Patent GB-675758-A (GB)
Title: Automatic steering of aircraft towards radio beams
IPC: G05D1/02
Filed: 1948-08-06
Abstract: 675,758. Radio navigation. BENDIX AVIATION CORPORATION. Aug. 6, 1948 [Sept. 19, 1947], No. 20832/48. Class 40 (vii). [Also in Group XXXV] General function. In an aircraft fitted with an automaticapproach-control-system (such as that described in Specification 675,751) for controlling flight along a directional radio beam through an automatic pilot (such as that described in Specification 662,831, [Group XXXV]), an "orientation unit is arranged to steer the craft initially towards the beam, when it is within the beam pattern, before the approach-control is allowed to operate. The orientator unit disconnects the approach-control from the automatic-pilot and feeds in a first turn-signal to cause the craft to take the shortest turn towards the beam, and a second turn signal to cause the craft to turn parallel to the beam after crossing it. The polarity of the first turnsignal is determined (i) by a signal developed from the master - direction - indicator and the known localizerbeam-heading (e.g. as obtained from a map) depending on whether the craft heading lies in a semi-circular sector " a " or " b " facing away from or towards the transmitter, Fig. 10, and (ii) by a signal from the initial stages of the flight-path-computor depending on whether the craft is on the " c " or " d " side of the beam, Fig. 11. Thereby an aircraft heading, as shown, for example, in sector " a ", Fig. 10, is caused to follow a path as shown in Fig. 9, the turn signal from the orientator unit causing the craft to fly towards the beam at right-angles to it, until it crosses the beam when a further turn signal developed from the flightpath-computor causes it to turn parallel with beam, after which normal approach-control operates. System arrangement, Fig. 1. The general arrangement of the orientationunit 10 with respect to the approach-controlsystem of Specification 675,751 is shown in Fig. 1. The flight-path-computor of that Specification is shown in Fig. 2 with modifications, described later, for orientation control. In that approach control system, the rudder servomotor 37 is controlled by (i) a signal developed in flight-path-computor 11 having a magnitude dependent on time of turn and a polarity dependent upon the " c " or " d " side of the beam as sensed by the localizer radio; (ii) a rate-of-turn-signal from pick-up 33 on gyro 15; (iii) a compass signal from direction indicator pick-up 27. These signals are fed in series to the servo-amplifier 29 together with an opposing follow-up signal from the rudder pickup 16. The ailerons are similarly controlled by a second output of the flight-path-computor, and bank-signals from the horizon-gyro to produce a co-ordinated turn. Glide-path control of the elevator is effected in like manner, but is of no interest to this application. Orientation unit, Fig. 3. Turning towards beam.-The " a " or " b " heading is sensed by an inductive direction device 12 comprising a stator 132 energized from a pick-off 128 in the master-directionindicator, Fig. 1, and a crossed coil rotor which is set to the known beam heading, whereby coil 134 will have a minimum signal when the craft is at 90 degrees to the beam. (The other coil 135 has a minimum output when the craft is parallel to the beam as is used for the second turn control). Coil 134 is connected to the grids of a discriminator valve 111 so that either the " a " or " b " heading self-holding relay 113 or 115 and their repeater relays 114 or 116 pick up when relay 123 is momentarily energized over button 124. Relay 123 also energized a changeover relay 122 to disconnect the outputs of the discriminator tube 74 in the flight-pathcomputor, Fig. 2, from the following stages, and insert self-holding relays 118, 120, so that either one or the other of the relays is energized according to whether a " c " or a " d " signal is sensed by the localizer radio. The respective repeater relay 119 or 121, maintains change-over relay 122 when press-button-controlled relay 123 drops out. The turn-signal obtained from transformer 117 is injected into the grid circuit of the computor output valve 102 by means of a potentiometer 189, Fig. 2, to control the rudder and ailerons (as in automatic-approach), the polarity of the signal being determined by relay 114 or 116 and 119 or 121. During the turn the compass signal which is normally fed into the computer at leads 100, 101, Fig. 2, from transmitter 27, Fig. 1, is removed by the heading relay 114 or 116 which disconnects lead 192 to de-energize the clutch 191 so that transmitter 27 is spring set to zero as described in Specification 662,831, [Group XXXV]. When the craft is turned at right angles to the beam, Fig. 6 (not shown), the signal in coil 134 falls to zero and heading relay 113 or 115 and its respective repeater drops out to remove the turn signal and re-energize the compass transmitter clutch so that the craft is kept on a 90 degrees heading towards the beam. Turning parallel to the beam.-As the craft crosses the beam, and the localizer radio output signal drops to zero, relay 118 or 120 and its associated repeater drops out, de-energizing changeover relay 122 so that the flight-patchcomputor is reconnected (as for approach control) to produce a turn-signal dependent on time of turn. The compass-signal from transmitter 27 will again be removed because the clutch 191 was de-energized when 122 released, and while the craft was steering towards the beam a maximum signal in coil 135 of direction device 12 applied to the grid of valve 126 energized self-holding relay 127. As the craft turns parallel with the beam, Fig. 8 (not shown), the signal in coil 135 falls to zero and relay 127 releases to re-energize the compass-transmitter-clutch, and thereafter approach-control is effected as described in Specification 675,751. Specification 662,836, [Group XXXV], also is referred to.