Pressure Distribution Measurements on the MK 13-1, 13-2, and 13-2A Torpedoes

This report includes measurements of the pressure distribution on the body of the Mk 13 torpedo, Modifications 1, 2, and 2A, and shows the effects of variations in yaw and pitch angle, velocity, and static pressure (i.e., submergence). The measurements were made without propellers. The main objective of the investigation was to determine whether or not the depth control mechanism is actuated by true hydrostatic pressure and to determine, if possible, the cause of the erratic depth-keeping behavior of these torpedoes. In addition, the pressure data is applied to discussing the depth and roll recorder performance, to checking cavitation characteristics, and to evaluating forces and moments acting on the projectile. The important observations and conclusions are presented in the following summary: 1. The pressure on the surface of the torpedo equals the static pressure of the undisturbed water (P = P_0) at two positions, one on the nose and one on the afterbody (Figure 8). Between these two stations (approximately 82% of the body length), the pressure is below static. 2. The position for P = P_0 on the afterbody depends on the proximity of the fins, being slightly farther forward near the fins (Figure 22, Station 19). 3. The position for P = P_0 on the afterbody is only slightly affected by yaw or pitch angles up to 3° (Figures 17 and 18). 4. The measure pressure distributions are unaffected by changes in velocity or static pressure (Figure 23). 5. The existing location of the pressure intake for the immersion gear gives a pressure lower than hydrostatic and causes the torpedo to ride below set depth. 6. True hydrostatic pressure, independent of velocity and small yaw or pitch angles, will be obtained if the immersion gear hydrostat is connect to points midway between the tail fins and about 23" ahead of the tip of the tail. 7. The depth and roll recorder is so located in the exercise head that it is subject to a pressure lower than true hydrostatic and too shallow a depth is recorded. Unfortunately, it is possible for the recorder to indicate the depth to be the set depth when the torpedo rides low, as described in Item 5 above. 8. Since there is no satisfactory location in the exercise head where a pressure connection will give P = = P_0, it is recommended that the included pressure data base used to estimate corrections for application to the recorder in its existing location. 9. Form drag and moment coefficients calculated from pressure distribution data are about 15% higher than given by Water Tunnel measurements while the calculated cross force is 27% lower than measured. 10. The K values for the inception of cavitation on the projectile nose as obtained by actual observation and by prediction from the pressure measurements are in good agreement. It should be noted that these tests were made with the standard fin tail without a shroud ring and some of the above conclusions (particularly Item 6), cannot be expected to apply when the ring is added. Additional measurements with a ring tail are being made