Patent Abstract:
A fin deployment system for missiles and munitions that deploys and activates straight flat fins for roll control authority. The fin deployment system employs numerous design features, among which are the following: A wrap-around fin concept generates space-savings within a projectile body whereby the fins are arranged in a wrapped configuration around a boomtail structure. The fins may be constructed of a super-elastic material; the system eliminates mechanical means of deploying the wrapped fins, eliminating the need for springs to deploy the fins. The fin deployment achieves substantial space savings for increasing the onboard towing capacity of electronic packaging or lethality in the missiles and munitions systems, while at the same time providing a good roll control authority during flight by enabling a straight fin deployment resulting from the use of super-elastic materials.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims benefit under 35 USC 199(e) of provisional application 60/320,144, filed Apr. 25, 2003, the entire file wrapper contents of which provisional application are herein incorporated by reference as though fully set forth at length. 

   FEDERAL RESEARCH STATEMENT 
   The inventions described herein may be manufactured, used and licensed by or for the U.S. Government for U.S. Government purposes. 

   BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates in general to the field of Missiles and Munitions used by the Armed Forces, and it particularly relates to a new design method for a fin deployment system that enables a substantial reduction in the volume of munitions as compared to those employing conventional fin deployment systems. More specifically, the present invention incorporates a novel wrap-around fin concept that is capable of achieving a straight fin deployment which is necessary in maintaining a proper roll control authority during flight while substantially reducing the volume, hence weight, of missiles and munitions. The volume reduction thus translates into significant tactical advantages of these new missiles and munitions incorporating the present invention by enabling more electronic payload or lethality to be packaged into the volume savings. 
   2. Background of the Invention 
   High explosive missiles and munitions are an essential part of the arsenals of the Armed Forces. Missiles and munitions are highly complex systems generally used for deploying projectiles capable of high-speed and long-range maneuvers to deliver lethality to a target or to intercept an incoming threat. A missile projectile is normally discharged by means of a gun tube, or a missile launcher, or the like. Upon exiting a muzzle of a gun tube, the projectile gains a rapid increase in speed and altitude. At a high speed flight, the trajectory and stability of a missile projectile are actively controlled by navigation and guidance electronics to operate various control surfaces such as fins and canards. 
   Fins are control surfaces generally deployed in the aft of a missile projectile to provide roll stability during flight. On the other hand, canards are control surfaces typically mounted in front of a missile projectile to enhance its maneuverability. Fins are normally deployed lengthwise and with a circular symmetry with respect to the projectile body to minimize asymmetric aerodynamic loading which can adversely affect the stability of the projectile. To provide a control authority, fins are constructed with hinges to allow them to be actuated individually so as to modify the aerodynamic forces on the projectile for guidance purposes. 
   A conventional missile projectile typically employs a fin deployment system that is housed within the projectile body and rotated perpendicular to the projectile body axis. Upon exiting a gun muzzle, the fins are activated to open up lengthwise on the projectile body to provide the roll stability. A conventional fin deployment system occupies a significant interior volume of the projectile body. For example, the boom part of a 105 mm tank projectile, which is the portion of the projectile body containing the fin deployment system, is typically about 8 inches in length and weighs approximately 11 lbs. This represents a 25% of the total volume of the projectile body. The volume taken up by a conventional fin deployment system generally is viewed as a non-utilizable space within a projectile body that could otherwise be used for carrying additional volume of warheads or other explosive materials as well as electronics packages such as guidance and control electronics. Therefore, it is a well-known design objective to minimize the take-up volume of the fin deployment system by alternate design methodologies. 
   Attempts to improve a fin deployment system for missiles and munitions have been considered. One such exemplary methodology utilizes a wrap-around fin deployment system on the 2.75-inch rockets. The wrap-around fin deployment system is housed in the exterior of the projectile body with the fins folded circumferentially around a center body. In theory, this conventional design is able to reduce the take-up volume of the fin deployment system. In practice, problems with this conventional fin deployment system have been encountered whereby the deployed fins have curved surfaces upon deploying from their housing, the fin itself is shaped to the profile of the missile projectile for a semi-circular fin shape. The curved fins can significantly compromise the roll control authority of a missile projectile, which is not an issue on non guided systems. Roll control authority is needed for guided missile projectile systems; therefore the deployment system used by the 2.75 inch rocket is not viable. 
   Thus, it is realized that the current attempts to provide a fin deployment systems that can achieve a considerable projectile volume savings while maintaining a good roll control authority heretofore remains unfulfilled. Consequently, it is therefore recognized that a further enhancement in the design methodology for a fin deployment system is still needed to achieve the foregoing objectives. Preferably, the new design methodology would provide a space saving fin deployment system capable of deploying straight fins to maintain a good roll control authority while achieving the design objective of reducing the volume of the projectile taken up by the fin deployment system. 
   SUMMARY OF INVENTION 
   It is a feature of the present invention to provide a new design methodology for fin deployment system for missiles and munitions that substantially reduces the volume taken up by the fin deployment system within a projectile body. Further, it is a novelty of the present invention to provide a new method for deploying and activating straight flat fins for roll control authority. In summary, the new design method for a space-saving straight fin deployment system employs a number of novel design features as follows:
     1. A wrap-around fin concept generates space-savings within a projectile body whereby the fins are arranged in a wrapped configuration around a boomtail structure.   2. The fins may be constructed of a super-elastic material such as Nickel Titanium or Multi functional Alloy in a preferred embodiment to enable the fins to assume straight flat surfaces upon deployment without inducing any radius of curvature during in-flight trajectories. Material selection for the fin system is missile projectile size dependent. Alternatively, the fins may be made of spring steel.   3. The system eliminates mechanical means of deploying the wrapped fins, no springs are needed to deploy the fins. Physics of system generates equal deploying fins.   

   The space-saving fin deployment system affords advantages over a conventional fin deployment system in achieving substantial space savings for increasing the onboard towing capacity of electronic packaging or lethality in the missiles and munitions systems, while at the same time providing a good roll control authority during flight by enabling a straight fin deployment resulting from the use of super-elastic materials. In some particular applications, the space savings could be reduced by a factor of two as compared to a conventional design. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The features of the present invention and the manner of attaining them will become apparent, and the invention itself will be understood by reference to the following description and the accompanying drawings, wherein: 
       FIG. 1  is an external view of a missile or munitions system according to a smart cargo concept, shown attached to its aft end by a space-saving fin deployment system of the present invention for roll control authority; 
       FIG. 2  is an exploded view of a preferred embodiment of the space-saving fin deployment system of  FIG. 1 , comprising of an obturator assembly, a cant-boomtail, a fin system, a hinge assembly, a back assembly, and a cover assembly; 
       FIG. 3  illustrates various views of the back assembly of  FIG. 2 ; comprising of a cant-back plate, a plurality of retaining bolts and O rings, and a plurality of alignment pins; 
       FIG. 4  illustrates the fin system of  FIG. 2  made according to the present invention; 
       FIG. 5  illustrates an assembly view of the fin system of  FIG. 4  and the hinge assembly of  FIG. 2  that is comprised of a plurality of cant hinges, a plurality of retaining bolts, a plurality of lock pins, and a plurality of compression springs; 
       FIG. 6  illustrates various orthogonal and perspective views of the cant hinges of  FIG. 5 ; 
       FIG. 7  illustrates an isometric and cross sectional views of the lock pins of  FIG. 5 ; 
       FIG. 8  illustrates various views of the cover assembly of  FIG. 2 ; 
       FIG. 9  illustrates various orthogonal and perspective views of the cant-boomtail of  FIG. 2 ; and 
       FIG. 10  is a perspective view of the space-saving fin deployment system of  FIG. 3 , shown with the cover and fins in the stowed position as viewed when the projectile is loaded into the cartridge. 
   

   Similar numerals in the drawings refer to similar elements. It should be understood that the sizes of the different components in the figures might not be in exact proportion, and are shown for visual clarity and for the purpose of explanation. 
   DETAILED DESCRIPTION 
     FIG. 1  illustrates a missile or munitions system  10  incorporating a space-saving fin deployment system  12  made according to the present invention. An exemplary munitions system  10  may be based upon a smart cargo concept that includes a 105-mm tank munitions used in the U.S. Armed Forces. The munitions system  10  is generally comprised of a number of major components; namely: a projectile body  14 , a nose cone  16 , and a preferred embodiment of the space-saving deployment system  12  that constitutes a novelty of the present invention. Each of these major components is further described as follows: 
   The projectile body  14  is generally made of a thin steel shell having a cylindrical shape. The interior volume of the projectile body  14  typically contains flammable propellant charges that provide a thrust force upon ignition to propel the munitions system  10  forward during flight. In addition, the interior volume also houses electronics packages such as guidance and control or lethality component. 
   The nose cone  16  is generally formed of an ogive shape designed to reduce the aerodynamic drag on the munitions system  10  during flight. The nose cone  16  normally holds an explosive charge or other payload materials to destroy a target upon impact. 
   With reference to  FIG. 2 , the space-saving fin deployment system made in accordance with a preferred embodiment of the present invention is comprised of an obturator assembly  18 , a cant boomtail  20 , a fin system  22 , a hinge assembly  24 , a back assembly  26 , and a cover assembly  28 . Referring to  FIG. 3A , the back assembly  26  is designed to provide a retention structure for holding the hinge assembly  24  in place. The back assembly  26  is comprised a number of components: a cant-back plate  30 , a plurality of retaining bolts  32  with corresponding O-rings  34 , an O-ring  36 , an O-ring  38 , and a plurality of alignment pins  40 . In a preferred embodiment, 8 retaining bolts  32  and O-rings  34  are used to connect the cant-boomtail  20  to the back assembly  26 . Further, two alignment pins  40  are used for precise positioning of the cant-boomtail  20  with respect to the back assembly  26 . 
   With further reference to  FIG. 3B , the cant-back plate  30  is geometrically defined by a saw tooth-like cam shape  42  having a circular symmetry on the outer surface and an inner circular opening  44 . According to a preferred embodiment, the cam shape is divided into four equal segments; each is formed by a quarter circular arcs with an offset radius. A plurality of pairs of bolt holes  46  are machined through the cant-back plate  30  to allow the corresponding retaining bolts  32  to be inserted through for connecting the cant-boomtail  20  with the back assembly  26 .  FIG. 3B  illustrates four such pairs of bolt holes  46 . A plurality of corresponding circular O-ring grooves  48  are present to accommodate the corresponding O-rings  34  to seal out potential gas leakage from underneath the retaining bolts  32  which may bleed into the cover assembly  28  to cause failure of the fin system  10 . The placement of the O-rings ensures the generation of a forward pressure force on the cover assembly. This is needed to keep the cover assembly on during gun launch. The outside profile of the back plate mimics the shape of the boomtail. 
   A circular O-ring groove  50  inscribing the bolt holes  46  is designed to accommodate the O-ring  36  to seal potential gas leakage between the cant-boomtail  20  and the cant-back plate  30 . Similarly, with reference to  FIG. 3D , a circular O-ring groove  52  circumscribing the bolt holes  46  is present on the other side of the cant back plate  30  to receive the O-ring  38  to seal out potential gas leakage between the cover assembly  28  and the cant-back plate  30 . 
   With further reference to  FIGS. 3B and 3C , a plurality of small cylindrical bores  54  are formed at a partial depth through and equidistance around the periphery of the cant-back plate  30 . In a preferred embodiment, there are four such cylindrical bores  54 . The cylindrical bores  54  are designed to provide an engagement of the hinge assembly  24  into the back assembly  26 . Moreover, a plurality of smaller pin holes  56  are machined into the cant-back plate  30  to allow the alignment pins  40  to be inserted through for precise positioning of the cant-boomtail  20  and the back assembly  26 . In particular, two pin holes  56  are used according to the present invention. A plurality of threaded bolt holes  57  are also formed in the cant-back plate  30 . For the present invention, two such threaded bolt holes  57  are used for attaching the back assembly  26  to the cover assembly  28 . Moreover, the cant back plate  30  also includes a plurality of lock pin holes  59  for the purpose of providing a fin locking mechanism upon deployment. For a preferred embodiment, four such lock pin holes  59  are employed as shown in  FIG. 3B . 
   Referring now to  FIGS. 2 and 4 , the fin system  22  is comprised of a plurality of fins  58 . According to the present invention, four such fins  58  are used in the space-saving fin deployment system  12 . The shape of the fins  58  is normally determined by an aerodynamic analysis to provide the stability needed for in-flight trajectories. According to a preferred embodiment, the fins  58  generally are constructed from thin structural plates shaped in a rectangular plan form with a radius corner cutout  60 . Alternatively, the shape of the fins  58  may also assume other forms as necessary. 
   According to a preferred embodiment, the fins  58  may be constructed from a super elastic metallic alloy of nickel titanium or a multifunctional alloy. Other materials of similar characteristics such as iron manganese silicon or even spring steel may also be used as alternate fin materials to provide a desirable radius of curvature of the fins  58  when in the stowed position. The super-elasticity of the fin material is an essential and enabling feature of the present invention in allowing the fins  58  to undergo a substantial deflection without suffering any permanent deformation resulting from the wrap-around towed position, thereby enabling the fins  58  to spring open flat upon deployment without introducing any undesirable curvature into the surfaces of the fins  58 . Hence, good roll control authority of the munitions system  10  is therefore achievable. 
   With further reference to  FIG. 4 , a plurality of bolt holes  62  perforate the fins  58  on one of its sides adjoining the radius corner cutout  60 . These bolt holes  62  are designed to secure the fins  58  to the hinge assembly  24  as illustrated in  FIG. 5 . 
   With further reference to  FIG. 5 , the hinge assembly  24  is comprised of a plurality of cant hinges  64 , each with a plurality of retaining bolts  66 , a plurality of lock pins  68 , and a plurality of compression springs  70 . In a preferred embodiment, four each of cant hinges  64 , lock pins  68 , and compressor springs  70  are employed in the space-saving fin deployment system  12 . Referring now to  FIG. 6A , the cant hinge  64  includes a hinge portion  72 , a larger end plug  74 , and a smaller end plug  76 . Both the end plugs  74  and  76  have a cylindrical construction disposed at either distal end of the hinge portion  72 . 
   With reference to  FIG. 6B , the hinge portion  72  is shaped is a form of a nearly circular cross section with a 270-degree circular arc tangent at either end to two flat sides  78  and  80 . A straight groove  82  is machined into the hinge portion  72  to span its entire length along the flat side  80 . The thickness of the groove  82  is substantially the same as the thickness of the fins  58 . 
   With reference to  FIGS. 6A and 6C , a plurality of bolt threaded holes  84  perforate the flat side  80  and further penetrate into the hinge portion  72  with a substantial depth of thread relative to the width of the hinge portion  72  thereat. The threaded bolt holes  84  are precisely machined so as to match dimensions and positions of the bolt holes  62  of the fins  58 . The bolts also act as stopping reference for hinge rotation. 
   With reference to  FIG. 6D , on a distal end surface  86  of the hinge portion  72  whereupon the smaller end plug  76  is formed, a straight cylindrical bore  88  is constructed lengthwise at a partial depth through the hinge portion  72 . The straight cylindrical bore  88  is designed to receive the lock pin  68  and the compression spring  70 . 
   With reference to  FIG. 7A , the lock pin  68  is comprised of a taper blunt nose section  90 , a mid section  92 , and a cylindrical aft section  94 . The taper blunt nose section  90  has a conical section feature that transitions to a hemispherical nose. The taper nose allows for insertion of the pin quicker than if the pin was cylindrical. As well the taper pin wedges itself into the mating hole in the back plate to remove all machining tolerance from the system. The mid section  92  is shaped as a constant diameter section having a plurality of shallow right angle slots  96  spaced at equidistance around the periphery of the mid section  92 . In particular, there are four such right angle slots  96  in a preferred embodiment. The right angle slots  96  are designed to relieve pressure from the bore of the lock pin. The lock pin  68  has a posted section that goes through the middle of the compression spring. The post protects the spring from being compressed more than it is designed to be. The lock pin  68  also is designed to have a specific wheelbase length relative to the length of the conical section to provide more stability of the pin while locked. The cylindrical aft section  94  has a smaller diameter and is designed to accept the compression spring  70  as shown in  FIG. 5 . 
   Referring now to  FIG. 8A , the cover assembly  28  is shaped as a thin cylindrical cap having a cylindrical wall  98  and a circular end plate  100 . The cover assembly  28  is designed to enclose the fin system  22  when in the stowed position. A plurality of circular holes  102  are formed at equidistance around the periphery of the cylindrical wall  98 . In a preferred embodiment, four such circular holes  102  are employed. These circular holes  102  are designed to allow for pressure equalization around the inside ands outside of the cover, they also provide means to evacuate gas after muzzle exit. These holes are needed for structural survivability of the cover, without them the cover will collapse from gun pressure while in the gun. 
   With reference to  FIG. 8B , a hollow cylindrical plug  104  is formed on the interior of the cover assembly and is integrally attached to the circular end plate  100 . The hollow cylindrical plug  104  is comprised of a cylindrical bore  106  and an O-ring groove  107  at the end. An O-ring  108  is installed on the O-ring groove  107  to maintain the gas pressure inside the reservoir for better deployment performance. 
   With further reference to  FIG. 8B , a small meter orifice  110  is formed in and positioned at the center of the circular end plate  100 . With reference to  FIG. 8C , the meter orifice  110  is comprised of a threaded hole  112 , a small circular aperture  114 , a thin cylindrical orifice  116 , and a conical opening  118  into the cylindrical bore  106  of the cylindrical plug  104 . Inside feature  112  is installed an orifice which determines amount of bleed pressure into the reservoir. The insert orifice is made from a copper tungsten material. This material does not erode as high velocity gas passes though the orifice. 
   With further reference to  FIG. 8A , a plurality of bolt holes  120  are machined into the exterior of the circular end plate  100 .  FIG. 8A  illustrates two such bolt holes  120  disposed diametrically opposite to each other. A plurality of break screws  122  are designed to be inserted into the bolt holes  120  and then threaded into the threaded holes  57  of the back assembly  26 . The break screws  122  are designed to hold the cover assembly onto the boomtail during handling as well as to provide initial squeeze of the o-ring between the cover and the back plate. The break screws then fail at the muzzle exit due to the force within the cover pressure reservoir to release the cover assembly  28  from the back assembly  26  for fin deployment. 
   Referring now to  FIG. 9A , the cant-boomtail  20  is the main structural component of the space-saving fin deployment system  12 . The cant-boomtail  20  is a structure of circular symmetry comprising of a number of features as follows: With further reference to  FIGS. 9A–B , a cylindrical plug  124  is formed at one distal end of the cant-boomtail  20  and is designed to provide a means of engaging the space-saving fin deployment system  12  into the projectile body  14 . A circular landing area  126  is formed integrally at the base of the cylindrical plug  124  and extends to an adjoining circular indexing step portion  128 . 
   The circular indexing step portion  128  then adjoins a smaller circular indexing step portion  130  having a slightly smaller width and radius. Referring to  FIGS. 9A–B , a plurality of indexing grooves  132  and  134  are formed at equidistance around the periphery of the circular indexing step portion  128 . With specific reference to  FIG. 9C , the indexing grooves  132  are generally curved passages extending from the peripheral surface of the circular indexing portion  128  to the bottom surface  136  of the smaller circular step portion  130 . With further reference to  FIG. 9B , the indexing grooves  134  are also formed of curved channels starting from the peripheral surface of the circular step portion  128  and terminating on a surface of a hinge pocket structure  138 . The purpose of feature  132  is to provide gas release from under the fin blades to outside the fin cover, this intern helps slow down deployment speed of the fin system. 
   Referring to  FIG. 9A , the hinge pocket structure  138  is generally located in the aft section of the cant-boomtail  20  and integrally adjoins with the smaller circular indexing step portion  130 . The hinge pocket structure  138  is comprised of a plurality of hinge pockets  140  formed lengthwise along the hinge pocket structure  138 . In  FIG. 9A , four such hinge pockets  140  are illustrated. The hinge pockets  140  are generally machined surfaces having nearly semicircular cavities recessed inward from the outer surface  142  of the hinge pocket structure  138 . The shape of the hinge pockets  140  is designed so as to provide a near zero-clearance fit with the hinge assembly  26  in order to maximize space savings. With specific reference to  FIG. 9D , the outer surface  142  of the hinge pocket structure  138  is geometrically constructed by a plurality of eccentric circular arc segments interposed the hinge pockets  140 . Boomtail surface  138  has a specific contour to it for system function. The surface provides a constant curvature for the fin to rest upon, when the fin is wrapped it goes over the next adjacent hinge. The surface ramps the fin up to the hinge and allows for the fin to transition unto the hinge without any harsh transitions. 
   With further reference to  FIG. 9D , a plurality of cylindrical bores  144  are machined at a partial depth through the bottom surface  136  of the smaller circular indexing step portion  130  within each hinge pocket  140 . There are four such cylindrical bores  144  as illustrated in  FIG. 9D . These cylindrical bores  144  are designed to enable the cant hinges  64  to be positively retained within the hinge pockets  140  by engaging the large end plugs  74  therein. Further, a plurality of pairs of smaller threaded bolt holes  146  are machined into the distal end surface  148  of the hinge pocket structure  138 . In a preferred embodiment, four such pairs of threaded bolt holes  146  are employed as shown in  FIG. 9D . These pairs of threaded bolt holes  146  are designed to enable a bolted joint connection between the back assembly  26  and the cant boomtail  20  via the retaining bolts  32 . 
   With further reference to  FIG. 9D , two diametrically opposed alignment holes  150  are formed on the distal end surface  148  and are located near the periphery of the hinge pocket structure  138 . These alignment holes  150  enable a precise positioning of the boomtail  20  with respect to the back assembly  26  via the alignment pins  40 . With reference to  FIG. 9C , a large cylindrical bore  152  is integrally formed within the hinge pocket structure  138  at a substantial depth from the distal end surface  148 . The cylindrical bore  152  extends beyond the distal end surface  148  to form a small hollow cylindrical plug  154 . 
   Referring now to  FIG. 2  again, the assembly sequence of the space-saving fin deployment system  12  is as follows: The obturator assembly  18  is shaped as a circular ring with an outer diameter nominally equal to that of the circular indexing portion  128  and an inner diameter nominally equal to that of the circular landing area  126 . The width of the obturator assembly  18  is also nominally equal to that of the circular landing area  126 . The obturator assembly  18  is slipped onto the circular landing area  126  abutted against the circular indexing portion  128  of the cant boomtail  20  to form a flush, tight tolerance fit. 
   With reference to  FIG. 5 , the fins  58  are slip fitted into the grooves  82  of the cant hinges  64 . Upon aligning the bolt holes  62  of the fins  22  with the threaded bolt holes  84  of the cant hinges  64 , retaining bolts  66  are torqued to secure the fin system  22  to the hinge assembly  24 . The compression springs  70  are fitted onto the cylindrical aft section  94  of the lock pins  68 , which are then inserted into the cylindrical bores  72  of the cant hinges  64 . 
   The hinge assembly  24  is now engaged with the cant boomtail  20  on one end by means of insertion of the larger end plugs  74  of the cant hinges  64  into the cylindrical bores  144  of the cant boomtail  20 . On the other end, the hinge assembly  24  is engaged with the back assembly  26  by means of insertion of the smaller end plugs  76  into the cylindrical bores  54  of the cant back plate  30 . The hinge assembly  24  is free to pivot while being axially restrained by the cant boomtail  20  and the back assembly  26 . 
   The back assembly  26  is then secured to the cant boomtail  20  via the retaining bolts  32  inserted through the pairs of bolt holes  46  of the cant back plate  30  and threaded into the corresponding pairs of threaded bolt holes  146  of the hinge pocket structure  138 .  FIG. 10A  illustrates the combined assembly of the cant boomtail  20 , the fin system  22 , the hinge assembly  24 , and the back assembly  26 . 
   With reference to  FIG. 10B , the hinge assembly  24  is rotated while the fins  58  are simultaneously curved into circular arcs to wrap around the hinge pocket structure  138  as illustrated in  FIG. 10C . The cover assembly  28  is then slipped onto the wrap-around fins  58  and abutted against the circular indexing step portion  128 . The break screws  122  are then inserted through the bolt holes  120  of the cover assembly  28  and threaded to into the threaded bolt holes  57  of the cant back plate  30  to secure the cover assembly  28  to the back assembly  26 . The space-saving fin deployment system  12  is now completed as illustrated in  FIG. 10D  and is ready to be assembled to the projectile body  14  via the cylindrical plug  124  of the cant boomtail  20  as shown in  FIG. 1 . 
   The functionality of the present invention may be appreciated by considering the following deployment sequence: 
   Upon exiting the muzzle of the gun tube, the base pressure on the munitions system  10  begins to decrease. The gas pressure inside the pressure reservoir of the cover assembly  28  and the cant boomtail  20  is maintained. The resulting differential pressure exerts a force onto the circular end plate  100  inside the pressure reservoir. As base pressure drops from behind the projectile the pressure within the reservoir deploys the cover from the fin system releasing the fin system. The cover retention screws  122  are broken as the cover ejects. The cover retention screws are designed as a low tensile strength material. The cover retention screws do not provide the strength required keeping the cover on the projectile during launch; rather that is the job of the base pressure inside the gun tube. The cover retention screws provide a mechanical means to squeeze the o-ring between the cover and cant back plate. The stored energy in the wrapped fin is all that is needed to rotate the hinge assembly and deploy the fin. 
   Upon exposure, the fins  58  begin to unwrap themselves from the cant boomtail  20 . The unwrapping of the fins  58  also inputs into the hinge assembly  24  a torque. This torque causes the cant hinges  64  to rotate 107 degrees from a closed position to a lock position whereupon the spring loaded lock pins  68  are propelled forward into the lock pin holes  59  of the cant back plate  30 . Upon locking, due to the super elasticity of the fin material, the fins  58  are now straightened themselves into zero-curvature surfaces. The space-saving fin system  12  is now in a fully deployed state for mission readiness. 
   It should be understood that the geometry, compositions, and dimensions of the elements described herein can be modified within the scope of the invention and are not intended to be the exclusive; rather, they can be modified within the scope of the invention. Other modifications can be made when implementing the invention for a particular environment.

Technology Classification (CPC): 5