Abstract: Quad-redundant signal processors in a flight control computer control valves to modulate airflow in a circulation control rotor system. The valves are arranged in a series and each valve is responsive to two signal processors. Loss of a valve occurs when both signal processors for that valve fail. A first valve, and every fourth valve in the series thereafter is responsive to a first signal processor and a third signal processor. The next valve in the series, and every fourth valve in the series thereafter is responsive to a second signal processor and a fourth signal processor. The third valve in the series, and every fourth valve in the series thereafter is responsive to the first signal processor and the fourth signal processor. The next valve in the series, and every fourth valve in the series thereafter is responsive to the second signal processor and the third signal processor.

Abstract: A helicopter stabilator, combining the functions of tail stabilizer and aircraft elevator, has its angle of incidence with respect to the helicopter controlled by means of a pair of reversible actuators acting in series, controlled in a closed-loop fashion by electronic hardware, the controls being disconnected when the actuators fail to track within a threshold disparity of either position or rate of change of position of each other. A test switch introduces an imbalance to test the fault circuitry. The stabilator is biased to assume a maximum incidence position at low speeds, including hover; and inputs from airspeed and collective pitch position cause it to assume a substantially level position at higher, cruise speeds. A pitch rate gyro input controls the stabilator for stable flight against pitch-inducing flight commands and external effects, such as gusts.

Abstract: In the cyclic pitch stick controls of a helicopter of the type in which feel is provided to the pilot by inducing a force which is proportional but opposite to the motion of the cyclic stick from an adjustable trim position, null offset errors which may be due, inter alia, to temperature variation of the hydraulic fluid in the system, are periodically overcome by means of sensing the pressure differential across the force augmentation hydraulic servo actuator at times when the differential pressure thereacross should be nearly zero, during trim release with small stick motion, and providing a countermanding bias in response thereto; the pressure differential is measured by a differential pressure transducer having a full scale which is only sufficient to measure the expected null errors, which may be about an order of magnitude lower than the full scale, operative pressure differentials which may occur.

Abstract: The automatic heading retention mode of operation of an automatic flight control system for a rotary wing aircraft is discontinued and reestablished through the use of a logic circuitry responsive to the yaw rate, bank angle and airspeed of the aircraft and to the force applied to the cyclic pitch control member by the pilot. The logic circuitry provides for the isolation of information commensurate with left and right turns and summation of the yaw rate and bank angle in each direction to determine if automatic disengagement of the heading hold is warranted.