the threads are all good, I'd be nervous about using the case again. Worst of all, the 54mm Aeropack retainer, which was epoxied with JB Weld to the rocket, blew off, along with the screw on retainer cap. We were unable to locate either the retainer or the cap.

    Any thoughts? We found the rear closure and the first thought from the local expert was that the O ring was missing and that caused the CATO. Compare the below picture of the closure with the photo of the closure in last year's thread, that also is missing the O ring. I'm fairly sure I saw the O ring when assembling the motor, is it possible it disintegrated or blew off?

    Low quality video of the CATO at . ejection charge and piece.jpg grains and piece.jpg rear closure.jpg
     
  2. May 5, 2019 #2

    jahall4

    jahall4

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    Have you seen the April 2019 bulletin about the igniter pellets causing an over pressure in the short 38s?
     
  3. May 5, 2019 #3

    mcderek

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    I don't think it applies here. The Cesaroni J595 uses the 6XL case. It's not a short 38.
     
  4. May 5, 2019 #4

    jahall4

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    Certainly, but maybe it should. Maybe the extra volume in the longer cores is still not large enough to avoid over pressurizing all motors all the time that use the incorrectly formulated pellets.
     
  5. May 5, 2019 #5

    Steve Shannon

    Steve Shannon

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    In order to drive the case out rearward there had to be pressure ahead of the case. But the delay/forward closure photo makes it appear that the ejection charge didn’t burn.
    Or, the case was driven forward when the aft closure failed and then recoiled off something like a bulkhead or baffle. Is that possible?
     
  6. May 5, 2019 #6

    billdz

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    Steve, I do not see any sign of a recoil. The nose cone and chute popped out, I suppose it is possible the case moved forward and caused that, but if so what caused the recoil. There is no baffle, and the only bulkhead is on the base of the nose cone. You are correct that the ejection charge did not burn.

    What do you make of the missing O ring on the rear closure?
     
  7. May 5, 2019 #7

    Steve Shannon

    Steve Shannon

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    I’ve seen o-rings disappear during catos, but I don’t know where they go. That sounds dumb, but I’ve wondered why myself.
     
  8. May 5, 2019 #8

    Steve Shannon

    Steve Shannon

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    If the case recoiled, I would expect to see a damaged case forward end. With nothing solid to recoil from, I would set that hypothesis aside. However, something forced the case rearward. A typical aft closure failure drives the case forward into the rocket, damaging lots of stuff on the way through. How could pressure get ahead of the case to force the case rearward? You mentioned an Aeropack 3854 adapter. That might be how that happened. Think about the sequence of events.
    I don’t recall seeing a picture of the adapter. How does the case fit in it now?
    I’m just not sure, but it’s interesting to figure out what happened.
    In any case, if either closure had been missing o-rings the damage would likely have been a blow-by or burn through. This definitely sounds like an over-pressure. Do any of the grains appear to have cracks or voids?
    Be sure to file a MESS report, please, and contact your vendor.
    I’ll keep thinking about this, but I really don’t know what happened exactly.
     
  9. May 5, 2019 #9

    Rainmaker

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    Sounds like my CATO with a 38 6gxl last year.
     
  10. May 5, 2019 #10

    jahall4

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    What about the stepped ring that sits between the retainer cap and the aft closure? I'm not seeing in the OP where that was mentioned. What I don't understand is why you did not find the aft closure inside the retainer with the stepped ring, cap and adapter attached if the aft closure simply came out of the case. With those hefty jack screw type threads on the retainer I don't really see how that assembly could separate.
     
  11. May 5, 2019 #11

    crossfire

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    Did the reload thread ok into the case? In picture they almost look cross threaded. I am sure most of the damage was when all hell let loose.
     
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  12. May 5, 2019 #12

    Steve Shannon

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    You’re exactly right. The Aeropack adapter has a washer that fits inside the larger retainer and surrounds the aft closure’s thrust ring. I could see the aft motor closure being forced through a greatly deformed retaining aluminum adapter ring that’s part of the Aeropack adapter. I would expect that adapter ring and the aluminum thrust ring from the adapter to be found inside the retainer assembly, which has not been found.

    The damage to the aft closure is telling. The aft closure was forced out of the case. The damage to the outside of the aft closure (the thrust ring) may be consistent with being forced through the Aeropack adapter ring.
     
  13. May 5, 2019 #13

    jahall4

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    Especially since he describes the adapter being damaged, but not the case. Once the closure was ejected from the case the case would not have any forces on it, but it may have traveled forward in the rocket pressurizing the airframe and popping the nose.

    We really need a pic of the ring.
     
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  14. May 5, 2019 #14

    billdz

    billdz

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    Could you tell us more about your CATO? Which motor?
     
  15. May 5, 2019 #15

    billdz

    billdz

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    It threaded in normally, not cross-threaded. At least I don't think it was cross-threaded.
     
  16. May 5, 2019 #16

    billdz

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    Unfortunately I did not recover the ring/washer. Attached is a photo of the adapter, the aft piece broke off. Also attached is a photo of the pad immediately after the CATO. We can see the case hanging out the bottom of the rocket. On the ground with some zoom we can see the aft piece of the adapter and 3 grains. The plastic aft closure and one add additional grain were found a few yards away. adapter post CATO.jpg Tomahawk on pad after CATO.jpg
     
  17. May 5, 2019 #17

    billdz

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    Here's a pic of both ends of the case. Aft side has two small dings. Threads look OK.

    Forward side looks normal. When the CATO occurred, first reaction from the spectators was, "Forward closure failure," but apparently not.

    There must have been tremendous downward pressure that blew the aft closure from the case with sufficient force to rip off the retainer, ring, and cap. What could cause that?
    6XL case after CATO.jpg
     
  18. May 5, 2019 #18

    Steve Shannon

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    A crack or bubble in a propellant grain will do that because more surface area burns. A plugged nozzle will also. As pressure goes up the burn rate rises also which leads to more pressure and greater burn rate until the pressure is too great.
     
  19. May 5, 2019 #19

    billdz

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    Nozzle looks clear. Doesn't the pressure follow the path of least resistance? Wouldn't it go through the open nozzle instead of pushing on the threads and the retainer?
     
  20. May 5, 2019 #20

    Steve Shannon

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    The pressure inside the motor works on all surfaces. The surface area of the inside of the closure will allow experience that pressure. Pressure x “normal” surface area = the force on the aft closure. By normal I mean perpendicular to the center axis of the motor.
    So some gases go through the nozzle, but there’s still pressure trying to push the aft closure rearward and forward closure forward. The forward closure has more surface area because it has no hole. Therefore there’s more force in the forward direction. That makes the rocket move forward.
     
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  21. May 5, 2019 #21

    gldknght

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    Did you have any issues installing your igniter? Did you use the igniter that came with the motor? Is there any way the igniter leads could have blocked the nozzle enough to cause an over pressure? How did you keep the igniter inside the motor prior to ignition?
     
  22. May 5, 2019 #22

    gldknght

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    Has this bulletin been published or posted online anywhere?
     
  23. May 5, 2019 #23

    timbucktoo

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    It’s on CTI website & as far as I know all CTI dealers have been notified (at least my local CTI dealer is aware of it). Have also seen it on Facebook.
     
  24. May 5, 2019 #24

    jahall4

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    Yes CTI regular page for that: http://www.pro38.com/news.php
     
  25. May 5, 2019 #25

    gldknght

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    Ok, I found the bulletin, thanks for your help
     
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  26. May 5, 2019 #26

    billdz

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    There were no issues installing the igniter. I used the igniter that come with the motor. I don't think the leads blocked the nozzle, which is quite wide. The igniter was kept inside the motor with the yellow cap that comes with the motor. The cap was recovered on the ground.
     
  27. May 5, 2019 #27

    Banzai88

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    Do you have the top grain? Was the pellet fully burned?
     
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  28. May 5, 2019 #28

    Alan Whitmore

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    The threads don't look OK to me. I can't enlarge the image, but it looks like the casing might be belled out at the threads.
    So, a question. When CTI replaced the motor, did they replace both the reload kit and the aluminum casing, or just the reload kit? Was the second launch attempt made with a brand-new casing, or with an older casing?

    Alan Whitmore
     
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  29. May 6, 2019 #29

    crossfire

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    Very good point Alan
     
  30. May 6, 2019 #30

    billdz

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    We recovered 4 grains. Two were not found, including the top one with the pellet.

    I'm beginning to think I should return to the launch site and look further for the missing components (2 grains, retainer, ring, cap).
     
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