Abstract: A hydraulic jack for the controlled displacement of a load, such as a platform used in the training of aircraft pilots, has a servo valve normally settable by an error signal Ve from an actuator including a subtractor followed by an amplifier, the subtractor emitting the error signal as the difference between an externally generated position-control signal Vc and a position-feedback signal Vx sent out by the jack. A monitoring device includes an error detector which generates a safety signal AL disconnecting the servo valve from its actuator whenever the position-feedback signal Vx deviates excessively from a reference signal V'x derived from the position-control signal Vc by means of a simulation circuit whose transfer constant equals, in first approximation, that of the servo system encompassing the jack and the actuator.

Abstract: The invention relates to the simulation of an aircraft's flight controls and particularly the mechanical reactions produced on the pilot's controls.The reaction force is produced by a servo-controlled, hydraulic actuator whose piston moves a distance X which is proportional to the deflection of the pilot's control. A servo signal, whose amplitude is proportional to the component of the reaction force depending on the displacement X, is obtained by digital calculation, filtering and analogue multiplication.The invention can be applied to flight training systems and to artificial feel systems (AFS).