STABILIZING FIN ASSEMBLY FOR PROJECTILE

Abstract: Stabilizing fin assembly for projectile (2) designed to be discharged from a barrel (1) by means of propellant charge gases from a propellant charge (5). During their passage through the barrel the fins (8) are in the retracted, on-edge position, and arranged to be extended when the projectile (2) leaves the barrel (1). With the fins in the retracted posi­ tion the space (13) between the fins (8) is at least partially open to the rear during passage through the barrel, so that the propellant charge gases have acces to the said space (13). The space (13) is exhausted of propellant charge gases when the projectile leaves the barrel (1), and the propellant charge gases as they rush out pass along the guide surfaces of the fins (8), causing a frictional force which jerks the fins (8) to the extended position. In some embodiments the guid­ ance mechanism is also provided with a further space (11, 18, 18a) under the edge (12) of the fins (8), which during passage through the barrel is filled with propellant charge gases which exert an extra extending force against the edge (12) of the fins (8).

Description: Stabilizing fin assembly for projectile The present invention relates to a stabilizing fin assembly for a rotating or non-rotating projectile designed to be discharged from a rifled or smooth barrel by means of propellant charge gases, having a plurality of elongated fins, rotatably mounted at one end, which are arranged so that during the passage of the projectile through the barrel they are in the retracted position, in which the fins are placed on edge extending mutually in parallel and mainly in the lengthwise direction of the projectile. With known projectiles having stabilizing fin assembly which have fins which in the retracted position are on edge relative to the projectile axis, the fins are normally extended by means of spring force or with the aid of lifting surfaces arranged on the fins which are affected by the wind velocity. The method is also known of utilising the gas pressure produced by the propellant charge for extension purposes. Here the pressure acts on a piston or the like which presses the fins outwards. The present invention is based on the new concept that it is possible to extend fins placed on edge without the use of either springs, pistons or lifting surfaces. In accordance with the invention the space between the fins and/or a further space which is located underneath one edge on the fins which faces the projectile axis, is during the passage of the projectile through the barrel at least partially open at the rear, permitting access by the propellant charge gases to the said space or the said further space respectively, whereby the passage of the projectile past the barrel muzzle results in the propellant charge gases in the said space or respective said further space rushing outwards to the atmosphere surrounding the barrel and thereby jerking with them the fins into the extended position, partly because of the assisting frictional force which is generated when the propellant charge gases pass along the guide surfaces of the fins and partially - in the event of the said further space being present - because of the pressure exercised by the gases in the further space against the said edge of the fins. Further developments of the invention are described in the subclaims. The invention will be described in greater detail by reference to the appended drawing. Figures 1 - 3 show in longitudinal section and partially in side view a first, second and third embodiment respectively of the invention. Figures 4 - 6 each illustrate a cross-section along the lines IV-IV, V-V and VI-VI respectively in Figures 1 - 3. Figures 7 - 8 show on a larger scale a skewing arrangement which is advantageous with the embodiment in accordance with Figures 1 - 3, Figure 7 illustrating the fins in the retracted position and Figure 8 in the extended position. Figure 9 shows a longitudinal section, half in side view, of the stabilizing assembly in accordance with a fourth embodiment of the invention, designed preferably for oversize head projectiles. Figure 10 illustrates a projectile having a stabilizing assembly in accordance with Figure 9 with the fins extended. In the various diagrams the same reference notation has been employed throughout for corresponding details in the various embodiments. Figure 1 shows a projectile 2 inserted in a barrel 1 which via a conventional girdle 3 is attached to a cartridge case 4 containing a propellant charge 5. The barrel 1 can be either smooth or rifled and forms part of a weapon which is not shown, e.g. a mortar. The projectile 2 has a rear section 6 which extends into the sleeve 4 up to the propellant charge 5. At its rear end the rear section 6 is provided with six fin attachments 7 (see Figures 2, 7 and 8), in each of which an extended fin 8 which is located on edge against the rear section 6 is rotatably mounted around a pivot pin 9 which is shown schematically. The pivot pin 9 are provided with friction-reducing devices in the form of teflon washers 10 so as to increase the swivel capacity of the fins. It is also feasible to employ other types of friction-reducing devices. For drafting purposes the teflon washers 10 are illustrated only in Figure 7 and then only in one of the fin attachments 7. The fins 8 taper to the rear, so that a wedge-shaped gap 11 is formed between the rear section 6 and the edge 12 of the fins facing the projectile axis. The space 13 between the fins 8 is open at the back towards the propellant charge 5, as can be best seen from Figure 4. When the propellant charge is ignited in the conventional manner, propellant charge gases are produced which attempt to discharge the projectile 2. During this the propellant charge gases fill on the one hand the space 13 between the fins and secondly the wedge-shaped gap 11. When the propellant charge gases overcome the resistance to release of the girdle 3, the projectile moves out of the barrel 1 (on the left in Figure 1). During the passage of the projectile 2 through the barrel 1, the girdle 3 also performs a sealing function in that it permits only a negligible leakage of propellant charge gases to the atmosphere surrounding the barrel. When the girdle 3 passes the muzzle of the barrel (shown schematically at la), the propellant charge gases however rush out of the barrel. That portion of the propellant charge gases which is present in the space 13 between the fins 8 and in the gap-shaped space 11 then passes along the guide surfaces of the fins 8, which are located on edge, so that the fins are jerked by the gases into the extended position (see Figure 8) because of the assisting frictional force which is generated between the rapidly emerging gases and the fins. Because the wedge-shaped space 11 is filled by propellant charge gases, and extending force is also imposed on the fins 8, because the gases in space 11 exert a direct pressure against the edges 12 of the fins. The fins 8 have their centre of gravity G closer to the projectile axis than the centre of rotation 9 of the fins, so that the acceleration forces on the projectile during its discharge bring about a moment which attempts to hold in the fins 8 during passage through the barrel. This location of the centre of gravity is particularly advisable for rotating projectiles. If required the fins 8 can be skewed at a pre-determined twist angle v so as to maintain or bring about a desired degree of rotation. This is illustrated in Figures 7 and 8 which show how the fins 8 are mounted in oblique grooves 14 in the fin attachment 7. Here the rear section 6 has a supporting heel 15 on the skewed side of each fin 8 which prevents the fin being deformed as a result of the accelerational forces to which it is subjected during its passage through the barrel. Such supporting heels can possibly be arranged on both sides of the fins. Alternatively, this support function can be provided by grooves in the rear section 6. To provide clarity in the illustrations, only one of the supporting heels 15 is sketched in Figure 4. Similar skewing arrangements with supporting heels are advisably (but not necessarily) arranged also in the embodiments described in the following, although to ensure greater clarity in the drawings they are not shown. Figure 2 illustrates a second embodiment of the invention which in principle differs from the embodiment shown in Figure 1 only in that the rear section of the projectile 2 is replaced by a guidance mechanism tube 16, shown partially in section, which tapers away forwards and which is open at the rear and which at the front by means for example of a screw connection is fastened to a centrally arranged heel 17 at the rear end of the projectile 2. The interior of tube 16 by this means forms a chamber 18 which is open rearwards towards the propellant charge 5. The tube 16 is provided with six longitudinal slots 19 through which the fins 8 can be partially introduced, as indicated by the dashed edge lines 12. Here the slots 19 provide support for the fins during the passage of the projectile through the barrel. On ignition of the propellant charge 5 in Figure 2, the chamber 18 and the space 13 between the fins 8 is filled by the propellant charge gases from the propellant charge 5. This ensures firstly that a larger quantity of gas passes along the guidance surfaces of the fins 8 as the gases rush out to the surrounding atmosphere, and secondly that the gases enclosed in the chamber 18 during their outward rushing motion bring about a pressure which is orientated directly towards the edge 12 of the fins 8 which increases the force which extends the fins. In the embodiment illustrated in Figure 2, the chamber 18 and the space 13 between the fins 8 are both open at the rear. However it is possible to allow the space 13 to be sealed towards the rear so that the propellant charge gases during their passage through the barrel can flow only into the chamber 18. Here the slots 19 can be so dimensioned that there is no alternative desired degree of gas passage permissible from the chamber 18 to the space 13 via the slots 19 even when the fins 8 are introduced into these. In accordance with a further modification of the embodiment shown in Figure 2 the chamber 28 can be sealed at the rear whilst the space 13 is open at the rear. Here the slots 19 are so dimensioned that they permit a flow of gas from the space 13 to the chamber 18 even when the fins 8 are introduced into the slots 19. The embodiment illustrated in Figure 3 differs from the embodiment shown in Figure 2 in that the conically-tapered, slotted guidance mechanism tube 16 is replaced by a guidance mechanism tube 20 of uniform thickness, the interior of which forms a cylindrical chamber 18a and which instead of slots has two apertures 21 all the way through, these being circular in the embodiment illustrated, located in the centre of each fin 8. The apertures 21 have roughly the same dimensions as the thickness of the fins 8. The rear end of the tube 20 in the embodiment illustrated is sealed by a wall 22 which has a central circular aperture 23 all the way through which provides a direct connection between the propellant charge 5 and the interior of the guidance mechanism tube 20. As a result of the provision of the apertures 21, the propellant charge gases in the tube 20 bring about a concentrated compressive force on the edge 12 on the fins 8 which faces the projectile axis, so that a particularly high force is obtained which tends to extend the fins. In the case of projectiles where the fins because of their length do not have sufficient room in the cartridge case, it is advisable to provide a slotted tube around the fins so that the propellant charge gases can be more easily retained in the space between the fins and so that a better aerodynamic shape is obtained. This arrangement is illustrated in Figures 9 and 10, where a tube 25 provided with slots 24 concentrically surrounds the fins 8. The slots 24 are somewhat longer than the fins 8 and also located in the centre of these so that the fins 8 can be extended between them. With this embodiment essentially the entire lower edge 12 of the fins 8 rests against a rear portion 6 on the projectile. In accordance with a modified embodiment, which is not illustrated, the fins 8 rest however only partially against the rear section 6. The rear section 6 is, possibly via a strap or girdle which is not shown, and preferably exhibiting leakage, fastened into a cartridge case 4 with propellant charge 5. The rear section 6 and the tube 25 have a diameter which is somewhat smaller than the barrel 1, so that a ring-shaped gap 26 is formed between them. In front of the fins 8 the tube 24 is provided with a strap or girdle 27. When the projectile 2 has started to move in the barrel 1 as a result of gases from the propellant charge 5 (on the left in Figure 9) the propellant charge gases flow via a gap 26 in through the slots 24 and fill up the interior of the tube 25. Some degree of leakage past the strap 27 can be permitted here, so that this can be omitted or if required can be replaced by a guide pad. When, during the passage of the projectile through the barrel, the fins 8 reach the barrel muzzle (not shown for reasons of clarity), the gases in the tube 25 rush outwards through the slots 24, taking with them the fins to extended position(see Figure 10) because of the entraining frictional force produced when the propellant charge gases pass along the guidance surfaces of the fins 8. In all the embodiments illustrated and described the fixed pivot of the fins is located at the rear end of the fins, as viewed in the retracted position of the fins. However, it is also possible instead to locate the fixed pivot at the forward end of the fins, as viewed in the retracted position of the fins. All the embodiments illustrated and described are provided with suitable conventional locking devices for maintaining the fins in the extended position. However since such locking devices are on the one hand state of the art, and secondly do not comprise any part of the present invention, they have not been illustrated or described in greater detail. The invention is not limited to the embodiments illustrated and described, a large number of modifications thereof being feasible within the framework of the following claims.

Claims: Claims 1. Stabilizing fin assembly for projectile (2) designed to be discharged from a barrel (t) by means of propellant charge gases comprising a plurality of elongated fins (8) rotatably mounted at one end which are arranged so that during the passage of the projectile through the barrel (1) they are in the retracted position in which the fins (8) are placed on edge, extending mutually in parallel and essentially in the lengthwise direction of the projectile (2), char a c t e r is e d in that the space (13) between the fins (8) and/or a further space (11, 18 18a) which is located under an edge (12) on the fins (8) which faces towards the projectile axis is at least partially open to the rear during the passage of the projectile (2) through the barrel (1), thus permitting access on the part of the propellant charge gases to the said space (13) or the said further space (11, 18, 18a), by means of which the passage of the projectile (2) past the muzzle of the barrel results in the propellant charge gases in the said space (13) or said further space (11, 18, 18a) rushing out to the atmosphere surrounding the barrel (1) and then jerking with them the fins (8) to the extended position, firstly because of the entraining frictional force which arises when the propellant charge gases pass along the guide surfaces of the fins, and partially - in the event of said further space (11, 18, 18a) being present - because of the pressure which the gases in the further space exert against the said edge (12) on the fins (8). 2. Assembly as in claim 1, c h a r a c t e r i s e d in that the said space (13) is at the front at least partially sealed in respect of the surrounding atmosphere by means of a projectile girdle (3) or guide pad arranged in front of the fins. 3. Assembly in accordance with either of claims 1 - 2, c h a r a c t e r i s e d in that the fixed pivot (9) of the fins is located at the rear end of the fins (8) viewed in the retracted position of the fins (8). 4. Assembly in accordance with any of claims 1 - 3, c h a r a c t e r i s e d in that the fins (8) in the retracted position have their centre of gravity (G) closer to the projectile axis than the fixed pivot (9) of the fins, so that a moment is brought about by the accelerational forces imposed on the projectile (2), which moment attempts to hold the fins (8) in during passage through the barrel. 5. Assembly in accordance with any of claims 1 - 4, c h a r a c t e r i s e d in that the fins (8) are rotatably around a pivot (9) which is provided with friction-reducing devices (10), e.g. teflon washers, so as to increase the swivelling capacity of the fins (8). 6. Assembly in accordance with any of claims 1 - 5, c h a r a c t e r i s e d in that the fins (8) are skew-mounted relative to the projectile axis in a pre-determined skew angle (v). 7. Assembly as in claim 6, c h a r a c t e r i s e d in that the skewing action is obtained in that the fins (8) are mounted in grooves (14) which together with the projectile axis form an angle which corresponds to the said skew angle (v). 8. Assembly in accordance with any of claims 6 - 7, c h a r a c t e r i s e d in that the fins (8) in the retracted position rest against at least one supporting heel (15) or the like. 9. Assembly in accordance with any of claims 1 - 8, c h a r a c t e r i s e d in that the space (13) between the fins communicates with the further space (11, 18, 18a). 10. Assembly in accordance with any of claims 1 - 9, c h a r a c t e r i s e d in that the further space comprises a chamber (18, 18a) which is essentially cylindrical and arranged centrally in the guidance mechanism, in the walls of which there are apertures (19, 21) which are faced by the said edges. 11. Assembly in accordance with claim 10, c h a r a c t e r i s e d in that the apertures are in the form of slots (19), through which the fins (8) can be introduced at least partially in the retracted position. 12. Assembly in accordance with any of claims 1 - 8, c h a r a c t e r i s e d by a cylindrical tube (25) which concentrically surrounds the space (13) between the fins (8), whereby the generatrix of the tube (25) is provided with slots (24) of at least the same length as the fins (8), and where the slots (24) are so placed that the fins (8) can be extended through them.

Inventors: ANDERSSON, SVEN, JOHANSSON, BORJE, LARSSON, BENGT, PRAMSKOG, TORBJORN, SANDBERG, JAN-ERIK, Johansson, Börje, Pramskog, Torbjörn
Applicants: AFFARSVERKET FFV
Application year: 1982
Main classification: F42B13
IPC codes: F42B10