Patent GB-1266931-A (GB)
IPC: G09G1/10
Filed: 1969-03-18
Abstract: 1,266,931. Aircraft instruments. KAISER AEROSPACE & ELECTRONICS CORP. 18 March, 1969 [20 March, 1968], No. 14238/69. Heading B7W. [Also in Division H4] The heading of an aircraft is displayed on a cathode-ray tube in the form of a " tape " which moves relative to an index with changes in the heading. The tape 16 (Fig. 1) which is produced on the upper portion of the tube screen 10 is formed by dot (or other shape) markers at 2-degree intervals and by vertical bar markers over numerical symbols, e.g. 29, 30 at 10-degree intervals (the two digit numerals representing 290 and 300 degrees respectively) this scale being read against a central V index marker which, as shown, indicates a heading of 295 degrees. The display also includes a flightcommand symbol 12 and may further include additional moving " tapes " 14, 18, 20 showing respectively vertical velocity, altitude and air speed against respective fixed markers 22, 24, 26, but the description is concerned only with the production of the flight-command symbol 12 and the heading tape display 16. All elements of the display are produced by the application of appropriate X, Y beam deflection and blanking signals to the tube, the operation being controlled by a 500 KHz clock oscillator driving a 14-stage binary counter, a specific count output from which is concerned with each movement of the tube beam and forms scan commands (identified in Fig. 1 by subscript S) each command being allotted a n umber of counts in dependence on the movemant to be performed (Figs. 4 and 5, not shown). Thus, in producing the flight command symbol 12 the beam is positioned during scan command 53 s  (Fig. 3) at the centre of the horizontal limb by presetting reversible X and Y counters (Fig. 5, not shown) to appropriate counts X=256, Y=256 which, during scan commands 54 s  to 57 s , are then counted up and/or down, as appropriate, to produce via digital-to-analogue converters the X and Y beam deflection waveforms shown in Fig. 2, the logic circuitry also producing the required Z axis beam signals. The tracing of the flight command symbol is completed at count 2880 at which scan command 57 s  then causes the X and Y counters to be pre-set to the co-ordinates X=156, Y=428 at which (the left-hand end of tape 16) the display of the tape 16 is to commence and a " fly-to " time of 160 counts (2880-3040) is allowed for the beam to reach this position (see Fig. 6). The production of the heading tape 16 commences at scan command 59 s  and consists in deflecting the beam horizontally whilst employing bright up pulses to produce the 2-degree markers (and, if desired, a continuous line trace) and a matrix scan technique to produce the numerical symbols and associated 10 degrees vertical bar markers under the control of heading circuitry which is supplied with the instantaneous heading in digital form. The latter information is initially modified by the introduction of a zero off-set quantity of - 8À5 degrees to produce centring of the heading tape relative to the heading index, the V pointer, which is traced by the beam during scan commands 61 s  to 63 s . This off-set quantity translates the actual heading of 295 degrees into a bearing of 286À5 degrees which, by means of a counter (Fig. 4, not shown), is effectively expanded into a 17 degree segment and decoding means then operates on the counter output to identify the 10-degree intervals at which the vertical bar and associated numerical markers are to be displayed. These markers are produced under the control of an auxiliary (clock controlled) timer (Fig. 4, not shown), which pre-sets the main X, Y reversible counter to cause the beam to trace the matrix patterns shown in Figs. 7 and 8, the required numerals being produced by blanking appropriate portions. In Fig. 7, which is concerned with the production of the two-digit number " 29 " the vertical bar marker (scan sequence 0-1) is positioned centrally with respect to the two digits, whereas in Fig. 8, which is concerned with the production of the single digit number " 9," the complete trace of the two matrices is shifted to the left to bring the vertical bar marker over the centre of the single digit. This is accomplished by reducing the slope of the (blanked) connecting vector during scan sequence 3-4 by replacing pulses of one-half clock frequency (operative in the control of the X, Y counters during scan sequence 2-3 in both Figs. 7 and 8) by clock frequency pulses for control of the X counter whilst continuing to apply one half clock frequency pulses to the Y counter. This technique may also be employed to vary the size of any symbol produced by the matrices as, e.g., the octagon A (Fig. 11) produced by controlling the X, Y counters by clock frequency pulses can be changed to octagon B by employing one-half clock frequency pulses for both counters. Stabilization of the displays, as required, with respect to earth and with respect to aircraft, may be effected, and a computer supplied with signals from a suitable sensor means may control the position-rotation of the flight command symbol or suitable analogue signals may combine via a multiplexer with the deflection (sawtooth) waves derived from digital to analogue converters supplied from the X and Y reversible counters.