Design, Optimization and Experiment of a Detachable Bi-Segment Hybrid Aerial-Underwater Vehicle With Morphable Arms

Abstract

Effective ocean observation requires hybrid aerial-underwater vehicles (HAUVs) to operate efficiently across both air and water. However, such cross-domain missions often lead to significant hydro-aerodynamic conflicts and endurance limitations caused by structural redundancy. This letter proposes Nezha-Split, a morphing detachable bi-segment HAUV that performs repeated cross-domain maneuvers and supports on-demand jettisoning of its positively buoyant, retrievable aquatic segment to eliminate structural redundancy and extend aerial endurance under demanding conditions. The vehicle features a multifunctional folding mechanism where the rotor arms double as an active center of gravity (CoG) adjustment system, achieving robust passive stability across four distinct configurations introduced by the detachable design. To balance the conflicting requirements of different configurations, a multi-objective optimization (MOO) framework is implemented. Furthermore, a squid-inspired tri-fin nose cone enhances roll stability and downward lift underwater, achieving an average 88% improvement in lift-to-drag ratio. Experiments from pool and flight tests confirm that the detachable architecture leads to a 42.2% reduction in hover power consumption while ensuring smooth water-air transitions and underwater depth-keeping. This work provides a novel methodology for developing high-efficiency, multi-domain robotic systems with on-demand structural reconfiguration.