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  1. #91
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    It's hard to say if it was a forward seal failure off the bat.

    To me it looks like you got a hot spot because of a liner deficiency, that let the case yield at high pressure - evidenced by the tearing of the aluminum case - and then you blow torched everything after it released.

    This also let the motor operate for a couple of seconds before the failure started.

    Cases I've seen that start out as a seal failure generally don't tear aluminum like that, they melt large holes through the casing. Just last year I saw it on a 4-inch hybrid where a pressure tap wasn't properly sealed. Motor fired, nominal for a couple seconds, then you could see hot gas then it was flames coming out of the motor. No tearing of the case like seen in your pictures.

    I'd put a six pack of beer down on liner failure, followed by case failure.

    Edward


  2. #92
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    That looks all torn and stretched to me, not melted. That’s most likely over pressurised not a leak, which explains the massive damage to the frame.

    QRS: 124
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    Largest Motor: CTI 1115J530 IM
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  3. #93
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    Cases I've seen that start out as a seal failure generally don't tear aluminum like that, they melt large holes through the casing.

    That looks all torn and stretched to me, not melted. That’s most likely over pressurized not a leak

    Yep.....liner leaks melt holes.....tears are from overpressure or high-speed impacts.
    Fred Azinger

  4. #94
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    Did you recover the forward closure?

    Where is the point of melt/tear in relation to the depth of the forward closure into the case?
    -John

    NAR/TRA L3
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  5. #95
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    Quote Originally Posted by FredA View Post
    Cases I've seen that start out as a seal failure generally don't tear aluminum like that, they melt large holes through the casing.

    That looks all torn and stretched to me, not melted. Thatís most likely over pressurized not a leak

    Yep.....liner leaks melt holes.....tears are from overpressure or high-speed impacts.
    Not necessarily over design pressure. Once the aluminum exceeds 250C its yield strength drops fast. Normal design pressure becomes burst pressure.

    With over pressure alone, it will shear the nozzle, or walk the snapring out, or tear at the snapring groove. Or it will tear at a previously weakened point in the casing, usually from overheating and loss of tempering from a previous firing. Each will burst with no sign of the case melting. Most often, the motor puts itself out with the sudden drop of pressure.

    Where you see evidence of some melting, there was unexpected hot gas flow with considerable heat transfer. It first becomes a "new nozzle" at that point, then more heat into the casing, then a tear. That's what this failure looks like to me. (And I've seen a few. )
    -John

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  6. #96
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    It first becomes a "new nozzle"

    Usually this drops the pressure and there isn't enough force to cause a tear.
    I'd say the primary cause was overpressure and a hot spot provided the weak spot that pushed it over the edge.
    Otherwise you would just get a second hole.
    Fred Azinger

  7. #97
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    Thanks, everyone, for the opinions and analysis. There is a lot of information here. For me it all boils down to one simple question:

    What did I do wrong?

    John S. ---- NAR #96911 ---- TRA #15253 ---- MDRA #067 ---- BARC #028
    L1, 3/15/14: Aerotech Sumo, CTI H133BS
    L2, 6/21/14: Giant Leap Vertical Assault, CTI J240RL
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    Altitude: 13,028', L3 flight; Speed: Mach ???, L3 flight

  8. #98
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    Knowing something about the formula, nozzle size, and the grain geometry would be helpful. That discussion would go in the research section though.
    Kevin Wuchevich
    Tripoli Pittsburgh
    TRA 12238

  9. #99
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    Quote Originally Posted by FredA View Post
    It first becomes a "new nozzle"

    Usually this drops the pressure and there isn't enough force to cause a tear.
    I'd say the primary cause was overpressure and a hot spot provided the weak spot that pushed it over the edge.
    Otherwise you would just get a second hole.
    It's a matter on milliseconds and not seconds. The leak heats the aluminum enough to bulge then tear. During the time a "new nozzle" might form, but it may not be much more than a pinhole, which won't drop the pressure much. Normal operating pressure -20%, for example, will tear the hot aluminum very quickly.

    As an example, some things I've seen:

    - A small hole on the side of a 5" ("Jeff Taylor" vintage Loki) motor near the nozzle inside the casing. It formed near the end of burn, bulging the (thick) casing slightly, without tearing. Nominal flight to 35Kft, one-time-use casing. Insufficient insulation with a full-dia graphite nozzle and heat-soaked damaged o-rings.

    - A bulge at the forward closure just inside the casing without breaching. CTI N5800. No grease added at the top end, case replaced by CTI.

    - 5-sec burn 54mm D-grain, tear at forward closure, insufficient insulation for longer burn. Next time, made a two o-ring fwd closure with molded fwd insulator, no problems.

    - Forgot to put the o-ring on a 38mm 4-gr motor, 2.5-sec burn. Formed a "second nozzle" near the end of the burn (video showed it). Another second and it would have burst and torn there. The casing lived out its life as a spacer in my test stand.

    Compare these normal-pressure leaks/pinholes/tears with over-pressure catos, which are more violent. Nozzles or fwd closures end up as mortar shots. Or complete shearing off of an end of the casing immediately. Or splitting open the case from end to end without a burn scar.

    I'm sure there are combinations of the two... burn-through and overpressure. Anything's possible if one tries hard enough to ignore things. ;-)
    -John

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  10. #100
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    You ever get hit by a lifted pickup truck while crossing a marked crosswalk and realize it wasn't your fault? I went sliding under a truck and realized it wasn't my fault. Luckily, I only had an elbow scrape and I shrugged it off then forgave the driver. He said the sun was in his eyes so bad he had no idea the cross walk was there until he heard a thump. I wasn't going to sue anybody over a slight cut. I told the guy I've seen worse in life. University clinic was a nightmare to just get a bandaid from, I had to cuss a bunch at them, because they stood in shock and horror that I got hit by a truck and was walkin' around... If that truck wasn't lifted on aftermarket shocks I don't think I'd still be around. You likewise had this incredible motor explosion and the little miracle is no one got hurt from any shrapnel.

    Sometimes in life sh*t happens and it wasn't your fault. Maybe there was a material flaw in that particular casing and no one had any idea then one day it failed?

  11. #101
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    Forensic analysis of a CATO is very hard to be absolute, as you can see from the varied responses.
    It is even more difficult when you don't know the formula and it's characterization, didn't witness the flight, don't have any flight computer data, weren't there to witness the motor assembly, weren't there to witness the actual flight, and can only look at pictures and not put your hands on the remains.

    Given what I've seen so far, I still don't believe it was a hardware incompatibility issue, if the hardware was incompatible it should have been noticed during the motor assembly.

    IMHO Dan theory in post #50 sums this up best.
    John Haught L3
    Prefect Tripoli Pittsburgh

  12. #102
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    Quote Originally Posted by sharkbait View Post
    Forensic analysis of a CATO is very hard to be absolute, as you can see from the varied responses.
    It is even more difficult when you don't know the formula and it's characterization, didn't witness the flight, don't have any flight computer data, weren't there to witness the motor assembly, weren't there to witness the actual flight, and can only look at pictures and not put your hands on the remains.

    Given what I've seen so far, I still don't believe it was a hardware incompatibility issue, if the hardware was incompatible it should have been noticed during the motor assembly.

    IMHO Dan theory in post #50 sums this up best.
    I agree with all that, except that a jagged liner has never bothered any of my motors. The liner is not supposed to act as a perfect pressure vessel. We do not know enough about everything else, as you pointed out. But, John S. did say it was mixed closure and casing from different manufacturers. If he can't recollect how easy it was to push the forward closure in, etc, there's not much else to speculated on.

    But, if someone reads this thread, they can make a pretty good checklist. ;-)
    -John

    NAR/TRA L3
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  13. #103
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    Yes, liners are not pressure vessels, but a good fit can make them fairly close to air-tight and the case will support it fairly well. I mix nozzles / closures / cases all the time and make some of my own nozzles. I had many catos due to a bad chem batch that I took too long to figure out the problem.

    Any leak will cause issues. O-rings can get damaged if pushed in / pulled out. I find the orange silicone ones get slivers pinched off the easiest. The inner edge of the snap ring groove is usually chamfered on the inner side to help with insertion of the O-ring. The outer square for support of the snap ring.

    You may want to check the O-ring depth on you closures. I'm pretty sure that one took a mortar shot into the air and will not be found. I lost every one from a forward closure failure.

    I always assemble the motor without propellant grains to make sure the liner is sized properly for my mix of components. If the motor won't assemble after that, I know the grains need trimmed and not the liner.

    Many things can go wrong. Looking at the case, it torn, has burn marks from propellant (didn't extinguish and burned your rocket), then maybe landed hard smashing the one piece back inward. Can't tell what burning was cutting through the case or caused by the burning propellant after.

    I ask about the geometry / formula because you can be using too small of a nozzle and the successes may have been very close to the edge. A pressure spike due to any voids / bubbles can mean game over.

    Sometimes it takes more than one failure to understand why. Just learn what you can from each, correct as needed until the problem is solved. Consult you mentor(s) of course. It is always less painful if you can learn from their mistakes.
    Kevin Wuchevich
    Tripoli Pittsburgh
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  14. #104
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    John S.- I agree with most everything that John DeMar has offered up. I'll just add that the cause could likely be a processing void that just happened to be at the top end of the motor, but you'll likely never know for sure. If it was packable propellant, I'd put my money there. If it was a good pourable propellant, then those odds go down a lot more. IMO this is definitely a thermal failure and not from over pressurization, but again, it could have been caused by a void in the top grain. A high quality liner possibly could have saved the day. It definitely would have stood a better chance anyway. You'll pay for them one way or another. ;-) Take it for what it's worth.

    I also wanted to touch on what Eric mentioned in post #31. When I look at the last photo you posted in post 86, from the look of it the snap ring eye doesn't look to be as close to the case wall as it should. It's hard to tell for sure. The edge of the eye should be about .040" from the ID of the case, +/-.005". I don't think it had anything at all to do with your failure, but it is something to take note of for sure.
    Scott Kormeier
    President/Owner
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  15. #105
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    John,

    Oh man. I just saw this for the first time. I'm so sorry to see this!!! Loved helping you out at LDRS and will most definately remember this bird! Really sorry to see this happened to you man.

    Kevin
    NAR# 100059 Tripoli# 17072 KM4TZU
    Level 1 (Madcow Torrent / Cesaroni I236 - March 13 2016 2023ft - Dual Deployment)
    Level 2 (Madcow Level-2 "RumbleBee" / Cesaroni J250 Sparky - April 3, 2016 2096ft)
    Highest Flight: Level 2 "RunbleBee" 9490ft Max Vel. 1530ft/s Apr 9, 2017 LDRS36



  16. #106
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    Quote Originally Posted by cavecentral View Post
    Can't tell what burning was cutting through the case or caused by the burning propellant after.

    From what I see, looks like a hot spot at the very most bottom of the split case. It is the only smooth part, looks like it was "cut" and from that point up ripped. Looking closely inside the casing looks like the top of the burnt up liner just below that smooth spot.


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  17. #107
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    There’s an excellent article in the upcoming issue of Tripoli Report which discusses burn through and over pressurization, and the many contributing factors. It’s a good read.

    -Bill Riley

    TRA: 12294
    NAR: 89196

    A good rule for rocket experimenters to follow is this: always assume that it will explode.
    ó Astronautics, issue 38, October 1937.


  18. #108
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    Quote Originally Posted by rcktnut View Post
    From what I see, looks like a hot spot at the very most bottom of the split case. It is the only smooth part, looks like it was "cut" and from that point up ripped. Looking closely inside the casing looks like the top of the burnt up liner just below that smooth spot.
    This is what I saw too- with a rough guesstimate it was at the bulkhead/propellant junction. Which is why I thought it might be some sort of liner failure.
    NAR# 99285
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  19. #109
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    Thanks, all. I will be going with convolute liners and Loki hardware from now on. Yes, Scott, it was packable propellant. But we used a specially-made tamper to really pound it down uniformly, so I think a void is unlikely. Possible maybe. Weights did not indicate a problem.

    Once I have this sucker rebuilt, I'll order up a 76/6000 from Teddy and we'll try again. This can be a good advertisement for Red Glare at MDRA in April. Not only will we have Tom's Big Blue 500 lb. rocket and Feckless Counsel's Redstone, but now we can all watch with bated breath to see if I can blow up two Formula 200s in a row!

    John S. ---- NAR #96911 ---- TRA #15253 ---- MDRA #067 ---- BARC #028
    L1, 3/15/14: Aerotech Sumo, CTI H133BS
    L2, 6/21/14: Giant Leap Vertical Assault, CTI J240RL
    L3, 3/12/16: MAC Performance Radial Flyer, CTI M1101WH
    Altitude: 13,028', L3 flight; Speed: Mach ???, L3 flight

  20. #110
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    But we used a specially-made tamper to really pound it down uniformly

    Could this be your problem.
    "Uniform" tampers - as I envision - don't "work" the propellant, they just try to squish/pack it.
    This won't remove any air.

    My packing tool is a small diameter dowel.
    Pushes down with propellant and any air squeezing out the sides.
    You need to work it around the inside of the tube to make sure you pack it all, while allowing movement.
    You need movement, sideways movement, to get air pockets out.

    Attempting to push it down all at once just compresses any trapped air - it will just spring back.
    Fred Azinger

  21. #111
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    Quote Originally Posted by FredA View Post
    But we used a specially-made tamper to really pound it down uniformly

    Could this be your problem.
    "Uniform" tampers - as I envision - don't "work" the propellant, they just try to squish/pack it.
    This won't remove any air.

    My packing tool is a small diameter dowel.
    Pushes down with propellant and any air squeezing out the sides.
    You need to work it around the inside of the tube to make sure you pack it all, while allowing movement.
    You need movement, sideways movement, to get air pockets out.

    Attempting to push it down all at once just compresses any trapped air - it will just spring back.
    Makes sense. Switching back to dowels next time. Thanks.

    John S. ---- NAR #96911 ---- TRA #15253 ---- MDRA #067 ---- BARC #028
    L1, 3/15/14: Aerotech Sumo, CTI H133BS
    L2, 6/21/14: Giant Leap Vertical Assault, CTI J240RL
    L3, 3/12/16: MAC Performance Radial Flyer, CTI M1101WH
    Altitude: 13,028', L3 flight; Speed: Mach ???, L3 flight

  22. #112
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    Quote Originally Posted by Bat-mite View Post
    now we can all watch with bated breath to see if I can blow up two Formula 200s in a row!
    That's the spirit John!
    NAR# 100059 Tripoli# 17072 KM4TZU
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    Level 2 (Madcow Level-2 "RumbleBee" / Cesaroni J250 Sparky - April 3, 2016 2096ft)
    Highest Flight: Level 2 "RunbleBee" 9490ft Max Vel. 1530ft/s Apr 9, 2017 LDRS36



  23. #113
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    Quote Originally Posted by Bat-mite View Post
    This can be a good advertisement for Red Glare at MDRA in April. Not only will we have Tom's Big Blue 500 lb. rocket and
    Feckless Counsel's Redstone, but now we can all watch with bated breath to see if I can blow up two Formula 200s in a row!
    Well sounds like a good day. Ill be going for my L2 Ive heard of other people bringing big rockets so there might be a bit of a line at the away pads :P
    Trevor Mushung
    NAR 99446

  24. #114
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    Well sounds like a good day. Ill be going for my L2 Ive heard of other people bringing big rockets so there might be a bit of a line at the away pads :P
    At our launches cert flights get priority. Not sure about the club you are flying with. I suspect similar.
    TRA 13430, Level 3

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  25. #115
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    Quote Originally Posted by OverTheTop View Post
    At our launches cert flights get priority. Not sure about the club you are flying with. I suspect similar.
    I don't need an away pad its just that the big rockets will distract me XD
    Trevor Mushung
    NAR 99446

  26. #116
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    So, looks like my nozzle may have been too small. When I ordered the nozzle, I was dumb and said, "Make it compatible with a <brand name> 75/6000 casing." I did not specify that it should be a #52, and it looks like it is a #48. Will not make that mistake in the future.

    John S. ---- NAR #96911 ---- TRA #15253 ---- MDRA #067 ---- BARC #028
    L1, 3/15/14: Aerotech Sumo, CTI H133BS
    L2, 6/21/14: Giant Leap Vertical Assault, CTI J240RL
    L3, 3/12/16: MAC Performance Radial Flyer, CTI M1101WH
    Altitude: 13,028', L3 flight; Speed: Mach ???, L3 flight

  27. #117
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    Quote Originally Posted by Bat-mite View Post
    So, looks like my nozzle may have been too small. When I ordered the nozzle, I was dumb and said, "Make it compatible with a <brand name> 75/6000 casing." I did not specify that it should be a #52, and it looks like it is a #48. Will not make that mistake in the future.
    What does your simulation say for peak pressure for the two nozzle sizes? It could still be within the normal design capability of the casing system. Other factors would still be the primary failure point, made worse by the extra chamber pressure.
    -John

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  28. #118
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    Quote Originally Posted by jsdemar View Post
    What does your simulation say for peak pressure for the two nozzle sizes? It could still be within the normal design capability of the casing system. Other factors would still be the primary failure point, made worse by the extra chamber pressure.
    From Scott S.: "With the #52 nozzle the Kn of the motor would have been 223 - 274 and with the smaller nozzle it ran from 261 to 322. I think the highest Kn I've run this formula at is 300 in a smaller case. It may not have been the sole reason for the cato but it definitely played a part."

    So maybe it was the nozzle, the liner, out-of-round casing, or any combination of any of the three.

    John S. ---- NAR #96911 ---- TRA #15253 ---- MDRA #067 ---- BARC #028
    L1, 3/15/14: Aerotech Sumo, CTI H133BS
    L2, 6/21/14: Giant Leap Vertical Assault, CTI J240RL
    L3, 3/12/16: MAC Performance Radial Flyer, CTI M1101WH
    Altitude: 13,028', L3 flight; Speed: Mach ???, L3 flight

  29. #119
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    Not trying to police this...but it's one thing to "grab the wrong nozzle" and another to just not have any idea what was in the motor. Thank you for posting this, it's how you and everyone else can learn.

    Design your motors, folks. Not saying everyone needs to know accurate C* numbers on all of their propellants, but knowing the motor's basic attributes, approximate Kn ranges, etc. is an absolute MUST for making propellant. Even with an advisor..these are some big motors.

    So you need your case shortened and nozzle throat opened...let me know!
    Dan Patell
    TRA 10904 L3

    Easy Research Rocketry
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  30. #120
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    Quote Originally Posted by Bat-mite View Post
    From Scott S.: "With the #52 nozzle the Kn of the motor would have been 223 - 274 and with the smaller nozzle it ran from 261 to 322. I think the highest Kn I've run this formula at is 300 in a smaller case. It may not have been the sole reason for the cato but it definitely played a part."

    So maybe it was the nozzle, the liner, out-of-round casing, or any combination of any of the three.
    Not knowing the propellant characteristics, the Kn doesn't tell what the Pc range would be. But, minor issues turn into major ones when pushing a casing to 1500 psi. For example, a slightly undersized forward closure gets really loose when the case bulges. ;-)

    I have run 400 Kn peak, around 2000 psi. But it was a casing designed for static tests and characterization. Normal grab-and-go hardware is good for 1500 psi if it doesn't get too heat soaked (from the current firing or previous ones).

    -John

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