Some Effects of Parameter Variations on the Lateral-Directional Stability of Aircraft

Methods of analyzing the effects of aerodynamic uncertainties on the stability of lateral-directional motions are presented. Truncated and residualized reduced-order models of the motion are developed. Together with covariance analysis, these models provide simplified estimates of the probability of instability. A Space Shuttle entry flight condition is examined with this technique, and the predicted probability of open-loop instability is found to be low (< 0.0001). Monte Carlo stability analysis illustrates that closed-loop control can increase the probability of instability as a consequence of uncertainty in the control derivatives.