Abstract
A captive piston projectile (40) comprising a payload housing (43), a piston assembly attached to the payload housing (43), and actuation means (46) for urging the piston assembly from a stowed configuration to an extended configuration. The piston assembly comprises a tubular piston member (41) attached around the periphery of the payload housing (43), the attachment optionally being in the form of a circumferential groove (42) within which the piston member (41) can slide. This provides increased thrust whilst maintaining payload volume. Particularly suited to use with barrelled weapons, and also relates to a method of manufacture.
Claims
1. A captive piston projectile for launching from a gun barrel, comprising a payload housing, a piston assembly attached to the payload housing, and actuation means for urging the piston assembly from a stowed configuration to an extended configuration, such that in use the piston assembly urges against the breech of a gun barrel to thrust the projectile from the barrel, wherein the piston assembly comprises a tubular piston member attached around the periphery of the payload housing.
2. The captive piston projectile of claim I wherein the tubular piston member is collapsible such that in the stowed configuration it is collapsed against the payload. housing.
3. The captive piston projectile of claim 2 wherein the tubular piston member comprises a bellows portion.
4. The captive piston projectile of claim 3 wherein in the stowed configuration the bellows portion is folded perpendicular to the axis of the captive piston projectile.
5. The captive piston projectile of claim 2 wherein the tubular piston giber comprises a plurality of telescoping sections.
6. The captive piston projectile of claim 1 wherein the tubular piston member is arranged to slide with the payload housing, such that in the stowed configuration the payload housing is at least partially received into the tubular piston member.
7. The captive piston projectile of claim 6 wherein the payload housing comprises a circumferential groove into which the tubular piston member is arranged to slide.
8. The captive piston projectile of claim 7 herein the circumferential groove comprises an end stop, the tubular piston member comprising a protrusion that abuts the end stop when in the extended configuration, such that the tubular piston member is retained within the circumferential groove.
9. The captive piston projectile of claim 6 wherein the tubular piston member is internally tapered.
10. The captive piston projectile of claim 6 further comprising stabilisation fins retractably attached to the tubular piston member.
11. The captive piston projectile of claim 10 wherein the stabilisation tins are recessed into respective longitudinal slots in the tubular piston member when the tubular piston member is in the stowed configuration.
12. The captive piston projectile of claim 10 wherein the stabilisation fins are biased outwards of the tubular piston member.
13. The captive piston projectile of claim 12 wherein the stabilisation fins are configured to act as detents for holding the captive piston projectile at a predetermined position inside a gun barrel.
14. The captive piston projectile of claim 6 further comprising a vent means for venting gases compressed by action of the tubular piston member sliding with the payload housing.
15. The captive piston projectile of claim 14 wherein the vent means comprises vent grooves defined between the tubular piston member and the payload housing.
16. The captive piston projectile of claim 15 wherein the vent grooves are arranged to extend partway along the length of either the tubular piston member or the payload housing, such that in the extended configuration gases compressed by action of the tubular piston member sliding with the payload housing are trapped to provide an air cushion.
17. The captive piston projectile of claim 1 wherein the actuation means comprises a propellant cartridge in fluid connection with the tubular piston member, such that in use propellant gases can flow into the tubular piston member to urge the piston assembly into its extended configuration.
18. The captive piston projectile of claim 17 further comprising vent holes in the tubular piston member.
19. The captive piston projectile of claim 17 wherein the tubular piston member is sealed to the payload housing, such that propellant gases are retained between the tubular piston member and payload housing.
20. An ammunition round comprising a projectile casing and the captive piston projectile of claim 1.
21. A method of manufacturing a captive piston projectile, comprising steps of: a) Providing a payload housing; b) Attaching a tubular piston member around the periphery of the payload housing, the tubular piston member being adjustable between a stowed configuration and an extended configuration; c) Arranging an actuation means to urge the tubular piston member from the stowed configuration to the extended configuration when the captive piston projectile is in-use.
22. The method of claim 21 wherein the step of attaching a tubular piston member comprises the step of configuring the tubular piston member to slide with the payload housing between the stowed configuration and the extended configuration.
23. The method of claim 22 wherein the step of configuring the tubular piston member to slide comprises the step of locating the tubular piston member inside a circumferential groove of the payload housing.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:
[0025] FIG. 1 illustrates in cross sectional view a prior art captive piston projectile;
[0026] FIG. 2A illustrates in perspective cutaway view an embodiment of a captive piston projectile comprising bellows in the stowed configuration;
[0027] FIG. 2B illustrates in perspective cutaway view the embodiment of FIG. 2A in the extended configuration;
[0028] FIG. 3A illustrates in perspective cutaway view an embodiment of a captive piston projectile comprising telescoping sections in the stowed configuration;
[0029] FIG. 3B illustrates in perspective cutaway view the embodiment of FIG. 3A in the extended configuration;
[0030] FIG. 4A illustrates in perspective cutaway view an embodiment of a captive piston projectile having a circumferential groove and a tubular piston member in the stowed configuration;
[0031] FIG. 4B illustrates in perspective cutaway view the embodiment in FIG. 4A in the extended configuration;
[0032] FIG. 5A illustrates in perspective cutaway view an embodiment of a captive piston projectile having a tubular piston member in the stowed configuration received around the payload housing;
[0033] FIG. 5B illustrates in perspective cutaway view the embodiment in FIG. 5A in the extended configuration;
[0034] FIG. 6A illustrates in perspective cutaway view an embodiment of a captive piston projectile having stabilisation fins in the stowed configuration;
[0035] FIG. 6B illustrates in perspective cutaway view the embodiment of FIG. 6A with tubular piston member in the extended configuration; and
[0036] FIG. 6C illustrates in perspective cutaway view the embodiment of FIG. 6B with stabilisation fins deployed.
DETAILED DESCRIPTION
[0037] FIG. 1 illustrates in cross sectional view a prior art captive piston projectile 10. The projectile 10 comprises a payload housing 11 having a concentric bore 12 into which a solid piston member 13 is received. The piston member 13 can slide within the bore 12 between a stowed position in which the base end 14 of piston member 13 abuts housing 11, and an extended configuration in which the piston member 13 protrudes from the bore 12. Propellant gases generated by the projectile 10 flow into bore 12 and urge the piston member 13 towards the extended configuration. The bore 12 is narrow and restricts gas flow making projectile 10 inefficient at generating thrust. Piston member 13 is also narrow and prone to rupture.
[0038] FIG. 2A and 2B illustrate an embodiment of a captive piston projectile 21 and a detachable casing 24. The projectile 21 las a tubular piston member comprising bellows 22. FIG. 2A shows the projectile 21 in the compressed configuration with bellows 22 folded against payload housing 23. The bellows 22 are permanently attached to housing 23 using welding or appropriate adhesive such that a fluid seal is achieved. A casing 24 is shown surrounding the bellows 22 supplying prelaunch protection and a means of holding the round within its weapon before launch. The casing 24 extends around part of the payload housing 23 and is crimped thereto. Mounted within the bellows 22 but accessible through the casing 24 is a propellant cartridge 25. The propellant cartridge 25 is in fluid connection with the interior of the bellows 22 such that propellant gases can flow into the bellows 22. The bellows 22 are folded perpendicular to the axis ‘A’ of the captive piston projectile 21 for compact storage and efficient piston stroke. The bellows 22 are formed from deformable metal with the payload housing 23 also being formed from metal. In use propellant gases from propellant cartridge 25 flow into the bellows 22 and cause an increase in pressure. This causes the bellows 22 to unfold increasing their length. The base end 26 of the bellows 22 urges against casing 24, itself urging against the breech of a gun barrel (not shown). The projectile 21 is therefore thrust from the casing 24 and out of the barrel. The casing 24 is left within the gun barrel and does not form part of the projectile itself. FIG. 2B illustrates the projectile 21 in the extended configuration where bellows 22 have unfolded to provide an overall piston stroke length of 91 mm. The diameter B of the cross section against which pressurised gases inside the bellows 22 can act is significantly larger (relative to projectile size) than the prior art shown in FIG. 1. This has been achieved without compromise to payload space in payload housing 23.
[0039] FIG. 3A and FIG. 3B illustrate an alternative embodiment of a captive piston projectile 30 and a detachable casing 36. The projectile 30 has a tubular piston member 31 comprising telescoping sections 32. FIG. 3A shows the projectile 30 in the compressed configuration with three telescoping sections 32A, 32B and 32C, stowed within each other. This provides compact storage against payload housing 33. The telescoping sections 32 are stored within payload housing 33. The outermost telescoping section 32A conforms to the interior surface of payload housing 33 and can slide within the housing 33 until an annular protrusion 34 abuts a narrowing ring end stop 35 of housing 33. Similar arrangements are provided for telescoping sections 32B sliding within outer section 32A, and section 32C sliding within section 32B. A casing 36 surrounds the piston member 31 and extends over part of payload housing 33 where it is held by interference fit. Providing a plug fit into the base end 37 of piston member 31 is a propellant carridge 38. The propellant cartridge 38 is in fluid connection with the interior of the piston member 31 such that propellant gases can flow into the space between the piston member 31 and payload housing 33. In use the propellant cartridge 38 is initiated by a firing pin mechanism and propellant gases flow into the piston member 31. This causes a pressure increase and the telescoping sections 32 are urged to slide away from the payload housing 33. This causes the piston member 31 to extend and urge against a breech face of a gun barrel, such that the projectile 30 can be thrust out of the casing 36 and out of the barrel. FIG. 3B illustrates the projectile 30 of FIG. 3A in the extended configuration. The telescoping sections 32 are fully extended giving a piston stroke length of 91mm. The casing 36 has been urged off the piston member 31. The cross sectional area against which propellant gases can act inside piston member 31 is significantly increased over the prior art and indicated by diameter C in the figure. The payload housing 33 and telescoping sections 32 are formed from metal.
[0040] FIG. 4A and FIG. 4B illustrate a further alternative embodiment of a captive piston projectile 40 and detachable casing 47. The captive piston projectile 40 comprises a payload housing 43 having a circumferential groove 42 into which a hollow tubular piston member 41 is received. The tubular piston member 41 can slide within the circumferential groove 42 until a circumferential protrusion 44 on piston member 41 abuts an annular end stop 45 on payload housing 43. The circumferential groove 42 in the payload housing 43 spans a length equivalent to that of the tubular piston member 41. This ensures in the stowed configuration (shown in FIG. 4A) for the projectile 40 is compact, but maximises piston stroke length in the extended configuration (shown in FIG. 4B). A propellant cartridge 46 is shown providing a plug fit into the end of piston member 41 and is in fluid connection with the interior of the piston member 41. A projectile casing 47 is also shown. In use propellant gases from the propellant cartridge 46 enter into the piston member 41 which causes a pressure increase. The piston member 41 is urged away from payload housing 43 and resultantly slides along groove 42. The piston member 41 urges against the breech face of a gun barrel (not shown), thrusting the projectile 40 out of the barrel. The embodiment shown is formed from metal, has a maximum piston stroke length of 90mm, and has a maximum exterior diameter of 40mm. The payload housing 43 is minimally compromised to provide for the piston member 41. FIG. 4B shows the captive piston projectile 40 in the extended configuration, and highlights the large cross sectional area D against which pressurised gases can act.
[0041] FIG. 5A and FIG. 5B show an alternative embodiment of a captive piston projectile 50 and detachable casing 53, with projectile 50 respectively in the stowed and extended configurations. The projectile 50 in these embodiments comprises a tubular piston member 51 mounted around a payload housing 52 on which it can slide. The payload housing 52 is narrowed to accommodate the piston member 51 whilst maintaining a uniform exterior diameter when in the stowed configuration. The mechanism for urging apart the piston member 51 from the payload housing 52 is the same as for the previous embodiments. FIG. 5B highlights clearly the maximised cross sectional area (courtesy of diameter E) against which pressurised gases inside the tubular piston member 51 can act.
[0042] FIGS. 6A, 6B and 6C illustrate an embodiment of a captive piston projectile 60 comprising stabilisation fins 61. FIG. 6A shows stabilisation fins 61 stowed within recesses 62 of a tubular piston member 63. The tubular piston member 63 is held within a sleeve 64 and is in the stowed position. The stabilisation fins 61 are biased outwards of the piston member 63 by springs (not visible) but cannot leave recesses 62 owing to them abutting cartridge 64. Also shown in payload housing 65 are cut outs 66 indicating locations for projectile payloads or sub-munitions. FIG. 6B shows piston member 63 in the extended configuration but with stabilisation fins 61 still stowed. FIG. 6C shows stabilisation fins 61 deployed as would occur post launch when the piston member 63 is in the extended configuration and the projectile 60 has exited its weapon barrel.
[0043] Whilst embodiments of the invention have been described with specific features, other embodiments are envisaged that comprise one or more features from a number of the embodiments shown. For instance stabilisation fins may be used by a number of embodiments of the captive piston projectiles. The projectiles may be formed from metal or hardened plastic, and may comprise fabric (for instance for bellows). The overall shape of the projectile shown in the embodiments is not intended to be limiting, although an ogive or rounded nose to the payload housing may be advantageous for aerodynamics. The projectile may be manufactured in a variety of sizes, but is well suited as a 40 mm round. Propellant gases generated during launch of the captive piston projectile are preferably fully contained, or at least contained until after launch (when the projectile has left the gun barrel). This may allow lighter weight gun barrels to be used with the projectile, because there are no pressurised gases from propellant to be contained by the barrel. The piston stroke lengths are for example only and may be tailored to specific applications, however maximising the stroke length provides for improved projectile launch velocities. The projectile cartridges shown in the figures may be 0.38″ or other custom size. Alternatively the propellant may be fully incorporated within the tubular piston member. The overall projectile mass is preferably less than 250 g, with the piston member mass being minimised to mitigate audible noise when the piston member impacts the projectile housing at the end of the piston stroke. Non circular cross section piston members may be used, provided that embodiments using such members seek to maximum the cross sectional area of the piston member to increase generated thrust. Whilst in some embodiments a projectile casing is provided this is not intended to be limiting, and all embodiments of the captive piston projectile may be operable without a casing (for instance detents may be used to retain the projectile in position inside a gun barrel pre-launch).
