Patent GB-554560-A (GB)
Title: Improvements in or connected with range and heightfinders for anti-aircraft gunnery
IPC: F41G5/08
Filed: 1941-09-19
Abstract: 554,560. Range-finders. BARR & STROUD, Ltd., STRANG, J. M., and FOSTER, C. Sept. 19, 1941, No. 12059. [Class 97 (i)] The deflecting prism, or the equivalent, of a rangefinder is moved by a constant speed motor through a variable-speed gear, and the drive ratio of the variablespeed gear is controlled by a mechanism which may be preset for the height and speed of an aircraft ranged upon, and is continuously adjusted in accordance with the course angle 6 of the aircraft and the angle of sight α ; the adjustments of the mechanism may produce a resultant movement, controlling the variable gear, which is in accordance with the rate of change of log sin α of the reciprocal of direct range, or of horizontal range. Fig. 1 shows the values to be considered in connection with a range-finder at a post S and an aircraft travelling on a horizontal course Rv at a height H. The relation d log sin α Sin # Sin 2α d Rv 2 H is deduced in the Specification. Fig. 2 shows apparatus based on this relation. A constant speed motor 18 drives a disc 19 variably engaged by balls 21 carried by a slide 13 and driving a roller 20 on a shaft 22. The mechanism controls the radial position of the slide 13 relatively to the disc 19 in accordance with the rate of change of log sin α, with the result' that the shaft 22 rotates in accordance with log sin α. This rotation is added to rotation in accordance with log H, applied by a hand-operated head 24, in a differential gear 23, and the output (log Rd) is applied, through conversion gear, to the deflecting prism of the range-finder. The control mechanism comprises a shaft B rotated in accordance with # and turning an arm 1 moving a sliding bar 2 in accordance with sin # a shaft 8 rotated in accordance with α turns on arm 9 to raise a slotted bar 7 according to sin 2α, a pivoted arm 4, linked to the bar 2 and, by a pin 6, to the bar 7 and a horizontally sliding bar 11, moves the bar 11 in accordance with sin # sin 2α. The bar 11 is connected by a ratio link 12 to the slide 13, the pivot 14 of this link being vertically movable by adjustment of the head 17 of a screw 16 in accordance with the height and speed of the aircraft, with the result that the slide 13 moves according to the rate of change of log sin α. The angle # is applied to the shaft B by means of a shaft A and a Hookes joint C, as described in Specification 554,559, [Group XIX], the shaft A being directed at the angle α and rotated in accordance with the angle of presentation ° of the aircraft, the angles being related by the formula tan °=tan #/sin α. A shaft 30 is rotated from the range-finder in accordance with α and turns an annular scale 31. The angle α is applied to the shaft 8, by operation of a head 26, through a differential gear 25 of which one element is driven from the shaft 22 and the third element is connected to a log sin α cam 27 engaging an α cam 28 geared to the shaft 8 ; the cam 28 is on a shaft carrying a scale 32 which is within the scale 31 and is made to follow it by operation of the head 26. Alternatively the shaft 30 may be directly geared to the shaft 8. Constructions of mechanism resulting in a movement in accordance with the others of the above-stated values are described. Specification 129,345,[Class 97(i)], also is referred to.