Optimization of Flexible Flapping-Wing Kinematics in Hover

Abstract

Hover-capable flapping-wing micro air vehicles are well suited for missions in confined spaces. The best design practices for flapping wings and their kinematics are largely unknown, especially for flexible wings. To address this issue, numerical optimization is applied to the design of the kinematics and structural sizing of a flapping wing using a surrogate-based approach. The surrogates are generated using kriging interpolation of the time-averaged thrust generated and power required by the wings. The thrust and power data are computed using a nonlinear approximate aeroelastic model developed in previous studies by the authors. A numerical optimization algorithm is used to identify designs that produce the desired combination of thrust and power. The design variables consist of parameters describing the flap–pitch kinematics and the stiffness of the flexible wings. A trend study of thrust and power indicate that the phase angle between flap and pitch motions significantly affects the wing performance when the stroke amplitudes and the frequency are fixed. Smaller amounts of pitch actuation produced peak thrust in flexible wings when compared to the rigid wings. Several flexible configurations produce higher thrust when compared to the best thrust-producing rigid configuration. However, rigid wings have higher propulsive efficiency when compared to flexible wings for the same amount of generated thrust. Thus, the actual design of a flapping wing will depend on the relative importance given to thrust production and propulsive efficiency.