Patent GB-803573-A (GB)
Title: Control systems for aircraft
Inventor: BOHNEL WILLIAM RICHARD
IPC: G05D1/00
Filed: 1954-08-25
Abstract: 803,573. Fluid-pressure servomotor-control systems. SPERRY GYROSCOPE CO., Ltd. Nov. 25, 1955 [Aug. 25, 1954], No. 24774/54. Class 135. In an aircraft control system in which an aircraft control surface is actuated by two alternative modes of operation in one of which the displacement of the surface is controlled in dependence on an electrical signal developed in the system and in the other of which the displacement is controlled in accordance with a mechanical signal, such as the displacement of a member, developed in the system, control transfer means are provided for changing the system from one mode of operation to the other mode, these means being constructed and arranged so that when the system is changed from the first mode of operation to the second, the first mode of operation is rendered ineffective rapidly and thereafter the second mode of operation is introduced gradually. Thus the elevator 2 is operated by an hydraulic servomotor 10 to control movements of the craft about the pitch axis. The servomotor 10 is normally controlled by a relay valve 9 responsive to signals from a potentiometer 6 adjusted by the pilot's control column 1 or to signals generated by short and long term automatic units 12, 13 forming part of an automatic electric control unit 5, such signals together with a feedback signal from a potentiometer 7 operated by the servomotor being fed to an electrical transducer 8 operating on the pilot valve of the relay valve 9. In an emergency or otherwise when desired, the valve 9 is rendered ineffective and the servomotor 10 is controlled by a control valve 11 operated through a differential lever device 4 connected to the control column 1 and to the output member 18 of the servomotor. This transfer of control is effected by a change-over valve 23 comprising a plunger 24 which in the position shown connects the valve 9 to the servomotor through annuli 25, 26. The plunger 24 is maintained in the position shown against the load of a spring 40 by the pressure in a highpressure supply duct 35 acting in a chamber 301. When a solenoid 29 is de-energized a valve 37 is opened to admit high pressure to a piston 32 and so move the plunger 24 to connect the annuli 25, 26 to the valve 11. The differential lever device 4 comprises levers 78, 80 with a common pivot 83 and a floating lever 84 pivoted at 85 on the lever 80. The lever 84 is pivoted to the lever 78 through a slot 87 and to the valve 11. The levers 78, 80 are connected by links 82, 81 to the control column 1 and the servomotor output member 18 respectively. Pressure fluid is supplied to the hydraulic part of system through a pump P1 or in the event of this failing through a pump P2, the change over being effected by a spring-loaded piston valve 71 subject to the delivery pressures of the two pumps at its opposite ends. The control column 1 is connected to the lever 78 through a linkage 55, 53, 82 the lever 53 of which is pivoted at 54 to a further lever 56 the pivotal movement of which is limited by a stop member 58. This introduces a degree of lost motion into the linkage so that effect of the short term unit 12 is not transmitted to the control column 1 when the aircraft is under manual control. The stop member 58 may be withdrawn by a solenoid 61 which is energized at all times except when the emergency manual control is operative. The lost-motion device comprising the lever 56, stop member 58 and solenoid 61 are omitted in a modification (Fig. 2, not shown). " Artificial feel " is provided by a spring centralizing device 16<1> operative on the lever 53. The device 161 may be adjusted by a trim motor 16<11> under the control of switches U, V on the pilot's control panel P. The effective stiffness of the centralizing spring is adjusted by a motor 93 operative to adjust the lever arm through which the spring acts. The motor 93 is responsive to signals from an air-speed indicator 91. The pilot's panel P is also provided with switches M, N, X and Y and with indicators 49, 50. The push-button switch X de-energizes a relay D and thus breaks contacts d2 to bring in the emergency manual control. The switch Y establishes electrical signalling by energizing the relay D so that contacts d<1>, d2 are closed and the solenoid 29 energized. For manual electrical signalling the switch M is closed so that a relay A is energized and contacts a<1> close. The short-term unit 12 is thus connected through the electrical differential 47 to an amplifier 48 controlling the transducer 8 through a relay C. The switch N energizes a relay B to close contacts b2 and open contacts b2<1> so that the longterm unit 13 acts through an electrical differential 45 on the amplifier 48 and the input from the potentiometer 6 is cut off. The signals from the potentiometers 6, 7 act through a third electrical differential 68 on an amplifier 69 controlling the trim motor 16<11> so that the device 16<1> is correctly trimmed prior to change over to emergency manual control. Irrespective of the switch X, the system changes over to emergency manual control if any of the contacts h, c<1>, el or k are broken. The contacts h are broken by overstress in the linkage 82 due to relative movement between two members 63, 64 against a pre-loaded spring 65. The contacts c<1> are broken by the relay C when the output from the amplifier 48 exceeds a predetermined value. The contacts e<1> are broken by a realy E when the error signal between the potentiometers 6, 7 gradually develops to exceed a predetermined amount. The contacts k are broken if one of the windings of the transducer 8 is burnt out or if the pilot valve of the valve 9 sticks. Some of the electrical details referred to above are described only in the Provisional Specification. Specification 803,572 is referred to.