Experimental Methodology for Flapping Wing Structure Optimization in Hovering Flight of Micro Air Vehicles

Abstract

It has been observed that, in both nature and experiment, flapping wing flexibility can significantly enhance aerodynamic performance. By tailoring the structural properties, passive deformation can be utilized to generate higher lift and thrust. This work has developed a systematic methodology to experimentally optimize the flapping wing structure for maximizing thrust production under a simple one-degree-of-freedom motion. Different flapping frequencies and amplitudes are also examined along with different wing structure to study the relationship between kinematics and thrust; because these variables are closely related to the passive inertial deformation. The aerodynamic performance is measured with a force sensor recording both the lift and thrust; the net time-averaged thrust is used as a benchmark to evaluate wing performance. The wing structural property is obtained by measuring wing deformation using a digital image correlation system capable of capturing the full-field out-of-plane deformation of the whole flapping stroke up to 90o in both air and vacuum. The data are presented as contours to reveal details of structural deformation and later extracted as phase plots that show a loop of the deformation versus flap angle. A certain design scheme is formulated to generate a number of designs, all of which are tested for thrust production. The force and deformation data are then correlated to understand the structure that benefits thrust and used to predict parameters for potential optimal flapping flight. It is concluded that for flapping wing structure optimization in hovering flight on this scale, each structure must be tailored according to a certain kinematics (with a desired flapping frequency and amplitude) and optimized for performance values such as thrust/lift coefficient/efficiency.