Optinal Aeroelastic Trim with Surrogate Structural Constraints

New rotorcraft configurations are emerging which have complex, non-unique trim solutions. A question that faces performance analysts is "what combination of controls and rotor speed produce the best steady-flight condition?" This work develops the concept of optimal rotorcraft trim based on the generalized reduced gradient (GRG) method and explores its application to advanced rotorcraft configurations with multiple, complex trim states. A second contribution of this work is a novel way to rapidly approximate elastic rotor blade stresses and strains from one-dimensional (1-D) beam representations in the aeroelastic trim analysis. The method developed herein captures the maximum cross-sectional stress/strain based on the trained response of an artificial neural network (ANN) surrogate. The stresses/strains are computed simultaneously with the optimal trim and are used as constraints in the optimal trim solution. Finally, an optimal trim analysis is applied to a highspeed compound gyroplane configuration to maximize cruise efficiency with structural constraints.