AUTOMATIC LOCK-POSITIONING OF FOLDABLE HELICOPTER BLADES

The foldable rotor blades (12) of a helicopter are automatically adjusted to pitch angles where they can be locked as a prerequisite to folding, by commands generated to cause trim actuators (39-41) to drive swash plate servos (17-19) to the correct positions, initially in response to stored trim references and eventually in response to the difference between stored swash plate servo positions and current servo positions (20-22). One embodiment uses values of servo positions (20-22), just before unlocking the blades upon re- spreading them, to store, in nonvolatile memory, deviations from nominal positions stored in read only memory, and generates trim references in a subsequent folding operation in response to integrated values to reduce actual position errors toward zero from desired positions indicated by the stored deviations.