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(11) | EP 2 322 896 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Collar for a munition |
| (57) There is disclosed a collar (100) which may be attached to a munition (200) in order
to control the trajectory of the munition (200). The collar (100) has a collar body
(10); a surface (12) for capturing the projectile (200) as it leaves the barrel; a
sill (14) for supporting the surface at the muzzle (310) of the barrel (300); and
a guidance means (50) for altering the flow of air around the collar (100). The collar
(100) supports itself at the muzzle (310) and may attach to the projectile (200) at
the surface (12) to integrate with the projectile (100) as the projectile (200) is
fired. The collar (100) is particularly suited for attachment to mortar rounds (200).
Such a collar (100) gives a weapon operator the option of increasing the precision
of a munition (200) without having to carry a plurality of munition types.
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[0001] The present invention relates to a collar for guiding a projectile, and in particular to a collar for improving the precision of a ballistic projectile.
[0002] In the field of ballistics, the term precision describes the ability of a projectile, fired from a weapon system, to follow a predicted trajectory and hence hit an expected target; a precise projectile will, by definition, follow a predicted trajectory more closely than an imprecise projectile. Ballistic precision is commonly measured using the circular error probability (CEP).
[0003] In most cases, it is desirable to have a precise projectile. However, the unit cost of a projectile tends to rise with increased precision. Accordingly, it is generally understood that in designing projectiles, the benefit of providing a particularly precise projectile must be balanced against the costs of such provision.
[0004] It is known to have a kit, such as the XM1156 Precision Guidance Kit (as may be supplied by Alliant Techsystems to the US Army), whereby a standard (i.e. non-guided) 155mm artillery shell may be converted into a guided munition. The kit comprises means for controlling the trajectory of the projectile. Such controlling means may include a set of control surfaces, a processor, and an actuator for moving the control surfaces in response to a correcting signal from the processor. The processor may be interfaced with Global Positioning System (GPS) and Inertial Navigation (IN) sensors to determine the correcting signal which is to be applied.
[0005] The kit, which further includes a fuze, can be retrofitted into a shell by detaching the fuze section of the shell from the body section of the shell and then attaching the kit to the body section. The kit may therefore give users the option of converting munitions and thus selecting the precision of each round fired.
[0006] However, the Precision Guidance Kit (PGK) may have a deep intrusion body that necessitates the removal of some of the shell's explosive payload in order to fit the PGK instead of the original fuze.
[0007] Further, the act of replacing the original fuze with the kit may be undesirably time consuming, particularly given the urgency with which a muniton may need to be fired. Indeed, it may not even be possible to replace the original fuse with the kit on the battlefield, for example if some of the payload must be removed as described above.
[0008] Further, the kit may only be applicable to munitions which have a detachable fuze. Where the munition does not originally have a fuze, the kit cannot readily be applied.
[0009] It is an object of the present invention to provide a collar for guiding a projectile which mitigates at least one of the disadvantages of the prior art identified above.
[0010] Accordingly there is provided a collar for guiding a projectile, the collar comprising a collar body, a surface for capturing the projectile as it leaves the barrel, a sill for supporting the surface at the muzzle of the barrel, and a guidance means for altering the flow of air around the collar, wherein the collar may attach to the projectile at the surface to integrate with the projectile as the projectile is fired.
[0011] Such a collar can be transported into battlefield with the munitions and the weapon system to offer a more precise firing should this be desired. The collar is simple to mount on the muzzle and does not require the detachment or reattachment of munition components prior to firing.
[0012] A further benefit when compared to guidance kits that require replacement of parts is that the use of the above collar will tend to minimise the number of components which must be transported after a set of precise firings. Thus this invention is in contrast to a system where fuzes may be replaced in the field because in that situation, the replacements must be brought into the field and the replaced fuzes brought back.
[0013] The law of the conservation of momentum dictates that as the mortar integrates with the collar, the velocity of the mortar will drop on account of the mass of the collar. It follows that the range of the integrated projectile will be less than that of an equivalent projectile. However, it is expected that in many situations, the benefits of a precise projectile compensate for the reduction in maximum range. It is nonetheless advantageous to minimise the mass of the collar wherever possible.
[0014] The collar may comprise a control surface, an actuator for altering the configuration of the control surface, and a guidance controller, the guidance controller comprising a navigation sensor for determining an actual trajectory the projectile is following, a memory at which data describing a predicted trajectory is stored, a processor operably connected to the actuator, the memory and the navigational sensor, wherein the processor calculates a correction signal which determines how the configuration of the control surface may be altered and transmits the correction signal to the actuator.
[0015] In particular the processor may calculate the correction signal by determining the difference (which may alternatively be referred to as the error or the deviation) between the actual trajectory and the predicted trajectory.
[0016] At the collar, the control surface may comprise a pair of canards, each canard comprising a pivot joint connecting the canard to the collar and wherein the actuator may be a ring actuator which connects to the canards so as to be able to alter the configuration of the control surface by rotating the canards about their pivots.
[0017] Where a pivot joint connects each of the canards to the collar body, the pivot joint is preferably connected forwards of the centre of pressure of the canard.
[0018] Where the ring actuator may correct the projectile course by applying a force to the control surface so as to move the control surface out of alignment with the air stream over the projectile body, such a location of the pivot leads to a stable control arrangement. This stability is conferred because as the actuator ceases to apply the force to the control surface, the air flow will return the control surface to its original configuration.
[0019] Such a position of the pivot should therefore also tend to simplify the control signals (i.e. the correction signal) which needs to be sent to the actuator because little consideration needs to be given to how the actuator must move in order to return the control surface to its original position; the correcting signal can consist of a set of identical signals, which rise in repetition frequency with the projectile deviation but need not be transmitted if the projectile follows the predicted trajectory.
[0020] By 'forwards', the reader will understand that this means that the pivot is mounted more towards the leading edge of the collar, i.e. further towards the oncoming air stream.
[0021] Further, each canard may be connected to the ring actuator at a point on the canard towards or at the trailing edge of the canard.
[0022] By thus positioning the interface between the actuator and the control surface, it tends to facilitate the best mechanical advantage and thus enables the weakest/lightest ring actuators to be used.
[0023] At the collar, the surface for capturing may be at an internal facet of the collar and may have a tapered inner diameter, operable to form an interference fit with said projectile, and thereby allow the collar to attach to the projectile.
[0024] Preferably, where the surface is to capture the projectile by way of an interference fit, the surface and the material providing the surface is capable of elastic deformation. Metals would be suitable materials for the material providing the surface.
[0026] As such the sill may support the frustoconical form defined by the surface at the barrel so that the axis defined by the frustoconical form is generally collinear with the axis defined by the barrel.
[0027] This supporting arrangement can promote an even interference fit around the projectile and so enable the collar to attach to the projectile and create a symmetrical integrated projectile. Such a symmetrical integrated projectile can be expected to have improved aerodynamic properties and tend to require less guidance.
[0028] Such a surface for capturing may be tapered at between 3° and 0.5°, and in particular may be tapered at approximately 1.2°.
[0030] Such a provision allows the air exhausted from the barrel prior to the exit of the projectile to escape without disturbing the supported collar.
[0032] A collar thus formed allows for transportation in a distributed and potentially less bulky form.
[0033] According to a further aspect of the invention there is provided a method of attaching a guidance collar to a projectile, the method comprising the steps of a) supporting a collar according to any one of the preceding claims at the muzzle of a barrel loaded with the projectile, b) firing the projectile from the barrel.
[0034] So that the invention may be well understood, an exemplary embodiment of the invention will now be described with reference to the following figures of which:-
Figure 1a shows a first aspect of a collar according to the present invention;
Figure 1b shows a cross section at X-X of the first aspect of the collar of figure 1 a;
Figure 2 shows a schematic diagram of the guidance controller for use in the collar of figure 1 a;
Figures 3a, 3b, 3c and 3d show the sequential firing of a mortar operating in conjunction with the collar of figure 1 a;
Figure 4 represents the action of the collar of figure 1 a in correcting the trajectory of a projectile at a point A and a point B.
Figure 5 shows an isometric aspect of the collar of figure 1a, integrated with the mortar and at Point A of figure 4.
[0035] A collar 100 for guiding a mortar shell, as shown for example in figure 1a, figure 1b and figure 5, comprises a collar body 10. The collar body 10 defines a generally cylindrical outer surface, which defines a collar axis 1. The leading edge of the collar (that is the top edge in figure 1 a) is filleted so as to have appropriate aerodynamic properties.
[0036] A plurality of canards 20a, 20b, 21a and 21b extend from the outer surface of the collar body 10. The plurality of canards 20a, 20b, 21a and 21 b are spaced at regular intervals about the outer surface of the collar body 10. The canards are arranged in pairs. A first canard pair, consisting of canard 20a and 20b, generally occupies a first plane with canards 20a and 20b mounted on diametrically opposite sides of the collar body 10. A second canard pair, consisting of canard 21a and 21 b, generally occupies a second plane with canards 21 a and 21 b mounted on diametrically opposite sides of the collar body 10
[0037] Each canard is pivotally attached to the collar body 10 by a pivot joint 30 which defines a rotational axis extending normal to the outer surface of the body 10. The canards are arranged to be able to align with the collar axis 1 but deflect from this arrangement as they rotate about the joints 30. Each pivot joint 30 is mounted towards the leading edge of the canard and so is forward of any component of the centre of pressure which may act laterally on the canard.
[0038] The collar 100 is hollow and is open towards both ends of its axis 1 to define a conduit. A first opening 16 of the conduit (alternatively referred to as the escape vent 16) is located at the leading edge of the collar 100 and defines a generally circular aperture, normal to the collar axis 10 and with a centre point which lies generally on the collar axis 1. A second opening 17 is located at the trailing edge of the collar 100. The second opening 17 defines a circular aperture normal to the collar axis 10 and with a centre point which lies generally on the collar axis 1.
[0039] An inner wall of the collar 100, which comprises a capture surface 12, a sill 14 and a cylindrical section 18, extends between the first opening 16 and the second opening 17.
[0040] The capture surface 12 starts at the first opening 16 and extends down into the collar body 10 up to approximately the mid point of the body length. As the capture surface 12 extends away from the leading edge of the collar it tapers out, thereby defining a generally frustoconical surface, and eventually meets the sill 14. The sill 14 is an annular surface normal to the collar axis 1 and with its centre point generally on the collar axis 1. The inner diameter of the annular sill 14 meets the frustoconical surface 12 and the outer diameter of the annular sill 14 meets the cylindrical surface 18. The cylindrical section 18 extends downwards to the second opening 17. The diameter of the second opening 17 is generally identical to the outer diameter of the annular sill 14.
[0041] A set of ring actuators 40 is disposed in the collar body 10 and there are connections to each of the canards 20a, 20b, 21a and 21 b. Each canard is connected to the ring actuator towards the trailing edge of the canard.
[0042] Embedded in the collar 100 is a guidance controller 50 which, as can be seen from figure 2, comprises a navigation sensor unit 54, a memory 52, a processor 56 and a ring actuator I/O unit 58. Guidance controller 50 is also provided with a power source (not shown).
[0043] The processor 56 is operably and independently connected to the sensor unit 54 and the memory 52 and generates as an output a correction signal 57 that is input to the I/O unit 58. The I/O unit is operably connected to the ring actuator 40.
[0044] The sensor unit 54 comprises an inertial navigation system (comprising accelerometers for sensing linear motion and gyroscopes for sensing rotational rate), a magnetometer and a Global Positioning System (GPS).
[0045] In operation, the collar 100 is placed loosely over the mortar shell 200 with a forked safety plate 400 slotted on to the mortar 200 to hold the mortar 200 at the collar 100. The collar 100 may then be placed at the muzzle 310 of a barrel 300 as shown in figure 3a to prepare the mortar 100 for firing. The collar 100 is supported at the muzzle 310 by the sill 14 which rests at the lip of the muzzle 310 and is of such a form that the collar axis is generally collinear with the barrel axis. The collar 100 is also supported by the cylindrical surface 18, which fits around the muzzle 310.
[0046] In order to fire the mortar 200 the user removes the plate 400, which may be done remotely using a string. This stage in operation is shown at figure 3b.
[0047] Once the safety plate 400 is removed, the mortar 200 drops in the known manner down the barrel 300 until the pin at the base of the barrel 300 is struck and the propellant charge at the rear of the mortar is initiated.
[0048] The initiation of the propellant charge accelerates the mortar towards the muzzle 310 and the collar 100. The collar 100 remains supported at the muzzle 310 until the mortar strikes and engages with the capture surface 12. The force of the mortar striking the collar 100 at the generally frustoconical capture surface 12 sets up an interference fit between the mortar and the collar 12. This interference fit attaches the collar 100 to the mortar 200, thereby integrating the collar 100 with the mortar 200.
[0049] Further, the frustoconical form of the capture surface 12 may cooperate with the outer surface of the mortar to tend to ensure that the collar axis and the mortar axis are collinear. Thus the integrated mortar 500 is generally symmetrical.
[0050] The guidance of the integrated mortar 500 is illustrated at figure 4. A ballistic trajectory can be predicted from the inclination of the barrel axis and the muzzle velocity using classical mechanics, with adjustments made for air resistance made in the known way. However, a predicted ballistic trajectory may not be followed in practice because of environmental inconsistencies (such as wind) which may cause the projectile to deviate.
[0051] During its flight the collar 100 monitors its trajectory 120 using the navigational sensors in unit 54 to feed data into the processor 56. Before applying any correcting signal, the processor 56 compares the monitored trajectory 120 to a set of predicted trajectories stored in the memory 52. The processor thus determines that, of the possible predicted trajectories which the projectile 500 may follow, projectile 500 is intended to follow a particular predicted trajectory 110. By making this determination in the early part of its flight, which is the part of its flight where the weather may have least effect on the trajectory, the selection of the predicted trajectory should tend to be correct.
[0052] Once the integrated mortar 500 has determined the predicted trajectory 110, the controller 50 may regulate the actual trajectory 120 of the integrated mortar 500, attempting to conform the actual trajectory 120 to the predicted trajectory 110.
[0053] In the present embodiment, where the projectile is a free falling mortar which is not spinning in flight, the processor will rely on signals from magnetometer sensors and GPS sensors to determine the position of the projectile 500.
[0054] Inertial Navigation sensors (in particular the accelerometers) at the projectile 500 will tend to give null readings for most of the flight because, in a projectile describing pure ballistic flight, there is a net zero acceleration at a strapdown accelerometer sensing the lateral axes within the projectile (a small deceleration followed by small acceleration will be sensed in the longitudinal axis). However, in other embodiments of the collar 100, especially those where the projectile spins in flight, the IN sensors may include solid-state rate gyros and their output may be considered in determining the actual position of the projectile.
[0055] The processor 56 may, by frequently sampling the position of the projectile 500 from the signals from the sensors 54, determine the actual trajectory 120 of the projectile 500.
[0056] Once the actual trajectory 120 is determined, the processor 56 can compare the actual trajectory 120 to the predicted trajectory 110. At the point A of figures 4 and 5, the processor 56 determines that the actual trajectory 120 differs from the predicted trajectory 110. In order to conform the actual trajectory 120 to the predicted 119, the processor 56 sends a correcting signal 57 to I/O unit 58. I/O unit 58 then outputs a more powerful signal to the ring actuator 40, which signal momentarily energises the ring actuator 40 so that the ring actuator 40 momentarily deflects the canard pair 20a, 20b to apply lift to the integrated mortar 500. The course of the integrated mortar should then alter and once the ring actuator is de-energised, the air flow will return the canard pair 20a, 20b to their original configuration.
[0057] In a similar manner, at the point B, the processor 56 determines that the integrated mortar 500 is now above the predicted trajectory 110 and so the correcting signal 57 is generated to energise the ring actuator 40 so that the canards deflect in the opposite direction to that at point A.
[0058] These exemplary corrective actions having been taken at the points A and B, the projectile 500 proceeds to land at the target Y, which is the predicted target for the predicted trajectory 110 and so avoids potentially sensitive targets X and Z.
[0059] For each canard pair, there are two types of corrective action which can be taken. The first type is for both canards to be deflected a specific amount in a first (glide) direction. The second type is for both canards to be deflected by the same specific amount but in a second (brake) direction. A simple control algorithm may be employed whereby the frequency of repetition of this corrective action is proportional to the deviation of the actual trajectory 120 from the predicted trajectory 110. However, the invention alternatively contemplates the use of more sophisticated control methods which employ for example PID control algorithms.
[0060] The collar body 10 may be made from milled aluminium or an alloy of aluminium. Where the collar is for attaching to an 81mm mortar, the first opening has a diameter of approximately 78mm and tapers at approximately 1.6° to a diameter of approximately 80mm at the inner diameter of the annular sill 14. The outer collar body diameter is 108mm. With such a fabrication, the capture surfaces are the surfaces of the milled aluminium form.
1. A collar for guiding a projectile, the collar comprising:
a collar body;
a surface for capturing the projectile as it leaves the barrel;
a sill for supporting the surface at the muzzle of the barrel; and
a guidance means for altering the flow of air around the collar,
wherein the collar may attach to the projectile at the surface to integrate with the projectile as the projectile is fired.2. A collar according to claim 1 wherein the guidance means comprises:
a control surface;
an actuator for altering the configuration of the control surface; and
a guidance controller comprising:
a navigation sensor for determining an actual trajectory the projectile is following;
a memory at which data describing a predicted trajectory are stored; and
a processor operably connected to the actuator, the memory and
the navigational sensor,
wherein the processor calculates a correction signal which determines how the configuration of the control surface is altered and transmits the correction signal to the actuator.3. A collar according to claim 2 wherein the processor calculates the correction signal
by determining the difference between the actual trajectory and the predicted trajectory.
4. A collar according to claim 3 or claim 4 wherein the control surface comprises a pair
of canards, each canard comprising a pivot joint connecting the canard to the collar,
wherein the actuator is a ring actuator which connects to the canards so as to be able to alter the configuration of the control surface by rotating the canards about their pivots.
wherein the actuator is a ring actuator which connects to the canards so as to be able to alter the configuration of the control surface by rotating the canards about their pivots.
5. A collar according to claim 4 wherein the pivot joint connecting each of the canards
to the collar body, is connected forwards of the centre of pressure of the canard.
6. A collar according to claim 5 wherein each canard is connected to the ring actuator
at a point on the canard towards or at the trailing edge of the canard.
7. A collar according to any previous claim wherein the surface for capturing is at an
internal facet of the collar and has a tapered inner diameter operable to form an
interference fit with said projectile, and thereby allowing the collar to attach to
the projectile.
8. A collar according to claim 7 wherein the surface defines a generally frustoconical
form.
9. A collar according to claim 8 wherein the sill supports the frustoconical form defined
by the surface at the barrel so that the axis defined by the frustoconical form is
generally collinear with the axis defined by the barrel.
10. A collar according to claim 8 or 9 wherein the surface is tapered at between 3° and
0.5°.
11. A collar according to claim 10 wherein the surface is tapered at approximately 1.2°.
12. A collar according to any previous claim wherein the collar comprises an air escape
vent.
13. A collar according to any previous claim wherein said collar is formed as one or more
portions operable to be fastened together.
14. A method of attaching a guidance collar to a projectile, the method comprising the
steps of:
a) supporting a collar according to any one of the preceding claims at the muzzle of a barrel loaded with the projectile; and
b) firing the projectile from the barrel.