Patent GB-918917-A (GB)
Title: Improvements in and relating to flight simulator display apparatus
Inventor: BARNES ARTHUR GEORGE
IPC: G09B9/30
Filed: 1959-01-02
Abstract: 918,917. Cathode - ray tube circuits. ENGLISH ELECTRIC CO. Ltd. Dec. 30, 1959 [Jan. 2, 1959], No. 184/59. Class 40 (7). [Also in Group XXXIII] The computed angles of pitch, roll, and yaw, and the height, forward velocity, and lateral velocity of a simulated aircraft are displayed on a cathode-ray tube screen by a pattern shown in Fig. 1 and comprising two sets of intersecting lines A and B, passing respectively through vanishing-points P2 and P1, and representing the appearance in perspective of a pattern of squares on the ground as they would be seen from the simulated aircraft. The parts of the lines shown full are shown on the screen, represented in Fig. 1 by the rectangle. The screen is 11 2/3 inches across, and viewed from 17 inches away. To display computed pitch, a pitch signal from the computer 1, Fig. 4, is fed to the Y deflection amplifier 2 energizing magnetic deflection coils 3 on the tube 4, to shift the display as a whole perpendicularly to the apparent horizon (the line joining P1 to P2). To display computed roll, a roll signal from the computer 1 is fed to servo mechanism 5 which rotates the Y deflection coils 3 and X deflection coils 6 about the tube axis, rotating the whole display. The lines are produced by simultaneous X and Y sawtooth deflection signals. A 2000 c/s. oscillator 7 feeds a squaring stage 8 which triggers an X sawtooth generator 9 producing the waveform shown in Fig. 6 (a) with a pulse width of 100 microseconds. This signal is fed directly, and through an invertor 10, to the two inputs of a switch 11a connected to the X deflection amplifier 12. The output of generator 9 also triggers a Y sawtooth generator 13, amplitude-modulated as described below, and feeding the Y deflection amplifier 2. The output of oscillator 7 is fed to two frequency-dividing phantastrons 14, 15, in cascade, which produce an output pulse every twenty-four lines. These pulses are delayed, as explained below, in a phantastron 16, and trigger a multivibrator 17 controlling switches 11a, 11b, and 11c, and trigger a generator 18. This generator has a part hyperbolic waveform, Fig. 5, with flattened peaks, produced for example by summing three or four exponentially decaying components. The angular depression of a point on the screen from the apparent horizon is 17h/R inches, where h is the computed aircraft height and R the range of the corresponding point on the ground from the aircraft. The computed value of h is available to generator 18 from computer 1, and determines the eccentricity of the hyperbolµ shown in Fig. 5. The output of generator 18 is sampled at the line frequency by a sampler 180, which holds its output at the sampled value until a fresh sample is taken. The output of the X amplifier 12 is as shown in Fig. 6 (c), the vertical broken line indicating change-over of switch 1 la every twenty-four pulses. The output of the Y amplifier 3 is shown at Fig. 6 (d), the broken line joining the pulse peaks showing the output of generator 18 on the same time scale. The resultant pattern is that shown in Fig. 1. For low h, many of the lines are at or near the horizon line, and the remaining lines are widely spaced across the screen. For high h, few lines are at or near the horizon, nearly all being closely spaced across the screen. Thus the apparent size of the " squares " is varied in accordance with computed height. This may be done in two stages, each simulated square on the ground having a diagonal of five miles for h between 10,000 ft. and 1000 ft., and half a mile for h between 1000 ft. and 100 ft. To display computed velocity, each set of lines is rotated about its vanishing point at a rate proportional to computed forward velocity. The effect of lateral velocity is displayed by increasing the rate of rotation of one set compared with the other. Two appropriate air-speed signals A and B (equal if there is no computed lateral velocity) from the computer 1 are fed to integrators 19A and 19B, respectively, which are alternately connected to control the delay phantastron 16 by a switch 11b controlled by multivibrator 17. While integrator 19A is connected to phantastron 16, the pulse delay imposed by the phantastron gradually increases as the integral of airspeed signal A builds up. This has the effect of moving the hyperbolic broken line, Fig. 6 (d), bodily along the time scale at a rate proportional to signal A. The set of lines through point P2, Fig. 1, thus appears to rotate anticlockwise. Similarly, airspeed signal B controls the delay of trigger pulses to generator 18 when switch 11b changes over, to trace the lines through point P1, which appear to rotate clockwise. When the delay occasioned by either integrator reaches 500 microseconds, this is detected by comparator 20A or 20B, which then operates device 21A or 21B to reset the integrator to zero. In the presence of a yaw signal, points P1 and P2 are shifted horizontally. For zero yaw, the distance of P1 and P2 from the vertical centre line of the display subtends an angle of forty-five degrees at the viewer's eye. For yaw #, these angles become 45 degrees+# for P1 and 45 degrees-# for P2. When the yaw is to be displayed, the waveform of Fig. 6(d) is not used, being replaced by that of Fig. 6 (e), being the sum of a sawtooth waveform of amplitude 2h/3R (that of Fig. 6 (d) having amplitude h/R), together with a vertical shift Kh/R, where K=2(1+2 tan #/3(1+ tan #) for lines B, and K=2(1 - 2 tan #)/3(1 - tan #) for lines A. These functions are computed in a generator 22 having a # input from computer 1, and modulated in accordance with h/R by sampler 180, the appropriate function being chosen by switch 11c controlled by multivibrator 17. The output is fed to the Y amplifier 2, ogether with a signal h/3R from generator 13.