Patent GB-961259-A (GB)
Title: Automatic stabilization of aircraft
IPC: B64C1/00
Filed: 1962-10-24
Abstract: 961, 259. Automatic control of aircraft; fluid-pressure servomotor systems. BOEING CO. Oct. 24, 1962 [Nov. 14, 1961], No. 40254/62. Headings G3P and G3R. In an aircraft attitude automatic control system the outputs of a number of similar control units are added and the control effect of one of the units is increased automatically on failure of another so as to produce the same total control effect. In Fig. 1 yaw, pitch and roll rate gyros 101Y, 101P, 101R of unit 1 respectively control differential hydraulic actuators 108Y, 108P, 108R correcting the attitude of a helicopter about each of the three axes. The control system is duplicated in a unit 2 (not shown) and the effects of the hydraulic actuators for each axis are made additive by arranging them in tandem in the manual control linkages, Fig. 6 (not shown). In each channel signals from an inductive pick-off associated with the rate gyro (e.g. 101P) are demodulated (102P), modified by resistance-condenser networks (103P), chopper modulated (104P), attenuated by a twostate selectable resistance network (105P), amplified by transistors (106P) and demodulated (107P) before application to an electric torque motor controlling the hydraulic actuator (108P). Follow-up signals from a potentiometer (109P) operated by the hydraulic actuator are applied to the input of the amplifier (106P). Should either hydraulic pressure or electric power fail in one of the units, e.g. unit 2, operation of a bellows or failure of the electric supply actuates a relay RY-1 to double the outputs of unit 1 by selecting the higher output settings of attenuators 105Y, 105P, 105R. At the same time, the hydraulic supply to unit 2 is cut off and the hydraulic actuators of unit 2 are clamped in a neutral positon. The resistance-condenser network 103Y also has a low frequency cut-off characteristic to prevent opposition by the gyro to turns produced when the human pilot rolls the aircraft. Initial opposition to such turns which would be experienced despite resistance-condenser network 103Y is removed by applying the demodulated roll rate signal through a lagging network 103RY to modulate 104Y in the yaw control channel. A signal dependent on side-slip is produced by a differential transformer type pick-off 114 moved in dependence on the difference in pressure between nozzles-symmetrically placed on the nose of the aircraft and added in the appropriate sense to the output of the modulator 104Y in the yaw control channel. This signal is modified in dependence on airspeed by causing the output of a differential transformer type pick-off 112, moved in dependence on the relation between dynamic and static pressure, to control, through a transistor amplifier and saturable transformer device 115, the AC supply to side-slip pick-off 114. Signals from a potentiometer 110 operated by the rudder pedals are applied to the yaw control channel to cancel signals produced by the gyro when turning the aircraft during hovering. Actuators. A combined manual and duplicated automatic electro-hydraulic actuator is shown in Fig. 6. The pilot's cyclic stick 90 (or the direction pedals in the case of the yaw axis) permits direct mechanical operation of a control shaft 74-2, while the duplicated electric control signals are applied to torque motors 60-1, 60-2 respectively. Torque motor 60-1, for example, controls the position of a flapper valve 68 relative to nozzles 69L, 69R and thus the position of a two-part double spool valve 67, so that a housing 61-1 may be moved relative to a main piston 74 in the direction necessary to correct the attitude automatically by moving output shaft 74-2 relative to manual control 90. A force opposing that of torque motor 60-1 is applied by means (not shown) dependent on the position of spool valve 67. Torque motor 60-2 contributes equally to the correction by moving, in a similar manner, shaft 74-2 relative to housing 61-2 which is bolted to housing 61-1. Electric feedback signals are derived from potentiometer 92, 92-2 operated by pistons 74, 74-2 respectively. Should the electric or fluid pressure supply to either of the duplicated systems fail, the gain of the other system is doubled and the fluid pressure supply to the ineffective system cut off. Wedges 81, 81-2 are normally positioned by fluid pressure acting in opposition to springs so that the maximum movement of pistons 74, 74-2 relative to housings 61-1, 61-2 is limited, but, if one of the fluid pressure supplies is cut off the corresponding piston is locket by its wedge. Separation of the two parts of spool valve 67 by spring 167, when fluid pressure is cut off, equalises the pressures on each side of piston 74 for centralisation.