Abstract: A positioning device for a critical aircraft surface, such as a stabilizing elevator in a helicopter, includes a pair of reversible electric jack-screw type actuators acting in series, each being controlled in a closed-loop fashion by separate electronic hardware, the position of each as well as the rate of change thereof being compared with the other, against limits which, according to the invention, are relatively broader at low speeds and are tightened at higher speeds. If either of the positions or the rate of change of positions of the two actuators fail to track within the variable threshold disparity, an alarm condition is manifested and the actuators are disconnected from automatic control and rendered operable by manual control.

Abstract: A differential pressure sensing valve has an axially shiftable spool including axially-spaced spool areas on which a pair of pressure sources connectable with such valve act in a predetermined direction with spool shifting force. Biasing means normally biases such spool with spool shifting force in a direction opposite to the predetermined direction. The opposite spool shifting forces are substantially balanced over the normal operating range of the pressure sources for maintaining such spool in an operating position for normal flow of fluid through the valve. Such opposite spool shifting forces are substantially unbalanced for shifting such spool out of such operating position when the pressure sources substantially deviate from their normal operating range.

Abstract: A hydraulic actuating arrangement for an aircraft control surface has a control circuit, responsive to a position selection input signal, for providing six nominally identical output control signals. Six pilot valves respectively responsive to the control signals provide six servo pressure signals to respective ones of six intermediate actuators. The intermediate actuators are resiliently coupled to each of two main hydraulic control valves. Three of the intermediate actuators and one of the main control valves are supplied from a first hydraulic pressure source, the remaining three intermediate actuators and the remaining main control valve being supplied from a second hydraulic pressure source. An output actuator is responsive to output pressures from either of the main control valves.

Abstract: A servo-system for controlling position as well as rate of movement of a controlled device. Any command signals are processed or shaped prior to comparison with the feedback position signals. This processing includes integration at one of two available integration rates in accordance with the magnitude of the difference between the command and shaped command signals to correct for synchro non-linearities. The processing also includes limiting the input to the integrator such that the velocity as well as position of the controlled member is controlled.A fail-detect system monitors critical signals and power levels and distinctively indicates a failure if any is detected.

Abstract: An electro-hydraulic system for controlling a hydraulic function includes a pump and reservoir connected to the function through an electro-hydraulic control valve, a pair of pilot operated check valves normally preventing fluid flow from the function, a pilot passage between the pump and check valves to pressurize and open the check valves, an electro-hydraulic drain valve connected to the pilot passage, and control means for the control and drain valves. The control means is responsive to a feedback signal from the hydraulic function and an operator-controlled input signal within a predetermined range to close and open the drain and control valves, respectively. The control means may further require the presence of a second input signal, such as a simple reference signal or a signal provided in response to operation of an additional function, before operating the control and drain valves.