Patent GB-449238-A (GB)
Title: Improvements relating to bomb-sights for aircraft
Filed: 1934-09-20
Abstract: 449,238. Bomb-dropping sights. HILLIER, A., c/o Sperry Gyroscope Co., Ltd., Great West Road, Brentford, Middlesex.-(Sperry Gyroscope Co., Inc. ; Manhattan Bridge Plaza, Brooklyn, New York, U.S.A.) Sept. 20, 1934, No. 18262. [Class 92 (ii)] Relates to means for automatically setting up the release angle in bombdropping sights so that the bomb may be released when the line of sight, which is continuously maintained on the target, makes this angle with the vertical. The invention particularly relates to bomb sights of the kind described in Specifications 186,099, [Class 92 (ii)], and 413,338, in which the line of sight is automatically maintained to intersect a plane at a fixed distance below the aircraft at a point travelling at a constant speed with respect to the aircraft, and in which this speed is set by the rotation of a handle so that the target is kept sighted, the instant of release being determined by this setting and by further settings for air speed, height and bomb characteristics. According to the present invention, the apparatus comprises (1) a prism or equivalent sight 8, Fig. 3, controlled by a horizontally moving member 74 representing the approaching target, (2) continuous driving means, adjusted by a speedcontrol handle GS, for moving the member 74 at a constant speed, and (3) means for setting the release angle on a range arm 50 including a horizontally-adjustable member 61 which receives two differential movements, one corresponding to the rotation of the handle GS, and the other corresponding to the rotation of a handle AS which latter applies the correction for trail of bomb. In the form shown in Fig. 3, a slotted range-bar 50 is freely mounted on a shaft 52 and carries a slider pin 57 engaging horizontal and vertical slots in bars 59, 61 which are set by adjusting screws 62, 67. The angle # which the range arm makes with the vertical is adjusted by the apparatus in accordance with the formula where GS is the ground speed, Y the trail distance, H the height, and T the time of fall. The bar 61 is moved partly by the rotation of the screw 67 when following the target by adjusting the handle GS and partly by endwise movement of the screw effected by gearing 99, 111, 112 to suit the trail correction Y/HT which is determined by a separate unit shown in Fig. 4. The bar 59 is moved a distance I/T in setting the height and bomb characteristics on a dial 66 by rotating a handle H. The target sighting means comprises a prism 8, Fig. 6, movable about a transverse axis 91 by a rod 12 geared to the shaft 52. The target is viewed with the aid of a fixed prism 15, lens system 16, and a reticule 3 the support 36 of which is stabilized by a gyroscope 4. The prism is moved to follow the target by a constant-speed motor 31, Fig. 3, through a variable-speed disc drive 33 the radiallyadjustable member 34 of which is moved by operating the hand wheel GS. The member 34 drives a cylinder 35 and spur gearing 70, 71, 72 for rotating a screw 73 which moves the member 74 in a slotted arm 78 fixed on the shaft 52 which is connected by a two to one gear 80, 81 with the prism 8. The arm 78 is fast with an arm 54 carrying electric contacts 122 which engage corresponding contacts on an arm 53 fast with the rangebar 50. When the sight line reaches the release angle, the contacts close a circuit first to operate a warning flag 121 in the field of the reticule and then to release the bomb. The height dial 66, Fig. 3, is marked with curves 168 for various heights which are read against a cross wire 166 carried by a sector 87 adjusted by turning handle TV to a scale T<1> marked for terminal velocities to suit different kinds of bombs. The cross wire 166 is also marked with these terminal velocities and the chosen mark is read against the known height curve in setting the dial 66 by a handle H. The trail unit, Fig. 4, driven by the handle AS is also connected with the height dial so that the adjustment for terminal velocity also sets the fulcrum 93 of lever gear which is inserted between the handle AS and the air speed drum 103. By setting the drum 103 to the appropriate height mark on a scale 104, the spindle 111 is rotated to apply the correction for trail to the bar 61. The drift angle for a cross-wind is obtained from the unit shown in Fig. 2 by moving the whole sight about a vertical axis by rotating a handle A until the motion of the ground viewed on the graticule through a window 23 and adjustable prism 17, Fig. 6, is parallel to the fore-and-aft line of the graticule. The angle of drift is shown on a dial D when the sight is moved round a fixed toothed ring 30. The off-set angle alpha is given to the sight by a variable crank device 107, 111<1> which calculates the formula tan alpha = AS sind /TvC where AS is the air speed, d is the drift angle, Tv the terminal velocity and C a constant. The correction is set up by turning a handle O to set a scale 115 of air speed to a scale 116 of terminal velocity thereby adjusting the crank radius to the factor AS/TvC The crank is turned through the drift angle d and the crank-pin 111<1> engages a slotted slide 112<1> connected to an arm 13 which turns the prism about a fore-and-aft bearing 10, as described in U.S.A. Specification 1,783,769. British Specification 386,329 also is referred to.