Fig. 1 shows a pilot-model vehicle named PTEROA150, which was designed and constructed in 1989. PTEROA150 can dive to 2000m depth and cruise for 1 hour in 2 knots. General arrangement is illustrated in Figure 2 and the principal particulars are shown in Table 1. The vehicle consists of a body, a pair of elevators, twin vertical stabilizing fins, twin skegs, and a pair of rudders. Principal dimensions of body are 150cm, 75cm, and 45cm in length, width, and thickness, respectively. Dry weight is about 220kg.
The shape of longitudinal cross section of the body at the center line is NACA0030 and the transversal cross section is approximately oval [2,3]. The center of buoyancy is located a little behind the 6 square station, and the center of gravity is located just before it. As the body is not cylindrical as torpedoes but rather flat, the lift force acts mainly on the body. Elevators enhance good performance of pull-up behavior and stability of swimming. A pair of propeller thrusters are fitted under the vertical stabilizing fins. They can be operated independently to let the vehicle yaw. Two oil-immersed induction motors of 300W are directly connected to propellers. The speed of revolution is about 600 rpm for 1 m/sec cruising. A small inverter was newly designed to supply electric power to the induction motor. Three actuators constructed of oil-immersed stepping motors are equipped to trim control surfaces, i.e. two for elevators and one for rudders, by which the elevator can be trimmed by about 30 deg/sec when the vehicle is cruising in 3 knots.Considering the convenience of handling and testing in the towing tank, the principal dimensions are designed so as to minimize the total volume. All apparatus are installed in 8 pressure cylinders. The main pressure cylinder is 27 cm in diameter, which is rather large compared to the dimension of the body, because commercially available CPU board and interface boards, which can be set at the slot of personal computer, are selected. This restricts the arrangement of other cylinders in the body. Though 65% of the void in the body is filled with buoyant, it is impossible to install cylinders for 6000 m depth diving. The design depth of these cylinders is, therefore, determined as 2000 m to reduce the total weight of the vehicle.