Patent GB-696793-A (GB)
Title: Improvements in position-indicating instruments, especially for aircraft
Filed: 1951-08-17
Abstract: 696,793. Electric indicating systems. SOC FRANCAISE D'EQUIPEMENTS POUR LA NAVI GATION AERIENNE S.F.E.N.A. Aug. 17, 1951 [Sept. 19, 1950, Feb. 9, 1951]. No. 19482/51. Class 40 (i). [Also in Group XX]. An instrument for indicating the geographical position of a craft, e.g. an aircraft, comprises a tubular arm 4 Fig. 1, universally mounted about a point 7, and carrying, at its rear end, a part spherical member 13 normally engaged and driven by a drive roller 23 which is rotated proportionately to the distance travelled by the craft, so that an index 34 at the rear end of the arm also moves proportionally to the craft displacement relative to a transparent part spherical dial 41 carrying geographical reference markings. The drive roller 23, Fig. 2 is carried in a casing 22 coupled at 48 to a receiver 21 set angularly in known manner by remote control in accordance with the compass heading of the craft. The plane of the drive roller 23 is thus correspondingly set and varies the direction of drive to the member 13 so that the index 34 moves over the dial in accordance with both the displacement and heading of the craft. The drive to the roller 23 is effected, e.g. by a log which impulses the fixed annular magnet 17 at a rate proportional to the speed of the craft. The magnet, through a sector shaped armature 24, carried by casing 22, a pawl 46, ratchet 47 and gearing 49- 51, then advances the drive roller 23 according to the craft displacement. The index 34, in the form of a miniature craft, is oriented according to the craft heading, and for this purpose is carried by a shaft 3, housed within the tubular arm 4, and carrying at its rear ends permanent magnets 12 which align themselves with the diametral poles of an annular magnet 15 secured to the drive-roller casing 22. To zeroise the instrument an annular magnet 9 is energized to move a slide block 26, carrying the outer gimbal ring of the universal mounting, to the left, whereupon the drive-roller 23 and the spherical member 13 disengage, and the arm 4 is pulled into axial alignment with the instrument casing 2 by the magnet acting on a ring armature 27 rigid with the arm 4. Wind drift may be corrected by marking the geographical references on a concentric transparent dial 40 in lieu of dial 41, the dial 40 being held against the dial 41 by a spring rod 39 adapted to be moved longitudinally at an adjustable rate correspondingly to wind velocity by a clockwork movement 36. The movement is carried by an annulus which is first adjusted relative to an index 1 on the casing 2 according to the wind direction, after which the knob 38 is adjusted according to wind speed whereupon the rod 39 moves the dial 40 relative to the dial 41 and to the index to compensate for wind drift. In a modification, Fig. 3 zeroising is effected by rotation of a knob 9 through 180‹. An annular cam Z on the knob shaft b, rocks, through a follower roller c, a cradle carrying the universal pivot point of the index arm to the left against a spring D to disengage the part spherical member 13 from the drive roller. Thereafter a further cam g on shaft b, through a link h, closes a three leaved iris diaphragm against the action of a spring m, the diaphragm centering the index arm. Further rotation of the knob 9 through 180‹ opens the iris diaphragm and re-engages the drive roller under the action of the respective biasing springs. A spring stop a holds the knob 9 in its respective positions, and a spring f ensures that it is rotated in one direction only. The angular movements of the casing 22 are, in this case, transmitted to orient the index arm 4 through a slotted crank S, a radius arm T and gearing in a casing G, and a further pointer p movable with the index 34 is provided.