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About Npa

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  1. Just had a quick scan, very informative! And I think the other content in your website would also help me learning rocket science a lot. Thanks!
  2. Drag coefficient is a function of Mach number! I missed that. Indeed, now I know (and truely appreciate) how complex aerodynamics is. As @Boris-Barboris suggested, KerbalWindTunnel seems a good mod where I can compute the aerodynamics of my vessel. The mod supports outputing the aerodynamic profile as a csv file. I think I can then take your idea, like using a polynomial function to empirically estimate the drag or just use the csv file as a lookup table to get a drag value? Damn, talk about doing science! This feels great. P.S. I've just started trying to look under the hood, I know some of my questions might be rather stupid. Really greatful for you guys replying and helping me out!
  3. So I have been trying to model the physics in KSP for a while, using kRPC. I am trying to compute the air drag acting on my rocket so I can compute the trajectory. The kRPC states that the dynamic pressure is a measure of the strength of the aerodynamic forces (link) and the formula is 0.5 * air density * velocity2. Now the KSP wiki states that the atmospheric drag follows the same fomula with an extra constant (coefficient of drag * cross-sectional area). Hence I assumed that when I fly my rocker straight up, where the aerodynamic forces is basicly air drag downwards (numericly checked), the dynamic pressure would be linear to the aerodynamic force. But the experiment shows the other way, as the following figure depicts, where Q is the dynamic pressure. So aerodynamic force is firstly near linear with repect to Q, then as Q hits 40000, is negatively linear and then follows this strange curve. After max Q, it's near linear again. Dynamic pressure data is acquired by vessel.flight().dynamic_pressure, while aerodynamic force data is acquired by norm(vessel.flight().aerodynamic_force). Can anyone share what is the relationship between dynamic pressure and aerodynamic force?