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  1. #1
    Join Date
    27th November 2016
    Posts
    7

    Override CG & CP function - need help

    I have been struggling with an issue with OR for a while. I am still a newbie, and I don't really understand when and when not to use these Override switches. I also don't understand why sometimes they seen to show up on the design list by default while other times they do not. Switching it on/off often makes a big difference in CG, but I don't know which is correct. Could someone point me toward some instruction of this feature? Thanks in advance.


  2. #2
    Join Date
    27th July 2014
    Location
    south beloit, IL
    Posts
    2,540
    So for every part (and the whole rocket) there is a mass override, and a CG override. The mass override is for the actual weight of the part- otherwise OR is going to calculate based on the given materials for each section. This is usually not very accurate, so it's better to get an actual weight. The CG override is to give the balancing point of that part (or rocket). This is vitally important for stability purposes.

    Note- On most of my rockets, I just give the CG and mass override for the whole rocket- I don't bother with measuring each individual part. The CG+ mass combo is important because it allows OR to calculate how much stability will be changed by adding a motor in the back end.. if the rocket is light, the motor will have more of an effect.

    FYI- the CP calculated is static by the design- you can't override it unless you put some "fake" pieces on the rocket that don't exist in reality.

    NAR# 99285
    Tripoli# 16283
    L1- 4/26/2015 Madcow Cowabunga- H123SK
    L2- 11/1/2015 Wildman Darkstar 2.6- J355RL
    L3- 11/3/2017 Wildman V2 6" - M1780NT
    Woosh
    QCRS

  3. #3
    Join Date
    5th December 2013
    Location
    MD
    Posts
    7,477
    djs nailed it. I'll just add: build and weigh your rocket in flight-ready condition, minus the motor (OR will add the motor weight). Right-click "Stage" (assuming it is a single-stage rocket), and use the actual weight for the override. Now your model shows the actual built rocket's weight, including all the "extras" that don't make it into your sim, like charge wells, black powder, dog barf, etc. Likewise, balance the rocket and get the actual CG. Put that in as an override for the stage.

    If that doesn't make sense, come back with specific questions.

    John S. ---- NAR #96911 ---- TRA #15253 ---- MDRA #067
    L1, 3/15/14: Aerotech Sumo, CTI H133BS
    L2, 6/21/14: Giant Leap Vertical Assault, CTI J240RL
    L3, 3/12/16: MAC Performance Radial Flyer, CTI M1101WH
    Altitude: 13,028', L3 flight; Speed: Mach ???, L3 flight

  4. #4
    Join Date
    27th November 2016
    Posts
    7
    Thanks to all. I am making progress. I wasn't sure what was overriding what. This helps a lot.

    Is that why some parts, when added from the default DB lists, already have these checked? Because they know how much the standard part weighs?

  5. #5
    Join Date
    27th July 2014
    Location
    south beloit, IL
    Posts
    2,540
    Quote Originally Posted by Boreas View Post
    Is that why some parts, when added from the default DB lists, already have these checked? Because they know how much the standard part weighs?
    Yes- but I wouldn't trust those weights, as there's always some variation in the parts (sanding, glue/epoxy, paint, etc). Also, trying to go part by part is kind of chasing your tail.. better to just work with the overall weight, unless you're trying to optimize the rocket for altitude or something like that.

    NAR# 99285
    Tripoli# 16283
    L1- 4/26/2015 Madcow Cowabunga- H123SK
    L2- 11/1/2015 Wildman Darkstar 2.6- J355RL
    L3- 11/3/2017 Wildman V2 6" - M1780NT
    Woosh
    QCRS

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