Abstract: The output response of a pilot valve controlled servo 10 is monitored by a computer 20 using a transducer 16 on the main control valve 12 and a transducer 11 on the servo output 10a. The response is compared by determining the predicted output response and response time from a mathematical model for the servo, and if the response or response time is incorrect, a warning indication is provided.

Abstract: A flight control system for a helicopter tail rotor having a semicircular quadrant 18 with bell cranks 36, 40 mounted on either end of the quadrant and flexible control cables 20, 22 connected to each bell crank. The bell cranks are spring loaded in opposition to cable tension, and a fixed abutment 72 provides a reaction against the bell crank springs in the event of a cable severance. The quadrant works against the spring loading of one bell crank in the event of breakage of the opposite control cable and is centered by the spring loading of both bell cranks if both cables are broken.

Abstract: 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 (98, 112) to cause trim actuators (39-41) to drive swash plate servos (17-19) to the correct positions, initially (98) in response to stored trim references (120) and eventually (112) in response to the difference (109) between stored swash plate servo positions (120) and current servo positions (20-22).