A Micro-Aerial-Vehicle (MAV) with figure-of-eight flapping induced by flexible wing frames

Relaxing from the conventional regarding of the "rigid" flapping mechanism, in this work we proposed using "flexible" carbon-fibers and parylene (poly-para-xylylene) films as the wing frames for palm-size micro aerial vehicles (MAVs) with the wingspan of 21.6 cm. We constructed the new flapping MAV with a small body mass of 5.9 g to set a successful 47-s flight record without the delicate multiple degree-of-freedom (DOF) motion previously formulated from the mechanism design. Via a high speed camera, we firstly reported the wing-tip trajectory of the MAV as a "figure-of-eight" which composes the original simple (four-bar linkage) flapping and the induced coherent streamwise vibration whereas the wingbeat frequency being about 10-25 Hz. The time-averaged lift, thrust coefficients and the structure aging of MAVs have been investigated to mention the influence of this figure-ofeight flapping. The experiment results preliminarily show that this biomimetic figure-ofeight is done by the very nature of the aero-elastic interaction as well as the symmetry-breaking of a simple flapping system. The bifurcation (duality) phenomenon of the MAV with figure-of-eight was shown accordingly. How the rigidity of the flexible wing frame influences the appearance of figure-of-eight flapping was addressed experimentally and empirically. Our flexible MAVs exhibit the peculiar characteristic away from the conventional domain of MAVs, and own the similar behavior to hummingbirds from the perspective of scaling laws in wingspan and wingbeat frequency (versus body mass).