Low-vulnerability device for the control of helicopter rotor by cyclic plates

Low-vulnerability device for the operation of plural lifting and propulsing rotor blades of a helicopter controlled by control linkages from a cockpit, the linkages being connected to a cyclic plate mechanism mounted coaxially on a rotor drive shaft, the cyclic plate mechanism including a rotating plate coupled by a peripheral part individually to a plurality of rods, each rod controlling the pitch of one rotor blade, and a non-rotating plate coupled at four points regularly distributed around a periphery of the non-rotating plate to four hydraulic actuating servocontrols, each servocontrol comprising a power jack, an anchoring system and a servocontrol-distributor, three of the servocontrols being used in normal working and the fourth being used as back-up in the event of a failure occurring on one of the other three normally working servocontrols wherein:

• each power jack is supplied by a hydraulic circuit, independent of the hydraulic circuits of the other jacks, each hydraulic circuit including a hydraulic supply, a fluid reservoir and a hydraulic return to said fluid reservoir, and each power jack is attached to the servocontrol-distributor which is operated by a mechanical input which is linked to the cockpit by the corresponding control linkage;
• each power jack being operatively connected to one of the anchoring systems, each anchoring system being disengagable;
• each of the servocontrol-distributors of the normally working servocontrols is structurally arranged so as to be active in normal working and to block the anchoring system of each corresponding power jack, and the one servocontrol-distributor of the back-up servocontrol is structurally arranged so as to be passive in normal working and to keep the anchoring system of the corresponding power jack disengaged;
• each mechanical input of the four servocontrol-distributors comprises a system which in the event of a certain force threshold being exceeded on one of the three normally active servocontrol-distributors, neutralizes this one servocontrol-distributor and initiates starting up of the normally passive servocontrol-distributor which then becomes operational in a safeguard working mode.