Abstract: AquaUAVs which can operate in both air and water, have wide applications in civil and military fields such as ocean environment investigation and island patrol monitoring, indicating great potential for development. In order to achieve loading and launching from underwater platforms, this paper proposes a novel amphibious UAV named ABDragon, which has three operating modes: seabed lurking, water surface floating, and air flight. Firstly, in terms of overall design, a cylindrical layout and modular cabin design are adopted, and a coaxial system is used as the power system, which not only maximizes the convenience of transportation but also enhances its maintainability and reliability. With the integration of a depth control cabin to adjust the relationship between gravity and buoyancy, the attitude stability of sinking, floating, and the entire process in water can be achieved. Secondly, the modeling of flight dynamics and analysis of water stability have been completed, and flight control laws have been designed and preliminarily verified in simulation. Finally, a prototype has been built, and sinking-floating, air flight, and cross-medium tests have been conducted gradually in the laboratory and field, which confirmed the feasibility and effectiveness of the ABDragon's overall design and multi-modal operational capability.

Key words: Amphibious water and air, Modular cabin, Flight experiment, Cross-domain, Coaxial UAV