# Configuration Design and Trans-Media Control Status of the Hybrid Aerial Underwater Vehicles
## 1 Introduction  
With the rapid development of industrial technology, aerial unmanned vehicles (AUVs) and underwater autonomous vehicles (UAVs) complete various tasks, playing an important role in both civil and military fields. However, they are greatly limited by being unable to operate in air or in water. In view of \"air-sea integration\", a forward-looking concept of water-air hybrid aerial underwater vehicles (HAUVs) was suggested, which are also known as underwater-aerial cross-domain vehicles, water-air trans-media vehicles and water-air amphibious/aqutic vehicles. HAUVs were the deep integration of aviation and navigation technologies, which could break through the single medium limitation by operating both in air and underwater seamlessly. This is essentially different from both UAVs and AUVs, with the ability of rapid flight in the air and underwater stealth navigation. Although HAUVs are still in the stage of exploration research, they could be widely used in both civil and military fields to meet more diverse needs and higher-level requirements, as demonstrated in Yang [1], Alzu'Bi [2], and Kaja [3].  
In the civil field, HAUVs could quickly fly to mission airspaces to collect aerial data, then submerge into water to collect underwater data, which could greatly improve a mission's efficiency. For example, HAUVs could be used for the detection of underwater pipeline leakages. Water surface and underwater detections are shown in Figure 1. In addition, they have unique advantages in terms of biological resource detection, port monitoring, chart drawing, seabed monitoring, meteorological detection, ecological environment detection, ecological observation, ship-bottom detection, offshore oil and gas-platform monitoring, pier detection, etc. [4].  
In the military field, HAUVs integrate the advantages of rapid flight in the air with good underwater concealment [5, 6]. They could make use of the physical separation of water and air mediums and realize long-distance concealed strikes by jumping between the water medium and the air medium. An imagined motion profile is presented in Figure 2. In addition, the emergence of HAUVs could ensure that military ships receive rapid support, playing an important role in the acquisition of information from the air and underwater.  
Although the prospects of this technology are bright, the development of HAUVs is also challenging due to two factors. First, the physical properties of water and air are very different, as shown in Table 1 adapted from [7]. As a result, it is difficult to accommodate the two mediums in the configuration design. Secondly, the research on HAUVs is multi-disciplinary, involving aerodynamics, hydrodynamics, air flight control, and underwater navigation control. It increases the complexity of the development of control methods and motion dynamics. Overcoming these contradictions and solving these problems are the keys to the development of HAUVs. This paper draws conclusions on the configuration design and trans-media control issues. The authors expect that the comments made here could help in their development.