Patent GB-1119832-A (GB)
Title: Aircraft instrument
Inventor: SULLIVAN NEIL
IPC: G05D1/06
Filed: 1963-11-08
Abstract: 1,119,832. Aircraft instruments. SPERRY RAND Ltd. 5 Feb., 1965 [8 Nov., 1963], No. 44118/63. Heading B7W. An aircraft instrument has an index 10 for indicating the difference between actual airspeed and a comparison speed and means for increasing the comparison speed from its initial, preset value, such as rotation speed, when the actual speed exceeds the comparison speed, at a rate proportional to the excess, and for maintaining the comparison constant when the actual speed is less than the comparison speed. The comparison speed is set, e.g. for aircraft weight by adjusting the position of the base of a pressure-sensitive capsule by a manual trimmer 28 and is also varied by a D.C. electric motor supplied with the speed error signal through an amplifier 26 and a rectifier 27, which blocks the signals when the actual speed is less than the comparison speed. The feedback loop passes through a switch 22, ganged to other switches 23, 24 having four positions, (a) the take-off position (shown), (b) the climb position, (c) the cruise position, and (d) the approach position. In positions (b), (c) and (d), the feedback loop is interrupted, but may be closed by pressing button 30 when the error signal energizes a relay 32 and maintains a switch 31 closed until the error signal is cancelled. The comparison speed may thus be set to the aircraft's actual speed for the time being. The instrument comprises a horizon ball 1 driven by servomotors 6, 9 in response to pitch and roll signals from a gyro 3. The instrument also has heading and flight path angle indicators 16, 14 respectively which have to be centralized to keep the aircraft on course. The heading indicator 16 is controlled by an instrument 18 which either generates heading error signals derived from a compass or transmits signals from navigational equipment 19. The signal passes through a limiter 20 responsive to the existing bank angle as derived from the gyro pick-off 4. The indicator 14 has inputs from the gyro pitch pick-off 7, an aircraft incidence indicator 39 (which together give the actual flight path angle) and the output from the switch 23. In the takeoff and climb positions this output is a climb angle manually set at 36. In the cruise position (c) it is a signal from an altitude unit 33 which is a barometric capsule which like the capsule in the airspeed unit 25 has a D.C. electric motor for adjusting the position of its base in response to an error signal. This motor is operated during the take-off and climb phases, through a loop containing the amplifier 34. This loop is opened by switching to the cruise phase (c) and the signal from the unit 33 to the switch 23 and indicator is the aircraft height relative to the height when the cruise phase is selected. This signal may be modified by a manually set device 35 which acts through the amplifier 34 of the feedback loop to vary the comparison height at the rate desired. In the approach position (d) the signal through the switch 23 to the indicator 14 is from a glide path receiver 41. In a modification, the climb out signal from 36 is held at zero until rotation speed when it is allowed to rise to give, e.g., a 2 deg./sec. pitch rate demand up to the desired flight path angle.