Combined Design of Gain-Scheduled C-Star and Maneuver Load Alleviation Laws

This paper presents an automated tuning of a longitudinal baseline load factor flight augmentation system (FAS) and a maneuver load alleviation (MLA) controller. The FAS is representative of those employed in modern fly-by-wire civil aircraft (regarding the pull-up maneuver loads), and the MLA function reduces sizing loads. These control laws are applied to a flexible and energy-efficient aircraft. During the iterative aeroelastic optimization of the preliminary aircraft design, the evolution of the aircraft design and structure calls for an adjustment of the control system tuning. An optimization-based procedure is proposed to fully automate the multi-objective control tuning process, which would allow considering their load reduction performance in an automated multidisciplinary optimization loop of the aircraft. The parameters of the active control functions are scheduled over the equivalent airspeed and Mach number using a candidate function to capture the change in the elevator authority. The closed-loop FAS shows good tracking of the pilot command over the entire flight envelope. The MLA function effectively alleviates the worst-case maneuver vertical bending moment throughout the wingspan as well as the entire flight envelope. Adding an input filter and a center-of-gravity scheduling law decreases the wing-root bending moment further.