GB701932A - - Google Patents

Abstract

701,932. Calculating-apparatus. MINISTER OF NATIONAL DEFENCE OF CANADA. April 30, 1951 [June 16, 1950], No. 10108/51. Class 106 (1) [Also in Group XV] An air navigational computer is constructed to show solar lighting conditions over air routes in polar regions, so that flights can be timed to avoid twilight when astronavigation becomes impossible. The computer shows the track of a projected flight in relation to the sunset-sunrise line as seen by an observer in space on the earth's axis, the sunset-sunrise line is seen stationary, and the flight track includes the earth's movement eastward as well as the movement of the aircraft relative to the earth. The computer comprises a frame 24 (Fig. 1) fitted with a rotatable transparent plotting window 42 below which is a slide 38 (see also Fig. 5) marked with a polar map A, the sunset-sunrise line B, a twilight line D, and a scale E for the sun's declination. In using the apparatus, the track V of the flight is first marked on the map A together with points reached after convenient intervals, e.g. one hour. The slide is then inserted in the frame with the map in register with the window 42 which is set with the zero of an hour's scale N opposite a stationary index Q. The takeoff point is now traced on to the window 42, and the interval points of the route are also traced after successive rotations of the window corresponding to the interval. The traced points are then joined by a smooth curve W (Fig. 8) and represents the track as seen by the imaginary observer. The slide 38 is next adjusted to position the sunset-sunrise line B according to the date of the flight by bringing the appropriate marking on the declination scale E into register with an index R. Finally, the flight track W is orientated in relation to the sunset-sunrise line B according to the time of day by turning the window 42 so that the hour angle of the time of take-off on a scale M registers with the index Q. It can then be seen whether and what parts of the flight are affected by the twilight belt between the lines B and D. Areas above and below this belt correspond respectively to daylight and darkness A line C is marked in the daylight area at which the sun's altitude is 5 degrees and below which bearings are affected by refraction. The declination scale E is repeated for flying heights of 10,000 and 20,000 feet at lines F and G so that the effect of flying height can be taken account of, and the scales mav be marked with dates instead of the sun's declination. A high latitude planisphere (see Group XV) is provided on the reverse side of the apparatus. The apparatus is constructed from plastic sheet, the frame 24 in five laminations bolted and/or glued together and apertured for accommodation of the discs 42 and slide 38.