To investigate the relation between the location of the center of gravity and the proportional gliding angle, sea trials were conducted at the Ashinoko Lake and the Suruga Bay. The gliding angle of the vehicle is calculated by the next equation based on the forward velocity and the rate of pressure.(6)
|FIG. 8 Results of Gliding Experiment of 0.4788L Longitudinal C.G.Location|
Fig. 8 shows examples of time histories of data of one test. The proportional gliding angle is measured 18.7 degrees which shows good agreement to the estimated value 20 degrees. Fig. 9 shows the correlation between the longitudial location of the center of gravity and the proportional gliding angle in both the descent and ascent stages, where results in the next empirical formulas (in deg).(7)
FIG. 9 Correlation between Longitudinal Center of Gravity Location and Gliding Angle
Here, x is the ratio of body length and the longitudinal location of the center of gravity measured from the body apex. It is shown in Fig. 9 that the gliding angle in a descent stage can be changed from 15 to 30 degrees.
*****FIG. 11 Correlation between Lateral Center of Gravity Location and Yaw Rate*****
When the location of the center of gravity is shifted laterally, the ALBAC rolls and starts to turn in a constant yaw rate as shown in Fig. 10. Because of small misalignment of the tail wings, the vehicle rolls a little even if the weight has not been moved.The relations between the lateral location of the center of gravity and steady state yaw rate are determined as shown in Fig. 11 both in the descent and ascent stages. From these results, the following empirical formulas of yaw rate (in deg/sec) are obtain as,(8)
Here, y denotes lateral shift of the location of the center of gravity from the body center line. Exactly speaking, the proportional gliding angle may increase when the vehicle rolls because of decrease of vertical component of lift force. From the results of trials, however, it is concluded that this effect is negligible.
Oceanographic measurement of the ALBAC Fig. 12 (Not yet included) shows an example of the distribution of temperature in a shallow water at the Suruga Bay measured by the ALBAC. Resolution and response of the thermistor are 1/100 degree and 1 sec, respectively. From these curves of data, it is expected that shuttle type AUVs can be competitive to the expandable bathythermograph (XBT).