Patent Publication Number: US-10788284-B1

Title: Grounded and vehicular mounted weapons with improved recoil stability

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The inventions described herein may be manufactured, used and licensed by or for the United States Government. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates in general to weapon systems and in particular to grounded and vehicular mounted cannons. 
     Recoil forces are generated in response to a projectile exiting a gun tube. These forces can reduce the stability of low elevation firing guns and in the case of certain weapon systems, such as baseplate mortars, limit the elevation angle from which they can be fired. 
     This problem has existed since the first grounded baseplate mortars were fielded. Baseplates often couple the recoil momentum of firing through a ball and socket joint that connects the breech of the cannon to the baseplate. The ball and socket joint allows the cannon to be oriented in both azimuth and elevation without requiring the movement of the baseplate. Often round, the baseplate couples the recoil forces to the earthen soil upon which it rests. 
     The horizontal component of recoil relative to total recoil increases as the elevation is decreased and may lead to undesirable rearward movement of the baseplate and a related loss of firing stability. Horizontal stability of soil subjected to a horizontal force may often be lost if insufficient vertical compressive force is not concurrently applied. Accordingly, mortars are generally limited to high-angle fire of at least 45°. 
     Limitations in minimum firing elevation prevents the use of these weapons in direct fire. This is unfortunate, as direct fire can engage close targets more accurately and with reduced time of flight which can be very important for self-defense. Direct fire also provides means to engage the vertical sides of targets such as buildings. Finally, direct fires reduces the maximum ballistic trajectory altitude of the round thereby reducing concerns of shared airspace with close support aircraft. 
     The problem of horizontal stability has also existed for grounded spade and outrigger emplaced weapons. Historic wheeled artillery cannon field carriages typically allowed the entire lower carriage to roll rearward in response to horizontal recoil. These carriages employed long beams or trails projecting rearward that were fitted with iron shoes that rested upon the ground prior to firing. While the carriage rolled rearward, the shoes would slide and float along the top of the earth developing some level of friction to slow the recoil but also providing a righting torque to prevent the carriage from overturning. The vertical component of recoil had to be endured by the carriage and was coupled to the earth largely through the wheels. 
     The 75 mm field gun M 1897, the French 75, was an early example of a gun fitted with a recoil system. With the advent of the French 75, spades were fitted in lieu of shoes to bind the trails to the earth and inhibit motion of the lower carriage. The recoil system attenuated the recoil forces which could then be managed by a lighter weight lower carriage. Nevertheless, the need for strong trails to endure compressive loading without buckling and large spades to distribute horizontal forces over larger areas of earth result in undesirable weight. This additional weight may be alleviated if horizontal recoil is reduced or eliminated. 
     It is well known that towed howitzers fired in loose soils are readily capable of not only shifting but their spades may raise and project soil rearwards in response to firing. These negative consequences may be lessened as horizontal recoil is reduced or eliminated. 
     Vehicular mounted weapons have been subject to recoil limitations when firing off their suspension. Most vehicle mounted cannons apply the horizontal component of recoil above the center of mass of the vehicle hull which is itself suspended above the terrain by its suspension (possibly augmented by spades or other stabilizing outriggers). The torque resulting from this momentum arm is coupled with the horizontal ground resistance in the opposite direction and beneath the center of mass. Thus, the two torques additively combine in the same rotational direction. The combined torque tends to rock the vehicle compromising stability and may tax the bearing strength of the soil beneath. By altering the resultant torque, the rocking may be reduced. 
     A need exists for an approach to recoil stability to solve several related issues which include reducing the minimum elevation for baseplate mortars thereby enabling horizontal or depressed fires, reducing the size, weight and emplacement burden of recoil spades that are commonly employed on towed artillery cannons to achieve firing stability and to reduce excessive vehicular horizontal recoil response. 
     SUMMARY OF INVENTION 
     One aspect of the invention is a system comprising a cannon for launching a projectile and a counter momentum generator coupled to the cannon for producing a counter momentum for countering a recoil momentum of the weapon system. The counter momentum is substantially concurrent with the recoil momentum and has a vertical component and a horizontal component. The vertical component typically combines with a vertical component of the recoil momentum. The horizontal component negates a portion of the horizontal component of the recoil momentum. 
     Another aspect of the invention is a weapon system capable of firing a projectile at low elevation angles, the mortar weapon system comprising a cannon, a barbette pedestal, a baseplate and a counter momentum generator. The cannon is mounted on the barbette pedestal and further comprises integral trunnion pins. The barbette pedestal mounts the cannon to the baseplate and serves as a pivot yoke for the integral trunnion pins to allow elevation of cannon. The baseplate has a bottom surface in contact with the external surface and a top surface on which the barbette pedestal is pivotably mounted. The counter momentum generator coupled to the cannon produces a counter momentum for countering a recoil momentum of the weapon system and includes a venturi nozzle and an outlet nozzle. The counter momentum is substantially concurrent with the recoil momentum and has a vertical component and a horizontal component. The vertical component combines with a vertical component of the recoil momentum to increase the compressive force between the baseplate and the external surface. The horizontal component negates a portion of the horizontal component of the recoil momentum. The counter recoil generator further includes a venturi nozzle extending from an interior of the cannon through the integral trunnion pins. The outlet nozzle has an input in communication with the output of the venturi nozzle and an output to the external environment. 
     It is an object of this invention to provide a solution to meet the minimum elevation stability constraints of baseplate mounted cannons. This is achieved by firing a projectile at a lower elevation while also discharging counter momentum opposite in azimuth and at its own angle of elevation. The direction of the combined forces may then be designed to satisfy the minimum elevation requirement of the baseplate. 
     As a corollary to this first objective, it is an objective of this invention to provide a means to reduce the reliance upon vertically projected elements to stabilize baseplates to meet a minimum firing stability constraint. E.g., we could use this invention to maintain a firing angle of α=45° but achieve a net angle of 0=69.30 to cut the horizontal momentum in half. This may cut in half the size of the required spades integrated into the baseplate making it lighter and easier to emplace. 
     It is an object of this invention to use this same inventive concept to reduce or eliminate the size and bulk of spades, trails, and turntables required of towed artillery carriages to endure recoil. 
     It is a further object of this invention to use this same inventive concept to reduce the rocking response of vehicles when firing mounted cannons from ground vehicles or watercraft. 
     It is an object of this invention to provide the design option to project the counter momentum material upwards to reduce the rearward extent of any hazard area presented behind the weapon. 
     It is an object of this invention to have the option to extend the length of the counter momentum generator to further remove the potential noise, blast, and other hazards away from weapon to better allow weapon servicing and manned access. This may be done using nozzle blast tubes or any means to extend the discharge location using a suitably compact passage. 
     The invention will be better understood, and further objects, features and advantages of the invention will become more apparent from the following description, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
         FIG. 1  is a cross sectional side view of a cannon system with a counter momentum generator, according to one illustrative embodiment. 
         FIG. 2  is a schematic showing momentum vectors of the cannon system of  FIG. 1 , according to one illustrative embodiment. 
         FIG. 3  is a contour plot of net momentum angles for direct fire with respect to both the ratio of counter to recoil momentum and counter momentum discharge angle, according to one illustrative embodiment. 
         FIG. 4  is a contour plot of net momentum angles for fire with a fixed counter momentum angle of 135 degrees with respect to both the ratio of counter to recoil momentum and launch momentum discharge angle, according to one illustrative embodiment. 
         FIG. 5  is a plot of the net vertical momentum for β=135° and (IC/IR) solved to follow the contour with the net angle θ=450, according to one illustrative embodiment. 
         FIG. 6A  is a side view of a mortar weapon system at a direct fire position with a counter momentum generator, according to one illustrative embodiment. 
         FIG. 6B  is a side view of a mortar weapon system at an elevated fire position, with a counter momentum generator, according to one illustrative embodiment. 
         FIG. 7  is top cross sectional view of the cannon of the mortar weapon system of  FIGS. 6A and 6B , according to an illustrative embodiment. 
         FIG. 8  is a top cross sectional view of the cannon and counter momentum generator of the mortar weapon system of  FIGS. 6A and 6B , according to an illustrative embodiment. 
         FIG. 9  is an isometric view of a mortar weapon system with a counter momentum generator, according to an illustrative embodiment. 
         FIG. 10  is a side cross sectional view of a recoiling artillery weapon system with a counter momentum generator, according to an illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A counter momentum generator is employed on a weapon system to allow for low elevation fires by baseplate mounted cannons, to reduce the size and weight of spade and outrigger supported cannons or to reduce the rocking response of vehicular mounted cannons. The counter momentum generators develops a counter momentum, also referred to as a counter momentum, that is structurally coupled to the weapon but which is not parallel to the recoil momentum. A horizontal component of the counter momentum negates a portion of the horizontal recoil momentum. A vertical component of the counter momentum combines with the vertical recoil momentum to aid in compression between the base of the weapon system and the ground. In combination, they produce a more desirable net momentum vector tailored to the particular application. Unlike recoilless guns and most muzzle brakes, the generated counter momentum is not parallel and coaxial with the launch recoil momentum. As the system does not seek to eliminate recoil, the magnitude of the cancellation momentum need not be fixed to eliminate recoil. 
     For baseplate mounted cannon, the net momentum may be oriented to satisfy the minimum launch elevation of a baseplate while enabling the launch momentum to be oriented below this minimum elevation. For spade and outrigger cannons, the horizontal component of the net momentum may be reduced and the resultant net momentum may be oriented to reduce or negate a net torque on the cannon. With less horizontal momentum, the size and weight of lower carriage elements intended to endure horizontal momentum, such as trails and spades may be reduced. For vehicular mounted cannon, the rocking response of the vehicle may be reduced thereby allowing for higher launch momentum to be tolerated without excessively raising road wheels in response. 
     The approach of utilizing a counter momentum generator is described in the context of baseplate mounted cannons, such as mortar weapon systems, outrigger or spade stabilized cannons, such as towed artillery systems and vehicular mounted cannons such as both mortar and artillery weapon systems. However, the approach is not limited to these weapon systems or to weapon systems alone. The teachings of this specification may be applied to any system which generates a recoil momentum. For example, a counter momentum generator may be employed by ship-borne cannons or railguns. Further, a counter momentum generator may be employed on a non-weapon system such as slingatrons, catapults, railguns and a space gun, or Verne gun, for delivering payloads into orbit. 
       FIG. 1  is an illustration of a cross sectional side view of a system with a counter momentum generator, according to one illustrative embodiment. The illustration is a simplified depiction of the system  10  to illustrate the operating principles. In practice, the system would comprise components including at least a mounting structure, such as a baseplate and support structure, such as a bipod. In other embodiments, the system may comprise a carriage or a vehicle including other stabilizing elements including spades, outriggers, firing jacks and floats and turntables. The depiction shows the cannon system  10  shortly after projectile  30  exit with the notional escape of propellant from both the muzzle of the cannon and the nozzle of the counter momentum generator. 
     The cannon system  10  comprises a cannon  100  and a counter momentum generator  200 . The cannon  100  is oriented at an elevation angle alpha  102  with respect to the horizontal and further comprises a breech  104 , a bore  106  and a muzzle  108 . The breech  104  serves as a pressure vessel thereby containing the propellant gases which propel the projectile  30  through the bore  106  and out of the muzzle  108 . 
     The counter momentum generator is oriented at a discharge angle beta  202  with respect to the horizontal. As will described in further detail below, the counter momentum generator  200  generates the counter momentum  210  by expelling mass. The mass may include a projectile or propellant gases. 
     For simplicity, the center of gravity may be considered to vertically pass the weight of the weapon through point  12  and is not shown. As the weight is very small relative to ballistic forces, it may be neglected. In addition, the bend in the barrel is depicted as a simple extended rigid structure forming a partition. In practice, the partition would more likely contribute as a pressure vessel containing propellant. The bottom of the curved bend is coincident with a horizontal rigid ground boundary condition. The recoil and counter momentum vectors are oriented through point  12  where the bend meets the boundary condition such that no torque is applied to the weapon. 
     The cannon system launches a projectile from the cannon. The exit of the projectile causes an opposing recoil momentum  110  in the direction alpha  102 . The counter momentum generator generates a counter momentum  210  in response which serves to reinforce the vertical recoil momentum and alleviate some of the horizontal recoil momentum. The counter momentum is applied at the larger angle β  202 . 
       FIG. 2  is a schematic showing momentum vectors of the cannon system of  FIG. 1 , in accordance with an illustrative embodiment. A simplified mathematic treatment of the advantages may be realized by considering the vector addition of the launch recoil momentum  110  and counter momentum  210  about a point where the two vectors cross. This may be envisioned as occurring at the pivot point of a rigid mortar baseplate although the findings are more general. 
     As shown in  FIG. 2 , i and j are the horizontal unit vector  40  and vertical unit vector  42  reflecting positive direction up and to the right with an elevation above the horizontal of a for the fired projectile. The launch recoil momentum  110  is oriented down and to the left. It is of equal magnitude but opposite direction of the launch momentum of the fired projectile and muzzle gases that would be upward and to the right. The firing elevation  102  is constrained such that −90°≤α≤90° with excessive depression being considered uncommon. 
     The counter momentum  210  is depicted down and to the right. This too is of equal magnitude but opposite direction to the discharge momentum of the material (propellant gas and possible incompressible Davis mass) ejected upwards and to the left at an angle of β  202 . The net momentum  410  is the vector addition of these two mimicking the recoil of an effective firing elevation above the horizontal of θ  402 . 
     While not absolutely constrained, a likely desired range for the net elevation  402  is α&lt;θ≤90° such that the net momentum  410  imparted is downward and the left (or lacking a horizontal contribution with θ=90°). The momentum imparted by the ground reaction would be equal and opposite to this pushing upwards and to the right. As all forces pass through the same point in space at a rigid boundary condition, no motion is imparted to the weapon. A broken line reflects the parallelogram law interpretation of vector addition. As the intent is for the counter momentum  210  to reduce net horizontal momentum the counter discharge angle  202  is constrained to 90°≤β≤270°. As the vertical component of the counter momentum  210  is generally desired to augment elevated firing momentum, P in excess of 180° is considered uncommon. 
     The recoil momentum  110  may be expressed by:
 
 Ī   R   =Ī   R ((−cos α)   l   +(−sin α))=− Ī   L  
 
     The counter momentum  202  may be expressed by:
 
 Ī   C   =Ī   C ((−cos β)   l   +(−sin β))   J   
 
     Accordingly, the net momentum  410  may be calculated as:
 
 Ī   N =( I   R (−cos α) I   C (−cos β))   l   +( I   R (−sin α)+ I   C (−sin β)   J   
 
     The angle  402 , theta, at which the net momentum  410  acts can be calculated by the following equation: 
     
       
         
           
             
               tan 
               ⁢ 
               
                   
               
               ⁢ 
               θ 
             
             = 
             
               
                 
                   
                     I 
                     R 
                   
                   ⁢ 
                   sin 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   α 
                 
                 + 
                 
                   
                     I 
                     C 
                   
                   ⁢ 
                   sin 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   β 
                 
               
               
                 
                   
                     I 
                     R 
                   
                   ⁢ 
                   cos 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   α 
                 
                 + 
                 
                   
                     I 
                     C 
                   
                   ⁢ 
                   cos 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   β 
                 
               
             
           
         
       
     
     It is illustrative to consider the case where θ=90°. This requires the elimination of the horizontal component of the net momentum  410 . To state another way, I R  cos α=−I C  cos β. 
     The minimum counter momentum  410  required to achieve this occurs at β=180° with a magnitude exactly equal to the horizontal component of recoil. Note that a recoilless gun achieves this feat with IR=IC and β=α+180°. As the discharge angle  202  is reduced from this case more counter momentum  210  is required. At β=135° the magnitude of the counter momentum  210  required increases by the square root of two (141%). 
     It is also illustrative to consider horizontal fire with α=0° as a function of both the ratio of counter momentum  210  to recoil momentum  110  (IC/IR) and counter momentum discharge angle β  202 .  FIG. 3  is a contour plot of net momentum  410  angles for direct fire with respect to both the ratio of counter momentum  210  to recoil momentum  110  and counter momentum discharge angle  202 , according to one illustrative embodiment. 
     Note that when the counter momentum  210  is equal to the launch recoil at β=180° we have a direct fire recoilless gun and a singularity as there is no angle associated with a zero magnitude net momentum  410 . If directed at β=90° the two equal magnitude and orthogonal vectors achieve a net angle of θ=45°. Interestingly, achieving a net θ=45° angle  402  can be met with a nearly 30% reduction in counter momentum  210  relative to the recoilless gun at β=135°. This could reduce the size and bulk of the munitions as the consumables required to achieve this are reduced. Small net firing angles  102  of 1°, 5°, and 15° are included to show the behavior at the extremes of counter momentum  210  being nearly horizontal (β near to 180°) and (IC/IR) vanishingly small. It is interesting to note that when the plotted contour lines provide two solutions for 180°≥β≥90° for a given ratio of (IC/IR), the more highly elevated orientation (β nearer to 90°) projects the hazard imposed by the counter momentum  210  higher up and away from the ground. But, the net vertical momentum is increased for this solution. 
     It is also illustrative to consider the net momentum angle  402  with a fixed cancellation momentum angle  202  of β=135° as a function of both the ratio of counter momentum  210  to recoil momentum  110  (IC/IR) and launch momentum discharge angle α.  FIG. 4  is a contour plot of net momentum angles  402  for fire with a fixed counter momentum angle of 135 degrees with respect to both the ratio of counter momentum  210  to recoil momentum  110  and launch momentum angle  102 , according to one illustrative embodiment. 
     If the minimum net elevation tolerable for a baseplate is 45° then no counter momentum  210  is required when the firing momentum angle  102  α≥45°. The magnitude of the required counter momentum  210  discharged at β=135° to maintain the net angle  402  θ=45° for 0°≤α&lt;45° may be read off the corresponding contour line  502 . Although slightly curved, this contour follows a nearly straight line from α=45° with zero counter momentum  210  to α=0° at approximately (IC/IR)=70% (or 30% less than 100% as observed above). The upper contour  504  represents the elimination of the horizontal component of net recoil with θ=90°. 
       FIG. 5  is a plot of the net vertical momentum for β=135° and (IC/IR) solved to follow the contour with the net angle  402  θ=45°, according to one illustrative embodiment. Firing elevations of α=0°, 15°, 30°, and 45° are plotted as points  512 ,  514 ,  516  and  518 , respectively, as well to clarify the relation between a and (IC/IR) shown above. 
     The net vertical momentum is negative to convey it is pushing downward into the ground (or water for watercraft). It is of interest to note that the net vertical momentum shown for α&lt;450 continuously decreases as a decreases despite the increasing counter momentum  210  IC to maintain θ=45°. The worst case vertical momentum would remain high elevation firing with α closer to 90° and no counter momentum  210 . The extreme would occur at −IR at IC=0 and α=90°. Historically firing at α=900 has not been desired due in part to the self-evident hazard such firing would present to the crew. However the development of reliable course altering projectiles may reduce this concern. 
     Advantageously, a larger baseplate is not required to endure recoil from both the launch and counter momentum generator. In addition to the reduction of the vertical momentum component, the partial cancellation of horizontal momentum for 0°≤α&lt;45° conveys the illustrative finding. The net momentum  410  is rendered smaller for both vertical and horizontal components relative to firing at α=45°. 
     The counter momentum generator may be embodied on a mortar weapon system, and in particular, a baseplate mortar weapon system. The counter momentum generator increases the minimum elevation stability constraints of baseplate mounted cannons by firing a projectile at a lower elevation while also discharging counter momentum  210  opposite in azimuth and at its own angle  202  of elevation. Baseplates often comprise a ball and socket joint that connects the breech of the cannon to the baseplate. The ball and socket joint allows the cannon to be oriented in both azimuth and elevation without requiring the movement of the baseplate. Often round, the baseplate couples the recoil forces to the earthen soil upon which it rests. The direction of the combined forces may then be designed to satisfy the minimum elevation requirement of the baseplate. 
     In addition, the counter momentum generator provides a means to reduce the reliance upon vertically projected elements to stabilize baseplates to meet a minimum firing stability constraint. For example, the counter momentum generator may allow a mortar weapon system to maintain a firing angle of α=45° but achieve a net angle of θ=69.3° to cut the horizontal momentum in half. This may cut in half the size of the required spades integrated into the baseplate making it lighter and easier to emplace. 
     The counter momentum generator may be embodied on a towed or self-propelled artillery weapon system. Contemporary field artillery is supported by carriage which may be towed or self-propelled. Contemporary field artillery cannon may further employ firing jacks and floats or turntables to endure the majority of vertical recoil without reliance upon the transportation wheels of the lower carriage to provide stability. Jacks raise the lower carriage and employ a float between them and earth to distribute the weight and much of the vertical recoil momentum of the weapon over a large enough area of soil that it may endure the forces. Turntables provide a similar function but are centered beneath the azimuthal pivot of the weapon to allow 360 degrees of traverse. Floats, turntables and mortar baseplates are similar in function in that they distribute recoil forces over a significant area of ground that is in contact with them. Baseplates are typically unique in that the elevation pivot point is integrated at or modestly below the ground level. Whereas, lower carriages supported by floats and turntables support upper carriages that pivot in elevation above the ground level. 
     The counter momentum generator may be employed on a towed artillery system to reduce or eliminate the size and bulk of spades, trails, and turntables required of towed artillery carriages to endure recoil. Additionally, the counter momentum generator may be employed to reduce the rocking response of vehicles when firing mounted cannons from ground vehicles or watercraft. 
     There are several approaches to implementing a momentum generator on cannon weapon systems, such as mortar weapon systems or artillery weapon systems. The momentum generator may be separate or isolated from the cannon pressure source. In these approaches the counter momentum generator may include separate rocket engines or guns intended to fire while the cannon is undergoing recoil motion to improve recoil stability. This approach is particularly suited for applications involving single use weapon systems. 
     In certain embodiments, the weapon system comprises a small conduit for communication of the cannon and counter momentum pressure sufficient to communicate heat and pressure for ignition from the one that fires first to the other. The conduit is sized and dimensioned sufficiently small such that the mass passing through it would be insignificant with respect to shifting momentum generation from the first one that fires to the second one that fires or vice versa. 
     In embodiments, the counter momentum generator may fire for a duration longer than that of the cannon. For cannon mountings within a recoiling gun mount, this may allow the duration and intensity of the counter momentum  210  to better align with those of recoil arresting force reactions applied through the gun mount to the vehicle, weapon platform, or ground. 
     In embodiments, the counter momentum generator may be a pre-fired momentum generator in which the counter momentum generator may commence fire before the cannon. Such a counter momentum generator may assist in achieving favorable fire out of battery performance. 
     Alternatively, the counter momentum generator may be a post-fired momentum generators which fires after the cannon. A post-fired momentum generator may increase accuracy by preventing disturbance loading while the cannon functions. 
     Integrated momentum generators couple the cannon propellant with that of the counter momentum generator with a significant shifting of momentum generating capability between the two. Those familiar with the art may appreciate that distance between the port(s) from the cannon to the ultimate counter momentum discharge location will result in internal forces and delay times as the propellant transits the passage between the two. 
     In baseplate mortar applications, caution should be exercised when using delayed counter momentum approaches such as ducted muzzle brakes. This is because peak recoil forces may occur earlier in the ballistic cycle when fired from stiff soil rendering the counter momentum  210  too late to prevent excessive motion. 
     The counter momentum discharge can be located at any design location along the length of the cannon or possibly extended beyond the muzzle or behind the breech some distance. In embodiments, the counter momentum generator shares a common pressure source with the cannon gun chamber (and thus before projectile motion). For example, a counter momentum generator may employ a port into a breech block or closure (as in the frame of a revolving cannon guns) of the cannon. This provides a simple method to alter a gun to employ a counter momentum generator or switch to a mode without such a generator by using a breech closure with a port, or using one that does not have a port. Alternatively, a counter momentum generator sharing a common pressure source with the gun chamber may employ a port or ports through the gun chamber wall. 
     In embodiments, the counter momentum generator may share a common pressure source with some intermediate location along the cannon bore before the muzzle that is not active until the projectile passes over the location. In other embodiments, the counter momentum generator shares a common pressure source with the muzzle. In other embodiments, the counter momentum generator may employ a delayed venting elsewhere along the bore as has been employed by sonic rarefaction wave recoilless gun systems which is further described in co-owned U.S. Pat. No. 6,460,446, entitled “Sonic Rarefaction Wave Recoilless Gun System” to the present inventor, the entire contents of which are herein incorporated by reference. 
     The integral counter momentum generator may be augmented in some embodiments. For example, the counter momentum generator may include additional propellant (initially not combusted) that is separated from the cannon volume. In this embodiment, the cannon volume and counter momentum generator are separated by a flow area restriction that chokes the flow at some point during operation. As another example, the counter momentum generator may employ a counter projectile for additional momentum generation. However, counter momentum generator, as used throughout this specification, does not comprise an additional cannon of the same caliber as the first cannon and concurrently firing a counter projectile of the same size as the original projectile from a common propellant. 
     Another design variable which may be selected according to desired performance and application is the location of the chocked flow point between the cannon pressure and counter momentum generator. 
     Un-choked counter momentum generators lack a flow restriction between the cannon and counter momentum generator. These are analogous to improved versions of recoilless or Davis guns that introduce a bend along the common chamber to produce off-axis momentum. Yet they do not introduce a flow restriction to choke flow between the two functions. 
     Choked generators introduce a flow restriction between the cannon and counter moment generator that serves to choke the flow during operation. A counter momentum generator having a cannon egress choke chokes the flow as it exits the cannon. By designing the downstream flow passage to be able to swallow any normal shocks that might otherwise form, such a design achieves relatively low pressure downstream of the egress choke. Turning the propellant flow to vector the thrust will need to be done carefully thereby generating oblique shocks with an ample increase in cross sectional area and bulk in order to take advantage of the lower downstream pressure. 
     A counter momentum generator comprising a downstream choke intentionally chokes propellant gas flow downstream of the cannon egress port. This results in high pressure subsonic flow between the high pressure cannon and the choke. Such a counter momentum generator is simpler in design as the subsonic flow is readily turned and vectored without concern of shock formation. However, the higher pressure places additional containment burden on the structure. 
     For counter momentum generators employing a counter projectile, this form of generator would initially arrest the flow of the pressurized gas within the counter momentum generator and may therefore be anticipated to achieve a downstream obstruction of the flow. 
     In embodiments, the counter momentum generator may comprise a reservoir volume. By coupling a downstream choke with a significant reservoir volume between itself and the cannon egress port, the momentum generator function will increase in duration with potential decreases in peak thrust force (and noise or blast hazards). For cannon mountings within a recoiling gun mount, this may allow the duration and intensity of the counter momentum to better align with those of recoil arresting force reactions applied through the gun mount to the vehicle, weapon platform, or ground. In embodiments, the reservoir may aid in flushing or evacuating the gun like a bore evacuator. 
     In embodiments of the invention, the counter momentum generator further comprises one or more ports to control the operation of the counter momentum generator. 
     The ports may be binary on-off ports to defeat counter momentum generators when off and allow counter momentum generation when on. 
     In other embodiments, the ports are throttled ports that regulate flow restriction area to control mass flow rates. For example, the ports may be analogous in operation to a rocket plug or pintle thrust controls. Controlling the mass flow alters the amount of counter momentum generated. It also alters the pressure within the launch bore and thereby alters the interior ballistics and launch momentum and velocity. 
     The ports may comprise open loop throttles or closed loop throttles. Open loop throttles are set prior to firing and lack feedback during the interior ballistics. Closed loop throttles change throttling performance during firing according to feedback. 
     The ports may comprise ignition throttles that inhibit propellant flow from the cannon during ignition to improve cannon performance. This may be achieved for example with a lightweight spring loaded flap valve. Another example would be to incorporate a rupture element within a disposable cartridge case. 
     It is an advantage of weapon systems comprising a counter momentum generator in that they provide the design option to project the counter momentum material upwards to reduce the rearward extent of any hazard area presented behind the weapon. Embodiments of the current invention may employ blast tubes to extend the discharge location of the counter momentum generator further from the weapon to reduce spatial encumbrance in reloading and otherwise interfacing with the weapon without exposure to excessive noise or blast hazards. Those skilled in the art of unsteady nozzle behavior and pressure vessel design may optimize the design to minimize size or weight of the resulting blast tube extended nozzles. In particular, for the blast tube to occur in a subsonic region of nozzle flow requires higher pressure containment but a smaller passage than one designed to operate in a supersonic region of flow. 
       FIG. 6A  is a side view of a mortar weapon system at a direct fire position with an integrated counter momentum generator, according to one illustrative embodiment.  FIG. 6B  is a side view of a mortar weapon system at an elevated fire position, with an integrated counter momentum generator, according to one illustrative embodiment. 
     The mortar weapon system  60  shown in  FIGS. 6A and 6B  is a barbette mounted mortar weapon system  60 . The mortar weapon system  60  comprises a cannon  62 , a counter momentum generator  64 , a lower pedestal  66  and a baseplate  68 . The baseplate  68  is in contact with the ground and serves to couple the combined momentum to the earthen soil upon which it rests. The lower pedestal  66  serves as a pivot yoke allowing elevation of the tipping parts within the trunnions  622 . It pivots with the tipping parts in traverse about a lower pintle integrated within the baseplate  68 . 
     For illustrative purposes, the mortar weapon system  60  is shown with trunnions  602  elevated well above the baseplate. In practice, these may be recessed, as is done for typical mortar ball caps, with concomitant loss of minimum elevation. Additionally, neither equilibrators nor bipods are depicted for simplicity. 
       FIG. 6A  shows the mortar weapon system  60  in a direct fire position with the central axis of the cannon  62  oriented at zero degrees with respect to the horizontal. The counter momentum generator  64  is oriented at an angle  202  of β=120° degrees with respect to the horizontal.  FIG. 6B  shows the mortar weapon system  60  at an elevated fire position. The cannon  62  is oriented at an angle of 33 degrees. The counter momentum generator  64  is held at the fixed angle of β=120° degrees with respect to the horizontal. 
     Embodiments such as this one may rigidly fix the counter momentum angle  202  to the upper carriage or baseplate  68  for all elevations of fire. This may aid in the providing a consistent servicing and user interface to the weapon regardless of its elevation of fire. Setting β=180° with a suitably long blast tube may significantly reduce impairment of access to the weapon at the expense of causing a more extensive back blast hazard zone. 
     However, other embodiments may rigidly fix the counter momentum angle  202  to the tipping cradle or cannon  62 . Stated another way, the counter momentum angle  202  would be set such that β=α+φ where φ would be fixed and would likely be constrained such that 90°≤φ&lt;180°. φ=180° corresponds to an alignment similar to a recoilless rifle or normal muzzle brake.) If φ=110° the launch angle  102  could elevate to typical howitzer levels of 700 with rearward horizontal counter momentum discharge. Such a design would have β=110° in direct fire. 
     Still other embodiments may adjust the counter momentum angle  202  to the actual firing of individual rounds to optimize performance. In addition to adjusting the counter momentum angle  202  to optimize performance, other embodiments may incorporate means to adjust the amount of counter momentum  210  developed to meet performance objectives. Further such adjustment may be coupled to the actual elevation of the cannon through devices such as gears and cams to ensure firing compliance with design intent. As a corollary to this embodiment, muzzle velocity variation may be achieved to augment or usurp propellant zoning intended to control muzzle velocity. 
       FIG. 7  is top cross sectional view of the cannon of the mortar weapon system of  FIGS. 6A and 6B , according to an illustrative embodiment.  FIG. 8  is a top cross sectional view of the cannon and counter momentum generator of the mortar weapon system of  FIGS. 6A and 6B , according to an illustrative embodiment. 
     The cannon  62  comprises integral trunnion pins  622  extending from an outer surface of the breech of the cannon  62 . The trunnions  622  interface with the lower pedestal  66  to allow tipping of the cannon  62  in the elevational plane to increase or decrease the angle of fire of the cannon  62 . 
     The counter momentum generator  64  is integral to the mortar cannon  62  and shares a common pressure source with the gun chamber  624 . The counter momentum generator further comprises a first venturi nozzle  642  and a second venturi nozzle  642 , each extending through a corresponding one of the integral trunnion pins  622 . The first venturi nozzle  642  and second venturi nozzle  642  serve as ports through the gun chamber wall  624  and provide access to the gun chamber and pressures within the chamber caused by projectile launch. The narrow neck  644  of each venturi nozzle  642  may serve to meter and accelerate the flow between the mortar cannon  62  and the outlet of the counter momentum generator during operation. The counter momentum generator  210  further comprises a first nozzle valve  646  and a second nozzle valve  646  to alter the ratio of counter momentum  210  to recoil momentum  110 . 
     The counter momentum generator  210  further comprises a first outlet nozzle  648  and a second outlet nozzle  648 . For clarity, the first outlet nozzle  648  and the second outlet nozzle  648  are shown oriented in line with the mortar cannon  62 . However, as described above, in this embodiment the first outlet nozzle  648  and the second outlet nozzle  648  are oriented at a constant discharge angle  202  of 120° with respect to the horizontal. Each outlet nozzle  648  receives expelled propellant gas from the venture nozzles  642  and directs the propellant gas away from the cannon  62  and the external environment at the desired direction. 
     In operation, a projectile is received in the cannon  62 . The projectile is propelled through the bore and out of the muzzle of the cannon  62  by high pressure gases caused by the ignition of a propellant within the breech of the cannon  62 . A recoil momentum  110  is generated by the ejection of the projectile in the direction of the elevation angle  102  and toward the baseplate. Concurrently, a portion of the high pressure gas is directed through the first venturi nozzle  642  and the second venturi nozzle  642  as determined by the position of the first nozzle valve  644  and second nozzle valve  644 . The high pressure gas exits each of the venturi nozzles  642  and is directed to the first outlet nozzle  648  and second outlet nozzle  648 . The high pressure gas is expelled to the external environment from the first outlet nozzle  648  and the second outlet nozzle  648  at a discharge angle  202  of β=120°. 
     The discharge of the gas from the outlet nozzles  648  produces the counter momentum  210  at the angle of the discharge angle  202  and toward the baseplate  68 . The vertical component of the counter momentum  210  combines in an additive relationship with the vertical component of the recoil momentum  110 . The combined momentum vertical momentum serves to the increase the compressive force directed onto the ground and thereby increase the stability of the baseplate on the earthen soil. The horizontal component of the counter momentum  210  combines with the horizontal component of the recoil momentum  110  in a subtractive relationship thereby reducing the shear forces between the baseplate  68  and the ground. As the recoil momentum  110  vector and the counter momentum  210  vector intersect the trunnion pin  602 , no torque is generated about the trunnion pin  602 . However, remaining horizontal recoil passing through the trunnion pin  602  could lead to instability. 
       FIG. 9  is an isometric view of a mortar weapon system with a counter momentum generator, according to an illustrative embodiment. The mortar weapon system  90  shown is a baseplate mounted mortar weapon system  90  capable of direct fire. The mortar weapon system comprises a baseplate  92 , a cannon  94 , a counter momentum generator  96 , a base cap extension  98  and a bipod  99 . 
     The counter momentum generator nozzle  962  is at a fixed angle  202  with respect to the cannon  94 . The counter momentum generator  96  is ducted from the chamber of the cannon  94  to generate the counter momentum  210 . The embodiment shown overcomes the impediment of the bipod  99  to allow zero elevation fire. This approach directs the momentum to place the base cap extension  98  into compression with minimum off axis loading. As the nozzle  962  is fixed at an angle of 120° with respect to the cannon  94 , the nozzle  962  would be defeated for fires above 45°. As it is not the intent to directly counteract all recoil, the counter momentum generator need not be opposite in direction or magnitude to the bore as in other direct fire weapon systems, including recoilless rifles. 
       FIG. 10  is a side cross sectional view of a recoiling artillery weapon system with a counter momentum generator, according to an illustrative embodiment. The artillery weapon system  1000  employs a counter momentum generator  1006  to change the direction of recoil thereby making the system more stable and decreasing the reliance upon weapon weight applied through the forward floats to stabilize the system. As described above, the counter momentum generator  1006  may be placed at different locations along the length of the cannon and  FIG. 10  shows an embodiment with the counter momentum generator  1006  located forward of the breech of the cannon  1004 . 
     The artillery weapon system  1000  comprises a carriage  1010 . The carriage  1010  is adapted from that of the US Army&#39;s M204 105 mm howitzer. The carriage  1010  further comprises a cradle  1012  which supports the cannon  1004 . The cradle  1012  includes an internal recoil arresting system for mitigating the magnitude of the recoil force required to transfer the recoil momentum  110  to the ground. A lower carriage  1014  supports the rear of the cradle  1012  and provides a pivot yoke for the cradle  1012  to rotate in the elevational plane. A telescoping elevation and equilibrator strut  1016  connects the cradle  1012  to the lower carriage  1018 . The telescoping elevation and equilibrator strut  1016  raises and lowers the elevation of the cradle  1012  and thereby the elevation of the cannon  1004 . The lower carriage  1018  rests on a turntable  1020  which in turn rests on the ground. 
     Similar to the M204, the carriage  1010  includes forward outrigger floats  1022  in the form of rollers. The arrangement is analogous to the 160 mm Tampella heavy mortar developed by Oy Tampella Ab of the Republic of Finland. The 160 mm Tampella heavy mortar employs two transportation wheels to stabilize the cannon forward of its baseplate. In the 160 mm Tampella heavy mortar, M204 and the embodiment shown in  FIG. 10 , the two wheels serve a function much like that of a mortar bipod mount. Unlike the 160 mm Tampella heavy mortar, the elevating trunnions of the M204 and present embodiment are located above the ground level, whereas mortar baseplates typically employ a ball joint within the baseplate that couples the plate to the cannon. 
     The launch recoil  110  is directed parallel to the recoil path of the cannon within the cradle  1012  that is elevated about the trunnions. As depicted, the recoil momentum  110  would intersect the horizontal ground some distance to the left of (behind) the turntable  1020 . Absent any counter momentum  210 , this will create a torque tending to raise the roller floats and tip the lower carriage  1018  counter clockwise about the left end of the turntable if the weight of the system is insufficient to hold it down. 
     The component of the counter momentum  210  that is orthogonal to the launch recoil  110  will become manifest as orthogonal translation and rotation of the cannon  1004  and cradle  1012  that develop compressive loads in the elevation strut  1016 , roller float  1022 , and ground. In effect, a suitably engineered strut  1016  may serve as a kind of off axis recoil arresting system. As before, the recoil momentum  110  and counter momentum  210  may be vectorally added to achieve a net momentum  410 . The counter momentum  210  will not only emulate a higher elevation of fire, it will shift the horizontal location where the net momentum  410  intersects the ground. Shifting the intersection point to occur within the span of the turntable  1020  and outrigger float  1022  will reduce or eliminate the tendency of the lower carriage  1018  to tip and thereby provide improved firing stability. However, it should be noted that shifting the intersection point to occur to the right of the float  1022  would tend to tip the lower carriage  1018  in the opposite direction. For example, this could occur if significant counter momentum  210  is developed too close to the muzzle of the cannon  1004 . 
     Forces developed at the trunnion bearing  1024  and elevation struts  1016  are of concern as recoil of the cannon within the cradle  1012  does not aid in attenuating the levels from those of the counter momentum generator  1006 . If the counter momentum generator  1006  functions over a duration commensurate with the launch, the forces may be rather large. The concept of the center of percussion of the tipping parts may be applied to consider desirable locations for the counter momentum generator  1006 . Accordingly, placement of the effective instantaneous pivot point of the tipping parts during their highest loading between the trunnion bearing and upper strut pivot bearing would be a design methodology to manage bearing force levels. This location may be shifted by altering the counter momentum generator location, orientation, and magnitude. 
     In an embodiment, these counter momentum generator forces arc reduced by allowing the generator mass to move and have its motion arrested in analogy with traditional cannon recoil. The motion may be constrained to the recoiling cannon or coupled separately to an independent cradle. 
     While the invention has been described with reference to certain embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.