Red‐crowned crane in beating flight with almost one hinge

　Since the beating period is large for a large-sized bird such as the crane, we can find the acting force on the wing, assuming steady two-dimensional flow on each wing section at any instant. Thus, when the wing with an angle of attack is flapped down, the upward ahead force act on the wing and both the lift and the thrust can be obtained. On the other hand, when the wing is flapped up, weakened lift and weakly negative thrust act on the joint area with small motion，and weakly negative lift and weakened thrust on the apex area with large motion. Thus, the negative lift and the negative thrust may be canceled out on the flapped up run by adjusting well the angle of attack and the flapped up speed. (Prod. Nov. 1997, scale 1/2, No.1)