Patent GB-1002340-A (GB)
Title: Improvements in or relating to aircraft flight systems
Inventor: BISHOP ROGER IVAN
IPC: G05D1/06
Filed: 1961-04-20
Abstract: 1,002,340. Controlling aircraft. S. SMITH & SONS (ENGLAND) Ltd. July 20, 1962 [April 20, 1961], No. 35933/60. Heading B7G. [Also in Divisions G3 and H4] Relates to the control (especially automatic) of an aircraft during one or more phases beginning with (i) a " track phase," during which the craft manoeuvres on to a radio-established glide path, followed by (ii) a " glide phase," during which the craft proceeds down the glide path and maintains constant airspeed V 0  and pitch altitude Po' (iii) an " altitude phase," during which the craft continues down an extension of the glide path, from a height (usually some 150 feet) at which the radio glide path is unreliable, and maintains V 0  and p 0 , (iv) a " flare phase," from a height of some 50 feet, at the beginning of which the throttles are closed and during which height h is maintained to satisfy the usual flare-out equation h+T<SP>1</SP>h=0, h being measured by, e.g. an F.M. radar altimeter of the kind described in " Journal of the Institute of Navigation," Vol. XII, No. 2, pages 115-132, and h being the temporal derivative of h, and finally (v) a " land phase," during which the aircraft continues the flare-out and drift is kicked-off at a predetermined height by controlling rudder and ailerons so as to rotate the craft in yaw with the wings level. Azimuth guidance during phases (ii) to (v) is provided by an I.L.S. localizer or a leader cable system as described in Specification 820,319 (see Group XL (c)), or a V.O.R. beacon. Due to the longitudinal spacing of the azimuth guidance means on the craft from its centre of gravity, in order that the craft shall land on or near the centreline of the runway after kicking-off drift, the invention combines a proportion of a signal representing drift, such proportion depending on the aforesaid longitudinal spacing, in the signal generated for azimuthal control of the craft. In the embodiment, Fig. 1, the upper part of the Figure includes the combination which computes signals representing craft heading deviation from the radio track, the lower L.H. of the Figure is the computer of a signal representing demanded bank angle #D, and in the lower R.H. of the Figure a block diagram represents the aileron channel of an automatic pilot and signal sources associated therewith. The D.C. output # of receiver 1 is fed as an A.C. signal to an amplifier 5, and shaft 8 is so controlled that it is positioned in accordance with a function S 1 = K 2 #/( 1 + T x D) where T x  is a time constant and D is the time-differential operator d/dt; K 2  and T x  are set in by resistors 13, 14 and 15, a changeover of contact G1 resulting in a change in T x - value. Shaft 8 also drives a synchro 16 the stator of which is energized from a synchro transmitter in a flight compass system 17 to generate signals representing the difference between actual heading #and the direction # T  of the selected track. The rotor winding of synchro 16 generates a signal S 2 = # - #- [K 2 #/(1+T 9 D)], where T 9  is the value of T x  for the track phase (e.g. T 9 = 0.15 sec.). Assuming that relays RC, AZM and AZD are energized but relay G is not, signal S 2  is passed to a potentiometer 20 the wiper of which is positioned according to indicated airspeed. For the glide phase a signal S 3 =K 4 K 2 #{-[1+{T 6 D/ (1+T 7 D)}] is provided on line 25: relay G is energized, contact G1 increases time constant T x  to a value T, (between 1 and 3 seconds) and contact G2 switches line 25 to the signal chain illustrated; K 4  is a further numerical constant and T 6  is a time constant. A switch operates when entering the glide path descent to energize relay PL and thus add a component A= a(# - # T ) to signal S 3 ; the limits of this component are confined by diodes 34, 35 and a is pre-set, according to the aerial-centre of gravity spacing, by a resistor 33. The relative signs of signal S 3  and component A are reversed as compared with the track phase to ensure that the aerial is up-wind of the radio track. When the radio track is defined by a V.O.R. beacon the servo system may be modified as described in Specification 984,754 [Division H4]. The automatic pilot may be controlled manually by signals from a unit 38. The signal V 25  on lead 25 is filtered by a circuit 40 and passed to one input of a magnetic amplifier 41 which sums its inputs and converts to A.C.; amplifier 41 output controls a servomotor 43 which drives a tachometer-generator 45 and, via a reduction gear 46, a shaft 47. Position feed-back to amplifier 41 is afforded from a potentiometer 48 and rate feed-back via a demodulator 51. The servo system positions shaft 47 in accordance with a demanded bank angle # D =V 25 /(1+T 2 D) where T 2  is a time constant. The signal across the rotor of a synchro 52 represents # - # D , where #is actual bank angle. Differentiating network 57 of time constant T 21  provides an input signal # D D/ (1 +T 21 D) to magnetic amplifier 56 and a signal proportional to # D  is fed to terminals 58 via contact AZM#. In the hydraulic aileron control system a conventional servo arrangement drives a tachometer-generator 72 (to afford rate feedback to amplifier 70), and drives the input shaft of an electro-magnetic clutch 73 the output of which controls aileron drive 75 via a torque switch 74. Signals representing rate of roll relative to earth axes (D # ) are fed to an input of amplifier 70 via a phase-advancing network 76 the input to which is the sum of signals representing rate of roll relative to craft body axes p and r#, where r is rate of yaw and # is pitch attitude: for small #, p + r# = D. Further inputs to amplifier 70 are from amplifier 56 in the bank demand computing circuit and from an integrator 81. The signal at terminals 32 may be replaced by a manual setting of estimated drift, Fig. 2 (not shown).