A simplified method for determining from flight data the rate of change of yawing-moment coefficient with sideslip

Abstract : A method is presented by which the directional stability derivative C sub n sub Beta, the rate of change of yawing-moment coefficient with sideslip angle, can be evaluated for a conventional airplane from flight records of a lateral or directional oscillation. For the method shown, the calculation of C sub n sub Beta for a particular high-speed-flight condition reduces to the determination of only the moment of inertia about the Z-axis and the period of a sideslipping, yawing, or rolling oscillation. When applied to conventional airplanes flying at low to moderate lift coefficients, the assumptions involved in this simplified method produce negligible error. A comparison of C sub n sub Beta as determined in flight and in the wind tunnel shows good agreement for the four conventional airplanes considered.