US3508335A

US3508335A - Method of and device for establishing the correct lead required for firing a projectile at a moving target

Info

Publication number: US3508335A
Application number: US576102A
Authority: US
Inventors: Erik Wilhelm Sundstrom
Original assignee: Bofors AB
Current assignee: Saab Bofors AB
Priority date: 1965-09-06
Filing date: 1966-08-30
Publication date: 1970-04-28
Anticipated expiration: 1987-04-28
Also published as: NO116953B; NL6612179A; DE1274471B; ES331224A1; CH502574A; BE686446A; GB1155185A

Description

Ap 1970 E. w. SUNDSTROM METHOD OF AND DEVICE FUR ESTABLISHING THE CORRECT LEAD REQUIRED FOR FIRING A PROJECTILE AT A MOVING TARGET Filed Aug. 30, 1966 2 Sheets-Sheet 1 INVENTOR.

ERIK w/wzm sawpsmbkv April 28, 1970 E. w. SUNDSTROM 3,508,335

METHOD OF AND DEVICE FOR ESTABLISHING THE CORRECT LEAD REQUIRED FOR FIRING A PROJECTILE AT A MOVING TARGET Filed Aug. 30, 1966 2 Sheets-Sheet 2 I 48 a) R V 4.9 fia) r FIG. 3

Xozgw p q 52A wrs b'm ,4 52

T 7; -f T FIG. 4

INVENTOR.

ERIK W/LHELM savasredm BY n A r To/EWE r:

United States Patent US. Cl. 33-49 Claims ABSTRACT OF THE DISCLOSURE Initially a sight line and gun barrel are moved both at the same angular velocity relative to a moving target until the sight line and the barrel are aimed at the target. An additional velocity component angularly opposite to the concurrent movement of the barrel is then applied to the sight line for a selected interval of time while the barrel and the sight line are being moved to aim the sight line at the target during this interval of time. The additional oppositely directed velocity component is se ected so that the angular velocity of the line of sight is of the angular velocity of the barrel during the selected interval of time, at being a constant. At the end of the time interval the relative movement of the sight line and the gun barrel is stopped but aiming the sight line at the target is continued at an angular velocity equal to that of the barrel.

The present invention relates to a method of achieving a correct lead when firing projectiles against a moving target, and a device for carrying out the method. This method is particularly well suited for firearms mounted on track-laying vehicles, and can also be used with advantage on track-laying vehicles in which the weapon has a fixed mounting in the vehicle and it is thus aimed by steering the whole vehicle.

BACKGROUND It is previously known, for obtaining a lead when firing projectiles against moving targets, to allow the reticule in the sight to be given a momentary displacement, the size of which has been dependent upon the speed of the target and the time of flight of the fired projectile. However, such a means of achieving an appropriate lead when firing projectiles against a moving target involves considerable disadvantages, for instance in that the aiming of the Weapon is made diflicult by the sudden displacement of the reticule, and that in order to be able to achieve a correct lead, it is necessary to be able to obtain satisfactory data, rapidly, for the speed of the target and the time of flight of the projectile.

THE INVENTION Through the present invention, the above-mentioned disadvantages have been eliminated, and it has become possible to achieve the lead without any sudden displacement of the reticule, and the only setting required, apart from the actual tracking of the target, is the one that is based upon the calculated range to the target.

SUMMARY OF THE INVENTION The aforepointed out object, and other objects which will be pointed out hereinafter are obtained by establishing the correct lead for firing a projectile from a gun barrel at a moving target by initially moving the sight line and the gun barrel both at the same angular velocity relative to the target until the sight line is tracking the target and the gun barrel is aimed at the target. The sight line is then driven angularly and oppositely relative to the gun barrel at a constant times the angular velocity of the barrel for a predetermined time interval of time or times the time 1 while seeking to continue tracking the target, a being a constant and t the time of flight of the projectile from the barrel to the target. At the end of this time interval the relative movement of the sight line and the gun barrel is stopped but aiming the line of sight and the barrel at the target is continued.

The method of the invention may be carried out by an apparatus which comprises a sighting assembly including a carrier bearing a reticule. This carrier is so mounted that the reticule can be vertically and transversely displaced alternatively with or relative to the gun barrel which, in turn, can be elevated and depressed. A relative movement is imparted to the carrier proportional to and in opposition to the angular movement of the gun barrel. Reduction of said relative movement reduces the angular velocity of the line of sight in relation to that of the gun barrel by a factor where a is a constant. The relative movement is imparted to the carrier by transmission means which are operated by actuating means coupled to the transmission means for a set interval of time and uncoupled therefrom at the end of this interval. Uncoupling of the transmission means frees the carrier and thus the reticule to move at the angular velocity of the gun barrel.

DETAILED DESCRIPTION OF AN EMBODIMENT The invention will now be described in more detail, with reference to an embodiment shown in the attached figures. FIG. 1 shows, schematically and in perspective, a track-laying vehicle, where a gun mounted in a rotatable turret has been provided with a device according to the present invention. In FIG. 2 the design of the device indicated in FIG. 1 is shown, also schematically and in perspective, in more detail. FIG. 3 contains a diagram in which certain angular velocities have been plotted as a function of the time, and in FIG. 4 finally, a diagram is shown of the corresponding angular positions as a function of the time.

The track-laying vehicle shown in FIG. 1 is provided with a rotatable turret 2, in which the gun barrel 3 is mounted. The movement of the turret 2 is provided for by a motor 4, which is fixed to the turret and drives a gear wheel 5, which is in mesh with a gear ring 6 rotatably fixed to the vehicle 1. In the corresponding way, the elevating movement of the barrel 3 is controlled by the motor 7 which is fixed to the turret 2, and which via the gear wheel 8 engages in a gear segment 9, which is fixed to the barrel. The movements of the motors 4 and 7 are transmitted to a lead generator 10A supported by a sight assembly 10 supported by the turret 2 for movement in unison with the gun barrel, by means of flexible shafts 1.1 and 12. There is also a cable 13 connected to the lead generator 10A and to a timer 14, which, in turn, via the cable 15 is connected with the pedal 16, which can be actuated by the gunner when aiming the barrel 3.

The further details of the construction of the lead generator 10A are shown in FIG. 2. In the sight 10, with its eyepiece 17, there is a glass plate 18, which has thereon a reticule and constitutes a carrier therefor. This glass plate 18 can be displaced in its own plane, both horizontally and vertically. The horizontal displacement is achieved by means of the gear rack 19 which via the sliding holder 20 laterally positions the strip 21 which is fixed to the glass plate 18. In a corresponding way, the vertical displacement of the glass plate 18 is achieved by means of the gear rack 22, which via the sliding holder 23 laterally positions the strip 24 fixed to the glass plate 18. The movement of the gear rack 19 is achieved by means of the gear wheel 25, which is fixed to the shaft 26. On this shaft 26 also, the gear wheel 27 and the knob 28 are fixed. There is also a gear wheel 29 arranged, which is permanently in mesh with the gear wheel 27, which gear wheel 29, by means of a clutch, can be actuated by the flexible shaft 11 from the motor 4. This clutch consists of a disk 30, which can be displaced on the shaft 12, which by means of keys which can slide in grooves made in the shaft 11, always participates in the rotation of the shaft 11. The disk 30 is provided with a number of friction linings 31, which under the influence of the electromagnet 32 can be made to bear against the gear wheel 29. h electromagnet 32 receives its current through the

cables

33 and 34, which via the cable 13 are connected with the timer 14.

In the corresponding way, the gear rack 22 can be actuated by the gear wheel 35, which is fixed to the shaft 36 on which also the gear weel 37 and the knob 38 are fixed. The gear wheel 39 can be actuated, by means of the clutch consisting of the displaceable disk 40 with the linings 41 and the electromagnet 42, by the flexible shaft 12, which is connected with the motor 7. The electromagnet 42 is connected with the timer 14 via the

cables

43 and 44 and 13.

The timer 14 is provided with a pointer 45, which can be set at different values, and is connected via the cable 15 with a switch 46, which can be actuated by the pedal 16.

The device described above functions in the following way. When aiming at a moving target, the pointer 45 of the timer is set so that the timer 14 gives a time impulse which is proportional to the time of flight (t,,) of a fired projectile from the barrel to the target. The time a-t set on the timer l4 naturally depends upon the value which is elected for the constant a as well as on the distance to the target and the velocity of the fired projectile. When a suitable value of the constant a has been chosen (which should appropriately be between 0.5 and 3) and the velocity of the projectile estimated, only the distance from the barrel to the target need be determined. Thus, the scale for the setting of the pointer 45 on the timer 14 can be graduated directly in said distance.

When the timer 14 has been set at an appropriate range, and after the reticule and therewith also the barrel have been aimed directly at the target, by depressing the pedal 16, through which the switch 46 is switched on, the gunner can start the timer 14. Current pulses are then emitted from this timer through the

cables

13, 33, 34, 43 and 44, to the windings of the

electromagnets

32 and 42. The duration of this series of current pulses depends upon the setting of the pointer 45, and is to be at times the time t of flight of the projectile from the barrel to the target, i.e. Ot'l During the period of time (at-t for which the

electromagnets

32 and 42 receive current from the timer 14, the disks 30 and 40 Will be displaced in the direction towards the

gear wheels

29 and 39, respectively, and under the influence of the friction linings 31 and 41, respectively, these

gear wheels

29 and 39 will have the same speed as the shafts 11 and 12, respectively, during said period of time (ot'l This movement of the

gear wheels

29 and 39 is transmitted via the

gear wheels

27 and 37 to the

shafts

26 and 36, respectively, and from there via the

gear Wheels

25 and 35 to the

gear racks

19 and 22, respectively.

Due to the impulse emitted from the timer 14, the glass plate 18 with its reticule will therefore during the period of time (ix-t have a displacement depending upon the movements of the shafts 11 and 12, respectively. During the time interval tit-t the gun barrel is to move through the angle co et-t traveled by the target plus the angle w t which is the proper lead angle. Therefore should be the average angular speed of the barrel relative to the craft during that interval. If the sight line is made to track the target still moving at w during that interval, its average angular speed realtive to the craft will be m which from the above is a rx/ 1+a) times the average angular speed of the barrel during that interval. The difference between the average angular speed of the sight line relative to the craft and the average angular speed of the barrel relative to the craft is that is, l/(l-i-a) times the average angular speed of the barrel and in the opposite direction. Through appropriate designing of the different gear wheels, it is achieved that this displacement of the glass plate 18 is proportional to the tracking movement of the barrel, but in a direction opposite the last-mentioned movement, and will also have an angular velocity which is only 1 +0: of the angular velocity of the barrel. In this way, the glass plate 18 with its reticule is displaced in relation to the sight 10 in a direction opposite the movement of the barrel, and in this way the sight is given reduced angular velocity relative to the barrel movement which is only 1 +0: of the speed of said movement. This displacement of the glass plate 18 with its reticule in relation to the sight 10 takes place only during the time (at-t which has n set, and after said time the reticule and sight do not move relative to each other, but both follow the rate of movement of the barrel exactly.

When the projectile has been fired with the lead desired, the position of the reticule in relation to the sight can be set back again with the aid of the

knobs

28 and 38.

The eifect of the displacements and movements described above are appropriately explained in more detail with the aid of the two diagrams in FIGS. 3 and 4. FIG. 3 shows the angular velocity u: in relation to a fixed base for the target and the barrel and the reticule as a function of the time T. The angular velocity to is plotted as ordinate, while the time has been plotted as abcissa.

On the time axis, T is the time when the gunner, by depressing the pedal 16, starts the timer 14, and T is the time when the timer interrupts the emission of current pulses at the end of the time interval axr The speed of the target m is assumed to be constant, and is indicated in FIG. 3 by the straight double line 48. Up to the time point T it is assumed that both the barrel and the reticule move with the same angular velocity as the target, and their movements will thus coincide with the line 48 up to the time T At the time point T as mentioned above, the reticule obtains the extra component of movement in a direction opposite the tracking movement of the barrel, and this involves that the angular velocity of the sight line in relation to the fixed base during the time immediately at the moment of time T will be somewhat lower than the speed of the target, which is shown in FIG. 3 by means of the dashed line 49. However, the gunner will try to cause the reticule to follow the moving target, and the barrel will thereby have a higher angular velocity than the target. The speed of the barrel is shown in FIG. 3 by the heavy curve 50. At the time point T the gunner has managed to set the reticule so that it coincides entirely with the position and speed (m of the target. At the time point T the barrel will thereby have a speed corresponding to At the time point T the current through the

electromagnets

32 and 42 is switched off, and the displacement of the glass plate 18 with its reticule in relation to the sight ceases. Therefore, at the same time point (T the angular velocity of the reticule suddenly increases from m to As the gunner still tries to follow the target with the reticule, after the time point T the speed of the reticule and thereby also the speed of the barrel will be decreased to the speed m of the target, and will eventually coincide entirely with this speed.

The way in which the variations shown in FIG. 3 as regards the angular velocities of the reticule and the barrel will affect the angular positions is shown in FIG. 4.

Here the angular position to in relation to a fixed base has been plotted as ordinate and the time T as abscissa. As the speed of the target is assumed to be constant, its angular position will increase uniformly during the whole of the time, and will follow the straight double line designated 51 in FIG. 4. Up to the time point T both the barrel and the reticule have the same angular velocity as the target, and its angular positions will therefore follow the line 51 up to this time. At said time point T the angular velocity of the reticule will be reduced to and this has the result that, immediately after the time T the reticule will assume angular positions which fall short of the angular positions of the target obtained for the corresponding times (according to the double line 51). These deviating angular positions are indicated in FIG. 4 by the dashed line 52. However, the gunner tries to make the reticule coincide with the target as closely as possible, and this has the result that the barrel is given an increased speed in relation to the target, and after the time point T the angular position of the barrel will be somewhat in excess of the corresponding angular positions of the target (according to the double line 51) and these larger angular positions in relation to the target are shown in FIG. 4 by the curve 53, drawn with a heavy line. At the time point T (otX! after the time T the gunner has succeeded in making the angular position of the reticule coincide with the angular position of the target, and during the interval between the times T and T aXt both the reticule and the target will have moved to the angle al Xw Between the times T and T the barrel constantly has an angular velocity which is times greater than that of the reticule, and this signifies that the angular position of the barrel at the time T will be at X greater than the angular position at the time T The differences between the angular position of the barrel and the angular position of the reticule and the target at the time T will therefore amount to t Xw which is the correct lead that it is desired to obtain. Immediately after the time T the reticule, as shown by FIG. 3, will have a greater speed than the speed of the target, which, however, can comparatively quickly be reduced by the gunner, so that immediately after the time T the speed of the target and the reticule and the barrel will coincide. This is shown in FIG. 4 by the increased angular position of the reticule (the dashed line 52A) immediately after the time T and a corresponding raising of the line 53. When the gunner has made the speeds of the reticule and the barrel with the target movement, the angular position of the reticule will coincide with that of the target, i.e. it will follow the double line 51, while the angular position of the barrel will be changed according to the part of the line 53 running parallel with the double line 51 at a distance of t Xw from same.

To summarize, it can thus be established that, by giving the reticule a reduced speed relative to the barrel, which is only of the speed of the barrel during the time interval T -T (=atXl and by the gunner trying to make the reticule coincide with the target, immediately after the time T the desired lead of the barrel r td will be obtained automatically.

In the example described above, the extra component of movement of the line of sight in the direction opposite the tracking movement of the barrel has been achieved by the reticule having been displaced in relation to the sight. It would also be possible to have the whole of the sight move in the way intended in relation to the barrel. The time interval fixed nt-t can, of course, be obtained in some way other than by means of a timer graduated for the range to the target. Thus, it would be possible to obtain this time function directly from a range-finding instrument, the setting device of which could possibly be mechanically connected to the pointer of a timer. Furthermore, the movement of the reticule can be complemented in such a way that, before taking out the lead, the tangent elevation and the corrections desired, eg for the influence of the wind, powder, temperature etc., can be set with the

knobs

28 and 38. Furthermore, the two

knobs

28 and 38 can be replaced by motors, so that automatic resetting of the reticule is obtained, and these motors will effect the above-mentioned setting of corrections.

The present invention can also be used in cases when the tracking movements of the barrel in relation to a fixed base cannot be registered directly. This is often the case, for instance, with track-laying vehicles with firearms in fixed mounting so that the aiming of the gun barrel must be carried out through movements of the whole vehicle.

In such cases, the changes of the angular position of the barrel are measured continuously in relation to a gyroscope, during the fixed period of time axis, and at the same time, a servomechanism gives the line of sight an extra component of movement, which has a direction opposite the movement of the barrel in relation to the gyroscope and an angular velocity which is 1 +0: of the angular velocity of the last-mentioned movement, whereby the movement of the line of sight in relation to a fixed base will be reduced in relation to the movement of the barrel and is given an angular velocity which is only times the angular velocity of the barrel.

In the claims:

1. In a method of determining the correct lead re quired for firing a projectile from a gun barrel at a moving target, the steps of:

initially moving the sight line and the gun barrel both at the same angular velocity relative to the target until the sight line and the barrel are aimed at the target;

then applying to the sight line an additional velocity component angularly opposite to the concurrent movement of the barrel for a selected interval of time while moving the barrel and the sight line to aim the sight line at the target during said interval, said interval being a constant at times the time of flight (t of the projectile from the barrel to the target, said additional oppositely directed velocity component being such that the angular velocity of the line of sight is 1+0: of the angular velocity of the barrel during said interval, a being a constant; and

stopping at the end of said time interval the relative movement of the sight line and the gun barrel and continuing to aim the sight line at the target at an angular velocity equal to that of the barrel.

2. In a method of determining the correct lead for firing a projectile from a gun barrel at a moving target, the steps of (a) initially moving the sight line and the gun barrel both at the same angular velocity relative to the target until the sight line is tracking the target and the gun barrel is aimed at the target;

(b) then driving the sight line angularly and oppositely relative to the gun barrel at a constant 1+0: times the angular velocity of the barrel for a predetermined interval of time at times the time t while seeking to continue tracking the target where a is a constant and t is the time of flight of the projectile from the barrel to the target; and

(c) at the end of said time interval stopping the relative movement of the sight line and the gun barrel and continuing to aim the sight line and the barrel at the target.

3. The method according to claim 2 wherein said constant a is selected in accordance with the desired firing accuracy and the velocity of the target, the selected value being within the range of 0.5 and 3.

4. An apparatus for determining the correct lead for firing a projectile from a gun barrel at a moving target, said apparatus comprising in combination:

a gun barrel mounted to be elevated and traversed;

a sighting asembly including a carrier bearing a reticule, said carrier being movably mounted for vertical and transverse displacement of the reticule alternatively with or relative to the gun barrel;

transmission means coupled to said carrier for imparting to the same a relative movement proportional to and in opposition to the angular movement of the gun barrel, said relative movement of the carrier with reference to the gun barrel reducing the angular velocity of the line of sight in relation to that of the gun barrel by a factor JZL 1+ where a is a constant; and

actuating means adapted to be coupled to said transmission means and means operable to couple said actuating means for a set interval of time, and to uncouple said actuating means at the end of said interval, the carrier then being free to be moved at the angular velocity of the gun barrel.

5. The apparatus according to claim 4 where said transmission means and actuating means comprise power drive means and gear means for displacing said carrier by said drive means to etfect vertical and transverse displacement respectively of the carrier and thus of the reticule; and wherein said operable means comprise clutch means for coupling the gear means to the drive means, said clutch means biased into a disengaged position, timer means connected to said clutch means to move the same into a position of engagement for said set time interval, and means operable to activate said timer means for the aforesaid purpose when the line of sight tracks the target and the gun barrel is aimed at the target.

References Cited UNITED STATES PATENTS 1,936,442 11/ 1933 Willard.

2,012,960 9/1935 Coupland.

2,356,189 8/1944 Tufts.

2,407,191 9/1946 Tear et al.

2,569,5 6O 10/ 1951 Ford.

2,690,014 9/1954 Draper et al.

ROBERT B. HULL, Primary Examiner