Updated lock-positioning of foldable helicopter blades

A helicopter having foldable main rotor blades, the pitch angles of which are positionable by push rods in dependence upon the vertical position and tilt of a swash plate cooperating with said push rods, said blades being lockable at specific pitch angles as a prerequisite to folding, said swash plate being positioned by a plurality of servos, each of said servos being separately operable in response to corresponding outputs of a mixer, the mixer in turn receiving inputs from pitch, roll and collective channels, each of said channels including an electrically operable trim actuator for providing a corresponding input to said mixer in response to a related trim command signal, a position detector for each of said servos, each position detector providing a servo position signal indicative of the position of a corresponding one of said servos, and signal processing means for storing a plurality of desired position signals indicative of corresponding predetermined servo positions at which rotor blade pitch angle would be correct for locking, for providing pitch, roll and collective reference signals indicative of corresponding trim commands to be applied to said pitch, roll and trim actuators, and for providing trim command signals to said pitch, roll and collective trim actuators in respective response to said pitch, roll and collective reference signals, characterized by:

• said signal processing means comprising means for providing said reference signals by generating, in response to all of said desired position signals, reference signals corresponding to trim command signals which will cause said trim actuators to provide inputs to said mixer to cause said servos to be driven substantially to said predetermined positions as indicated by said servo position signals.