Patent GB-689029-A (GB)
Title: Improvements in and relating to gun sight computing mechanism
IPC: F41G5/18
Filed: 1944-05-04
Abstract: 689,029. Gun-sight computers. SPERRY GYROSCOPE CO., Inc. May 4, 1944 [Aug. 22, 1942], No. 8483/44. Class 92(ii) A gun sight computing mechanism for use on an aircraft comprises a ballistic - correction computing arrangement that is adapted to compute correction in a predetermined plane as a function of two inputs that are supplied to the arrangement, one input being the azimuth component of gun orientation and the other being a composite function of the slant range of the target, the indicated air speed, and the altitude of the aircraft. Ballistic corrections. The entire apparatus schematically shown in the drawing is mounted on the gun, and comprises a reflex mirror 33 through which the target is viewed and on which is projected the images of two slots 27, 28 in members 23, 24, the projecting means consisting of a light source 29, azimuth mirror 31 and elevation mirror 32. The members 23, 24, which are interconnected by a pivoted link 25 so that they move in opposite directions, are moved by the follower 22 of a cam 13 which receives rotational and axial movements by mechanism as shown actuated by control knobs 10, 17. In use the control 17 is adjusted in accordance with the known target dimensions and the control 10 then adjusted until the images of slots 27, 28 in mirror 33 just circumscribe the target. Cam 13 and graduations on the dial 34 of control 17 are so arranged that shaft 11 is angularly displaced from a neutral position by an amount proportional to the natural logarithm of a function of the slant range. Similar functions of altitude (H) and indicated air speed (I.A.S.) are set into shafts 41, 46, by controls 37, 42 having appropriate' graduations on their dials, and the motions of these two shafts are added in a differential 47 and the result is added by a differential 49 to the movement of shaft 11. The output displacement of differential 49, as determined by a shaft 51, is thus proportional to a linear combination of functions of slant range, altitude and indicated air speed. Shaft 51 rotates a cam 54 whose anti-logarithmic cam groove 57 is engaged by a follower 58 fixed to the gun, whereby the cam is moved axially on its shaft, taking with it but not rotating two rigidly interconnected cams 59, 60. These cams are rotated by a shaft 62 in accordance with the angular displacement of the gun in azimuth from a given datum line, and cam 59 is designed so that the lift of its follower 64 is proportional to the required azimuth ballistic correction. Such movement of the follower serves as shown to move a link 72 about a movable pivot 73 and thereby to cause arm 74 and link 76 to rotate mirror 31 by the necessary amount to compensate for relative wind, gravity, and projectile spin upon the path of the projectile. The follower 77 of the other cam 60 displaces axially a further cam 78 which is rotated by a shaft 81 in accordance with the angular displacement of the gun in elevation, the cams being so designed that follower 83 of cam 78 will lift in accordance with the correct super-elevation correction. The follower is adapted to move an arm 94 about a movable pivot 96, the arm causing movement of links which tilt elevation mirror 32 through an angle corresponding to the super-elevation correction. Prediction correction. The apparatus includes two gyros 99, 101, of the kind forming the subject of Specification 684,667 their output arms 102, 103, being angularly displaced from predetermined datum positions by amounts proportional to the angular velocity of the gyro mount about axes perpendicular to their respective spin axes. As in Specification 684,667 their output angular displacements for a predetermined impressed angular velocity may be adjusted by control members 104, 105, and in the present instance such sensitivity is adjusted in proportion to the projectile time of flight. Arms 102, 103 are thus displaced by an amount proportional to the product of the time of flight and angular velocity of the gun in slant plane and in elevation respectively, and such displacements are therefore proportional to the required prediction corrections. The time of flight, being a function of slant range, is applied to members 104, 105, by shaft 11 through gearing 106, 108, shafts 107, 109, cam and cam follower device 111 and rack 114. The angular displacement of crank 102 is transmitted by links 116, 1.17, shaft 118, crank 119 and link 121 to a lever 122 which is pivoted about a fixed axis 123 in the instrument housing. The other end of lever 122 is rigidly connected to the pivot 73 and thus serves to tilt mirror 31 by an amount corresponding to the azimuth prediction correction. Similar means are employed to produce the elevation prediction correction of mirror 32 as, the result of movements of the cam 103. Gyros. In order to ensure that the speed of the air spun gyros 99, 101, are maintained constant at different altitudes, a variable output pump 131 is employed having a control members 134 adapted to vary the output in the ducts 132, 133 leading to the gyros. The control is actuated by rack and pinion mechanism, cam and groove mechanism and gearing, as shown, controlled by the altitude control 37. Specifications 592,645, [Group XX], 606,656, 606,957, also are referred to.