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  1. #1
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    Gap staging questions

    so I am planning a gap staged two stager, and have a few questions.
    lower stage motor mount tube extends how far forward? rocket I am planning will have a bt-60 airframe
    paper punch holes in the mmt end, check. would a couple of paper punch size holes in the centering rings suffice to vent the lower stage?
    all I can think of ATM...likely have more later . thanks
    Rex

    L2-competitor 3, AT J350W, 8/27/2016, Bong, 2557'
    my youtube channel http://www.youtube.com/channel/UC0gB...?feature=watch

  2. #2
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    I like to extend the booster MMT to engage the upper stage motor. Hole punch holes about 1/4" down from the front of the tube.
    I think 1 hole is enough in the lower CRs to let the pressure escape to prevent blow off.

    kj


  3. #3
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    sounds like a plan to me, thanks. just have to adjust the design file and I'll be ready to consider building the booster .
    Rex
    L2-competitor 3, AT J350W, 8/27/2016, Bong, 2557'
    my youtube channel http://www.youtube.com/channel/UC0gB...?feature=watch

  4. #4
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    Another thing I've done when the booster is pretty long, is to make the booster MMT slide out the back of the booster to deploy a streamer. There are a couple of drawings of one way to do that here: http://meatballrocketry.com/booster-recovery/
    I used this on a small scale-altitude model with 13mm motor mounts using standard centering rings. It takes some thinking about how to get all the parts glued to the right place, but is fairly reliable.



    kj
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  5. #5
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    I think that I am okay with a firmly affixed tube, the booster tube is only 5" long and it will use 18mm motors.
    Rex
    Last edited by Rex R; 31st December 2016 at 02:11 AM. Reason: add a word
    L2-competitor 3, AT J350W, 8/27/2016, Bong, 2557'
    my youtube channel http://www.youtube.com/channel/UC0gB...?feature=watch

  6. #6
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    Quote Originally Posted by Rex R View Post
    so I am planning a gap staged two stager, and have a few questions.
    lower stage motor mount tube extends how far forward? rocket I am planning will have a bt-60 airframe
    paper punch holes in the mmt end, check. would a couple of paper punch size holes in the centering rings suffice to vent the lower stage?
    all I can think of ATM...likely have more later . thanks
    Rex
    At least two ways to do it.
    Extend your motor mount all the way up to the encase the lower say 1/4 to 1/2 inch of the sustainer (or next stage in 3+ stages.). Put a hole (punch size is fine) just below where the upper stage engine will stop when stages joined.

    YOU WILL ALSO NEED EITHER A HOLE IN THE OUTER BODY TUBE (unless you are minimum diameter) OR SOME GAPS IN YOUR MOUNT CENTERING RINGS to let the the gas further vent from between motor mount and outside tube and outside of the rocket

    Second option is to extend your motor mount tube to about 1/4 inch below the upper stage engine. The gap will allow the igniting hot gases to duct right to your upper stage nozzle. You will still need a vent hole in the outer body of the booster (or tail of sustainer below the lowest motor mount centering ring) to vent the gases.

    I have successfully gapped up to 36" with these techniques.

    Looking forward to the pics and a good flight!
    It is amazing what you can do when you don't have a choice.

    Smart people learn from their mistakes.
    REALLY SMART PEOPLE learn from OTHERS' mistakes.

  7. #7
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    going to be a bit longer before I can start building due to a hiccup in my parts order(which I am sure will be swiftly taken care of).
    Rex
    L2-competitor 3, AT J350W, 8/27/2016, Bong, 2557'
    my youtube channel http://www.youtube.com/channel/UC0gB...?feature=watch

  8. #8
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    Quote Originally Posted by BABAR View Post
    At least two ways to do it.
    Extend your motor mount all the way up to the encase the lower say 1/4 to 1/2 inch of the sustainer (or next stage in 3+ stages.). Put a hole (punch size is fine) just below where the upper stage engine will stop when stages joined.

    YOU WILL ALSO NEED EITHER A HOLE IN THE OUTER BODY TUBE (unless you are minimum diameter) OR SOME GAPS IN YOUR MOUNT CENTERING RINGS to let the the gas further vent from between motor mount and outside tube and outside of the rocket

    Second option is to extend your motor mount tube to about 1/4 inch below the upper stage engine. The gap will allow the igniting hot gases to duct right to your upper stage nozzle. You will still need a vent hole in the outer body of the booster (or tail of sustainer below the lowest motor mount centering ring) to vent the gases.

    I have successfully gapped up to 36" with these techniques.

    Looking forward to the pics and a good flight!
    So a 2 stage STM-012 is feasible?
    Bill

    I won't be wronged, I won't be insulted, and I won't be laid a hand on. I don't do these things to other people and I expect the same from them.
    John Wayne, The Shootist

    In the Hangar:
    A pile 'O' Fun

    On The Bench:
    Pieces 'O' Fun

  9. #9
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    you would want some sort of recovery device for the booster, but I think it could work.
    Rex
    Last edited by Rex R; 4th January 2017 at 01:45 AM. Reason: add word
    L2-competitor 3, AT J350W, 8/27/2016, Bong, 2557'
    my youtube channel http://www.youtube.com/channel/UC0gB...?feature=watch

  10. #10
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    I have seen it suggested that a 2 stage STM would have a booster stage that is at the limits (maybe a bit beyond) of how long the gap can be for successful staging but it begs to be a 2 stage rocket. I will be ordering a Quark shortly and may just have to give this a try. If BABAR has done a 36" gap, this one should be fine.
    Bill

    I won't be wronged, I won't be insulted, and I won't be laid a hand on. I don't do these things to other people and I expect the same from them.
    John Wayne, The Shootist

    In the Hangar:
    A pile 'O' Fun

    On The Bench:
    Pieces 'O' Fun

  11. #11
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    Quote Originally Posted by Screaminhelo View Post
    I have seen it suggested that a 2 stage STM would have a booster stage that is at the limits (maybe a bit beyond) of how long the gap can be for successful staging but it begs to be a 2 stage rocket. I will be ordering a Quark shortly and may just have to give this a try. If BABAR has done a 36" gap, this one should be fine.
    It will probably stage fine, but due to the stability of the booster it will probably lawn dart (the booster not the sustainer).
    Rich

    NAR# 99154

    L3-4x upscale Estes Cherokee-D- AT M1297W 5/28/2016 http://www.rocketryforum.com/showthr...r-rharshberger

    TriCities Rocketeers NAR section# 736 http://www.tricitiesrocketeers.org/

  12. #12
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    Here is a gap staged EPM-010
    http://www.rocketryforum.com/showthr...ighlight=stage
    Above posters are right, booster will come in ballistic without some modifications, the gap ignition itself really isn't a problem so long as you vent it right.
    Modification include adding a pod wth an engine, nose cone, and streamer or small chute on the booster

    Here is an example
    http://www.rocketryforum.com/showthr...ight=gap+stage

    Others have come up with putting a pod on the upper stage with a streamer (attached to the BOOSTER) that gets pulled out the back at staging.
    It is amazing what you can do when you don't have a choice.

    Smart people learn from their mistakes.
    REALLY SMART PEOPLE learn from OTHERS' mistakes.

  13. #13
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    On the other hand, particularly if you reinforce the tube of the booster, coming in ballistic may be an okay
    From a NAR safety code standpoint, you might call it featherweight recovery. This is ballistic recovery, but the rocket is so light it is not damaging to bystanders or the rocket.
    If you build otherwise light, you could launch with a B6-0, it will stage low and not fall very far.

    My preference for staged rockets is to stage low, where everyone can see it, since I fly for fun and not for altitude.

    So ballistic may actually work for you.
    It is amazing what you can do when you don't have a choice.

    Smart people learn from their mistakes.
    REALLY SMART PEOPLE learn from OTHERS' mistakes.

  14. #14
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    This has given me food for thought. I just may have to get another STM, one for staging and one as a DD practice mule.
    Bill

    I won't be wronged, I won't be insulted, and I won't be laid a hand on. I don't do these things to other people and I expect the same from them.
    John Wayne, The Shootist

    In the Hangar:
    A pile 'O' Fun

    On The Bench:
    Pieces 'O' Fun

  15. #15
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    This will help you understand why you need to vent the booster of a gap staged rocket. It also helps understand what is going on when you tape two motors together in the more common butt-staging.



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