A control apparatus comprising a plurality of servomechanisms for controlling the Control surface of an aircraft and control signal producing means for producing first and second control signals to said servomechanisms, the first control signal of said control signal producing means being produced to at least one of said servomechanisms which happens to be damaged, and said second control signal of said control signal producing means being produced to all of said servomechanisms which happen to be damaged, each of said servomechanisms comprising:
- a hydraulic working oil source for supplying hydraulic working oil under pressure;
- a hydraulic working oil reservoir for reserving said hydraulic working oil;
- an actuator assembly for driving said control surface of said aircraft, said actuator assembly having a cylinder member and a piston member slidably received in said cylinder member, said cylinder member and said piston member collectively defining a pair of hydraulic chambers, said piston member being operatively connected to said control surface of said aircraft;
- a control valve held in fluid communication with said hydraulic chambers of said actuator assembly through a pair of fluid passageways, with said hydraulic working oil source and with said hydraulic working oil reservoir, said control valve being operative to assume a first control valve position in which said hydraulic working oil is supplied from said hydraulic working oil source to one of said hydraulic chambers through said control valve and discharged from the other of said hydraulic chambers to said hydraulic working oil reservoir through said control valve to force said piston member of said actuator assembly to be moved in a first driving direction, a second control valve position in which said hydraulic working oil is supplied from said hydraulic working oil source to said other of said hydraulic chambers through said control valve and discharged from said one of said hydraulic chambers to said hydraulic working oil reservoir through said control valve to force said piston member of said actuator assembly to be moved in a second driving direction, and a third control valve position in which said hydraulic working oil is interrupted from being supplied from said hydraulic working oil source to said hydraulic chambers of said actuator assembly and discharged from said hydraulic chambers of said actuator assembly to said hydraulic working reservoir through said control valve to prevent said piston member of said actuator assembly from being moved;
- a switching valve provided on said pair of fluid passageways between said actuator assembly and said control valve to be held in fluid communication with said hydraulic chambers of said actuator assembly and said control valve and having a throttle valve member, said switching valve being operative to assume a first switching valve position in which said hydraulic working oil is permitted to be supplied from said hydraulic working oil source alternatively to one and the other of said hydraulic chambers and discharged alternatively from one of the other said hydraulic chambers of said actuator assembly to said hydraulic working oil reservoir to move said piston member of said actuator assembly alternatively in said first and second directions in the state of the first and second control valve positions of said control valve, a second switching valve position in which said hydraulic working oil is interrupted from being supplied from said hydraulic working oil source to said hydraulic chambers of said actuator assembly and from being discharged from said hydraulic chambers of said actuator assembly to said hydraulic working oil reservoir to cause said hydraulic chambers of said actuator assembly to be held in fluid communication with each other through said pair of fluid passageways, and a third switching valve position in which said hydraulic working oil is interrupted from being supplied from said hydraulic working oil source to said hydraulic chambers of said actuator assembly and from being discharged from said hydraulic chambers of said actuator assembly to said hydraulic working oil reservoir to cause said hydraulic chambers of said actuator assembly to be held in fluid communication with each other through said throttle valve member and said pair of fluid passageways;
- first change-over means for causing said switching valve to assume said second switching valve position in response to said first control signal from said control signal producing means;
- and
- second change-over means for causing said switching valve to assume said third switching valve position in response to said second control signal from said control signal producing means.