Patent GB-135490-A (GB)
IPC: F41G3/24
Abstract: 135,490. Boettcher, A. H. Nov. 18, 1918, [Convention date]. Sights. - Relates to sights for use in bomb or mail dropping from aircraft, of the kind having means for indicating the course on which to steer in order to pass over an object, and consists (1) of a sighting-instrument, comprising a universallymounted sighting-member, a ground-speed bar adapted to be set by a known vectortriangle device in the direction of motion of the aircraft relatively to the ground, and means actuated by the sighting-member for operating an indicator in the pilot's cabin to show the position in azimuth of the ground-speed bar relatively to the sighting- member; and (2) in mounting the sighting- member on a vertical bar adapted to be elevated in accordance with the height of the aircraft above the target, and employing in conjunction with it, for determining the dropping angle, a foresight adjustable by the aforesaid vector-triangle device along the grilind-speed bar. A combined compass and level forms part of the sighting-instrument. The invention is described as applied to a flying- boat. The sighting-instrument is carried on a support, universally mounted on a bracket 9 secured to the bow in front of the cockpit. Rigid with a sleeve 20 secured to the support is a graduated air-speed bar 23 set parallel to the centre line of the boat body and rotatable round the sleeve 20 is a tube carrying a graduated ground-speed bar 35 and, parallel thereto, a bar 38 slotted to receive a pivot member 39 slidably mounted on a graduated wind-speed bar 28, and adjustable therealong for wind-speed by operating a head 40. A compass 27 is rigidly connected with the wind-speed bar 28 by means of a vertical shaft mounted to rotate in a carrier adjustable along the air-speed bar 23. Rigid with the ground-speed bar 35 is a box 42 in which are slidably mounted two parallel racks 43, 44 geared together by a pinion set in the box so that their movements are equal and opposite. The rack 43 is connected to the pivot 39 so as to move therewith; and the rack 44 carries a stem 46 supporting a carrier 47 slidable along the ground-speed bar 35, the stem 46 and the pivot 39 being equidistant from the axis of the sleeve 20. The bombing foresight 48 is mounted on the carrier 47. The backsight comprises ring sights 66, 67 on an arm 64 pivoted horizontally to a graduated height-bar 62 elevatable without rotation by rack-and-pinion gear in a sleeve 39 turning within the sleeve 20. The compass 27 has a convex glass cover rigid therewith, and is almost filled with liquid, the residual air-bubble beneath the glass acting as a level for the instrument. An arrow 54 is painted on the glass in a direction parallel to the wind-speed bar 28, and a clampable ring 50 carrying a mark 56 is rotatably mounted on the casing above the swinging compass card. Holders 31, 32 contain correcting magnets. Mounted below the pinion box 42 and rigid with the ground-speed bar 35 is a casing 37 containing an horizontal insulating-board 57. Fig. 7, on which are nineteen electric contact-studs 58 individually connected to nineteen electric lamps mounted in a frame 73 in the pilot's cabin. The lamps are of the telephone-switchboard type, each set between jack springs 79, Fig. 10, secured to an insulating- strip 80. The sleeve 59 supporting the heightbar 62 carries an horizontal arm having a brush 60 adapted to wipe over the studs 58 as the sleeve 59 is rotated in consequence of the movements in azimuth of the sight-arm 64. The electric circuit through the lamps is completed from the brush 60 through a switch 12 on the bracket 9 and a battery, by a cable common to all the lamps. The arrangement is such that, if the sight-bar 64 is parallel to the ground-speed bar 35, the brush 60 rests on the centre contact A, and when the switch 12 is closed, the centre lamp on the pilot's board 73 is alight. Before the machine leaves the ground, the compass is rotated until the arrow 54 points in the known direction of the wind, and the ring 50 is turned until the mark 56 coincides with the N-point of the compass card. The observer can subsequently keep the direction of the windspeed bar constant by rotating the compass to maintain this coincidence. The compass carrier is slid along the air-speed bar until a pointer 30 indicates the estimated air-speed. The pivot 39 is adjusted along the wind-speed bar until a pointer 41 indicates the known wind-speed. In this manner, a vector triangle for air-speed, windspeed, and ground-speed is established by the three bars 23, 28, 38. The bar 35, being parallel to the bar 38, gives the direction of the groundspeed, and the effect of the racks 43, 44 is to displace the foresight 48 along the bar 35 so that its position with respect to the scale thereon gives the magnitude of the ground-speed. In the air, the pilot at first steers roughly in the direction of the target. When the target is sighted, the observer sets the height-bar 61 to the known height of the aircraft, and maintains the sights 66, 67 in alinement with the target. He then closes the switch 12, whereupon one of the lamps on the pilot's board 73 will light. The pilot steers until the illumination shifts to the centre lamp, the observer all the while maintaining the aforementioned coincidence on his compass. The sight-bar 64 and the ground-speed bar 35 will then be parallel, and the target will eventually be picked up on the edge of the bar 35, moving therealong towards the foresight 48. At the instant that the target alines with all three sights 66, 67, 48, the observer releases the bomb. The zeros of the air-speed and ground-speed scales are adjusted to correct for ' lag " in dropping. A method is described of determining the wind vector during flight. It is stated that the electric indicating-means may be replaced by a mechanical indicator.