Experimental designs on studies of flapping locomotion

Flapping flight and undulating swimming are perhaps the most fascinating biological locomotion means found in nature. To study such fluid-structure interactions in laboratory settings, we introduce mechanical systems that execute reciprocal motions. Model wings or fins are flapped at a desired frequency and amplitude. Perpendicular to actuation, the systems are allowed to move freely, rendering forward swimming or flight. Here, we present two mechanisms that have been used in our research on flap-and-swim locomotion. In the first system, which is designed in a cylindrical water tank, a wing is vertically flapped and its resulting horizontal rotation is regarded as forward flight. The second system operates in a water tunnel; a wing is flapped in an incoming flow but is restricted within a force potential, with which the net thrust or drag can be precisely measured.