Flight mode change with wing phase relationship of dragonfly-type flight

In this research, Dragonfly-type Ornithopers (DTOs) were developed to reveal the effect of the phase relationship between forewings and hindwings on flight performance. The DTO has high aspect four wings. The Reynolds number of the ornithopter is the same order as that of real dragonflies (10³ - 10⁴). The DTO's phase relationship ranges from 0° to 315° with 45° intervals. Flights of DTOs with various phase relationships were recorded with a high speed video camera, and their motions were analyzed. In the stable flight, the flight speed varied depending on the phase relationship. We also visualized the airflow around the wings in a wind tunnel. It was revealed that there were suitable phase relationships for accelerating flight (45°), low speed flight (180°) and high speed flight (270°, 315°). This relationship between the flight mode and the phase relationship was in good agreement with that of dragonflies.