Abstract: A constant force mechanical spring and a varying force hydraulic actuator combine to provide feel to a pilot of his movement of an airplane's elevators. A constant force bias spring works against the hydraulic actuator to reduce the actuators effectiveness to nearly zero at minimum feel force conditions.

Abstract: In a servoactuator system for an aircraft, a strapdown series servoactuator having an external linkage assembly is coupled between the pilot's control stick and a control surface member. The external linkage assembly includes a differential link and servo link having specially tapered stop surfaces adapted to be varied in dimensions to accommodate a wide variety of installations, which stop surfaces cooperate with fixed stops on the servoactuator housing whereby to provide a variety of pilot authority limits and series servo authority limits depending upon particular installation requirements.

Abstract: A control stick simulator for use in a part task trainer for pilots utili a bending beam in cooperation with deflection sensing transducers to output pitch and roll commands. The control stick is a cantilevered metallic beam, arrested by stops in a mounting flange near a handgrip at its upper end, thereby presenting an isometric feel to the pilot.

Abstract: To provide the pilot with the "feel" that he is inadvertently moving his cyclic control stick from its midposition when the helicopter is on the ground, and thereby possibly changing the rotor plane from a safe to an unsafe position for ground personnel, a restraint member is provided which includes an over-center spring, and which may be pivoted from its stowed position into an operable position where it bears against the cyclic stick so midpositioned. The over-center spring thereof offers resistance to cyclic stick motion if the pilot inadvertently begins to move the stick forward or laterally of its midposition, but the spring biasing force can readily be overcome by the pilot by manually pushing the cyclic stick forward and thereby cause the restraint member to move to its stowed position.

Abstract: A four axis force stick provides signals indicative of force applied to the stick in an axis corresponding to a control axis of an aircraft, including pitch, roll, yaw and lift/speed. The force-related signals are applied through proportional and integral gain signal paths to operate electrohydraulic servos that control the aerodynamic surfaces of the aircraft, such as the cyclic and collective blade pitch of the main rotor and the tail rotor blade pitch of a helicopter, or the ailerons, rudder, elevator and thrust of a fixed wing aircraft. Signal conditioning provides a dead band to avoid integrating minute, inadvertent force stick signal outputs, and vernier sensitivity at low forces with high gain at high forces. Analog and digital embodiments are discussed. The relationship between this wholly new mode of aircraft control and ancillary aircraft functions, such as ground steering, autopilot and stability functions, are also discussed.

Abstract: A bifurcated feel unit for use in a dual path flight control system includes separate input levers for the pilot and copilot control paths. The input levers pivot about a common axis but are capable of independent rotation upon override of the breakout pogos associated with the control system external to the feel unit. Each input lever is coupled to a source of resistive force, preferably a piston within a hydraulic chamber. Normally the feel force supplied is the sum of the resistive forces applied to each input lever. In the event of a jam in one path of the flight control system, the feel force supplied to the remaining operable path is reduced in proportion to the reduction in available control surface.

Abstract: A flight simulating system is provided with a manually operated control member connected to a servomechanism which responds to manual input by the control member and reacts to provide realistic feedback to the control member in accord with simulated flight conditions. For this purpose, a combining circuit, a dividing circuit and two integrator circuits are provided in series. The combining circuit has an input which represents manual input force to the control member and another input from the flight-simulating computer which represents simulated internal forces acting on the controlled member and the dividing circuit divides the output of the combining circuit by a value representing the mass of the control member to produce a control member acceleration-related signal. This acceleration-related signal is integrated twice to produce, respectively, a control member velocity-related signal and a control member position-related signal.

Abstract: A pair of input sense signals are processed and passed to inputs of two servo amplifiers. The amplifier outputs are summed and converted to a corresponding hydraulic pressure in a T-valve. Transducers monitor the produced pressure and provide feedback signals to the servo amplifiers. A comparator compares the servo amplifier outputs and activates a warning device if the signal difference therebetween exceeds a threshold level. Equalizer circuitry processes the comparator output and provides correction signals to the servo amplifier inputs to wash-out offset effects.

Abstract: A bias voltage, which can be added to force commands applied to a helicopter control stick actuator, to compensate for static null offset errors, is generated as the average of the summation or integral of actuator pressure, or pressure differential, sensed while the force is moved from a first position which is halfway aft through null to a second position which is halfway forward and back through null to the first position, the pressure readings which are averaged being taken only through the central portion of the motion, the motion being controlled to be extremely slow compared to normal permissible stick motion.

Abstract: Strapdown, multifunction actuator apparatus comprising one or two integral units adapted for installation in an aircraft, particularly a helicopter, and coupled between the pilot's control stick linkage and the aircraft control surface (or surface servo boost) linkage to perform the functions of series actuation, trim actuation, artificial feel, control position sensing, and control authority limits. The apparatus includes a series actuator installed in the vehicle and connected to the vehicle control linkages in the conventional parallel actuator manner; that is, it is secured directly or strapped down to the airframe and therefore greatly simplifies control system installation and reduces problems such as those associated with control rod vibration resonances normally encountered with conventional integral-with-linkage series actuator installations.

Abstract: A system which provides feel-force to the control stick of an aircraft by means of hydraulic pressure is provided with non-nulling, proportional, direct feedback loop, and a limited integral feedback loop in the drive of the pressure control servo valve that commands the pressure-generating hydraulic force actuator. Static nulls are compensated in the integral path; integration is corrected when the static null and integral output exceed a limiting value. Embodiments include software and/or hardware portions.

Abstract: In a system which provides feel-force to the control stick of an aircraft by means of hydraulic pressure, a fault indicating system which responds to excessive differences between desired and actual force in the actuator, only of a polarity in the same direction as concurrent stick motion, to separate pilot induced pressure excesses from force-system faults, is provided with directional sensitivity in the fault-indicating output logic. Excessive pressure errors in either direction of stick travel institute the monitoring of changes in stick position. Changes in stick position of an excessive magnitude are recognized as fault only if they occur in the same direction as the direction of excessive pressure error. A simple analog embodiment utilizes threshold detectors and a track store device; a dedicated-digital embodiment utilizes comparators, registers and a subtractor; and a computer embodiment utilizes a software routine.

Abstract: The system is used in power-assisted control systems to provide a restoring force to the control stick indicative to the pilot of the deflection of a control surface. The feel system is trimmable in that the neutral position can be altered. In prior systems trimming was accomplished by releasing a brake which permitted movement of a part of the control stick linkage toward an equilibrium position in response to the restoring force. In prior systems the released part acquired sufficient momentum to cause it to overshoot and oscillate about the equilibrium position. If the brake were engaged prematurely, the momentum was imparted to the control stick resulting in a disagreeable "kick" felt by the pilot. To overcome these problems, the brake is repetitively disengaged and engaged at a repetition rate in the range 5-40 Hz. The small amount of momentum built up in each of the successive cycles results in an almost imperceptible vibratory reaction on the control stick rather than a single large "kick".

Abstract: A single actuator unit is installed in an aircraft, for example, a helicopter, and is coupled to the control linkage from the pilot's stick to perform the functions of series actuation, trim actuation, artificial feel, control position sensing, control limits and, if needed, force boost. Although the device performs as a series actuator, it is installed in and connected to the vehicle surface control linkages in the conventional parallel actuator manner and therefore greatly simplifies control system installation and reduces problems associated with control rod vibration resonances normally encountered with series actuator installations.