Patent GB-1404762-A (GB)
Title: Electro-hydraulic actuating systems for aircraft control surfaces
IPC: G05D1/00
Filed: 1971-10-07
Abstract: 1404762 Actuating aircraft control surfaces LUCAS INDUSTRIES Ltd 26 Sept 1972 [7 Oct 1971] 46626/71 Heading B7G An electro-hydraulic arrangement for actuating aircraft control surfaces comprises means 45 responsive to the position of the surfaces to generate electrical signals on selected ones of inputs X, Y, Z to comparators 98, 154, a selection switch 80 for selecting desired positions for the surfaces and generating electrical signals on selected ones of further inputs A, B, C to the comparators, which produce, in response to predetermined combinations of signals at the inputs, signals at outputs L to a servo control valve arrangement to apply fluid pressures to urge control flaps 11 respectively towards and away from a fully retracted position. The valve arrangement includes solenoid valves 34, 35 controlled by the switching amplifiers 152, 153 receiving the outputs from the comparators 98 154, which apply control pressures to opposite ends of spool 23 of valve 14 to supply fluid to respective outlets 18, 19 connected by conduits 36, 37 to hydraulic motors moving the flaps 11; if the pressures from the valves 34, 35 are absent or are equal the spool is centred and the flaps fixed. Switch 80 selects discrete desired flap positions and provides a signal on one of lines 82-84 feeding matrices 94, 157 communicating with the inputs A, B, C of the respective comparactors, while shaft encoder 45 produces signals corresponding to actual discrete flap positions which are fed to matrices 103, 161 communicating with the inputs X, Y, Z of the respective comparators. If there is no signal, or more than one signal, on the lines 82-84 then failure detection circuits 139, 162 cause the respective comparators to produce no output signal. The aircraft also has leading edge slats 13 moved by motors supplied with pressure fluid by valve 66 controlled, in the same way as valve 14, by solenoid valves 67, 68 set by switching amplifiers (168), (174), Fig. 2b (not shown), responsive to signals from comparators (163), (169) receiving inputs from the switch 80 and from an encoder 70 detecting slat position. A further switch (115) is provided to select a single dessired position of both flaps 11 and slats 12, and feeds a signal to switching circuits 125, 160, (166), (172) providing inputs to the respective comparators. The aircraft wings 10 may be swept back towards a position 10a under the control of a unit 44, and a valve 16 prevents the flaps 11 being extended when the wings are in other than their most forward position. If a command is given to sweep the wings back, a switch 159 is opened, feeding a signal to comparator 154 to cause the flaps 11 to be retracted, movement of the wings being prevented by valve 62 until flap retraction is complete. If the wing sweep exceeds a certain angle then a switch 119 is opened, re-setting the switching circuits 125, 160, (166), (172) to retract the slats 12, movement of the wings being inhibited by a valve 69 until this is complete. Further flaps 13 at the leading edge root are moved by motors controlled by a valve 49 adjusted by a cam 48 in the flap position encoder 45, so that the flaps 13 are extended automatically when the flaps 11 are extended beyond a certain position. The switching amplifiers 152, 153, (168), (174) have additional inputs from an asymmetry detection arrangement as described in patent Specification 1,400,449, so that if there is a difference in position between the flaps 11 or between the slats 12 the valves 34, 35, 67, 68 are de-energized, the spools of valves 14, 66 centred, and the flaps and slats immobilized. The electrical circuitry described is duplicated, the solenoid valves being controlled by both circuits in parallel.