Patent GB-738452-A (GB)
Title: Navigational training or instruction apparatus
Inventor: CUTLER ALBERT ERNEST
IPC: G09B9/24
Filed: 1953-09-11
Abstract: 738,452. Navigational training apparatus. COMMUNICATIONS PATENTS, Ltd. Sept. 11, 1953, No. 25197/53. Class 97 (2). [Also in Groups XXXIII and XXXVIII] In navigational training apparatus for indicating the course of a craft by means of a Mercator chart, voltages corresponding to the east-west and north-south craft co-ordinate ground speeds are fed into the apparatus. The north-south speed component is used to compute the latitude of the craft, the movement of the craft indicator over the chart being controlled as a function of the craft co-ordinate movements and the secant of the latitude. As shown, the craft N-S ground speed voltage is fed over terminal 3 and amplifier 5 to drive a two-phase integrator motor 7 at a speed proportional to the input voltage, proportionality being achieved by a tacho-generator 8 driven by the motor 7 feeding back a rate voltage to the amplifier input. The motor drives through gearing 12 the wipers of potentiometers 13, 14 which are thus positioned continuously according to the craft latitude, being initially set manually by a knob 15. The craft E-W ground speed voltage is fed over terminal 4 to the other ends of potentiometer 13 the centre tap of which, corresponding to zero latitude, is earthed over a resistor 16. The potentiometer is so wound that the output derived from its wiper corresponds to the input E-W ground speed voltage multiplied by the secant of the latitude. This output is applied over an amplifier 22 to an integrator motor 24 which drives through gearing 27 the E-W lead screw 21 for the indicator 17. The motor 24 drives a generator 26 which feeds back a rate voltage to the amplifier 22 to render the motor speed proportional to input voltage. The N-S movement of the indicator 17 relative to the Mercator chart 18 may be effected by a motor similarly controlled in accordance with the N-S ground speed multiplied by secant of latitude but the following arrangement is preferred. Instead of using an integrating motor a follow-up motor 31 is used which drives the N-S lead screw 19 and the wiper of a potentiometer 33 until the voltage derived therefrom balances that derived from potentiometer 14. The potentiometer 14 is connected across an A.C. source 28-29. Its centre tap, representing zero latitude, is earthed, and the potentiometer is contoured so that the output at its wiper, which is set by motor 7 according to the latitude #, is proportional to R. log. tan (0/2 + #/4), the vertical distance on a Mercator chart between latitudes zero and #, where R is the earth's radius. The potentiometer 33 is linear and connected across the same source as potentiometer 14 so that for balance of the system the indicator 17 is set correctly in the N-S direction. Second embodiment, Fig. 2. The N-S and E-W ground speed voltages at terminals 3, 4 respectively are applied via amplifiers 30, 22 directly to the motors 31, 24 driving the N-S and E-W lead screws 19, 21 respectively, the variation of the speed of the recording pen 17 with craft latitude being achieved by varying the voltage applied to the excitation windings 39, 38 of the rate signal generators 32, 26. These excitation windings are fed from an amplifier 40 energized from the wiper of a potentiometer 41 set in accordance with the N-S movement of the indicator 17, i.e. the latitude. The potentiometer is contoured so that its output varies as the cosine of the latitude. As the speeds of the motors 24, 32 vary inversely according to the excitation of their respective generator windings 38, 39 as described in Specification 726,397, [Group XXXVII], these motor speeds in addition to their dependence, respectively, on the E-W and N-S ground speed signals, will also vary as the reciprocal of the cosine, i.e. as the secant of the latitude, as is required for a Mercator chart. The apparatus shown in Fig. 1 may be used with skew Mercator charts.