Patent GB-979417-A (GB)
Title: Chart recording system
IPC: G01C21/14
Filed: 1961-02-01
Abstract: 979,417. Electric analog calculating. CURTISS-WRIGHT CORPORATION. Feb. 1, 1961 [Feb. 5, 1960; June 3,1960]; No. 3884/61. Heading G4G. Apparatus recording flight course of an aircraft employing electric analog computers to integrate ground speed signals connected according to earth curvature changes as represented on a Lambert projection map, comprising one set of analog computers receiving input signals ultimately derived from the ground speed signals, from which directional output signals are obtained to trace the flight path along orthogonal directions, and a second set of analog computers receiving input signals ultimately derived from the ground speed signals to produce output signals representing the instant location of the aircraft in longitude and latitude; the first and second computer sets having a master and slave relationship during "on-map" flight conditions; with means for independently recomputing the output signals of one set of computers as functions of the output signals of the other set of computers, means for comparing the recomputed and the corresponding original output signals to provide error signals, means for applying such error signals to the second set of computers under "on-map" flight conditions and to the first set of computers under "off-map" conditions to force the computers into agreement one with the other and relay means sensing "on-map" and "offmap" conditions to appropriately reverse the master and slave relationship between the computer sets. Projection. In Lambert projection (Fig. 2) maps are prepared by developing the surface 11 of a notional cone with apex P above the geographical pole intersecting the earth at standard latitude parallels # 1 , # 2  appearing as circular arcs centred on P, while other latitude parallels # o , # c , # of # 0 , # c , # define a map 11a whose geometrial centre 0 is the intersection of parallel # c  and meridian # c  and is the origin of a cartesion coordinate system for the map, on which an aircraft location is given by X A  and Y A  and defined by latitude # and meridian #. The map scale is unity at parallels # 1  and # 2  and reaches a minimum scale K at parallel # 0  midway therebetween. ## is the angular deviation of the aircraft location from the meridian # c  along the parallels and # # is the angular deviation of the aircraft along its meridian from the minimum scale parallel, so that ## = # -# c  and ## = # 0  - #, also # is the angle of meridian tilt between meridian # and the vertical through the aircraft location, which is distant p from the point P, while d#/dZ is the scale at any point of the map equal to the rate of change of p with respect to the separation of the parallels # of which Z is the complement. System control relays. In Fig. 3 a computer 13X (Fig. 6) determining the instant X 0  position of an aircraft with regard to the origin 0 of map 11a (Fig. 2) mechanically drives cam 14X engaging contact 15X so as to de-energize relay X-OM when the aircraft is within the confines of the map and its horizontal extensions and to energize the relay when it is without those confines. Similarly computer Y for the instant Y position of the craft drives cam 14 Y to operate contact 15Y to deenergize relay Y-OM when the craft is within the map confines and its vertical extensions, and to energize the relay when it is without those confines. Energization of at least one of the X and Y relays energizes an off map relay OM, and hereafter each relay is denoted by its symbol underlined, its normally open contacts by its symbol and its normally closed contacts by its symbol overlined. In Fig. 4 error signals X-E and Y-E representing X and Y deviations between the instant aircraft position and the plotted map position are rectified at 16X, 16Y, amplified, and applied to energize relays X-LE and Y-LE at a centred threshold in either sense, so that either or both contacts X-LE and Y-LE close and energize a larger error relay LE. In Fig. 5 a selector switch 18 selects five alternative modes of operation; viz. "normal" when computers 13X, 13Y operate as masters for latitude and longitude computers 30, 36 (Fig. 7 below) so long as the flight path lies "on map" and are subordinate to the computers 30, 36 when the path is "off map"; "hold" when XY position relay XYP is energized over contacts OM and/or LE so that computers 30, 36 are masters for computers 13X, 13Y under all conditions; "set" for initial adjustment and map changing when XY locator relay XYL is energized; "test" for navigation, e.g. over limited areas when no earth curvature-correction is required, in which ## locator relay ##L is energized with a balancing diode 20 to prevent spurious operation when pen lift relay PEN is energized with switch on "normal", "hold" or "set", and "off" when all computers are locked and the navigational problem is frozen; relays XYL and ##L being energized with blocking diode 19 to prevent spurious energization of the ##L relay in the "set" position. Relay PEN is also energized in the "off" position through blocking diode 21 preventing spurious energization of the XYL and ##L relays, and this relay is also energizable for large errors by contacts LE or manual operation of pen lift switch 22; the relay contacts PEN then operating through pen solenoid PDS. X and Y position computer circuits. Fig. 6 shows X- computer 13X (to which the corresponding Y computer is similar) in which a resistance summation amplifier 23 receives an external X ground speed signal V-X, an X error signal X-E, and a feedback velocity signal FB from tachogenerator 26 to energize a phase sensitive motor 24 driving the generator at speed proportional to the net input signal. Normally, contacts XYP and XYP disconnect the X error signal and earth its input so that the error signal is applied only on energization of relay XYP, and the system operates as an integrating servo under "on map" conditions and a position servo under "off map" or error conditions when it is subordinate to the latitude and longitude computers. Motor 24 is geared down to drive through slip clutch 26 or the sliders of linear potentiometers 27, 28a by a mechanical displacement X-M. The centre taps are grounded and the bipolar energization produces opposed bipolar integrated analog signals of aircraft displacements X and -X; the latter being utilized as an answering signal ANS (see below). Relay contacts XYL shunt the motor input on energization in "set" and "off" positions to lock the motor driven member is position. Complete navigational apparatus. In navigation using the apparatus of Fig. 7, the latitude # and longitude # of the point of take off are set in by knobs 31, 37 and indicators 32, 38 which are thereafter controlled continuously by latitude and longitude computors 30, 36. Switch 18 (Fig. 5) is initially at "hold" to energize relay XYP so that X and Y position computers 13X, 13Y are subordinated to the computers 36, 30 by error signals X-E, Y-E over relay contacts XYP, #XYP. A selected chart is placed in frame 49 and chart central longitude # c  is inserted by knob 53 (Fig. 8), chart minimum scale latitude # o  by knob 56 (Fig.9),minimum scale factor K by knob 80 (Fig .10) radius vector # 0  of parallel # 0  by knob 84 (Fig .10) and radius differ - ence (# c  -# 0 ) by knob 88 (Fig. 10) so as to determine the origin 0 at the centre of chart 11a and position the pen 48 at the take off point; also to control a meridian tilt (#) servosystem 40 (Fig. 7) and a scale factor (# p /# z ,) servosystem 43 to compute these parameters at the take off point which are indicated at 41, 44. Switch 22 (Fig. 5) is closed to de-energize the pen solenoid PDS so that no trace appears, and is opened when the pen reaches the take off point to allow plotting, while switch 18 is set at "normal" to de-energize relay XYP. Relays OM, LE are also de-energized since the pen is "on map" and errors are zero. The X and Y computers integrate input speed signals and latitude and longitude computers 30, 36 receive error signals YE, XE (Fig. 10) through relay contacts #OM, OM in subordination to computers 13Y, 13X and function as position servo systems. Flight computer 29 delivers north-south and east-west velocity signals V-NS and V-EW respectively applied as converted latitude velocity V-# signals to latitude computer 30 delivering electrical and mechanical outputs #, and to dividing longitude velocity computer 33 delivering a longitude velocity output (1) V-# = V - EW/cos # to the integrating longitude computer 36 producing electrical and mechanical outputs #. A sin/cos inductive resolver 35 receiving mechanical input # produces output signal (-cos #) for multiplier 34 receiving mechanical input V-# from 33 to develop signal- (V-#) cos # as answer signal to computer 33. The longitude computer 36 is subordinate to the X computer 13 X since error signal (X-E) is applied thereto over the relay contacts OM and continuous latitude and longitude indication are given by indicators 32, 38. The V-NS and V-EW signals are also fed to an inductive sin/cos resolver 39 also receiving a mechanical meridian tilt input from correction servosystem 40 (Fig. 8) to produce output signals V-XU and V-YU partially corrected for earth curvature and given by (2) V - Xu = V - EWcos # - V - NS sin # (3) V - Yu = V - EWsin # + V - NS cos # which are applied to multipliers 42X, 42Y together with mechanical scale factor inputs d p /d z , from scale factor computer 43 indicated at 44 to produce outputs V-X, V-Y fully corrected for meridian tilt and scale factor for application to X and Y computers 13-X and 13Y whose remaining inputs are presently earthed over relay contacts XYP, to drive the pen 48 in X and Y directions over lead screws 46X, 46Y to trace the flight path on chart 11a movement being limited by stops at the chart limits. When these are reached along the Y (or