Abstract:
The illustrative embodiment provides bumpers which are roughly shaped like skis that face towards the air-water boundary of the air cavity. When the projectile fishtails and one or more of the bumpers come into contact with the air-water boundary, the water imparts torque and a rebounding force to push the projectile completely back into the air cavity. Furthermore, because the bumpers are shaped roughly like skis and not like knives, the bumpers do not penetrate the water or create unnecessary water drag.

Description:
FIELD OF THE INVENTION 
     The present invention relates to supercavitating projectiles in general, and, more particularly, to control surfaces for supercavitating projectiles. 
     BACKGROUND OF THE INVENTION 
     A supercavitating underwater projectile can achieve speeds of 150 knots, and, therefore, it is especially useful in naval applications. A supercavitating underwater projectile achieves these speeds because it comprises a special tip on its nose known as a “cavitator.” As the projectile travels through the water, the cavitator contacts the water in such as way as to create many small air bubbles. The small air bubbles then coalesce into one big air bubble that is large enough to completely encompass the projectile. The effect is that the projectile is traveling inside a giant air bubble that is itself moving through the water. 
       FIG. 1  depicts a side view of the salient components of supercavitating projectile  100  as known in the prior art inside cavity  103 . Supercavitating projectile  100  comprises projectile body  101  and four prism-shaped fins  102 - 1 ,  102 - 2 ,  102 - 3 , and  102 - 4  (not shown), which are equally spaced around body  101 , and cavitator  103 . 
     As projectile  100  travels through the water, there is a tendency for projectile  100  to swerve or fishtail, and the purpose of fins  102 - 1  through  102 - 4  is to keep projectile  100  completely inside air cavity  104 . This minimizes the amount of projectile  100  which touches the water, which enables projectile  100  to go fast. 
     SUMMARY OF THE INVENTION 
     One disadvantage of supercavitating underwater projectiles in the prior art is that the prism-shaped fins tend to penetrate the air-water boundary of the air cavity, which increases the water drag on the projectile. Another disadvantage is that the position of the fins is fixed and does not adjust to changes in the shape of the cavity that are caused by changes in the speed of the projectile. 
     The present invention enables a supercavitating underwater projectile to stay within the air cavity without some of the costs and disadvantages for doing so in the prior art. For example, the illustrative embodiment provides bumpers which are roughly shaped like skis that face towards the air-water boundary of the air cavity. When the projectile fishtails and one or more of the bumpers come into contact with the air-water boundary, the water imparts torque and a rebounding force to push the projectile completely back into the air cavity. Furthermore, because the bumpers are shaped roughly like skis and not like knives, the bumpers do not penetrate the water or create unnecessary water drag. 
     Furthermore, the illustrative embodiment comprises an actuator for changing the positioning of the bumpers based on the speed of the projectile and a cavity-shape model. 
     The illustrative embodiment comprises: a projectile body capable of creating a air cavity inside water, wherein the air cavity is defined by a air-water boundary; and a first ski-shaped bumper connected to the projectile body, wherein the bottom of the first ski-shaped bumper faces the air-water boundary of the air cavity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a side view of the salient components of supercavitating projectile  100  as known in the prior art inside cavity  103 . 
         FIGS. 2A and 2B  depict left side and front views, respectively, of the salient components of supercavitating projectile  200  in accordance with the illustrative embodiment. 
         FIGS. 3A and 3B  depicts left side and front views, respectively of the salient components of supercavitating projectile  200  with respect to elliptic paraboloid  301  and frustum  302  of elliptic paraboloid  301 . 
         FIG. 4  depicts a cut-away view, along line A-A in  FIG. 2B , of the salient components of supercavitating projectile  200 . 
         FIG. 5  depicts longitudinal axis  501  of supercavitating projectile  200  and line  502 , which is perpendicular to longitudinal axis  501 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 2A and 2B  depict left side and front views, respectively, of the salient components of supercavitating projectile  200  in accordance with the illustrative embodiment.  FIGS. 3A and 3B  depicts left side and front views, respectively of the salient components of supercavitating projectile  200  with respect to elliptic paraboloid  301  and frustum  302  of elliptic paraboloid  301 .  FIG. 4  depicts a cut-away view, along line A-A in  FIG. 2B , of the salient components of supercavitating projectile  200 .  FIG. 5  depicts longitudinal axis  501  of supercavitating projectile  200  and line  502 , which is perpendicular to longitudinal axis  501 . 
     Supercavitating projectile  200  comprises: projectile body  201 , bumpers  202 - 1  through  202 - 4 , bumper struts,  203 - 1  through  203 - 4 , cavitator  204 , sensor  401 , controller  402 , and actuator  403 . 
     Although supercavitating projectile  200  comprises four bumpers and four struts, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention which comprise any number of bumpers and struts. 
     Projectile body  201  is a non-explosive, propelled object, such as a bullet, for imparting kinetic energy to a target. It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which projectile body  201  is an explosive object. Furthermore, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which projectile body  201  is a self-propelled object, such as a missile, rocket, or torpedo. 
     Bumper  202 - i , wherein iε{1, 2, 3, 4}, is a ski-shaped structure for keeping projectile body  201  within air cavity  205  and minimize the projectiles yaw angle relative to its trajectory. The purpose of bumper  202 - i  is to generate torque and rebounding forces when projectile body  201  fishtails and bumper  202 - i  contacts the air-water boundary of air cavity  205 . 
     The sum of the outer surfaces of bumpers  202 - 1  through  202 - 4  are shaped so as to suggest a frustum  302  of elliptic paraboloid  301 , as depicted in  FIGS. 3A and 3B , which frustum is designed to conform to the shape of air cavity  205 . The vertex of the elliptical paraboloid is coincident with cavitator  204 . It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which the bumpers suggest another shape, such as for example, and without limitation, a frustum of a conic section, a box, a pyramid, sphere, or polyhedron. The parabolic shape of bumper  202 - i  is intended to present a low-drag surface to the air-water boundary of air cavity  204 , in contrast to the high-drag surface of the bumpers in the prior art. In accordance with the illustrative embodiment, the shape and orientation of bumper  202 - i  is such that bumper  202 - i  has more surface area facing in parallel with line  502  than perpendicularly to the line (i.e., in parallel with line  503 ) as depicted in  FIG. 5 . 
     Strut  203 - i  is a rigid member that structurally connects bumper  202 - i  to actuator  403  within projectile body  201 . It will be clear to those skilled in the art, how to make and use strut  203 - i.    
     Cavitator  204  is a tip, as is well-known in the prior art, on the nose of projectile body  201  that contacts the water in front of supercavitating projectile  200  in such as way as to create many small air bubbles. The small air bubbles then coalesce into one big air bubble that is large enough to completely encompass the supercavitating projectile  200 . It will be clear to those skilled in the art how to make and use cavitator  204 . 
     Sensor  401  is a mechanism for detecting the speed of supercavitating projectile  200  through the water and for transmitting an indication of that speed to controller  402 . It will be clear to those skilled in the art how to make and use controller  402 . 
     Controller  402  is electronics for estimating the shape of air cavity  205  based on the speed measurement from sensor  401  and for controlling actuator  403  to position bumpers  202 - 1  through  202 - 4  so that they are in the correct position with respect to the air-water boundary of air cavity  204 . To do this, controller  402  uses a cavity-shape model based on the speed with which supercavitating projectile  200  is moving through the water. For example, when controller  402  determines that air cavity  205  is expanding, controller  402  directs actuator  403  to extend bumpers  202 - 1  through  202 - 4 , but when controller  402  determines that air cavity  205  is contracting, controller  402  directs actuator  403  to retract bumpers  202 - 1  through  204 - 4 . 
     Actuator  403  is a mechanism for extending and retracting bumpers  202 - 1  through  202 - 4  under the direction of controller  402 . It will be clear to those skilled in the art how to make and use actuator  204 . 
     It is to be understood that the disclosure teaches just one example of the illustrative embodiment and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure and that the scope of the present invention is to be determined by the following claims.