Shape of The ALBAC The body of the ALBAC consists of a 1/2 ellipse shape front cap, a cylindrical pressure hull, a corn shape tail cap with a vertical stabilizing fin, a pair of wings and tail wings, which are made of FRP except the pressure hull.The dimensions of the vehicle basically depend on that of the cylindrical part of the body which should provide enough space for electric and electronic devices, i.e., a depth sensor, a gravity sensor, a magnetic sensor, two CPUs, interface boards and two actuators to trim and roll. A ranging sensor, a velocity sensor, a deballastor, a tail angle trigger and a transponder are fitted in the front and the tail caps (cf. Table 1 and Fig. 5). Consequently, a prototype vehicle of 140 cm in length, 120 cm in span and approximately 45 kg in mass was designed and constructed as shown in Photo 1, Figs. 1, 5 and Tables 1, 2.
*******Table 2 Specifications of the ALBAC******
The pressure hull made of aluminum alloy is designed for diving to 300 meter depth with 2.0 safety factor, and provides a space for instruments listed in Table 1 including a 3-liter dry pay load space of 1-atmospheric pressure for scientific measurement devices.
Wings and horizontal tail wings have a NACA 0009 symmetrical foil section considering both upward and downward gliding. The vertical stabilizing fin which prevents side slip has a NACA 0018 foil section.
Since the instruments consume 44 watt electric power and time for one mission is estimated about 30 minutes, a nickel-zinc battery cell of 100 watt hour is selected and fitted on the fore bulkhead of the pressure hull.
A forward ranging sensor of 500 kHz with 4 degrees in beam width to detect obstacles, and a transponder with which relative position from the mother ship can be detected using a SSBL system, are fitted in the front cap and the tail cap. The transponder is self-contained and has not a link to the CPU of the vehicle
A compact inertial navigation system which consists of a three-axis gravity sensor and a flux gate magnetic sensor is installed to measure the attitude of the vehicle. From the roll, pitch and yaw angles, their angular velocities are calculated at every 0.1 second.
A propeller type velocity meter with a electric magnetic encoder to measure the forward velocity and a temperature compensated pressure transducer for the depth are fitted at the top of the front cap and the fore bulkhead, respectively.
To control the location of the center of gravity, two DC servo motors are driven with PWM by a computer system as illustrated in Fig. 6. Capacity of motors are enough to move the weight even if the pitching angle is 90 degrees.
The computer system consists of two NEC V50 CPUs, i.e., one for control of attitude of the vehicle and the other for data logging. The structure of computer system is schematically illustrated in Fig. 7.
Data transmission to load a program and to acquire measured data is utilized RS-232c serial interface between the computer system of the ALBAC and a host computer on deck.
A program for one mission is loaded from a host computer to the CPUs of the ALBAC on deck, then the umbilical is disconnected and the vehicle is hung from the deck and released to the sea. When the output of pressure transducer is over a specified level for example 0.6 meters, the control and data acquisition sequence is started As in the same way of starting, the control and data acquisition sequence is ended when the vehicle ascends to the specific shallow depth. The vehicle on deck is connected to the umbilical and the measurement data are saved. A charged battery is exchanged for the next operation.