Patent GB-1301895-A (GB)
IPC: B64D43/00
Filed: 1970-08-11
Abstract: 1301895 Aircraft vertical flight position display instrument BENDIX CORP 11 Aug 1970 [14 Aug 1969] 38665/70 Heading B7W An aircraft vertical flight position display instrument comprises a display plate 31 bearing grid lines 32 and a point 35, and means to project a beam of light to produce a first spot 75 indicative of the position of the aircraft, measured on altitude scale 26 and distance scale 28, relative to a chosen aimpoint represented by the point 35. The spot 35 may be a red spot produced by light from-lamps 62 which has passed through red discs 55 and 57 after passing through an aperture defined by the intersection of a radial slot in a blue disc 58 and a spiral slot in a blue disc 60. The desired altitude at the aimpoint is selected by the pilot and displayed by lamps 45, and a navigation computer derives therefrom the angle to the aimpoint in the vertical plane and produces a signal, whose phase depends on the sign of the angle and whose amplitude depends on the magnitude of the angle, which is compared in the primary winding of a transformer (431), Fig. 3C (not shown), with a signal indicative of the position of the disc 58, and the resultant signal in the secondary winding is amplified to drive a two-phase servomotor (493) which drives the disc 58 and also a follow-up potentiometer (425) which completes the servo loop. The computer also produces a "from" signal if the aircraft is receding from the aimpoint, which energizes a relay (450) so that a signal is fed via ambiguity switch 536, driven by the servomotor (493), to the amplifier to drive the motor so that both the slot in the disc 58 and the rotating contact element 534 of the switch 536 are moved to the right, so that the spot 75 appears to the right of the point 35. Similarly the absence of such a "from signal" will render the relay (450) de-energized, and if the spot 75 is at that time on the right then a signal via ambiguity switch 530 will cause it to be returned to the left. The servomotor (493) controlling the disc indicating the actual angle to the aimpoint also drives a sine potentiometer (610) the output from which is combined with a signal from the computer representing the difference in altitude between the aircraft and the aimpoint to produce a signal indicative of the short distance to the aimpoint, and by means of a servoloop of the kind already described this controls the position of the blue disc 60 having a spiral slot. A selected flight path may be indicated by a line 61 on a clear disc 53 whose position is determined by a closed servoloop in response to a selected angle signal produced by the pilot. But if a switch (145), Fig. 3A (not shown), is thrown then the line 61 willindicate a preselected fixed angle of descent, unless a signal is received from the computer via line 250 to indicate that the actual altitude is less than the desired altitude, in which case a resistor network producing the fixed angle signal is short-circuited and the line 61 is horizontal. The aimpoint may be coincident with a point vertically above a navigational aid such as a radio beacon, or it may be offset from it, the waypoint then being indicated by a blue dot 77 produced by light which has passed through blue discs 58 and 60 and then through an aperture defined by the intersection of a radial slot in the red disc 55 and a spiral slot in the red disc 57. The position of the disc 57 is controlled by a closed servoloop in response to a voltage representing an offset distance selected by the pilot. The instrument may include means for positioning the red disc 55 to indicate the angle to the waypoint, but in the enbodiment described the disc is fixed with the slot horizontal, i.e. the aimpoint and the waypoint are at the same altitude. Those signals, representing angles, for driving the discs 53 and 58, are tapped off from potentiometers across which is applied a constant A.C. voltage from a source (135), Fig. 3A (not shown); on the other hand potentiometers for producing signals, indicative of distances, for driving the discs 57 and 60 may be supplied with one of three voltages from the source (135), for varying the scale on which these distances are represented on the display plate 31. If either the slant distance or the selected offset distance signal is above a certain level then a voltage detector will supply a signal via line 780 or 765 respectively to OR gate 737 which will cause a relay (745) to be energized so that a relatively high voltage is used for the servo systems, and lamps 37 and 39 are lit, indicating that distances are being indicated over a large range, e.g. 200 miles distance and 100,000 feet altitude. The relay will continue to be energized as long as either signal is above that level or as long as range switch 735, which is driven with the disc 60, is closed, the spot 75 being away from the central area of the plate 31; in the event of the distance signals falling below that level, but being above a medium level, and the spot 75 having moved so close to the point 35 that the switch 735 is open, then no signal will be supplied to the OR gate 737 and the relay (745) will be de-energized, but a second relay (755) will be energized by means of OR gate 837, causing the medium voltage to be used, and lamps 35A and 41 to be lit, indicating a medium range. Finally, should the distance signals fall below that medium level both relays will be de-energized and a low range and low voltage used. Likewise as the distances increase successively higher voltages and scales are used. The nagivation computer may also produce an altitude capture signal when the desired altitude has been attained, and this supplied via conductor 902, may cause a flag 49 to be displayed in a window 48 on the instrument so long as that altitude is maintained; the computer then transferring the control of the aircraft to an altitude hold mode. The altitude capture signal may also serve to provide an audible warning in the pilot's headset 940 should the plane deviate from this altitude.