Effects of flapping wing kinematics on hovering and forward flight aerodynamics

The effects of wing kinematics on the aerodynamic characteristics of a flapping insect wing are investigated experimentally. The time-varying aerodynamic forces acting on the flapping wing are measured in hovering and forward flight using a dynamically scaled mechanical model in a water tunnel, which simulates a bumblebee flapping wing in hovering and forward flight. Wing kinematics can be categorized as trapezoidal or sinusoidal types. The trapezoidal flapping motion is divided into translational and reversal phases, and the trapezoidal feathering motion is divided into fixed-angle and rotational phases. In the sinusoidal type, the time histories of angles for the flapping and feathering motions are represented as sinusoidal functions. The feathering rotation during the flapping translation causes an increase in aerodynamic power rather than lift and thrust for hovering and forward flight. Therefore, it is preferable for the feathering rotation to be conducted during the flapping reversal phase for high efficiency. The trapezoidal flapping motion and trapezoidal feathering motion with a shorter duration of rotation should be selected for a higher efficiency in hovering and forward flight. This result indicates that many insects using the trapezoidal type attach importance to a good efficiency in selecting the wing kinematics. For a larger lift in hovering and slower forward flight, the sinusoidal flapping motion and trapezoidal feathering motion with a shorter duration of rotation should be selected.