Drag Studies in Water Entry of the MK 13-6 Torpedo

Abstract

An experimental investigation was made of the drag characteristics of a 2-in. diameter model of the standard (Head F) Mk 13-6 torpedo during the cavity phase of the underwater trajectory. The data used in this analysis were available from a previously completed trajectory study. These data were sufficient to determine the instantaneous velocity of the model along its trajectory. Hence, the deceleration and the instantaneous drag coefficient could be determined. The model was dynamically and geometrically similar to the prototype; its entry velocity of 120 fps was scaled from the prototype velocity of 406 fps in accordance with the Froude law. Results from model runs made at nominal atmospheric pressures of 1, 1/2, 1/11, and l/22 atmospheres with initial pitches between ± 6° are presented. A fixed trajectory angle of 19° was used in all tests. Prototype data from the Naval Ordnance Test Station, Morris Dam, taken at a nominal trajectory angle of 19° with initial pitches between ± 1° were available for comparison. Results from three tests of the Mk 13-6 torpedo model with the finer Dunn nose (Head I) made at air pressures of 1, 1/11, and l/22 atm. are also presented. These runs were made with a nominal trajectory angle of 20° and entry velocity of 120 fps with initial pitches between ± 0.5°. There were no prototype data from this shape suitable for drag analysis. The results of the investigation are summarized in the conclusions at the end of the report.