FULL CALIBER PROJECTILE FOR USE AGAINST UNDERWATER OBJECTS

Abstract: A projectile (50) is propelled from a location in air, through anair/water interface, and toward an underwater object (24). The projectile (50) is of a full caliber that is directly received into and fired from a gun barrel (22). The portion of the projectile (50) that contacts the bore of the gun (22) is made of a material that will not unduly damage or be transferred to the bore of the gun upon firing. The projectile (50) includes a forward end stinger head (74) that forms a cavitation void (30) around the projectile (50) in water, minimizing water drag on the remainder of the projectile (50). The projectile (50) further includes a shoulder (90) that contacts the side of the cavitation void (30) in the event that the projectile (50) yaws into a wall of the cavitation void (30) as it passes through water, producing a restoring force that prevents the projectile (50) from tumbling.

Description: FULL CALIBER PROJECTILE FOR USE AGAINST UNDERWATER OBJECTS BACKGROUND OF THE INVENTION This invention relates to munitions, and, more particularly, to a projectile system that can be fired from air against underwater objects located at moderate underwater ranges. Projectiles are widely used against targets in air. In the most common approach, the projectile is placed into a gun, together with a propellant. The propellant is ignited, driving the projectile out of the barrel of the gun and toward the target. Projectiles have extremely limited capability to be fired from air against targets in water, primarily for three reasons. First, the trajectory of the projectile can be radically altered when it encounters the interface between the air and the water (i.e., the surface of the water). At a shallow angle of incidence to the water, the projectile may not enter the water at all, and instead may skip away. At a higher angle of incidence to the water, the projectile may enter the water but its path is altered. This problem is always a consideration, but it is of particular concern to the accuracy of the projectile when the surface of the water exhibits a constantly varying state due to wave motion. Second, the drag produced by the water rapidly slows the projectile and drastically limits its range. The range of conventional projectiles in water varies according to the weight and velocity of the projectile, but is typically at most no more than about 3 feet under optimal conditions for a conventional .50 caliber projectile. Third, the lateral hydrodynamic forces on the projectile can cause it to tumble, further limiting its range and effectiveness. For these reasons, projectiles are seldom fired from air against targets submerged in water. If conventional projectiles are fired from air toward a target submerged in water, they are largely ineffective. Instead, self-propelled devices such as torpedoes are used, and even in this case the torpedo is usually dropped into the water before its propulsion is started. There are applications where a projectile that can be fired against underwater targets from the air would be useful. For example, a standard defense against amphibious military operations is underwater mines placed at moderate depths in near-shore landing areas. Such mines are now removed by specially trained swimmers at considerable risk or robotic devices which have significant constraints in their operation. An alternative approach would be to fire a projectile at the underwater mine from the air, as from a helicopter. Projectiles are far less costly than self-propelled devices in such applications, and could be made of different sizes and types for firing from a range of weapons of both small and large bores. Projectiles that can be fired from air against a submerged target would also be useful against swimmers attempting to infiltrate a defensive position. Thus, there is a need for a projectile that can be fired from air against underwater targets. The present invention fulfills this need, and further provides related advantages. SUMMARY OF THE INVENTION The present invention provides a projectile system and a method for its use. The projectile system is fired from a gun with a conventional rifled barrel located in air against submerged underwater objects, passing through the air/water interface on its way to the target. The projectile is directly received into and fired from the mechanism of a gun of a preselected barrel bore. The demonstrated range of the projectile is about 15 feet under water in a 0.50 caliber size. The projectile can pass through the air/ water interface with little or no deflection, regardless of the angle of incidence of the projectile. The projectile is relatively inexpensive and can be produced for a variety of both conventional and unconventional weapons of various bores. In accordance with the invention, a projectile having a projectile forward end and a projectile rearward end comprises a generally cylindrically symmetric stinger head at the projectile forward end. The stinger head includes a stinger nose having a nose maximum diameter and a stinger body having a stinger body forward end joined to a rearward end of the stinger nose. The stinger body includes a stinger nose support having a nose support diameter, and a flow separation groove between the stinger nose support and the stinger nose. The flow separation groove has a groove diameter less than the nose maximum diameter. The projectile further comprises a generally cylindrically symmetric projectile body joined to the stinger head and having a projectile afterbody with a projectile afterbody diameter operable for direct insertion into and firing from a gun of a preselected bore. The projectile afterbody diameter is greater than the nose maximum diameter. The projectile body further includes a projectile forebody joined to the stinger nose support at a forward end and to the projectile afterbody at a rearward end, and a stabilizing shoulder between the projectile forebody and the projectile afterbody. More generally, a projectile comprises a generally cylindrically symmetric projectile body with a projectile body forward end and a projectile body rearward end. The projectile body comprises a projectile forebody adjacent to the projectile body forward end and a projectile afterbody adjacent to the projectile body rearward end. The projectile afterbody has a projectile afterbody diameter operable for direct insertion into and firing from a gun of a preselected bore. The projectile includes means for forming a cavitation void around the projectile body when the projectile body is passed through water, the means for forming being located at the projectile body forward end. The projectile further includes means for stabilizing the projectile body against lateral instability. The means for stabilizing is joined to the projectile body at a location intermediate the projectile body forward end and the projectile body rearward end. The projectile of the invention is a full caliber projectile. That is, the projectile is received into and fired from the mechanism of a gun of a preselected bore (caliber) without any intermediate structure such as a sabot. Accordingly, that portion of the projectile which contacts the bore of the gun must not cause unduly large wear to the bore of the gun and must not deposit to an undue extent upon the bore of the gun. In the present design, the projectile is preferably formed of at least two, and most preferably three, component sections. The stinger is of reduced diameter that does not contact the bore of the gun and can therefore be made of the hard, durable material such as a high-speed steel, tungsten carbide, or a tungsten alloy. That portion of the projectile body which contacts the bore of the gun, preferably the projectile afterbody, must be made of a material that does not unduly wear or deposit onto the bore. Examples of such a material include brass, copper, or lead. The projectile forebody does not contact the bore of the gun, and is preferably made of a dense, hard material such as tungsten. The projectile forebody is preferably formed as a third component and joined to the stinger and projectile afterbody. With this projectile, the cavitation void is a substantially liquid-free volume extending radially outwardly and rearwardly from the wetted forward end of the projectile, when the projectile travels through water. This volume, filled only with air and water vapor, exerts little drag and/or lateral force on the body of the projectile. Consequently, the projectile can travel for moderately large distances through water. If, as the projectile enters or travels through water, it experiences lateral instability so that the cylindrical axis of the projectile does not coincide with its trajectory (flight path), the stabilizing means, preferably in the form of the stabilizing shoulder between the projectile forebody and the projectile afterbody, interacts with the surface of the cavitation void and exerts a restoring force that tends to bring the cylindrical axis of the projectile back into coincidence with the trajectory. Absent such a restoring force, the projectile would quickly deviate from its trajectory and begin tumbling. As used herein, a "projectile" is an object that is propelled by an external force, and which has no capacity for self propulsion. Thus, in this use, a bullet, mounted to a canister of propellant that remains in a gun after the bullet is fired, is a projectile because the bullet itself has no self-propulsion capability. For example, aircraft, rockets, and torpedoes that have a built-in engine and carry their own fuel are not projectiles. The present invention relates to a projectile and a system for its utilization, not to a self-propelled device which presents an entirely different set of problems in relation to its design and use. The present invention provides an important advance in the art of projectile systems. The projectile of the invention can be fired from air effectively against an underwater target. In the air, the projectile is spin stabilized along a straight trajectory. The projectile passes through the air/water interface with little deflection, for a wide range of angles of incidence. In water, the trajectory is maintained and there is a moderate underwater range. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic drawing of a series of projectiles being fired from air toward a target submerged in the water; Figure 2 is a side elevational view of one embodiment of the projectile; Figure 3 is a forward-end elevational view of the projectile of Figure 2; Figure 4 is a detail of Figure 2, illustrating the stinger head; Figure 5 is a schematic view of the projectile as it travels on a straight trajectory through water; Figure 6 is a schematic view similar to that of Figure 5, except that the projectile has experienced a lateral instability; Figure 7 is a side elevational view of a second embodiment of the projectile; Figure 8 is a detail of Figure 7, illustrating an alternative body of the stinger head; and Figure 9 is a block flow diagram of a method for damaging underwater targets. DETAILED DESCRIPTION OF THE INVENTION Figure 1 depicts a series 20 of projectiles being propelled from a gun 22, which is located in air, toward a target 24, which is immersed in water. The first-fired projectile 26 has passed through an air/water interface 28 and is surrounded by water. The first-fired projectile 26 resides within a cavitation void 30, so that the surrounding water does not actually touch the first-fired projectile 26 except at its wetted forwardmost end. A second-fired projectile 32 is still travelling along its trajectory in air. A third-fired projectile 34 is still within a bore 36 of a barrel 38 of the gun 22. The bore 36 of the barrel 38 is desirably rifled, so as to impart a spin to the projectile as it travels the length of the barrel 38. The spin gyroscopically stabilizes the projectile to travel along a trajectory that is initially defined by the direction in which the barrel 38 is pointed. The bore 36 has a diameter D R , which is slightly larger than the maximum diameter of the body of the projectile, D p . The bore diameter D B is of a preselected size or caliber, such as, for example, .50 caliber. The bore diameter may be of a preselected standard size such as .50 caliber or a preselected nonstandard size. The projectile body diameter D P is sized for direct insertion into and firing from the bore 36 of the gun 22. The term "direct insertion into" means that no intermediate structure, such as a sabot, is positioned around the projectile. The projectile is inserted into the receiver or breech mechanism of the gun (not shown). Typically, D P is less than D B by less than about 0.003 inches, depending upon the value of D B . If the diameter of the projectile 34 is too small, the propellant gases will partially escape in the overly large clearance between the projectile and the bore when the gun is fired, resulting in a loss of propulsive efficiency. Additionally, the rifling of the barrel 38 will not function properly to impart a spin to the projectile which gyroscopically stabilizes the projectile. If the diameter of the projectile 34 is too large, the projectile will physically not fit within the bore 36 or, if it does fit within the bore, will cause excessive wear as it passes along the bore when fired. Figure 2 illustrates one embodiment of a projectile 50 in side elevation, and Figure 3 shows the front elevation of the same projectile. The projectile 50 is generally cylindrically symmetric with a forward end 52 and a rearward end 54. As used herein, "generally cylindrically symmetric" means that the body is cylindrically symmetric about a cylindrical axis 56, except that there may be discrete features such as deployable fins (discussed subsequently) which are spaced around the circumference of the body. The majority of the length of the projectile 50 is a projectile body 58. The projectile body 58 includes a generally cylindrically symmetric projectile afterbody 60 that occupies approximately the rearmost half of the projectile body 58. The projectile body 58 also includes a generally cylindrically symmetric projectile forebody 62 whose rearward end 64 is contiguous with the projectile afterbody 60. In the projectile body 58, the projectile forebody 62 is in the shape of a frustum of a cone. A structure that creates the cavitation void 30 around the projectile 50 when the projectile 50 travels rapidly through water is located at the forward end 52 of the projectile 50. This structure passes through the water such that the water does not flow along the projectile body 58. Instead, the water is forced in a transverse direction so that it does not contact and wet the sides of the projectile body 58. Only the cavitation-producing structure contacts and is wetted by the water. The cavitation void 30 is a partial vacuum that may contain some air and water vapor. Figure 4 illustrates one form of the cavitation-producing structure, a stinger head 74. The stinger head 74 is cylindrically symmetric about the cylindrical axis 56 and is affixed to a projectile body forward end 76. The stinger head 74 includes a forwardmost stinger nose 78. In this embodiment, the stinger nose 78 includes a flat, blunt forward face 80 with a nose maximum diameter D N . This forward face 80 is preferably very smooth, with a surface roughness of no more than about 16 microinches. Rearwardly of the forward face 80, the stinger nose 78 tapers radially inwardly at an angle A, which is preferably about 80°, relative to the forward face 80. The stinger nose 78 is supported on a stinger body 82, which in turn is affixed to the projectile body forward end 76. The stinger body 82 includes a cylindrical stinger nose support 84 and a circumferential flow separation groove 86 between the stinger nose support 84 and the stinger nose 78. In the illustrated preferred embodiment, the flow separation groove 86 may alternatively be viewed as a forwardly facing shoulder between the stinger nose support 84 and the stinger nose 78. A diameter D G of the flow separation groove 86 is less than the diameter D N of the forward face 80 of the stinger nose 78. The stinger head 74 is preferably made of a hard material such as high speed steel, tungsten carbide, or tungsten alloy to resist impact with the water. The stinger head 74 impacts the water at velocities as high as 3000-4000 feet per second, which imposes a loading of about 50 kilobars on the stinger head in a period of about 0.1 microsecond. The stinger nose 78 portion of the stinger head 74 should be very smooth to promote a thin boundary layer dimension. Testing has shown that the stinger nose 78 desirably has a surface roughness of no greater than about 16 microinches in order to achieve the desired boundary layer dimension as the projectile travels through the water. As the projectile 50 passes through the water at a high velocity, a water flow boundary layer is produced at the stinger nose 78. The water flow boundary layer adheres to the surface of the stinger nose 78. Along the sides of the stinger nose 78, the inwardly tapered shape of the stinger nose 78 cooperates with the flow separation groove 86 to cause an intended flow separation of the water from the projectile 50 as the projectile 50 passes through the water. As shown in Figure 5, this flow separation creates the cavitation void 30. Thus, only the forwardly facing surface 80 of the stinger nose 78 portion of the projectile 50 contacts the water, and the remainder of the projectile 50 is not wetted. The pressure and skin drag on the projectile 50 is therefore minimal, resulting in greatly extended underwater range of the projectile as compared with conventional projectiles. Hydrodynamic effects on the projectile that potentially cause trajectory deviations are also reduced. The stinger nose 78 is not optimally streamlined for passage through the air, but because of its small diameter the added air resistance is not significant and the projectile 50 is capable of supersonic flight through air. Nevertheless, there may be lateral forces applied to the projectile 50 as it enters the water at the air-water interface 28 or as it travels through the water. In normal movement of the projectile 50, its cylindrical axis 56 rotates about its trajectory 88 to gyroscopically stabilize the projectile on that trajectory as a result of the rifling of the barrel 38. When lateral instability occurs in the absence of a lateral stabilizing means such as discussed next, the rearward end 54 moves laterally relative to the forward end 52. The side of the projectile contacts the wall of the cavitation void 30, wetting the side of the projectile. In this event, a tumbling motion of the projectile 50 is induced, leading to increased water drag, collapse of the cavitation void 30, and a rapid slowing of the projectile 50. To counteract lateral instability, a means for stabilizing the projectile against lateral instability is provided on the projectile body 58. As its stabilization means, the projectile 50 preferably includes a forwardly facing stabilization shoulder 90 positioned between the projectile afterbody 60 and the projectile forebody 62, as seen in Figures 2, 3, 5, 6, and 7. This stabilization shoulder 90 is formed by making the diameter of the projectile afterbody 60 larger than that of the projectile forebody 62 at their point of joining. The shoulder 90 may be at 90° to the cylindrical axis 56, or rearwardly tapered. The stabilization shoulder 90 functions in the manner shown in Figure 6. If the projectile 50 yaws into the wall of the cavity 30 due to the imposition of a lateral force, the stabilization shoulder 90 is brought into contact with the envelope of the cavitation void 30 at a location indicated by arrow R. Water pressure against the stabilization shoulder 90 creates a restoring force that pushes the cylindrical axis 56 of the projectile 50 back toward coincidence with the trajectory 88. The projectile 50 is desirably manufactured in three pieces shown in Figure 2: the stinger head 74, the projectile afterbody 62, and the projectile forebody 64. This approach allows the stinger head 74 to be made of a hard, erosion-resistant, and impact-resistant material such as high speed steel, tungsten carbide, or tungsten alloy. The stinger head 74 can be machined to an extremely smooth finish. The projectile forebody 64 is made of a soft, dense material such as tungsten, to provide mass at a location as far forward in the projectile as possible. The projectile afterbody 62 is made of a softer material that does not damage the barrel of the gun during firing, such as brass, copper, or lead. The projectile 50 preferably has a length-to-diameter ratio (L/D) of greater than 4:1, and is preferably from about 4:1 to about 8:1. For smaller values of L/D, the restoring force moment arm is insufficient to counteract lateral instability and there is insufficient mass in the projectile for satisfactory penetration. For larger values of L/D, the projectile becomes difficult to stabilize gyroscopically and cannot be accommodated in conventional gun mechanisms. By comparison, conventional fired projectiles have L D ratios of about 2-3. Various modifications may be made to the projectile, as shown in Figures 7-8. The features of projectiles having these modifications are otherwise the same as those previously described for the projectile 50, and those descriptions are incorporated here. The features may be used in various combinations as may be appropriate. Figure 7 illustrates a projectile 100 having a set of fins 102 at the rearward end 54 of the projectile. This projectile 100 is designed for firing from guns having barrels which are not rifled and therefore do not impart a gyroscopic stabilizing spin to the projectile as it is fired. The set of fins 102 provides aerodynamic stabilization of the projectile 100 as it flies through the air. The fins 102 fold against the side of the projectile 100 when it is within a casing (not shown) prior to firing. The fins 102 remain folded against the side of the projectile 100 as it travels the length of the barrel 38 when fired, and then unfold after leaving the barrel. The opening action of the fins 102 can be produced in any of several ways. In one, the fins 102 are formed of a springy metal such as a spring steel and cantilevered from the side of the projectile. The fins are folded down to lie against the sides of the projectile within the cartridge. When the projectile 100 leaves the barrel, the fins 102 unfold. In another approach shown in Figure 7, the fins 102 are mounted to the body 58 of the projectile 100 by hinges 104 that operate between a closed position with the fins folded flat and an open position with the fins extended. Another embodiment of a stinger head 106 is also shown in Figure 7 and in greater detail in Figure 8. The stinger head 106 is like the stinger head 74, except that a conical forward face 108 is substituted for the flat forward face 80 of Figure 4. An included conical angle B of the conical nose 108 can be as large as about 130° while still permitting the stinger head 106 to cooperate with the flow separation groove 86 to induce the flow separation that leads to the formation of the cavitation void 30 as the projectile 100 travels through the water. The flat forward face 80 of Figure 4 is preferred to induce the flow separation, but the use of the conical forward face 108 has the advantage that it reduces the shock loading on the projectile 100 as it enters the water at the air/water interface 28. For designs utilizing a high mass of the projectile and a propellant creating a high muzzle velocity, it may be necessary to reduce such shock loading so that the projectile does not fragment when it enters the water. Figure 7 also shows another embodiment of a projectile forebody 110. The projectile forebody 62 of Figure 2 is generally conical. The projectile forebody 110 of Figure 7 is ogival in shape. An ogive, having a shape generally describable as comprising a portion of an ellipse, is convexly curved outwardly as compared with a conical shape. The ogive permits additional mass of the projectile 100 to be concentrated toward the forward end of the projectile 100, as desired, rather than toward its rear. Ogival shapes are used in some other contexts such as some conventional bullets, missiles, and rockets for another reason, the reduction of aerodynamic drag. The ogival projectile forebody 110 has little effect on aerodynamic drag as compared with the conical projectile forebody 62. Instead, as noted, its function is to increase the mass of the projectile 100, with the mass positioned near the forward end. Other shapes of the projectile forebody can also be used. Figure 9 illustrates a preferred method for utilizing any of the projectiles made according to the present invention to damage an underwater object. A projectile is provided, numeral 120. The projectile is as previously described, or has a combination of the features previously described. The projectile is propelled toward an underwater target from a location in the air, numeral 122, as illustrated in Figure 1. The projectile travels through the air initially, passes through the air/water interface, and then travels through the water. Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.

Claims: CLALMS What is claimed is: 1. A projectile having a projectile forward end and a projectile rearward end, the projectile comprising: a generally cylindrically symmetric stinger head at the projectile forward end, the stinger head including a stinger nose having a nose maximum diameter, a stinger body having a stinger body forward end joined to a rearward end of the stinger nose, the stinger body including a stinger nose support having a nose support diameter, and a flow separation groove between the stinger nose support and the stinger nose, the flow separation groove having a groove diameter less than the nose maximum diameter; a generally cylindrically symmetric projectile body joined to the stinger head and having a projectile afterbody having a projectile afterbody diameter operable for direct insertion into and firing from a gun of a preselected bore, which projectile afterbody diameter is greater than the nose maximum diameter, and a projectile forebody joined to the stinger nose support at a forward end and to the projectile afterbody at a rearward end; and a stabilizing shoulder between the projectile forebody and the projectile afterbody. 2. The projectile of claim 1, wherein the stinger nose comprises a blunt forward face. 3. The projectile of claim 1, wherein the stinger nose comprises a conical forward face. 4. The projectile of claim 1, wherein the stinger nose comprises a stinger nose forward region having a stinger nose forward region maximum diameter, a stinger nose rearward region adjacent to the flow separation groove, the stinger nose rearward region having a stinger nose rearward region diameter less than the stinger nose forward region maximum diameter. 5. The projectile of claim 1, wherein the flow separation groove comprises a forwardly facing separation groove shoulder between the stinger nose and the stinger nose support. 6. The projectile of claim 1, wherein the projectile forebody diameter gradually decreases from the afterbody diameter at its rearward end to the nose support diameter at its forward end. 7. The projectile of claim 6, wherein the projectile forebody is conical. 8. The projectile of claim 6, wherein the projectile forebody is ogival. 9. The projectile of claim 1, wherein the stinger nose has a surface finish of no greater than about 16 microinches. 10. The projectile of claim 1, wherein the stinger head is made from a material selected from the group consisting of steel and tungsten carbide. 11. A method for damaging an underwater target, comprising the steps of providing a projectile comprising a generally cylindrically symmetric projectile body with a projectile body forward end and a projectile body rearward end, the projectile body comprising a projectile forebody adjacent to the projectile body forward end and a projectile afterbody adjacent to the projectile body rearward end, the projectile afterbody having a projectile afterbody diameter operable for direct insertion into and firing from a gun of a preselected bore, means for forming a cavitation void around the projectile body when the projectile body is passed through water, the means for forming being located at the projectile body forward end, and means for stabilizing the projectile body against lateral instability, the means for stabilizing being joined to the projectile body at a location intermediate the projectile body forward end and the projectile body rearward end; and propelling the projectile toward an underwater target from a location in air, through an air/water interface, and into water.

Inventors: BROWN JEFFREY A, COPSEY REED, KLINE ROY, TULIN MARSHALL, BROWN, JEFFREY, A., COPSEY, REED, KLINE, ROY, TULIN, MARSHALL
Applicants: HUGHES AIRCRAFT CO, HE HOLDINGS, INC., DOING BUSINESS AS HUGHES ELECTR
Application year: 1996
Main classification: F42B10
IPC codes: F42B10