Controllability Evaluation for VTOL Aircraft in Velocity Envelope: A Distance-Based Metric

Abstract

This paper introduces an approach for evaluating and quantifying the controllability of vertical takeoff and landing (VTOL) aircraft across various flight states. By employing the controllability theory for linear systems subject to bounded control, this study derives sufficient conditions for the local controllability of the nonlinear VTOL system. These conditions are cohesively integrated with the trimmability condition directly derived from nonlinear dynamics, establishing a comprehensive criterion that facilitates the assessment of both trimmability and controllability of VTOL aircraft. This unified criterion elucidates the relation between desired and achievable specific forces and moments with clear implications for flight mechanics. Building upon this criterion, a distance-based metric is proposed to quantify the controllability, with an optimization-based algorithm developed for its calculation. Focusing on an exemplary lift plus cruise VTOL aircraft, this study investigates controllability variations within the aircraft’s velocity envelope and assesses the impact of rotor failures on controllability. These applications demonstrate the proposed method’s effectiveness in quantifying the controllability of VTOL aircraft in various flight conditions.