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I am currently going through all of my stability and control calculations and am a bit confused on how to find $C_{m_{ac,wb}}$. The only things I'm finding online is that they are given through airfoil data? Not sure how to acquire this information for my NACA 4415 airfoil. Any help would be much appreciated!

$$\large C_{m,_{0}} = C_{m_{ac,wb}} + V_HC_{L_{α,t}} (ε_0-i_t)$$

Aditya Sharma
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Andrew
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    A bit more of background would help in deciphering your equation – sophit Feb 14 '23 at 06:35
  • Sorry if the question wasn't clear enough. Essentially I am trying to calculate Cm,0 for my RC plane. The equation can be found in Dynamics of Flight Stability and Control by Bernard Etkin and Lloyd Duff Reid third edition on page 32. Cm,0 is the zero lift moment coefficient. Needing to estimate the downwash e0, tail setting angle it, and Cmac,wb which is the moment coefficient about the aerodynamic center of the wing body combination. I'm plugging in my current values (estimating the downwash is 0) and my Cm0 is turning out negative which is not accurate. Cm0 is supposed to be a + value. – Andrew Feb 14 '23 at 07:21
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    I'll get in there before someone suggests it; I think this question is MUCH better suited to the expertise here than [drones.se] – Jamiec Feb 14 '23 at 08:16
  • Recently found a "longitudinal dihedral" source: Albert Zahm, circa 1893, one of the earliest publications regarding static stability. – Robert DiGiovanni Feb 14 '23 at 17:00
  • "my Cm0 is turning out negative which is not accurate. Cm0 is supposed to be a + value". Cm should be zero to have a trimmed aircraft; positive to pitch the nose up and negative to pitch the nose down; the horizontal stabiliser is used to change Cm as needed. Derivative of Cm in respect to alpha should be negative to have a stable aircraft. The book you are using doesn't explain any method to estimate the values on the equation? – sophit Feb 14 '23 at 17:45
  • I suggest you get OpenVSP, build a simplified model, and run the thin-surface analysis there. It will calculate CM0 and CMalpha, SM, Xnp, etc. for you. – Rob McDonald Feb 14 '23 at 17:52

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