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  1. #1
    Join Date
    11th November 2015
    Posts
    27

    Commanche 3 - Stage tightness

    Rookie question: This is my first multistage rocket. How snug should the stages be into each other? I figure they should be more snug than you would want a nose cone to be, but not so snug that the stages don't separate when the next engine ignites.

    Sent from my MotoG3 using Rocketry Forum mobile app


  2. #2
    Join Date
    19th February 2017
    Location
    The world, probably
    Posts
    468
    Short answer, you'll be fine no matter what.

    Staging, especially direct staging, gives you a lot of leeway. The motors should be taped together and under compression for the entire flight so they're unlikely to fall apart, but the ignition of the motor produces so much pressure they're unlikely not to separate on a nominal flight. My custom Boosted Arcas stager has a rather tight coupler, but a D12 lighting up has enough pop to separate the stages, pressurize the entire foot long BT-50 stuffer, and kick said stuffer with a parachute wrapped around it out the back of the booster.

    Many LPR stagers don't even bother with a coupler- they just use the motor itself. The coupler is just added insurance.

    Another note, don't overlap the Scotch tape on itself. The one flight I did this I got a nice little 90 degree turn at staging.... That may not be the problem, but I've had 100% success ever since.

    NAR #104043

    crmrc.org

  3. #3
    Join Date
    6th February 2015
    Posts
    681
    Tight, but not so tight that this happens:

    Click image for larger version. 

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  4. #4
    Join Date
    22nd January 2009
    Location
    Plano, TX
    Posts
    3,137
    Ok RocketRoll, all in with a 3-stager for your first one !

    The challenge with this puppy is to get a good friction fit on each motor and it's airframe section and get the interstage couplers nice and smooth. You don't want a flight where the booster motor lights the second stage then ejects leaving the booster airframe attached. Note step 6 where you wrap the couplers with cellophane tape to reduce the friction of the paper surface. On some models I've sanded off almost all of the red layer of the coupler to get the right fit. Another method I've used is thin CA and 400 grit to get those coupler surfaces nice and smooth. More snug that a nose cone ? I don't think so. You don't want them falling off under their own weight but it shouldn't take alot of effort to pull them apart.

    The Commanche is kind of a hybrid. The booster motor has no connection to the 2nd stage motor, like gap staging. The 2nd and 3rd stage motors are taped together old school style. My own preference for a gap staged booster is to always have pressure relief holes to keep it from separating before the 2nd stage ignites. A couple of 1/8th or 3/16th diameter holes through airframe and coupler just below the forward end of the airframe would be my choice. I believe the Chief Designer at Estes, Jumpjet, has a different opinion so you have to make you own call there.

    Click image for larger version. 

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    Good Luck !

  5. #5
    Join Date
    13th October 2014
    Location
    SouthEastern, WA
    Posts
    5,709
    While I have never had a stage seperate before ignition on a Comanche-3, the second stage is well known to spit the motor without the stage separating and when the sustainer ignites it burns the second stage up. The second stage motor should be tightly friction fitted to the motor tube and the second stage coupler should be loose enough that only the two motors being taped together is holding the second and sustainer stages together (for alignment more than anything).
    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/

  6. #6
    Join Date
    17th June 2011
    Location
    The fertile fields of Malta, IL
    Posts
    3,228
    I have problem with my Commanche. Somehow the motor mounts never make it into the 2nd and 3rd stages...
    I keep trying but the 3rd stage always seems to light somewhere in the upper atmosphere
    Makes it a little hard to find.
    I need to try this once more with a small tracker in the upper stage. D12, D12, to E9 was pretty cool.

    Adrian Butler
    jd2cylman@mchsi (dot) com
    NAR 73787 L3
    Tripoli 13524 L3
    QCRS, Princeton, IL
    Chicago Rocket Mafia "The Mechanic"

    Buckle up back there, we're going into "Hyperactive!"

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