Pressure Distribution Measurements on the MK 14-1 and MK 15-1 Torpedoes

Abstract

This report covers measurements of the pressure distribution around the bodies of the Mk-1.4-1 and Mk 15-1 Torpedoes, both when equipped with the standard tail assembly and with a shroud ring tail added, and includes studies of the effect on the pressure distribution of variations in yaw and pitch angles, velocity, and static pressure (i.e., submergence). These two torpedoes are both 21 inches in diameter, made up with heads and afterbodies having the same external shape, and both are equipped with identical fin and rudder assemblies. The only difference between their external shapes, therefore is due to the different lengths of cylindrical mid-sections, and resultant different over-all lengths. (The Mk 1.4-1 is 20.5 ft long, and the Mk 1.5-1 is 24 ft long). The tests were made on 2-inch diameter models (model scale 1:10.5). In addition to providing a general picture of the pressure distribution as affected by the different variables the data presented herein are useful in determining the best locations and arrangements for the pressure intakes to the immersion mechanism and to the depth and roll recorder, and also as a check on cavitation measurements. Because the pressures on the fins themselves were not measured in these tests, the data cannot be used to calculate the over-all forces acting on the complete torpedo The main observations and conclusions are summarized in the following paragraphs: 1. Within the range of these tests the pressure, distribution, as presented in terms of p/q was found to be independent of variations in velocity and static pressure or submergence. That is, the difference between the pressure at any station on the body and the static pressure of the undisturbed water is independent of the static pressure and is directly proportional to the velocity head. 2. The addition of the shroud ring around the fins of these torpedoes has no measurable effect on the pressure distribution. 3. The pressure distributions around the head and afterbody of the Mk 1.5 i-1 ere found to be practically identical with those of the Mk 14-1. That is, increasing the length of the cylindrical mid-section does not, in this case affect the pressure distribution on the head or afterbody. 4. The pressure on the surface of these torpedoes equals the static pressure of the undisturbed water at two positions, one on the projectile nose and one on the afterbody (See Figures 12, 18, 24, and 30). Ahead and behind these two stations the pressure is above static, while between the two (which includes about 83% of the over-all length of the Mk 14-1, and 86% on the Mk 15-1) the pressure is below static. 5. The position on the afterbody at which P = P_0 is only slightly affected by yaw or pitch angles up to 3°. 6. On the basis of these measurements, made without rotating propellers, it appears that the best arrangement for the pressure intake to the immersion mechanism would be through a piezometer ring connecting to four pressure taps uniformly distributed about the circumference of the afterbody and about 35 inches ahead of the end of the tail. The pressure imposed on the diaphragm would then be equal to true hydrostatic pressure, and practically independent of yaw or pitch The influence of the propellers may shift this point slightly either aft or forward. 7. Placing the pressure take-off for the depth and roll recorder where P = P_0 on the nose is not recommended because P changes rapidly in this zone and large errors can result from small inaccuracies in locating the connection Connection of the depth and roll recorder to the point of the afterbody where P = P_0 is, of course, physically impracticable. It is recommended, therefore, that the pressure intake be left unchanged and, if necessary, determine the corrections to be applied to the depth record.