A mechanical feedback is transmitted through the differentiating lever, the load-relief bungee, and the mechanical input lever back to the power valve shuttle, causing it to return to the neutral position. For a constant velocity pilot input, a small constant valve error is established, and the stabilizer moves at a constant speed. When the pilot input stops, the power shuttle valve is returned to neutral, and the stabilizer stops until a new input is introduced.

SERIES MODE. In this mode, input signals from the automatic flight control system (AFCS) may be used independently or combined with manual input to control stabilizer movement. The series mode solenoid valve is energized, porting flight system hydraulic pressure to the electrohydraulic servo valve. Input signals from the AFCS amplifier are applied to the coils of a torque motor in the servo valve, regulating flow from the valve to the servo ram.

The servo ram is connected to the auxiliary lever. Movement of the lever moves the mechanical input lever floating-pivot point. This movement causes mechanical input lever rotation about the manual input point and moves the power shuttle valve, causing a valve error.

A linear transduce, mounted on the servo ram center line, provides electrical feedback signals to the AFCS. Mechanical feedback is provided by the differentiating lever, as in the manual mode. When operating in the series mode, control surface displacement is not reflected at the control stick.

PARALLEL MODE. In this mode, stabilizer movement is controlled by input signals from the AFCS alone. Both series and parallel mode solenoid valves are energized. Flight system pressure is ported to the electrohydraulic servo valve and the mechanical input lockout piston. Fluid pressure stabilizes the lockout piston and holds the mechanical input lever.

The transducer mounted on the servo ram provides an electrical signal feedback to the AFCS. There is no mechanical feedback, since the mechanical input is locked. Additional electrical signal feedback is provided by a transducer, which is mechanically linked to the stabilizer actuating arm. In the parallel mode, the control stick follows the motion of the stabilizer. Should the pilot desire to override the AFCS, he/she can overpower the lockout actuator with a stick force of 24 pounds.

Stop bolts are attached to the control stick pedal to limit fore-and-aft stick movement. The eddy current damper dampens out any rapid fore-and-aft stick movement.

All joints between the pushrods and bell cranks or idlers contain self-aligning bearings to compensate for any misalignment during operation and airframe deflections in flight that might cause binding. Artificial feel is provided by the artificial-feel bungee. The bungee consists of two springs, which have different spring constants. The stick force caused by the bungee is proportional to stick displacement. At near neutral, the bungee provides a high stick force that decreases a short distance from neutral and gradually increases with the amount of stick displacement.

The electric trim actuator is mechanically linked to the artificial-feel bungee, and varies the neutral position of the bungee to provide longitudinal trim of the aircraft. The actuator consists of one high-speed and one low-speed motor, a gearbox, a brake, a ball detent clutch, and a threaded power screw. The actuator is manually controlled through inputs from the trim switch on the control stick grip. When the stabilizer is in automatic trim, the actuator receives inputs from the AFCS. High speed is used during manual trim, and low speed during automatic trim.

The stabilizer shifting mechanism, shown in figure 9-7, consists of a shift sector and its linkage, plus cable that runs from the flap drive gearbox and the rudder cam shift mechanism. A spin recovery cylinder is also attached to the shifting mechanism, and provides an alternate method of shifting the stabilizer and rudder from the "clean" configu-ration to the "dirty," or increased throw con-figuration. In normal operation, when flaps are extended, a cable running from a drum on top of the flap drive gearbox to the sector assembly of the shifting mechanism rotates the sector. Linkage connecting the sector assembly and the control stick linkage is shifted. Linkage shifting increases control stick travel. Stabilizer down travel is increased to a 24-degree maximum. A cable is also connected from the sector assembly to the rudder cam stop shifting mechanism, which increases rudder travel from 4 to 35 degrees each side of neutral.

The pilot, at his/her option, may obtain increased stabilizer and rudder throw by actuation of the spin recovery assist switch, eliminating the necessity of lowering the flaps. This action ports hydraulic pressure through the spin recovery selector valve and its flow regulators and check valve to the spin recovery cylinder, causing it to extend and shift the mechanism in the same manner as provided by the cable action.

The two nonbypass-type filters in the system protect the intricate valving mechanisms of the actuator from contamination, and are vitally important to proper stabilizer operation. They are checked with the requirements listed in the maintenance requirements card deck, and should not be overlooked when troubleshooting stabilizer system malfunctions.

The stabilizer power package, used on various Navy aircraft, is linked to the approach power compensator system (APC). This system aids the pilot in maintaining optimum angle of attack for approach and landing. An APC potentiometer is mechanically linked to the power package, and provides electrical inputs to the APC system to compensate for changes in pitch attitude required during landing approaches. The APC system regulates the throttle position to provide the engine thrust required to establish and maintain the desired angle of attack. The potentiometer provides inputs relative to the position of the horizontal stabilizer.