Patent GB-636180-A (GB)
Title: Improvements in or relating to devices for determining the divergence from a preselected course of a mobile vehicle
Filed: 1946-08-12
Abstract: 636,180. Radio-navigation. DECCA RECORD CO., Ltd., WAYNE KERR LABORATORIES, Ltd., CALVERT, R., FENNESSY, E., and ROBERTS, G. E. Aug. 12, 1946, Nos. 23899, 27085 and 29708. [Class 40 (vii)] [Also in Groups XXXVIII] and XL (b) A system for indicating the relation between the existing and planned positional ordinates of a mobile vehicle on a journey comprises means for measuring the existing values of said ordinates, a record of said planned ordinates and means for determining and indicating the difference between the existing and corresponding planned values of the other ordinate or ordinates at the instant of identity of the existing value of one of said ordinates with the planned value. The record is preferably provided with a succession of values of the planned ordinates and may also include values of other data such as the time corresponding to each set of position ordinate values. The invention is described with reference to an imagined flight by an aircraft from A to B, Fig. 2, the positional ordinates of the craft being determined in flight by a radio-frequency hyperbolic equi-phase contour navigation system such as is described in Specification 620,479. The stations of the system are marked M, SG, SR and SP, and the appropriate contour system of the pairs of stations comprising M and SG, SR and SP, indicated at 14, 13 and 15. For the first portion of the flight from A to the point marked 17 the most accurate positional information is provided by the red and green co-ordinate systems and the red contours are crossed more frequently than the green, therefore the red co-ordinate system values are those used for control and when the existing and planned red co-ordinate values correspond, the difference between the existing and corresponding planned green ordinate value is indicated. For other portions of the route AB the red, green and purple co-ordinates may be used for control or indication as required. Fig. 1 shows the instrument panel with meters 10, 11 and 12 indicating the existing co-ordinate values with respect to they red, green and purple contours. Meter 10 (Fig. 3) is connected to a follower 27 which completes a circuit 33 whenever the meter is at a position different from that fed in by drive unit 70. The follower comprises a conductive disc moved by unit 70 on which is an insulating segment engaged by a wiper arm on a shaft coupled to the meter when meter and drive values are equal. A change in meter reading moves the wiper on to the conductive part of the disc and completes the circuit through units 36, 38 and 40, to cause the movement of a recording medium. This latter may comprise a length of motion picture film driven by shaft 41 which passes in front of a gate at which a narrow beam of light is projected across the film and through the separate channels thereof to separate photo-electric devices for each record channel. The pick-up device for the red channel 65 is connected to drive mechanism 70 and when the film has moved sufficiently for the recorded value to once more equal the actual value of the red co-ordinate the wiper ceases to make contact in unit 27 and the film drive ceases. In this way the film drive is kept in step with the actual value of the red position co-ordinate. The recorded value of the corresponding green co-ordinate is derived by pick-up unit 83 and fed to comparator 87 which is also fed with the actual green co-ordinate values from follower 73 and drive unit 76 from which a subsidiary channel 78 is taken to maintain coincidence in the follower; the comparator comprises a differential potentiometer, Fig. 5 (not shown), which is inserted in one arm of a bridge circuit 91 having an indicator 2 (Figs. 1 and 3) showing the amount and sense of the deviation from course. Because of the hyperbolic character of the contours the accuracy of indication is greater closer to the line joining the transmitter pair concerned; to make the course indicator 2 indicate the actual magnitude of the deviation of the craft from its course a separate record channel is provided on the film and the pick-up 96 associated with this controls a circuit which varies the sensitivity of the bridge circuit. The film record is made to ensure that a given deflection of the indicator always corresponds to the same absolute distance off course. As shown in Fig. 3, similar apparatus is provided for the red, green and purple phase meters and record channels and switches provided so that any one may be used for control of the record film or to actuate the indicator as required. A film length counter 102 may be used to actuate a preset contactor 104 operating relays to alter the switches when and as required to maintain the greatest accuracy of indication. Elevation information as to the height of the ground over which the craft is passing on a further record track controls pick-up 106 whose output drives differential 110 also connected to altimeter 112 so that the height above ground is the difference value shown on indicator 7. In a similar way the schedule indicator 9 shows the difference between the recorded time value and that of the clock 117 and thus the number of minutes the craft is behind or ahead of schedule. As the film movement corresponds to craft movement counter 102 may be connected directly to distance indicator 5 which preferably indicates the distance to the craft's destination. Counter 102 may also feed differentiating mechanism 124, the output of which is applied to ground speed indicator 3, and counter 102 and differentiator 124 jointly feed dividing circuit 127 to give an output proportional to the time required for the craft to reach its destination at its present speed. This output is multiplied by a factor corresponding to the rate of fuel flow to give an indication on meter 6 of the fuel required to finish the journey. Preset contactor 104 can also include a set of contacts coupled to a visual or oral warning device 8, the contacts being set to close at points along the route where there are special known hazards. The apparatus may also be used for orbit and landing indications when the craft arrives at its destination. For this purpose the film record may also include records of airport orbit paths and landing paths and the record of any particular one of these may be selected by a manual control 135. For the orbit control reverse gear 38 is arranged to return the chosen record portion to its commencement after each orbit. As an alternative to the film record a tape or strip of paper may be used, each channel comprising a double row of perforations associated with positive and negative values, the tape or strip being run over a metallic anvil contacted by finger strips through the perforations in each row, Figs. 10 and 11 (not shown). In order to indicate at an airport the progress of the craft, a transmitter is keyed to radiate a pulse of energy each time the craft traverses a given unit distance and each pulse received at the airport is used to move on a film in a projector or frame. The film shows a chart with the aircraft indicated on it at positions unit distances apart along the route as between adjacent frames so that the frame projected at any time shows the position of the craft, Fig. 12 (not shown).