Patent GB-769939-A (GB)
Title: Aircraft navigation instruments
IPC: B64D45/00
Filed: 1955-04-04
Abstract: 769,939. Aircraft instruments. SPERRY CORPORATION. April 4, 1955 [April 7, 1954], No. 9760/55. Class 4. [Also in Groups XIX and XL(c)] Relates to aircraft navigation apparatus of the type described in Specification 690,985 in which a vertical pointer 53 is displaceable horizontally by the algebraic sum of electrical signals proportional respectively to (1) the deviation of the aircraft heading from a desired selectable heading (2) the roll angle and, if required, (3) the displacement of the aircraft from a ground track or landing approach path defined by an overlapping-beam or nomidirectional radio beacon, a horizontal pointer 54 being displaceable vertically by the algebraic sum of signals proportional to (1) the pitch angle and (2) displacement of the craft from a predetermined altitude or from a radio defined glide path. According to the present invention the actual heading, the heading error and the pitch and roll are all indicated by a single instrument which includes the crossed pointers 53, 54 such that when the aircraft is on the correct flight path pointer 53 and the heading and roll indices are vertically aligned with a first fixed reference index and pointer 54 and the pitch index are horizontally aligned with a second fixed reference index, Instrument display. As shown in Figs. 1, 3 and 4 the desired heading is indicated by the position of a cursor 40 on an annular compass scale 28 whose angular position is controlled by a gyro-magnetic compass such that the actual heading is indicated by the reading of the scale 28 against fixed indices 52 and 52<SP>1</SP>, any heading error being indicated by displacemnt of cursor 40 from indices 52, 52<SP>1</SP>. Pitch is indicated by vertical displacement of a vertical screen 76. Figs. 3 and 4, mounted behind pointers 53, 54 and having a coloured lower portion 75 with a normally horizontal boundary 81, a non-linear pitch scale 73 of interposed dots and dashes being marked on screen 76 perpendicular to boundary 81 ; roll is indicated by rotation of screen 76 in its plane about a horizontal longitudinal axis. When the aircraft is on the correct flight path cursor 40, pointer 53 and scale 73 are aligned vertically with fixed indices 52, 52<SP>1</SP> and pointer 54 and boundary 81 are aligned horizontally with fixed indices 55. In a modification, Figs. 15 and 16 (not shown), the pointers 53, 54 and the screen 76 are curved. Constructional details of the instrument (see Group XIX) are illustrated in Figs. 2 and 4 (not shown). System operation. The angular position of compass card 28 is controlled by the gyromagnetic compass 100 of the type disclosed in Specification 638,971 [Group XX], via Selsyns (S) 102, 103, amplifier 104 and servomotor 34. The angular position of the heading cursor 40 is controlled by the output shaft from differential gear 43 whose two inputs are coupled respectively to the compass servo motor 34 and the heading selector knob 41 so that operation of knob 41 positions cursor 40 relative to card 28 and when knob 41 is locked by the friction clutch 47 cursor 40 moves with card 28. The azimuth and elevation guidance pointers 53, 54 are controlled by the ouputs from amplifier-limiters 107, 119 respectively via servo motors 62, 69 and the roll and pitch movements of screen 76 are controlled by the corresponding electrical outputs from gyro 110 via Selsyns 111, 112; 115, 116 and servo motors 83, 86. A stabilizing velocity generator G is included in each servo loop. The inputs to azimuth amplifier 107 comprise (1) a roll signal from Selsyn 111 and (2) a heading error signal from differential Selsyn 48 which is electrically coupled to the compass Selsyn 102 and mechanically coupled to the heading selector knob 41. When following a ground track defined by an overlapping beam or omnidirectional radio beacon a further input proportional to displacement of the aircraft from said track is applied to amplifier 107 from receiver 132 by selector switch 131. The inputs to elevation amplifier 119 comprises (1) a pitch signal from Selsyn 115 and (2) a signal from altitude control 133 or from the glide slope receiver 134 depending on the position of switch 131. Figs. 8-14 (not shown) illustrate the changing indications of the instrument during anapproach. Fig. 7 (not shown), to a radiodefined ground track.