Measurement of unsteady aerodynamic forces of 3D flapping wing in hovering flight (2nd report, comparison between trapezoidal and sinusoidal flapping motions)

An experimental study of the aerodynamic characteristics of 3-dimensional flapping wing in hovering flight is conducted. Lift and power are measured in water on a scaled flapping wing of bumblebee. Two types of flapping motion are employed. One is a trapezoidal type of flapping motion which consists of translational, reversal and rotational phases; the other is a sinusoidal type of flapping motion, in which a wing is rotating continuously. The results show that the trapezoidal type has higher efficiency than the sinusoidal type. The shorter rotational phase enhances a fluid force normal to the wing surface. However, the rotational phase during the flapping translational phase contributes the increase of power rather than that of lift. This is because the enhanced fluid force vector due to the rotational phase is directed to the stroke plane, which requires more flapping power. In order to attain higher efficiency in hovering flight, the rotational phase should be done during the reversal phase rather than the flapping translational phase.