Parachute Deployment Failure

Discussion in 'Recovery' started by PedroTheRocketNerd, Dec 8, 2019.

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  1. Dec 8, 2019 #1

    PedroTheRocketNerd

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    Today I had an interesting recovery failure. I was test-flying my 4" scratch-built Nike-Smoke payloader on an Aerotech G78G-4 LMS. The takeoff was perfect, but instead of deploying the chute just after apogee, it lawn-darted into the ground. I checked out the wreckage and launch footage, and I discovered that although the ejection charge had gone off, the red cap that holds it in place was still there, and neither the rocket's interior or recovery wadding were sooty or charred. It seems as if the charge went off, but instead of popping off the red cap and deploying the chute like it was supposed to, the cap got stuck and the gases were vented out the back of the motor. Has this ever happened to anyone here? Is there anything I can do in the future during motor assembly to avoid this?

    P.S. I am relatively new to the forum, so if this needs to be moved to something like Propulsion or Mid-Power Rocketry, please move it.
     
  2. Dec 8, 2019 #2

    dhbarr

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    If you still have the delay assembly, was the spacer toward the motor or toward the ejection charge?
     
  3. Dec 8, 2019 #3

    Nick Hutton

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    If the red cap was still on and there was no powder residue, how do you know the charge went off? Was there definitely powder in the cap?
     
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  4. Dec 8, 2019 #4

    afadeev

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    +1 on no black-powder in the charge well.
    BTDT.
     
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  5. Dec 8, 2019 #5

    Voyager1

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    I have experienced this on two occasions with single use G80 motors. On both occasions the deployment charges were observed to ignite at the end of the delay charge, but no parachute deployed. It was believed that the deployment gases vented out the nozzle because the red cap was still in place when recovered. There was powder residue on the cap and inside the ejection pot.

    In future I will remove the already installed red cap, pack the BP down with dog barf and use masking tape to secure the top of the deployment pot. Don’t trust the red cap!
     
    Last edited: Dec 8, 2019
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  6. Dec 8, 2019 #6

    PedroTheRocketNerd

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    I still have it; however, since it is a LMS motor, which is single use and epoxied together, I would have a hard time getting at it. However, I don't think that was the issue, as I was working along with the instructions as well as a video from Apogee.
    I removed the cap and saw BP burn residue. In addition, I looked at the video and saw a puff of white smoke, different from the normal delay smoke, right at about the time the ejection charge was supposed to go off. The places without burn residue were the motor mount and inside of the airframe, as well as the recovery wadding.
    This sounds exactly like what happened to me. It is reassuring to know that it is a design flaw in the motor, not a result of me jamming the cap down too hard. Thank you for the tip about the dog barf; I will use it next time I fly an AT single use or LMS.
     
  7. Dec 8, 2019 #7

    Wallace

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    I've personally witnessed one of the Officers in my Club have a lawn dart on an Aerotech single use 29mm motor. Inserted untouched, It had no ejection powder from the factory..The red cap was still there btw..You will see evidence of residue behind the cap from when the delay grain burns through. Although not impossible, I do doubt that cap is strong enough to cause 1.3g of BP to vent out the nozzle end through that tiny hole.
     
    Last edited: Dec 8, 2019
  8. Dec 8, 2019 #8

    Wallace

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    Anything manufactured by and or for man can and will have glitches occasionally..
     
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  9. Dec 8, 2019 #9

    PedroTheRocketNerd

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    There was definitely BP in the motor. It was an LMS, so I built the motor and poured in the BP myself.
     
  10. Dec 8, 2019 #10

    dhbarr

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    My suspicion then must return to an upside down delay stack. This could allow the BP to migrate through the touch hole, and there might be plenty of volume to receive it due to the 1/2" or so cylinder of empty space.
     
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  11. Dec 8, 2019 #11

    PedroTheRocketNerd

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    I will look into that. How should I get the motor open? I have a jigsaw with a wood cutting blade, a hacksaw with wood and metal blades, and a Dremel with metal cutting wheels.
     
  12. Dec 8, 2019 #12

    Wallace

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    Sounds then like you had the classic "BP shook it's way through the hole" syndrome. If you put it in there, it went somewhere...
     
  13. Dec 8, 2019 #13

    Wallace

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    Cut 'er open with whatever's easiest. There's nothing left inside that'll burn..
     
  14. Dec 8, 2019 #14

    Voyager1

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    I had considered the possibility of there being no BP in the pot. I also considered that if it was there that that amount of BP would surely pop the cap, rather than vent back through a small hole. However, the very distinct puff of smoke at the end of the delay burn suggests that the BP was there.

    Unfortunately, I will never know what actually occurred, except for the fact that I had two spectacular lawn darts. However, when using a single use motor in the future, I will now always remove the red cap and reseal with dog barf and masking tape.
     
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  15. Dec 8, 2019 #15

    SecondRow

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    OP, did you puncture the red cap after insertion? The instructions call for it, but I don’t know why since I haven’t seen any RMS motors make you do it. I wonder if this is why.
     
  16. Dec 8, 2019 #16

    PedroTheRocketNerd

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    I cut the motor open. It was built correctly - the delay element's plastic exterior, as well as the delay O ring, were at the front, toward the BP hole.
     
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  17. Dec 8, 2019 #17

    PedroTheRocketNerd

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    I did puncture the cap, using a safety pin or push pin IIRC.
     
  18. Dec 8, 2019 #18

    PedroTheRocketNerd

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    I just want to say thank you all for the helpful comments. I think I will use dog barf and masking tape rather than the red cap from here on out. However, the strange thing is that I flew a G77R-10 LMS - virtually identical to the G78G I flew yesterday - back in the spring, and the red cap popped out for a near perfect deployment and recovery. I guess they are just hit and miss.
     
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  19. Dec 8, 2019 #19

    SecondRow

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    My only other thought was that epoxy got where it shouldn’t have. But it sounds like the BP burned, so that doesn’t seem to be the issue.

    FWIW, I’ve flown about 5 or 6 of these, and I haven’t had any problems.
     
  20. Dec 9, 2019 #20

    Wallace

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    I agree. If you put it in there, "something "else was the cause. I'd not bet on it being the cap, but that's just my opinion.
     
  21. Dec 9, 2019 #21

    crossfire

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    It's not the cap. You could use a little barf and the cap. Take a look at the notice AT put out on the DMS K535 a few years ago sounds like your powder was sucked out the nozzle.
     
  22. Dec 9, 2019 #22

    Voyager1

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    I have generally had very successful flights with single use motors. However, the two instances described above have caused me to not trust the installed caps anymore.
     

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