Aerodynamic and Visualization Study Based on Advance Ratio and Insect-like Wing Shape in Insect Forward Flight

Abstract The present study investigated the effects of wing shape and advance ratio (J) on aerodynamic force generation during forward flight. Wing shapes of bumblebee, hawkmoth, and hummingbird were applied to hawkmoth kinematics at J = 0, 0.13, 0.25, and 0.35, and aerodynamic forces were measured in a water tank. Flow visualization was conducted to support the aerodynamic characteristics. The results showed that the average difference in lift-to-drag ratio due to wing shape was 4.2%, with the difference between bumblebee and hawkmoth wings being less than 3%, indicating a negligible effect. In contrast, the average difference in lift-to-drag ratio with changes in J was 32.9%, which was much greater than that caused by wing shape and appeared to result from changes in the angle of attack with increasing J. As J increases, the stroke plane angle tilted forward, which increased the angle of attack relative to the stroke plane and consequently increased the drag component. Vortex structures were more strongly affected by changes in J than by wing shape, showing a tendency to dissipate as J increased. By extending our previous hovering-flight study to realistic forward-flight conditions, this study demonstrates a clear progression from hovering to forward flight, in which wing kinematics and J dominate aerodynamic force generation within an aspect-ratio range of AR≈ 3–4. These findings provide practical insights for the design of flapping-wing micro air vehicles, suggesting that adaptable kinematic control is more critical than wing planform optimization alone for efficient operation across multiple flight modes.