Analysis of Lateral Stability Variations Across the Flight Envelope Using Flight Test Data

The lateral static stability of an aircraft, typically characterized by the rolling moment generated due to sideslip (������), is not constant throughout the flight envelope—a fact acknowledged by certification standards that require its assessment under multiple flight conditions. While traditional models attribute this stability primarily to geometric factors assumed invariant with flight condition, this study reveals significant variability in ������, influenced by both angle of attack and thrust. The present research investigates how ������ varies across the flight envelope of a turboprop aircraft by applying system identification techniques to flight test data. A set of well-structured flight maneuvers was executed at different altitudes, airspeeds, and thrust settings to excite the lateral-directional dynamics. A parametric model was developed to capture these effects, offering a compact representation that outperforms conventional interpolation in steady maneuvers and highlights limitations under dynamic conditions. The estimated local derivatives were used to construct a global model of ������ as a function of non-dimensional thrust coefficient. The results indicate a nonlinear behavior of ������ with respect to both angle of attack and power, with thrust effects often dominating under certain conditions. These preliminary results support the more efficient development of high-fidelity flight simulators while reducing dependency on extensive flight testing.