Hydrodynamic Evaluation of a Flying Fish Robotic Model Organism: A Study on the Effects of the Caudal Fin Shape

Flying fishes are renowned for their ability to glide hundreds of meters through the air, after a taxi and takeoff behavior that is possible because of their asymmetric tail shape. To taxi, the ventral lobe of the tail, which is almost double the length of the dorsal lobe, is the only part of the fish that is in the water. The hydrodynamic effects of this asymmetric, or heterocercal tail, have never been studied. Herein, we developed a bioinspired robotic model organism based on the functional morphology of flying fishes, to experimentally control for the effect of the shape of the tail on thrust production. Using both force transducers and particle image velocimetry, we found that there was no significant difference in thrust generation between the heterocercal flying fish tails and the homocercal tails, where both tail fin lobes are equal in length, as is typical of other fishes. However, the current study employed rigid fin designs, and we anticipate that the addition of flexible fins that are more similar to the material properties of fish fins may have different results.