Investigating Impaired Aircraft's Flight Envelope Variation Predictability Using Least-Squares Regression Analysis

Abstract

Aircraft failures alter the aircraft dynamics and cause the maneuvering flight envelope to change. Such envelope variations are nonlinear and generally unpredictable by the pilot, as they are governed by the aircraft’s complex dynamics. Hence, to prevent in-flight loss of control, it is crucial to practically predict the impaired aircraft’s flight envelope variation due to any a priori unknown failure degree. This Paper investigates the predictability of the number of trim points within the maneuvering flight envelope and its centroid using both linear and nonlinear least-squares estimation methods. To do so, various polynomial models and nonlinear models based on the hyperbolic tangent function, which incorporate the influencing factors on the envelope variations as the inputs and estimate the centroid and the number of trim points of the maneuvering flight envelope at any intended failure degree, are developed and compared. Results indicate that both the polynomial and hyperbolic tangent function-based models are capable of predicting the impaired fight envelope variation with good precision. Furthermore, it is shown that the regression equation of the best polynomial fit enables direct assessment of the impaired aircraft’s flight envelope contraction and displacement sensitivity to the specific parameters characterizing aircraft failure and flight condition.