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This paper presents preliminary results of an experimental investigation of the aerodynamics of rigid and flexible flapping wings with bio-inspired kinematics. We consider rigid and isotropic flexible wings undergoing two degrees of freedom periodic motions of the flapping angle and the pitch angle. The wing models are thin flat plates with Zimmerman elliptical planform of aspect ratio 7.2. We present comparisons of two bio-inspired kinematics derived from the hawkmoth kinematics along with a purely sinusoidal motion. The experiments are conducted at conditions relevant to biological flight, properly scaled for water tests, which are Reynolds number of 7100 and a reduced frequency of 0.21 based on flow properties at the 75% span location. The performance of the flapping motions is compared between the differing motions and between flexible and rigid wings. Time resolved phase-averaged force measurements show the development of two force peaks during the flapping cycle for the bio-inspired kinematics and a single peak for the sinusoidal kinematic. These features are not strongly influenced by wing flexibility. Propulsion efficiency is characterized by the measured figure of merit for each case and it is found that flexibility improves performance in terms of both thrust and efficiency compared to rigid wings.

Force Measurements of a Flapping Wing with Two Angular Degrees of Freedom and Bio-Inspired Kinematics