Patent GB-186099-A (GB)
Title: Sighting device for adjusting the sight line when dropping projectiles from air-crafts
IPC: F41G3/24
Filed: 1921-05-17
Abstract: 186,099. Zeiss, C., [Firm of], and Killat, G. May 17, 1921. Sights.-Relates to bomb-dropping sights in which allowance is made for lag in dropping due to air-resistance, and for wind, and consists in a device in which the sight-line is displaced (1) rearwardly from the vertical in the central longitudinal plane of the aircraft by an angle depending on the height and the air-speed of the aircraft, and (2) laterally, from the position so determined, in the direction of the ground-speed of the aircraft by an angle depending on the height and the ground-speed of the aircraft. Fig. 1 illustrates the theory underlying the invention. O represents the dropping-point on the aircraft moving horizontally in the XZ plane with air-speed Vo and ground speed V, and subject to a wind-speed W as indicated by the velocity, triangle V0 V W. K represents the trajectory, and C the impact-point in the absence of wind. If t is the time of fall of the bomb, then, owing to wind, the point C suffers a displacement equal to Wt in the direction of the wind, bringing it to Zo, which should coincide with the position of the target at the instant of release of the bomb if a hit is to result. The displacement triangle CZoD is shown completed, its sides being parallel to those of the velocity triangle. Thus, with the notation shown, if the sight line is displaced (1) rearwardly from the vertical OP, in the plane XZ containing the longitudinal axis of the aircraft, to the position OD determined by the line PD, equal to V0t-R, and then (2) laterally to the position OZ0 determined by the line DZo, equal to Vt, a hit should be secured if the bomb is released when the target comes into alignment with the sight-line OZ0. If, for example in an air-ship, the aiming- point O<1> does not coincide with the dropping- point O, a correction M must be applied in the expression for PD. In the devices described, a horizontal plane of reference in the aircraft is employed, and reduced distances B, A corresponding to PD and DZo are employed in the settings. In one form, shown in plan in Figs. 4 and 5, a glass plate a carrying cross-marks x, y is mounted in a stabilized frame d cardansuspended in a socket g, and viewed through a diopter p which is situated above the plate., and is adjustable in the central longitudinal plane of the aircraft by a screw q to deflect the sight-line by an amount corresponding to the displacement B defined above. For a given air-speed, this displacement is a function of the height of the aircraft, so that interchangeable displacement scales for different air-speeds, graduated according to height, may be employed. The plate a and its mounting are rotatable in the socket g to direct the longitudinal mark x on the target, and the deflection of the sight-line corresponding to the displacement A defined above, which is a function of the height and the ground-speed of the aircraft, is imparted by displacing the plate a by means of a mechanism comprising a slotted lever b pivoted at 20 on the frame d, and engaging a pin 22 on the plate a. The lever b is set by first adjusting a slide 23 along a heightscale H by operating a wheel l, and then adjusting a slide 25 along a ground-speed scale V on the slide 23 by operating a wheel m, the resultant of these adjustments being communicated to the lever b by a pin 26 engaging a slot in the lever. The ground speed of the aircraft may be determined in known manner by means of a transparent travelling band c, driven by clockwork and carrying marks j, the speed of the band being adjustable until the marks appear stationary with respect to objects on the ground. A modification is described in which a telescope 17, Fig. 8, is mounted to pivot at 0, corresponding to the position of the diopter p, and to engage slidably at E a stabilized body 1, which may be rotated about a vertical axis through 0 to set the sight-line in a vertical plane containing the target. The point O is adjustable in the same manner as the diopter p to impart to the sightline the deflection corresponding to the displacement B. The point E is adjustable by means of a travelling band 6, similar to the band c, driven by friction-disc gearing 10, 11 operated by clockwork, at a speed adjustable by a screw 9, which transmits through a horizontally displaceable slide 12 to a slotted link 3 pivoted at O a displacement corresponding to the ground speed of the aircraft. The link 3 is also movable by means of a slide 15, which is displaceable vertically according to the height of the aircraft by operating a screw 14. A mark 4, carried by the link 3 so that it may move from outside the telescope into the plane of the cross-wires, is thereby adjusted in accordance with the displacement A defined above. The speed of the clockwork is adjusted to maintain the target 'stationary in the field of view of the telescope, and the bomb is released when the mark 4 coincides with the cross-wires. Specifications 27584/13, 359/14, 18482/14, 125,468, 135,490, 145,810, and 147,486 are referred to.