Patent GB-579136-A (GB)
Title: Improvements in or relating to navigation instruments
IPC: G01C21/20
Filed: 1943-12-15
Abstract: 579,136. Navigating instruments. NEWTON, E. P. (Reece Buttonhole Machine Co.). Dec. 15, 1943, No. 21058. [Class 106 (i)] A navigation instrument comprises two relatively coaxial turnable discs, a straight link parallel to said discs, a first transverse pivot on said link radially slidable in one disc, another pivot parallel to said first pivot slidable on said link and radially slidable in the other disc, and mechanism for adjusting either pivot radially of its respective disc about a fixed .common axis parallel to 'said slidable pivots. Fig. 1 illustrates the principle of the invention. A pivot 18 is adjusted radially until the length a represents the indicated air speed. A pivot 19 is adjusted until b represents the prevailing wind. A scale 17 joining the pivots 18, 19 then represents the ground speed of the aircraft vectorially. If the true course is represented by z, the pivot 18 must be rotated round the fixed centre x until the scale 17 is parallel with z to give the course a' for the pilot to follow. Fig. 2 is a plan of the instrument and Fig. 15 an exploded view of the component parts, which are all transparent. A wind velocity disc 22 has a spiral cam slot 81 and a circular scale- 80 graduated in m.p.h. A wind direction disc 23 has an index line 82 and a slide 84 with a pin 87 projecting into the spiral slot 81 whereby the position of the slide 84 and therefore of the pivot 19 carried thereby is determined by the relative angular positions of the discs 22, 23. The pivot 19 projects into a slot 115 in the track link 24 which is uniformly graduated and represents ground speed. A track pointer 26 is connected by a four-bar linkage 25 to the track link 24 in such a manner as always to be parallel to the track link. A fixed pivot 18 on the track link is secured to a slide 92 in a heading disc 27 which has a radial index line 90 and an arcuate scale 96 representing drift angles. An air speed disc 28 has a circular scale 100 graduated logarithmically in altitudes and a logarithmic spiral cam slot 101 whereby the pivot 18 and the slide 92 are positioned according to the relative angular positions of the discs 27, 28. An air-speed correction disc 29 has a logarithmic scale 105 graduated according to air temperature for evaporation with the scale 100 and a further logarithmic scale 106 graduated according to indicated air-speed. A magnetic compass disc 30 is marked in degrees and has a radial arrow 108 and a true compass disc 31 is marked in degrees and in the usual points of the compass, with an inner scale 112 for indicating magnetic variations. The discs 22, 38 can. drive the other discs in the groups I, II, respectively, shown in Fig. 15, the driving connection to discs 32, 27 and 29 being normally effective but being disconnected at the depression of levers 145, 146, 147, respectively. A drive to disc 30 becomes effective only at the depression of a lever 148. The disc 31 is fixed. Operation. With lever 148 depressed, the magnetic compass disc 30 is rotated at the manual turning of the disc 28 until the arrow 108 indicates the known magnetic variation on the scale 112 on the top disc. The lever 148 is released and the lever 147 is depressed to disconnect discs 28, 29 while the disc 28 is set relatively to the disc 29 to correct for altitude and temperature. The lever 146 is depressed to release disc 27 and the lever 147 is released to re-establish the drive to the disc 29 which is then turned until the indicated air-speed on scale 106 aligns with the line 90 on the disc 27. The disc 22 is then turned with the lever 145 released until the line 82 on the disc 23 indicates the direction of the wind on the top plate 31. The lever 145 is then depressed to release the disc 23 and the disc 22 is turned until the line 82 indicates the wind speed on the scale 80, the relative rotation of discs 22, 23 shifting the pivot 19. The instrument is then set to the true bearing of the objective by turning the disc 28 until the track pointer 26 indicates the bearing on the scale 110 and therefore the magnetic bearing on scale 107, discs 27 and 29 turning with the disc 28. The line 90 now indicates the magnetic course on the scale 107 while ground speed is shown on the scale 17. The several scales 110, 112, 107, 106, 105, 100, 96, 80 are concentric but of different radius so as to be clearly distinguishable.