FLIGHT CONTROL SYSTEM EMPLOYING THREE CONTROLLERS OPERATING A DUAL ACTUATOR

An aircraft flight control system for use with a dual or tandem hydraulic actuator coupled to a flight control surface through an actuating rod. Each half of the tandem actuator is controlled by a respective electrohydraulic servovalve. Each electrohydraulic servovalve is controlled by signals applied to either of two actuating coils. Control signals are applied to the actuating coils from three controllers. The control signals are generated as a function of the difference between the flight control signal and a feedback signal indicative of the position of the actuating rod. Each electrohydraulic servovalve includes a pair of linear variable differential transformers generating feedback signals indicative of the position of the valve stem in each electrohydraulic servovalve. The valve feedback signals are compared to each other and to reference signals corresponding to the expected value of such feedback signals in order to detect and identify malfunctions in the flight control system. In one embodiment, the electrohydraulic servovalves are controlled by two channels of a primary controller in normal operation. In the event of a malfunction, control is transferred to one of two secondary controllers. In another embodiment, the electrohydraulic servovalves are controlled by respective primary controllers, with control being transferred to one of two channels of a secondary controller in the event of a malfunction.