Patent Publication Number: US-2016223305-A1

Title: Projectile

Description:
The present invention relates to a finned projectile for a small arms weapon having a barrel, such as a shotgun, and in particular to a small arms projectile having improved fin configuration. 
     Small arms projectiles for small arms weapons are packaged with a cartridge cover or sleeve, which also houses a propellant charge at the rear of the projectile, adjacent to an initiator or primer provided on the cartridge&#39;s cap. In use, the cartridge is loaded into a barrel of a small arms weapon and firing causes the detonation of the initiator, which in turn detonates the propellant charge, thereby propelling the projectile out of the cartridge cover, along the weapon&#39;s barrel, and though the air. 
     Small arms projectiles which have stabilising fins for improved accuracy are known in the art. For example, WO 02/090870 describes a known projectile having four deployable fins mounted around the circumference of the rear section of the projectile body. Each of the fins has a curved form which matches to fit the outer surface of the projectile body when folded there against. This thereby allows the projectile to fit within and move along the weapon&#39;s barrel when fired. The projectile&#39;s fins are held in this inward folded (un-deployed) position by the cartridge cover prior to firing. On firing, the projectile is ejected from the cover and forced along the weapon&#39;s barrel. Once the projectile has exited the weapon&#39;s barrel, the fins are no longer constrained, and are hence able to move to a radially outward (deployed) position. Once deployed, the fins help to provide stability during flight, resulting in a relatively higher level of accuracy over a given range. 
     According to an aspect the present invention there is provided a projectile for a small arms weapon, the projectile comprising: 
     a projectile body; 
     a plurality of peripheral fins each pivotably coupled to the projectile body at a pivot for movement from a un-deployed position to a deployed position; 
     wherein each of the fins comprises a straight section and a connecting section connecting the straight section to the pivot and being configured so that the plane of the straight section is offset from the pivot axis. 
     In this way, the present invention allows for improved stability during flight, thereby resulting in improved accuracy over a given range. In this respect, the inventor has found that the major air flow past the projectile is at a distance from the projectile&#39;s body. As such, there is normally only a limited interaction between the air flow and the deployed fins because only the distal ends of the fins encounter any significant air flow for assisting in providing stability. To address this, rather than adopting a curved profile, the fins of the present invention have a straight section which provides a flat or planar profiled region at the distal end of the fin. This allows the fins to project radially further outward from the projectile&#39;s longitudinal axis once deployed because the radial vector component of the fin is longer for a given fin length. This in turn allows a greater proportion of the fin to extend into the major air flow, thereby improving their stabilising effect. 
     One of the difficulties with adopting a straight fin profile for small arms projectiles is accommodating the fins when they are in an un-deployed or folded position because the fins must be located within the outer circumferential profile of the projectile in order that the projectile may fit within the weapon&#39;s barrel. However, in the present invention, the connecting section forms a coupling with the projectile&#39;s body and positions the straight section so that its plane does not pass through the fin&#39;s pivot axis. As such, rather than the fins projecting away from the projectile body at a tangent from the fins pivot when folded, the connecting section has the effect of allowing the fin to reach around the projectile&#39;s body. That is, when in the un-deployed position, the connecting section is able to angle the straight section back toward the circumferential surface of the projectile&#39;s body. This allows a longer fin to be accommodated within the projectile&#39;s outer circumferential profile. 
     Preferably the plane of the straight section of each fin lies substantially at a tangent plane to the circumferential surface of the projectile body when in the un-deployed position. In this way, longer fins may be incorporated without protruding from the projectile&#39;s outer circumferential profile. In this respect, in a preferred embodiment, the tangent point is substantially in the centre of the fins straight section. This maximises the length of the straight section which can be accommodated. 
     Preferably, the projectile further comprises a channel formed around the circumference of the projectile body for receiving the plurality of fins when in the un-deployed position. In this way, the channel provides a region for locating the fins within the outer circumferential profile of the projectile, when they are in their un-deployed position. 
     Preferably, the straight section of each fin extends straight out from the projectile&#39;s body when in the deployed position. In this way, the distance by which the fins project outwardly from the longitudinal axis of the projectile is maximised. 
     Preferably the bottom surface of the channel further comprises a flat section adjacent to the pivot of each fin. This allows each fin to reach further around the body of the projectile, thereby allowing longer length fins to be incorporated. In a preferred embodiment, the inner surface of the connecting section of each fin may lie flush with the adjacent flat section of the channel. 
     Preferably, when in a deployed position, the plane of the straight section of each fin projects substantially radially outward. 
     Preferably, each fin is integrally formed. In this this way, a simple reliable construction is provided. 
     Preferably, the length of the straight section of each fin is longer than the length of the connecting section. In this way, the outward projection of each fin in a radial vector is maximised. 
     Preferably, the straight section of each fin comprises at least one flat surface parallel to the plane of the straight section. In this way, a simple, yet aerodynamically efficient configuration is provided. 
     Preferably, the connecting section of each fin comprises a coupling connected to the respective fin&#39;s pivot and a linking region between the coupling and the fin&#39;s straight section, the linking region being angled relative to the straight section. 
     Preferably, the projectile further comprises biassing means for biassing each fin toward its radially deployed position. In this way, the fins automatically deploy to their maximum radial position as soon as they leave the constraints of the cartridge cover and the weapon&#39;s barrel. 
     Preferably, the biassing means comprises a spring located at each pivot. In this way, a simple and mechanically reliable bias is provided. 
     Preferably the distal end of each fin comprises a tapered edge. In this way, when in the un-deployed position, the distal edge of each fin can lie flush with the curvature of the projectile&#39;s outer circumferential profile, as defined, for example, by the sides of the channel. 
     In an embodiment, each fin is configured to overlie the pivot of an adjacent fin. This allows longer length fins to be incorporated. 
     Preferably, the projectile comprises three or four fins. 
     According to a further aspect of the present invention, there is provided a projectile for a small arms weapon, the projectile comprising: a projectile body; a plurality of peripheral fins each coupled to the projectile body at a pivot for rotation from a folded position to a deployed position, where each of the fins comprises a straight section and a connecting section connecting the straight section to the pivot, the straight and connecting sections being angled relative to one another so that, when in the folded position, each fin extends around a portion of the projectile body and, when in the deployed position, the straight section of each fin extends straight out from the projectile&#39;s body. In this way, the straight/flat fin profile allows the fin to extend further into the major airflow past the projectile during flight, thereby improving its stability. 
     According to yet a further aspect of the present invention, there is provided a projectile for a small arms weapon, the projectile comprising: a projectile body a plurality of peripheral fins each pivotably coupled to the projectile body at a pivot for movement from a radially un-deployed position to a radially deployed position; a channel formed around the circumference of the projectile body for receiving the plurality of fins when in the un-deployed position, wherein the pivot for each fin is positioned sufficiently towards the longitudinal axis of the projectile body to enable the distal end of each fin to overlie the pivot of the adjacent fin when the fins are in the un-deployed position. In this way, longer fins can be accommodated. 
     Preferably, each fin has a generally L shaped form to define a major portion distal from the pivot and a minor portion proximal to said pivot. 
     Preferably, the major portion provides a substantially flat surface. 
     Preferably, the minor portion of each said fin includes opposing lugs and each pivot comprises a pin located through said lugs. 
     Preferably, the distal end of the major portion is shaped to enable it to fit between the lugs of an adjacent fin in the un-deployed position. 
    
    
     
       Illustrative embodiments of the present invention will now be described with reference to the accompanying drawings in which: 
         FIG. 1  shows a perspective view of a projectile according to a first embodiment of the invention, with the fins shown in a deployed position; 
         FIG. 2  shows a rear cross-sectional view of the projectile shown in  FIG. 1 , with the fins shown in the deployed position; 
         FIG. 3  shows a rear cross-sectional view of the projectile shown in  FIG. 1 , with the fins shown in an un-deployed position. 
         FIG. 4  shows a rear cross-sectional view of the projectile according to a second embodiment of the invention, with the fins shown in an un-deployed position. 
         FIG. 5  is a perspective view of a fin according the second embodiment. 
     
    
    
       FIGS. 1 to 3  show a projectile  1  according to a first embodiment of the present invention. The projectile  1  has a body  3  comprising a front section  4 , containing the warhead, and a rear section  8 . The rear section  8  includes mounting formations  7 , which support coupling pins  5 , onto which fins  2  are pivotably coupled. The coupling pins  5  provide a pivot axis which is parallel to the longitudinal axis of the projectile body and allow the fins to rotate or swing outwardly. As such, the fins  2  are able to move from a un-deployed or folded position, as shown in  FIG. 3 , to deployed position, as shown in  FIGS. 1 and 2 , where the fins extend straight out from the projectile body. 
     Fin deployment springs  6  are provided on coupling pins  5 , with one end of each spring  6  engaging the projectile body  3  and the other end received by a formation provided at the base of its respective fin  2 . The springs  6  act to bias the fins  2  outwardly to their deployed position. As well as the ends of the spring  6  applying a rotational force between the projectile body  3  and the fin  2 , they are also configured to bias the fins  2  rearwardly along the longitudinal axis of the projectile  1  for locking the fins  2  into the deployed position once deployed. The mounting formations  7  also support stopping pins  9 , which prevent the fins  2  from rotating beyond their deployed position. 
     The projectile body  3  comprises a recessed channel defined between the mounting formations  7  into which fins  2  are received when in the un-deployed position. In this respect,  FIG. 3  shows a rear cross-sectional view of the projectile  1  when the fins are in the un-deployed position. As shown, in this position the channel  11  allows the fins to be located within the outer circumferential profile of the projectile body, as viewed looking down the projectile&#39;s longitudinal axis. This thereby allows the projectile to fit within the bore of a small arms weapon&#39;s barrel. 
     As shown in  FIG. 3 , each fin  2  comprises a connecting section  13  adjacent to the coupling pin  5  which connects to a straight second section  14 . The connecting section  13  is configured such that the plane of the straight section  14  (i.e. the notional plane passing through the middle of the straight section  14 , parallel with its major surfaces) is offset from the pivot axis formed by coupling pin  5 . That is, the plane of the straight section does not pass through the pivot point formed by the coupling. As such, the connecting section  13  angles the straight section  14  back toward the bottom circumferential surface of the channel  11 . 
       FIG. 3  also shows that, in the un-deployed position, the planes of each straight section of each fin  2  lie substantially at a tangential plane to the curve of the recessed surface of the channel  11  of the projectile body  3 , with the middle of the straight section  14  being located substantially at the tangent point. The planes of each straight section are indicated by dotted lines in  FIG. 3  and pass through the centre of the planar or flat part of each fin&#39;s straight section  14 . With this arrangement, the length of the straight section  14  of each fin which can be stowed within the outer circumferential profile or boundary of the projectile is maximised. 
     The bottom surface of the channel  11  further comprises a flattened section  12  adjacent to the coupling  5  of each fin  2 , as can be seen in  FIG. 1 . This allows the coupling pins  5  to be recessed radially toward the projectile&#39;s central axis, which in turn allows the fins to reach further around the projectile&#39;s body when in an un-deployed position. 
     In this embodiment each fin  2  is additionally provided with a tapered edge  15  along its distal end. The tapered edges  15  lie flush with the curvature of the sides of the channel  11  when in the un-deployed position so as to help maximise the length of each fin, without extending beyond the outer circumferential profile of the projectile. 
     In use, the projectile  1  is initially enclosed within a cartridge cover, which holds the fins  2  in their un-deployed position. When the weapon is fired, the propellant detonates, propelling the projectile  1  from its cartridge and along the weapon&#39;s barrel. When the projectile  1  emerges from the weapon&#39;s barrel, the fins  2  are no longer constrained by the cover or weapon&#39;s barrel, allowing them to deploy under the bias of springs  6 . 
     Initially, the fins  2  are prevented from rearward movement as the rear edge of the fin  2  is biased against the rear rim of mountings  7 . However, the radially outward bias acts to rotate each fin  2  out to its deployed position. Once in this position, the back of the fin  2  contacts its stopping pin  9 , thereby preventing further rotation of the fin  2 . At the same time as the above, as the fins  2  radially move to their deployed position, a notch provided at the rear of the fin aligns with the rear rim of mounting  7 , thereby allowing each fin  2  to slide rearwardly along its coupling pin  5  under the bias of its spring  6 . This acts such that the notch slides over the rim of mounting  7  into an engaged position, with the surfaces of these formations mating with one another. Once in this engaged position, the width of each fin  2  mates with a counter surface on the rim of mounting  7  providing a circumferential support surface on the projectile body for supporting each fin  2 . Once in this position, the fins  2  are effectively locked in their deployed position since they are biased rearwardly into this engaged position. Locking the fins into place in this manner has the advantage of providing enhanced stability during flight. 
     This configuration helps to provide improved accuracy over long ranges when compared to curved fins. This is because, for a given length, the fins extend further outward in a radial direction, allowing a greater proportion of their surface to interact with the major airflow past the projectile during its flight. 
       FIGS. 4 and 5  show a second embodiment of the invention, with  FIG. 4  showing a rear cross-sectional view of the projectile with the fins in an un-deployed position, and  FIG. 5  showing a perspective view of one of the fins. This second embodiment is similar to the first embodiment, except that each fin  2  is configured to extend beyond the mounting of the next adjacent fin. Like features have been assigned the same reference numerals. 
     In this connection, as with the first embodiment, each fin  2  is pivotally mounted to the projectile body  3  by a pin  5  which forms a pivot. However, in this embodiment, the straight section  15  of each fin  2  extends around the circumference of the projectile body  3  by a distance sufficient to enable the distal end of the straight section  15  of each fin  2  to overlie the adjacent fin&#39;s pivot  5 , when in the un-deployed position. To help facilitate this, flattened sections  12 , allow each fin&#39;s pivot  5  to be positioned closer to the longitudinal axis of the projectile body  3  than the curved surface of the channel  11 . 
     In addition, as shown in  FIG. 5 , fin  2  is formed from a single piece of thin flat metal, which is bent into a generally L shaped form. Thus, the fins have a major portion forming straight section  14  and a minor portion forming connecting section  13 . In this embodiment, the connecting section  13  is provided with two opposing lugs  16  which form the mounting through which the fins pivotally couple to pin  5 . The fin&#39;s straight section  14  is also provided with a narrowed region at its distal end which allows it to fit between the lugs  16  of the adjacent fin  2 . This enables each fin to overlie its next adjacent fin  2 , allowing a longer fin shape to be accommodated. 
     It will be understood that the invention illustrated above shows an application only for the purposes of illustration. In practice the invention may be applied to many different configurations, the detailed embodiments being straightforward for those skilled in the art to implement. 
     For example, although in the above examples, the straight sections of the fins have a uniform thickness defined by two substantially flat side surfaces, it will be understood that the fins could have an alternative cross sectional profile. For example, the fin may have a tapered construction, where the flat surfaces taper inward toward the plane defined though the middle of the straight/planar section of the fin.