Abstract
The variation in aerodynamic forces acting on an ornithopter and an airplane with one or two propellers, which generate the same thrust under no gust wind, is compared when they encounter a gust of wind. The consumed power, or the period of one cycle of flapping motion and that of one rotation of propeller(s), remains constant before and after they encounter a wind gust. The following results are obtained under both conditions. The variation in aerodynamic forces caused by vertical and frontal wind gusts of an ornithopter are a little smaller than that of an airplane with one or two propellers. The difference in variation in aerodynamic forces caused by a side wind gust between them are often larger than that caused by vertical and frontal wind gusts. The variation in aerodynamic forces caused by a side wind gust of the former is smaller than that of the latter when the reciprocal of the advance ratio of the propeller and the flapping amplitude of the ornithopter are small.
