Nezha-X: A Self-Foldable HAUV That can Launch From a Tube

Hybrid aerial underwater vehicles (HAUVs) are developing rapidly with the urgent need for joint air-sea observation missions. This letter proposes a novel HAUV that combines a folding wing mechanism and an underwater thrust system with a centralized tail in an inverted triangle configuration. In addition to ensuring underwater and aerial maneuverability, the design's overall streamlined structure minimizes the drag of underwater movement and is more suitable for working in confined spaces. The hydrodynamic performance of the system was evaluated using computational fluid dynamics (CFD) simulation. The results indicate that the folding wing design effectively reduces underwater motion drag by 41.9$\%$. Additionally, the centralized underwater thrust system located at the tail generates sufficient torque to ensure the underwater maneuverability of the HAUV. Field experiments further validate the vehicle's capability to operate in confined environments, execute complex underwater missions, and maintain stable aerial flight. This study provides valuable insights into the drag reduction of HAUV folding wings and the optimization of thruster configuration.