US2526677A - Sight for moving targets - Google Patents

Description

Oct. 24, 1950 r L. MACKTA I 2,526,677

SIGHT FOR MOVING TARGETS Filed April 11, 1945 I 2 Sheets-sheaf. 1

IN V EN TOR. LEO MACKTA ATTORNEYS BY v L. MACKTA SIGHT FOR MOVING TARGETS Oct. 24, 1950 2 Sheets-sheaf 2 Filed April 11, 1945 INVENTOR. LEO MACKTA ATTORNEYS- 1 effective range.

Patented Oct. 24, 1950 UNITED STATES PATENT OFFICE 2,526,677 SiGHT FOR MOVING TARGETS Leo Mackta, Brooklyn, N. Y.

Application April 11, 1945, Serial No. 587,818 '7 Claims. (01-. 33-49) (Granted under the act, of .March a, 1883, as

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

The invention relates to a gun sight specially,

suitable for use on guns directed against rapidly -moving targets at moderate ranges, as involved in battle with airplanes and land vehicles. The weapon usually involved is a machine gun, pivoted for direct manual transverse and elevation, known as a flexible gun.

In the situations which frequently develop in such actions, the necessary lead may ultimately be found by noting the courses of tracer bullets included in the ammunition at intervals, and:-

swinging the gun accordingly. But ofttimes the variance between the gunners estimate of the necessary lead and the actual requirement, together with progressively varying requirement due to target progress, results in considerable de-,

lay in getting the fire on the target; and, indeed, in man instances there is a complete failure to attain accurate fire before the target is beyond This is accompanied by great waste of ammunition, and even when the projectiles are gotten on the target, it is usually late in the period of encounter, so that effective placement is usually not accomplished. When the encounter actually occurs, the target is at close range and there are only four or five seconds Within which the fire of a gun with the necessary quick traverse can be effective. Under these conditions, in prior practice when the personal factors, such as good judgment of distance, elevation, speed, and bullet times; determination of operation of the gun in traverse and elevation, operation of the trigger, psychological reactions and time factors of motor reflexes, have become manifest,

there is often no possibility of accurate action of the Weapon, and the fire is purely chance hit-ormiss with a general direction toward the target.

It is therefore an aim of this invention to remove from the gunner the need for basing the aim of the piece on observation of preliminary trial bursts to determine whether the necessary lead i is included in the angular relation of the bore axis to the line of sight, so that an early placement of projectiles on the target may be efiected within a short period of encounter, with correspondingly 1 increased chances of placement in vital or crippling spots on the target.

It is a specific purpose to embody a sight device with included functions of such nature that, as to lead, the gunner only has to keep the view of amended April 30, 1928; 370 0. G. 757) trolling the function of the gun sight in a novel way.

The invention seeks also to present: a novel structure in a sight for enabling the automatic assurance of correct lead if the gunner simply maintains the image of the target within simple stadia lines, which constantly movein accordance with the rate of movement of the target across the fieldof view in th sight device at the given range. It is a special purpose to provide the gunner with a device coordinated with front and rear sights, which may be controlled from a range finder, a part of the device having an angular lateral movement at a rate accordingto the required deflection of the gun from the line of sight, ,co-

ordinated with the range and speed of the target,

so that the gunner need only'deflect thegun until a laterally moving part in the sight remains in registry with the target in order to assure the proper lead, after which firing may be begun.

Additional objects, advantages and features of invention reside in the construction, arrangement and combination of parts involved in the embodiment of the invention, as will be apparent from the following description and accompanying ified mounting;

drawings wherein:

Fig. 1 is a side elevation of a gun, mount, and sight system, constructed in accordance with my invention; Fig. 2 is a front view thereof; Fig 3 is a top view showing the gun with the bore axisat an angle to the line of sight; Y j Fig. 4 is an elevation partly insection of a mod- Fig. 5 is a section on the line 5 5 Greg. 4;

v Fig. 6 is a rear elevation ofan elevation tracking sight mounting;

Fig. 7 is a side elevation thereof. There is illustrated a tripod mount element Ill,

which may conform to conventional practice for a gun of the caliber and weight selected for use with my invention, and on the tripod there is freely rotatable on a vertical axis a bracket H I having upstanding arms I2 between which a cradle i2 is pivoted on a horizontal axis for elevational movement. The cradle carries a gun l3, which may be of any of several kinds suited to the use indicated, and is therefore only formally shown here, my invention being adaptable to use with the several kinds by suitable adaptation of the sight elements and supports. While I have shown the invention with a sight axis close above the gun, it will be clear that this is not essential and that the support elements by which the sight elements are mounted on the gun or cradle may be extended to permit the use of conventional magazines and shields.

The cradle includes a base bar [4, at the forward end of which an upstanding standard I5 is provided, on the upper end of which the barrel l6 of the gun is pivoted for transverse movement of the breech end on the cradle. The cradle is provided at its rear end with a horizontal sector guide rail ll concentric with the standard [5. The gun is provided with a grip I8 on its underside, the lower end of which rests slidingly on the guide l1. The guide is grooved as at H on its rear edge and the grip has a retainer plate l9 fixed thereon, extending downwardly beside the guide and having an inturned flange engaged slidingly in the groove [1' to prevent the rear part of the gun from swinging loosely upward relatively to the cradle. A trigger 20 for the gun action, may be conventionally located and operative adjacent the forward side of the grip.

The cradle is provided with a cradle grip 2|, fixed on the rear end of the bar l4 and projecting somewhat toward the left and rearwardly, although it may be otherwise positioned as the construction of the gun and developed firing practice may require.

The gun pivot on the cradle includes a ring 22 pivoted on the standard l5, through which the barrel extends, but is releasably secured therein by pins 23 inserted through the ring and into a collar 2-13 fixed permanently on the barrel. The ring has a front sight 25 comprising an upstanding tapered rod 26 set in the upper side of the ring, at the extremity of which a sight bead is fixed, constituting the front sight 25 proper in my invention.

At the rear end of the cradle a rear sight arm 2'! is fixedly mounted on the rear end part of the bar, being bowed rearwardly to afford a clearance to permit a gunner at the rear of the gun to readily reach the gun grip I3 with one hand, and at the upper end of this arm a rear sight is mounted consisting of a ring sight 28 or other, suitable to the uses indicated. An example of alternative use not here illustrated, is the direct sight device such as one known as the reflex sight, with or without the front bead 25, the reflex sight being of such function that the bead 25 may not be needed.

On the gun, spaced a suitable distance forwardly from the rear sight, there is mounted an upstanding bracket arm 29, on which there is revolubly mounted a stadia disc 3!}, which in the 36 suitably mounted fixedly on the gun. A speed reduction element 31 is indicated as included between the motor 38 and pulley 35. Flexible electrical power and control lead-in cables 39 are indicated, leading to the motor and a motor speed control device 40, which is formally represented. It is contemplated that this control device will be remotely operated, or that the motor will be otherwise remotely controlled so that its speed will accord with a range finding made at the remote station of control and signal or control currents transmitted from the remote station; these details being well understood, forming no novel details in this invention, and therefore not illustrated.

On the disc 30 there is delineated, by marking or grooving, a volute figure, scroll or spiral 4| consisting of a continuous line beginning at or near the center of the disc and extending counterclockwise in circumvolutions of gradually increasing pitch or divergence from a concentric direction, throughout its length. Thus at the inner part, the successive convolutions are quite closely spaced, but toward the outer part of the disc the spaces between the mutually adjacent parts of the line are successively more widely spaced, until at the outermost part the convolutions are comparatively widely spaced.

When the gaze of a person is directed through the disc to a distant object, and fixed so, while the disc rotates, the spiral line on the disc will create the impression of outward or inward movement from or toward the axis of the disc according to the direction of rotation of the disc; This apparent movement may be only hazily seen, due to the observers vis'ion not being focused so near, but may be noted very definitely, nonetheless. It may be made more definite by including a number of radial stationary bars 42 on the bracket 29, and these may support a guard ring 43 to protect the disc 30.

It is the purpose to make this apparent lateral movement of the spiral coincide in angular rate with the angular rate of motion of a target transverse to the direction of gaze (taking the gun pivot as the center of these angular motions) when the movement of the spiral is noted through that concentric ring or zone on the discwhich is located in the line of sight when the gun is moved azimuthally to the proper angle to the bore sight to give the necessary lead to a projectile fired during such coincidence.

With the gun stationary, this simulated lateral movement of the spiral may be in the samedirection and at the same rate as those of a target viewed through the disc, and by having the pitch less than necessary inwardly of the d'esiredzone on the disc and greater outwardly of such zone, there will be coincidence of the target" movement and apparent radial movement of the scroll only when the target is seen through the limited zone where the scroll'has theproper pitch. This';'zone may be so located or distant from the axis ofthe disc that at the instant of. such sight coincidence, the axis of the .gun will be at the proper angle to the. line of sight, so thata projectile fired on the instant will reach the projected path of .the target at the moment the target reaches the intersection. In effecting this function the spiral'must be rotated at a rate proportionate to the known range and speed of the. target and remote control means. are provided to rotate the disc at speeds variable at will.

The scroll illustrated is simply suggestive and may require to be varied to fit a particular ammunition and target, but there are certain constants affecting its form which are customarily used in computing trajectories, and'bywhich a workable device may be embodied. Thus it is convenient to assume a target speed of 200 miles per hour as a minimum or average speed for computations to fix on a definite pitch, and a standard ammunition for antiaircraft combat involves a known muzzle speed of 2600 feet per second for the bullet, with a known deceleration and gravity drop. The latter and trajectory factor, or harmonization, may be disregarded in the present case.

The variation in range distances for which any sight device can be effective is limited at a minimum short range, at which the decrease of range, and acceleration of relative angular rate of movement of the target, as well as changes of direction of the target, are so rapid and uncertain as to leave too little time for perception, mental reaction, and motor reflex action by the gunner. Consequently, at some point, he must abandon all attempt at use of a sight, however effective, and rely on direct observation of tracer paths and reckoned or instinctive aiming 0f the piece. It may be assumed for the purpose of explanation that something less than 600 feet is the minimum range to be included in my sight element, and that the speed of the bullet is as above stated.

Also, as effective antiaircraft fire with small machine guns cannot with present ammunition be effectively carried on at ranges much over 1500 yards due to deceleration of the bullet, it will be sufllcient to design the device for ranges between 400 feet and about 1500 yards, or somewhat further.

On this basis, a minimum speed of rotation of the disc appropriate to the maximum range may be used, with means to increase the speed when targets at shorter ranges are fired on.

This speed may, for the purpose ofexemplification be arbitrarily set as one turn per second.

This rate of rotation might be chosen for a maximum range of 1000 yards or more, but for convenience it may be assumed here that 500" yards shall be the maximum range at which an encounter will be undertaken.

On account of the highly effective flight or flat trajectory of the bullet in the ordinary ranges of battle with airplanes and tanks, there is not a change in the lead angle proportionate to comparatively wide differences in range, but there is a wide variance in the rate of movement of the target angularly, proportionate to the range.

Thus the flight time of the bullet decreases so much as the range decreases, that the same or nearly the same angle of lead will be effective on the same moving target over a substantial variation in ranges, especially as experience has shown that more effective fire may be obtained by using And there is little difference in the angle of lead for such target when at a range of 500 yards.

At the 600 foot range, however, the plane moves at an angular rate of about 500 mils per second and at 400 feet moves over an angle of about 700 section. At intervals it-is provided-with idler,

mils per second, and the traverse is then gov;-

erned by keeping the target in the sight and '7 manipulating the speed of thedrive to the disc manually. to maintain the lead at different rates, and in the same zone or area of the disc in each instance or in ,such other zone as required.

Thus if the disc, is rotating two and one half times per second for a 600 foot range, it'would be rotated three androne half turns per second for a 400 foot range. At a range of 600 feet the bullet flight would occupy 0.23 second, and a crossing target at the speed assumed would travel approximately 69 feet or over an angle of mils. The target movement in one second would subtend an angle of approximately 500'mils.; At 500yards range the bullet flighttime is known to .be 0.6 second, the target moving in that time 1 over a distance of 180 feet or an angle of mils.

The rate v of movement of the target angularly azimuthal plane of the target, that portion or zone of the disc intersected by the line of'sight at that position of the gun should have the spiralv line thereon so inclined and curved eccentrically that the spacing between one and the-next is 200 mils within the zone indicated representing by rotation of the scroll the rate of angular change of position of the target at the range of 500 yards. H

With such pitch in the particular'part of the scroll at the line of sight, and rotating one turn per second, the intersection of the convolutions with a horizontal radius of the disc axiswou-ld move radially inward or outward (according to the direction of rotation) at the rate; of. 200

mils per-second. Toward the center of the pitch should be increased progressively in a degree proportionate to some determined ratio between shorter range measurements and rates of rotation of the disc, and also proportionate to various target speeds at the one range. In consequence, coincidence between angular movement of the target and the apparent movement of the scroll convolutions will occur only in that'zone of the disc which will define the proper angle of lead when intersected by the line of sight through the center of the rear sight ring 28 and across the bead 25. I

The ratio of change of pitch may be' coordinated with movements of a target angularly when approaching on paths oblique to.the'1ine' of sight, the inner part of decreased pitch servin'g to enable properIlead to be; maintained; when-2 the path of the ea-rget is at fangles iof less"than I 90 degrees to the line of sightJT-he outeripart of the scroll having the greatest pitch'ifw'illl :be f useful for planes'crossing at short'distancesi or' moving at greater rates of I speed at 1 greater.

ranges. r v

In Figs. 4 and 5 there is shown a mounting of the disc: enabling sighting therethrough very close to its axis without obstruction by,v the mounting or driving pulley. d

'In this instance a low hollowpedestal or foot piece 45 is formedwith a circular frarne or ring 46. thereon having a generally U-shape in cross rollers, two indicated at 41 in the upper partof 4 V disc from "Eerie j I i the pitch of.-:the spiral should be progressively less, and outwardly of the zone referred to the the ring and one centrally located at its lower part. These rollers have central ribs 48 which set in a deep circumscribing groove 49 'of a mounting ring 50, supporting a discl which is identical with the one 30, except that it does not have an axial mounting shaft, but is exposed to view throughout its area to the center. The disc is held by screws or other fastenings to an inwardly projected flange 52 of the ring 50. The pedestal 45 is hollow and has two idler pulleys 53 therein close to the ring 50 and the pedestal extends downward outwardly of these pulleys to respective openings in the base of the pedestal. An endless cord 54 is engaged around the ring 50 in the groove 49, passing inwardly around the idler pulleys 53, through the base of the pedestal and to the operating unit 36 before described.

That portion of the scroll line disc-which at any moment is apparently moving radially at the same angular speed as the target may be considered as the stadia element for the current encounter and will be distinguished from the remainder of the scroll by its coincidence in rate of movement with the rate of movement of the image of the target, or apparent static relation to objects on the landscape.

In the use of this invention embodied as described, upon selecting a target for encounter, the gunner sets the gun at a zero traverse position, parallel with the bar l4, and centers the target in the sights by rotating the cradle in azimuth and elevation so that the line of sight passes through the centers of the ring sight 28, center of disc 38 and bead 25. Then, upon receipt of a signal that the director or other c0ntrol has made range contact-that is, that a range and target lead equivalent in rate of rotation of the disc 30 has been established, the

cradle is kept stationary on the bracket I I while.

the gun is traversed, until the angular change of position of the target appears to be the same as the corresponding rate of apparent radial movement of the scroll. In other words, the target appears to remain for a moment in a'stationary relation to one or more of the convolutions of the spiral line. Immediately then the gun is held stationary on the guide rail I! while the cradle is moved in traverse so as to maintain the target in this relation to the scroll line, while the trigger of the gun is operated. Thereafter, pointing may be entirely or in part governed by observation of tracer paths, or further pointing may be continued with entire dependence on the scroll sight.

It ma be appreciated that if traverse of the cradle is not started soon enough the target will move out of the zone of the disc 30 where the ,described apparent coincidence of angular rate of the scroll andtarget exist and the scroll will then appear to have a faster or slower angular rate than the target, according to the direction of the latter. Correction can then be accomplished by moving the cradle faster or slower than required to stop the target relatively in the zone of the disc where it was located on beginning the cradle movement, and the target will thereby be soon brought into agreement with the scroll rate in the proper zone. Corrections may also be made from time to time by swinging the cradle and gun as a unit so that the motion of the target is toward the annular medial zone of the disc (between center and primer) and then beginning tracking again as soon as fixed registry of the targetcand. scroll line. is again secured.

If desired a grip-released. latch or other means, not illustrated, may be used to hold thegrip l8 or plate l9 to the sector IT releasable by gripping the grip Iain the handypreparationto adjusting the gun in azimuth 0n thecradle,

For convenience in illustrating the principle of the invention, it is shown in Figs. 1 to 5 applied to azimuth tracking only which would be useful for instance against tanks on level terrain, or against naval.v craft. from a land emplacement. Elevation functioning of the" invention may be effected by adding the necessary structure to enable corresponding vertical adjustmen of the sight 28 around the axis 23. l 1

In Figs. 6 and 7, there is indicated a simplifie means to import automatic elevation corrections, consisting in mounting the rear ring sight 28 on a curved bar 60 (corresponding'to thearm 21) which is concentric with the pins 23, adjustable in a guide 6| on the frame of the grips 21.

This guide has a slot similarly. curved with the same center, receiving the lower end .of the bar 60 slidably, and by means of an adjusting knob 62 and the bar 69 may be adjusted-vertically in the same manner as the azimuth adjustment is secured. Thus far an approaching target, after the equivalent of range has been established in the rate of rotation of the disc, the bar 60 is raised, while the cradle is elevated so that a line of sight is maintained on the target and the vertical apparent movement of the scroll lines finally coincides with the vertical angular movement of the target. The bar 60 is then secured and tracking proceeded with as before explained. Components of both azimuth and elevation may be obtained by utilizing the two adjustments appropriately. a

I claim:

1. In a gun sighting system, a frame" mounted for movement in traverse, sighting means carried by said frame to determine a line of sight to=a target, a gun carried-by said frame for angular movement over a limitedfrange with respectto said frame, first meansmova'blewith sjaidgun and defining a spiral rota'table.aboiitits in a plane normal to the bore of said gun, said line of sight intersecting said spiralforall angular positions of said gun and frame, and means operable to rotate said firstmea'ns. 1

2. In combination, a azimuthally pivoted gun mount structure, a front sight. thereon, a rear sight thereon, a gun azimuthally pivoted ,on the mount structure, a stadia sight element thereon comprising a planiform transparent disc mounted on the gun for rotation on the symmetrical axis of the disc, in a plane normal to the bore axis and spaced from the said pivot of the gun, saidclisc having a scroll figure formed thereon symmetrically with respect to said axis, and extending laterally to include the line of sight of the front and rear sights under lead movement of the gun on said mount, and means to rotate the disc at a predetermined speed variable at will. v

3. The structure of claim 2 in whichs a id scroll figure has convolutions progressively increased in pitch from its inner part to its' outer part.

4. In a sighting system. for a gun, a" frame mounted for movement in elevation about a fiirst axis, means mounting said gun on said frame for angular move in train relatively thereto about a second axis substantiall perpendicularto said first axis, spaced sights carried by said frame and defining a, line of sight parallel to the bore of said gun in one position of the latter on said frame, means defining a rotatable spiral movable as a unit with said gun and interposed across said line of sight for all angular positions of said gun relatively to said frame, and variable speed means connected to efiect rotation of said spiraldefining means.

5. In a lead-determining system for agun, a transparent plate having a spiral comprising a plurality of convolutions delineated thereon, means adapted to mount said plate on said gun to lie in a plane normal to the bore axis of said gun and for rotation about an axis parallel to said bore axis, and variable speed driving means for continuously rotating said plate about its said axis at a speed variable in accordance with the range and speed of a target.

6. In a lead-determining device for a gun, a transparent disc having a spiral delineated thereon of increasing pitch from the origin outwardly, means adapted to mount said disc on a gun for rotation about an axis through the origin of said spiral, normal to said disc and parallel to the bore axis of said gun, variable speed means connected to rotate said disc, a frame, sighting means carried by said frame and determining a line of sight fixed relatively thereto, and means adapted to pivotally mount said gun n said frame at a point spaced along the bore thereof from said disc.

7. In a lead-determining sight for a gun, a frame adapted to be mounted upon said gun and including a ring adapted to lie in a plane normal to the bore axis of said gun, a transparent disc, rollers journaled at spaced points about REFERENCES CITED The following references are of record in the file of this patent:

. UNITED STATES, PATENTS Number i Name Date 1,107,163 1 Grauheding Aug, 11, 1914 1,127,230 Grauheding Feb.'2, 1915 1,724,093 Kauch et al. Aug. 13, 1929 2,372,613 Svoboda Mar. 2'7, 1945 2,396,701 Holschuh et al. Mar, 19, 1946 2,401,530 Vought June 4, 1946 2,407,191 Tear et al Sept. 3, 1946 2,426,744

'Pontius et a1 Sept. 2, 1947

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