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  1. #1
    Join Date
    18th August 2012
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    Athol,Ma.
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    Estes Gemini DC Question

    I am currently working on an Estes Gemini DC. This kit has dual rear eject 12" parachutes from two ported side pods. It is also notorious for only ejecting one chute, if it ejects any thing at all.
    My question is; is there any way to make this more reliable? I was thinking of adding a bulkhead just above the tubes to the side pods to increase the amount of ejection gas forced through the ports.
    Any other suggestions would be most welcome.

    Mike L.
    NAR #97175
    CMASS & MMMSC
    L1, LOC Cyclotron
    L2, Madcow Areobee Hi

  2. #2
    Join Date
    23rd July 2011
    Location
    Butte, MT
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    2,273
    Your idea of a bulkhead makes sense. I considered adding pistons to the two sides but unless they have a stop to inhibit ejection they might not help. Plus the additional weight might not help.

    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  3. #3
    Join Date
    23rd July 2010
    Location
    Seattle, WA
    Posts
    224
    On mine, I decided it was too much hassle, and made it nose eject and set it up as a 3 motor cluster. I fly it on 1, 2, or 3 motors, depending on what I feel like.

  4. #4
    Join Date
    18th August 2012
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    Athol,Ma.
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    Quote Originally Posted by tsai View Post
    On mine, I decided it was too much hassle, and made it nose eject and set it up as a 3 motor cluster. I fly it on 1, 2, or 3 motors, depending on what I feel like.
    I'm keeping this as an option, but I'd like to keep it stock and clone another one to cluster.
    Mike L.
    NAR #97175
    CMASS & MMMSC
    L1, LOC Cyclotron
    L2, Madcow Areobee Hi

  5. #5
    Join Date
    18th January 2009
    Location
    Near Denver, Colorado
    Posts
    307
    The problem with the Gemini DC is not the rear ejection or the porting, or that the ejection gas is split to two paths. The problem is that the pressure will eject the parachute that has the least amount of resistance, and then once it is pushed out, then the other parachute will not move, because there is no pressure left since there is an open vent where the first parachute was. To get it to work you must pack both parachutes into the tubes as close to the same as possible, not impossible to do, but not easy to be consistent over several launches.
    If you could put spring ejectors that would both be released at the same time by the ejection charge, that would be more reliable.
    I did what Tsai did, made mine a cluster with a nose blow ejection.

  6. #6
    Join Date
    18th January 2009
    Location
    Saint Louis
    Posts
    1,488
    Mine has a fairly good ejection rate and is built stock (few single deploys, never a zero deploy). The bulkhead idea maybe good as it will reduce the pressurization volume, but Goose-in_co hit's the nail on the head, the chutes need to be packed with similar resistance. My procedure is a little wadding in the chute tubes, very loosely packed, chutes in next, then a quarter square of wadding on top of the chutes for protection. Blow test through the motor mount. You are just looking for a little movement not trying to eject everything. If the chutes don't move with me pretending the rocket is a balloon the ejection charge wont do any good either. I unload and repack until satisfied. My bird is heavy cause I couldn't get it to swing test as a kid and put some led in the nose but flies great. However she's flown so much that the tubes opposite the duct have had to be patched due to burn through, I suggest some small squares of aluminum foil to act as a heat shield, did that many years ago and worked great. But recently I've find soot coming from one of the fin roots so I have leakage there that needs fixing and suspect that is the more likely cause of the recent single deploys. Also not sure if mine uses 12" chutes they are small orange ones from the 90's don't recall what size that equates too. I hope you get as much enjoyment out of yours as I have with mine.
    Michael NAR# 89304
    Somewhere, something incredible is waiting to be known. Carl Sagan

  7. #7
    Join Date
    23rd November 2013
    Posts
    2,219
    I made one tiny modification and mine works reliably.

    I had to place a piece of foil tape on the outside of each side pod. The problem I have seen is that the ejection gases burn a hole through the side pod and release the pressure. Once I installed the tape I have had at least ten successful deployments.

  8. #8
    Join Date
    13th April 2009
    Posts
    3
    I haven't flown my DC for several years, but I seem to recall that I didn't have any recovery problems. I problem I did have was that the ejection charge eventually burning through the body tube for the parachutes. A small piece of aluminum foil glued to body tube where the gasses entered the parachute tube fixed that problem pretty easily.

  9. #9
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    I may just be a little thick, but I can't seem to figure out just where you guys are putting the foil/foil tape. Can someone explain a little clearer on where the the reinforcement goes? A picture would be even better. Sorry for being a dumbass.
    Mike L.
    NAR #97175
    CMASS & MMMSC
    L1, LOC Cyclotron
    L2, Madcow Areobee Hi

  10. #10
    Join Date
    27th March 2013
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    Has Changed
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    Quote Originally Posted by MALBAR 70 View Post
    I may just be a little thick, but I can't seem to figure out just where you guys are putting the foil/foil tape. Can someone explain a little clearer on where the the reinforcement goes? A picture would be even better. Sorry for being a dumbass.
    You want it on the inside of the smaller body tubes, opposite of the vents. So, when the hot gasses pass through the vent tubes, the smaller body tubes don't get "blowtorched".
    Dreaming of making the rockets I dreamed of as a kid (and then some).


    NAR L1 Cert flight: Sheridan, Oregon, USA. Sept. 19, 2015. Flew Deep Space OFFl on an I357T-14A Blue Thunder

  11. #11
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    Ok, that's what I assumed but I wasn't 100% on it.
    Thanks K'Tesh
    Mike L.
    NAR #97175
    CMASS & MMMSC
    L1, LOC Cyclotron
    L2, Madcow Areobee Hi

  12. #12
    Join Date
    18th January 2009
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    Saint Louis
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    yup inside is best mine is outside as it's a retrofit from where it did burn through
    Michael NAR# 89304
    Somewhere, something incredible is waiting to be known. Carl Sagan

  13. #13
    Join Date
    18th August 2012
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    Athol,Ma.
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    Thanks for the tips. I ended up cutting some small pieces of BT 20 (about a 1/2" square) and laminating some foil to them. I then glued them in place, inside, opposite the ejection ports. Hopefully this will make the tubes last a little longer.
    Mike L.
    NAR #97175
    CMASS & MMMSC
    L1, LOC Cyclotron
    L2, Madcow Areobee Hi

  14. #14
    Join Date
    5th February 2009
    Location
    Montreal, Qweebec
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    I also had issues with eh chutes getting tangled with the motor hook & fins.. Also, getting the chutes packed into those little tubes!

    -paul

    NAR# 101258 - L1
    www.CRMRC.org
    I don't know the same things you don't know..

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