GB2195749A

GB2195749A - Practice projectile

Info

Publication number: GB2195749A
Application number: GB08108802A
Authority: GB
Inventors: James Michael Greenhough; Basil Victor Gunn
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1980-03-26
Filing date: 1981-03-24
Publication date: 1988-04-13
Also published as: GB2195749B

Abstract

The invention relates to a sub-projectile for a discarding sabot practice shot, and provides a close ballistic match to a service sub-projectile whilst having a limited range for use on small firing ranges. The invention comprises a central longitudinal rod (10) attached to a finned tail member (11), and two hollow cylindrical body members (13 and 14) slidably assembled on the rod (10) and secured by a nose member (15) attached to the rod (10) remotely from the tail member (11). Separating means are provided actuatable after a given time of flight by aerodynamic heating to initiate break-up of the sub-projectile and limit its range. The separating means may be a joint between the rod and nose member which fails at a certain temperature, and/or a structurally weak annular portion (22), Fig. 2 not shown, of the nose member (15) which has a thermal failure threshold. <IMAGE>

Description

SPECIFICATION Improvements in or relating to sub-projectils for discarding sabot practice shot This invention relates to a sub-projectile for a discarding sabot practice shot, and in particular to a practice sub-projectile which both closely matches a service device in ballistic characteristics and has a limited range for safety of use on small firing ranges.

Discarding sabot practice shot utilise a comparatively large calibre sabot to position a smaller calibre sub-projectile within the gun barrel. The large calibre sabot provides a greater pressure area for propelling the shot than would be available with the sub-projectile alone. Once projected from the gun barrel the sabot is rapidly discarded to leave the subprojectile free to continue its ballistic trajectory.

One of the problems associated with discarding sabot practice shot is the relatively long range associated with their trajectory and ricochet characteristics. These limit the use of practice shot to firing ranges of large area, or may limit the use of a particular firing range to shots aimed in a particular direction.

Various proposals have been made for a practice shot designed to break-up or become unstable at a given distance within the limits of a typical firing range. Such earlier proposals have either not been particularly successful or have failed to provide a ballistic match with the service sub-projectile.

An object of the present invention is to provide a practice sub-projectile which closely matches the ballistic geometry of the service sub-projectile but has controlled and fail safe range characteristics.

According to the present invention a subprojectile for a discarding sabot practice shot comprises a longitudinally disposed rod member attached at one end to a tail member, a body member slidably assembled on the rod member and retained in position by a nose member secured to the other end of the rod member, and separating means operative after a given time of flight to cause separation of the nose member from the rod member.

The body member might comprise two or more discrete cylindrical portions retained in longitudinal contiguity by the nose member.

Advantageously there is provided in the subprojectile resilient biasing means arranged to urge separation of the nose member from the rod member to assist the separation means.

Conveniently the biasing means may be a compression spring housed within the subprojectile in the region of the nose members body member interface.

The separating means, in one embodiment, comprises the use of a jointing material to secure the nose member to the rod member, the jointing material being designed to fail on the application of heat, ie on aerodynamic heating. Suitable jointing materials include sol der, woods metal and thermoplastic adhesive.

In a further embodiment, the nose member may include a region of weakness which in use fails due to aerodynamic heating. If desired the region of weakness may be stressed by the spring bias means.

A washer shaped plug of material of relatively low thermal conductivity may with advantage be provided between the nose member and the body member to retain and maximize kinetic heating effects in the nose member of the sub-projectile.

The body member and, if appropriate, part of the tail member can be provided with external thread-like projections to engage with corresponding recesses in the bore of the sabot.

Two embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 shows in sectional elevation the sub-projectile of a discarding sabot practice shot of the invention, and Figure 2 shows also in sectional elevation the forward portion embodying an alternative thermal trigger separating means.

Referring initially to Fig. 1 the sub-projectile comprises a rod member 10, a tail member 11 having fins 12, a body member having cylindrical portions 13 and 14 and a nose member 15.

The rod member 10 is securely attached to the tail member 11 by thread, brazing or any other suitable means. The main body of the sub-projectile comprises the cylindrical body member portions 13 and 14 which are arranged to be a sliding fit on the rod member 10. The body portions 13 and 14 are maintained in place by the nose member 15, which is soldered to an end length of the rod member 10 of reduced diameter.

A washer-like plug 16 of thermo-setting plastic or other low thermal conductivity material is located between the nose member 15 and the forward cylindrical portion 13.

Resilient biasing means 17 in the form of an axially compressed coil spring is located in a tubular recess 18 in the forward end region of the cylindrical body portion 13.

The diameter of the rod member 10 is stepped over a first length in the region of the recess 18 and over a second and final length where it is attached to the nose member 15, the stepping being compatible with the reducing cross-section of the sub-projectile. The reduced diameters also facilitate nose member separation and subsequent break-up as the body member portions slide fowardly along the rod member 10 as will be described later.

The assembled sub-projectile is located within a conventional sabot 19 by means of external thread-like projections 20 on, as shown, the cylindrical portion 14 of the body member and part of the tail member 11.

In operation the sub-projectile is located within the sabot 19 and fired, the sabot 19 discarding in the conventional manner once free of the gun barrel. The sub-projectile then assumes a ballistic trajectory. As the sub-projectile moves through the atmosphere it is subjected to aerodynamic heating particularly in the forward region of the nose member 15.

The provision of the low conductivity plug 16 inhibits any tendency for the body member 13 and 14 to act as a heat sink. This maximises the effect of aerodynamic heating in the nose member 15.

Aerodynamic heating melts the jointing material by which the nose member 15 is retained on the rod member 10, and these separate with the assistance of the coil spring -17 to initiate break-up.

The cylindrical portions 13 and 14 of the body member are considerably heavier than the combined rod member 10 and tail mem ber 11, and decelerate more gradually after break-up is initiated. Accordingly the portions 13 and 14 slide forwardly off the rod member 10. Drag on the fins 12 of the tail member 11 also contributes to separation. The stepping of the rod member 10 as previously described assists clean separation of the individual component parts, since less sliding resistance is presented by the reduced diameter lengths of the rod member 10. Aerodynamic integrity of the sub-projectile is lost after break-up, and its component parts tumble to the ground.

For any particular size of sub-projectile, it is necessary to determine the point at which the separation means operate to initiate break-up.

This is a function of aerodynamic heating, thermal conduction rates through the nose member 15 and the softening or melting point of the jointing material. To achieve reproduci bility of break-up in terms of time of flight and/or range, experimentation is required. Cur rent technology provides materials which are capable of giving reproducible performance for the purposes of the invention.

An alternative design of nose member 15 incorporating a so-called thermal trigger as the separating means is shown in Fig. 2, like reference numerals being used for identical or similar integers.

The nose member 15 is a hollow thinwalled design, and is attached to a thermally Insulating nylon sleeve 21 mounted on the rod member 10. The sleeve 21 is secured to the nose member 15 and rod member 10 by thread or adhesive means. The nose member 15 includes an annular relieved section 22. A recess 18 in the cylindrical portion 13 of the body member houses a stack of belleville washers (ie disc springs) 17, these being retained substantially in a fully compressed condition to prevent further compression during acceleration.

In operation of the Fig. 2 embodiment, aerodynamic heating is concentrated in the forward tip region of the nose member 15 and is particularly effective in the relieved section 22, and this section rapidly overheats.

The low conductivity nylon insulating sleeve 21 also increases in temperature to some extent, but inhibits heat loss to the rod member 10. The nose member 15 is manufactured from aluminium alloy which, as is well known, loses strength quite dramatically above a threshold temperature. The nose member 15 consequently fails in the region of the relieved section 22 and separates from the body member portions 13 and 14 aided by the spring means 17. The insulating sleeve 21 is also designed to fail at the appropriate time, and in an optimum design would fail simultaneously with failure of the relieved section 22. At failure the cylindrical portions 13 and 14 of the body member sequentially separate as with operation of the embodiment of Fig. 2.

The sub-projectile of the described embodiment has two cylindrical body portions 13 and 14, although in some designs it might be preferred to have more. The particular construction of the invention allows a very close ballistic match and a high degree of geomentrical fidelity during flight when compared with the in-service sub-projectile.

Variations in detailed design but within the broad principle outlined are clearly possible.

Claims

1. A sub-projectile for a discarding sabot practice shot comprising a longitudinally disposed rod member attached atone end to a tail member, a body member slidably assembled on the rod member and retained in position by a nose member secured to the other end of the rod member, and separating means operative after a given time of flight to cause separation of the nose member from the rod member.

2. A sub-projectile according to claim 1 comprising two or more discrete cylindrical portions retained in longitudinal contiguity by the nose member.

3. A sub-projectile according to claim 1 or 2 containing resilient biasing means disposed to urge separation of the nose member from the rod member.

4. A sub-projectile according to claim 3 wherein the biasing means comprises a compression spring housed within the sub-projectile and disposed to urge apart the nose and body members.

5. A sub-projectile according to any preceding claim wherein the separating means includes a portion of the sub-projectile which is arranged to fail upon experiencing aerodynamic heating during the given time of flight.

6. A sub-projectile according to claim 5 wherein the separating means includes a joint between the nose and rod members, the joint being formed by a thermally softenable material.

7. A sub-projectile according to claim 6 wherein the joint material is solder, Woods metal or a thermoplastic adhesive.

8. A sub-projectile according to claim 5, 6 or 7 wherein the separating means includes a region of structural weakness which is part of the nose member and which is designed for structural failure after aerodynamic heating during the given time of flight.

9. A sub-projectile according to claim 8 wherein the region of structural weakness is a generally annular region of the nose member coaxial with the longitudinal axis of the subprojectile.

10. A sub-projectile according to claim 8 or 9 wherein the region of structural weakness is stressed by the resilient biasing means.

11. A sub-projectile according to any preceding claim wherein the diameter of the rod member is reduced towards the end secured to the nose member.

12. A sub-projectile for a discarding sabot practice shot substantially as herein described with reference to and as illustrated in the accompanying Fig. 1 or 2.

12. A sub-projectile according to any preceding claim including means for inhibiting thermal conduction between the nose and body members.

13. A sub-projectile according to claim 12 in which the means for inhibiting thermal conduction includes a washer-shaped plug of relatively low thermal conductivity material disposed between the nose and body portions.

14. A sub-projectile according to any preceding claim wherein the body member has external formations for engaging complementary formations of a sabot.

15. A sub-projectile according to any preceding claim wherein the tail member has external formations for engaging complementary formations of a sabot.

16. A sub-projectile for a discarding sabot practice shot substantially as herein described with reference to and as illustrated in the accompanying Fig. 1 or 2.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 to 16 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:

1. A sub-projectile for a discarding sabot practice shot comprising a longitudinally disposed rod member fixed at its rear end to a tail member, a body member slidably assembled on the rod member and retained in position by a nose member located at the forward end of the rod member, thermally degradable retaining means for retaining the nose member on the rod member, and spring means housed within the sub-projectile and disposed to urge separation of the nose member from the rod member whereby after a pre-determined flight time the retaining means fails by aerodynamic heating and the spring means causes separation of the nose member from the rod member to initiate break-up of the sub-projectile.

2. A sub-projectile according to Claim 1 in which the body member comprises two or more discrete cylindrical portions retained in longitudinal contiguity by the nose member.

3. A sub-projectile according to either preceding claim in which the retaining means comprises a joint securing the nose member to the rod member, said joint being made of a thermally softenable material.

4. A sub-projectile according to Claim 3 in which the joint material is solder, woods metal or a thermoplastic adhesive.

5. A sub-projectile according to any preceding claim including a region of structural weakness, stressed by the spring means and located adjacent and to the rear of the nose member and which is designed for structural failure after aerodynamic heating during the given time of flight.

6. A sub-projectile according to Claim 5 in which the region of structural weakness is generally annular and coaxial with the longitudinal axis of the sub-projectile.

7. A sub-projectile according to any preceding claim in which the diameter of the red member is reduced towards its forward end.

8. A sub-projectile according to any preceding claim including means for inhibiting thermal conduction between the nose and body members.

9. A sub-projectile according to Claim 8 in which the means for inhibiting thermal conduction includes a washer-shaped plug of relatively low thermal conductivity material disposed between the nose and body members.

10. A sub-projectile according to any preceding claim in which the body member has external formations for engaging complementary formations of a sabot.

11. A sub-projectile according to any preceding claim in which the tail member has external formations for engaging complementary formations of a sabot.