Understanding micro air vehicle flapping-wing aerodynamics using force and flowfield measurements

Experimental studies were conducted by flapping a rigid rectangular wing with a mechanism that is capable of emulating complex insect wing kinematics, including figure-of-eight motions, in order to explore the fundamental unsteady flow on a flapping wing at micro-air-vehicle-scale Reynolds numbers. Force and moment measurements were obtained from a miniature six-component force transducer installed at the wing root. The wing was flapped in air and vacuum at the same frequency, and wing kinematics, and the resultant forces, were subtracted in order to obtain the pure aerodynamic forces. In the first part of this paper, the forces produced on the wing undergoing singledegree- of-freedom fixed-pitch pure flapping motions (no pitching or out-of-the-plane coning motions) were determined for a variety of pitch angles. The unsteady aerodynamic coefficients measured during these tests were almost six times the steady-state values measured in the wind tunnel. Flow visualization and particle image velocimetry tests were also conducted, which showed that the key reason for the force increase on the flapping wing is due to a strong leading-edge vortex for which the strength varied throughout the flapping cycle. In the second part of this paper, complete three-degree-of-freedom (flapping, pitching, and coning) insect wing kinematics were investigated for different pitching and coning variations. The aerodynamic forces obtained in these tests were compared with coefficients obtained from the single-degree-of-freedom flapping tests and wind-tunnel tests. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved