What is the purpose of the "extended" forward closure?

Discussion in 'Propulsion' started by Buckeye, Jun 10, 2019.

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  1. Jun 10, 2019 #1

    Buckeye

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    OK, I am getting into some more, ahem, "exotic" commercial motors. I have the 54mm AT K250 and it calls for the "extended" forward closure. I ordered the closure from Wildman on Black Saturday over 6 months ago, and I have frankly lost all hope in receiving it in time for my launches this year.

    Anyway, why the need for a longer forward closure, with presumably longer delay grain (called "smoke charge" in the instructions)? If the motor is to be flown plugged with no BP charge anyway, as I intend to do, then what is the purpose of the long delay element? Is it needed for proper propellant burn? Can I use the standard length closure/delay instead?
     
  2. Jun 10, 2019 #2

    Eric

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    The extension allows for a longer delay / smoke grain.

    If being flown as a research motor, I don't see why you couldn't use the standard forward closure with any length delay grain. Especially if you grease both ends of the delay
     
    Last edited: Jun 10, 2019
  3. Jun 10, 2019 #3

    Rocketjunkie

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    You need the extended forward closure for motor ejection of the long burn J90, J135, K185. If using electronic ejection, you can just fill the ejection well with a smoke grain but you MUST use a plugged closure. A RDK-34 (long burn short) delay grain fills the standard ejection well with no spacer ring. There is no room for an O-ring seal. This is the reason why you must use a plugged closure.
     
  4. Jun 10, 2019 #4

    Buckeye

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    Is a plugged closure of my own making (filling charge well with grease) sufficient?
     
  5. Jun 10, 2019 #5

    Andrew_ASC

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    I’ve taken a standard Aerotech 38mm forward closure and filled it where the powder goes with cotronics 4700 then oven cured it for sixteen hours to effectively plug the closure. It survived an I299N/P flight. That’s how I converted a standard closure to a plugged configuration.

    That’s a 11,100 psi tensile epoxy at 600 degrees Fahrenheit. Dunno what would happen on bigger motors. Not recommending it just saying that’s what I’ve done before and it worked.
     
  6. Jun 10, 2019 #6

    MClark

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    if you use a standard closure with ejection (even with no powder and grease) it will burn through while the motor is under pressure and your rocket will be incinerated.

    M
     
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  7. Jun 10, 2019 #7

    mikec

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  8. Jun 10, 2019 #8

    Rocketjunkie

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    No, won't prevent blow by.
    54 mm closures, L-R Extended, plugged, plugged & tapped for recovery anchor, inside. All have space for a smoke grain. All are certified and sold by Aerotech and dealers.
    If all you have is open (for motor ejection) closures you can tap the touch hole 6-32, insert a short screw, and fill the ejection well (where the BP goes) with epoxy.
    54 Closures 1a.jpg 54 Closures 4a.jpg
     
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  9. Jun 10, 2019 #9

    BF Rockets

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    Not sure it has been stated, but the purpose of the extended closure is to allow for a longer smoke grain necessitated by a long burn motor. Since the smoke grain is consumed during motor burn, the shorter closure smoke grain would likely not last the length of the motor burn, or certainly not much longer than motor burn.
     
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  10. Jun 10, 2019 #10

    DaveW6DPS

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    K250 is a single-use and comes plugged.

    Do you mean a K185 or a K270?

    In any case, a reload is certified in a particular casing or casings, and should be flown in that configuration unless you are at a research launch.
     
  11. Jun 10, 2019 #11

    mikec

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  12. Jun 10, 2019 #12

    Buckeye

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    Correct, this is what I have.

    "LMS-PLUS?" More confusing and pointless acronyms from our friends at Aerotech. There is nothing LMS or PLUS about this thing. It requires the same effort and assembly as any other reload.
     
  13. Jun 10, 2019 #13

    Buckeye

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    Thanks for all the replies. I guess these are my options for electronic (no motor BP charge) deployment of the K250:

    1. Wait for the open extended forward closure to arrive. Assemble as normal. Omit BP, fill charge well with grease.

    2. Use my existing open regular forward closure (floating type). Insert any delay assembly. "Mechanically" plug the charge well. A #6 screw and epoxy was suggested.

    Does this sound correct?
     
  14. Jun 11, 2019 #14

    mikec

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    2 is not certified and thus not permitted except at a research launch and probably won't work anyway because the delay element won't fit in a standard closure (maybe you could trim it down, again, not certified). If you had the official AT Delrin plug you could perhaps plug your standard closure and omit the delay element. Filling the closure with something like a wooden dowel (or JB Weld, if you never wanted to use it again as a standard closure) would probably work but also not be certified.

    What you don't want to do is let the flame from full combustion hit the closure metal, because if that happens it will likely be severely damaged and perhaps burn through.
     
  15. Jun 12, 2019 #15

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