# Configuration Design and Trans-Media Control Status of the Hybrid Aerial Underwater Vehicles
## 2 Configuration Design
These vehicles were designed to verify the feasibility of the jet thruster for inclined water exit, regardless of the whole water-air trans-media process of water exit, stability flight, water entry, and underwater navigation. The stored compressed air of the thruster could only achieve a single water-exit process. [PERSON] designed an amphibious vehicle which was driven by a high-power motor, as shown in Figure 2(b), and completed the whole water-air trans-media process. It could only achieve vertical water exit, since the power came from a single air propeller. The next step was to research the design of the variable-sweep wing configuration, which could potentially decrease the water entry impact acceleration [14; 15]. Similar prototypes were designed by [PERSON] and [PERSON] with detailed designs, fabrication, and testing presented in their literatures [16; 17]. [PERSON] proposed an interesting and perfect bimodal system, which consisted of a foldable blade propeller with a variable-sweep wing for aerial and underwater power and a compressed gas thruster for the egress process, as shown in Figure 2(c) [18]. The prototype was not manufactured. It was in the stage of conceptual design and experimental test for the bimodal system. Figure 3: The morphing configuration of the HAUV. (a) [PERSON]’s team; (b) [PERSON]’s team; (c) [PERSON]’s team. Compared with multi-rotor HAUVs, morphing HAUVs have the advantage of fast flight in air. However, the accommodation of the aerial and underwater movement efficiencies, as well as the water entry impact acceleration problem, are not being considered at present. Morphing HAUVs are at a very early stage where researchers are focused on the verification of the whole trans-media process with a manual remote-control mode. Nevertheless, it only achieved partial success in the whole trans-media process. At present, the vehicle is equipped with very little electronic equipment that would be susceptible to impact acceleration. In future, slow, vertical landings or the application of impact load-resistant electronic equipment could be considered as a solution to the impact load problem. A jet thruster could achieve a fast incline egress, while an air propeller could only achieve a vertical egress. Jet thruster power and variable-sweep configuration seem to be promising technical solutions. In addition, multirotor HAUVs were designed and tested for multi-locomotion, benefiting from high maneuverability and hover capability. [PERSON] proposed the first concept of a multirotor HAUV with four underwater propellers and four air propellers [19]. Following this, [PERSON] [20], [PERSON] [21], and [PERSON] [2] designed and manufactured multirotor HAUVs, as presented in Figure 4. They repeatedly completed the experimental verification of the air flight, underwater navigation, and vertical water-air multi-locomotion. [PERSON] and [PERSON]'s HAUVs were neutrally buoyant with a dual-propeller system. A coaxial design was adopted, with [PERSON] using eight of the same specially designed gas propellers for both air and water mediums, while [PERSON] preferred four gas propellers and four water propellers. The dual-propeller system guaranteed seamless multi-locomotion with continuous aerial and underwater power. [PERSON] also proposed an HAUV with four aquatic water and four aerial gas propellers [22]. Four aerial propellers were used both in air and underwater in [PERSON] design. It floated on the surface of the water with a depth control system and then achieved flight. Furthermore, a student team proposed an amphibious collapsible helicopter called the Waterspout [23]. It would totally depend on buoyant force, ascending from a released point underwater to the water's surface. [PERSON] attempted to develop an HAUV with four gas propellers and two fixed side wings to provide the lift necessary for flight and underwater gliding. Further to this, it could achieve three modes: forward-flight mode, VTOL mode for the water-air trans-media process, and underwater-glide mode [24].