Birds and insects achieve various maneuvers such as hovering, snap turn, and vertical takeoff and landing by using vortices around the wings. Above all, a butterfly is suited to the model of insect-scale flapping robot because of a lower flapping frequency and a fewer degrees of freedom compared with other creatures. In this study, to develop a butterfly-style flapping robot, we clarified the angular moment during the flight by computational fluid analysis based on high speed camera images. The result showed that the reaction forces on the left and right wings were nearly equal each other in the pitch rotational flight. The angular moment around the pitch axis was dominant. On the other hand, the difference of forces increased and the angular moment around roll axis was dominant in the roll rotational flight.
