Patent GB-791670-A (GB)
Title: Improvements in or relating to navigational fix computor
IPC: G01S7/295
Filed: 1949-12-28
Abstract: 791,670. Electric analogue calculating systems. GENERAL PRECISION LABORATORY, Inc. Dec. 28, 1949, No. 33163/49. Class 37. [Also in Group XL (c)] In a navigational system, which continuously displays the present latitude and longitude of the craft, periodic manual corrections of cumulative errors may be made. The position of a known object with respect to the craft is displayed simultaneously by two sets of traces on a C.R.T., the first of which, the datum, is derived from a plan-position indicator and the second is produced by the navigation system, which is manually adjustable so as to bring the two traces into coincidence and correct for errors in the system. As shown there are displayed simultaneously in the C.R.T. 78 the P.P.I. mark 96 and the azimuth and range marks 81, 77 of the present system, both 96 and 81, 77 giving the position of a known object with respect to the craft. 96 is produced by a known circuit, not shown, while 77, 81 are derived from the known longitude and latitude determining devices 11, 12 and the resolver 37, the manual adjustment of 77, 81 over the C.R.T. screen 78 being effected by operation of the switches 106, 108. The latter cause rotation of shafts 116, 117 associated with the gearing of the navigation system counters 16, 17 which continuously indicate the craft longitude and latitude and are operated from 11, 12 by rotating shafts 13, 14. The counters 26, 46 are manually set, respectively, to the longitude and latitude of the known object so that the settings of potentiometer tappings 29, 49 are continuously adjusted by the outputs of differentials 22, 42 and the voltage developed at 29 is proportional to the difference in longitude between the known object and that indicated by the system and is applied to winding 36 of resolver 37; the voltage at 49 similarly corresponds with the difference between the indicated and set latitude and is applied to winding 56. The movable windings 66, 67 of 37 are positioned by servomotor 69 energized from coil 67 and the voltage generated in 66 is applied with a voltage representative of the craft altitude to 73, the output of which is proportional to the slant distance from the indicated craft position to the known object and which controls the range mark 77. The azimuth mark 81 is formed by the transmitters 82, 87, 91 each having a mechanical input respectively from 69, the radar antenna and the compass. Failure to coincide between 81, 77 and 96 is corrected by the separate adjustment of 81, 77 by means, respectively, of switches 106, 108. Closure of the former causes the speed of rotation of shafts 116, 117 to be such as to produce voltages at 36, 56 which alter the apparent length of the radius vector of the polar co-ordinates of the known point from the craft but maintain the angular position of the azimuth mark 81 constant; 81 therefore remains fixed and the radius of 77 changes until it lies on point 96. Similarly with switch 108 closed, the speeds of shafts 116 and 117 are such that 77 remains fixed and 81 is rotated until it meets 96. In further modifications, not shown, a fix is obtained on two known fixed points and the shafts 116, 117 are controlled directly from resolver 37.