Primary deployment charges near backup charges...

Discussion in 'High Power Rocketry (HPR)' started by base890, Jun 14, 2019.

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  1. Jun 14, 2019 #1

    base890

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    I’m a noob to duel deployment. It was suggested that to save space on the bulkheads of my 38mm AV bay that I place the charges in the body tubes.
    Since I’m using pyrodex, (I know I know and will try to get the good stuff at the festival), I encased charges in plastic blood tubes as shown below. They ground tested beautifully with very consistent separations. The powder was first ground very fine, e-match inserted, dog barf tamped tight and lid hot glued.
    In ground tests as I worked up from 0.5g, the 0.75g didn’t separate well and the charge hit the tube enough to crack some paint off the outside of the fiberglass. No trouble with paint when I got good separation using 1g.
    To be on the safe side I’ve been placing the charge quip inside a small kevlar pouch to catch the plastic shrapnel. Unfortunately I only did tests with one quip inside this pouch, (I will be using redundant computers and charges in this rocket).

    Question #1:
    Is it safe to assume putting two charges nearby each other will blow both at the same time and potentially do what 2g would have done- this might not be tolerated by the thin walled fiberglass.
    #2:
    If so, how do you space the charges in skinny rockets- I assume his trying to space vertically but that may be tough in the payload/main compartment which is quite short.
    #3:
    Will the RSO allow me to bring charges like this to the inspection table? Something I read sad you can’t have the electric match in the powder when the connection is made. I’d like to know why this would be a problem so long as nothing is powered on (I have pull switch on one computer and a finger tech on the other). I can keep the charges safe (wires crossed in Kevlar bag) until I connect them up and move these little Kevlar bags into the rocket but this could be difficult to do at the pad compared to a table.

    Thanks for all your help and advice, I’m excited to learn more and more.

    Craig

    7C285314-0EA8-4C7E-A369-0F0E4FB27EFD.jpeg 0EA19EFF-32A5-47B4-B2A8-CDF9CC1009DB.jpeg
     
  2. Jun 14, 2019 #2

    Zeus-cat

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    A minor thing first; it is dual deployment, not duel. Two deployment events (dual), not ones that are fighting (duel).

    #1 If your Pyrodex is properly contained only one SHOULD go off at a time. Are you thinking blowing one will blow the other one? Or are both altimeters set to go off at exactly the same time? If the latter, I would have one altimeter go off at apogee and the second go off a second or two later. Most altimeters let you do this; read the manuals.

    #2 I think dual altimeters is overkill on a rocket this small, but I don't know all the details of what you are trying to do. I have 20 H and I flights and have never done it and it is not required until you get to L3.

    #3 The charges should be in the rocket and ready to go. Altimeters are only turned on when the rocket is on the pad and pointing up. Only after the altimeter(s) are beeping that they are ready is the igniter installed.
     
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  3. Jun 14, 2019 #3

    base890

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    Thanks! Spelling miscorrection, but I guess what I’m wondering about is the chance of a duel...joke ...but in so far that the first would blow up my second resulting in both going off together.
    I know redundancy isn’t required but I had some room in the bay so I filled it
     
  4. Jun 14, 2019 #4

    Voyager1

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    I agree with Zeus-cat. Probably overkill in a 38mm rocket, unless you're going for serious altitude.

    However, if you are using redundant charges in the same chute compartment, don't have them beside each other on the outside of the avbay bulkhead. I would stagger them along the compartment and offset them radially. I have been using this technique for a while now with no issues in a 54mm airframe.
     
  5. Jun 14, 2019 #5

    base890

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    Thanks guys
     
  6. Jun 14, 2019 #6

    Zeus-cat

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    I would be more concerned with the first charge destroying the second charge. Pyrodex needs to be contained to work properly and the first charge isn't going to set off the second charge if it destroys the tube holding the second charge. It could start the Pyrodex burning if it ruptures the case, but that seems unlikely given the finicky nature of Pyrodex. All bets are off if you switch to black powder.
     
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  7. Jun 15, 2019 #7

    kc9qzf

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    I have been flying dual charges in most of my hardware. I feel the least reliable part is the firing output and the initiator. 38mm is close, but I just keep a Nomex shield between them, and a 1 second delay between. If one sets off the other the charge will definitely dump the laundry....
     
  8. Jun 16, 2019 #8

    David Schwantz

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    Flew 3" Black Hole yesterday, Quark and a Quantum for alt's, BP held in vials. They are held near each other at the bulkhead of the payload section. Quark failed, due to battery, but both charges went off in the payload section, only Quantum charge in the booster. One main charge lit the other as they were next to each other.
     
  9. Jun 17, 2019 #9

    shonc182

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    I stuffed dual altimeter and tracking inside a 60 mm rocket for years...not because it was necessary, because I could. I used two charges in each end - surgical glove fingers with 4F and masking tape.

    If the first charge ever set off the backup, I never knew it. They were both detonated and the rocket came apart.
     
  10. Jun 17, 2019 #10

    cwbullet

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    What is the benefit of using a kevlar or Nomex ejection charge baggies? I have never done this but I am curious.
     
  11. Jun 17, 2019 #11

    Voyager1

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    Who sells ejection charges bags? I have deployment bags for chutes, but I haven't seen the ejection charge bags.
     
  12. Jun 17, 2019 #12

    dhbarr

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    Top of the thread appears to show a sack for keeping vial charges. Makes sense to me, not much cost to guarantee pressure and filter the flame.
     
  13. Jun 17, 2019 #13

    CzTeacherMan

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    Redundant altimeters should always be used whenever possible, in my opinion. Even a 38mm airframe coming in ballistic can kill someone. Would you rather be under a rocket coming down on a chute or one that is coming in hot? Redundancy is not required, but you're absolutely right to do it anyway. Overkill or not, I applaud your desire for safety. All it takes is one time where that single Altimeter fails. One time.
     
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  14. Jun 17, 2019 #14

    cwbullet

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  15. Jun 17, 2019 #15

    Zeus-cat

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    I always use the motor ejection charge as a backup. I consider that my redundancy.
     
  16. Jun 17, 2019 #16

    Voyager1

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    That’s a reasonable backup for most composite motors that give you that option, but when you’re a hybrid flyer like myself, that’s not available. So, most of my flights are redundant dual deployment, even with composites, because there are many occasions where the motor ejection delay is not long enough for the planned flight.

    Whatever works for the individual flyer and situation. Some like the technology; some like it simple.
     
  17. Jun 17, 2019 #17

    base890

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    I made these bags for the charges to keep the plastic debris shrapnel contained during the highest velocity portion of the explosion... at first I had them just as additional insurance for fire protection but then I had my paint damaged when I did a test and the charge wasn’t enough to separate... I’m surprised the thin walled fiberglass held up - see the photo for damages.

    They’re pretty simple to make- 4 layers of Kevlar- and when they’re baggy around the charge they hold up well-I tried one tight to save space and the stitching blew out. Cheaper for me to make my own kevlar- I’ve now done 4 rockets worth (and lots of customizing and experiments) for the price of one or two commercial with shipping. I found some Kevlar that’s pretty heavy duty on clearance through amazon. I do own a commercial walking foot machine which helps when you get 8 layers deep as this is really sturdy fabric. My current design has no in hemmed edges so across the hems it’s 16 layers thick and my consew doesn’t care a bit .

    I have since this post just gone and tested the scenario- in a single bag with 1.5g packed ground fine pyrodex in these tubes one did set off the other. I made a larger bag and sewed down the middle and the middle stitches blew out, the second charge’s plastic was burned but the second charge didn’t blow. My plan now is to use a separate bag for each.

    And as for redundancy I can’t think of a reason it’s a bad thing, I found the space.
     

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  18. Jun 17, 2019 #18

    David Schwantz

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  19. Jun 19, 2019 #19

    base890

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    What is the proper process for checking continuity of these types of charges - wait until it's on the pad I assume?
     
  20. Jun 19, 2019 #20

    Voyager1

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    Definitely! The continuity of the deployment charges should be tested at the pad with the rocket vertical on the rod or rail just prior to launching.

    A couple of relevant quotes from the TRA "Safe Launch Practices" guide:

    "Firing circuits and onboard energetics shall be inhibited until the rocket is in the launching position."
    "Firing circuits and onboard energetics shall be inhibited prior to removing the rocket from the launching position."
     
  21. Jun 19, 2019 #21

    kc9qzf

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    Prior to putting the charge in, I do check to make sure the “initiator” has continuity, but once the charge container comes out it is “power OFF” until it is on the pad pointing “UP”. I do NOT check the “initiator” at the launch site, I always do that prior to coming to the launch and in an area that is safe.
     
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  22. Jun 19, 2019 #22

    Bat-mite

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    kc9qzf got it right. Check continuity of the e-matches before installing them. Check full continuity of the entire avioincs chain before adding BP. Once BP is in, do not check again until upright on the pad. And yes, it is frustrating as all get out to have to take down the rocket, go back to your table, and troubleshoot after you have already been RSOed and made the trip to the pad. But hopefully that proves to be rare.
     
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  23. Jun 20, 2019 #23

    Voyager1

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    Yes, checking continuity prior to adding BP is worthwhile. It’s very frustrating to get to the pad and find that an ejection circuit is open.
     
  24. Jun 23, 2019 #24

    ksaves2

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    Here's where you get your ematch tester two styles: http://www.oda-ent.com/Products.htm

    I've never had a match go off with one of these but for safety's sake, only test with no powder in
    the canister. That's simply common sense. Kurt
     
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  25. Jun 24, 2019 #25

    cerving

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    You could always put the two ematches in the same canister/well... I do that all the time. Whichever one goes off first will pop it. And, check the continuuity of the ematches before you install them... I've caught a few bad ones that way.
     
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  26. Jun 28, 2019 #26

    base890

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    Thanks all for your guidance. I flew the rocket last weekend and everything went great. The charges all went off without damage or complications. I hade the primary inside the bags and the secondary (backups) wrapped up outside by the bag with the primary.

    Other than troubles with my featherweight tracker everything was simple and nominal. Great fun and good results!

    Blue skies,

    Craig
     
  27. Jul 1, 2019 #27

    DavidMcCann

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    Doesn't work if you're flying past the longest delay....
     

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