Abstract: A control system for controlling displacement of the aerodynamic control-surfaces of an aircraft includes a first signal processor that is supplied with input signals from the pilot's control column and also with predominantly lower-frequency components of feedback signals derived in accordance with the actual position of the control surfaces. The first signal processor derives an intermediate signal from the input and feedback signal components by digital processing and supplies this intermediate signal to a second signal processor which also receives the predominantly higher-frequency components of the feedback signal. The second signal processor derives an output signal from the intermediate and feedback signal components by analogue processing and supplies this to an actuator for controlling displacement of the control-surfaces. The second signal processor may also receive additional feedback signals directly from the actuator.

Abstract: A quadruplex, double-failure survival, fly-by-wire aircraft control system includes two monitor lanes whose outputs are consolidated with those of the four main control lanes to drive the aircraft control-surfaces by hydraulic rams via individual spool-valve actuators. Nominally-identical sets of pilot's-demand, instrument, and position-feedback signals are derived independently for the four lanes respectively, and digital representations of all these are exchanged between the control lanes for the selection of their mean or median values by digital processors that also serve to compute the control outputs of the lanes from the selected values. The sets of signals supplied to one pair of the four lanes are reversed in sense compared with the sets supplied to the other pair so as to ensure that the same digitally-encoded data is represented differently in the different pairs and the possibility of a context-dependent failure occurring simultaneously in both pairs is thereby avoided.