Experimental evidence of Hopf bifurcation induced by wing–wing interaction in Flapping flight

The current study presents the transition of large amplitude oscillations to a fixed hovering point in the context of bio-inspired flapping robots (BIFRs). The experimental arrangement allows two degrees of freedom for the BIFRs under study: body pitching and translation. The primary objective of this investigation is to compare the flight mechanics characteristics of two almost-identical BIFR configurations: a two-winged configuration and a four-winged one that exploits wing–wing interaction for aerodynamic effects. A motion capture system is utilized to track the two degrees of freedom of each BIFR. The study reveals that the four-winged BIFR exhibits passive transition of large amplitude oscillations to a fixed point beyond a certain frequency, whereas no such transition was observed for the two-winged BIFR at any frequency within the considered range. Realizing that the main difference between the two systems lies within the wing–wing interaction, this study thus underscores the significance of the wing–wing interaction for the transitional response upon the four-winged model. This response might be due to a phenomenon called vibrational stabilization. From the study, it can be implied that wing–wing interaction promotes the transitional response beyond a critical frequency.