Aerodynamics of dragonfly flight and robotic design

A pair of dynamically scaled robotic dragonfly model wings was developed to investigate the aerodynamic effect of wing-wing interaction in dragonfly flight. Instantaneous aerodynamic forces were measured while forewing-hindwing phase difference (γ) was systematically varied. Experimental results showed that, i) for hovering flight, γ=0° enhanced the lift force on both forewing and hindwing; γ=180° reduced the total lift force, but was beneficial for vibration suppression and body posture stabilization. In nature, 0° is employed by dragonflies in acceleration mode while 180° is usually in hovering mode. ii) For forward flight, wing-wing interaction enhances forewing lift while reduced hindwing lift at all phase differences. Furthermore, the total lift was slightly reduced for γ= 0° to 90° and significantly reduced by 18% when γ=270°. The results consist well with the fact that, dragonflies usually employ 50° to 100° for forward flight, but seldom employ 270°. PIV results are shown for wing-wing interaction analysis.