Field gun

A field gun comprising: a chassis, a barrel defining a barrel axis and having a traverse range and an elevation range, a cradle supporting the barrel, a joint for enabling pivoting in at least two axes, the joint connecting the cradle to the chassis, a first linear actuator, extensible along a first linear actuator axis, pivotally attached to a first point on the chassis and pivotally attached to a first point on the cradle, a second linear actuator, extensible along a first linear actuator axis, pivotally attached to a second point on the chassis and pivotally attached to a second point on the cradle, such that a first combination of first linear actuator and second linear actuator actuation varies the traverse a second combination of first linear actuator and second linear actuator actuation varies the elevation.

The invention relates to a field gun.

A known field gun50is shown in prior artFIGS. 5aand5band comprises a soleplate52and a saddle54. The soleplate52rests on the ground and supports the weight of the gun50. Extending from the general centre of the soleplate52is a swivel mount53. The saddle54has a base55connected to the swivel mount53so that the saddle is able to rotate relative to the soleplate52in an azimuth plane generally parallel to a surface of the ground51. A geared drive59is provided for controlling rotation of the saddle with respect to the soleplate.

A cradle supports a gun barrel and comprises trunnions58which form a pivot joint57with saddle54. The cradle can pivot about pivot joint57and a pair of linear actuators are provided for controlling rotation of the gun barrel in a vertical plane with respect to the soleplate. A nearside actuator56is shown inFIG. 5aand extends between the cradle and the saddle.

Accordingly, the gun barrel can be aimed by controlling rotation in the azimuth plane about swivel mount53and in a vertical plane about pivot joint57. Rotation of a gun barrel in the azimuth plane is typically referred to as traversing.

Such an aiming mechanism provides a range of potential trajectories from a single grounding when the field gun is in a fixed or temporary position. However, in the prior art, the saddle is the only means by which the soleplate is connected to the cradle and therefore the saddle must absorb the substantial recoil forces generated when the gun is fired. In order to withstand these forces, the saddle therefore tends to be of an appropriately substantial form, for example the saddle tends to have a wide base. This in turn adds weight to the gun.

It is therefore an aim of the present invention to provide an improved field gun. The embodiments of the invention, described in more detail with reference to the drawings, do not rely upon the provision of a saddle and soleplate arrangement to effect aim. This can lead to a simplified aiming mechanism, thus potentially enabling lighter aiming mechanism designs.

According to an aspect of the invention there is provided a field gun comprising: a chassis, a barrel defining a barrel axis and having a traverse range and an elevation range, a cradle supporting the barrel, a trunnion joint for enabling pivoting in at least two axes, the trunnion joint connecting the cradle to the chassis, a first linear actuator, extensible along a first linear actuator axis, pivotally attached to the chassis by a first chassis joint, and pivotally attached to the cradle by a first cradle joint, a second linear actuator, extensible along a second linear actuator axis, pivotally attached to the chassis by a second chassis joint and pivotally attached to the cradle by a second cradle joint, such that a first combination of first linear actuator and second linear actuator actuation varies the traverse a second combination of first linear actuator and second linear actuator actuation varies the elevation.

Advantageously this reduces the overall mass of a field gun because there need be only two linear actuators for varying both the azimuth and the elevation. Comparing this with the M777, this does away with the need for a saddle rotating gear. Such a reduction in mass makes the gun easier to transport e.g. by a transport aircraft and also makes the gun easier to reposition to other firing sites.

Additionally, this provides more than one interface between the chassis (which can be static as the barrel is aimed) and the cradle. In particular these interfaces are provided by the trunnion joint between the cradle and the chassis, the first linear actuator between the cradle and the chassis, and the second linear actuator between the cradle and the chassis. Thus the firing forces are transmitted to the chassis not only via the trunnion joint but also via the linear actuators. This reduces the maximum load on the trunnion joint and hence allows the use of a less substantial aiming means than the saddle of the M777.

Preferably when the barrel is in the midpoint of the barrel traverse range the first linear actuator axis is substantially inclined to the barrel axis, in particular this inclination may be 20-60°.

Advantageously this enables the linear actuators to move the barrel effectively, whilst still providing structural support along the barrel axis. Shallower angles than this would require longer linear actuators due to the smaller component of the force contributing to barrel displacement. Deeper angles would not provide enough axial support to the barrel over the course of firing.

Preferably when the barrel is in the midpoint of the barrel traverse range, the second linear actuator axis is substantially inclined to a plane defined by the barrel axis and the first linear actuator axis, in particular this inclination may be 20-60°.

Advantageously, this effectively forms a tripod which is a robust shape that is simple and light.

Preferably the first chassis joint, relative to a polar axis extending forwards from the trunnion joint along an elevation datum line generally parallel to the ground plane, is at a position displaced from the trunnion joint by radius r1and angle θ1, wherein the magnitude of θ1is greater than 90° but less than 180°.

Preferably, when the barrel is at zero elevation, the first cradle joint is displaced from the trunnion joint by radius r2and angle θ2wherein r1is less than r2and θ2is less than 90° but greater than 0°.

Each of these preferential embodiments advantageously act to maximise the elevation range.

Preferably the first and second linear actuators are arranged generally symmetrically about the barrel axis when the barrel is at the traverse range midpoint.

Advantageously this tends to distribute forces and stresses evenly over the gun when firing the barrel from the midpoint and tends to reduce the maximum moment arms when the barrel is fired from the extremities of its axis range. Hence the gun is more robust.

Preferably, the first and second linear actuators are connected to each respective site on the cradle and chassis by a global pivot joint or alternatively by a universal joint.

Advantageously this provides an infinite-axis pivot and so does not constrain the field gun so as to substantially prevent the extension of the linear actuator from moving the barrel; as the barrel varies its traverse, the pivot joint should enable pivoting in a first direction and as the barrel varies its elevation, the pivot joint should enable pivoting in a second direction perpendicular to the first. The pivot joint should also enable the simultaneous varying of traverse and elevation.

Preferably the chassis is for contacting a ground plane and comprises: at least one back stabilising leg for contacting the ground plane at a backmost point, at least one front stabilising leg for contacting the ground plane at a foremost point.

Advantageously this tends to provide a stable platform for firing and so improves the accuracy of the weapon.

Preferably the chassis comprises a self-propulsion means.

Advantageously this allows coarse alterations of the aim (i.e. those outside of the range of the barrel movements relative to a static chassis) to be effected swiftly by relocating the chassis under its own power. This can reduce the size of the operational crew and so make the weapon easier to deploy.

Preferably the chassis comprises an automated handling system for re-loading the gun between firing.

This can reduce the size of the operational crew and so make the weapon easier to deploy.

Referring toFIGS. 1 and 2, a field gun100is shown which comprises a chassis2deployed on a surface of the ground, which for simplicity is shown as ground plane1. The chassis2comprises a base3and stabilising legs5a,5b,5cand5d. Trailing stabilising legs5aand5b(also known as trails) can be rotated about a hinge7so that legs5aand5bcan be moved to a deployed condition (as shown in solid lines inFIGS. 1 and 2) for stabilising the field gun100in use and to a collapsed condition (as shown in broken lines) for transport.

As shown, base3and stabilising legs5cand5dcontact the surface of the ground at respective positions and define a contact plane that is coplanar with the ground surface1when the field gun is in the deployed condition. the trailing legs5aand5bcontact the ground plane1at respective positions. The trailing legs may comprise feet which can be driven into the ground to provide additional stability as shown.

The chassis2comprises a multi-axis trunnion joint10provided generally in the region of the base3so that trunnion joint10may be positioned close to the ground plane1. The trunnion joint10connects the chassis2to an arm9of a cradle8thereby allowing the arm to be pivoted in multiple axes.

A barrel4is attached to the cradle8to allow for sliding relative movement so that the barrel4can recoil along a barrel axis6when a projectile is fired from the gun barrel. Relative sliding movement can be achieved by any suitable means, for instance by chase bearings (not shown).

The chassis2is provided with a first and second post15a,15beach of which extends from the base3and generally away from ground plane1. The first and second posts15aand15bextend from the base3at a region that is backwards (to the left as shown inFIGS. 1 and 2) of the trunnion joint10.

First and second linear actuators14a,14bextend between the cradle8and the first post15aand the second post15b, respectively. The linear actuators are lengthwise extendable. The linear actuators14a,14bare connected by first and second chassis joints16a,16bto respective upper portions of the first and second posts15a,15band by first and second cradle joints18a,18bto the cradle8. Chassis joints16a,16bare rearward of multi-axis joint10and Cradle joints18a,18bare forward of the trunnion joint10.

Linear actuators14a,14bare pivotal about chassis joints16a,16band cradle joints18a,18bin a vertical plane and a horizontal plane. Joints16a,16b,18a,18bmay be global pivots, which may comprise a spherical interface between moving parts.

The extension or retraction of the linear actuators14a,14bcan be manually actuated by rotating hand wheels17aand17b. Extension and retraction of linear actuators14a,14bcontrol a distance between joints16aand18aand between joints16band18b, respectively. Accordingly, the orientation of the cradle8, and gun barrel4, with respect to the chassis can be controlled by actuation of the linear actuators.

Hand wheels17aand17beach actuate a respective screw drive (not shown) that is internal to the linear actuator and which extends or retracts the linear actuator according to the direction of hand wheel17aand17brotation. The dimensions of the field gun100and the arrangement of the hand wheels17aand17bare such that a single operator is able to rotate both drives at once.

As an alternative to screw drive actuation, the linear actuator14a,14bcan be actuated by hydraulic means. Hydraulic means allow hand drives to be remote from the actuator and thus can be located in an optimal ergonomic arrangement.

Referring toFIG. 2a, trunnion joint10is coincident with an elevation datum line11. Elevation datum line11is generally parallel with the ground plane1and hence generally parallel to the barrel axis6when elevation is zero.

The positions of joints16aand18awill now be described in more detail using polar coordinates. Chassis joint16bis a distance r1from trunnion joint10and at an angle of θ1with datum line11. Cradle joint18bis distance r2from trunnion joint10and at an angle θ2with datum line11. As shown in this embodiment r1is less than r2, θ1is greater than 90° but less than 180°, and θ2is less than 90° but greater than 0°.

Although not specifically shown inFIG. 2a, joints16aand18aare arranged with respect to multi-joint10and datum line11in a manner equivalent to joints16aand18a.

In order to control an initial path of a projectile fired from the barrel4of the field gun, it is necessary to control an orientation of the gun barrel with respect to the chassis. Orientation can be controlled in a vertical plane which is generally referred to as elevation and in a horizontal, or azimuth, plane which is generally referred to as traverse.

As shown inFIGS. 1 and 2, arm9and linear actuators14aand14bform a tripod arrangement. The linear actuators form lengthwise extensible legs of the tripod while the arm9forms a leg of fixed length. For any given length of the first linear actuator, extension and retraction of the second linear actuator causes pivotal movement of the barrel axis6in a plane which intersects an angle between the first linear actuator and the arm. Likewise, for any given length of the second linear actuator, extension and retraction of the first linear actuator causes pivotal movement of the barrel axis6in a plane which intersects an angle between the second linear actuator and the arm. Accordingly, appropriate selection of lengths of the first and second linear actuators causes the barrel axis to be orientated at any one of a plurality angles with respect to both the vertical and azimuth planes thereby controlling traverse and elevation of the gun barrel.

For example, the barrel4is orientated in the midpoint of a traverse range12(as shown inFIGS. 1 and 2where the barrel is also aligned with a centreline of the gun), by arranging the linear actuators symmetrically relative to the barrel axis6. As shown, the first linear actuator14ais orientated at an angle13to the barrel axis6which is approximately +25° and second linear actuator14bis orientated at an angle to the barrel axis6which is approximately −25°. Equal extension or retraction of the first and second linear actuators14a,14bcauses the barrel axis6to be orientated at a selected elevation at a traverse which is aligned with a gun central axis.

Also, the distances from the ground plane of the first chassis joint16aand the second chassis joint16bare equal and therefore both joints are contained in a plane which is parallel to the ground plane1. Within this plane both joints16aand16bare laterally offset, by a generally equal amount, from a gun centre line.

The trunnion joint10, the first chassis joint16aand the second chassis joint16bdefine a triangle. The barrel axis6passes through the triangle over the entire range of traverse and elevation configurations.

In operation, the gun barrel4can be aimed whilst the chassis2remains stationary. In order to vary the traverse only, one linear actuator extends at a certain rate and the other linear actuator retracts at the same rate. In order to vary the elevation, both linear actuators must either retract at the same rate (to increase elevation) or extend at the same rate (to reduce elevation). Forces generated during recoil are transferred principally through from the cradle8through arm9to the chassis2and are therefore more easily absorbed and transmitted to the ground than is the case with the prior art gun shown inFIGS. 5aand5b.

Referring toFIGS. 3 and 4, a field gun200is shown which comprises a barrel24slidably attached to a cradle28such that the barrel24can slide along a barrel axis26. The barrel24can be orientated, so as to aim the barrel24, by means of linear actuators34aand34b. The cradle28comprises an arm29that extends to a multi-axis trunnion joint30whereby the cradle28is connected to a self-propelled chassis22. The self-propelled chassis22is provided with a motorised tracked wheel base32for effecting self-propulsion and a handling system33for automatically reloading the gun between firings.

The linear actuators34a,34bare connected between joints38a,38bat the cradle28and joints36a,36bat the chassis22, respectively. Chassis joints36a,36bare closer to the ground plane1than the trunnion joint30.

The barrel24is aimed by extension or retraction of the linear actuators34a,34b, in the same manner as the first embodiment, with the exception that extending both linear actuators34a,34bincreases the elevation and retracting both linear actuators decreases the elevation since chassis joints36a,36bare lower than the multi-axle joint30whereas in the first embodiment chassis joints16a,16bare higher than the trunnion joint10.

A gun traverse can also be effected by the tracked wheel base32, for example by running nearside track in the opposite direction to far side track.

In both embodiments, the linear actuators (14a,14b;34a,34b) are arranged symmetrically about the centreline of the gun chassis (2;22). Further, joints between the chassis and linear actuators are in each embodiment equi-distant from the ground plane1. Also, joints between the cradle and the linear actuators are in each embodiment equi-distant from the ground plane1.

Whilst the arrangements of the linear actuators in the first and second embodiments are advantageous because in both cases the linear actuators are symmetrical and therefore loading on the actuators is generally equal. It will be appreciated that other arrangements are possible. For instance and referring to the first embodiment, chassis joint16amay be higher than chassis joint16b. Such an arrangement requires asymmetrical control of linear actuators in order to achieve selected orientation of the gun barrel axis and may lead to a reduced locus of the orientations in the vertical and azimuth planes.

In a further exemplary arrangement, linear actuators may be arranged such that a first actuator extends in a vertical plane (i.e. perpendicular to the ground plane) and a second actuator extends in a horizontal plane (i.e. parallel to the ground plane). In this case, the vertical plane linear actuator effects the elevation axis and the horizontal plane linear actuator effecting the traverse axis of the gun barrel.

The gun can be made of materials and components that would readily suggest themselves to the skilled man. Aluminium alloys would be particularly suited for forming the simpler structures. Wherever possible, the chassis2can be constructed from hollow rectangular sections. The posts of the chassis2, for example, are constructed in this way. Each of these provisions minimise weight without incurring large costs.

The joints may be universal joints or may be gimballed joints so as to be able to permit the pivoting required.

The gun is suited to firing 155 mm and 105 mm munitions but the invention is equally applicable to all calibres of munition.