Investigation of Flow Field and Performance of Tandem Flapping Wing Micro Air Vehicle

To clarify aerodynamic mechanisms of tandem flapping wing to generate thrust force/induced flow, thrust force measurements and particle image velocimetry (PIV) measurements were carried out with the variation in the phase difference between fore and hind wings \(\varphi \) . We have self-developed a tandem flapping wing drone whose phase difference could be changed every 30°. This drone was used to measure the thrust force and flow field in 48 different conditions, with the variation in the flapping frequency \(f\) (5, 8, 10, and 13 Hz) and \(\varphi \) (every 30°). As the major trends for the thrust force, the thrust force became minimum around \(\varphi =0^\circ \) and 180°, while there were two performance peaks when the fore wing was leading and when the hind wing was leading. In the case of \(f=13\,{\text{Hz}}\) , the peaks were shown at \(\varphi = 60^\circ \) when the fore wing was leading, and at \(\varphi = 210^\circ \) when the hind wing was leading. As the results of PIV measurements, in the case when the fore wing was leading, the fore and hind wings behaved as a single flapping wing, producing fast induced (backward) flows at the moment of the wing rotation (switch of the direction of the flapping motion). In the case when the hind wing was leading, fast induced (backward) flows were generated when the fore and hind wings crossed each other. These results indicated that the mechanisms to generate induced flows were complex and different with the variation in \(\varphi \) .