Abstract:
A housing ( 1; 100, 104, 102 ) of a cartridge for a device for firing a projectile has separate first and second chambers ( 10, 12; 106, 114 ), each of which contains a respective charge ( 34, 36; 108, 110, 116, 120 ) of propellant material. Gas produced by the detonation of one of the charges exits the first chamber to propel the projectile, whilst gas from the detonation of the second charge exist rearwardly from the device so as to counteract recoil. A one way valve may also be provided to help to achieve a high pressure difference between the chambers, where the cartridge has a common igniter assembly.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a cartridge for a device for firing a projectile and to a device for firing a projectile. Although described in relation to a device for de-arming/disrupting an explosive device, the invention is not limited in application to de-arming and disrupting devices. 
       BACKGROUND TO THE INVENTION 
       [0002]    A conventional de-arming device (also referred to as a disrupting device or a de-armer disrupter) operates by firing a solid, liquid or gel projectile at an explosive device so as to disrupt the fuse assembly of the latter, ideally without detonating the explosive device. Such a de-arming device comprises a barrel, the breech of which contains a conventional gun cartridge which, when detonated, propels the projectile, also initially contained in the barrel, towards the target. 
         [0003]    It is generally desirable to provide means for reducing the recoil caused by the firing of the projectile, and to that end it is known to fit the end of the barrel with rearward facing venturi ports through which some of the gas caused by the detonation of the cartridge passes. However, these ports reduce the pressure of the gases which are used to propel the projectile, and thus result in the device requiring a relatively large charge and long barrel in order to be able to accelerate the projectile to a sufficiently high velocity. 
         [0004]    It has also been proposed to deal with the problem of recoil by fitting the de-arming device with a retro-active rocket taking the form of a second cartridge housed in a second barrel breech opposed to the first barrel. The second gun cartridge is fired simultaneously with the first cartridge so that the recoil caused by firing the first cartridge is counteracted by that caused by the firing of the second cartridge. 
         [0005]    Although the anti-recoil system of such device does not require a longer primary barrel (for the projectile), the additional barrel breech does increase the size and weight of the device. Furthermore, the device can take a relatively long time to be primed for firing and it can be difficult to detonate both cartridges simultaneously. 
         [0006]    The present applicant&#39;s European Patent No. EP0549659B discloses a de-arming device in which recoil is counteracted by means of water initially contained in an annular chamber around the breech of the barrel. The gun cartridge used to fire the projectile also propels the water rearwardly from the device. The inertia of the water enables the gun cartridge to generate sufficiently high gas pressures to fire the projectile at a sufficiently high velocity without the need to lengthen the device&#39;s barrel. However, the water and the additional components needed for the firing device to contain the water increase the weight of the device, and the need to fill the chamber with water prior to firing the device (and to close the chamber once full) also increases the time needed to prime the device for firing. 
         [0007]    Over recent years, small robotic vehicles, weighing in the region of 30 kilograms, have increasingly been deployed to carry out remote reconnaisance work and to carry a de-armer which can be remotely fired. One example of such a device is the pakbot mini rov produced by iRobot. Such vehicles are able to carry recoilless de-armers such as the de-armer shown in EP0549659 on their lower or middle arms. There is an increasing need for the vehicles to be provided with recoilless de-armers on their upper arms in order for the vehicle to be able to de-arm or disrupt targets in, for example, overhead luggage lockers on aircraft, trains, buses and in other high reach situations. However, the upper arm of such a vehicle would not be able to carry a de-armer which weighs more than 1.5 kilograms whereas the various designs discussed above generally weigh at least 3 kilograms. 
       SUMMARY OF THE INVENTION 
       [0008]    According to a first aspect of the invention, there is provided a cartridge for a device for firing a projectile, the cartridge comprising a housing having first and second chambers, respectively containing first and second charges of propellant material, and each having a respective outlet, wherein, in use, the outlet of the first chamber allows the expulsion from the cartridge of gas produced by the detonation of the first propellant charge, so as to fire the projectile, whilst the outlet of the second chamber allows the expulsion from the cartridge of gas produced by the detonation of tie second propellant charge, which gas exits the device rearwardly so as to counteract recoil. 
         [0009]    Since the two charges of propellant, one for firing the projectile, the other for counteracting recoil, are contained in a common cartridge, a device which fires a projectile using that cartridge can have a single breech, and can therefore be more compact and lightweight than a device which uses two separate cartridges. The device is also more compact and lightweight than types of anti-recoil de-armer that do require a jacket of water. Since the propellant charge for firing the projectile is in a separate chamber from that for counteracting recoil, the force with which the projectile is fired is not affected by the gases by which are ejected so as to counteract recoil. Accordingly, the amount of the first propellant charge can be varied independently of the second propellant charge during the stages of design and development of the cartridge. This facilitates the creation of a cartridge which provides a desired force of firing and adequate anti-recoil characteristics. Indeed, it has been found that a cartridge in accordance with the invention can completely neutralise recoil. 
         [0010]    Preferably, the chambers of the cartridge are situated one in front of the other in the housing, the first chamber being in the front portion of the cartridge, the second in the rear. 
         [0011]    Thus, each chamber is situated adjacent to the part of the device (the barrel containing the projectile or a rearward facing outlet port (as the case may be) to which gases from the chamber need to be expelled. In this case, the outlet of the first chamber made to advantage comprise a port in the front of the cartridge, the outlet of the second chamber comprising a port in the rear of the cartridge. 
         [0012]    Preferably, the ports are substantially circular, and are coaxial. 
         [0013]    Preferably, the chambers are elongate and are also coaxial with the ports and hence with each other. 
         [0014]    This facilitates the balancing of the device so that the force generated by the rearwardly ejected gases is coaxial with the recoil force caused by the firing of the projectile. 
         [0015]    Preferably, the second charge of propellant is more powerful than the first charge. 
         [0016]    This could be achieved by having a more powerful formulation of charge, but is preferably achieved by an arrangement in which the second charge is bigger than the first charge. 
         [0017]    The reaction forces on the device caused by the exiting projectile are higher than the reaction caused by ejecting gas alone. This is accommodated in the cartridge by increasing the amount and/or velocity of the gases ejected through the outlet of the second chamber compared with those ejected by the detonation of the first charge. 
         [0018]    The second chamber may therefore to advantage be of a larger volume than the first chamber. 
         [0019]    Conveniently, the second chamber has a larger cross-sectional area than the first chamber. Thus, if the chambers are cylindrical, the second chamber preferably has a larger diameter than the first chamber. 
         [0020]    Consequently, the increased volume of the second chamber does not require an increased length of cartridge. 
         [0021]    Preferably, the propellant material is explosive. 
         [0022]    Preferably, the two chambers have a common igniter assembly. 
         [0023]    This helps to ensure that the detonation of the two charges of propellant material is synchronised. 
         [0024]    The igniter assembly may comprise an ignition chamber having ignition ports to each of the first and second chambers and containing an initiator charge of explosive material, hot gases produced by the detonation of which pass through the ignition ports to ignite the first and second charges of propellant material. 
         [0025]    The ignition chamber is preferably interposed between said first and second chambers. 
         [0026]    Preferably, the cartridge housing comprises a one piece casing which is hollow to define the first and second chambers, and includes a wall or bulkhead separating those two chambers. 
         [0027]    The bulkhead isolates the two propellant charges from each so that the firing force exerted on the projectile by the detonation of the first charge is not affected by the venting of the gases produced by the detonation of the second charge. 
         [0028]    The bulkhead may to advantage also contain the igniter assembly. 
         [0029]    Preferably, the second chamber has a portion of reduced cross section adjacent to the outlet of that chamber. 
         [0030]    This acts as a choke which helps to increase the pressure of gases ejected from the second chamber. 
         [0031]    According to a second aspect of the invention, there is provided a device for firing a projectile, the device comprising a barrel for housing the projectile and a cartridge in accordance with the first aspect of the invention, wherein the barrel has a rear outlet through which said gas from the detonation of the second propulsive charge of such a cartridge is expelled so as to counteract recoil. 
         [0032]    Preferably, the barrel has a breech module, the rear portion of which is of a larger cross sectional or area than the front portion. 
         [0033]    Consequently, the rear portion of the breech can accommodate the part of the cartridge which in turn contains the second, larger propellant charge. 
         [0034]    Preferably, the rear outlet is connected to a constriction, preferably a venturi, for accelerating the flow of gas from the rear of the device. 
         [0035]    The invention also lies in a device in accordance with the second aspect of the invention when loaded with a cartridge in accordance with the first aspect of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    The invention will now be described, by way of example only, with reference to the accompanying drawings in which: — 
           [0037]      FIG. 1  is a sectional side view of a first embodiment cartridge in accordance with the invention; 
           [0038]      FIG. 2  is a corresponding view of a device, also in accordance with the invention, for firing a projectile, the device being shown when loaded with the cartridge shown in  FIG. 1 ; 
           [0039]      FIGS. 3 and 4  are isometric views, respectfully from the front and rear, showing the exterior of the device; 
           [0040]      FIG. 5  is a sectional side view of a second embodiment of cartridge in accordance with the invention; 
           [0041]      FIG. 6  is an end view of the cartridge of  FIG. 5  and 
           [0042]      FIG. 7  is an isometric view of the cartridge of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0043]    The cartridge shown in  FIG. 1 , comprises a one piece cylindrical housing  1  machined from solid stainless steel, and having a front portion  2  and a rear portion  4  of a larger diameter than the portion  2 . On the exterior of the casing, the portions  2  and  4  meet at an annular step  6 . At the region of the shoulder  6  the casing includes internal bulkhead  8  which extends across the entire width of the casing to separate the interior of the latter into a first chamber  10  in the front of the cartridge and a second, larger diameter chamber  12  in the rear portion  4 . 
         [0044]    A further, ignition chamber  14  is provided in the centre of the bulkhead  8 , in order to house an igniter assembly. 
         [0045]    In this particular case, the igniter assembly includes an electrical fusehead shown diagrammatically at  16 , comprising an electrical bridge wire connected to a positive electrical contact  18  and to the casing of the cartridge (which is in turn connected to an earth contact as described below) and coated with a suitable explosive. The fusehead wire is spaced from the walls of the chamber  14 , which chamber is also packed with a charge of black powder that acts as an initiator charge. 
         [0046]    One side of the chamber  14  is defined by the part  20  of the bulkhead  8  that separates the chamber  10  from the chamber  14 , which part includes a pair of ignition ports in the form of axial passages,  22  and  24 . The other side of the chamber  14  is defined by a cylindrical externally screw threaded plug  26  which is screwed into a correspondingly screw threaded cylindrical recess  28  in the side of the bulkhead that bounds the compartment  12 . The plug  26  also has a pair of axial passages  30  and  32  which act as ignition ports. As can be seen from  FIG. 1 , the passages  22 ,  24 ,  30  and  32  enable the chamber  14  to communicate with the chambers  10  and  12 . 
         [0047]    The chamber  10  contains a first propellant charge  34 , whilst a second propellant charge  36  is contained within the chamber  12 . The propellant charge  36  is larger than the charge  34 , in this case the charges being respectively constituted by 5 and 8 grams of gun powder. Each of the charges is held in a substantially cylindrical shape, and the end of each charge opposite the bulkhead is abutted by a respective one of two circular card discs  38  and  40  which separate the charge from a respective one of two felt closure wads  42  and  44 . The opposite side of each wad is abutted by a respective one of two tufnell discs  46  and  48  which is held in position by means of a respective one of two roll crimps  50  and  52  on the end of the cartridge. The forward end of the cartridge constitutes a circular opening which is closed by the disc  46  and which acts as an outlet for the chamber  10 . The outlet for the chamber  12  is provided by the opening at the rear end of the cartridge, which opening is closed by the disc  48 . The wall of the cartridge casing includes an annular thickened portion  54  adjacent to the disc  48 . This portion acts as a choke for restricting the flow of gases from the chamber  12  and thus increasing the pressure exerted by those gases. 
         [0048]    Referring to  FIG. 2 , the device for firing a projectile, comprises a barrel having a forward portion  56  and a breech module  58  which, in use, accommodates the cartridge. Prior to firing, the projectile (not shown) is accommodated in the forward portion  56 . 
         [0049]    The device is annular, and the breech module  58  is stepped, having a forward smaller diameter portion  60  and a rear larger diameter portion  62 . The interior of the breech module is correspondingly stepped so that the portion  60  accommodates the portion  2  of the cartridge, whilst the portion  62  accommodates the rear portion  4  of the cartridge and the shoulder  6  abuts an internal, correspondingly annular shoulder formed at the step in diameters of the breech portion. This abutment of the two shoulders limits the forward movement of the cartridge within the breech module. The rear of the breech module  58  includes an internal screw thread via which a correspondingly screw threaded end portion  64  can be removably attached to the breech module  58 . The portion  64  is open ended, annular and includes a venturi port  66  through which gases generated by the detonation of the charge  36  are expelled from the rear of the device. 
         [0050]    As can be seen from  FIGS. 3 and 4 , the end piece includes a flat  68  to enable the end piece to be rotationally keyed to a suitable tool for tightening and loosening the end piece. 
         [0051]    The device is primed for firing by removing the end piece  64  and inserting a cartridge into the breech portion  58  until the shoulder  6  abuts the corresponding shoulder on the interior of the breech portion  58 . The end piece  64  is then screwed onto the rear of the breech module  58  and tightened using a tool (as mentioned above). A projectile to be fired from the device is loaded into the device through the front of the barrel  56  until the trailing end of the projectile abuts the front of the breech portion  58 . In this particular case, the projectile is a solid, but the projectile could be a liquid or gel (in which case containment of the projectile prior to firing is achieved in the same way as with a conventional projectile of that type). 
         [0052]    The breech module  58  carries a pair of terminals, one of which, the terminal  70 , is in electrical contact with the contact  18 . The other terminal, referenced  72 , is in contact with the body of the breech module, and hence is in electrical contact with the casing of the cartridge. Accordingly, the contact  70  comprises a conductive pin  74  which extends through an insulating sleeve  76  that lines the interior of a radial passage in the breech module  58  in registry with the contact  18 . 
         [0053]    An electrical firing circuit (not shown) is connected to the device by connecting the positive terminal of the circuit to the terminal  70  and the negative terminal of the circuit to the terminal  72 . 
         [0054]    In response to a suitable firing command, the circuit passes an electrical current through the fuse head wire  16 . This detonates the charge of explosive in the chamber  14 , causing hot gases to pass through the passages  22 ,  24 ,  30  and  32  into the propellant charges  34  and  36 , both of which are thus ignited. Since both charges  34  and  36  are ignited from a common fuse wire, the detonation of the two charges occurs substantially simultaneously. This would not necessarily be the case if two separate fuse wires were used since, in general, the resistances of fuse wires (even of the same type) tend to vary so that two such fuse wires will take different amounts of time to heat up to ignition temperatures even if they are subjected to the same voltage simultaneously. 
         [0055]    The detonation of the charge  34  shatters the disc  46 , ejects the wad  42  and disc  38  and propels the projectile through the front of the barrel  56 . As this happens, the bulkhead  8  provides a reaction surface via which the reaction to the force exerted on the projectile by the explosive charge is transmitted into the device. The detonation of the charge  36  causes the disc  48  to disintegrate, and ejects the wad  44  and disc  48  through the venturi  66 . As this happens, the wad  44  will fleetingly block the venturi  66  which causes a further build up of pressure of gases generated by the charge  36 . 
         [0056]    Once the wad  44  and disc (or remnants thereof)  40  have cleared the venturi port  66 , gases are ejected through the rear of the device, and the reaction to this is transmitted, via the bulkhead  8  to the rest of the device so as to counteract the recoil caused by the firing of the projectile. 
         [0057]    It has been found that a device such as the one described can be made to a weight of approximately one-third of the current designs (which utilise water jackets to counteract recoil), and can therefore be deployed on the upper arm of a mini ROV. The device is also shorter and significantly smaller in diameter than the aforesaid known device, which also make it easier to deploy on an ROV. Furthermore, collateral danger to the rear of the device significantly lower since only gas, rather than water, is ejected. This means that positioning of the system on a robotic vehicle is less critical than in the case of known designs which use water jackets and which therefore require a clear field behind the device to avoid damage to cameras, cables, connectors and antennas. The device according to the invention is also simple to manufacture and easy to operate and maintain. 
         [0058]    Turning to  FIG. 5 to 7 , the second embodiment of the cartridge in accordance with the invention has a three part housing formed from two cupped aluminium end pieces  100  and  102  attached one to either side of a central, cylindrical, stainless steel connector  104 . 
         [0059]    The cupped piece  102  defines a chamber  106  which contains two propellant charge portions  108  and  110  which correspond to the first propellant charge  34  of the first embodiment. The charge portion  110  is of a relatively slow burning explosive propellant material, whilst the charge portion  108  is of a faster burning explosive material. The two charge portions are separated by a paper disc  112 . Similarly, the cupped end piece  100  defines a chamber  114  in which are contained a charge portion  116  of slow burning explosive propellant separated by a paper disc  118  from a charge portion  120  of fast burning explosive propellant. The charge portions  120  and  116  correspond to the second propellant charge  36  of the first embodiment. As can be seen from  FIG. 5 , each of the slow burn charge portions  110  and  116  is interposed between the connector  104  and a respective one of faster burn charge portions  108  and  120 . 
         [0060]    Each of the aluminium end pieces  100  and  102  has a closed end, respectively referenced  122  and  124  which, on firing of the cartridge, bursts open to provide an outlet for the respective chamber. In order to facilitate this change, the end  122  is scored with a generally star-shaped burst pattern  126 . A similar pattern  128  is scored into the end of the cupped piece  102 . 
         [0061]    The charge portion  110  is constituted by 7.5 grams of SP12, whilst the charge portion  108  is constituted by 4 grams of OBP473-31 (also known long shot). The charge portion  116  is constituted by 3 grams of SP13 and the charge portion  120  by 7.5 grams of long shot. 
         [0062]    The end of the piece  102  opposite the closed end  124  is provided with an internal screw thread at  130  via which the piece  102  is screwed onto a correspondingly externally screw threaded collar portion  132  of the connector  104 . A similar screw threaded connection is provided between the connector  104  and the end piece  100  as shown at  137 . A central radial flange  135  of the connector  104  provides a stop against which the inboard ends of the pieces  100  and  102  abut. 
         [0063]    The collar  132  also has an internal screw thread  134  via which an externally screw threaded stainless steel plug  136  is attached to the connector  104  to define a bulkhead for the chamber  106 . An eccentric axial bore  138  connects the chamber  106  to an ignition chamber  140 , which contains an electrical fuse head  142  (similar to the fuse head  16  of the first embodiment). As with the fuse head  16 , one side of the fuse head wire is connected to a positive electrical contact  144 , the other to earth, and an axial brass ferrule  146  lines the ignition chamber  140 . 
         [0064]    The side of the chamber  140  opposite to the plug  136  is provided with a short passage  148  which is concentric with the connector  104 , and which leads a dished seat portion  150 . The seat portion leads to a small, generally cylindrical gallery  152  which accommodates a valve member  154  comprising a steel ball. The gallery  150  is formed in a stainless steel, axial plug  156  which is provided with a central axial bore  158  situated between two diametrically opposed 1.2 nm bores  160 . The plug, along with the adjacent face of connector  104 , provides a bulkhead for the chamber  114 . 
         [0065]    The plug  156  carries an external screw thread which co-operates with an internal screw thread in the portion of the connector  104  in which the plug  156  is accommodated so as to retain the plug  156  in position. 
         [0066]    The operation of the igniter assembly results in hot gases from the burning black powder in the chamber  140  passing through the bore  138  to ignite the propellant charge portion  110 , and thus causes subsequent ignition of the portion  108 . The detonation of these two portions provides the propulsive force for the projectile (for example a slug of water) to be fired from the device. Because of the mass of projectile, it has been found that less pressure is needed to impart the desired momentum to the projectile than is required to counteract the recoil of firing the projectile. Accordingly, the detonation of the charge portions  120  and  116  generates higher gas pressure than the detonation of the portions  110  and  108 . In order to prevent the gas pressures on both sides of the connector  104  tending to equalise through the effect of the chambers  114  and  106  communicating through passages in the connector  104  and the plugs  136  and  156 , the valve member  154  and the seat  150  act as a poppet valve. 
         [0067]    More specifically, hot gases from the burning black power in the ignition chamber  140  pass through the bore  148  and unseat the ball  154 , driving the latter against the passage  158 . However, the passages  160  remain clear of the ball so that the gases can still flow through the gallery  152 , into the passages  160  and hence into the chamber  114  where they ignite the charge portion  116  and (subsequently) the charge portion  120 . 
         [0068]    The ignition of the two charge portions causes a large increase of pressure in the chamber  114 , and this acts, through the passage  158 , on the ball  154 , forcing the latter back against its seat  150 , and thus closing the passage  148 . Consequently, those gases are prevented from reaching the chamber  140 , the chambers  106  and  114  thus being sealed from each other. Accordingly, the second embodiment of cartridge can be configured to provide a relatively high differential of pressure between the gases exiting its opposite ends.