Patent GB-621838-A (GB)
Title: Improvements in or relating to radio aerial navigation systems
IPC: G05D1/02
Filed: 1944-07-21
Abstract: 621,838. Automatic control systems. CURTIS PUMP CO. July 21, 1944, No. 14026. Convention date, Nov. 29, 1943. [Class 38 (iv)] [Also in Groups XL (a) and XL (c)] In a radio navigational system for enabling an aircraft to follow automatically predetermined flight path, a directional radio beam is propagated towards the ground below the aircraft and the radiation reflected by corner reflectors located along the course is picked up on the aircraft by a receiver, the output from which is used for automatically controlling the course and elevation of the aircraft. The radio system is identical with that disclosed in Specification 621,837, [Group XL (a)], in which the course is defined by pairs of corner reflectors located on the ground with a constant lateral spacing and the ground is scanned laterally and longitudinally by a directional radio beam, the reflections being picked up on the aircraft by a relatively low-gain receiver, the output from which is applied to intensity modulate a cathode-ray tube which is scanned horizontally and vertically in synchronism with the aerial scanning, resulting in the formation of electron image spots of the reflectors. The lateral spacing of a pair of image spots depends upon the altitude of the aircraft and the lateral displacement of a pair of image spots with respect to a reference line on the screen of the cathode-ray tube depends upon the amount by which the aircraft is off course. According to the present invention four collector electrodes 77 - 80, Figs. 8 and 9, are included in the cathode-ray tube, which are shaped so that the electron images 198 and 199, Fig. 9, fall in the spaces between the plates when the aircraft is on the correct flight path, but the electron beam impinges on one or more of the plates when the aircraft deviates from the path. When the electron beam impinges on the plates, voltages are developed across the associated load resistances 114-117, which are applied through the rectifiers 126-129 and the long-timeconstant circuits 134-136, to trigger off the gas discharge valves 118-121 and thus energize the relays 149-152, the operating coils of which are included in the anode circuits of the valves. Each of the relays 149 and 150 has a single normally open contact 156 and 157 and each of the relays 151 and 152 has a pair of normally open contacts 158, 159 and 160, 161, the closure of a selected combination of these contacts connecting one of the windings 172, 173 and 170, 171 of the reversible rudder and elevator motors 169 and 168 to an A.C. voltage 174. The circuit to the winding 172 of the rudder motor is completed through the normally closed contact 181 of the relay 178, the operating coil of which is in parallel with the rudder motor winding 173, the circuit of which is completed through the normally-closed contact 183 of the relay 180 whose operating coil is in parallel with the motor winding 172 so that the energization of one winding automatically open-circuits the other winding. Operation of relays. When the aircraft is on course but too low, the spacing of the image spots 198, 199 is increased symmetrically so that the electron beam impinges on the plates 77 and 80 to energize the relays 149 and 152 and hence close the contacts 156, 160 and 161. Contacts 156 and 161 energize the relays 178 and 180 to open-circuit the rudder coils and the contacts 156 and 160 complete the circuit to the elevator motor coil 170, causing the aircraft to ascend. Similarly, when the aircraft is on course but too high the electron beam impinges on the plates 78 and 79, energizing the relays 150 and 151 to close contacts 157, 158 and 159, which open-circuit the rudder coils and energize the elevator motor coil 171, causing the aircraft to descend. When the aircraft is at the correct altitude but to the right of the course the image spots 198, 199 are displaced to the left in Fig. 9, causing the electron beam to impinge on the plates 78 and 80, energizing the relays 150 and 152 to close the contacts 157, 160 and 161, which complete the circuit to the rudder motor winding 172, causing the aircraft to turn left; similarly when the aircraft is to the left of the course, the electron beam impinges on. the plates 77 and 79 and the rudder coil 173 is energized, causing the aircraft to turn to the right. When the electron beam impinges on a single plate, the aircraft has deviated from both the correct course and altitude and in such cases the relays operate to correct the course deviation first and then the altitude deviation.