Abstract:
The water-exit process of hybrid aquatic-aerial drones is a critical step for their cross-media operation, presenting a series of technical challenges due to abrupt changes in physical properties between media. We systematically review the core issues, solutions, and research progress of this process, providing a clear technical development roadmap for future research. Firstly, the core challenges of the water-exit process are summarized into three major problems: propeller efficiency degradation in the near-water surface airspace, surface tension-viscous effects, and attitude instability during the water-exit process. Secondly, the latest domestic and international solutions are reviewed from three dimensions: Power system design, structural material optimization, and control algorithm strategies. Their principles, advantages, disadvantages, and applicability are analysed. The analysis indicates that, regarding propeller efficiency degradation, increasing vertical active force and buoyancy adjustment are two mainstream technical paths: the former offers a faster response, while the latter has lower underwater energy consumption. For surface tension-induced viscosity, superhydrophobic materials and streamlined structural designs effectively reduce water-exit resistance. For attitude instability, control algorithms have evolved from traditional proportional-integral-derivative (PID) control to adaptive robust control and deep reinforcement learning to address dynamic uncertainties caused by media switching. Cooperative optimization of power, structure, and control technologies is crucial for solving water-exit challenges. Future research should focus on the integration of smart materials and structures, efficient cross-domain energy management, and intelligent adaptive control in complex sea conditions.