Madcow Twitch and a couple questions

Discussion in 'Mid Power Rocketry (MPR)' started by CoachSteve, Jan 10, 2020.

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  1. Jan 15, 2020 #31

    crossfire

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    Ok I missed that.
     
  2. Jan 15, 2020 #32

    CoachSteve

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    Still have to do the internal fillets - with the aluminum tail cone, the aft CR is just extra weight - I may leave it out
     
  3. Jan 15, 2020 #33

    Buckeye

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    The tailcone has a strong influence in OR barrowman equations. Try RasAero. It is not as pessimistic.
     
  4. Jan 16, 2020 #34

    wsume99

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    Another thing to not overlook, the motor will be positioned further aft with a tailcone retainer than it would be with a normal retainer. This will reduce your stability margin. I am lamenting moving the MMT 1/4" aft on a recent build because of the stability impact. If I had used a tailcone the effect would have been even greater.

    Love the build BTW. Thanks for the build thread.
     
  5. Jan 16, 2020 #35

    CoachSteve

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    Agreed - the tail cone hurt me for sure (but you cannot deny the cool factor) - And since I am not going for performance here (will be flown on 29mm RMS stuff until I go for my cert) -I will just add the necessary nose weight and take the altitude penalty.
    This build does fall into the short rocket stature as well so I will be getting a good bit of base drag stabilization. Adding a truncated, zero mass cone at the tail of my Open Rocket sim approximates that I should be good with about 100g nose weight.
    [​IMG]
     
    Last edited: Jan 16, 2020
  6. Jan 20, 2020 #36

    CoachSteve

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    Here is my first try at epoxy fillets - I think they came out pretty good.
    I went with small radius fillets and no sanding after application.
    30 min BSI with black pigment added:
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    Once I do some internal fillets it will be ready to fly
    [​IMG]
     
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  7. Jan 23, 2020 #37

    Forever_Metal

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    Coach,

    Had the same weight issue with my MC Patriot... Even with a loaded AVX bay still needed 500+grams of nose weight to counter the 54mm mount and big-I/small j motor

    With the fins drilled out like that maybe use 2 part foam to lock everything in?

    fm
     
  8. Jan 23, 2020 #38

    Nytrunner

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    I dunno, foam ends up being non negligible weight at the wrong end of the rocket
     
  9. Jan 25, 2020 #39

    CoachSteve

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    plan will be to do some internal fillets with epoxy and add some nose weight - anybody know how much base drag these guys get - they do fall into the short fat rule. I know the tail cone removes some of it - following the advice from Apogee on short fat rockets with tail cones and adding a zero mass cone to the tail of your sim- the sim above shows I should be cool with about 100g up front
     
  10. Jan 25, 2020 #40

    AfterBurners

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    I see you like RC trucks too! Anyway I think you did a nice job on your epoxy fillets. I think for me the hardest part making epoxy fillets is the leading and trailing edges. Getting it to form properly without having the problems with the epoxy running. For me I switched to epoxy clay. It allows you 3 hours of work time and you can do the entire rocket. I still mask the fillets with tape, just so they stay uniform and then when I pull it up I just make sure the edges are nice and smooth by running my finger on them with denatured alcohol. After they dry they are solid like concrete. I come by with rubber grips and sand paper and shape them.
     
  11. Jan 26, 2020 #41

    timbucktoo

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    My actual altitudes have been pretty close to sims without zero mass cone. My Twitch has an 11:1 L to D ratio which is greater than what Apogee considers short fat rocket.
     
  12. Jan 26, 2020 #42

    CoachSteve

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    So if the Twitch is 11:1 then I should not sim it with a drag cone - that means I need ~200g up front - I can do it but that makes the rocket around 1480g with a G76 in it.
    [​IMG]
     
  13. Jan 26, 2020 #43

    CoachSteve

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    And yeah - I have way too many RC cars too
    Vintage Tamiya Midnight pumpkin
    Vintage Associated RC10T
    Losi XX
    Traxxas 1/16 revo
    Full custom Axial Wraith
    Custom built 1/8 super crawler
    Wpl 1/18 Toyota
    Losi micro crawler
    ECX Doomsday Barrage
    Bolink Digger
    full 3D printed 1/32 ford raptor
    I think I have a problem :)
     

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