Patent GB-963983-A (GB)
Title: Improvements in plotting systems
IPC: G09B9/24
Filed: 1960-08-18
Abstract: 963,983. Electric course recording apparatus. CURTISS-WRIGHT CORPORATION. Aug. 18, 1960 [Aug. 27, 1959 (2)], No. 28709/60. Headings G1F, G1J and G1N. [Also in Division G4] Apparatus for recording the actual or simulated course of an aircraft comprises means for changing the scale of the record when the aircraft enters the approach area of the intended destinations, replacing a small scale course map by a larger scale map of the approach area. As shown (Fig. 1), signals representing x, the E-W velocity, and y, the N-S velocity are fed into computers 47, 57 respectively. The x signal is integrated by a servo 68 driving the slider 78 of a potentiometer 80 to a position representing x, the distance travelled in the E-W direction. The potential on slider 78, after amplification at 70, causes a servo 66 to position the slider 48 of a potentiometer 50, the voltage from this slider being fed back into amplifier 70 to balance the x signal. The servo 66 also positions a recording pen 26 in the E-W direction, over a chart assembly consisting of a top transparent sheet 16, a semi-transparent sheet 18, the course map 10, and a bottom transparent sheet 20. During course recording a bank of lamps 28 shine through the assembly from the rear to allow the course map 10 to be visible from above. The x co-ordinate of the centre of an approach area 14, containing e.g. a landing field, for the aircraft, is preset on the slider 84 of a potentiometer 82 by a calibrated knob 74, and compared with the instantaneous x signal from slider 78 in an amplifier 100. The difference is fed to a unit 104 when it is modified at 107 (Fig. 2) to produce the output voltage characteristic 108 (Fig. 2A) giving zero voltage between limits 110, 112 corresponding to the E-W limits of the approach area 14. This output voltage is taken in parallel to the grids of two triodes 128, 132 fed with antiphase A.C. on the anodes whereby only one valve conducts on the slopes of characteristic 108, but both valves conduct when the grid voltage is zero. Hence relays E-W in the anode circuits are simultaneously energized when the instantaneous x signal is within the E-W confines of the approach area 14. The y signal is similarly processed at 57 and two further relays N, S are simultaneously energized when the instantaneous y signal is within the N-S confines of the approach area 14. When all four relays E, W, N, S are simultaneously energized, indicating that the aircraft is within the approach area 14, a relay A is energized automatically or manually by a switch 24, whereby the lamps 28 are extinguished and side lamps 30 are lit, enabling an approach area map etched, cut or painted onto the rear surface of sheet 16 to become visible from above. At the same time the voltage distribution across potentiometer 50 is changed by the contacts of relay A so that the origin of the chart area is moved from the bottom left hand corner to the centre. Also the direct input from slider 78 to amplifier 70, representing the instantaneous x value of the aircraft position, is replaced by a signal from amplifier 100, representing the distance of the aircraft from the centre of the approach area 14 on a larger scale. A relay system including relays PXA, PXB, PYA, PYB cause the pen 26 to be lifted from the chart during changes. The pen 26 may be made to trace a dashed line when charting over the approach map, or two pens having different colour ink may be used, the colours being complementary to the colours of the lamps 28, 30. In a modification (Fig. 5, not shown), the x and y voltages derived by integration of the x and y input signals are corrected for plotting on a map provided with conic projection coordinates. The preset co-ordinates of the centre of the approach area 14 are similarly corrected. Specification 963,984 is referred to.