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Thread: Rocksim Help

  1. #1
    Join Date
    31st October 2017
    Posts
    25

    Rocksim Help

    Ok, starting to get nervous about my L1 flight next month.

    So I'm trying to get everything loaded into Rocksim, but was having trouble making it all work out to the totals. I finally just done a mass override on the weight/cg without the motor, then added the motor.

    I'm not sure how to change each part to get the mass correct any other way.

    For what I have loaded, does there appear to be any concerns?

    Thanks for any feedback you may have.

    ROY

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2
    Join Date
    6th September 2009
    Posts
    1,761
    Looks about right. Overriding the overall mass and CG (no motor) is the best way to do it once your rocket is built.

    Altitude, launch rod departure velocity, and optimal delay are the three most important things I look at in the simulation when it comes to choosing a motor.

    I have the same cardboard DX3 (with dual deploy). Works just fine with H128 and H180 to moderate altitudes of 1700- 2200 ft. These may be better choices for cert, rather than I200 at 3000 ft.


  3. #3
    Join Date
    7th July 2013
    Location
    Toronto
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    3,543
    A mass override with manual CG will get you there. Did you do a CG manually?

    I usually do an individual CG and mass for each component while making design choices. However once the rocket is fully assembled I then do a mass and CG override.

    Beyond that I am assuming you're going with motor eject? If so then make sure your delay matches the sim as close as you can get it. Rocksim does a good job in estimating this. Once you have run your sims, just double click each one to bring up the simulation results, then scroll down to "Time data", specifically "Optimal ejection delay" and round up if you can.

    Once you have this number you can adjust the delay on the simulation, where you add the engine and set your events.

    Good luck.
    Michael Pitfield
    TRA 14579 L2
    NAPAS BoD
    URRG
    MARS
    CRC

  4. #4
    Join Date
    31st October 2017
    Posts
    25
    Oh, for sure. I plan on my cert with either H210 or H180. The I200 is my fun motor.

  5. #5
    Join Date
    21st February 2012
    Location
    Texas
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    2,250
    I agree with buckeye and mpitfield. You are good to go, good luck on your certification flight.


    Composite Addict
    Alexander Solis

    Level 1 - Mariah 54 - CTI I100 Longburn Red Lightning - 6,345 Feet

  6. #6
    Join Date
    26th October 2016
    Posts
    155
    I did both my L1 &L2 on a cardboard 4" DX3. The L1 flight was an Aerotech H123 to about 750ft. I used motor ejection to pop the near apogee and it made for a great cert flight.

    As everyone else said, once the rocket is built, the weight of individual components no longer matter; you've added epoxy, hardware, paint, etc., which are (nearly) impossible to know in advance. Override the weight and CG and enjoy the flight.
    NAR level 2: Mad Cow Super DX3

  7. #7
    Join Date
    9th March 2018
    Location
    U.S.
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    13
    Quote Originally Posted by tHoagland View Post
    I did both my L1 &L2 on a cardboard 4" DX3. The L1 flight was an Aerotech H123 to about 750ft. I used motor ejection to pop the near apogee and it made for a great cert flight.

    As everyone else said, once the rocket is built, the weight of individual components no longer matter; you've added epoxy, hardware, paint, etc., which are (nearly) impossible to know in advance. Override the weight and CG and enjoy the flight.
    Yes, and just fyi: I also did both my L1 and L2 on a 4" cardboard SuperDX3. It's a nice sturdy kit for a wide variety of H-I-J motors. For L1, I used AT I305 to 2206 feet, and then later for L2 used CTI J330 to 3724 feet. Worked great both times, although both of my peak altitudes were lower than sim by about 25%, probably due to my very poor paint job, not smooth at all. Anyway, rather than details about motor choice, I was more worried about avoiding CATO by drag separation or lack of separation on motor ejection -- i.e., trying to get the friction fit just right between booster and payload section. I asked the RSO to help me double-check it each time, held it for a shake test, added a bit of masking tape, then got perfect recovery both times (JLCR, not DD).

    Best of luck.
    James
    L2 NAR

  8. #8
    Join Date
    4th March 2018
    Location
    Nashville, TN
    Posts
    23
    My L1/L2 was also a 4" super dx3. lol. I way overbuilt mine. L1 was on a 54mm CTI I218 (barely scraped 1000ft and L2 was an aerotech DMS J250 (2500+ft).

    I agree with the guys above. Don't go ham on a cert flight. There's more than enough time to push limits after you Cert. You don't get extra points for turning heads. It's pass or fail. Make sure you pass.
    Nathan Krupla ----> "Trust me... I'm an Engineer... kinda "

    L1 - Heavily Modified Madcow Super dx3 (paper) - 54mm CTI i218 - 2-18-18
    L2 - See above - 54mm Aerotech DMS J250 - 3-3-18
    L3 - Soon?

  9. #9
    Join Date
    10th July 2007
    Location
    Melbourne, Australia
    Posts
    1,468
    Roy, sounds like you sim just like I do. Go for it. Good luck
    TRA 13430, Level 3

    "Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

  10. #10
    Join Date
    7th July 2013
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    Toronto
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    Quote Originally Posted by pendrin2020 View Post
    I agree with the guys above. Don't go ham on a cert flight. There's more than enough time to push limits after you Cert. You don't get extra points for turning heads. It's pass or fail. Make sure you pass.
    The above is not my personal philosophy.

    I push my certs flights because it is much more rewarding to take risks when I have something on the line. I have never subscribed to the "make sure you pass then take risks later" mantra. Failure is an option", you just dust yourself off, figure out where you failed and try again. Failure is often when the deepest knowledge is gained and a big part of the hobby is about learning through personal experiences for me.

    Why if someone does more than a pop and drop does it automatically have to be about "turning heads", its not always about the destination, there is also a journey to enjoy. If it was all about ego I would be burning through my certs.
    Michael Pitfield
    TRA 14579 L2
    NAPAS BoD
    URRG
    MARS
    CRC

  11. #11
    Join Date
    23rd July 2011
    Location
    Butte, MT
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    2,548
    Quote Originally Posted by mpitfield View Post
    The above is not my personal philosophy.

    I push my certs flights because it is much more rewarding to take risks when I have something on the line. I have never subscribed to the "make sure you pass then take risks later" mantra. Failure is an option", you just dust yourself off, figure out where you failed and try again. Failure is often when the deepest knowledge is gained and a big part of the hobby is about learning through personal experiences for me.

    Why if someone does more than a pop and drop does it automatically have to be about "turning heads", its not always about the destination, there is also a journey to enjoy. If it was all about ego I would be burning through my certs.
    It all depends on the primary reason for attempting a certification flight. If the primary reason is certification, show us what you know. Thatís really all that the certification witnesses need to see.
    If you want to push it, you raise the risk of failing that goal, but we leave it up to the flyer. Thereís no place on the forms for style points. . Either way, weíre there to help.


    Steve Shannon
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  12. #12
    Join Date
    7th July 2013
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    Quote Originally Posted by Steve Shannon View Post
    It all depends on the primary reason for attempting a certification flight. If the primary reason is certification, show us what you know. Thatís really all that the certification witnesses need to see.
    If you want to push it, you raise the risk of failing that goal, but we leave it up to the flyer. Thereís no place on the forms for style points. . Either way, weíre there to help.


    Steve Shannon
    No disrespect however "primary reason" and taking risks are not mutually exclusive. If the small percentage of humans that push our species forward didn't take risks then we would still be sitting in caves if at all.
    Michael Pitfield
    TRA 14579 L2
    NAPAS BoD
    URRG
    MARS
    CRC

  13. #13
    Join Date
    23rd July 2011
    Location
    Butte, MT
    Posts
    2,548

    Rocksim Help

    Quote Originally Posted by mpitfield View Post
    No disrespect however "primary reason" and taking risks are not mutually exclusive. If the small percentage of humans that push our species forward didn't take risks then we would still be sitting in caves if at all.
    No worries, I didnít feel any disrespect from you. This is a philosophical difference, nothing more. I absolutely agree about pushing forward. Where we disagree is in when to take risk and itís really a personal choice. A certification flight already entails risk: a person may fail. I wouldnít see how fast I could accelerate during a driverís license test either.
    In my opinion only (absolutely no relationship to Tripoli policy), if you truly want to be able to be in a position to take greater risks to advance your knowledge, you focus on passing the test, then once you pass the test that allows you to progress to higher powered motors so you can fly to higher altitudes, launch larger payloads, learn about building larger motors, etc.
    I wanted to add that this doesnít mean you shouldnít have fun with your cert flight, just make sure the main reason for the flight isnít neglected.



    Steve Shannon
    Last edited by Steve Shannon; 12th March 2018 at 04:18 PM.
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  14. #14
    Join Date
    10th July 2007
    Location
    Melbourne, Australia
    Posts
    1,468
    I always make sure I am thinking about pushing the envelope and learning something from each flight. My certs were at higher impulse motors (I, K, N) than the requirement, but that was my personal choice.

    Choose how you want to fly and keep within the rules

    TRA 13430, Level 3

    "Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

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