# Development of an Autonomous Underwater Helicopter with High Maneuverability
## 1 Introduction  
In deep-sea exploration, Autonomous Underwater Vehicles (AUVs) play an important role by virtue of their unique characteristics, which include their autonomous, long-time and long-range operation capabilities [1]. The research on them is booming all over the world, and they have caused a revolution in the field of ocean research [2]. On one hand, the demand for AUVs comes from the need for large-scale underwater observation and resource exploration in traditional scientific research. On the other hand, based on the application and development of seabed infrastructure equipment and various types of underwater machinery, the maintenance of seabed constructions also puts forward new requirements for AUVs [3]. These tasks require high maneuverability in small areas and stability while performing tasks. To satisfy various applications, including bionic submarines, various forms of AUVs have been proposed [2]. However, near-seabed operation remains a great challenge for AUVs. Shape is very important for the maneuverability of AUVs. The requirements of traditional AUVs are long-range, high-speed and long-duration operation. Therefore, most research has been focused on one-axis streamlined underwater vehicles, such as torpedo-shaped submersibles of the water-droplet type or the long cylindrical type [4]. Although these types of AUV are suitable for long-distance navigation [5], most of them have poor maneuverability [6]. Obviously, it is difficult for them to adapt to new modes of work that combine large-scale cruising over several kilometers with small-scale flexible operation over a few meters. High maneuverability in the horizontal plane and stability in the vertical direction are required in small-scale operations. The disc shape has one prominent advantage. It has the characteristics of good motion stability at low speeds [7]. Furthermore, disc-shaped AUVs have several unique advantages: they are highly maneuverable in harsh working environments; they can explore from all angles and directions within a narrow space; their utilization of internal space is more efficient; their completely symmetrical shape is not easily caught by weeds during navigation [8]; and the resistance caused by flow in all directions is low due to the centrally symmetrical shape [9]. The research on disc-shaped AUVs is still in the laboratory, and most mature disc-shaped AUVs are glider forms, which only use buoyancy and gravity for long-distance navigation, similar to the principle of a glider in the air. With CFD technology, a variety of more mature underwater gliders have been developed. The motion characteristics of classic underwater gliders have been studied to some extent using CFD technology [10], such as the CIDESI Underwater Glider [11]. The first disc-shaped AUV was Discuz of the Webb Corporation in the United States. It has been demonstrated to be capable of resisting the disturbance of advection and landing on the seabed for observation [12]. In addition, there are LUNA [13] and BOOMERANGE [14] of the Research Institute for Applied Mechanics, Kyushu University, and a disc-shaped underwater glider of Dalian Maritime University [15]. These disc-shaped AUVs utilize the isotropic properties of the disc shape in resisting plane flow and achieving excellent steering characteristics. However, due to the lack of active driving, they cannot carry out complex and flexible planar motion. For example, BOOMERANG is almost unable to move in the horizontal plane, and its steering speed is about 5 deg/s [16]. In addition, for the disc-shaped glider made by the Dalian Maritime University, it takes nearly \(40\times 40\) m space to make a \(180^{\circ}\) turn. To be maneuverable in the horizontal plane, we consider the application of the disc shape to the common AUV with propulsion components and propose a new disc-shaped AUV, namely, the Autonomous Underwater Helicopter (AUH).