Abstract:
An apparatus and method for sealing the barrel of an underwater gun between firings is disclosed. The apparatus comprises a turbine that is disposed at the outlet of the muzzle of the gun. The turbine draws in water and, in various embodiments, either (a) vaporizes it, forming a vapor barrier along the spin axis that keeps water out of the barrel, (b) expels it radially, thereby re-directing it so that it does not enter the barrel, or (c) generates water jets that prevent water from entering the barrel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This case is related to the following U.S. patent applications: Atty. Dkt. Nos.: 711-196us (Underwater Gun Comprising a Valve-Type Barrel-Seal), 711-197us (Underwater Gun Comprising a Barrel Adapter including a Barrel Seal), 711-198us (Underwater Gun Comprising a Plate-Type Barrel Seal), and 711-199us (Underwater Gun Comprising a Passive Fluidic Barrel Seal), all of which were filed on even date herewith and all of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to underwater guns. 
       BACKGROUND OF THE INVENTION 
       [0003]    Underwater guns are useful as anti-mine and anti-torpedo devices. Recently, autonomous underwater vehicles (AUVs) have been fitted with underwater guns for torpedo defense and underwater “hunter-killer” CONOPs. 
         [0004]    A gun, especially one with a high muzzle velocity, cannot be fired when water is in its barrel. If a firing where to incur in a water-filled barrel, a very high breach pressure would result as the ignited propellant charge forces (or tries to force) the water out of the barrel. The likely result would be material failure of the barrel. 
         [0005]    The prior art is replete with approaches for waterproofing the barrel of an underwater gun, or for clearing water from its barrel before firing. U.S. Pat. No. 5,639,982 discloses a means for firing a fully automatic gun underwater using a blank barrel-clearance round. Blank barrel-clearance rounds are alternated with live rounds of ammunition. To begin the process, a blank barrel-clearance round is first detonated. This creates gas and steam within the chamber that forms a bubble at the muzzle end of the barrel, thereby displacing water from the chamber. A live round is then immediately fired. The process is repeated, whereby the subsequent detonation of a blank barrel-clearance round displaces any water that has re-entered the barrel subsequent to the firing of the live round. 
         [0006]    U.S. Pat. No. 5,648,631 discloses a spooled tape seal for sealing the barrel of an underwater gun. The system includes a tap that covers the opening of the gun barrel and sprockets for advancing the tape across the opening. Hydrostatic pressure keeps the tape pressed to the end of the barrel to create an effective seal. When a bullet is fired, it perforates the tape. During this brief period of egress, the exhaust gases from combustion of the propellant charge keep water from entering the barrel. Almost immediately, a non-perforated portion of the tape is advanced by the sprockets to cover the barrel opening. External hydrostatic pressure re-seats the tape, thereby preventing water from entering the barrel. 
         [0007]    U.S. Pat. No. 5,687,501 discloses a sealing plate for providing a watertight seal for a multi- or single-barreled underwater gun. The sealing plate provides one or more firing apertures in an otherwise solid surface. Between firings, the gun muzzle is sealed by a solid surface of the sealing plate. To fire a bullet, the sealing plate or muzzle rotates to align the gun muzzle with one of the firing apertures. This permits unimpeded egress. After the bullet fires, the plate or muzzle again rotates so that a solid portion of the sealing plate covers the muzzle. 
         [0008]    These are but a few of the many patents pertaining to various aspects of underwater gun design in general, and to the water-in-the-barrel problem, in particular. Notwithstanding the many approaches to the problem, no truly satisfactory approach has been developed for keeping water out of the barrel of an underwater gun between and during operation. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides an underwater gun having a barrel seal for preventing water from entering the barrel between the firing of rounds. 
         [0010]    In the illustrative embodiment, the barrel seal comprises a turbine that is disposed near the muzzle end of the barrel of a gun. The spin axis of the turbine is coincident with the barrel of the gun (i.e., the turbine and the barrel are concentric). The turbine is driven by a motor. The motor&#39;s controller responds to commands from the gun&#39;s fire-control system. 
         [0011]    In various embodiments, the turbine is configured and/or operated in different ways that ultimately determine how the barrel seal operates to keep water from entering the gun&#39;s barrel. In the embodiments described herein, the turbine remains spinning once a round is fired. This ensures that water is kept out of the barrel so that subsequent rounds can be fired. 
         [0012]    In a first embodiment, the turbine comprises a plurality of radially-disposed turbine blades. When the turbine spins, the blades scoop water from the surroundings. This water is forced out of the turbine in the axial direction through a plurality of very small exit orifices, thereby generating a high pressure water jet. The pressure of this water jet is greater than the water pressure at the operating depth of the gun, such that the water jet prevents water from entering the barrel. 
         [0013]    In a second embodiment, a supercavitating turbine is used. The supercavitating turbine has internal blades. When water contacts the blades of turbine during operation, the water is vaporized. Bubbles of water vapor accumulate near the centerline of the barrel due to the spin of the turbine. The barrel seal is effected by operating the turbine such that a steady-state condition is attained wherein the rate of water entry into the supercavitating turbine is equal to the volume of water vapor that is leaving the supercavitating turbine. 
         [0014]    In a third embodiment, the turbine comprises a plurality of internal blades. A plurality of exit orifices are disposed in the side wall of the turbine. During operation, water is drawn into the turbine through an axially-disposed entrance orifice and expelled in a radial direction through the exit orifices. 
         [0015]    In some embodiments, in particular the first embodiment discussed above, other types of rotating equipment can be used instead of a turbine. For example, and without limitation, a centrifugal pump can be used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1A  depicts an underwater gun having a turbine-based barrel seal in accordance with the illustrative embodiment of the present invention. 
           [0017]      FIG. 1B  depicts further detail of the turbine-based barrel seal of the underwater gun of  FIG. 1A . 
           [0018]      FIG. 2  depicts a first embodiment of the turbine-based barrel seal of  FIG. 1B , wherein the turbine is configured and operated to draw water in along a radial direction and expel it along the axial direction as a high pressure water jet. 
           [0019]      FIG. 3  depicts a second embodiment of the turbine-based barrel seal of  FIG. 1B , wherein the turbine is configured and operated to generate water vapor. 
           [0020]      FIG. 4  depicts a third embodiment of the turbine-based barrel seal of  FIG. 1B , wherein the turbine is configured and operated to draw in water along the axial direction and expel it in a radial direction. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The terms appearing below are defined for use in this specification, including the appended claims, as follows:
       Axially-oriented (or axial orientation) refers to an orientation that aligns with the longitudinal axis of an element. This orientation is orthogonal to a radial orientation.   Barrel is a narrow, hollow cylindrical portion of a firearm through which a bullet travels.   Bore is the hollow portion of the barrel through which a bullet travels during its acceleration phase.   Breech is an opening in the rear of a barrel of a gun where bullets can be loaded.   Chamber is the portion of a barrel where a cartridge is placed just prior to being fired. This is a high pressure containment area which is very precisely aligned with the bore of the barrel.   Fluidically coupled or fluidic communication means that liquid, gas, or vapor from a first region can flow to or otherwise cause an effect in a second region. For example, if two regions are fluidically coupled (or in fluidic communication), a pressure change in one of those regions might (but not necessarily will) result in a pressure change in the other of the regions.   Muzzle is the end of the barrel where the bullet exits as it is being fired.   Operatively coupled means that the operation of one device affects another device, wherein the devices need not be physical attached to one another. For example, a laser and a mirror are operatively coupled if a laser directs a beam of light to the mirror. An actuator and a valve are operatively coupled if the actuator actuates the valve. Operatively-coupled devices can be coupled through any medium (e.g., semiconductor, air, vacuum, water, copper, optical fiber, etc.) and involve any type of force. Consequently, operatively-coupled objects can be electrically-coupled, hydraulically-coupled, magnetically-coupled, mechanically-coupled, optically-coupled, pneumatically-coupled, thermally-coupled, etc.   Radially-oriented (or radial orientation) refers to an orientation that is coincident with the radial direction of an element. See “axially-oriented.”       
 
         [0031]    The present invention pertains to guns that are intended for (1) use in an underwater environment and (2) firing rounds that include a chemical propellant. The underwater guns described herein will typically, although not necessarily, be fitted to AUVs. For clarity, gun  100  is typically depicted in the Figures as having a single round in the chamber or bore. It is to be understood, however, that gun  100  is typically a multi-shot weapon. 
         [0032]      FIG. 1A  depicts underwater gun  100  having a turbine-based barrel seal in accordance with the illustrative embodiment of the present invention. Gun  100  includes barrel  102 , chamber  104 , bore  108 , fire-control system  110 , turbine-based barrel seal  114 . A live round  112  is depicted in bore  108 . 
         [0033]    In the illustrative embodiment that is depicted in  FIG. 1B , turbine-based barrel seal  114  comprises motor controller  115 , motor  116 , and turbine  118 , interrelated as shown. 
         [0034]    The barrel  102 , chamber  104 , and bore  108  are conventional features of most guns. Fire-control system  110  is basically a computer and ancillary elements that enable gun  100  to hit a target. The relative sophistication of any particular embodiment of fire-control system  110  is primarily a function of the intended application for gun  100 . That is, a relatively more sophisticated fire-control system is required for a relatively more autonomous application (e.g., for use in conjunction with an AUV, etc.). 
         [0035]    In a typical embodiment, fire-control system  110  interfaces with one or more sensors (e.g., sonar, radar, infra-red search and track, laser range-finders, water current, thermometers, etc.). The sensor input is used to develop a firing solution for a target. To the extent that gun  100  is located on an AUV, etc., fire-control system  110  advantageously takes into account movements of the AUV itself. And, when associated with an AUV, fire-control system  110  is operatively coupled to aiming and firing mechanisms. 
         [0036]    The fire-control system is not particularly germane to an understanding of the invention and, furthermore, is well understood by those skilled in the art. As a consequence, fire-control system  110  will not be described in further detail. 
         [0037]    Upon receiving an indication to fire round  112  from gun  100 , fire-control system  110  sends a signal to motor controller  115  to energize motor  116 . The motor is operatively connected to turbine  118  and spins the turbine to a desired angular velocity. As described further below in conjunction with three specific embodiments of turbine-based barrel seal  114 , the turbine draws in water to function as a barrel seal. The way in which the water is used as a barrel seal varies, in the three specific embodiments, as a function of turbine configuration and operation. 
         [0038]    This specification now proceeds with a description of three specific embodiments of a turbine-based based barrel seal of  FIG. 1B  for use in conjunction with underwater gun  100 . The description and drawings showing those embodiments focus primarily on turbine  118  and its operation, since this is the primary distinction between the embodiments. It is understood, however, that various embodiments of gun  100  that are depicted in  FIGS. 2-10  include elements such as fire-control system  110 , motor controller  115 , etc., which are depicted in  FIGS. 1A and 1B , but not in  FIGS. 2-10 . 
         [0039]      FIGS. 2 through 4  depict a first embodiment of turbine-based barrel seal  114  of  FIG. 1B .  FIG. 2  depicts motor  116  and turbine  218  coupled to muzzle end of barrel  102 . Rupture disk  224  is disposed at the end of barrel  102 .  FIG. 3  depicts a three-quarters perspective view of turbine  218  and  FIG. 4  depicts a front end view of turbine  218 . 
         [0040]    Referring now to  FIGS. 2 through 4 , turbine  218  comprises a plurality of blades  220  that extend radially outward about spin axis A-A of the turbine. Blades  220  are curved to facilitate “scooping” water from the surroundings. Channel  221  is formed between adjacent turbine blades  220 . 
         [0041]    A plurality of orifices  223  are disposed in forward wall  222  of turbine  218 , one orifice in each channel  221 . Orifices  223  are situated at the most radially-inward portion of forward wall  222  (i.e., at the bottom of each channel  221 ). As a consequence, the diameter of the “ring” of orifices  223  is only slightly larger than the diameter of barrel  102 . 
         [0042]    Before gun  100  is initially fired, water is kept out of barrel  102  via rupture disk  224 , which is disposed at the muzzle of barrel  102 . Upon receiving a command to fire gun  100 , fire-control system  110  sends a signal to motor controller  115  to energize motor  116  (see,  FIG. 1B ). The motor spins the turbine  218  up to a desired angular velocity before round  112  is fired. 
         [0043]    Spinning turbine  218  draws in water between from the surroundings and expels it as a high-pressure water jet through orifices  223 . The turbine is designed and operated so that the pressure of the water jetting through orifices  223  is greater than the ambient water pressure (based on the actual depth underwater of gun  100 ). 
         [0044]    After the high-pressure water jet is established, round  112  is fired. Firing the round causes rupture disk  224  at the muzzle of barrel  102  to rupture. Rupture is due to the increase in pressure in bore  108 . Turbine  218  continues to spin after the first round is fired so that the high-pressure water jet it creates keeps barrel  102  free of water after rupture disk  224  has ruptured. Additional rounds can be fired through the now water-free barrel (as long as turbine  218  is spinning). 
         [0045]      FIGS. 5 through 7  depict a second embodiment of turbine-based barrel seal  114  of  FIG. 1B .  FIG. 5  depicts a cross-sectional view of motor  116  and turbine  518  coupled to muzzle end of barrel  102 . Rupture disk  224  is disposed at the end of barrel  102 .  FIG. 6  depicts a cross-sectional view of turbine  518  in operation wherein water vapor forms as water contacts the turbine blades.  FIG. 7  depicts a cross-sectional view of turbine  518  in operation, wherein the vapor bubbles that are formed migrate to the spin axis of the turbine and leave the turbine in equilibrium with water that enters the turbine. 
         [0046]    Referring now to  FIGS. 5 through 7 , turbine  518  comprises a plurality of internally disposed turbine blades  528  that extend radially inward from wall  526 . 
         [0047]    In operation, turbine is spun up to a desired operating speed via motor  116 . Water enters turbine  518  through orifice  530 . The spin of the turbine  518  forces the water radially outward such that water contacts blades  528 . The operating speed of turbine  518  is sufficient to cause supercavitation; that is, contact with the blades causes the water to vaporize, generating bubbles. The vapor bubbles propagate to spin axis due to the spin of the turbine. 
         [0048]    To prevent water from entering barrel  102 , a steady state condition is attained in which the rate of water entry into turbine  518  is equal to the volume of water vapor leaving orifice  530 . The barrel seal is created by operating the turbine such that a steady-state condition is attained wherein the rate of water entry into the supercavitating turbine is equal to the volume of water vapor that is leaving the supercavitating turbine. 
         [0049]    The rate at which water vapor is produced is a function the design of turbine blades  528 , the length of turbine  518 , and the angular velocity at which the turbine rotates. Those skilled in the art will be capable of designing and operating a turbine to vaporize water at a rate needed to achieve the aforementioned steady state condition. 
         [0050]    As in the previous embodiment, turbine  518  is brought up to speed before gun  100  is fired. That is, upon receiving a command to fire gun  100 , fire-control system  110  sends a signal to motor controller  115  to energize motor  116  (see,  FIG. 1B ). The motor spins the turbine  518  up to a desired angular velocity before round  112  is fired. Rupture disk  224  is used to keep barrel  102  dry before the first firing. 
         [0051]    After the steady state condition is established, round  112  is fired. The round, and/or pressure from the combustion gases that are generated when the round&#39;s propellant charge is ignited), causes rupture disk  224  at the muzzle of barrel  102  to rupture. Turbine  518  continues to spin after the first round is fired so that barrel  102  is kept free of water after rupture disk  224  has ruptured. Additional rounds can be fired through the water-free barrel as long as turbine  518  is spinning. 
         [0052]      FIGS. 8 through 10  depict a third embodiment of turbine-based barrel seal  114  of  FIG. 1B .  FIG. 8  depicts a cross-sectional view of motor  116  and turbine  818  coupled to muzzle end  106  of barrel  102 . Rupture disk  224  is disposed at the end of barrel  102 .  FIG. 9  depicts a cross-sectional view of turbine  818  in operation.  FIG. 10  depicts a front end view of  818  in operation. 
         [0053]    Referring now to  FIGS. 8 through 10 , turbine  818  comprises a plurality of internally-disposed turbine blades  828  that extend radially inward from wall  826 . A plurality of orifices  830  are disposed in wall  826  between blades  828 . In the embodiment that is depicted in these Figures, a grouping of four orifices  830  is disposed at ninety-degree intervals around wall  826  between successive blades  828  (see,  FIG. 10 ). In some other embodiments, the grouping contains a different number of orifices  830  (e.g.,  7 , etc.) and in some additional embodiments, the groupings are disposed at different axial locations than is shown in  FIGS. 8 and 9 . 
         [0054]    As in the previous embodiments, turbine  818  is brought up to speed before gun  100  is fired. Upon receiving a command to fire gun  100 , fire-control system  110  sends a signal to motor controller  115  to energize motor  116  (see,  FIG. 1B ). The motor spins the turbine  818  up to a desired angular velocity before round  112  is fired. Rupture disk  224  is used to keep barrel  102  dry before the first firing. 
         [0055]    The spinning turbine draws water in through orifice  832  and expels all such water through orifices  830 . When round  112  is fired, the round, and/or pressure from the combustion gases that are generated when the round&#39;s propellant charge is ignited, causes rupture disk  224  at the muzzle of barrel  102  to rupture. Turbine  818  continues to spin after the first round is fired so that barrel  102  is kept free of water after rupture disk  224  has ruptured. Additional rounds can be fired through the water-free barrel as long as turbine  818  is spinning. 
         [0056]    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.