GB560952A - Improvements in apparatus for graphical computation for the solution of navigation problems and similar problems - Google Patents

Abstract

560,952. Calculating- apparatus. BYERLY, R. W. June 2, 1942, No. 7483. Convention date, June 27, 1941. [Class 106 (i)] Apparatus for graphically solving navigational problems for obtaining the great circle distance between two points on a spherical surface comprises a chart bearing a gnomonic projection and an element pivoted on the chart at the point of contact of the said projection on which can be plotted the data to set off a line of position. In the form shown in Fig. 1, the chart A bears great circle projections of the parallels and meridians of a sphere with the contact point at the equator and the plotting element is formed as a transparent sheet 10 with a roughened surface to facilitate marking. After numbering the meridians with the desired graduations the position C1 of an observed celestial body and the dead-reckoning position S1 are marked on the transparent sheet. The sheet is then swung round the pivot until the line C1-S lies on, or is parallel to, a common meridian as shown at C<1>1-S<1>1. The latitude of these points are read off and the algebraic difference gives the great circle distance which is the zenith distance of the celestial body. By comparing the calculated distance with the observed zenith distance, the off-set of the line of position from the dead-reckoning position is obtained. In a modification, the chart is divided into two halves ; the plotting half bears a projection with the contact point at a pole, while the measuring half has a projection with the contact point at the centre. In another form, the chart has the point of contact on an intermediate parallel of latitude. Instead of a transparent sheet, other types of elements for plotting the data may be used. These elements may comprise slidable and pivoted rules.