Note: Descriptions are shown in the official language in which they were submitted.
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Me~lns for Incre~sill~ the Dr~ on ~ Mllnition
This invention relates to a means of increasing the drag on a munition in order to correct
the course of the munition, in particular a drag means for correcting the course of a
projectile or unguided bomb.
There is a constant military requirement to enhance the accuracy of munitions in order to
increase effectiveness and minimise coliateral damage. For the attack of high value targets
this has led to the development of'smart' guidance systems which are capable of
discriminating between target types and selecting and engaging the appropriate target.
However, such an approach is inappropriate for use with munitions such as conventional
artillcry or unguided bombs, which are used against a wide variety of targets and may use
an area target approach for the destruction of multiple low value targets. The increased
cost and complexity of 'smart' guidance systems is unjustified for such generally low cost
munitions and can lead to a loss of flexibility of the weapon system if the munitions are
programmed to select only one target type. For projectiles and unguided bombs the
accuracy requirement is that the munition shows only a small deviation from the target
impact point and that several munitions launched at the same target point have an
acceptable dispersion.
The dispersion of projectiles and unguided bombs is often greater in the longitudinal
direction, due to discrepancies in launch velocity, than the dispersion in the transverse
direction. Thus, the accuracy of such munitions can be greatly increased by correcting the
deviances in range. A simple means of correcting these deviances is to provide the
munition with a means of altering its air resistance in flight in response to a deviation from
some measured trajectory parameter.
European Patent specification No. 0 138 942 discloses a course correction system for gun
launched ballistic munitions which measures the launch velocity of the munition, predicts
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the impact point and relays a signal to the munition to activate a braking means at an
appl Opl iale point. The braking means consists either of protruding braking flaps or of nose
sections which can be ejected to leave a substantially flat forward face However, due to
the relatively small area presented by the protruding braking flaps or flat nose section, the
braking effect produced is limited and the amount of range correction achievable is
correspondingly limited. Also, the volume contained within the ejectable nose segmf~nt~ is
redundant and reduces the available volume for the payload.
Projectiles and the like often have external constraints on size and or weight, for example
gun bore sizes or maximum breech pressures and therefore to maximise efficiency of the
munition any course correction means should be as compact as possible. Also, the low cost
of such munitions and the stresses encountered during launch of projectiles dictate that the
system should be inexpensive and fairly simple.
It is therefore an object of the present invention to provide an inexpensive, compact and
non complex means of creating a large consistent increase in the drag of a munition at a
point during flight.
Thus, according to the present invention there is provided a means for increasing the drag
on a munition to effect a course correction comprising at least one pair of coplanar drag
plates being laterally slidable in opposite directions between an undeployed configuration
wherein the drag plates are adapted to interlock and be substantially contained within the
body of a munition, and a deployed configuration and a deployment means for ret~ining the
drag plates in the undeployed configuration until receipt of a signal from a control means,
wherein each drag plate has at least one projection and at least one slot, the extent of the
projections being adapted such that the distance from the tip of the projection to the outer
edge of the drag plate measured along a line parallel to the sliding direction of the drag
plate is greater than half the width of the interlockecl drag plate pair along that line and the
slots being adapted such that in the undeployed configuration each projection is
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accommodated in a complementary slot, the extent of the drag plate deployment being
deterrnined by the extent of the projections.
Using co-planar interlocking drag plates allows the drag plates to have a large surface area
whilst minimi~ing the volume of the drag means in the munition. As the ~ t~n~e from the
tip of the projection to the outer edge of the drag plate is greater than half the width of the
interlocked drag plate, in use the projections extend beyond halfway into the munition.
This means that the allowable extension of the drag plates to the deployed configuration is
high and virtually all of the surface area of the drag plate can be deployed outside the body
of the munition whilst the ends of the projections are retained within. The amount of
extension is therefore determined by the extent of the projections as clearly the longer the
projection then the greater extension possible. Pairs of plates are used as the projections of
one plate have to be able to slide out of the slots in the other plate which, to maximise the
surface area of the plates, requires two plates sliding in opposite directions.
In order to maximise the increase in drag that the plates provide, the drag plates are
preferably adapted such that in the undeployed configuration the circumference of the
interlocked drag plates is substantially the same as the circumference of the munition at the
point from which the drag plates extend. This ensures that the maximum possible surface
area is being presented by the plates when in the deployed configuration and yet the plates
can be entirely contained within the munition in the undeployed configuration.
Preferably there are two pairs of drag plates, a first pair of drag plates being laterally
e~tlontlz~ble in opposite directions along a first axis and a second pair of drag plates being
laterally extendable in opposite directions along a second axis wherein the first axis is
sub~ 11y perpendicular to the second axis.
L~
Four drag plates extended in perpendicular lateral directions present a large surface area
thus giving a large increase in drag, whilst only requiring two layers of plates. Additional
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plates would take up greater space in the munition and would result in overlap of the plates
when extended. Overlap of plates would reduce the weight/space to drag effect eff~ciency
and would not greatly increase the drag performance.
(:~onveniently the drag plates are adapted such that both drag plates of a pair are identical.
This re~uires that the drag plates be asymmetrical and that the interlocked drag plate pair
be rotationally symmetric. Use of a single plate design in the drag means offers obvious
advantages in terms of cost of manufacture and ease of assembly and repair.
According to an embodiment of the invention a munition comprises a payload volume and a
fuze having a control means and a drag means The control means determines deviations of
the trajectory of the munition from a nominal trajectory and, at a determined time,
generates a control signal to effect deployment of the drag means. Preferably the control
means comprises a GPS receiver and a logic unit.
The GPS (Global Positioning System) receiver and logic unit can locate the position of the
munition by tri~ngl1]~fion with GPS satellites in linown orbits around the earth as is well
known in the art and can compare the evolving traJectory of the munition against a stored
nominal trajectory. This nominal trajectory can be based on a standard range and need not
be programmed for separate firing locations altllough specific target locations could be
chosen if required. Range corrections are effected by deploying the drag plates at differing
times.
According to a further embodiment of the invention the munition is a spin stabilised
munition and the deployment means comprises at least two retaining pins, the ret~inin~ pins
being arranged so that at least one retaining pin passes throu~h each drag plate in the
undeployed configuration A retaining pin removal means is provided for removing the
ret~ining pins from the drag plates on receipt of a control signal and the drag plates are
freely slidable between the undeployed and deployed configurations such that, in use,
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removal of the ret~ining pins allows the centrifugal forces on the munition to cause the drag
plates to slide to the deployed configuration.
Deployment of the drag plates under the action of centrifugal forces increases the simplicity
of the device and removes the need for internal pyrotechnic devices to push the plates
outward. The centrifugal forces experienced by a spin stabilised munition are quite
sufficient to effect deployment of the plates and retain them in the deployed configuration
during flight. Removable pins are again simple and inexpensive and can be made robust.
Preferably there are two retaining pins to reduce costs and complexity.
Further advantages and embodiments will be shown by way of example only with reference
to the following drawing in which;
Figure I shows a projectile having a drag means according to one
embodiment of the invention,
Figure 2 shows an exploded view ofthe drag means of figure 1,
Figure 3 shows the top of the projectile of figure I with the drag plates
extended,
Figure 4 shows an alternative design of drag plate
Figure S shows an embodiment of the drag means using the drag plate
design of figure 4.
Referring now to figure I a spin stabilised projectile, generally indicated 1, has a fuze 2
located forward of the payload volume 3. At the base of the fuze 2 is a drag means
consisting of a forward base plate 20, two pairs of drag plates 22, 24 and a rear base plate
26.
.~
The drag means is shown more clearly in figure 2. Rear base plate 26 is connectecl to the
forward base plate 20 by circular connecting member 30 (connection not shown in
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exploded view). Located between the base plates 26 and 20 are rearward drag plate pair
24, con~ tin~ of drag plates 101 and 103, and forward drag plate pair 22, consisting of
drag plates 105 and 107.
Each of the drag plates is generally semi-circular, having a ~ m.oter the same as that of the
munition and a semi-circular recess 32 to enable the plate to fit around connecting member
30 when in the undeployed configuration.
Base plate 101 has projections 34 and slots 36 and base plate 103 has projections 38 and
slots 40, the drag plates being arranged such that in the undeployed configuration
proiections 34 are accommodated in slots 40 and projections 38 are accommodated in slots
36. Similarly projections 42 of plate 105 fit into slots 44 of plate 107 and projections 46 of
plate 107 fit into slots 48 of plate 105 when in the undeployed configuration.
Projections 34 and 38 of plates 101 and 103 respectively are provided with rearward
projecting studs 50 which locate into tracks 52 in rear base plate 26. Similarly forward
facing studs 54 on projections 42 and 46 locate into tracks (not shown) in the forward base
plate 20 which run perpendicular to the tracks 52 in the rear base plate 26.
Each drag plate is also provided with a hole 56, the holes 56 being arranged so that when
all the plates are in the undeployed configuration then the holes 56 on plates 101 and 105
line up, as do holes 56 on plates 103 and 107.
Two retaining pins 60, 62 pass through the holes 56 in the drag plates in the undeployed
configuration and locate in recesses 64, 66 in the rear base plate 26. The ret~ining pins 60,
62 also pass through holes (not shown) in base plate 20 and are held by gas actuators 70,
72.
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The recesses 64, 66 and tracks 52 in the rear base plate do not extend through the rear base
plate 26 so that rear base plate 26 acts as a complete seal between the drag plates and the
rest of the projectile to prevent entry of moisture or dirt. Similarly the gas actuators and
ret~ining pins are sealed to prevent moisture entering the rest of the fuze through the holes
in forward base plate 20.
A removable cover may be provided around the drag plates in the undeployed configuration
to protect the drag means during storage. This cover would be removed prior to loading
similarly to the removable covers provided around the driving band of shells. Alternatively
a wax coating could be applied to the perimeter of the projectile around the drag means
which would prevent dirt from entering and jamming the drag plates but which would not
interfere with the deployment of the drag plates.
The plates may be conveniently made from either aluminium or steel. The thickness would
typically be 3mm for steel plates and 5mm for aluminium plates. Thus the drag means can
offer a substantial increase in drag whilst only taking up approximately 20mm in the
projectile. The plates may conveniently be made by stamping out the shape and friction
welding the studs onto the projecting members. Stamping offers an inexpensive and non
complex method of m~nnf~cture. Alternatively the plates could be machined to the desired
shape, but thicker than required, then the top layer could be rcmoved to leave the required
studs. The base plates are structural parts of the fuze and are constructed from the same
material as the fuze casing.
In use the projectile is launched with the drag plates held in the undeployed configuration
by retaining pins 60, 62. A GPS antenna 4 in the front of the fuze receives GPS signals and
a processor 5, powered by battery 6 tracks the projectiles trajectory and compares it to the
desired trajectory, however, it will be apparent to one skilled in the art that other sensors
could be used to monitor the trajectory of the projectile. An algorithm is used to compare
the actual with the required trajectory and calculate a deployment time for the drag device.
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The solution is continually refined throughout the flight until the deployment time is
reached, at which point a control signal is generated. The control signal causes discharge
of capacitors which activate gas actuators 70, 72 to pull the retaining pins 60, 62 forward.
The pins are pulled forward through the forward base plate rather than through the rear J
base plate 26 to prevent the possibility of launch stresses from falsely actuating the drag
means.
Once the pins 60, 62 have been removed the centrifugal forces due to the projectiles spin
cause the drag plates to move outwards. Studs 50 located in tracks 52 allow the plates 101
and 103 to move in a lateral direction only so that the plates slide outward until the studs
reach the end of the tracks 52. Similarly studs 5~ in plates 105~ 107 slide along the tracks
in the forward base plate which are perpendicular to tracks 52. It will be apparent that the
length of the tracks in the base plates and the positioning of the studs on the projections
define the amount of extension of the plates.
The top of a projectile with the drag plates in the deployed configuration is shown in figure
3. The extension of the plates is such that when fully deployed the corners of the plates are
overlapping. The corners overlap as the studs on the projections are not secured in the
tracks in the base plates and so without being sandwiched bet-veen the other pair of plates
and the base plate the drag plates could come completely away from the projectile.
An alternative design of drag plate are shown in figures 4. The drag plate 201 has
projections 203, 205 which are adapted to locate in slots 213 and 215 respectively of
another identical drag plate whilst leaving space for a central connecting member. The
plate 201 has two holes 220 located such that one design of plate can be used and the holes
of layers of plates will align.
A st~d 230 is located on projection 203 to locate in a track in a base plate. As only one
stud is used per plate the stud 230 is elongated in ehe direction of movement of the plate to
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prevent rotation of the plate about the stud. The projection 205 is present to aid in
deployment of the plates and could be omitted.
Figure 5 shows a drag means using the drag plate of figure 4 with the plates in the deployed
configuration. The extension of the plates is such that the plates do not overlap at all when
fully deployed. Therefore to retain the plates in position a middle base plate 90 is provided.
A further alternative design of drag plate is shown in figure 6. Here the drag plate 301 has
only one projection 303 and one slot 313. Again the drag plate is asymmetrical but
rotationally symmetric when interlocked with another identical plate.
The projection 303 is thicker than the drag plate 301, being raised above one surface by a
small amount, typically not greater than the thickness of the plate 301 itself. The increased
thickness of the proiection 303 extends to the outer edge of the drag plate. The raised part
ofthe projection 303 locates into a groove in a base plate, which aids in deployment ofthe
plates and gives rotational rigidity. A stud 330 is located on the raised surface of
proiection 303 and locates into a track in the groove of the base plate to define the amount
of extension of the drag plates.
The proiection 303 is only raised on one side of tlle plate 301, the other side being flat.
This keeps m~nllf~cture of the plates as simple and inexpensive as possible and is necessary
when there is no middle base plate, to enable the plates to slide over one another. ~t will be
apparent however, that where a middle base plate is used this could incorporate grooves to
locate raised parts of the drag plates or tracks to accommodate studs on the drag plates,
either in addition, or as an alternative, to those for location in the front or rear base plates.
The flat surface area presented by the extended drag plates is approximately twice the area
of the cross section of the munition. Deployment of the plates increases the drag on the
munition by about two and a half times which allows for a significant correction in range to
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be made. The increase in drag effected by the drag piates is therefore appl~Ain~alely double
that available from known braking means.
