Patent GB-536682-A (GB)
Abstract: 536,682. Anti-aircraft gun sights. DANSK INDUSTRI SYNDIKAT, COMPAGNIE MADSEN AKTIESELSKABET. Nov. 16, 1939, No. 30187. Convention date, Aug. 1. [Class 92 (ii)]  Open sights for anti-aircraft guns comprise a gimbal-mounted stretched-wire foresight frame with oppositely-moving pointers adjusted for enemy speed and a peep-hole back sight adjusted longitudinally with respect to the foresight for range and spotting and vertically by an automatic cam to suit tangent elevation, the gun and foresight frame being connected by gearing for opposite motions both in elevation and training to keep the sight on the target when adjusting the gun to the desired lead angle. In the form shown, the sight comprises a foresight frame in the form of a pair of parallel threads 23, Fig. 5, co-operating with oppositely-adjusted needles 29 moved by knob 25 with respect to a central point 24 to set the sight for estimated enemy speed. The foresight frame is mounted on a second frame 16, Fig. 3, mounted on an arm 19 connected with the gun trunnions for synchronous movement in elevation and training with the gun. The frame 16 also carries a peep-hole back-sight 40, Fig. 7, having a roller 45 engaging a solid tangent elevation cam 46 rotating in elevation with the gun, the back-sight being set along the frame 16 longitudinally with respect to the foresight by rotating a screw 43 to suit the range and to correct spotting errors. The foresight frame is gimbal mounted about the centre 24 to the frame 16 and is moved about the vertical support 30, Fig. 5, by gearing 35, 66 connected with the gun-training gear and about the horizontal axis x-x by gearing 38, 34 connected with the gun elevating gear. The arrangement is similar to that used in guns having an "independent line of sight" and is such that, after initial adjustments of the foresight frame to bring the target motion between the parallel threads, the gearing moves the sight through an equal and opposite angle to the gun both in elevation and training and the required angle between the gun and sight is obtained when the back sight, the needle 29, and the target are in line. Similar sights as above described are mounted for use by the gun elevator who occupies a seat E, Fig. 3, on the right hand side of the gun and by the gun trainer occupying a seat T. The sights are cross connected for synchronous movements by shafts passing through tubes 17. The sight-carrying frames 16 are mounted on pivots 18 on arms 19 on the gun trunnions 2. The shafts 60, 70 leading from the training and elevating gear to the gimbal mounting of the foresight frame have disconnectable couplings operated by handwheels 64<SP>1</SP>, 100 for setting the sight threads parallel to the direction of movement of the target, a further handwheel 56 serving to control the sight to suit a diving or climbing target. The sight spotter operates the handle 50 controlling the back sight and a further knob 20 for moving the frame 16 about the pivot 18 for correcting the aim by noting the bursts. The sight is shown mounted on the trunnions of a gun provided with a vertical pivot supported by legs 6 but it may be mounted on a director stand remote from the gun position when a battery of guns is to be controlled.