Patent GB-495416-A (GB)
Title: Improvements in and relating to calculating apparatus for use in navigation
IPC: G05D1/02
Filed: 1937-05-14
Abstract: 495,416. Calculating-apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. May 14, 1937, No. 13672. Convention date, May 16, 1936. [Class 106 (i)] An apparatus for use in steering a craft, such as an aeroplane or ship, either manually or automatically, on a straight course and employing two reference points located laterally to the course and on a bearing making a known angle with the course and at known distances from the reference points, comprises means for initially setting the known quantities and means for continually feeding in the variable quantities. Means are also provided for indicating the distance travelled by the craft, the speed thereof, and the direction and velocity of the wind. Regarding the diagram, Fig. 1, which represents an aircraft flying on a straight course D, the reference points A and B are at distances m and n from a point O on the course which makes an angle C with the line AB. Radio transmitters 2 and 3 are situated at the points A and B and tuned to act upon receivers with directional loops 5 and 6 mounted on the aircraft which loops form varying angles M and N with the course and points A and B. As long as the aircraft is maintained on the course D, the known and variable quantities are related by the equation (m + n) Cot C - m Cot M + n Cot N =O. The distance travelled is given by the equation D=m Sin (C-M) Cosec M. In the apparatus shown in Fig. 2A, the loops 5 and 6 are maintained oriented with respect to the transmitters 2 and 3 by known means and a magneto compass 8 is provided with means similar to that described in Specification 428,212, [Group XL], for maintaining the pole pieces in an east and west direction. For entering the known quantities, three sets of mechanism I, II and III are provided, each set including a pivoted arm 16, gear segment 17, pinion 18, horizontal slide 19, vertical slide 21 with rack 22, and pinion 23, the arm 16 and slides 19, 21 being engaged by a pin 24. The angle C is initially set by rotating a crank 26 connected with an indicator 28 and with the pinion 18 to set the arm 16 of the mechanism I. The distance m is set in the mechanism I by rotating a crank 30 connected with an indicator 32 and with a differential gear 33 to set the slide 19. The distance n is also set on the slide 19 by the operation of a crank 35. In the mechanism II, the angle of rotation of the loop 5 by the orienting means 12 is added to the angle of the aircraft axis with respect to the north by the operation of the compass and by means of the differential gear 40 to give the angle M<1>, Fig. 1. The magnetic bearing of the course J is set by operation of the crank 44 and is subtracted from the angle M<1>; the difference M<1>-J which is equal to 180-M is transmitted to the arm 16'. The slide 19<1> also receives a displacement proportional to the distance m. In the mechanism III is set up on the arm 16<11> the angle 180-N through the movements of the compass 8 and the orienting means 13, the operation of the crank 44 and the action of the differential 51. Also the slide 19<11> by its operative connection with the crank 35 receives a displacement proportional to the distance n. By means of these three mechanisms, the three terms of the first equation are transmitted by the slides 21, 21<1> and 21<11> to the pinions 23, 23<1> and 23<11>, and differential gearing 57, 59 to an indicating dial 61 giving the algebraic sum of the three terms. So long as the zero mark on the dial stands opposite the index 62, the aircraft is on its course. If the course passes through one of the reference points, say B, the quantities N and n will be zero, and the mechanisms II and III will be disconnected by opening clutches 43 and 53. The aircraft can be steered automatically in a manner similar to that described in the above-mentioned Specification. As shown in Fig. 2A, the rudder 65 is attached by cables 66 to a gear-wheel 67 adapted to be rotated in one or other direction by a reversible motor 68 controlled by a relay 69 having windings 70, 71 in the circuit of a battery 72 and controlled by discharge devices 73, 74 associated with a polarized relay 75 arranged to be energized in one direction or the other in accordance with the position of a contact 76 on the dial 61 that co-operates with a resistance 77 in parallel with a similar resistance 78 and on which bears a contact 80 carried by the gear 67. Distance and speed indications. The crank 26 whereby the angle C is set is connected by a shaft 88 to a gear 85 having a slot 87 forming a cosecant cam. Mounted concentrically with the gear 85 is an outer gear 89 having a radially slotted arm 90 which is adapted to be rotated by means of a differential gear 91 and spur gearing 92 by the shafts 42 and 88 through an angle C-M whereby the relative movement of the gears 85, 89 is equal to the angle M. By this means a pin 96 working in the cam 87 and slotted arm 90 receives a vertical displacement proportional to sin (C-M) Cosec M. This displacement is imparted to a vertical slidable bar 95 movable between guides and slotted to receive a pin 104 working in the slot of a pivoted arm 98 and that of a vertical slide 103. The arm 98 engages at its lower end a pivot pin 99 and at its upper end is attached to a nut 100 on a screwed shaft 101 that receives a displacement proportional to the distance m by its connection with the crank 30 so that the slide 103 is moved horizontally a distance proportional to that travelled by the aircraft and this movement is transmitted to an odometer 107. The average rate of movement of the slide 103 is a measure of the speed and is shown on a known form of speed indicator 108, Fig. 2B, by its connection with an overrunning clutch 109 and fly-wheel 110 with the shaft 106. Direction and velocity of wind indications. With regard to the diagram of velocities, Fig. 3, wherein W represents the wind speed relative to the ground, G the ground speed of the aircraft, and S the speed relative to the wind, the direction and velocity of the wind may be expressed by the equations The angle of drift w is obtained by subtracting the angle of the course relative to the northsouth line from the angle of axis of the aircraft relative to that line. This is effected by the differential gear 116 that is connected to the differential gear 51, crank 44, compass 8 and differential gear 50. The differential gear 116 transmits the angular movement w to a shaft 119 that is connected directly to the outer gear 120 of a pair of ring gears 120, 121 and indirectly through a differential gear 122 to the inner gear 122. The gear 120 carries a yoke 123 in which is mounted a screw 124 on which is threaded a pinion 125. Co-operating with a pin 127 on the screw 124 is a vertical slide 126 and a horizontal slide 128 mounted in guides. The position of the pin 127 with respect to the centre of the ring gears is proportional to S, the velocity of the aircraft with respect to the wind and is obtained by a known means comprising an air chamber 130 with an open-ended tube 132 terminating in a bellows 134 and a closed pipe 131 with perforations 133 and ending in the wall of the chamber. The bellows is connected by a crank 135 to a shaft 136 carrying a contact 141 that cooperates with contacts on a wheel 139 adapted to be rotated in one or other direction by a reversible motor 138 to impart a movement to the differential 122 and shaft 143. By this means the displacement of the slides 126, 128 is proportional to S cos w and S sin w respectively. The quantity S cos w is transmitted to one side of a differential 151, the other side of which is moved in accordance with the value G by the rotation of a shaft 149 from a reversible motor associated with the speed indicator 108. The difference of these values is imparted by a screwed shaft 152 to a vertical slide 155 operatively connected to an arm 154 that takes up a position in accordance with the angle X and transmits this value to an indicator 158. The mechanism by means of which the velocity of the wind is indicated comprises ring gears 160, 161 and 160<1>, 161<1> similar to the ring gears 120, 121 and vertical slides 165, 165<1> that impart movements to the opposite sides of a differential 174 is in accordance with the terms S cos (w-X) and G cos X, the result of which is transmitted to an indicator 176.