US2520943A - Computing sight - Google Patents

Description

Sept. 5, 1950 A E. H. L UDAEMAN'A n A 2,520,9434

COMPUTING SIGHT `Filed Aug. 5, 1947 4 shets-sheef 1 E. H. LUDEMAN c`oMPUTING .SIGHT Slept. 5, 1950 4 Sheets-Sheet 2 Filed Aug. 5, 1947 l ln/veniva Edwin Lud emu-n.

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Sept. 5, 1950 v E. H. UDEM`AN COMPUTING SIGHT 4 Sheets-Sheet v3 Filed Aug. 5, 1947 Y SSN E dwn H- Ludemnn Mza.

SePt- 5, 1950 E. H. LUDEMAN 2,520,943

COMPUTING SIGHT Filed Aug. 5, 1947 4 Sheets-Sheet 4 Fig- 7 l E dWin H. Ludemun l Wma/MMM Patented Sept. 5, 1950 UNITED STATES FTENT OFFICE (Granted under the act of March `3, 178823, as amended pril 30, 1928; 370 0. G. 7577) 27 Claims.

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

This invention relates to lead-computing gun sights. It is well known that, to efeetively engage a moving target in combat, the gun must be aimed ahead of the target by an angle that is a factor of range, average velocity of the projectile, and speed of the target. In making such computations, the assumption is necessarily made that the target will continue in rectilinear moven ment at constant Velocity during the time of flight ci' the projectile. Under such conditions, the angle of lead is the angle subtended at the gun by a distance equal to the productof velocity of target and time of flight of the projectile, such distance being laid on along the path of the target projected ahead of the position of the target at the time the gun is fired.

It is therefore an object of my invention to provide a lead-computing gun sight that is entirely self-contained and that, except for .one manual adjustment, operates automatically to compute and apply the necessary lead-angle merely by the act of keeping a sight trained upon the target.

A further object is to provide a sight of the type described wherein reticle lines are projected into the eld of view and are automatically moved and manipulated by the operation of the gun in tracking the target so .that the gun has the proper lead when the target is properly positioned or framed between the reticle lines.

Another object is to provide a leadecomputing sight of the type aforesaiclwherein the apparent spacing of reticle range lines is varied in accordance with a function of the angular velocity of the target and range.

A still further object is to provide a leadcomputing gun sight wherein an image of the reticie lines is projected into the'eld of view including the target and the observable images varied along each of two mutually-normal coordinate axes in accordance with the .angular velocity of the target from the gun position.

Another object is to vary the relation ofthe scale of reticle lines in the field of View of the telescope to correct for differences between the actual and measured angular rates of the gun.

A further object is to provide .an angular raterneasuring mechanism wherein the settling time oi theinstrument, that is, the time required for the instrument to reach 1a .steady state, varies in accordance with a function of the rate measured.

Yet another object is to provide an angular ratc-measuring mechanism which .is highly .accurate and sensitive to small changes iny angular rates and which, at the .sametinarnayzberene -2 dered insensitive to high rates, as when the gun is slet/,ed to piel; u p a new target.

Still another object is to provide a lead-computing gun sight that is, except for an initial setting for range, automatic in operation, that is operable if desired, by one person, relatively simple in use, inexpensive to construct and capable of being used to a high degree of accuracy.

Another object is the provision of a method of determining the lead angle for a moving target by the mere act of moving a gun to maintain a line kof sight directed thereon.

@ther objects and advantages of my invention Will become :apparent as the description proceeds.

AIn the drawings; 1

Fig. l isa velocity diagram taken in a plane determined by the gun position and target `path and showing the principle upon which my com'- puter operates;

Fig. 2 is a vector diagram showing the lfactors determining the angle substended at the gun by the. assumed sphere lof diameter equal to the wing span of an aerial target;

Fig. 3 is a perspective View of the left side of a gun equipped with my lead computer and showing the manually-operated elevation and azimuth controls and their `extensions to the computer proper;

Fig. 4 -is .side elevation of .the computer With cover plate removed;

Fig. 5 is a sectional View to an enlarged scale, taken upon a plane as indicated by line '5-5, Fig. 6;

Fig. 6 is a View corresponding to a portion of Fig. 4, but on an enlarged scale and showing in section the casing mounting the variable speed drive, sphere-driven castor and interconnected parts;

Fig. '7 is a View corresponding to a. portion of Fig. 4 and showing to an enlarged scale the means for projecting the reticle into the eld of View of thesight;

Fig. 8 is a section taken upon a plane indicated by the line 8-8,'Fig. 5-showing the perforated reticle-forming disc pivoted into a typical position;

Fig .9 is adetail View uponan enlarged: scale, of the knob for adjusting the instrumentrto ob'- served or apparent target size.

Figs. 10 and 10a Show two typical views of a targetas seen when correctly framed between reticleglines, for large and small ranges, resp.ec. tively;

r.Figs- .1.1 land 12 show various suitable Ltypes of perforations in the reticleforming discnf, n

Fig. 13 is a Wiring diagram oi a circuit to prevent the production of excessive lead angles durassuma ing slewing or rapid angular movement of the gun, as when picking up a new target;

Fig. 14 is an elevational detail view of a modied form of reticle-tilting mechanism;

Fig. 15 is a detail sectional view upon a plane indicated by the line I5-I 5, Fig. 6;

Fig. 16 is a schematic view of a cosine corrector suitable for use in introducing corrections for superelevation.

Referring to Fig. 1 wherein all points shown are supposed to lie in the slant plane determined by the gun and the target path, assumed to be a straight line, G indicates the position of a gun equipped with my computer, and which is to be red at a target pursuing a course indicated by the line To-Tp. To indicates the present position of the target and Tp the predicted or future position at which a shell from gun G will strike the target. The distance To--Tp is, then, equal to the linear speed S of the target, assumed to be constant, multiplied by the time of iiight tp of the projectile from G to Tp. The angle A is the angle subtended at the gun by the slant plane distance TQ-Tp or Stp.

From the figure, it is clear that, approximately,

EDctp Dp 1) Where A is the lead angle between the present and. future gun-target lines, E is the angular velocity of the target in the slant plane as measured by the computer, tp is the time of flight of the projectile, and Dp is the future or predicted range. Also. very closely,

Dp=vtp where o is the average velocity of the projectile to the point of impact Tp.

Substituting the value of Dp in (2) into (1),

sin A= Since A is always small, the difference between the angle and the sine thereof is negligible, whence,

For a given engagement, S is assumed to be constant during the travel of the target from To to C. Also for this run, TOC, as well as for any other specic run, DM and v are constant. Hence the value of Equation 8 is constant (k) and, for any tw particular Values of A such as A2 and A1,

HeIlCe all angular positions of its fore and aft axis relatively to the gun-target line so that the image of the target is in the correct position relatively to the reticle lines or segments, in the manner subsequently explained, From the gure D09=W or D0=W/0 (10) Equating the two values of Do of Equations 6 and 10,

and =(-Sm-2% (1l) For a given target run S, DM and W are constant Hence is constant C, and for any two particular values of 0, a1=C2 and 02:022

Hence bi 36 g-: and 02:01

Thus, by varying the linear size of the pattern of reticle range lines within a eld of view of the target, the correct lead angle between the gun and the line of sight to the target, may be introduced by framing the target between two reticle range lines and varying the linear dimentions of the pattern in proportion to E".

The manner in which this is accomplished will be made clear from the subsequent description of the operation.

Referring particularly to Fig. 3, I identifies a fixed base having a ring gear 2 formed upon its periphery. An upper gun carriage includes a disc 3 pivoted at its center on base I and having a ange or skirt 4 depending therefrom and serving to protect gear teeth 2. The carriage also includes spaced standards 5 and 6, fixed to disc 3 and formed at their upper ends with bearings, one of which is shown at 'I. Aligned trunnions, not shown, extend from gun cradle 8 of gun 9 and are journaled in bearings 'I to define a gun elevation or trunnion axis I0.

A gunners seat I I is adjustably mounted upon rotatable disc 3 by means of a socket I2 and 90 arm I3 having a vertical portion tting in socket I2 and a horizontal portion slidably received by the sleeve I4 affixed to seat II. Set screws I5 threaded into the socket and sleeve, enable adjustment of seat II in a manner obvious from bracket I8. This shaft has its other end .attached to one end of the core of a flexible shaft 23, whose other end extends to the computer and, as shown at Fig. 5, is there xed to a shaft 34 journaled in a bracket 24 fixed to standard 5 by cap screws 25.

A stub shaft 26 is journaled in standard 5 and has an elevation hand wheel 21 and a pinion 28 attached to its outer and inner ends, respectively. A second shaft 29 is journaled in standard 5 adjacent and parallel to shaft 29, and haslfixed thereto a pinion 30, in mesh with pinion 28, and a pinion 3l in mesh with'an elevation gear sector 32 attached to cradle 8 concentric of trunnion axis i8. One end of the core of a flexible shaft 33 is attached to the outer projecting end of shaft 29. This shaft extends to the computer where its other end is attached to a shaft 35 journaled in bracket 24. The hand wheel 21 is in position convenient to the right hand of the gunner in seat ll. The connections are such that each hand wheel rotates in a plane parallel to and in the same sense as, the gun motion which it effects. Thus rotation of hand wheel l1 clockwise looking down therein, rotates the gun clockwise in train, while rotation of handwheel 21 clockwise, as seen in Fig. 3, elevates the gun. Thus the movements of the hand Wheels correspond to the desired direction of movement of the gun, and facilitates smooth tracking, While reducing vertigo on the part of the gunner. The optical parts of the instrument will be subsequently described but it should be noted at this point that the eyepiece or occular 35 is positioned conveniently to the eye of the gunner when in seat Il.

As best shown upon Fig. 5, a circular plate 36 is secured to bracket 24, concentric of trunnion axis I0. This plate has a central aperture in which a combined bracket and gear unit 31, is journaled for rotation about axis I0. This bracket comprises a vertical arm 38v andN an integral hub 39 fitting the aperture in plate 36, and having a gear 49 attached to its end. Bracket 31 also has a horizontal arm 4l having a bearing 43 on its outer end. A shaft 44 is journaled on a normally vertical axis in this bearing and has a bevel gear 45 xed thereto. At its top, shalt 44 carries a cup 156 on which a hollow sphere 41 rests and to which it is secured. The relations and dimensions are such that axis I9 passes hrough the center of sphere 41. A 90 angle 42 is fixed to the end of arm 4I. A shaft 43 is journaled at its ends in this angle and vertical arm 35, and has a pinion 49 in mesh with pinion 45. A gear 59 is secured on shaft 48 and meshes with an idler gear 5l journaled on a stud shaft 52 on arm 38. Idler 5l meshes with a gear 53 which is fixed to a shalt 54 journaled in a bearing aperture in hub 39 on axis l0. A bevel gear 53 forms one side of a differential 55 and is attached to the outer end of shaft 54. The other side 'of this differential comprises a bevel pinion 55 and a gear 51 forming a composite element journaled on sli-ait The center of diierential 55 is formed el? two or more planetary gears 5,3 journaled on a shaft 59 fixed to the end of shaft 34, in a manner clear from -inspection 'of Fig. 5.

Shaft 35 is journaled at both ends in ybracket 24 and has a pair of pinions 59 and El iixed thereto. An idler v62 is journaled on bracket 24 and is in mesh both with gear 51 and .pinion '69. Pinion '6l is in mesh with gear 40.

"all-lie purpose of Ythe foregoing construction is gun.

6 to rotate bracket 31 equally andoppsil'ely to the movement of the gun as it changes elevation about axis It, to thereby maintain shaft 44 vertical for all positions of the gun in elevation, and to rotate shaft 44 equally and oppositely to movement of the gun in train to maintain all diameters of sphere 41 normal to the axis 'of shaft 44.; fixed in direction.

Considering the case where handwheel l1 only is being turned to thereby train the gun. Shafts 23 and 34 are thus rotated proportionately to drive the planetary gears 58 of diierential 55. Since )ide 55 of the differential is motionless at this time, by reason of being xed through gears 51', EL 536 to shaft Z" o which is not rotating, the drive continues through differential 55 by way of 'side 53 to shaft 54.. Rotation of shaft'54lv rotates sphere 41 about the axis of shaft '44. by way of gears 53, 5i, 55.5, shaft 48, gears 49 and 45 and shaft 4?. The driving ratios are so selected' that, for any rotation oi 'gun t clockwise in azimuth, for example, sphere l1 will be given an equal rotation counterclcckwise. In this manner, sphere o1 .is maintained fixed in azimuth for all posttions ci the gun in train.

Consider next the case where handwheel 21 amy is rotated to 'change the elevation angle of the gan. The resulting rotation of shafts 33 and 35. drives pinion 5l and thereby gear 49, to rotate bracket 3'? about axis lli. The connections and ratios are such that for any given change in the angie of gun elevation, bracket 31 is rotate@ equally and oppositely to maintain. shaft 45.1 vertical However, in case gear 53 were held stationary during change of elevation of the gun, dier 5i revolves or Walks around gear 53 as bracket 31 rotates about axis Il! relatively to the The resulting rotation of gear 5I and sphere 41 would cause a rotation in azimuth of sphere 41 which, unless compensated, would effeet erroneous operation of the computer. To compensate this rotation, operation of shaft 35 also effects a drive by way of gears 6i), '62 and 51 to side of diierential 55. Since planetary Agears '53 are held motionless at this time, the drive continues through gears 58 and 63 to shaft 54 and thence, over the drive previously traced, to shaft t4 and sphere 41. The connections and gear ratiosV are such that gear 53 is rotatedV vin the .saine direction and to the same extent, as vertical arm 36. As a result, pure elevation of the gun causes equal and opposite rotation of bracket 31 about axis lll, while gear 5l remains motionless relatively to the bracket and no rotation of shaft ill and sphere 41 is effected thereby. For clarity or description, the two angular movements or" the 'gun have been separately explained. However, it will lbe understood that the mechanical action is not altered in any way when the gun is simultaneously trained and --elevated. The mechanism just described maintains the two component motions separate and distinct so that each is 'applied :to the sphere about an axis parall'el te the corresponding -axis of `'gun movement. As a result sphere 41 is maintained lrotationa'lly .space for all angular ymotion and for all angular positions yoi the gun. 1

The computer Ii's housed inra ycasing ifi which, as Vsl'iown by Fig. 3, is `fixed 'to cradle 8 by a lbracket t5. `A. removable lcover 3:6 closes `one side of the casing and is held in position by screws 1 engaging in tapped apertures in lugs 38, Fig. 4.

The other side of casing B4 has an aperture 69,

Fig. lfsm'oothily fitting mate 36 and on which :it rotates. :as 'the-gun -fchange's elevation.

The tcp of casing 64 carries a frame I0 which. as best shown at Fig. 6', includes two raceways for antifriction bearings 1I and 12 dening an axis H2 concurrent with and normal to, axial I0, and also passing through the center of sphere 41. A frame or housing 13 is journaled in and by these bearings. Frame also carries a plurality of slip rings 15 and 16 mounted on dielectric inserts carried by bars 11 located at spaced intervals about the frame. At its top casing 64 has an aperture closed by the male portion 18 of a separable plug connector whose prongs 19 are electrically connected with the respective slip rings 15 and 16. Housing 13 has a dielectric plug 88 closing an aperture in its side wall. Brush connectors 82 and 83 are mounted in this plug, each resiliently engaging a respective one of slip rings 15 and 16.

A constant speed motor 84 is mounted by flange 85 within an aperture in the wall of housing 13 and has its leads 85 connected with respective connect-ors 82 and 83. Motor 84 drives a disc 83 of a variable speed drive 93 through reduction gearing including pinion 81 on the shaft of motor 84, gear 89, pinion 90 and gear 9|, the latter being xed to the shaft of disc 88. The reduction gearing, as Well as the disc, are mounted upon a support 92 xed to one end of housing 13.

Variable speed drive 93 is of conventional construction, and includes driven roller 94 journaled cage for balls 98. This shaft also has a rack 99 formed thereon and, at its inner end, carries a cam |80, whose purpose and function will be subsequently described. The shaft 91 is guided for axial translation at the end adjacent cam |00, by rollers IOI journaled on the housing wall. Such translation moves balls 98 radially of disc 88 so that roller 94 is driven at a speed proportional to the radial position of the balls.

The end of housing 13 remote from support 92 is open, to receive the adjacent portion of sphere 41. An arcuate slide |02 is mounted Within the open end of the housing concentric to the center of sphere l1 and is guided for angular movement about such center in a plane that passes through the center of the sphere for all rotational positions of housing 13 about the axis of bearings 1I and 12. This plane coincides with the plane of the sheet of Fig. 6 for the positions of the parts there shown. The movement of slide |02 is guided by any suitable construction such as that shown upon Fig. l5, where slide |02 is provided adjacent opposite ends with ribs Ia lying in a common diametral plane of sphere 41 and received in slots in the rim 13a. of housing 13.

While if desired, means may be provided to positively prevent separation of slide |02 from housing 13, it is contemplated that the slide may be held in position by the action of a spring |03 and a roller or caster |05. Spring |03 is connected at one end to housing 13 and at its other end to an eye |04 on slide |02. The position of the spring is such that it exerts a force on slide |02, having one component holding the slide upon its seat, and a second component urging the slide into clockwise rotation as seen at Fig. 6. This latter component is sulcient to at all times hold a knob |06, secured to slide |02, in engagement with cam |00. In this manner, the axial position of shaft 91 and cam |00, determines the displacement of slide-|02 from its normal or central position.

Slide |02 has a slot |01 in its lower half Within which caster |05 is journaled on a lever |08, pivoted to slide |02 atV |09. A spring ||0 acts between an abutment III on slide |02, and lever |08, to urge caster |05 into contact with sphere 41. The caster is so mounted in slide |02 that its point of contact with sphere 41 is at all times in the plane of movement of slide |02 about sphere 41 while its axis of rotation is perpendicular to that plane. Thus since housing 13 is free to turn about axis II2, roller |05 acts to place itself in parallelism with the plane of rotation of casing 64 about sphere 41. Since the casing moves as a unit with the gun as the latter moves in tracking a moving target, the caster thus acts to determine the apparent angle of approach or departure of the target, while the rate of rotation of the caster is dependent, with other factors, upon the speed of the target. For example, the position of the parts shown in Fig. 6, Icorresponds to a condition where the target is moving in a horizontal path directly toward the gun position. The effect of the relative rotation of casing 64 and sphere 41 can be readily visualized by imagining that the sphere is grasped and rotated in various planes about its center. Actually however, the sphere remains angularly xed while the casing 64 and parts carried thereby, rotate about its center aS the gun is moved to track a target.

Caster |05 is mounted in arm |08, by a shaft having one end attached to the core of a flexible shaft II3. The other end of this shaft II3 is connected with a worm I I4 journaled in a portion of frame 96. This worm meshes with a gear unitary with bevel pinion I I5 and forming one side of a differential generally identied by numeral I I6. The -center of differential IIB comprises a shaft II1 journaled in frame 96 and having planetary gears I I8 mounted on one end and a pinion I|9 on the other end. A second side of diierential I i0 comprises a composite gear |20 having one bevel pinion in mesh with planetary pinions I|8, and a second bevel pinion in mesh with a pinion fixed to roller 94. The arrangement is such that side |20 of differential II6 is driven by motor 84 through variable speed device 93, in a direction opposite to that which caster |05 drives side I I5. Hence, when the two sides are rotating at equal speeds, differential center I I8 is motionless and shaft 91 remains xed in position. This condition, for example, corresponds to a constant angular rate of tracking of the gun. However, when the rate changes the rate of rotation of side II5 differs from the rate of rotation of side |20. As a result center II8, shaft II1 and pinion II9, are rotated to effect axial translation of shaft 91 and shift balls 98 radially of disc 88. This acts to vary the speed of roller 94 and diiferential side |20 until the rates of the two sides are again equal. Thus, the axial position of shaft 91 is proportional to, and measure of, the angular rate of gun movement in tracking the target. Incidentally, it should be mentioned that housing 13 and all parts carried thereby, are balanced about axis I I2 so that there is no pendulousness thereof and no tendency of the same to rotate, apart from the control imparted by caster |05. It will also be noted that axis II2 is maintained parallel to the bore axis of the gun.

From Figs. 4 and 6 it will be noted that housing 13 has a bevel gear I2I xed to its end, and concentric of axis I I2. This gear has a central aperture through which shaft 91 may pass with a.

smooth fit. Gear |2| meshes with and `drives a pinion |22 which is xed to the upper end of a shaft 23. This shaft is journaled in a frame |24 attached to the adjacent wall of casing E4 and carries at its lower end, an elongated pinion |25 in mesh with a .ring gear |26 nxed to the upper end of one section of an optical unit identified generally by the numeral |21.

The optical unit |2| includes three generally tubular axially, aligned sleeves. The upper sleeve |25 carries gear |25 and just below said gear is provided with a circumferential channel |3|. An opaque, perforated reticle disc |32, Figs. '1 and 8, is provided with pivots |33 and |35, defining an axis coincidental with a diameter of the disc. These pivots are journaled in aligned bearing apertures in sleeve |25 whereby the disc is pivotallg,7 mounted in the sleeve. The pivot |34 extends beyond the outer surface of the sleeve where it carries a lever arm |35. The end of this lever is connected by a pivoted link |56, to intermediate sleeve |29.

Sleeves |28 and |29 are connected, by any suitable means, which permits relative axial translation only. Such means is shown, merely by way of example, with three guides |31, |38 and |39 extending upwardly from the periphery thereof, each slidably received in a corresponding channel in sleeve |28. Thus the two sleeves may have relative axial sliding but are compelled to rotate as unit, and because or link connection |35, |33 between the two sleeves, any relative axial motion effects a proportional pivotal movement of disc |512. The purpose and function of the perforations in the disc will be subsequently explained. Sleeve |25 has a circumferential channel MI.

Sleeves |28 and 25 are thus mounted for independent movernent in the direction of their common axis. This movement of sleeve |28 is controlled by a rod |52 guided for axial translation by a bearing |44 in frame |25 and a socket |45 formed in base |55. A projection |41, attached to shaft |22 has an arcuate end forming a rider fitting within channel 53| and identical with the |55 on the upper end or" the rod, into contact with a three-dimensional control cam iixed to a shaft |52. The purpose of this cam will be subsequently explained.

Likewise, rod |53 is guided for axial translation by a bearing |53 provided in frame |24 and a socket |54 in base This rod has a projection |58 forming a rider at its end which rider engages in channel iai. A coil spring |55 is located in socket |55 and acts to sup-port the Weight ol rod |53 as well as sleeve |23, and to urge the anti'lrietion call |55 at the ton of rod |53, upwardly into Contact with three-dimensional cam |51 xed upon shaft |52. It is contemplated that means may be provided for adjusting the thrusts exerted by springs |45 and |55 such as adjustingI screws threaded through the base |45 and projecting into sockets |25 and i5 The lower sleeve i Se is adapted to have a snug fit within aligned apertures in base |55 and casing 5d and to be axially adjustable therein. Means for positively so adjusting the sleeve may be provided if desired or found necessary. A circular bezel |58 is secured within sleeve |35 near its top and mounts a ground glass screen |59. A lens system, shown as a simple projecting lens |60, is secured over the lower 'end of sleeve |30 by a bezel ring |6| threaded thereon. A source of illumination .such as a lamp |62 and reflector |53 are mounted on the wall of casing 64 above and centrally of sleeve |28. This source acts to cause an image of the perforations to be Vprojected upon screen |55, to produce an .image thereof which is projected by lens |35 `upon a partially silvered reilector |55 mounted by bracket |55 upon the Wall of a sight'casing i 66. The reilector is positioned at 45 both to the common axis of sleeves I 28, |29 and |30, as Well as to the optical axis of eyepiece 35. f

The construction just described operates to project an image of the slots in disc |32, upon ground glass screen |59 and thence to reflector |64 so that the gunner, looking through eyepiece 35, may see an image of the reticle vsuperposed over the image of the target.

Shaft 52 is connected in alignment with a second shaft |58 by a swivel joint |61. Shaft |58 is mounted in a bearingr |59 carried by the casing wall. Axial translation of shafts |68 and |52 as a unit, is effected by a lever |10 pivoted at 11|, Fig. 4, upon frame |24 and connected by apin and slot connection 1| to'shaft |68. Atits other end, lever |10 is connected by a pin and slot connection |12 to a shaft |13. v'Shaft |13 is mounted at one end in a bearing |15 on the wall of casing 54. The other end of this shaft is connected by a swivel joint |15 to the adjacent end of'shaft 91. The two arms of the lever |15 are conveniently, but not necessarily, of equal length so that shaft |52 is axially translated in the same amount, but in the opposite direction, as shaft 51 under the action of differential H6, pinion ||9 and rack'SS. This translation, it will beA remembered, is proportional to the rate of rotation ofroller |05 over sphere 41 which, in turn, is proportional to the angular rate of movement of the gun in the slant plane determined by the gun position and target path. In short, shaft |52 and camsv |5| and |51 carried thereby, are translated axially in proportion to 2.

Shaft |52 has its end remote from joint'l61 splined as at |16, Fig. 9, to the sleeve'portion of an adjusting knob |11. This portion vis journaled in an aperture in casing 65 convenient to the gunner, as shown upon Fig. 3. Axial movement of the knob is prevented by a circumferential channel |18 and a screw |19 having its end engaged therein. It is intended that knobV |11, shaft |52 and cams |5| and |51shall be rotated in accordance with the wing span ofthe target. To facilitate this adjustment, a scale |11a., grad# uated in wing span measured in feet, for example, may ,be attached to casing 54, for cooperation with a pointer |1119 xed to rotate with knob |11. In this manner, cams |5| andl 51 are axially translated in proportion to the angular velocity of movement of the gun in the target slant plane as the gun is moved to track a target; and-are rotated in proportion to the wing span of the tar-get.

In Fig. 14, I have shown a modification of the reticle disc tilting'mechanism wherein the projecting end of pivot |35 has a pinionll secured thereto, in mesh with a rack |8| pivoted at |83, to sleeve |25. The rack is held in engagement with the pinion by means of a leaf spring V| 84. In thisv manner relative motion of the two sleeves effects tilting of disc |32 in exact lproportion t the amount of such motion.

Where a manually controlled source ofjpower -v is used to control the gun, rapid slewing of the gun, as when picking up a new target will generate excessive lead angles and lengthen thev time necessary for the computer to reach a new steady state and for successful engagement of the new target. To obviate this, I use the circuit shown in Fig. 13 wherein are shown the leads 8E, supplying constant speed motor 84 under normal operation, from ground at |84, lead |85, doublepole double-throw switch |86, lead 14, governor switch |81, leads 8B, and current supply |88 to ground at |89.

Switch |88 is located in position for convenient operation by the gunner. Thus, Where a single handle-bar control is used, the switch would be mounted directly thereon for ready operation. When so operated, connection between leads |85 and 14 is opened while connection is made between leads 8| and |90. The motor is now supplied over a circuit from ground at ISI, auxiliary source of potential |92, lead |88, switch |86, leads 8| and 86, to ground at |89. The additional potential from source |92 causes motor 84 to rotate at increased speed and, since the rapid angular movement of the gun cuases roller to rotate at a greater rate, excessive axial displacement of shaft 91 is avoided.

Operation The gunner has been trained to imagine the target surrounded and encompassed by a sphere having a diameter equal to its wing span W. This diameter is the controlling dimension used in framing the target between the reticle lines. Tests were conducted to obtain an initial estimate of the errors that might be expected by reason of the various possible attitudes of a target craft with respect to the line of sight. It was found that the average error to be expected is 2.4%. those inherent in prior art gun-lead computing systems and may be further reduced by practice and experience in actual combat. Figs. l0 and 10a show typical appearances of the target when correctly framedj the former being for a large range and the latter for a small range.

As soon as a target has been selected and identied, knob |11 is turned until pointer |111) indicates upon scale I 11a the known wing span of the target. The gunner, while viewing the target through eyepiece 35 manipulates his controls to move the gun at a rate and in a direction necessary to continuously maintain the target framed between the image of the reticle lines. Since sphere 41 is maintained rotationally fixed, this movement of the gun causes roller |85 to move over the surface of the sphere in the slant plane in which the gun moves. Since housing 13 is pivoted in bearings 1| and 12, the caster action of roller |85, turns the housing until the plane of the roller lies in the aforesaid slant plane. This turning of housing 13, operates through gear |2|, pinion |22, shaft |23, pinion |25 and ring gear |25, to rotate sleeves |28 and |29 as a unit about their common axis, to thereby rotate disc |32. The gear ratios and connections are such that the sleeves rotate synchronously with housing 13 and the axis of symmetry of the image of the reticle lines is parallel to the plane of rotation of the roller |05 and extends from the center of the field of view in the direction of displacement of the roller relatively to the adjacent intersection of axis I2 with sphere 41. For example, in the position of the parts shown upon Fig. 6, the aforesaid axis would eX- This error is small in comparison tot;

12 tend vertically downward away from the center of the eld of view.

Because of the action of the variable speed drive 93, the differential H5 and the connection with roller and shaft 91, the later is translated axially in proportion to the velocity of rotation of the roller. This translation is imparted through joint |15, Fig. 4, shaft |13, lever |18, and shafts |88 and |52, to impart a proportional translation to cams |5| and |51. These two cams are essentially of the same shape, the only difference being that cam |51, connected to sleeve |29, in addition to imparting to sleeve |29 the same axial movement that is imparted to sleeve |28 by cam |5|, also imparts to sleeve |29 an additional axial movement that is a function of the angular velocity of caster roller |85 and the wing span of the target craft. The purpose of this feature will be subsequently explained.

Translation of cams I5! and |51, then, effects axial movement of rods |42 and |43, respectively, and sleeves |28 and |29. This movement shifts reticle disc |32 toward or from screen |59 and correspondingly varies the size of the image cast thereon and upon partial reflector |64. The cam |5| is shaped depending upon the constants oi' the instrument and the average Velocity of the projectile for the most effective and usual range of the gun, to translate the reticle proportional to the Square root of the angular velocity, e. g., proportional to E in accordance with Equation 8, supra, so that any element thereof intersected by a radial plane through the axis of shaft |52, will translate sleeve |28 by an amount proportional to the square root of the angular speed of the castor or roller |85. The actual distances by which the sleeve is moved for any given translation of shaft |52, will, of course, depend upon the constants of the instrument, the ammunition used, and the average projectile velocity for the usual or most elective range of the gun. Each said element corresponds, under the conditions noted, to a craft of given wing span and is selected by rotation of knob |11 after the target craft has been identified as to type and size.

The lead angle thus computed is based upon the assumption that the average velocity of the projectile remains constant for all ranges. This of course is not strictly correct since the average velocity will decrease with increase of range. Assuming that the path of the target remains xed in direction during the period between initial observation and impact of the projectile, and that a perpendicular is dropped to this path from the gun position and the intersection of the path and its perpendicular is the mid-point of the path. That portion of the path traversed by the target up to mid-point is termed the incoming leg while that portion of the path traversed by the target after passing mid-point is termed the outgoing leg.

On the incoming leg of the target path the angular speed of roller |05 will be a little less than the actual angular velocity of the target while on the outgoing leg, its angular speed will be a little greater than the actual value. At midpoint the two values are congruen The slight errors thus introduced can be significantly reduced if the average velocity V0 of the projectile toI the present target position, To, is substituted for the velocity, o, to the point of impact Tp, used in Equation 4. Thus, on the incoming leg, the value of Do/Vo is greater than the corresponding value or Do/c and the product of Do/Ve with 2 as measured by the instrument, will be very close to the required lead angle. Likewise, on the outgoing leg of the target/s path Dal/V is less than the corresponding value of DO/c and again the product of DO/Vo with Z as measured by the instrument, will afford substantially correct values of A.

If in addition, the error caused by assuming sin A to equal A, is reduced, accurate lead values are obtained.

The foregoing errors are substantially eliminated by the use of the additional cam l? which, for increasing values ci E, for example, translates sleeve 29 a distance greater than the corresponding translation of sleeve i effected by cam ll, by an additional distance. 'The cam is so proportioned that the corresponding pivotal movement of disc i312 is e function ol E and W.

Superelevation corrections may be introduced by pivotally mounting reiiector ld in sight casing 4&6 about a normaliy horiaontal axis lying in the plane of the reflector. Since superelevation is a function ci the cosine of the angle oi' gun elevation, any well-known cosine corrector may be connected to be connected to be operated by elevation drive iii-32, inclusive. Such corrector may be directly connected to the pivotal mountn ing for the reector. Fig. l5 shows a suitable corrector for this purpose where reflector lili-i is indicated in dotted lines and is pivoted in casing l upon a shaft SH3 having its axis in the piane of the reflector and to which a roller itil is attached. A second roller is journaled a short distance from left. A frame iii@- has arms res ing upon rollers and isi whereby, in ccniunetion with auxiliary rollers i9? and ist the frame is guide for translation only. Frame iet has a slot therein, extending perpendicuiarly to the direction of translation of the frame. A nei;- ible steel band les extends about rollers it. and H35 and may be secured to as indicated at This band has its ends connected to frame ist at points such as 2li! and whereby translation of the frame effects corresponding rotation of reflector ld. Preferably the arms of the frame rest upon the adjacent portions of the band. An eccentric its has a smooth in the slot of traine ist and is journaled for rotation about an anis offset from its center. in Fig. 1S the direction ci this offset is vertically downward so that, the position of the parte si'iown corresponds to a 9G" angle or gun elevation with relector 351i at 45 to the of gun bore. A tightener may be provided ior band tri# in the form of a roller 2te guided for movement transversely of and in Contact with the band. Turning of screw 2:35 thus acts to tighten the band without causing any rotation of roller i951. Elccentric 2% is connected by any suitable drive means, not shown, for rotation by elevation shaft 3S or pinion (il. The driving ratio is .such that the eccentric is rotated equally and oppostely to movement ci the gun in elevation and hence remains angulariy relatiifely to the vertical. Thus as the sight moves with the gun in changing elevation, reflector i is pivoted in accordance with the cosine of angle of gun elevation.

Corrections for changes in muzzle velocity of the projectile and in air density, may be effected by modifying the target size adjustment of knob il?. For example, scale Villa may itself be rotatable in accordance with a combined factor of muzzle velocity and air density. Knob lil may then be set relatively to the scale, in accordance with the known size of the target, as previously explained.

It will thus be noted that I have invented a lead-computing gun sight that is relatively simple, entirely automatic in operation after setting for target size, and simple and easy to operate. The proper lead angle is continuously introduced so long as the gun is properly tracking the target so that firing is limited only by the loading mechanism of the gun itself. Except for the motor 84, all parts are mechanical in operation and there are no delicate and easily deranged telemetric drives from a remote computer. The sight can be made relatively small and compact and once attached and adjusted, remains constant in operation throughout the life of the gun.

In the specification, the term elevational movement includes movement of the gun to clecrease its angle of elevation, as Well as movement to increase its angle of elevation.Y l'

For simplicity of explanation and illustration; the gun has been shown as being directly manually actuated. This 'disclosure is illustrative only.V The' actual control used will depend'upon the type and size `cf gun'. It is clear'that, for guns of relatively large caliber, hydraulic `or electric power will be used under the controlof the gunner. Such control maybe 4elected by any of the Well-known joystik or handlebar controls where a single controlelement is used mounted for movement in two ahgularl'yrelated planes. This element is connected to the power means such that movements inthe'tvvo planes effects motion of thegun in correspond# ing planes. Suitable controls of this type are illustrated in the patents to Rolcik, 2,107,803, February 8, 1938, for Adjusting Mechanism for Firearms and Adams et al., 2,350,662, June 6, 1944, for Hydraulic System and Control. Any other of the control systems of this type may be used so long as the motions of the gun in azimuth and elevation are transmitted to shafts 35i and 35 respectively.

The term axis of the reticle lines is the line corresponding to the radius of disc i232 about which the reticle range lines dened by slots IM, are symmetrical. This axis, as shown upon Fig. 8, is perpendicular to the pivot axes determined by pivots |33 and |34.

The term framed as used in the claims means a, position of the gun and sight in which the imaginary sphere surrounding the target, and having a diameter equal to the Wing span of the target is tangent to both of the reticle range lines.

The caster angle of roller |05 is the angle deu Iined by axis H2 and the radius of sphere lil th'ugh the point of Contact of roller H35 therew1 While I have disclosed the preferred form of the invention as now known to me, it will be clear to those skilled in the art, to which this specication is addressed, that numerous substitutions of equivalents, and modications are possible without altering in any Way the basic principles upon which the instrument operates. It is 'therefore intended that the present disclosure shall be taken in an illustrative sense only. It is my desire and intention to reserve all such changes as fall within the scope of the subjoined claims.

Having now fully disclosed my invention what I claim and desire to secure by Letters Patent is:

i. In a computing gun sight Vadapt-ed to be carried by a gun for angular movement'therewith in elevation and train, a bracket adapted to be journaled on said gun for pivotal movement relatively to said gun about a first axis coincident with the axis of gun elevation, a sphere pivoted on said bracket for rotation about a second axis coincident with a diameter of said sphere and normal to and concurrent with said first axis, a drive shaft journaled in said bracket coincidental with said first axis, means carried by said bracket and connected with said shaft and sphere to rotate said sphere about said second axis in response to turning of said shaft, a differential having one side connected to rotate said shaft, an azimuth shaft connected to drive a second side of said differential, an elevation shaft, and means connecting said elevation shaft to simultaneously rotate said bracket about said first axis and turn the third side of said differential.

2. In a lead-computing gun sight, a sphere adapted to be mounted upon a gun for universal rotation with respect thereto, means connecting said sphere with the gun to maintain the sphere angularly i'lxed for all positions of train and elevation of said gun, a housing, means mounting said housing for angular movement as a unit with said gun and for rotation about a first axis coincident with a diameter of said sphere parallel to the bore axis of said gun, and roller means carried by said housing and in driven engagement with and rotated by said sphere whereby said housing is rotated about said rst axis in accordance with the plane of movement of said gun in tracking a target.

3. The combination with a gun elevatable upon a trainable support, a sphere mounted upon said support for pivotal movement about a first axis parallel to the axis of elevation of said gun, and a second axis normal to said first axis, means responsive to change of elevation of said gun to rotate said sphere about said first axis equally and oppositely to said change to thereby maintain said second axis normally vertical, means responsive to training movement of said gun to rotate said sphere about said second axis equally and oppositely to said movement, a housing, means mounting said housing A.for elevation vand training with said gun and for rotation about a third axis parallel to the bore axis of the gun and forming a diameter of said sphere, a slide carried by said housing arcuately movable about the center of said sphere in a plane containing said third axis, a roller engaging said sphere and journaled on said slide for rotation in said plane, said roller acting to turn said housing about said third axis in accordance with the plane of movement of said gun and third axis in tracking a target.

4. The combination specified in claim 3, a variable speed drive carried by said housing, a motor connected to operate said drive, a differential having one side connected with the output of said drive and a second side connected to be driven by said roller, and means operating the speed-varying element of said drive in response to operation of the third side of said differential.

5. The combination specied in claim 3, a constant speed motor carried by said housing, a variable speed drive having an input operated by said motor and a speed-varying element translatable along said third axis, a differential, a driving connection between a first side of said differential and the output of said variable speed drive, means operating a second side of said dif- A16 ferential by and in response to rotation of said roller, a driving connection between the third side of said differential and said element, and means operable to move said slide by and in response to translation of said element.

6. For use in a lead-computing gun sight, a housing adapted to move fwith the gun in elevation and train and rotatable about an axis parallel to the bore axis of a gun, a spherical surface adjacent said housing adapted to be angularly fixed, said axis being coincident with a radius of said surface, a slide mounted on said housing for rotation about the center of said surface in a plane containing said axis, a roller journaled on said slide for rotation in said plane, means yieldingly holding said roller in contact with said surface, .and means operable to angularly displace the point of contact of said roller and sphere from said axis proportional to the speed of rotation of said roller over said surface.

7. In a lead-computing gun sight, a sphere, a roller, means mounting said roller in contact with said sphere for rotation thereby and for revolution about a diameter of said sphere, and means responsive to the rate of relative rotation of said roller and sphere about the center of the sphere to vary the angle between said diameter and the radius of said sphere to the point of contact of said roller therewith.

8. In a lead-computer for guns, a sphere, a housing rotatable adjacent said sphere on a rst axis coincident with a diameter of said sphere, a roller, means carried by said housing mounting said roller in driven contact with said sphere and for revolution about the center of said sphere in a plane containing said rst axis and for rotation about a second axis normal to said plane, and means responsive to the rate of rotation of said roller about said second axis in response to rotation of said sphere about its center to revolve said roller relatively to said sphere in said plane and thereby to vary the angular relation between said rst axis and the radius of said sphere to the point of contact of said roller.

9. In a lead-computing gun sighting device, a sphere, a housing rotatable about a first axis coincident with a diameter of said sphere, a Variable speed power drive carried by said housing, a slraft axially translatable in said housing along said first axis, means varying the driving ratio of said variable speed drive by and in response to translation of said shaft, first means connected to rotate with said housing about said rst axis and slidable in an arcuate path about the center of said sphere in a plane containing said first axis, a roller carried by said means in driven engagement with said sphere and rotatable about a second axis nonmal to said plane, a differential carried by said housing, and having first and second sides driven respectively by said roller and the output of said variable speed drive, means connecting a third side of said differential to axially translate said Shaft, and means to slide said first means by and in response to translation of said shaft to vary the displacement of said roller from said first axis in accordance with a function of the speed of rotation of said roller about said second axis.

10, The device recited in claim 9, said last named means including a cam secured to said shaft and engaging a portion of said rst means to displace the same, said cam being formed to displace said roller in accordance with the square ltion of said roller about said second axis.' l"11. "In a computing gun sight, a casing adapted to be montedfor lmovmentvvith 'a""gtin'"in l'ei: Vation and train, means/"carridby Said casing din'g a iiriof'signt`para111 td tiratore 41ai s'adgun and includiig'a feld f viewsurr'ounding'saiii une; a disc' beariiig'a'pair or reticia'rari'ge lines thereon symmetrical ab'i't ah'axis, nfeans projecting an image of said1iri'es"'intof 'said eld of view, meansV responsive to the nive'r'entf saidl gun in trackig'a t'argetto maintain the axis if said reticie lines parallela@'tiiaapparerit path of movement of' the target, an'cn'feaiis" r'ei sponsiveto the rate' of A 'aiflgilla'i"Iilo'veliient'tif said gun' and sight to bodily moi/'e sairl'disc "relatively to said'casing to 'vary tlie apparent s iZe"oi"th-e 'page 'of said reiici unas in arcor' with a function of said rate.' :12."In a computing-sight for a gun, a frame adapted to move synchronously with 'said gun in train andelevation i`n`tracliii`g a moving target, rst means responsive to` moveme'nt 'o'f saidgun in tracking a target to determine the directiorf the path of saidY movement,"secondi'means r'espcnsive to said movement to `deterniinetlfie angular rate thereof, a sighting'device'determining'a line of sight parallel' to rthe bor'e'of said gu'nan'd d ening'a field of view'surrdundihgsaid nire, means defining apair'of parabolic'reticle range lines symmetrical about an 'ax'isgv means 'project'- ing an imageof said'lihesintsaidldiview with said axis concurrent with said line of signi, means responsive to said iirst means to rotate'said axis aboutsaid line to Inair'tain'saidaxilal parallel to the plane of movement of the gun Lasit i's'm'oved te cause said line of sightto track ther target', and means responsive to said second means t Ava'ryth'e separation of the images of saidlinesas' seenin root of the rate of rot said iield of vievv in accordance with the rate of angular movement of 'said gun.

13. A computing gun sight for a gun elevatable upon a trainable platfrm c0m`p`r`isig`a casing adapted to be connected With 'sai'clg'un' for move'- ment as a unit therewith, istineans carried' 'by said casing to determine a 'line fs'i'glitsub'stan'- tially parallel with said gun and includng'a'iie'ld of View about said line, second means? in said'oasing defining a pairof spaced reticle range lines symmetrical about an axis, means projecting an image of said ylines into said field of View with said axis concurrent'vvithsaidline, means re snensiye .to .angular movement o f Vsaid gun in tracling a target maintaining said -axis parallel with the apparent path ofsaid target, a nd means responsive' te the rate of said' anulanmovement to move said second means to 'vary the linear di'- mensions of the image of saidline's.

14. In a lead-computing" gun" sight, first and second elements connected for rotation asa 'unit about a first axis and mounted vfor independent translation along said axis, a reticle disc".ni'voted on said first element on a second'axis normaltb said is't'axis and lyingin the plaide of "saiddis'c, means pivoting said disc about "said seonaxis hy and in response to relative'axial.translation of normai 'ibisaiii""nrstraxis and' lying firrftireipiaria r'sad disci' near'is torprojeet ari mage-brama ond axis.

"17".For use in a lead-computing gun sight, a y

sighting meansfadapted tow 4lbe rnaimaine-ai"par-l allel t the' borelaxis of agun and t'include` a field view"about klsaid axis", "rst'and secnd sleeves' connectedfor "c'on'joir't rotation aboutffa disc in response to relative axial translation' of Speeder said; gun'rriovereiit and akriownninin;

sion of the target?"v '18."".A"'le ad'cmputing gun-sight comprising a s ig'htfmzeans'deninga 'pair Vof parabolic reticl'e range lilies syirn'netr'ical ahou'taiiaxi's; meansto project an imagilof s aid lines intd thefe'ld l'of the 'fildof 'view r:of said "sighting'rneans, said linesleing` symmetrical "aboiian"i axis radial-'af said iield* ofi View," means' responsive -to iangular n'riovementv of' said 'sighting meansimmantainig amoving target 'framed btweensaidilines;,to rotate 'said-axis into"tparallelismwith the apparentpath of said' targetyandmeansto .vary-tl1e scalefof "said lines "as lviewedin 'said sighting means, iniaccordance with the Wingspan ni' said target; andthd'square root of the rate Q angular"movement"d'said sighting '.meaIlS, '20.l` In a Sleadi-computing'Y gun sight', sighting meansmea'ns operable .to projecttheimage gf twi).V reticle range lines into Athe ield of view of saidsighting vni'eans, said;` imagelinesbeing sym-V 'the` nietrica'l aboutan axis extendingradially 9 M center ofsaid field of. View, means responsivelto angular movement of said sighting means amado-r maintaining a moving aircraft framed between said lines to rotate said axis into the plane of said movement, and means adjustable in accordance with the wing span of said aircraft and automatically responsive to the rate of said angular movement, to vary the scale of said image lines in said field of View.

21. In a lead-computing gun sight adapted to be mounted for movement as a unit in train and elevation with a gun, a sight including a partially silvered reflector interposed at an angle across the eld of View of said sight and pivoted on an axis in the plane of said reector transversely of said sight, means projecting an image of a pair of reticle range lines upon said reflector, said image lines being symmetrical about an axis radial of said field of View, and means responsive to the angle of gun elevation to pivot said reflector in accordance with the cosine of said angle to correct said sight from superelevation.

22. In a lead-computing gun sight, a casing adapted to be mounted for movement as a unit with a gun in train and elevation, a spherical surface, means rotating said surface about its center in response to angular movement of said gun, a housing in said casing rotatable on a iirst axis parallel to the bore axis of said gun and forming a radius of said surface, a slide guided for movement on said housing in an arcuate path about the center of said surface and in a plane containing said first axis, a caster engaging said surface and rotatable on said slide on an axis normal to said plane, a shaft in said housing extending along said iirst axis, means responsive to rotation of said caster over said surface to p,-

axially translate said shaft proportional to the rate of caster rotation, a sighting means movable with said casing in parallelism with said rst axis, an optical unit in said casing to project the image of spaced, symmetrical reticle range lines into the field of view of said sighting means, said unit comprising a pair of elements relatively translatable along a common second axis and rotatable as a unit about said second axis, a reticle disc pivoted on one said element and connected with the other said element for pivoting in response to relative translation of said elements, means rotating said elements about said second axis in response to rotation of said housing by said caster about said iirst axis, and means dierentially translating said elements to thereby pivot said disc in response to translation of said shaft.

23. A computing gun sight as specified in claim 22, said last-named means comprising a second shaft, iirst and second three-dimensional cams thereon, means operable by said cams in one dimension to differentially translate said elements, respectively, and manually operable means for adjusting said cams in a second dimension in accordance with a known dimension of a target.

24. That method of aiming a gun at a moving target comprising, establishing a line of sight parallel to said gun and including va surrounding field of View, providing a pair of reticle range lines in said field of View, symmetrical about an axis radial of said line of sight, rotating said axis about said line of sight to maintain the, same parallel to the apparent path of said target as said gun and sight are angularly moved to maintain said target framed between said reticle lines, and varying the spacing of said lines in accordance with a function of the rate of said angular movement.

25. That method of aiming a gun at a moving 20 target, comprising, establishing a line of sight parallel to said gun and surrounded by a field of view, providing a pair of spaced reticle range lines in said field, symmetrical about an axis extending radially of said line of sight, angularly moving said gun and line of sight as a unit to maintain the target framed between said reticle lines, simultaneously rotating said axis to maintain the same parallel to the apparent path of said target, and varying the spacing of said reticle range lines in accordance with the square root of the rate of angular movement of said gun, while maintaining said target framed therebetween.

26. In a lead-computing gun sight, a casing carried by a gun to move therewith in train and elevation, a sphere in said casing, means maintaining said sphere xed against rotation for all angular positions of said gun, a frame journaled in said casing for rotation on a rst axis parallel to said gun and passing through the center of said sphere, a caster engaging said sphere and mounted on said frame for angular movement about the center df said sphere in a plane containing said rst axis and for rotation in said plane, a motor carried by said frame, a variable speed drive driven by said motor, a diierential carried by said frame and having one side driven by the output of said variable speed drive, a second side driven by rotation of said caster and a third side connected to Vary the speed of said variable speed drive, and means driven by said third side to alter the caster angle of said caster about said sphere.

27. In a lead computer for a gun, a fixed sphere, a support, means mounting said support for angular movement about the center of said sphere in synchronism with the gun and for rotation about a iirst axis coincident with a diameter of said sphere, a roller, means mounting said roller on said support for driven contact with said sphere for revolution about said sphere in a plane containing said rst axis, and for rotation about a second axis normal to said plane, and means responsive to rotation of said roller for revolving the same about said sphere to vary the angular relation between said first axis and the radius of said sphere to the point of contact of said roller therewith.

EDWIN II. LUDEMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,880,174 Dugan Sept. 27, 1932 1,913,793 Clementi et al June 13, 1933 1,963,457 Avery June 19, 1934 2,069,417 Murtagh et al. Feb. 2, 1937 2,139,636 House Dec. 6, 1938 2,339,508 Newell Jan. 18, 1944 2,372,613 Svoboda Mar. 27, 1945 2,383,952 Bates Sept. 4, 1945 2,396,701 I-Iolschuh et al Mar. 19, i946 2,405,028 Ford July 30, 1946 2,407,665 I-Iolschuh et al Sept. 17, 1946 2,426,744 Polntius et al. Sept. 2, 1947 2,428,870 Essex Oct. 14, 1947 2,430,108 Crooke et al. Nov. 4, 1947 FOREIGN PATENTS Number Country Date 777,913 France Dec. 15, 1934 852,200 France Oct. 23, 1939

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