Open Rocket CD adjustments.

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CZ Brat

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I am mentoring some TARC teams this year. This is my first time mentoring TARC, but the other mentor is very experienced, and thus he is also "Mentoring the Mentor". This is also the first year the school chose to use Open Rocket vs RocSim, due to it being good, free, and the ability of every student to own and use a copy of it at home. I use OR as my only Sim, and love it.

Question: How do I adjust the CD of a rocket? As we start flying, and get real world results, I would like to be able to adjust the CD till predicted altitude is the same as what we get in the field. Thanks in advance for any help.
 
I am mentoring some TARC teams this year. This is my first time mentoring TARC, but the other mentor is very experienced, and thus he is also "Mentoring the Mentor". This is also the first year the school chose to use Open Rocket vs RocSim, due to it being good, free, and the ability of every student to own and use a copy of it at home. I use OR as my only Sim, and love it.

Question: How do I adjust the CD of a rocket? As we start flying, and get real world results, I would like to be able to adjust the CD till predicted altitude is the same as what we get in the field. Thanks in advance for any help.

For starters: adjusting Cd is useful strictly in the subsonic regime, because once you hit transonic, then the CD is no longer constant. That's one reason why OpenRocket is far more accurate with supersonic simulations than RockSim. Of course, this doesn't matter to TARC, but that's a "just so you know" kinda thing.

However, that means you can't directly adjust the Cd. Instead, you want to adjust other parameters, such as fin edge constraints, fin thickness, and surface roughness, to make the simulations match as closely as possible to your results.
 
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