Help with CG vs. CP on a Delta II

Discussion in 'Scratch Built' started by ToneDeafJunior, May 15, 2019.

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  1. May 15, 2019 #1

    ToneDeafJunior

    ToneDeafJunior

    ToneDeafJunior

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    Hello All,
    I have a thread posted in Low Powered Rocketry regarding a scratch build Delta II rocket. Most of my builds are scratch semi (or best I can do) with nothing greater in diameter than 66mm but mostly 56mm and no motor greater than a Estes E12. My question for you scratch builders is below and #2, should I be posting scratch builds for LPR in this category? I figured this category was for much more experienced mid and high powered rocketry builders. Please let me know and thank you in advance. Hopefully someone can help with my question below.

    The GEM's are installed. Now to work on the fins. I ran the model through OpenRocket without the GEM's of course and tried to maximize the distance between the CP and CG with fin design. You can see from the picture the distance is only 9.8 cm between the two. You can also see the fin design. I'm using acrylic sheets and will cut them to size on the table saw. I don't know if the drag of the GEM's will push the CP forward or back. I'd like to make the rocket as stable as possible, but, I believe it's impossible to do in OR with GEM's, boosters, etc. Anyone know the answer as to forward or back for the CP?
     

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    Last edited: May 15, 2019
  2. May 15, 2019 #2

    jsdemar

    jsdemar

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    I flew a 4" dia Delta II about 9 years ago with no fins. For that, the CG needs be about 1/2 way up the rocket.

    You'll see more discussion here:
    https://www.rocketryforum.com/threads/delta-ii.11592/

    With only 4 boosters attached, you'll need some plastic fins. My guess is make the root and span about 1.5 times the body diameter. The tip about 1x the body diameter. Sweep leading edge only.
     
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  3. May 26, 2019 #3

    ToneDeafJunior

    ToneDeafJunior

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    Added a significant amount of weight in the cone and made larger fins as suggested. Thank you for the help.
     

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  4. Jun 15, 2019 #4

    ToneDeafJunior

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    Launch video attached. Too bad the sun got in the way. Motor E12-4.
     
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  5. Jun 15, 2019 #5

    kuririn

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    Beautiful flight! Nice and straight. Well done on the design and construction.
     
  6. Jun 15, 2019 #6

    jsdemar

    jsdemar

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    "Perfect" ... I agree 100%. Flies well and looks good. Delta's are always challenging to scale and fly.
     

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