Abstract:
A projectile having a fin deployment system disposed about its circumference. The fins are initially contained by a fin cover that is removed by aerodynamic force. The fins are then rotated around a rotational axis parallel to and offset from the central axial axis of the projectile body by the centrifugal forces created by the rotation of the projectile as the projectile passes through a barrel of a gun system or tube launcher. The fin deployment system can also have locking systems that lock the fins in the deployed position and prevent the fins from rotating back into the retracted position after deployment.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is generally directed to a gun or tube launched projectile having a fin deployment system that radially extends a plurality of fins from the projectile body as the projectile leaves the gun barrel or tube launcher. Specifically, the present invention is directed to a deployment system that stores the fins within a cover about the circumference of the projectile then radially deploys the plurality of fins from the projectile body through the spinning generated by launch of the projectile. 
       BACKGROUND OF THE INVENTION 
       [0002]    Certain large bore projectiles, such as artillery shells and recoilless rifle bullets fired from gun systems or rocket propelled grenades, missiles and rockets fired from tube launchers, typically comprise radially extending fins that are sized to be loaded within the gun barrel of the artillery system or tube launcher. The fins stabilize the projectile in flight maintaining the alignment of the projectile with the aimed trajectory. Many large bore projectiles also include a rocket motor or similar means for self-propelling the projectile or supplementing the primary propellant means for the projectile. With these projectiles, the fins are a necessary feature that prevents the self-propelled projectile from veering off course due to the thrust generated by the motor or the propellant means. 
         [0003]    The inherent challenge with finned projectiles is positioning the fins such that they extend radially outward past the outer diameter of the main projectile body during flight to maximize the engagement of the fins to the air as the projectile flies while still fitting the projectile within the gun barrel or tube. A contravening concern is engaging the larger exterior surface of the projectile body to the gun barrel or tube allows the barrel or tube to more efficiently aim the projectile than with the smaller surface area provided by the tips of the fins. Fixed fins create a tradeoff between superior aerodynamic qualities of fins that extend beyond the outer diameter of the primary projectile body and the superior accuracy of sizing the projectile body to engage the barrel or tube. Accordingly, many finned projectiles comprise deployable fins that retract prior to firing to allow the projectile body to engage the barrel or tube and deploy upon exiting the barrel or tube to extend radially outward past the outer diameter of the projectile body. 
         [0004]    Deployable fin projectiles typically comprises a main projectile body that engages the walls of the barrel or tube to axially align the projectile with the barrel or tube and engage the projectile to the rifling of the barrel when fired from a gun system. Prior to firing, the fins are retracted behind or hidden within the projectile body such that the projectile body defines the maximum outer diameter of the projectile. Upon leaving the barrel or tube, the fins deploy radially outward from behind or within the projectile body to engage the air. The projectiles typically comprise mechanical assemblies having springs or other similar biasing means that retain the fins in the retracted position during loading and deploy the fins as the projectile leaves the barrel or tube. 
         [0005]    As both fixed and deployed fins are typically positioned at the rear of the projectile to maximize the aerodynamic advantage of the fins, the mechanical assemblies for deploying the fins are also positioned at the rear of the projectile and thereby proximate to any initial propellant charge for firing the projectile from guns. The heat and pressure from the ignited propellant gases can damage the mechanical assemblies resulting in failure of the mechanical assemblies to deploy or fully deploy the fins. In addition, the rapid acceleration of the projectile coupled with the heat and pressure can also cause the mechanical systems to fail. 
         [0006]    Similarly, many tube launched rocket assisted projectiles have starter motors or propellant charges that launch the projectile from the tube before the primary motor ignites. The starter motor or propellant charge can also damage the mechanical fin deployment assemblies. Similarly, the mechanical fin deployment assemblies can often comprise additional assemblies for synchronizing deployment of the fins. The additional synchronization systems further increases the likelihood that some or all of the fins will fail to deploy as a result of damage during firing. 
         [0007]    Although the mechanical assembly can be shielded to reduce the likelihood that the mechanical assemblies will be damaged during launch, the shielding increases the weight and bulk of the projectile. As the chamber of the gun or the tube launcher is fixed volume governed by the caliber of the projectile or standard missile or rocket size, any additional bulk to any portion of the projectile, such as from increased shielding, must result in a corresponding reduction in size in another portion of the projectile. Specifically, the additional shielding often reduces the possible projectile volume allotted to the projectile motor and/or payload. 
         [0008]    Similarly, the fins themselves can reduce the size of the projectile volume allocated to the motor or payload or alter the shape of the projectile. As depicted in U.S. Pat. No. 4,334,657 and U.S. Pat. No. 7,083,141, the fins typically scissor between the retracted position and deployed position within a single plane transverse to the central axis of the projectile to minimize any potential disturbance to the trajectory of the projectile from the deploying fins. However, the scissoring of the fins into the projectile reduces the internal space of the projectile that can be allocated for the payload or the motor or creates an irregularly shaped space within the projectile. The reduction in motor size and/or payload reduces the range and overall effectiveness of the projectile. 
         [0009]    The inherent tradeoff between preserving the mechanical function of the fin deployment mechanisms and reducing the performance of the projectile creates a need for a means of consistently deploying the fins without reducing the projectile volume allocated to the payload, primary motor or other projectile systems. 
       SUMMARY OF THE INVENTION 
       [0010]    A projectile, according to an embodiment of the present invention, comprises a projectile body and a fin deployment system positioned against the rear of the projectile body and having a plurality of fins rotatable along a rotational axis parallel to and offset from the central axial axis of the projectile body. Each fin is rotatable around the rotational axis between a retracted position and a deployed position. Each offset rotational axis is proximate to the exterior of the projectile body such that each fin can be rotated into the retracted position, wherein the fin is generally aligned with or contoured to follow the exterior of the projectile body when positioned in the retracted position. In this configuration, the projectile body provides the primary engagement surface that aligns the projectile with the barrel or tube, while the fins do not or minimally engage the barrel or tube as the projectile travels through the barrel or tube. The fins are deployed by rotating the fin around the offset rotational axis until the fins are positioned within a plane transverse to the central axis of the projectile. In this configuration, the fins are positioned around an internal space aligned with central axis rather than scissoring into the internal space as with conventional fins that rotate within the plane transverse to the central axis. The exterior arrangement allows for more efficient use of the internal space that can contain additional payload, the motor or other features of the projectile. 
         [0011]    In one aspect, the fin deployment system can comprise a cylindrical mount assembly defining a plurality of axial channels each aligning with the offset rotational axis of a corresponding fin. In this configuration, each fin comprises a fin portion and a barrel portion at one end of the fin portion and rotatable within the channel between the retracted position and the deployed position. During firing, the centrifugal force created by the rotation of the projectile from the barrel rifling causes the fin to rotate within the channel to move the fin portion from the retracted position in which the fin portion is generally aligned with the exterior of the projectile body to the deployed in which the fin extends radially outward from the central axis of the projectile. The reliance on the rotation of the projectile to extend the fins rather than mechanical assemblies reduces the likelihood that the pressure and heat of the launch will damage the fin deployment system resulting in unopened fins or lopsided fin deployment. Similarly, as the centrifugal forces act equally on each of the fins, fins are deployed together without the aid of synchronization systems. The lack of complex fin deploying mechanical assemblies reduces the potential systems that could fail during launch and also minimizes the amount of space that must be allocated for the deployment system, thereby freeing additional space for a motor or additional payload. 
         [0012]    In one aspect, the projectile further comprises a fin cover positioned over the fins when positioned in the retracted position to facilitate loading of the projectile without accidental deployment of the fins during handling of the projectile. The fin cover engages each fin to prevent rotation of the barrel within the channel until the fin cover is removed. In one aspect, the fin cover further comprises inwardly indented portions for engaging the fins to prevent rotation of the fins. As the projectile exits the barrel, aerodynamic drag separates the fin cover from the projectile allowing the centrifugal force of the rotating projectile to rotate the fins into the extended position. The separable cover provides a means of unlocking the fins for deployment with a low probability of failure and relatively immune to the heat and pressure created by the ignited propellant charge. Moreover, unlike conventional deployment systems where the fins are typically biased to open and the cover is fitted to the projectile to restrain the fins, the fins of the present invention do not apply any outward bias apart from the centrifugal forces created by the rotation of the projectile generally. The unbiased fins reduce the friction between the fins and the cover, thereby reducing the likelihood that the cover will become stuck to the projectile and fail to separate from the projectile. 
         [0013]    In one aspect, the fin cover can comprise at least one vent for equalizing the pressure of any air contained within the fin cover with atmospheric pressure as the projectile leaves the barrel or tube launcher. The propellant charge or starter motor can substantially increase the pressure proximate to the fin deployment system within the barrel or tube launcher. Upon exit of barrel, the air pressure around the fin deployment system rapidly decreases as the propellant gases dissipate and the projectile accelerates through “clean” air. The rapid depressurization of the surrounding air pressure without a correspondingly rapid depressurization of air within the fin cover can cause the fin cover to burst or otherwise damage the mechanical assemblies of the fin cover. The vents prevent high pressure air pockets from forming within the fin cover. 
         [0014]    In one aspect, the fin deployment system can further comprise a locking ring defining a plurality of engagement surfaces corresponding to each of the axial channels. In this configuration, the barrel portion of the fin can comprise a protrusion or define a cutout that is rotated into engagement with the stop when the fin is rotated into the deployed position. The stop protrusion is positioned to engage the fin portion and stop the rotation of the fin when the fin portion is positioned in a plane transverse the central axis of the projectile, thereby preventing over rotation of the fin portion and maintaining the proper spacing of the deployed fins. 
         [0015]    In one aspect, each fin can comprise a drive axle extending through the barrel of the fin, wherein the locking ring defines a first plurality of ports each corresponding to one of the plurality of axial channels and adapted to rotatably receive one end of the drive axle. Similarly, in one aspect, the fin deployment assembly can further comprise secondary ring positioned opposite the locking ring against the opposite end of the cylindrical mount assembly. The secondary ring defines a second plurality of ports each corresponding to one of the plurality of axial channels and adapted to rotatably receive the opposite end of the drive axle. In this configuration, the locking ring and secondary ring cooperate to maintain the barrel portion of each fin within the corresponding axial channel. In another aspect, the cylinder mount assembly can comprise a flared portion at one end defining the second plurality of ports for receiving the corresponding end of the drive axle. 
         [0016]    In one aspect, the barrel of each fin can define a cutout portion providing an engagable locking surface. In this configuration, each axial channel defines a groove that aligns with the cut out portion when the barrel is rotated into the deployed position. The cylinder mount further comprises a locking tab with a corresponding spring positioned within each groove. Upon rotation of the fin into the deployed position and the alignment of the cutout portion with the groove, the spring is biased to push the locking tab out of the groove such that locking tab at least partially protrudes from the groove and engages the locking surface to prevent the fin from rotating back to the retracted position. In one aspect, the locking tab and stop protrusions of the locking ring cooperate to maintain the fin in the deployed position. 
         [0017]    A projectile, according to an embodiment of the present invention, can comprise a projectile body and a fin deployment system. The fin deployment system can further comprise a plurality of fins and a cylindrical mount assembly. Each fin further comprises a fin portion and a barrel positioned at one end of the fin portion such that rotation of the barrel rotates the fin portion around the rotational axis of the barrel. The cylindrical mount assembly defines a plurality of axial channels each corresponding to one of the fins and adapted to rotatable receive the barrel of the corresponding fin. In operation, the barrel portion is rotatable with the axial channel to rotate the fin portion before a retracted position in which the fin portion is generally aligned with the exterior of the projectile body and a deployed position in which the fin portion is aligned with a plane transverse to the central axial axis of the projectile body. The barrel portion is rotated between the retracted position and the extended position by the rotational of the projectile. 
         [0018]    In operation, a projectile, according to an embodiment of the present invention, is loaded into a gun such that the fin deployment system is positioned proximate to a propellant charge at the breech end of the barrel of the gun. Upon ignition of the propellant charge, the projectile is accelerated through the barrel by the expanding propellant gases. In one aspect, the projectile body engages the rifling of the barrel to impart spin to the projectile. The rotation of the projectile imparted by the rifling of the barrel creates centrifugal forces causing the barrel of each fin to rotate the fin portion until the fin portion extends axially outward from the central rotational axis of the projectile upon exiting the muzzle of the barrel. In one aspect, each fin can comprise a stop protrusion preventing further rotation of the fin portion once the fin portion has achieved the proper alignment with the central rotational axis. In addition, each fin can comprise a locking tab that extends from the cylindrical mount assembly to engage the barrel of each fin to prevent backwards rotation of the fin portion. 
         [0019]    In operation, a projectile, according to an embodiment of the present invention, is loaded into a tube launcher. In one aspect, a motor can be positioned against or within the cylindrical mount assembly of the fin deployment system. The motor or a starter motor can be initially ignited to propel the projectile from the tube launcher. The motor can be adapted to direct the thrust stream at an angle to impart axial rotation to the projectile. Alternatively, the projectile body can comprise air scoops shaped to create axial rotation of the projectile. The rotation of the projectile imparted by the motor or air scoops creates centrifugal forces causing the barrel of each fin to rotate the fin portion until the fin portion extends axially outward from the central rotational axis of the projectile upon exiting the muzzle of the tube launcher. In one aspect, each fin can comprise a stop protrusion preventing further rotation of the fin portion once the fin portion has achieved the proper alignment with the central rotational axis. In addition, each fin can comprise a locking tab that extends from the cylindrical mount assembly to engage the barrel of each fin to prevent backwards rotation of the fin portion. 
         [0020]    A method of deploying the fins from a tube or barrel launched projectile comprising mounting a plurality fins to a projectile body of the projectile, wherein the fins are rotatable along a rotational axis offset form the central axis. The method further comprises rotating the fins into a retracted position such the fins are generally aligned with the exterior of the projectile body. The method also comprises fitting a removable fin cover over a portion of each plurality of fins to maintain the fins in the retracted position. The method also comprises firing the projectile from a tube or barrel, wherein the barrel or tube rotates the projectile body around the central axial axis to extend the fins. 
         [0021]    The above summary of the various representative embodiments of the invention is not intended to describe each illustrated embodiment or every implementation of the invention. Rather, the embodiments are chosen and described so that others skilled in the art can appreciate and understand the principles and practices of the invention. The figures in the detailed description that follow more particularly exemplify these embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The invention can be completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
           [0023]      FIG. 1  is a perspective view of a projectile, according to an embodiment of the present invention, prior to fin deployment. 
           [0024]      FIG. 2  is an exploded perspective view of a projectile according to an embodiment of the present invention. 
           [0025]      FIG. 3  is a perspective view of a projectile, according to an embodiment of the present invention, after fin deployment. 
           [0026]      FIG. 4  is an exploded perspective view of a fin cover and a fin deployment system, according to an embodiment of the present invention, prior to fin deployment. 
           [0027]      FIG. 5  is a perspective view of a fin cover and a fin deployment system assembly, according to an embodiment of the present invention, prior to fin deployment. 
           [0028]      FIG. 6  is a perspective view of a fin deployment system after fin deployment according to an embodiment of the present invention. 
           [0029]      FIG. 7  is a partial cross-sectional view of a fin deployment system prior to fixation of the fins in the deployed position. 
           [0030]      FIG. 8  is a partial cross-sectional view of a fin deployment system after fixation of the fins in the deployed position. 
       
    
    
       [0031]    While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0032]    As depicted in  FIGS. 1 and 3 , a projectile  20 , according to an embodiment of the present invention, comprises a projectile body  22  and a fin deployment system  24 . The projectile body  22  further comprises an ogive tip portion  26  and a cylindrical end portion  28 . The projectile body  22  defines a central axial axis extending between the tip portion  26  and the cylindrical end portion  28  and intersecting the tip of the tip portion  26 . In one aspect, the cylindrical end portion  28  is sized to engage the barrel walls or the walls of the tube launcher to align the projectile  20  with the central axis of the barrel or tube launcher. In one aspect, the projectile body  22  can define an internal cavity for receiving ordinance and other payloads. As depicted in  FIGS. 1 and 3 , the fin deployment system  24  is positioned at the rear of the projectile body  22  against the cylindrical end portion  28 . 
         [0033]    As depicted in  FIGS. 1-3 , the fin deployment system  24  comprises a plurality of fins  30  and a cylindrical mount assembly  32 . Each fin  30  further comprises a fin portion  34  and a barrel  36  positioned at one end of the fin portion  34  such that the barrel  36  can be rotated to rotate the fin portion  34  around the barrel  36 . While fins  30  are depicted as flat in the attached drawings, it is envisioned that fins  30  may have a curvature to more closely fit the outer circumference of the projectile, or may be shaped with varying thickness depending upon expected flight dynamics. In one aspect, the fin portion  34  can comprise a cutout portion  35  angled to facilitate rotation of the projectile  20  in flight to facilitate continued rotation of the projectile  20  in flight after leaving the barrel or tube. The cylindrical mount assembly  32  similarly defines a plurality of axial channels  38  each corresponding to one of the plurality of fins  30  and adapted to rotatably receive the barrel  36  of each fin  30 . Each channel  38  provides a bearing surface for allowing the barrel  36  for rotating within the channel  38  to move the fin portion  34  between the retracted and deployed positions. The channel  38  defines a rotational axis for barrel  36  that is parallel to, but offset from the central axial axis. In one aspect, the cylindrical mount assembly  32  defines an internal space that can be used to receive a rocket motor, additional ordinance or other payloads. 
         [0034]    As depicted in  FIGS. 2-4  and  6 - 8 , each barrel  36  is rotatable to move the fin portion  34  between a retracted position and a deployed position. In the retracted position, the fin portion  34  is generally aligned with the exterior of the cylindrical end portion  28  such that plurality of fins  30  are arranged around the interior space defined by the mount assembly  32  when in the retracted position. In one aspect, the fins  30  are sized such that the tip of each fin portion  34  is proximate to the barrel  36  of the next fin  30  and no portion of the fin portion  34  protrudes past the outer diameter defined by the projectile body  22 . In this configuration, the cylindrical end portion  28  provides the primary engagement between the projectile  20  and the barrel or tube that aligns the central axis of the projectile body  22  with the central axis of the barrel or tube. In the deployed position, each fin portion  34  is positioned within a plane transverse to the central axis of the projectile body  22 . Similarly, a portion of the fin portion  34  extends beyond the outer diameter of the projectile body  22  to better engage the air in flight. 
         [0035]    The rotation of the fin portions  34  between the retracted position and the deployed position is facilitated by the centrifugal force created by the rotation projectile  20  as the projectile  20  leaves the barrel or tube. The rotation can be facilitated by the barrel rifling, shaped air scoops in the tip  26 , angling of the starter motor nozzles and other conventional means of imparting spin to the projectile  20  as the projectile  20  travels through the barrel or tube. Unlike conventional fin deployment systems, the present fin deployment system  24  deploys the fins  30  without any mechanical assembly, such as a spring or lever, and relies on the natural or created rotation of the projectile  20  to deploy the fins  30 , thereby reducing the risk that fins  30  will fail to deploy due to mechanical failure or damage. 
         [0036]    As depicted in  FIGS. 4-5 , in one aspect, the fin deployment system  24  can further comprise a fin cover  40  positionable over the fins  30  and the mount assembly  32 . The fin cover  40  further comprises plurality of indented portions  42  that engage the fin portions  34  to maintain the fin portions  34  in the retracted position as the projectile  20  travels through the barrel or tube. The fin cover  40  separates from the fins  30  and the mount assembly  32  as the projectile  20  exits the barrel or tube allowing the fins  30  to rotate into the deployed positions. In one aspect, the fin cover  40  is retained by a friction fit such that the drag caused by the air as the projectile  20  leaves the barrel or tube overcomes the friction fit and separates the fin cover  40  from the projectile  20 . In one aspect, a portion of the fin deployment system  24  can engage the barrel or tube to assist the projectile body  24  in maintaining the alignment of the projectile  20  to the barrel or tube. In one aspect, the fin cover  40  can comprise a plurality of vents  74  that equalize the air pressure within the fin cover  40  with the surrounding air pressure to avoid formation of high pressure air pockets beneath the fin cover  40 . As depicted in  FIGS. 4-5 , the vents  74  can be positioned within the indented portions  42  to prevent the edges of the vent  74  from engaging the rifling of the barrel or otherwise impacting the flight of the projectile. 
         [0037]    As depicted in  FIGS. 7-8 , in one aspect, the fin deployment system  24  can further comprise a locking ring  44  affixed to an end of the mount assembly  32 . The locking ring  44  defines a plurality of engagement surfaces  46  each corresponding to one of the axial channels  38  and positioned to engage the fin portion  34  as the fin portion  34  is rotated into the deployed position. In this configuration, each barrel  36  comprises at least one stop protrusion  47  that engages the engagement surfaces  46  to prevent the fin portion  34  from over-rotating past the deployed position. In one aspect, the locking ring  44  can define a plurality of ports  48  for receiving a plurality of fasteners  50  for securing the locking ring  44  to the mount assembly  32 . 
         [0038]    As depicted in  FIGS. 7-8 , in one aspect, each barrel  36  can define a cutout portion providing a locking surface on the barrel  36 . In this configuration, the mount assembly  32  defines a groove  50  that aligns with the locking surface of the barrel  36  when the fin portion  34  is positioned in the extended position. The mount assembly  32  further comprises a locking tab  52  and a flat spring  54  positioned within the groove  50 . The flat spring  54  biases the locking tab  52  against the barrel  36 . The barrel  36  retains the locking tab  52  within the groove  50  until the engagement surface aligns with the groove  50  at which point the locking tab  52  is free to be pushed by the spring  54  from the groove  50 . The locking tab  50  engages the engagement surface to prevent the rotation of the fin portion  34  back to the retracted position after the fin portion  34  is rotated into the extended position. The locking tab  50  and the stop protrusion  46  to maintain the fin portion  34  in the deployed position. 
         [0039]    As depicted in  FIG. 2 , in one aspect, each fin  30  further comprises a drive axle  56  extending axially through the barrel  36 . The barrel  36  can further comprise at least one loop  58  for receiving the drive axle  56 . As depicted in  FIG. 2 , each fin  30  comprises two drive axles  56  each extending from one end of the barrel  36 . In this configuration, the locking ring  44  defines a first plurality of ports  60  for rotatably receiving one end of the drive axle  56 . In one aspect, the locking ring  44  can further comprise a plurality of fasteners  57  for securing the end of the drive axle  56  within the first plurality of ports  60 . In one aspect, the mount assembly  32  further comprises a flared portion  62  defining a plurality of second plurality of ports  62  for rotatably receiving the opposite end of the drive axle  56 . The first and second plurality of ports  60 ,  64  cooperate to maintain the barrel  36  in the axial channel  38  as the barrel  36  rotates the fin portion  34  between the retracted position and the extended position. In one aspect, the flared portion  62  can further comprise a second plurality of stop protrusions  64  for engaging the fin portion  34  and preventing over-rotation of the fin portion  34  past the deployed position. 
         [0040]    As depicted in  FIG. 2 , in one aspect, the cylindrical mount assembly  32  can further comprise a protector plate  66  shielding the ends of the drive axles  56  from damage from the heat and pressure generated during firing. The protector plate  66  can define a plurality of ports  68  for receiving corresponding fasteners  70  to secure the protector plate  66  to a corresponding plurality of ports  72  defined by the locking ring  44 . 
         [0041]    According to an embodiment of the present invention, in operation, a projectile  20  can be loaded into a gun barrel or a tube launcher such that the tip portion  26  of the projectile  20  is oriented toward the muzzle of the barrel or tube launcher. In a gun launch, a propellant charge can be placed behind the fin deployment system  24 . In a tube launch, a motor can be placed within the cylindrical mount assembly  32  or behind the fin deployment system  24 . In one aspect, the fin cover  40  can be positioned over the fins  30  to retain the fins  30  in the retracted position while the projectile  20  is in the barrel or tube launcher. 
         [0042]    During firing, the propellant gases generated by the ignited propellant charge or the thrust generated by the launch motor accelerate the projectile  20  through the gun barrel or tube launcher. In a gun launch, the rifling of the barrel engages the projectile body  22  to impart spin to the projectile  20 . In a tube launch, the motor can be aimed to impart a spin to the projectile  20  as the projectile  20  travels through the tube launcher and through the air. Similarly, the tip portion  26  of the projectile body  22  can comprise air scoops shaped to cause axial rotation of the projectile  20  in flight. 
         [0043]    Upon exiting the muzzle of the tube or barrel, the vents  74  in the fin cover  40  rapidly equalize the pressure within the fin cover  40  with the surrounding air. Aerodynamic drag on the fin cover  40  slows and separates the fin cover  40  from the fin deployment system  24 . The axial rotation of the projectile  20  causes the now freed fin portions  34  to rotate into the deployed positions in response to the centrifugal forces created by the rotation of the projectile  20 . The fin portions  34  continue to rotate until the barrel  36  engages the stop protrusion  46  preventing further rotation of the fin portion  34 . Similarly, a locking tab  52  is then deployed from the cylindrical mount assembly  32  to engage the barrel  36  and prevent backwards rotation of the fin portion  34 . 
         [0044]    While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and described in detail. It is understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.