748,641. Electric indicating systems. SVENSKA AEROPLAN AKTIEBOLAGET. May 15, 1951 [May 17, 1950], No. 11367/51. Class 40(1) [Also in Group XL(c)] A navigation system for aircraft. comprises two mechanical calculating devices responsive to instruments measuring the horizontal speed and the heading of the aircraft which combine and integrate the measured quantities to produce electrical outputs representative of the variations of the respective rectangular co-ordinates of the aircraft position referred to its position at the instant at which integration commenced; such outputs being applied to the X and Y deflection members of a cathode ray tube to produce on the screen thereof a spot image representing the coordinate position of the aircraft. The heading from a gyro-compass 4 (Fig. 1) and the resolved horizontal component of air-speed from a climb and descend compensator 7 responsive to airspeed and angle of climb or descent indicators 5, 6 are coupled into a mechanical integrating computor 3 (Fig. 2) controlling a spot position transmitter 8 which derives the spot deflection voltages. The airspeed indicator mechanically adjusts the sliders of potentiometers 22, 23 to supply cosine potentiometers 7 whose sliders are adjusted mechanically by the angle of climb and descent instrument to derive voltages proportional to horizontal airspeed which control the energization and the speeds of D.C. motors 20, 21 respectively driving discs 28, 29 whose surfaces are engaged by other frictional discs 30, 31 displaceable radially thereacross in accordance with the heading set in by gyro-compass 4 through linkages 32. When the aircraft heading is north disc 30 is at the centre of disc 28 and disc 31 is at the periphery of disc 29, and as the heading varies through east south and west disc 31 is moved through the centre of disc 29 to the opposite side of the periphery and back again while disc 30 is moved from the centre of disc 28 towards its periphery, across its face to the opposite periphery and back to the centre in proportion to the gyrocompass deflection. The rotating discs 30, 31 are geared to rack and pinion arrangements 35, 37 and 36, 38 producing linear motion of the sliding contacts 39, 40 of potentiometers 41, 42, in combination with further superimposed linearmotion of telescopically operating racks 46, 47 driven selectively through pinions 52, 53 by a manual control 56 which initially positions the indicatng spot. The centre point of each of the potentiometers is earthed, while their resistance elements are energized from balanced positive and negative D.C. sources. The output signals from the potentiometer sliders are respectively connected to the X and Y plates 10, 12 and 9, 11 of a C.R. oscillograph 1 through switch 67 and series resistances 57, 58. A transparent map 2 covers the tube screen, and the spot 13 is initially, located by observation of a known point and adjustment of the spot thereto by control 56, after which the spot position indicates the co-ordinate displacement of the aircraft therefrom. The heading of the aircraft is indicated by a beam arrow transmitter 60 switchable by a control 63 to extend the spot into a line 61 (whose length is determined by control 64) angularly representing the aircraft heading. In the beam arrow transmitter (Fig. 3) an inverter 69 generates an alternating voltage energizing through a switch operated by control 63 a square wave generating pentode 70 whose output is differentiated by capacitance-resistance circuits 71, 72 whose peaked outputs energize triodes 75, 76. The respective grid returns are connected through resistors to the sliders of ring potentiometers 79, 80 each of which is tapped at four equally spaced points a, b, c, d. Points 79b, d and 80a, c are interconnected to earth through a resistance 81 whose voltage drop normally biases triodes 75, 76 to cut off while points 79a, c and 80b, d are interconnected to a negative bias supply. The gyro-compass 4 is mechanically connected to rotate the sliders of potentiometers 79, 80 together with the sliders of switches 88, 89 comprising semicircular sectors mutually disposed at right angles and connected to energize relays 86, 87 respectively. The anodes of triodes 75, 76 are respectively resistance coupled through potentiometers 65, 66 to the moving contacts of the relays 86, 87, whose operative and inoperative contacts are respectively connected to the X plates 10, 12 and the Y plates 9, 11 as shown. When the aircraft is on a northerly heading triode 75 is biased beyond cut-off, triode 76 is biased just to cut-off, and relay 87 is operated, so that the pulse appearing on the anode of triode 76 is applied to the appropriate Y plate to produce a repetitive northerly displacement of the spot, and its consequent extension into a line pointing north. When the heading is southerly triode 76 again produces a repetitive anode pulse applicable to the appropriate Y plate for southerly spot deflection since relay 87 is then inoperative. For east or west headings, triode 75 is biased to cut-off and triode 76 is biased beyond cut-off, while relay 86 is alternatively operative or inoperative to apply the resultant repetitive anode pulse to the X plates of the tube in appropriate sense for the correct deflection. For headings intermediate between the cardinal points, both triodes 75, 76 are each conductive to a degree controlled by the biasing voltages from potentiometers, so that the resultant amplitude controlled repetitive anode pulses are applied by relays 86, 87 controlled by switches 88, 89 to the X and Y plates in appropriate senses to extend the spot into a line pointing along the aircraft heading. The length of the line into which the spot is extended is adjustable by the control 64 of ganged potentiometers 65, 66, and the -control 67 operates a switch disconnecting the spot position transmitter, so that the spot reverts to the tube centre and the line into which it is extended indicates the aircraft heading on a scale 68 surrounding the screen of the C.R. tube. The beam spot may be manually adjusted in position in accordance with observations of landmarks or radar beacons, and may be deflected in position by the aircraft radiocompass when the latter is within range of its ground stations. Wind velocity correction voltages may be introduced at point A (Fig. 2). Specification 748,689 is referred to.