GB147486A - Improvements in sighting devices for air-craft - Google Patents

Abstract

147,486. Zeiss, C., [Firm of]. Aug. 13, 1917, [Convention date]. Sights.-Relates to bomb-dropping sights of the kind comprising a telescope having a sighting-mark which is rotatable relatively to the aircraft, either by itself or along with the telescope, and is therefore adjustable in the direction of flight, the sighting-line being primarily inclined at an angle a to the vertical in the vertical plane of flight of the aircraft, the angle a being determined by the equation tan a = vgt-R/H where vg is the overland-speed of the aircraft, t the time of fall of a bomb, R the lag of the bomb on the assumption that the air resistance acts only in the plane of flight, and. H the height of the aircraft. According to the invention, a wind correction is applied to the angle a by rotating the telescope objective, such correction having a component in the plane of flight and a component perpendicular to this plane. The invention is shown applied to a telescope sight mounted in gimbals to maintain the tube a vertical. The tube a is rotatably mounted in a ring b. The objective a<1> is carried by a ring d adapted to be rotated about a vertical axis Y Y to apply the wind correction. Below the objective are two reflecting prisms a<5>, a<6>, one of which a<6> is rotatable to incline the sight-line at the angle a. The tube a, ring d and fixed ring b are so connected by gearing that when the telescope tube a is rotated the ring d carrying the objective is rotated through the same angle in the opposite direction. In the zero position of the sight, the principal section of the prisms a<5>, a<6>, which is indicated by a course wire in the telescope, lies parallel to the fore-and-aft axis of the aircraft. In use the prism a' is rotated to set the sight-line at the angle a, and the tube a is rotated to bring the course wire parallel to the line of flight of the aircraft. The objective is thereby rotated and the wind correction applied.