Patent GB-540291-A (GB)
Title: Improvements in or relating to navigation of aircraft, ships or the like
IPC: G01C21/20
Filed: 1940-03-09
Abstract: 540,291. Calculating-apparatus. GRAVES, A., and ALLTOOLS, Ltd. March 9, 1940, No. 4436. [Class 106 (i)] [Also in Group XX] Apparatus for indicating to a navigator the compass bearing appropriate to great circle navigation between two points comprises a setting device adjustable to represent the latitude of the vertex of the required great circle, a setting device capable of initial adjustment to represent the distance of the starting point from the vertex measured along the great circle and of subsequent adjustment to represent the variations in the distance at successive points on the great circle, and means responsive to the adjustment of the setting devices for indicating, at each stage of the journey, the compass bearing necessary for continued travel along the great circle. As shown in Fig. 6 a compass 15 is clamped by an intermediate adaptor ring 17 to a ring 10 carrying a semi-circular arm 12 and rotatable on ball bearings 16 within an outer fixed ring 11. Pivoted to the fixed ring, on horizontal bearings 27, 30, is a semi-circular arm 14. The semi-circular arm 12 is provided with a groove engaged by a pin 41 adjustable along the outer semi-circular arm 14 by a knob 47 which at the same time correspondingly sets on a dial 55 the latitude of the vertex of the great circle along which the journey is to be made. A shaft 33 may be turned by a knob to rock the outer semi-circular arm 14 about its horizontal pivots 27, 30 until a scale 37 attached to the semi-circular arm indicates its equatorial position. The adaptor ring 17 is now set, by means of a scale on the ring 10, to the initial course position of the equator. The shaft 33 is turned to rotate the semi-circular arm 14 until the scale 37 (and a fine adjustment scale cooperating therewith) indicates the calculated distance of the point of departure from the vertex of the great circle to be travelled upon. This adjustment is repeated from time to time as the craft proceeds, or the adjustment is made automatically by a flexible cable driven in unison with the speed of the craft, with the result that the inner ring 10 (and compass 15) will be turned by the action of the pin 41 into the position to indicate the correct compass course along the great circle. In an alternative arrangement, Fig. 10, the movements of the parts are arranged to take place in substantially the same plane. In this arrangement an arm 72 slidable along a bar 71 is connected by sliding connections S<SP>1</SP>, S<SP>2</SP> to arms A<SP>1</SP> A<SP>2</SP> pivoted on a U-shaped bracket 75. The arms A<SP>1</SP>, A<SP>2</SP> register against a scale 74 of degrees. The arms A<SP>1</SP>, 72 are graduated respectively in terms of sin # and cos #<SP>1</SP>, where 6 is the latitude of the vertex of the great circle to be travelled along. To set the device the slides S<SP>1</SP>, S<SP>2</SP> are adjusted to correspond to the great circle to be navigated, and the arm A<SP>1</SP> is moved to a point of the scale 74 corresponding to the distance of the starting point from the vertex and is thereafter further adjusted as the craft proceeds. The second arm A<SP>2</SP> will then indicate the correct compass course and the necessary adjustments may be applied to the compass by the navigator or by direct application of the device to the lubber line. The arm A<SP>1</SP> may be moved continuously in accordance with the speed of the craft. The two arms A<SP>1</SP>, A<SP>2</SP> may register against separate graduated scales.