GB2243901A

GB2243901A - Projectiles

Info

Publication number: GB2243901A
Application number: GB8630208A
Authority: GB
Inventors: Spencer Meston; A E M Barton
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1986-01-29
Filing date: 1986-05-21
Publication date: 1991-11-13
Anticipated expiration: 2006-05-21
Also published as: FR2665762A1; SE8704512L; IT8748589A0; DE3730359A1; FR2665762B1; SE8704512D0; NL8715001A; IT1235707B; GB2243901B

Abstract

A discardable sabot assembly 72 for a gun launched projectile comprises sabot means 73 configured to surround the projectile 76 and having inwardly projecting flanges 81, 82 at its forward end which locate in grooves 83, 84 in the projectile so that at least some of the launch forces are transmitted to a forward section of the projectile body by the sabot means. Use of the sabot assembly enables the body wall at the rear of the projectile to be made thinner thus providing more space for sensors and associated electronics. A piston 95 transmits the remainder of the launch forces to the rear of the projectile. Erectile fins 92 are retained in a folded condition within the piston. <IMAGE>

Description

2 2 tE-::) C 1 PROJECrILES This invention relates to sabots for

projectiles and is more particularly, but not exclusively, concerned with sabots for gun-launched guided projectiles.

Sabots are used to provide the interface between sub-calibre projectiles and a gun barrel. They are normally made in two or more separate parts so that they can separate from the projectile on leaving the gun muzzle. It is usual to provide a clamping ring at the front of the sabot and an obturator, which forms a gas Beal between the sabot and the gun barrel, at the rear. The obturator may also provide means by which the projectile is decoupled from the spin imparted from the barrel rifling.

In the design of gun-launched guided projectiles it is desirable to provide as large an internal volume as possible to house sensors and associated electronics. Thus it is preferred for the wall of the projectile to be as thin as possible. In addition, for aerodynamic stability, fin-stabilised projectiles need a forward centre of gravity and this leads to a requirement for the wall of the projectile to be relatively thin around its aft portion.

This requirement may uLean that the wall has insufficient inherent structural strength to withstand the launch forces.

According to one aspect of this invention, there is provided sabot means for a projectile, said sabot means being configured to surround the projectile and being adapted to transmit at least some of the launch forces during launch of the proje,_tile from launch means to a forward section of the projectile body, said sabot means being separable from the projectile after exit of the projectile frcm. the launch means. As well as transmitting scme or all of thelaunch forces to the front of the projectile, the sabot means also performs the important function of protecting the body of the projectile from the very high gas pressures prevailing during launch.

Use of sabot means of the invention enables a marked reduction in the thickness of the rear wall of a projectile to be achieved eg. from 5mm. in a conventional projectile down to Inn in a projectile adapted for used with a sabot of the invention.

The sabot means may ccmprise one or more formations adapted for locating in complementary formations in the projectile body.

Preferably, the sabot means comprises one or more flanges for engaging in a groove or grooves in the projectile body.

Preferably, the sabot means is adapted so as to separate into at least two parts after exit from the launch means. In one embodiment, said sabot means comprises a multipart sabot member; in another embodiment said sabot means ccmprises a sabot member having two or more fracture grooves to facilitate fracture of the sabot member into at least two parts after exit of the projectile from the launch means.

Preferably said sabot mans includes an aft portion which extends rearwardly of said projectile and which houses plug means in load transmitting engagement with a rearward portion of said projectile and which is adapted to transmit at least some of the launch forces during launch of the projectile to said rearward portion.

Preferably said plug means and said aft portion are each separable into at least two portions during or after launch of the projectile from the launch means.

Where the projectile is fin stabilised, it is preferred for the fin carrying portion of the projectile to be contained at least partially within said aft portion.

Advantageously, said sabot member and said aft portion may be formed as a single item.

Preferably, seal mans are provided for preventing penetration of propulsion gases into said aft portion member during launch. In one embodiment, said seal means comprise a flexible member covering the rearward end of said aft portion. In another embodiment said seal means comprise a seal member associated with one of said aft portion and said plug means, and sealingly contacting the other of said aft portion and said plug means.

Conveniently, said sabot means is used together with obturator means surrounding a rearward region of said sabot means adapted to provide a seal between said sabot means and the launch gun barrel. Where the sabot member and the aft portion are formed separately, it is preferred for the obturator means to provide a seal between said portion and said_ sabot member.

According to another aspect of the invention, we provide sabot means for a projectile configured so as to surround the projectile and to transmit a portion of the launch forces via a forward section to the projectile, and to transmit a furt her portion of the launch forces via a rearward section to the projectile so as to distribute the loading of the projectile during launch.

- A - Advantageously, the sabot mans includes an aft portion and a sabot member, the aft portion configured to envelope said fins and extending forwardly to interface with the sabot member, and a piston member configured to enclose said fins and to interface with both the rear of the projectile and the aft portion.

For a better understanding of the invention, reference will now be made, by way of example, to the accoq)anying drawings in which:- Figure 1 is a schematic side view in cross-section of a gun-launched guided projectile; Figure 2 is a partly sectioned side view of a projectile fitted with sabot means according to the invention; Figure 3 is a section on the line III III of figure 2; Figure 4 is a perspective view of a fin holding ring; Figure 5 is a part-sectioned side elevation of a projectile incorporating a second embodiment of sabot assembly; Figure 6 is an exploded view of the sabot assembly shown in Figure 5; Figures 7a and 7b are detailed views on circle VII of Figure 5 illustrating alternate forms of construction; Figure 8 is a part-sectioned side elevation of a projectile incorporating a third embodiment of sabot assembly; Figures 9 and 10 are transverse section views on lines IX - IX and X - X respectively of Figure 8 with parts omitted for clarity; and Figures 11 and 12 are partial views illustrating alternative forms of piston for use in the embodiment of Figures 8 to 10.

Figure 1 shows a gun-launched guided projectile indicated generally at 10 which comprises a nose cone 12, a main body portion 14 and a rear body portion 16. The nose cone has a penetrator 18. and a base member 20 which forms a wall 22 dividing the nose from the main body portion 14. A region 24 of the main body portion 14 comprises a series of cavities for propellant and each cavity is provided with a thruster jet, one of which is shown at 26. The surface of the main body portion ccxq:)rises two annular grooves 28 and 30 configured to engage projections on a sabot. A rear closure plate 32 divides the main body portion 14 and the rear body portion 16 and carries a series of thin film igniters, one of which is indicated at 34. The rear body portion has a cavity 36 for housing a battery and guidance electronics. The wall 38 of the rear body portion is made of steel and is relatively thin so as to maximise the room available for the electronics. The rear of the missile 10 is provided with deployable fins 40 and a lens 42.

Figures 2 and 3 show part of a gun-launched guided projectile, indicated generally at 50 cmprising several spring loaded fins 52 pivotally mounted at its rear end. The fins are held folded inwardly towards one another by a holding ring 53 having three forwardly extending f ingers 54 each with an upturned end 55 as can be seen in f igure 4. The holding ring 53 can be provided with any number of fingers according to the number of fins on the projectile. A three-part sabot 56 is fitted around the body of the projectile 50.and held assembled and in place by two plastics material rings 57 and 58 which are each fitted in a circumferential recess at the rear and front respectively of the sabot. A further circumferential recess in the sabot located just forward of the rear holding rings 57 supports an obturator assembly 59.

Towards the forward end of the sabot 56,, two annular flanges 60 and 61 project inwardly from the inner surface of the sabot 56 into respective complementary recesses formed in the projectile body. The forward end of each part of the sabot 56 is formed with an inwardly directed bevelled portion 62. Adjacent its rear end, the sabot 56 is formed with an inwardly facing annular groove 63 and three recesses 64 a, b, c, which extend longitudinally from the groove 63 to the rear end of the sabot 56. When the sabot 56 is in place on the projectile 50, the holding ring 53 can be installed and the upturned ends 55 on each of the f ingers 54 can be entered through the recesses 64 a, b, c into groove 63. The sabot 56 can then be turned slightly so that the ends 55 become locked into the groove 63.

A stretchable boot 65 of plastics material is fitted over the rear end of the sabot 56. The boot 65 has a rear part having a narrow diameter which fits stretchably around the projectile body, over the f ingers 54 of the holding ring 53, and a forward part having a wider diameter which is a stretch fit over the end of the sabot 56. The function of this boot 65 is to prevent the gas pressure, generated by the propellant charge (not shown), from getting beneath the sabot 56 at its rear end.

Figure 3 illustrates the three parts of the sabot 56 in cross-section and shows that each part has a butting edge 66 which is inclined relative to the radial direction. This feature enables the sabot 56 to be assembled within the obturator assembly 59 i.e. two parts of the sabot 56 can be butted together within the obturator and then the third sabot part can be extended obliquely into the obturator assembly 59 and then turned and slid into its proper relationship with the other two parts. Furthermore, with the rear fixing ring 57 in place, but not the front ring 58, the front of the sabot 56 can be opened out and the sabot 56 slid over the body of the projectile 50 from the nose. The front of the sabot 56 can then be closed in towards the projectile body so that the flanges 60 and 61 enter their respective matching recesses in the projectile 50 and the front holding ring 58, while expanded, can be positioned in its recess.

Alternatively,, if the obturator assembly is expandable so that it can be slid over the sabot 56 in position on the projectile, the sabot 56 may be made of three parts which butt along radially extending faces.

In the projectile described above, if the launch pressure were applied directly to the rear part of the projectile 10 i.e. as a compressive force, the relatively thin wall 38 might distort.

In the embodiment described above, at least a part of the accelerating force of launch is transmitted by the relatively thick walled,, and hence strong, sabot 56 to a forward portion of the projectile 56 via the flanges 60 and 61. Not only are these flanges 60 and 61 relatively far forward where it may be more convenient for the projectile wall to be relatively strong but, in addition, they have the effect of pulling, rather than pushing, the projectile 50 from the gun barrel thus relieving the compression to which the rear portion of the projectile 50 is subjected during launch. The sabot acts to protect the rear part of the projectile fr(n the high gas pressure prevailing during launch. This pressure may be of the order of 50,000 psi and would cause buckling of a thin steel wall.

As will be appreciated, once the projectile 50 has left the gun barrel, the centrifugal force and air pressure force the parts of the sabot 56 outwardly breaking the rings 57 and 58 and the obturator assembly 59. The bevelled portion 62 for:m a kind of air scoop which assists fragmentation of the sabot after launch. The force of the launch blast acting on the rear also helps to separate the sabot 56 and the obturator assembly 59 from the projectile 50. Bevelled portions may also be provided at the rear end of the sabot if desired. Once the sabot 56 is separated, the fin holding ring 53 also separates.

Referring to figures 5 and 6 initially, modified sabot means 70 comprises a cylindrical sabot rr 72 which consists of three parts 73, 74, 75. These parts are held together on a projectile 76 at their forward end by a clamp band 77 which f its into a groove 78 formed in the outer wall of each part, and at their rearward end by an obturator assembly 79 which f its into a further groove 80. The forward end of the sabot member 72 has two annular, internally projecting ridges 81, 82 which engage with two annular grooves 83, 84 formed in the wall of the projectile 76. The obturator assembly 79 consists of two ring elements 85 and 86 which are mounted between flanges 87, 88 of a further ring element 89 made from a suitable bearing material such as P.T.F.E. (The obturator is described in more detail in our copending 4 patent application No. 8602099). Its function is to provide sealing between the sabot mans 70 and the gun barrel from which the projectile 76 is to be launched. The rear end 90 of the projectile 76 is covered by a cylindrical shell 91 which is part of the sabot means 70 and which encloses the spring-loaded outwardly deployable fins 92 of the projectile 76. The shell 91 interfaces with the maltipart sabot member 72 at its forward end 93 and is locked to it by mans of a seal 94. Referring to Figures 7a and 7b, the seal 94 is formed as an extension of the ring element 89. In Figure 7a, the extension extends rearwardly of the main ring and the seal 94 and can have an inwardly directed lip which fits over the ends of the parts 73, 74 and 75. In Figure 7bi the rearward flange 88 of the ring 89 is dispensed with and the ring extension terminates with seal 94.

A piston 95 is slidably received within the open end 96 of theshell 91 and is shaped so as to encase the fins 92 and contact the rear end 90 of the projectile, the fins 92 fitting into slots 97 formed in the piston 95. A sealing ring 98 fits into a groove in the piston 95 and provides a gas seal between the internal wall 100 of the shell 91 and the piston 95.

During launch of the projectile, the launch forces are transmitted to the forward end of the projectile 76 by the engagement of the sabot means 70 in the grooves 83, 84 and to the rear of the projectile 76 by pressure exerted on the piston 95 which transmits the force to the rear end 20 of the projectile. This arrangement enables the loading on the projectile due to launch to be distributed. Suitably designed, the sabot means can be made to provide an optimum distribution of ccmpressive forces so as to minimize the overall stress in the body wall of the projectile.

After the projectile is launched f rom the gun, the centrifugal force and air pressure force the parts 73, 74, 75 of the sabot 56 outwardly breaking the clamp band 77 and obturator assembly 79. Air then enters the cylindrical shell 91 causing it to slide rearwardly off the projectile.

Referring now to the embodiment of sabot assembly illustrated in Figures 8 to 12, this embodiment is broadly similar to the one just described except in that the saboi member 100 and the cylindrical portion 106 are of "one-piece" construction and the shape and sealing of the piston member are different.

The sabot member 100 is of generally cylindrical form including adjacent its forward edge a pair of annular inwardly directed ribs 101 which engage in a pair of grooves 102 in the projectile body to allow transmission of forward thrust forces from the sabot member 100 to the projectile. Three equispaced, longitudinal slots 103 extend from the forward edge of the sabot member 100 to a position immediately forward of a groove 104 in which an obturator 105 is located. Rearwardly of this position, in the cylindrical portion 106 of the assembly, there are provided three elongate internal fracture grooves 107, which lie colinear with the slots 103.

At the rear end of the cylindrical portion 106 is provided a thickened collar 108, the inner surface of which slidably receives. a piston 109 having slots 110 to allow it to fit over the stowed f ins 111 of the projectile. The outer surface of the collar 108 sealingly Q 1 supports the periphery of a flexible membrane 112 which prevents the admission of propulsion gas into the cylindrical portion.

As previously described the sabot member 100 is cl onto the projectile by means of a clamp ring 113 located in a forward groove of the sabot assembly.

Referring to Figures 11 and 12, the piston 109 is designed so that it fragments when the sabot is discarded. This may be achieved either by making the piston from a number of separate segments, two of which are indicated at 115 and 116, each shaped to fit between adjacent fins (Figure 11) or by providing fracture grooves colinear with slots 110 (Figure 12).

In operation, on launch from a gun barrel, the sabot assembly is thrown of f by a ccmbination of centrifugal force and ram air pressure at the forward edge of the sabot, and fragments into three pieces. At about the same time the piston 109 also separates into six parts,, also aided by centrifugal force and thus the size of the debris is reduced, thereby reducing the possibility of a successive projectile being damaged by the debris.

As a modification of the embodiments described above, a sabot assembly could extend rearwardly and inwardly so as completely to enclose the rear of the projectile. As a result, all of the launch pressure would be transmitted via the sabot assembly to the forward portion of the projectile.

It is envisaged that the sabot assembly may be manufactured as a number of identical petals, for example three identical petals, which, in use, normally butt against each other.

As a further modification, the rear portion of the projectile may be covered by a flexible cup-shaped membrane which has a thickened angular rim at its mouth which butts against the obturator assembly so as to seal all gaps aft of the obturator assembly.

The present specification describes cylindrical projectiles and correspondingly cylindrically shaped sabot assemblies. Fkmvero, it is envisaged that the sabot means according to the invention may be configured to fit a projectile which is generally frustoconical or which has a frustoconical portion.

Whilst the embodiments described relate to gun launched projectiles, it will be understood that sabot means according to the invention may also find application in projectiles adapted for rocket launching from a smooth barrel.

t t

Claims

1. Sabot means for a projectile, said sabot means being configured to surround the projectile and being adapted to transmit at least some of the launch forces during launch of the projectile from launch means to a forward section of the projectile body, said sabot means being separable f rom. the projectile after exit of the projectile frcm the launch means.

2. Sabot mans according to claim 1 comprising one or more formations adapted for locating in ccmplementary formations in the projectile body.

3. Sabot means according to claim 2 comprising one or more flanges for engaging in a groove or grooves in the projectile body.

4. Sabot means according to any preceding claim being adapted so as to separate into at least two parts after exit of the projectile from thelaunch mans.

5. Sabot means according to any preceding claim comprising a multipart sabot member, the parts being adapted to separate after exit of the projectile from the launch means.

13 Sabot mans according to claim 4 or claim 5 comprising a sabot member having two or more fracture grooves to facilitate fracture of the sabot member into at least two parts after exit of the projctile from the launch means.

7. Sabot means according to any preceding claim including an aft portion which extends rearwardly of said projectile and which houses plug means in load transmitting engagement with a rearward portion of said projectile and which is adapted to transmit at least some of the launch forces during lauch of the missile to said rearward portion.

8. Sabot means according to claim 7 wherein said plug means and said aft portion are each separable into at least two portions after exit of the projectile frcm the launch mans.

9. Sabot means according to claim 7 or claim 8 wherein the aft portion is configured so as at least partially to envelope a fin carrying portion of the projectile.

10. Sabot means according to any of claims 7 to 9 wherein the aft portion is integral with the sabot member.

11. Sabot means according to any of claims 7 to 9 wherein the sabot member and the aft portion are formed separately and wherein obturator mans is used to provide a seal between the aft portion and the sabot member.

12. Sabot means according to any of claims 7 to 11 comprising seal means for preventing penetration of propulsion gases into the aft portion during launch.

13. Sabot mans according to claim 12 wherein the seal means comprises a seal member associated with one of the aft portion and the plug means, and sealingly contacting the other of said aft portion and said plug means.

14. Sabot means for a projectile configured so as to surround the projectile and to transmit a portion of the launch forces via a forward section to the projectile and to transmit a further portion of the launch forces via a rearward section to the projectile so as to distribute the loading of the projectile during launch.

15. Sabot means according to claim 14 which is adapted for use with a projectile comprising rearwardly positioned deployable fins and 1 W i which cmprises an aft portion and a sabot member, the aft portion configured to envelope said fins and to extend forwardly to interface with the sabot member,, and the piston member configured to enclose said fins and to interface with both the rear of the projectile and the aft portion.

16. Sabot means substantially as herein described with reference to, and as illustrated -iii--figures..2 and 3-optionally as modified by figures 4a and 4b, and figures 5 - 7 optionally as modified by figures 8 and 9 of the accompanying drawings.

I 1 Published 1991 at The Patent Office, Concept House, Cardiff Road, Newport, Gwent NP9 IRH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys. Newport. NPI. 7HZ. Printed by Multiplex techniques lid, St Mary Cray. Kent.

16. Sabot means according to any preceding claim which is generally cylindrical in shape.

17. Sabot means according to any of claims 1 to 15 which is generally frustoconical in shape.

18. Sabot means substantially as herein described with reference to, and as illustrated in f igures 2 - 4, f igures 5 and 6 optionally as modified by f igures 7a and 7b, and figures 8 - 10 optionally as modified by figures 11 and 12 of the accompanying drawings.

0 Amendments to the claims have been filed as follows 6 1. Sabot means for a projectile, said sabot means being configured to surround the projectile and being -adapted to transmit a proportion of the launch forces during launch of the projectile from launch means to a forward section of the projectile body, and including an aft portion which extends rearwardly of said projectile comprising seal means for preventing penetrating of propulsion gases into the aft portion during launch, said sabot--means -being separable from the projectile after e)dt of the projectile from the launch means.

2. Sabot means according to Claim 1 comprising one or more formations adapted for locating in complementary formations in the projectile body.

3. 5,abot mea-.,s a.,cca-ding to Claim 2 comprising one or more flanges for engaging in a groove or grooves in the projectile body.

4. Sabot means according to any preceding claim being adapted so as to separate into at least two' parts after exit of the projectile from the launch means.

6. Sabot means according to Claim 4 or Claim 5 comprising a sabot member having two or more fracture grooves to facilitate fracture of the sabot member into at least two parts after e.Xit of the projectile from the launch means.

z z 1 Z -4 17 7. Sabot means according to any preceding claim including plug means carried by said aft portion in load transmitting engagement with a rearward portion of said projectile and which is adapted to transmit the remainder of the launch forces during launch of the missile to said rearward portion.

8. Sabot means according to Claim 7 wherein said plug means and said aft portion are each separable into at least two portions after exit of the projectile from the launch means.

11. Sabot means according to any of Claims 7 to 9 wherein the sabot member and the aft portion are formed separately and wherein obturator means is used to provide a seal. between the aft portion and the sabot member.

12. Sabot means according to any on:e of the preceding claims wherein the seal means comprises a seal member associated with one of the aft portion and the plug means, and sealingly contacting the other of said aft portion and said plug means.

13. Sabot means according to any one of the preceding claims which is adapted for use with a projectile comprising rearwardly positioned deployable fins and which comprises an aft portion and a sabot member, the aft portion configured to envelope said 1 f Is fins and to extend forwardly to interface with the sabot member, and a piston member configured to enclose said fins and to interface with both the rear of the projectile and the aft portion. 14. Sabot means according to any preceding claim which is generally cylindrical in shape.

15. Sabot means according to any of Claims 1 to 13 which is generally frustoconical in shape.