GB825228A - Improvements in and relating to navigational calculating instruments - Google Patents

Abstract

825,228. Calculating-apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Sept. 2, 1957 [Sept. 7. 1956], No. 27407/56. Class 106 (1). Calculating apparatus for predicting the shortest future distance between two relatively approaching objects, such as ships, given two successive values R 1 , R 2 of the range of one ship from the other and the corresponding change in bearing a, comprises two relatively movable members, one of which bears a reciprocal scale of range and the other of which bears a set of reciprocal scales graduated according to the shortest distances of approach for different values of the change in bearing. The latter set of scales may be replaced by a set of curves passing through points of equal value on the set of scales. It is shown that, as an approximation, the shortest distance of approach d=sin α/R 2 <SP>-1</SP> - R 1 <SP>-1</SP>) and consequently the shortest distance of approach scales are calibrated to take account of the factor sin a. Then, if R 1 on the range scale is aligned with the datum line from which the other scales are drawn, the required value d may be read on the appropriate shortest distance scale opposite the value R 2 on the range scale. In one embodiment, Fig. 3, the range scale 8a is marked on a stock member 8 and the other scales 9a on a slide 9. Eight scales 9a provide for changes in bearing angle from “‹-2‹ at “‹ intervals. A cursor 10 facilitates reading. In another embodiment, Fig. 1 (not shown), the shortest distance scales are drawn radially on a disc and the range scale is marked on a bar pivoted at the centre but slidable relatively thereto. In this case two alternative range scales are provided and co-operate with alternative sets of shortest distance scales. In another arrangement, Fig. 2 (not shown), the range scale is marked round the periphery of a disc rotatable on a base member in which moves a slide bearing the set of shortest distance scales, in this case arcuate, a selected one of which may be moved into juxtaposition with the range scale. In a fourth embodiment, Fig. 4, curves 11a of equal shortest distance values are marked on a drum or endless band 11 in a casing 15 having a window 15a through which the change in bearing value corresponding to the portion of the curves visible through a window 15b may be read. The range scale is marked on an endless band adjustable by a knob 14a and also passing across the window 15b.