Abstract:
A pneumatic launcher has a plenum chamber section, an intermediate chamber section and a launch tube section connected together in a generally linear arrangement. The plenum chamber section defines a plenum chamber that has a closed end and an open end. The intermediate chamber section has aft and forward rupture disks consecutively arranged to define an intermediate chamber. The plenum chamber is pressurized with a pressurized gas to a design plenum pressure and the intermediate chamber is pressurized with a pressurized gas to pressure that is about one-half the design plenum pressure. The intermediate chamber is then depressurizing to produce a pressure imbalance between the plenum and intermediate chambers that causes said aft and forward rupture disks to rupture. As a result, pressure equilibrium occurs between the plenum chamber and launch tube thereby discharging the fluid and projectile from the interior of the launch tube.

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a pneumatic launcher apparatus. 
   2. Description of the Prior Art 
   Supercavitating underwater vehicles and projectiles are known in the art. One such supercavitating underwater projectile is described in Harkins et al. U.S. Pat. No. 5,955,698. Typically, such supercavitating underwater vehicles and projectiles are launched by a launcher system. The launcher for a supercavitating vehicle must meet several important requirements. Specifically, the launcher must achieve the necessary exit velocity for the selected vehicle or projectile design. The launcher must be of an economically efficient design. Preferably, the launcher should utilize a non-explosive, non-hazardous energy source and be capable of remote firing. Furthermore, the launcher must be configured to facilitate easy assembly and disassembly for maintenance and repair. It is also preferable that the launcher does not contain any components that exceed 1000 lbm (pounds mass). Another important requirement is a relatively short launch-ready time, preferably in the order of 3 hours including plenum chamber recharge time. Furthermore, the launcher should be designed for being submerged or immersed in water for extended periods of time, e.g. 24 hours. 
   The prior art discloses several devices and systems for launching projectiles or other objects. Dragonuk U.S. Pat. No. 4,444,085 discloses a pneumatic launch system for an aircraft for ejecting sonar buoys. Kayaian U.S. Pat. No. 5,109,750 discloses a closed-breech missile and weapon system for infantry in anti-armor or anti-personnel applications. Walton U.S. Pat. No. 5,365,913 discloses a rupture-disk gas launcher to launch a projectile toward a target. The launcher uses a source of compressed air to launch the projectile. Mattern et al. U.S. Pat. No. 5,460,154 discloses a pneumatic gun for propelling a projectile substance. This pneumatic gun is used for disarming explosive devices. Horlock U.S. Pat. No. 6,170,477 discloses a pneumatic spear gun. None of these prior art patents discloses a launcher for a supercavitating vehicle that meets the important requirements set forth in the foregoing discussion. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a launcher apparatus for launching a supercavitating vehicle or projectile that meets the requirements described in the foregoing discussion. 
   It is another object of the present invention to provide a launcher apparatus that is inexpensive to manufacture, implement and maintain. 
   Other objects and advantages of the present invention will be apparent from the ensuing description. 
   Thus, the present invention is directed to a pneumatic launcher for use with high-speed projectiles or supercavitating underwater vehicles. In one embodiment, the pneumatic launcher comprises a plenum chamber section, an intermediate chamber section and a launch tube section connected together in a generally linear arrangement wherein the intermediate chamber section is between the plenum chamber section and the launch tube section. A support base having upstanding support members supports the plenum chamber section, intermediate chamber section and launch tube section. The plenum chamber section defines a plenum chamber that has a closed end and an open end. The intermediate chamber section has aft and forward rupture disks consecutively arranged to define an intermediate chamber. The aft rupture disk is exposed to the open end of the plenum chamber. The launch tube section comprises a launch tube that has an open breech end. The forward rupture disk is exposed to the open breech end of the launch tube. The launch tube has an interior that is in communication with the open breech end and is sized for receiving a projectile or supercavitating vehicle. The launch tube further includes an open exit end opposite the open breech end through which a projectile or supercavitating vehicle exits from the interior of the launch tube. In one embodiment, the aft and forward rupture disks are configured to rupture at two-thirds the design plenum pressure. When the pneumatic launcher is submerged in fluid (e.g., water), the fluid floods the interior of the launch tube. In order to launch a projectile or supercavitating vehicle, the plenum chamber is pressurized with a pressurized gas to a first predetermined pressure. The intermediate chamber is then pressurized with a pressurized gas to pressure that is generally the same as the first predetermined pressure in order to achieve a state of pressure equilibrium. Next, the plenum chamber is pressurized to the design plenum pressure. Preferably, the design plenum pressure is about twice the first predetermined pressure. Next, the intermediate chamber is then depressurizing to produce a pressure imbalance between the plenum and intermediate chambers that causes said aft and forward rupture disks to rupture. Once the aft and forward disks have ruptured, pressure equilibrium occurs between the intermediate chamber and the interior of the launch tube thereby discharging the fluid and projectile or vehicle from the interior of the launch tube. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features of the present invention will become more readily apparent and may be understood by referring to the following detailed description of an illustrative embodiment of the present invention, taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a side elevational view of the pneumatic launcher tube of the present invention; 
       FIG. 2  is a side elevational view of the pneumatic launcher tube of  FIG. 1  connected to a control system in accordance with the invention; and 
       FIG. 3  is graph showing required exit velocity for a range of projectile masses and launch transient time allowances. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , there is shown pneumatic launcher  10  in accordance with the invention. Pneumatic launcher  10  is to be used to launch supercavitating vehicles or other projectiles. As used herein, the term “projectiles” shall include supercavitating vehicles, torpedoes, sonar buoys, and other similar objects. Pneumatic launcher  10  comprises support base member  12 , forward support  14 , middle support  16  and aft support  18 . Pneumatic launcher  10  further comprises plenum chamber  20  which is supported by middle support  16  and aft support  18 . In a preferred embodiment, plenum chamber  20  is attached to middle support  16  and aft support  18 . Plenum chamber  18  includes end cap  22 . Pneumatic launcher  10  further comprises intermediate chamber  24  that is formed by aft rupture disk  26  and forward rupture disk  28  which are arranged in series. Pneumatic launcher  10  further includes contraction member  30 , the purpose of which is described in the ensuing description. Aft rupture disk  26  and forward rupture disk  28  are configured to rupture when the pressure imbalance between plenum chamber  20  and intermediate chamber  24  reaches a predetermined pressure. This feature is discussed in the ensuing description. 
   Referring to  FIG. 1 , pneumatic launcher  10  further includes launch tube  32  that has an open breech end  34  that is connected to contraction member  30  and open exit end  36  that is opposite open breech end  34 . Launch tube  32  has an interior for receiving a projectile. Open exit end  36  of launch tube  32  allows launch tube  32  to be flooded with fluid (e.g. water) when pneumatic launcher  10  is submerged under the fluid. The portion of launch tube  32  near open exit end  36  is supported by forward support member  14 . The diameter of intermediate chamber  24  is larger than the diameter of launch tube  32 . Therefore, contraction member  30  provides a transition from the diameter of intermediate chamber  24  to the smaller diameter of launch tube  32 . Pneumatic launcher  10  further includes muzzle brake  38  which is attached to launch tube  32  and is positioned about open exit end  36 . Muzzle brake  38  also abuts forward support member  14 . Muzzle brake  38  minimizes the pre-launch recoil force associated with the initial discharge of fluid within launch tube  32 . 
   Referring to  FIG. 2 , there is shown pneumatic launcher system  50  in accordance with the present invention. Pneumatic launcher system  50  comprises pressurized gas source  52  that provides compressed air or gas that is discharged into plenum chamber  20  in order to charge pneumatic launcher  10  to the design plenum pressure. As used herein, “design plenum pressure” is the pressure to which plenum chamber  20  is pressurized in order to achieve the desired launch velocity. In one embodiment, pressurized gas source  52  comprises an air compressor. In a preferred embodiment, such an air compressor is capable of producing pressure between about 3000 PSI (pounds per square inch) and 3500 PSI. In another embodiment, pressurized gas source  52  comprises a plurality of compressed gas tanks that would be discharged into plenum chamber  20 . 
   Referring to  FIG. 1 , in accordance with the invention, aft and forward rupture disks  26  and  28  each have a pressure rating that causes these rupture disks to rupture when exposed to a predetermined pressure that is less than the design plenum pressure. In a preferred embodiment, the pressure ratings of aft and forward rupture disks  26  and  28  are such as to cause these rupture disks to rupture when exposed to a pressure that is about two-thirds of the design plenum pressure. 
   Referring to  FIG. 2 , pneumatic launcher system  50  further includes a venting system that effects pressure equilibrium between plenum chamber  20  and launch tube  32  in order to launch a projectile. This venting system comprises vent valve  54  and muffler  56  and is used to vent pressurized gas from intermediate chamber  24 . The purpose of this feature is described in the ensuing description. In accordance with the invention, intermediate chamber  24  is pressurized to a pressure that is less than the design plenum pressure. In a preferred embodiment, intermediate chamber  24  is pressurized to a pressure that is about one-half the design plenum pressure in plenum chamber  20  in order to prevent rupturing aft and forward rupture disks  26  and  28 , respectively, prior to launching the projectile. Consequently, the pressure drop from plenum chamber  20  to intermediate chamber  24  is one-half of the design plenum pressure in plenum chamber  20 , and the pressure drop from intermediate chamber  24  to launch tube  32  is about one-half of the design plenum pressure. 
   Referring to  FIG. 2 , when the pressurized gas in intermediate chamber  24  is vented with vent valve  64 , the pressure to which aft rupture disk  26  is exposed increases to above its pressure rating and consequently, ruptures thereby allowing pressurized gas to flow from plenum chamber  20  into intermediate chamber  24 . Consequently, the pressure to which forward rupture disk  28  increases thereby rupturing forward rupture disk  28  and completing the launching sequence. Pneumatic launcher system  50  includes main valve  60  and intermediate chamber valve  62  which control the flow of pressurized gas. Specifically, main valve  60  is connected between pressurized gas source  52  and plenum chamber  20  and controls the flow of pressurized gas from pressurized gas source  50  to plenum chamber  20 . 
   Intermediate chamber pressure valve  62  is connected between main valve  60  and intermediate chamber  24  and controls the flow of pressurized gas into intermediate chamber  24 . Pressurized gas flows throughout pneumatic launcher system  50  via pressurized gas lines or conduits  65 . In a preferred embodiment, pressurized gas source  52  incorporates adequate air-drying equipment to ensure that icing does not occur within pressurized gas lines or conduits  65 , or within plenum and intermediate chambers  20  and  24 , respectively. 
   In a preferred embodiment, the ensuing steps are implemented to launch a projectile using pneumatic launcher system  50 . The first step is to close intermediate chamber pressure valve  62  and venting valve  54 . Next, main valve  60  is opened. Pressurized gas source  52  is then activated so as to pressurize plenum chamber  20 . In a preferred embodiment, plenum chamber  20  is pressurized to a pressure that is about 75% of the pressure rating of aft rupture disk  26 . Once the desired plenum chamber pressure is attained, pressurized gas source  52  is then deactivated and main valve  60  is closed. Next, intermediate chamber pressure valve  62  is opened to pressurize intermediate chamber  24 . Intermediate chamber  24  is pressurized to a pressure that is substantially the same as the pressure in plenum chamber  20 . 
   Thus, at this point in the method, plenum chamber  20  and intermediate chamber  24  are in equilibrium. Once intermediate chamber  24  is pressurized, intermediate chamber pressure valve  62  is then closed. Next, main valve  60  is then opened again and pressurized gas source  52  is activated so as to pressurize plenum chamber  20  to the design plenum pressure. In a preferred embodiment, the design plenum pressure is about twice the pressure of intermediate chamber  24 . Pressurized gas source  52  is then deactivated and main valve  60  is closed. The last step is to open vent valve  54  to vent the pressurized gas from intermediate chamber  24  causing an immediate pressure imbalance between plenum chamber  20  and intermediate chamber  24 . This pressure imbalance cause aft rupture disk  26  to rupture. Pressurized gas immediately rushes through intermediate chamber  24  and causes forward rupture disk  28  to rupture. As a result, pressurized gas flows into launch tube  32  causing immediate discharge of all fluid within launch tube  32  as well as the projectile. 
   Referring to  FIG. 2 , pneumatic launcher system  10  further comprises muffler  56  which reduces noise produced when venting valve  54  is opened to vent pressurized gas in intermediate chamber  24  to the atmosphere. Pneumatic launcher system  10  further includes pressure transducers  70  and temperature transducers  72  that provide transducer signals that represent the pressure and temperature within plenum chamber  20 , intermediate chamber  24  and launch tube  32 . These transducer signals are routed to signal conditioner  80  via wires or cables  90 . Signal conditioner  80  has conversion, amplification, shaping, and filtering electronics (not shown, but known in the art) that process the transducer signals and convert these transducer signals to voltage signals of sufficient magnitude which can be used by system monitoring equipment (not shown). Hooks  90  are attached to forward and aft support members  14  and  18 , respectively, to allow pneumatic launcher  10  to be lowered into a body of fluid or retrieved therefrom. 
   The total mass that is moved by the pressurized gas rushing into launch tube  32  from plenum chamber  20  and intermediate chamber  24  is equal to the mass of the projectile plus the mass of fluid (e.g. water) in launch tube  32 . As the projectile forces fluid out of launch tube  32 , the mass of the fluid in launch tube  32  decreases. The pressurized gas rushing into launch tube  32  from plenum chamber  20  and intermediate chamber  24  after rupture disks  26  and  26  rupture is sufficient to overcome launch tube exit pressures and hydrodynamic losses as fluid exits launch tube  32 . 
   There is a minimum launch velocity that must be achieved for a given set of projectile or vehicle parameters (including mass), a specified data acquisition time, a specified time of flight before data acquisition begins, and a specified minimum vehicle velocity during data acquisition.  FIG. 3  shows required exit velocities for a range of projectile masses and launch transient time allowances. It has been found that particular combinations of design parameters have provided several pneumatic launcher system designs, in accordance with the invention, that meet the requirements shown in  FIG. 3 . Table I provides examples of such pneumatic launcher system designs. 
   
     
       
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
           
         
             
               TABLE I 
             
             
                 
             
             
                 
                 
                 
                 
                 
                 
               Quantity 
             
             
                 
                 
                 
                 
                 
                 
               Of 
             
             
                 
                 
                 
                 
               8″ ID 
                 
               Com- 
             
             
                 
                 
                 
               Launcher 
               Pipe 
                 
               pressed 
             
             
                 
               Vehicle 
               Vehicle 
               Tube 
               Plenum 
               Plenum 
               Nitrogen 
             
             
               Design 
               Diameter 
               Mass 
               Length 
               Length 
               Pressure 
               Tanks/ 
             
             
               No. 
               (inches) 
               (lbm) 
               (feet) 
               (feet) 
               (psi) 
               Charge 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               4.72 
               110 
               10.9 
               8.3 
               2020 
               2.3 
             
             
               2 
               4.72 
               132 
               8.0 
               9.5 
               2020 
               2.6 
             
             
               3 
               6.25 
               110 
               9.3 
               8.5 
               1900 
               2.7 
             
             
               4 
               9.00 
               110 
               15.4 
               10.0 
               1960 
               2.6 
             
             
                 
             
           
        
       
     
   
   For example, Design No. 1 is directed to a pneumatic launcher system that is configured to launch a vehicle having a diameter of 4.72 inches and a mass of 110 lbm. The launcher tube has a length of 10.9 feet. The inner diameter of plenum chamber  20  is 8.0 inches and its length is 8.3 feet. The design plenum pressure is 2020 psi. The required number of compressed nitrogen tanks per charge (i.e. per launch) is 2.3. In Design No. 3, the pneumatic launcher system is configured to launch a vehicle having a diameter of 6.25 inches and a mass of 110 lbm. The launcher tube has a length of 9.3 feet. The inner diameter of plenum chamber  20  is 8.0 inches and its length is 8.5 feet. The design plenum pressure is 1900 psi. The required number of compressed nitrogen tanks per charge (i.e. per launch) is 2.7. It is to be understood that the pneumatic launcher system designs described in Table I are examples and that other combinations of pneumatic launcher design parameters be used to realize a pneumatic launcher system, in accordance with the invention, that meets the requirements shown in  FIG. 3 . 
   In an alternate embodiment, high speed valves can be used in place of the rupture disks  26  and  28 . Furthermore, launch tube  32  can be operated as a dry launch tube wherein a thin membrane is placed over the exit end of launch tube  32  to prevent infiltration of fluid into the interior of launch tube  32 . The thin membrane can easily be ruptured by the projectile as it leaves launch tube  32 . 
   The present invention provides several important advantages. The venting system for venting intermediate chamber  24  is simple in design, does not utilize electronics or hydraulic systems, and is easy to install. Furthermore, the venting system is low cost and easily controllable. The collinear arrangement of plenum chamber  20 , intermediate chamber  24 , and launch tube  32  simplifies the design and the assembly of pneumatic launcher  10 . Furthermore, muzzle brake  38  minimizes the pre-launch recoil force associated with the initial discharge of the fluid in launch tube  32 . 
   The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein should not, however, be construed as limited to the particular forms disclosed, as these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the invention. Accordingly, the foregoing detailed description should be considered as exemplary in nature and not as limiting the scope and spirit of the invention as set forth in the attached claims.