Abstract:
An improved muzzle brake for reducing the momentum of the recoiling components of a gun or cannon when fired, thereby reducing the forces acting on the support platform of a weapon system, is provided. In the presence of the muzzle brake, the projectile fired from a cannon to restrains the gas flow in the axial direction until gases are allowed to be diverted to a baffle in the main body of the muzzle brake. The resultant gas flow impinges on the baffle, thereby inducing a forward thrust. The diverted gas flow then exits through a plurality of exhaust ports provided to the atmosphere to create a thrust applied to the recoiling components of the gun system. Additional thrust is created by the inclusion of a second stage baffle, offset from the main body of the muzzle brake at an optimal distance by a plurality of standoffs. This thrust generates an impulse that is applied in the opposite direction of the recoil momentum by the amount of the muzzle brake impulse. The resulting reduced forces result in lighter cannon support structures, enhancing mobility and effectiveness.

Description:
RELATED APPLICATIONS 
     This application claims benefit under 35 USC 119(e) of provisional application 60/235,192 filed Sep. 25, 2000, the entire file wrapper contents of all of which application are herewith incorporated by reference as though fully set forth herein at length. 
    
    
     GOVERNMENTAL INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment of any royalties thereon. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of military ordnance and, in particular, to the field of large caliber cannons, as typified by artillery weapons, where recoil forces are of major concern in the overall design. More specifically, the invention pertains to muzzle brakes as applied to large caliber guns and cannons and to the use of these brakes in the control of recoil forces during firing. 
     BACKGROUND OF THE INVENTION 
     Large caliber military weapons, of which the U.S. Army&#39;s 155 mm Self-Propelled Howitzer (one example known and referred to herein as “Crusader”) is an exemplary case, deliver heavy rounds at relatively high velocities to distant targets. Simple conservation of momentum considerations dictate that the weapons and their support platforms are subject to heavy recoil forces during firing and, hence, to the negative effects of the recoil. It is common practice to mitigate the recoil and, thus, reduce the forces acting on the support platform of the weapon by installing or integrating a so-called muzzle brake at or near the muzzle end of the gun. These reduced forces result in lighter cannon support structures, enhancing mobility and effectiveness. 
     A muzzle brake is a device used to reduce the momentum of the recoiling components of a gun or cannon when fired by diverting the flow of propellant gases to produce an impulse that counters the breech-directed recoil of the gun. In traditional forms the brake may include a series of baffles either perpendicular or nearly perpendicular to the cannon tube axis or, alternatively, may be implemented as an integral perforated tube that consists of a series of radial holes located in the muzzle region of the cannon. 
     The need for, and efficacy of, such a device may be understood by considering the following: When the weapon is fired, the propellant burns rapidly and expands in volume inside the cannon. The projectile is accelerated along the length of the barrel by the expanding gases and is ejected at high velocity (on the order of 1000 m/s) from the muzzle end of the barrel. The high pressure propellant gases, exerting pressures of thousands of pounds per square inch, follow the projectile and are expelled into the atmosphere at velocities equaling and even exceeding those of the projectile. The combination of the accelerated projectile and propellant gases exiting the muzzle of the weapon produces a large breech-directed recoil thrust that is transmitted to the support structure. 
     It is understood that the magnitude and temporal characteristics of the recoil directly affect the design and implementation of the support structure. By installing or integrating a muzzle brake to the weapon the magnitude of the recoil and the forces transmitted to the support structure can be reduced by diverting the propellant gases and taking advantage of the impulse that is generated. 
     The firing event can be analyzed in two general scenarios: with and without a muzzle brake. In the case where no muzzle brake is installed, the high pressure, high velocity gases exit the muzzle and expand into the ambient atmosphere, creating substantial thrust and, thus, contribute an appreciable bore-directed force that is subsequently transmitted to the gun&#39;s support structure. In contradistinction, when a muzzle brake is installed, a different sequence of events ensures. The projectile, accelerating down the length of the barrel, passes the muzzle brake and continues to restrain the propellant gases in the axial direction. Consequently, the expanding, high pressure gases are diverted to the baffles or to the forward face radial holes that comprise the muzzle brake. The diverted gases exit through ports in the muzzle brake to produce an impulse-like thrust that counters the breech-directed recoil of the gun, thereby reducing the recoil and the force transmitted to the gun&#39;s support structure. 
     Muzzle brakes have traditionally been implemented in two major types. The first is an integral, perforated brake. In this implementation, an array of radial holes is drilled into the existing barrel of the weapon, at or near the muzzle. As an example, the Crusader has 120 radial holes arranged in ten axial rows, each with twelve equally-spaced circumferential locations. Gases impinge on the forward faces of the radial holes and subsequently change direction, ultimately being expelled axisymmetrically and almost radially around the muzzle of the brake. The interaction between the gas and the brake results in a momentum that counteracts the recoil of the gun. 
     The gas dynamic efficiency, β, of such a brake is 0.6 or less, meaning that the reduction in recoil is somewhat limited. The lack of efficiency is offset somewhat by the simplicity (i.e., no components are added to the design), ease of fabrication, low cost, low added weight and minimal length of the design. It should also be noted that due to the axisymmetric placement of the exhaust ports, a fraction of the propellant gas is expelled downward, producing what is known as a ground surface disturbance that may affect the weapons platform and the crew that is operating the weapon. 
     A second type of muzzle brake is the so-called “German baffle.” In this design, a small number of baffles (typically 1 or 2) is incorporated into a separate assembly that attaches to the muzzle end of the barrel. The baffles and gas exhaust ports of this design lie in the horizontal plane and, thus, gases are expelled laterally, that is, parallel to the plane of the local ground. Thus, this design avoids the ground surface disturbance associated with the perforated brake. Advantageously, the German brake has a gas dynamic efficiency, β, that may approach or exceed 1, implying a strong reduction in force transmitted to the support platform. However, the increased efficiency is offset by the cost and complexity of the units along with the penalties paid in weight. In addition, the relative complexity of the German baffle increases stress concentrations in undesirable areas and increases its manufacturing costs, with reliance on complex castings to produce the final product. 
     These two types of devices exemplify the current state-of-the-art in muzzle brake design. Though the structures described above may have satisfied their intended purpose, there still remains an unsatisfied need for an improved muzzle brake that achieves the desired goals of increased gas dynamic efficiency without endangering the crew of the weapons platform, decreased production costs, ease of manufacturing and assembly, and flexibility/tenability, as well as reduced weight and length. 
     SUMMARY OF THE INVENTION 
     The radial venting baffled muzzle brake of the current invention addresses the forgoing need. It also meets the following criteria: 
     1. minimized weight; 
     2. ease of manufacture and assembly; 
     3. optimized gas dynamic efficiency balanced with crew and platform safety; 
     4. minimized size; 
     5. flexibility and tenability; and 
     6. optimized material stress distribution. 
     It is a feature of the present invention to minimize the weight, size and length associated with the muzzle brake while achieving and maintaining a rugged and reliable design. This is achieved by fabricating the brake from lightweight materials and employing a novel, high efficiency design. 
     In a preferred embodiment, the brake is manufactured from lightweight, surface-treated titanium. Furthermore, the design achieves its desired performance with a compact, multistage, axisymmetric implementation that further minimizes weight, length and overall size of the brake. 
     An integral first stage baffle allows for a smooth transition to the radial exit passages, thereby maximizing its efficiency. In addition, the design and implementation of the main body of the brake allows for a radially uniform muzzle exit nozzle and incorporates a radially uniform first stage baffle. Thus, the geometry of these features strongly and positively influence muzzle brake efficiency. 
     Furthermore, the fillet radii transition between the main body&#39;s integral gas deflection baffle and the exit passages are carefully engineered to assure uniform stress distribution and structural integrity, while maximizing brake performance. 
     The second stage baffle of the multi-stage design also allows for a smooth transition to the radial exit passages, thereby maximizing its efficiency. In addition, the second stage baffle design also incorporates a radially uniform muzzle exit nozzle, which strongly influences muzzle brake efficiency. 
     Furthermore, the fillet radii transition between the baffle and the exit passage is designed to assure structural integrity while maximizing brake performance. One further advantage of the invention is the design&#39;s uniformity of structure, which enhances stress distribution from firing loads and thereby allows the structure size to be reduced to optimize overall system weight. 
     Another feature of the present invention is to employ standard manufacturing and assembly techniques in the implementation of the brake. In the preferred embodiment individual parts display a high degree of cylindrical symmetry, allowing them to be produced with standard machine tools, and/or simple casting methods. For final construction, the individual parts are readily assembled with standard tools and in final installation the brake, simply threads onto the muzzle of the cannon barrel. The design and implementation of the preferred embodiment reduces the overall cost of the brake. 
     Yet another feature of the present invention is to increase the gas dynamic efficiency of the brake to a level that will not endanger the crew or the support platform for the weapon. A high gas dynamic efficiency, β, estimated to exceed 1.2, is achieved by employing a two-stage baffle design with axisymmetric venting. This gas dynamic efficiency may be increased or decreased as required by altering certain physical characteristics including baffle size, baffle deflection angle, and gas exit area. 
     The present design improves upon the gas dynamic efficiency of traditional “German Baffle” type design by utilizing full axisymmetric gas expulsion to achieve optimized propellant gas exit passage area per unit length. Additional baffles (e.g., a tertiary baffle) can be added to the design to further increase the gas dynamic efficiency, β, of the muzzle brake with minimal weight impact. 
     Still another feature of the present invention is flexibility and “tunability” of the brake. The secondary baffle (or baffles, in the most general case) may be easily installed and removed enhancing internal stowage for transportation by reducing the total payload volume. In fact, the brake may be efficaciously and safely operated with the second stage baffle removed. It is estimated that the brake can achieve a gas dynamic efficiency, β, approaching 1.0 with no secondary baffle installed. 
     In addition, the second stage baffle is readily adjusted by changing the length and diameter of the standoffs that couple the secondary deflection baffle to the main body of the brake. In this manner, the brake may be adjusted to conform to the particular operating conditions of the weapon. 
     The foregoing and additional features and advantages of the present invention are realized by implementing a multi-stage baffle design with full radial venting of expelled propellant gases. The main body of the device comprises an internally-threaded, cylindrically shaped lug, a cylindrically symmetric gas baffle, and a plurality of gas exhaust ports which are arranged in such a manner as to take maximum practical advantage of available exhaust gas energy. 
     The main body of the muzzle brake is threaded onto an existing gun barrel and further secured with a key and collar arrangement to prevent loosening as a result of repeated use. A secondary gas deflection baffle may be secured to the main body of the muzzle brake by means of a plurality of cylindrical standoffs and an equal number of nuts. The axisymmetric secondary baffle is installed a predetermined distance from the first, to optimize braking efficiency. The intervening spaces between the standoffs serves secondary gas exhaust ports. 
     The muzzle brake of the current invention is easily produced using conventional manufacturing techniques, easily assembled with standard tools, achieves high gas dynamic efficiency without endangering the weapons platform or the gun crew, and is both lightweight and compact. The axisymmetry of the design prevents unbalanced forces and moments from being applied to the barrel of the cannon and, furthermore, assures high efficiency for the design. In particular, the gas dynamic efficiency, β, of the invention exceeds that of the traditional German baffle and doubles the gas dynamic efficiency, β, of a standard, integral perforated brake. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features of the present invention and the manner of attaining them, will become apparent, and the invention itself will be best understood, by reference to the following description and the accompanying drawings, wherein: 
     FIG. 1 is an isometric view of the muzzle brake of the current invention; 
     FIG. 2 is an isometric view of the muzzle brake of FIG. 1 as installed on a large bore cannon, showing the relative size and installed location of the brake; 
     FIG. 3 is a cross sectional view of the muzzle brake of FIG. 1 displaying the important components comprising the current invention including the main body and the secondary baffle; 
     FIG. 4A is an isometric view of the details of the main body of the brake of FIG. 1 as viewed from the aft position, displaying the key construction and operational details of the invention; 
     FIG. 4B is yet another isometric view of the main body of the brake of FIG. 1 as viewed from the muzzle end of the invention; 
     FIG. 5 is an exploded view of one method of fabrication of the main body of the brake of FIG. 1 with emphasis on the uniformity, simplicity and manufacturability of the invention; and 
     FIG. 6 is an exploded view of the muzzle brake of FIG. 1 emphasizing the components and assembly details of the second baffle onto the main body. 
     Similar numerals refer to similar elements in the drawings. It should be understood that the sizes of the different components in the figures are not necessarily in exact proportion or to scale, and are shown for visual clarity and for the purpose of explanation. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 provides an isometric depiction of a radially-venting baffled muzzle brake  10  of the current invention. In a preferred embodiment, the radially-venting muzzle brake  10  comprises a main body  15  and a second stage baffle  40 . The main body  15  displays a number of important features including internal threads  20  for mounting the main body directly to the muzzle end of a cannon or other large caliber gun. A pair of slots  25 , located 180 degrees apart, are used as part of a secondary locking mechanism. 
     The primary deflection baffle  30  deflects and redirects a major fraction of the expanding, high velocity propellant gases such that their velocity vector contains both components that are radially outward and axially directed back toward the breech of the gun. The resulting change in the velocity vector of the gas and accompanying impulse leads to the desired reduction in recoil force. The deflected gases are ejected into the ambient atmosphere through a plurality of gas exhaust ports  35 , located symmetrically around the circumference of the main body  15 . Gas dynamic efficiency may be increased or decreased by altering physical characteristics of the baffle, including its size, gas deflection angle, corner radii, and gas exit area. 
     In the preferred embodiment, the main body is augmented by a second stage baffle  40  that is attached to the main body by multiple standoffs  45 . A secondary deflection baffle  50  is secured between the standoffs  45  and nuts  60 . A fraction of the exhaust gases not deflected by the primary deflection baffle  30  is intercepted and redirected by the secondary deflection baffle  50 . Propellant gases are vented to the atmosphere via the secondary gas exhaust ports  55 . This redirection and venting of the propellant gases produces a second impulse that counters the recoil force of the gun. 
     The efficiency of the second stage baffle  40  can be “tuned” by adjusting the length and number of standoffs  45  as well as by changing the design of the secondary deflection baffle  50 . The addition of the second stage baffle  40  can raise the gas dynamic efficiency of the radially-venting baffled muzzle brake of the current invention to a value exceeding 1.2, substantially exceeding that of the “German baffle” and doubling that of the integrated, perforated tube brake. 
     In some cases, it may be advantageous to include additional baffles, thus raising the gas dynamic efficiency, β, to a value that further exceeds 1.2. Tertiary and subsequent baffles may be observed to mimic the axisymmetric design and implementation of the second stage baffle  40 . 
     FIG. 2 illustrates the primary use and deployment of the invention of FIG.  1 . The radial-venting baffled muzzle brake is installed on the threaded muzzle end of a large caliber gun. In particular, the threaded main body  15  is secured to the muzzle end of the barrel  100 . To prevent the brake  10  from loosening under repeated firing, the main body is further secured to the muzzle of the gun by means of a key system  75 . A collet  65 , slid over the muzzle before the brake  10  is installed, is tightened on the outer diameter of the barrel by means of locking screws  70 . This provides an interference fit between the collet and the main body and a mating function with the slot  25 , thus impeding rotation and preventing loosening of the muzzle brake during repeated firing. in a specific embodiment, a key fits into slot  25 , and also into a slot in the cannon. The collet  65  houses a pair of setscrews, which secure the key and thus prevents the relative rotation between the key, the collet, the cannon, and the muzzle brake. 
     FIG. 2 further serves to illustrate the efficacy of the invention. Propellant gases traveling axially along bore of the barrel  105  reach the brake  10 , are deflected, and then ejected in a direction that has both radial- and breech-directed components. The change in the momentum of the gases resulting from the redirection of their velocity vector produces an impulse that substantially reduces recoil force. 
     FIG. 3 provides a cross-sectional view of the invention of FIG.  1  and illustrates the major features of the invention. Within the main body  15 , integral threads  20  cut into the cannon interface lug  80  provide the mating mechanism for mounting the muzzle brake to the muzzle of the gun barrel. Slot  25  is used to mate the body of the brake  10  to the cannon and the collet  65 , shown previously in FIG. 2, which prevents loosening of the muzzle brake under repeated firing. The primary deflection baffle  30  efficiently redirects a large fraction of the expanding propellant gases emanating from the muzzle of the gun barrel. The gases are ejected uniformly around the periphery of the muzzle brake through the gas exhaust ports  35 . The change in momentum associated with the redirection of the gases leads to the desired reduction in recoil force. 
     The primary baffle  30  is radially uniform and, further, is designed to produce smooth transition to the radial exit passages, thereby maximizing its efficiency. In addition, the radial venting baffled muzzle brake incorporates axisymmetric exhaust ports  35  separated by an equal number of gas exit area plates  85 . The geometry of each of these features strongly contributes to muzzle brake efficiency. Furthermore, the fillet radii transition between the main body&#39;s primary baffle  30  and the exhaust ports  35  is carefully engineered to assure structural integrity while maximizing brake performance. Specifically, the design&#39;s uniformity of the structure enhances stress distribution from firing loads while maintaining high gas dynamic efficiency. 
     Propellant gases not redirected by the primary deflection baffle  30  and, thus, not expelled through the primary exhaust ports  35 , continue to move axially through the structure of the brake  10  transitioning from the main body  15  into the area of the second stage baffle  40 . As in the case of the integral first stage brake, the projectile impedes flow of gas in the axial direction. A significant fraction of the remaining gases interact with the secondary deflection baffle  50 , passing between the standoffs  45  and through the secondary gas exhaust ports  55 . The result is secondary impulse that serves to further counter the recoil of the gun. In particular, the desired momentum is generated by a gas velocity vector that contains both outward and rearward components. 
     The second stage baffle design allows for a smooth transition to the radial exit passages, thereby maximizing its efficiency. In comparison to a traditional “German baffle”, the second stage baffle allows for a more radially uniform muzzle exit nozzle, which also strongly influences muzzle brake efficiency. Furthermore, the fillet radii transition between the baffle and the exit passage is designed to assure structural integrity while maximizing brake performance. 
     Standoff design is yet another important feature in the performance of the design of the second stage baffle  40 . The standoffs thread directly into the front of the main body to position the second baffle at a predetermined distance away from the main body to maximize braking efficiency. The number of standoffs required are determined by the required structural integrity of the muzzle brake assembly. In general, the number and diameter of the standoffs is minimized to prevent exhaust gas restrictions. The standoffs arranged symmetrically to prevent any chance of asymmetric loading of the muzzle brake or the cannon. The six standoffs illustrated in FIG. 3 are typical of an efficacious design of a brake of the current invention. During assembly the secondary deflection baffle  50  is subsequently and readily secured to the standoffs  45  by nuts  60 . 
     The symmetry and simplicity of the baffle design are important features leading to reductions in manufacturing costs and permitting standard manufacturing techniques to be employed. Simplicity and symmetry is further emphasized in the perspective views of the main body  15  as depicted in FIGS. 4A and 4B. In both FIGS. 4A and 4B, the cylindrical symmetry of the main body  15  may be observed to be broken only by the slots  25 . 
     FIG. 4A emphasizes the construction of the cannon interface lug  80 , which is equipped with internal threads  20  and slots  25  that facilitate the mating to the muzzle of the cannon barrel. A plurality of gas exit area plates  85  separate the individual primary gas exhaust ports  35 . Gas is expelled into the atmosphere through the exhaust ports  35  after interacting with the integral gas deflection baffle  30 . 
     FIG. 4B serves to further illustrate the high degree of symmetry of the main body  15  and the design of the exhaust ports and gas exit area plates that provide axisymmetric ejection of gas and uniform loading on the structure. Both features are important to high gas dynamic efficiency and a robust mechanical design. 
     It is envisioned that the main body and the baffle components will be fabricated from a lightweight, high-strength titanium alloy as opposed to traditional steel alloys. Previous efforts in fabricating such components from titanium have resulted in premature failure, due to erosion of the baffle surfaces by the high-temperature, high-speed propellant gases. Thus, the affected surfaces of the proposed design will be treated with a unique high velocity oxy-fuel (HVOF) coating, similar in type to those which are currently utilized on titanium alloy gas turbine blades, in order to prevent and/or delay the erosive effects. The utilization of the titanium alloy for the main structural components will result in a system weight comparable to that of the perforated muzzle brake designs that are currently employed on other artillery systems. If weight savings is not paramount, the main body can be constructed from steel, if desired. 
     FIG. 5 provides an exploded view of the component parts of the main body  15 . As previously noted, an important feature of the current invention include relatively low production costs as afforded by conventional fabrication. In particular, the uniformity in design of the main body of the radial venting baffled muzzle brake enhances the producibilty of the item, thus reducing manufacturing costs. The threaded cannon interface lug  80  may be either forged or machined with conventional tooling (e.g., lathes and milling machines) from round bar stock. This manufacturing technique offers superior structural strength as compared to complex castings that are typically employed in certain baffles. 
     An exemplary number (eight) of radially-oriented gas exit area plates  85  are shown, but this quantity may vary based upon physical conditions and desired muzzle brake characteristic. It is envisioned that the exit are plates  85  will be machined from plate stock and welded to both the cannon interface lug  80  and the gas deflection baffle  30  to form the main body  15 . These plates may be chamfered to modify the geometry of the gas exit nozzles, which will affect the gas dynamic efficiency of the muzzle brake. The gas deflection baffle  30  will be either forged or machined from plate stock. The fillet radii transition between the main body&#39;s primary baffle  30  and the exhaust ports  35  are engineered to assure structural integrity while maximizing brake performance. 
     FIG. 6 offers an exploded view of the primary components of the second stage baffle  40  along with the assembled main body  15 . In keeping with the general design constraints and guidelines, the standoffs  45  and secondary deflection baffle  50  display axial symmetry, thus permitting conventional production techniques to be employed. In the assembly of the unit the plurality of symmetrically located standoffs  45  are threaded into the main body  15 . The secondary deflection baffle is fitted over the threaded ends of the standoffs  45  and held in place with nuts  60 . These secondary baffles can be formed, forged or machined to provide more flexibility in manufacturing. 
     As noted, the design of the second stage baffle allows it and its contribution to recoil reduction to be readily changed. For instance, the diameter and length of the standoffs can be changed to effectively “tune” the efficiency of the second stage baffle. In particular, the standoff length and diameter determine the area, and thus the efficiency, of the exhaust gas exit passage for the second stage baffle. In addition, the secondary baffle may be easily removed when operational conditions warrant. Examples include stowage for enhancement vehicle transportability and operations where overall weapons length must be minimized. 
     It should be apparent that many modifications may be made to the invention without departing from the spirit and scope of the invention.