Analysis of turning dynamics and aerodynamic performance in butterfly free flight

This research investigates the effects of body motions on the turning flight trajectories and aerodynamics of butterflies across varying turning radii. In the butterfly free-turning flight motion capture experiment, 15 flapping cycles were recorded to classify the butterfly's turning radii, from sharp to slight turns. Eleven body and wing kinematic parameters were extracted to characterize turning motions. Based on these measurements, three-dimensional numerical simulations were performed to reproduce the observed flight postures and to systematically analyze the resulting aerodynamic forces and flow field structures during turning maneuvers. The study results revealed that body posture was the primary factor influencing the turning radius, specifically the pitch and roll angles. When butterflies adopted high and low pitch angles, the turning radius of the fitted flight path decreased by 36.9% and increased by 26.3%, respectively, compared to the moderate turning mode. These changes were attributed to variations in the wing flapping plane angle. Additionally, notable differences were observed between flapping-wing and fixed-wing turning behavior. During a roll angle of approximately 44°, the left wing of the butterfly generates a normal force during the downward stroke, while the right wing maintains a vertical force, thereby sustaining flight altitude. In contrast, fixed-wing aircraft at the same roll angle must additionally adjust the pitch attitude and increase the flight angle of attack to maintain lift. This study provides theoretical and experimental insights that offer qualitative guidance for the design and development of turning mechanisms in flapping-wing aerial vehicles.