The Effects of Atmospheric Pressure Upon the Water Entry Behavior of a Missile Having a Hemispherical Nose and Flared-Cone Tail

At the request of the Naval Ordnance Test Station, Inyokern, Pasadena Annex, several tests were made at the Hydrodynamics Laboratory, California Institute of Technology, under contract NOrd 9612 to supplement the investigation being made at the Naval Ordnance Test Station (NOTS) under NOTS Task Assignment Re 3d-454-1-52. The NOTS study refers to air-launched missile shapes which oscillate in the cavity during the cavity phase of the underwater trajectory. The purpose of the study is to correlate the behavior of these missiles in terms of distance traveled between the contacts of the tail of the missile with the cavity wall. It is hoped that this parameter can ultimately be used to predict missile stability. In order to decrease the number of variables, the study was begun with only two nose shapes: the hemisphere and a subcalibre flat plate having the same drag coefficient as the hemisphere. The various tail sections used on the cylindrical body section were flared cones of half angles ranging between 0° and 22.50°. Five slenderness ratios from 5.5 to 9.5 were investigated. The slenderness ratio was varied by increasing the distance from the cg to the tail. The distance from the cg to the nose was held constant and the weight and moment of inertia were the same for all of the models. Since it is not possible to vary the air pressure in the open model tank at NOTS, it was desirable to make a few tests in the Controlled Atmosphere Launching Tank (CALT) at the Hydrodynamics Laboratory to see if the behavior of these missiles was altered by changing the air pressure (i.e. changing the cavitation number)