Minimum-Power Trim of Overactuated Multi-Tiltrotor Aircraft in Transition

Multi-tiltrotor aircraft concepts capable of vertical takeoff and landing along with efficient high-speed cruise often incorporate multiple propulsors, aerodynamic lifting surfaces, and control surfaces. The trim problem for a configuration with more control actuators than degrees of freedom is underdetermined, but an optimal solution can be found that maximizes some measure of desirability while satisfying constraints. This article presents an optimization-based method for analyzing the trim problem for an overactuated multi-tiltrotor aircraft through transition from rotor-borne to wing-borne flight. A three-degree-of-freedom longitudinal dynamics model is constructed for a notional multi-tiltrotor aircraft, and a gradient-based optimizer is used to solve for the trimmed control allocation that minimizes propulsive power while satisfying operational constraints. Results are presented for power-optimal trim points in level flight and at varying climb rates in the transition corridor. The methodology enables exploration of assumptions, design parameters, and constraints that influence the performance and design of multi-tiltrotor aircraft.