GB601893A - Improvements in or relating to navigation instruments - Google Patents

Abstract

601,893. Course - recording apparatus. REILLY, H. L., and SEYMOUR, K. Oct. 10, 1945, No. 26456. [Class 97 (ii)] Relates to course-recording apparatus in which the N-S and E-W mileages are modified before being transmitted to the tracer in order to compensate for distortion of the scale of a map according to Mercator's projection at latitudes other than the true to scale latitude. A lever 30, moved in accordance with true distance N or S is coupled, e.g. by a pin 45 and slots 36, 37, to a lever 31 and the pin 45 is constrained to move along a predetermined path, e.g. the straight track 43 intersecting the line joining the fulcrums 32, 33 of the levers 30, 31 respectively at an angle other than 90 degrees, so that the lever 31 is given a movement proportional to the change in the latitude in the relation of projected to true distance. The N-S and E-W mileages are transmitted from a ground position indicator (not shown), through friction couplings 3, 4, to differential gears 7, 8 and through gears 28, 29 to the driving discs 9, 10 of continuously variable friction gears. The N-S mileage is also transmitted, through a gear 40 for reversing the motion when the instrument is used in the southern hemisphere, to a worm 38 driving a quadrant 34 to which the lever 30 is frictionally attached. The driven rollers 11, 12 of the friction gears are carried by frame 13 and are adjusted relatively to the driving discs 9, 10 by the engagement of a toothed quadrant 35 on the lever 31 with a rack 42 on the frame 13. Rotation of the rollers 11, 12 is transmitted through gears 56, 57 to the differential gears 7, 8, the output from which corresponds to N-S and E-W mileages corrected for map distortion and is used to drive a tracer over the map by means of two traverser rods intersecting at right angles. Multi-speed gear boxes 54, 55 are provided to adapt the instrument to maps of different scale. Handles 50, 51 enable the tracer to be set to the initial position of the craft. When the tracer is at the true to scale latitude on the map the pin 45 is arranged' to be in line with the fulcrums 32, 33, the rollers 11, 12, to be at the centres of the discs 9, 10, and a pointer 48 on lever 30 to indicate zero on a scale of N-S mileage 49. The guide 43 is displaced parallel to itself according to the latitude of the true to scale part of the map by operation of the handle 47a, the pin 45 being retained in coincidence with the fulcrum 32 when this latitude is the equator.