What is the danger from an unintentional on-ground deployment?

Discussion in 'Rocketry Electronics and Software' started by Kelly, Feb 11, 2020.

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  1. Feb 11, 2020 #1

    Kelly

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    This question relates to the adjacent discussion on mechanical switches being required for deployment electronics, but I didn't want to clutter up that thread.

    It seems that "accidental sustainer firing", and "accidental deployment charge firing" are being thrown in the same bucket as equivalent dangers. While I'm terrified by the thought of an engine going off at the wrong time, it seems that this is orders of magnitude more serious than a deployment charge accidentally going off. I usually size my charges to separate the airframe assertively, but not violently, and so an accidental deployment shouldn't be a big deal. I've seen a few accidental deployments at the pad, and they were not a big deal, just an embarrassing walk back to the prep area with rocket and laundry in hand.

    I'm probably missing something. Can somebody school me in the worst case scenarios for bad things that have happened with an accidental deployment, say at the RSO table, the prep area, or while putting the rocket on the pad?
     
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  2. Feb 11, 2020 #2

    Brent

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    Here is a good example. How would you like being hit by this nose cone? It weights around 30 lbs. The rocket had a faulty altimeter and the pad area was just cleared.
     
  3. Feb 11, 2020 #3

    hobie1dog

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    I was talking to a guy who was working on his rocket at his table, when the nose cone shot off in the direction of the RSO table
     
  4. Feb 11, 2020 #4

    mikec

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    I could easily imagine a pointy nosecone fired into someone's head at close range causing a severe injury, can't you? That said, I agree that a motor ignition is a much worse hazard in general.

    One thing I haven't heard discussed is that in many respects the traditional RSO table is unnecessarily risky and not all that effective anyway. Somebody looking at the rocket while it's being prepped but before it's buttoned up would be both safer and more likely to catch problems IMHO.
     
  5. Feb 11, 2020 #5

    Voyager1

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    It’s not just about accidental deployment, there is also the potential risk of a second stage ignition for a two stage rocket.
     
  6. Feb 11, 2020 #6

    Steve Shannon

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    You’re right, and that’s what’s typically done for cert flights, but it would require a lot more volunteers at every launch. If they watch the entire prep that would require a lot more. So, we’re looking for ways to reduce the risk at the RSO table.
    Large launches with extreme projects often have a small group of traveling rocket inspectors to substitute for the RSO table. They usually don’t watch the whole prep, but they go to your project and sign off.
     
  7. Feb 11, 2020 #7

    Steve Shannon

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    Somebody please report this post. I can’t report my own post. This is the error I got earlier when trying to post. View attachment 406348
     
  8. Feb 11, 2020 #8

    dhbarr

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    Done.
     
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  9. Feb 11, 2020 #9

    RocketDestroyer

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    I experienced something just like this first hand. I had helped my friend load his large rocket on the pad and was standing near the rocket watching as he armed the electronics. The altimeter was defective and fired the separation charges as soon as the power came on. We were lucky, the nose cone came down between us and missed us both. It all happened so fast there was no time to look up and spot the nose cone and run away. I can only imagine what would have happened if he had powered up the electronics in the prep area.
     
  10. Feb 11, 2020 #10

    timbucktoo

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    Using Taptalk?
     
  11. Feb 11, 2020 #11

    dhbarr

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    A standard deployment charge is about 0.5g (7.5gn) - 2.1g (32.5gn ). At table-to-head distance that's potentially permanent-hearing-loss territory, not to mention we've all seen bodytubes blown out the side. RSO table is often fairly crowded, so...
     
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  12. Feb 11, 2020 #12

    jadebox

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    The ejection charges (main then drogue) went off in my YouBee as I was standing on a ladder arming the altimeter. The nose cone of the rocket weighs about a pound. It shot about ten feet into the air then fell between my two friends on the ground. Fortunately, it didn't hurt either if them.

    I wasn't hurt either, though my arm was covered with soot.

    Now, I make sure everyone else is away from the rocket when I arm the altimeter.

    With a wireless, remote switch, I could have been farther away, too.

    -- Roger
     
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  13. Feb 11, 2020 #13

    Steve Shannon

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    Yes. My first error was a slightly off-English message saying that there was a problem, something like “We are have problem posting.” When I tried again I got the error I captured.
    So I copied the post I was going to make and saved it in a note on my iPad and tried to post again 13 minutes later. Once he screen refreshed I saw that the original attempt had been successful and that the error message was in error and now I had two identical posts spaced 13 minutes apart. Feeling like I’m already looking pretty stupid here I edited the second post and pasted the screenshot just in case it helps the management.
     
  14. Feb 11, 2020 #14

    heada

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    That *should* never happen because the starter for the second stage should never be inserted into the second stage motor except at the pad with the rocket on the rod/rail. I know that people have gone through RSO with the the staging setup already done because I've seen it done and it violates the safety rules.
     
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  15. Feb 11, 2020 #15

    Angie

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    If you didn't use the Taptalk, and went to mobile browser it would have acted better. By any chance, are you using an Iphone?
     
  16. Feb 11, 2020 #16

    Bat-mite

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    Two instances to report, one very embarrassing.

    First, a friend at MDRA with a large, square-tubed rocket had a nose cone ejection on the pad. The NC weighs 150#. Could have been tragic.

    Second, the embarrassing one ... I had a 3 gram charge go off while connecting my Av bay wires. I had an undetected short that was bypassing the switch. Got 2nd degree burns and had to go to urgent care.

    It hurt.
     
  17. Feb 11, 2020 #17

    Steve Shannon

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    Yes, but I’m a member of several other forums and by using Tapatalk I’m able to use one app.
    And yes, I’m using an iPhone.
    Thanks [emoji120]
     
  18. Feb 12, 2020 #18

    Dipstick

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    Up here in Canada we do exactly this. We take the rocket inspection off the shoulders of the RSO, who remains responsible for the range and all operations. Inspections are done by Rocket Inspectors (RIs). Most launches still have a table, but a good percentage of fliers are certified RIs (we have a training process for that), so before I button up a rocket I have any of them take a look (usually the guy prepping next to me), they sign the inspection sheet, and when the rocket is buttoned up and ready to fly I simply have to give that signed sheet to the LCO on my way to the pad. This system has been in place for years and is very effective. An added benefit is that you don't have lineups at a table.

    http://www.canadianrocketry.org/files/CAR_Flight_Data_Combo.pdf
     
  19. Feb 12, 2020 #19

    NikeMikey

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    All very interesting, but none of these would have been prevented by the rule change.
     
  20. Feb 12, 2020 #20

    ksaves2

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    Agreed. Nothing can protect against a defective altimeter. Except if one does a dry run activation with bare contained snatches the day before a launch.
     
  21. Feb 12, 2020 #21

    Greg Furtman

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    You have an ass cam? :rolleyes:
     
  22. Feb 25, 2020 #22

    dratliff

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    Seems like the only person actually injured had a failure of a mechanical switch.
     
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  23. Feb 25, 2020 #23

    cerving

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    You should always do this anyway (with NO POWDER, of course!) to check your battery/switch/altimeter. If you blow a FET somewhere and it's going to fire when you power up the altimeter, better to find it out with a bare ematch than a big boom.
     
  24. Feb 25, 2020 #24

    OverTheTop

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    I have heard of two people who have hearing deficits now due to premature ejection of rockets.

    I always use either safety glasses/spectacles/face shield (sometimes more than one :)) when handing charges or loaded rockets. A big rocket on my shoulder usually causes me to reach for the earmuffs too.
     
  25. Feb 25, 2020 #25

    HVArcas

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    Consider a nosecone in the eyeball propelled at gunpowder speeds..
     
  26. Feb 25, 2020 #26

    ksaves2

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    That would occur if the charge was out in the open. When I've ground tested deployment charges in rockets and there is usually just a low pitched "FRRRRRMP" and not a report. That said, I had a fully prepped rocket I didn't have
    the time to fly and it was going to be a long time until the next launch. I removed the charges and took them out back to remotely set them off. The first one was "holy cow" LOUD! After that time, I buried charges I had to dispose of
    and ignited them underground. No noise then. My rockets are smaller so not more than 2 grams usually. Sometimes put a heavy flat rock on top of the buried charges.

    I've had deployment on ascent and deployments on the pad due to Rf interference. The pad deployments I had turned on the altimeter, it cycled and I stepped away. The altimeter stopped beeping and I thought "Oh shiest." I was going to try to put the key back into the switch but checked myself. The apogee charge blew and it wasn't that loud in this 4 inch rocket. I was going to try to put the key in but didn't have enough time to prevent the main. I just made sure there was no one in front of the nosecone when it popped. It was lying on the ground when it blew and since this was a sparsely attended launch, no one was nearby. Again, there was no loud report. Embarrassing to say the least but no harm done.

    Staging is a different story. I think the ignition device needs to be mechanically switched to say the least and if it's wireless, all the better. It's easy to bench test that setup the night before to make sure there aren't any "stray" shorts that everyone talks about. Once the switch is turned on, wirelessly arm it at a distance.

    Remember in the old days, some altimeters would automatically fire the matches if the battery polarity was reversed at the input terminals! Switch on and all the attached charges would blow.

    It is very easy to attach contained ematches and cycle your electronics on your bench to guard against premature firing. Heck, If I haven't flown a device in a long time it's a habit I've gotten into and gives
    some peace of mind. Kurt
     
  27. Feb 25, 2020 #27

    OverTheTop

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    Not necessarily. Depends on proximity of ear to rocket, the size of ejection charges and luck. Large rockets have larger charges and deserve greater respect.
     
  28. Feb 26, 2020 #28

    ksaves2

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    Agreed. I haven 't done anything over 4 inches so yeah, the rockets that contain tens of grams of BP I suppose would make a ruckus. That makes the case to test the electronics with bare contained ematches in advance to make sure they turn
    on as designed. I've heard the story of the altimeter that took a hard hit from a drogue only deployment. Flier didn't cycle and test before the next flight. Turned on with the rocket on the pad and both charges blew immediately. Kurt
     

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