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  1. #31
    Join Date
    13th June 2014
    Location
    Cocoa Beach, FL
    Posts
    3,551
    Quote Originally Posted by Steve Shannon View Post
    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.
    Thatís what I believe anyway.
    One question: was the forward closure still screwed tightly in the case when you first examined it?

    Steve Shannon
    Quote Originally Posted by billdz View Post
    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?

    Tim
    L3 NAR 98225

  2. #32
    Join Date
    23rd July 2011
    Location
    Butte, MT
    Posts
    2,262
    The reason I ask is because this is exactly the behavior Iíve 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

    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  3. #33
    Join Date
    12th April 2015
    Location
    Arizona
    Posts
    293
    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.
    I aim at the stars. But sometimes I hit London.

    NAR #99868
    L1: MDRM on CTI H175, 7/26/2015 @ NARAM 57
    L2: "Flugel der Freiheit", AT J420R, 11/4/2017 @ GHS Memorial

  4. #34
    Join Date
    11th February 2017
    Location
    south Florida
    Posts
    571
    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.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by billdz; 22nd November 2017 at 07:38 PM.

    L1 3/25/17 H135
    L2 8/12/17 J180

  5. #35
    Join Date
    11th February 2017
    Location
    south Florida
    Posts
    571
    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?

    L1 3/25/17 H135
    L2 8/12/17 J180

  6. #36
    Join Date
    1st July 2011
    Location
    Pittsburgh, PA
    Posts
    2,927
    I follow the instructions.
    Kevin Wuchevich
    Tripoli Pittsburgh
    TRA 12238

  7. #37
    Join Date
    23rd July 2011
    Location
    Butte, MT
    Posts
    2,262
    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? Itís the one that forms the forward seal.


    Steve Shannon
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  8. #38
    Join Date
    11th February 2017
    Location
    south Florida
    Posts
    571
    There's a 1/16" inch O-ring and two 1/8" rings, have measured.

    L1 3/25/17 H135
    L2 8/12/17 J180

  9. #39
    Join Date
    23rd July 2011
    Location
    Butte, MT
    Posts
    2,262
    Quote Originally Posted by billdz View Post
    There's a 1/16" inch O-ring and two 1/8" rings, have measured.
    Okay. Thanks for checking. Happy Thanksgiving!
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  10. #40
    Join Date
    11th February 2017
    Location
    south Florida
    Posts
    571
    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?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    L1 3/25/17 H135
    L2 8/12/17 J180

  11. #41
    Join Date
    23rd July 2011
    Location
    Butte, MT
    Posts
    2,262

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

    Quote Originally Posted by billdz View Post
    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?
    Heís 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.
    Itís really not possible to see in your pictures. You have to inspect the individual grains.

    Steve Shannon
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  12. #42
    Join Date
    11th February 2017
    Location
    south Florida
    Posts
    571
    OK thanks.

    L1 3/25/17 H135
    L2 8/12/17 J180

  13. #43
    Join Date
    26th October 2009
    Location
    Sheboygan WI
    Posts
    1,253
    Quote Originally Posted by Steve Shannon View Post
    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!!
    _______________________
    Jeff - NAR #76531 -L2

  14. #44
    Join Date
    30th January 2016
    Location
    US > OK > NE
    Posts
    3,476
    Well, the thing backfired and got rebuilt, so.... yeah, some double checking is probably in order.

  15. #45
    Join Date
    26th October 2009
    Location
    Sheboygan WI
    Posts
    1,253
    Quote Originally Posted by dhbarr View Post
    Well, the thing backfired and got rebuilt, so.... yeah, some double checking is probably in order.
    OK got it, I thought it was a new complete reload. Been following the thread, forgot post #17.

    _______________________
    Jeff - NAR #76531 -L2

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