L3 – post-mortem analysis….

Forums Knowledge Base L3 – post-mortem analysis….

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  • #52804
    sserell

    Adrian if you can somehow pull some data off of these that would be amazing:

    Doug downloaded some of the GPS data from the Garmin DC 20 system I was using and ballpark data from the GPS put the flight at 33,000+ feet AGL. So its also possible the BP had reduced efficacy at a significantly higher altitude.

    Chris the coupler was shortened about an inch. In my original desing it rested on the casing, once I trimmed it down the only thing supporting the fiberglass coupler was the all-thread and the washers sandwiched between two nuts, so it would have been easier for the coupler to torque and possibly bind.

    #52805
    Chris LaPanse

    Was it only connected up to that mark on the coupler? If so, that does seem awfully short, and it lends credence to the idea that maybe the coupler bound.

    Warren: Doubled? 4+g in a 4″? I’m sure it separates quite reliably, although that seems a bit unnecessary. I’ve had essentially perfect luck with 2.5g or so in my AMRAAM for drogue (4″), and I used 4g in my L3, which had significantly more volume to pressurize.

    As for the reduced efficiency, I’ve noticed that even in a 17k flight – I had my AMRAAM just barely separate on the M1300 last October, but it did not have any significant charge containment. For my L3, I went to a much more thorough surgical tubing and electrical tape containment, and deployment at 18+k was quite solid. How were you containing your charges?

    #52806
    edward
    Moderator

    What method did you use to hold your charges?

    Edward

    #52807
    sserell

    The green mark on the coupler was used for shear pin alignment. Maybe I’m not explaining it clearly but the motor casing was used as the coupler – It had about 4.5″ of casing in the upper body tube and then the fiberglass coupler extended above that another 2.5″. When it was shortened for the second flight the coupler was still the same height but now there was a gap between the fiberglass and the casing so I could get a wrench in there.

    Yeah maybe I shouldve gone with more BP. The calculated charge amount by equation was 2 grams and thats what I tested it with successfully. Maybe for the next flight Ill go with the old addage – yeah that amount seems about right, better double it!

    It was very wierd being out at the launch site with no one else there, quite a stark contrast from last weekend.

    -Sean

    #52808
    sserell

    The 2 gram charge was in a plastic centrifuge tube, ematch epoxied through the bottom with lots of electrical tape, the 2.5 gram charge was in a metal charge container that was part of the ebay setup – the BP was packed tight with wadding and a plastic cap which was then electrical taped over it.

    You can see the metal charge holder on the right.

    #52809
    Chris LaPanse

    Ahh, I see now. I would think that containment would have been enough, but I do think that maybe the glass coupler bound. I’d be surprised if the charge were the problem, given your charge system.

    #52810
    edward
    Moderator

    Wow – that is a lot of re-kitting of parts. Your containment seems to be well thought out. I know a few people who use surgical tubing with great success…maybe if you have redundant charges you can have one set with centrifuge tubes and one with surgical tubing. Cover both bases.

    For a long time I’ve been trying to figure a way to deploy laundry better. The Estes way of pressurizing a body tube doesn’t scale up very well. A piston helps quite a bit getting the laundry out, but still you are pressurizing a decently big volume.

    I saw in Volume 2, Issue 1 April 2007 of Rockets magazine something called a Z-PaRD. I’ve got one built, but still working out the logistics. You take a 1/2″ aluminum tube and then a corresponding 3/8″ aluminum rod. Put your charge inside and seal one end. When it goes off the rod goes flying out of the tube. You attach the tube to the bulkhead and rod to the other end (nosecone, another bulkhead, etc). You are not pressurizing a big volume and you have a very repeatable amount of force you can apply to the two parts. I’ve built one and tested it quite extensively. It works. My small one (about 6″ total length) will throw a brick 10′ into the air. My only bug to work out is how to pack everything around that center rod that is now in your rocket. I’ll be building mock-ups soon of it and then I”ll be using it in a re-do of my L3 rocket (I think I can squeeze 30k out of the M900) if I can make myself happy with a solution on the center rod.

    Edward

    #52811
    sserell

    Edward,
    Very interesting, never heard of the Z-pard but makes sense, however I can see how the center rod could be a major PITA and an additional potential cause for failure due to recovery elements becoming twisted.

    I had considered using Rouse tech CO2 deployment devices rather than BP but I read a nice write up of some home experiments comparing BP and CO2 to 100,000 simulated feet. You can view it here:

    http://www.spacewarptechnology.com/SWT/High%20Altitude%20Tests/TABLE_CONTNETS.htm#experiment4

    Kinda made me feel ok sticking with the BP.
    -Sean

    #52812
    edward
    Moderator

    Contained properly BP is a great choice. Less bulky, has plenty of punch, easy to handle and use.

    http://www.libertylaunchsystems.com/RocketsMagazine/Issue0007/sample.pdf

    At the end of that PDF you can see the author’s Z-PaRD. Mine doesn’t have that shackle on the left side – just screws in to the bulkhead.

    That is the sticking point for me on it. How do I pack around it? Do I make my parachute into a snake and put it into the biggest chute protector ever and wrap it loosely around it? Do I go naked with the chute and just have plenty of cord on top. I have found that during testing if I sleeve the contraption in 3/4″ Tubular Nylon longer than the device then it pulls over the gap and you get no black powder/hot gasses escaping onto your chute.

    Edward

    #52813
    Adrian
    Participant

    Adrian if you can somehow pull some data off of these that would be amazing:

    Ouch. Your data is on the part that used to be attached to the pads labeled “U$9” and is apparently now somewhere in a deep hole. ūüôĀ

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