Patent GB-970704-A (GB)
Title: Improvements in or relating to navigational apparatus
IPC: G01C21/20
Filed: 1959-10-19
Abstract: 970,704. Navigational computers. J. G. WRIGHT, J. R. B. STEACIE and J. P. DUHAMEL. Oct. 19,1960 [Oct. 19,1959], No. 35335/59. Heading G4G.  An aircraft navigational computer (Fig. 1) of the type which presents the instantaneous range and bearing to the selected geographical reference by means of an indicator 13R and pointer 13B comprises an air plot sub computer (units 12, 40, 46) to provide an analogue signal of distance travelled along the aircraft heading from a starting point in cartesian form, a wind plot sub computer 11 providing an analogue signal in cartesian form of the accumulated drift due to the wind speed and direction for the duration of the aircraft's flight and a vector generator (units 10 and 20) providing signals representing the cartesian co-ordinates of the selected geographical reference relative to the starting point. An arrangement is provided for algebraically summing these three analogues to produce an output signal analogous to the instantaneous value of the cartesian co-ordinates of the selected geographical reference relative to the aircraft position and for converting this output signal into polar co-ordinates and generating analogues of instantaneous range and bearing of the aircraft relative to the selected geographical reference. Driving arrangements are incorporated to position the range indicator and bearing pointer according to these generated analogue signals. Furthermore, an arrangement for disconnecting the drive from the range indicator and bearing pointer is incorporated, so that the presentation may be manually adjusted. A feedback signal corresponding to this adjustment is applied to the summing arrangement to cause an out of balance signal to be generated and this signal is applied as a correcting signal to a selected sub computer so as to balance the summing arrangement. The command vector is supplied by means of a push button unit 10 which is arranged to enable one of a number of predetermined positions relative to a given datum to be selected. The voltages representing the cartesian co-ordinates of the selected position are supplied on lines 16, 17 (Fig. 2A) to the summing unit 25 (Fig. 2G). To select positions not given by the unit 10, correcting factors may be added from the vector adder 20, which includes a resolver to convert from distance and bearing as set in to the unit to voltages representing cartesian parameters. These voltages are also supplied to the summing unit 25. The resolver 34 of a wind unit 11 is initially positioned by manually setting into it the wind direction (derived from meteorological forecasts) and feeds output voltages to the potentiometers 32, 33, whose sliders are set in accordance with the wind speed. The outputs from these potentiometers feed potentiometers 36P, 37P whose sliders are controlled from a timing unit 38 so that the outputs from these potentiometers, which are fed to the summing unit 25 represent the accumulated wind vector in cartesian co-ordinates. An input of true air speed is obtained from an air speed indicator 12 and is applied via a servo follow-up unit to a ball and disc integrater 41. A clock mechanism 42 drives the integrator so that a shaft rotation representing distance travelled is obtained and applied to the mechanical resolver 45. Also applied to this resolver is a shaft rotation representing grid heading, derived from a motor 52 which is driven by signals from a synchro differential 53 operated from a transmitting compass 46. The synchro differential 53 corrects the signal from the compass according to latitude by means of a link 162 to a "grivation" motor 161, operated according to signals set in representing latitude. The mechanical resolver 45 yields outputs as shaft rotations representing the cartesian parameters of the distance travelled. These are fed through the mechanical stores 60, 61, and converted to voltage signals before being applied to the summing unit 25. In accordance with its three input signals, the unit 25 produces a difference signal which is fed (with all switches in the positions shown) to a resolver 85 wherein the cartesian co-ordinates are converted to polars. The signals representing these co-ordinates are then supplied through the amplifiers 93, 94 to a range motor 101 which drives the indicator 13R and to a bearing motor 108 which drives the pointer 13B. By means of a resolver 120 and potentiometers 123, 124, the range and bearing are converted back to cartesian co-ordinates and the signals representing these are fed back to the input of the unit 25, so that feedback is established round the system. Should at any time the pilot by means of some other navigational check determine that the readings given by the computer are incorrect, he may correct either the wind or air data in accordance with the determined position. By suitable switching operations, described in detail in the Specification, the amplifiers 93, 94 may be disconnected while the new information is set in to the range and bearing indicators by controls 112A, 110A. If the air data is to be corrected a fixed shaft resolver 170 is brought into the system following the unit 25; this is arranged to feed the motors 180, 181 and these, through their output shafts 185, 186 drive the differentials 62, 63 to correct the air data and rebalance the bridge. To correct the wind data the resolver 200 is brought into the system; this drives the wind motors 210, 211 to reposition the wind resolver 34 and the potentiometer wipers 32, 33. A facility is provided for looking at the wind value so derived, and correcting it again if unreasonable.