Patent GB-793243-A (GB)
Abstract: 793,243. Apparatus for aiming weapons. MATHEMA CORPORATION REG. TRUST. July 26, 1954 [Aug. 4, 1953], No. 21703/54. Class 92 Apparatus for aiming a gun at a moving aircraft comprises two parallel rotatable discs 33, 32, Fig. 8, arranged one in front of the other in the field of view of a sighting device, one disc 32 being transparent and provided with a series of curves 40 indicating aiming-off values for various aircraft velocities, the aiming-off values for each curve being calculated for an assumed rectilinear flight path in which the least distance of the path from the gun corresponds to the minimum range of the gun, the other disc 33 being opaque and having a radially disposed slot 34 providing a radial line of light in the sighting device. Computer mechanisms, Fig. 3, operate in dependence only upon the bearing and elevational angles of the gun and are adapted to rotate the discs 33, 32 differentially through angles dependent upon the bearing angle in the plane of flight # 0 <SP>1</SP> and the apparent angle of flight # in such manner that the intersection of the radial line of light produced by the slot 34 and a selected curve on the disc 32 indicates the point of contact to be maintained on the aircraft in order to aim the gun with the correct aiming-off value to hit the target. In Fig. 1, f is the plane of flight of the aircraft, points M W M, lie on the path of flight and an assumed path of flight is chosen in which the charge-point range G W corresponds to the minimum range of the gun. In finding the target the bearing angle # 0  is assumed to be, e.g. 45 degrees for "approach from left to right" or 135 degrees for "approach from right to left." The point M under observation is determined by the angle of elevation y which appears as an arc M 0 M 0 <SP>1</SP> with radius = 1 on the surface of the sphere imagined as surrounding the observer at G, and which gives the bearing angle # 0 . In the right angle spherical triangle KM 0 M 0 <SP>1</SP>, Fig. 2, the arc M 0 M 0 <SP>1</SP> = angle of elevation y, the arc KM 0 <SP>1</SP> = bearing angle # 0 , the angle of flight KM 0 M 0 <SP>1</SP> = # and the arc KM 0  = bearing angle # 0 <SP>1</SP> in the plane of flight. For each value of the bearing angle # 0  and of the angle of elevation y, the corresponding bearing angle # 0 <SP>1</SP> in the plane of flight is calculated from the equation cos # 0 <SP>1</SP> = cos # 0  cos y and the apparent angle of flight # is calculated from the equation sin # 0  = sin # 0 <SP>1</SP> sin 8. To each value of the bearing angle # 0 <SP>1</SP> belongs a particular aircraft point M whereby the range GM dependent upon # 0 <SP>1</SP> is known for the entire path of the aircraft. With the time of flight of the projectile for each point M also ascertained from the range table, aiming-off values in the plane of flight mar be calculated for certain selected aircraft speeds, these aiming-off values being indicated as points of burst or of contact on the flight direction line on the screen of the sighting device. Fig. 3 shows a geared mechanism for solution of the equations above. Gear 1 engages with the elevation mechanism of the gun and thus rotates in proportion to the angle y. It drives the worm screw 2 along which a nut 3 is displaced which carries with it a curved body 4 guided on a shaft 5 by a slot and key arrangement. The shaft 5 engages with the azimuth mechanism of the gun through a clutch 6, 7 which, when closed, causes the shaft 5 to rotate in proportion to the bearing angle # 0 . The curved body 4 is so constructed that the finger 8 pressing against it by spring tension follows paths which are proportional to the bearing angle # 0 <SP>1</SP> in the plane of flight. By means of the finger 8, the angle # 0 <SP>1</SP> is conveyed to the sighting device through a pinion 9 to provide the aiming- off value and the curved body 10 is rotated. The finger 11 in contact with the body 10 is displaced by connection to the shaft 5 through bevel gears 12, 13, pinion 14 and rack 15 in proportion to the angle # 0 . The curved body 10 is such that the finger rotates in portion to the angle # which is conveyed to the sighting device through pinion 16. The angle of elevation on the elevating mechanism of the gun differs from the angle of elevation y in that it is increased by the effective angle of sight α which is conditioned by the path of the projectile under influence of gravitation. The sum y + α is the barrel or quadrant elevation # and in the computing device in Fig. 3 the "geometric" angle y is required without the "ballistic" angle cc. To allow for this the spindle 2, Fig. 3, is rotated in proportion to the angle # given by the elevating gear and is mounted for longitudinal displacement by means of a pin and slot coupling 20. The end 21 of the spindle is in contact with a curved body 22 rotated in proportion to the bearing angle # 0 <SP>1</SP> and displaced in proportion to the angle # by means of connections to the shaft of the pinion 9, Fig. 3, and to the shaft of the elevating gear. The spindle 2 is actuated by movement of the nut 3, Fig. 5, and consequently of the curved body 4, in proportion to the difference p - α, i.e. to the geometric angle of elevation y. The surfac of the curved body 22 is such that the path of the finger 21 at every point of contact for each range value corresponding to the bearing angle # 0 <SP>1</SP> in the plane of flight and of the quadrant elevation # is proportional to the angles of sight obtainable from the range table. Sighting device. The rotation of the pinion 16, Fig. 3, which is proportional to the flight angle # is conveyed by gear 30, Fig. 8 to the opaque disc 33 and the U-piece 41 of a geared differential 35, 36, 37 is rotated from the shaft of the pinion 9, Fig. 3, proportional to the angle # 0 <SP>1</SP>, the pinion 35, Fig. 8, of the differential being rotated by means of gears 31, 30 proportional to the angle #. The transparent disc 32 on which the aiming-off curves 40 for various speeds of flight are represented, is thus rotated proportional to # 0 <SP>1</SP> -#, and the rotation of the disc 32 relative to the disc 33 is proportional to # 0 <SP>1</SP>. The radial slot 34 of the disc 33 therefore assumes at all times the position corresponding to the angle # which is given by the position of the angle # 0 <SP>1</SP> Through the optical system 38, Fig. 9, the radial line of the slot 34 is indicated in the field of view of the sight as a luminous line interrupted by the aiming-off curves 40. The interruptions caused by the aiming-off curves 40 give the contact points dependent upon the selected speed of flight, the flight direction line 34 with contact points being projected on to the reflex screen 51 and the gunner being required to cause these contact points to coincide with the aircraft. The rotation produced by the laying motion of the gun and proportional to the quadrant elevation # is employed to displace the curved body 22. A lever 50 is connected to the reflex screen 51 and inclines the screen so that the aiming line with the direction in which the gun barrel points includes the effective angle of sight cc.