Abstract: Many aquatic species exhibit the extraordinary ability to leap out of water, with flying-fish being a prime example, capable of gliding impressive distances through the air after breaching the surface. Inspired by this remarkable mode of locomotion, researchers have pursued innovative designs for amphibious robots capable of seamlessly traversing the water-air interface. In this study, we present the development of an untethered bioinspired flying-fish robot actuated by the reciprocating motion of its caudal fin. The robot features retractable and rotatable pectoral fins on both sides, allowing active pitch control during submerged swimming. To enhance propulsion performance, we developed a dynamic model that describes the coupled head-tail beating motion and conducted a numerical optimization of the beating angles using FLUENT simulation. The results indicate that increasing the tail beating angle substantially boosts thrust albeit at the cost of greater lateral force, whereas increasing the head beating angle slightly reduces thrust while exerting minimal influence on lateral force. An optimal configuration, consisting of a 15 head beating angle and a 35 tail beating angle, achieves a balance between high thrust and low lateral force. Under these parameters, the robot attains a simulated swimming speed of 1.3 m/s and a jumping height of 86.14 mm, sufficient to breach the water surface. Experimental validations demonstrated a maximum swimming speed of 1.12 m/s, a jumping height of 112 mm, and a peak thrust of 9.819 N at a maximum beating frequency of 12 Hz. The robot also exhibits high maneuverability, with a minimum turning radius of 35 mm. Comparative analysis of simulation and experimental results shows relative errors of 16.07% in speed, 23.11% in jumping height, and 4.51% in thrust, with overall trends consistent between the two. These findings offer valuable insights for the design of next-generation amphibious robots capable of efficient water-to-air locomotion.

Key words: Flying-fish-inspired robot')">Flying-fish-inspired robot, Beating propulsion, Mechatronic system design, Fluid simulation optimization