tandem-mounted power pistons, a servo ram, an
valves are energized. Flight system pressure is ported
to the electrohydraulic servo valve and the mechanical
electrohydraulic servo valve, a lockout actuator, and
input lockout piston. Fluid pressure stabilizes the
parallel and series mode solenoid valves. The actuator
lockout piston and holds the mechanical input lever.
can operate in any of three modes-manual, series, or
parallel. Refer to figure 16-7 to help you understand the
The transducer mounted on the servo ram provides
three modes of operation.
an electrical signal feedback to the AFCS. There is no
mechanical feedback, since the mechanical input is
MANUAL MODE.--In this mode, the pilot input
locked. Additional electrical signal feedback is
alone controls the power valve. Inputs are transmitted
provided by a transducer, which is mechanically linked
through linkage to the mechanical input lever. The
to the stabilizer actuating arm. In the parallel mode, the
auxiliary lever is locked in neutral by the servo ram
control stick follows the motion of the stabilizer.
centering springs, causing the mechanical input lever
Should the pilot desire to override the AFCS, he/she
to rotate about its pivot point, moving the power shuttle
can overpower the lockout actuator with a stick force of
valve. As the valve shuttle is displaced from neutral, a
valve error is established, and pressure is ported to the
actuating pistons. The pressure moves the pistons and
Stop bolts are attached to the control stick pedal to
the attached stabilizer in proportion to the input.
limit fore-and-aft stick movement. The eddy current
A mechanical feedback is transmitted through the
damper dampens out any rapid fore-and-aft stick
differentiating lever, the load-relief bungee, and the
mechanical input lever back to the power valve shuttle,
All joints between the pushrods and bell cranks or
causing it to return to the neutral position.
idlers contain self-aligning bearings to compensate for
For a constant velocity pilot input, a small constant
any misalignment during operation and airframe
valve error is established, and the stabilizer moves at a
deflections in flight that might cause binding.
constant speed. When the pilot input stops, the power
Artificial feel is provided by the artificial-feel
shuttle valve is returned to neutral, and the stabilizer
bungee. The bungee consists of two springs, which
stops until a new input is introduced.
have different spring constants. The stick force caused
SERIES MODE.In this mode, input signals
by the bungee is proportional to stick displacement. At
from the automatic flight control system (AFCS) may
near neutral, the bungee provides a high stick force that
be used independently or combined with manual input
decreases a short distance from neutral and gradually
to control stabilizer movement. The series mode
increases with the amount of stick displacement.
solenoid valve is energized, porting flight system
hydraulic pressure to the electrohydraulic servo valve.
The electric trim actuator is mechanically linked to
Input signals from the AFCS amplifier are applied to
the artificial-feel bungee, and varies the neutral
the coils of a torque motor in the servo valve,
position of the bungee to provide longitudinal trim of
regulating flow from the valve to the servo ram.
the aircraft. The actuator consists of one high-speed
and one low-speed motor, a gearbox, a brake, a ball
The servo ram is connected to the auxiliary lever.
detent clutch, and a threaded power screw. The
Movement of the lever moves the mechanical input
actuator is manually controlled through inputs from
lever floating-pivot point. This movement causes
the trim switch on the control stick grip. When the
mechanical input lever rotation about the manual input
point and moves the power shuttle valve, causing a
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.
A linear transducer, mounted on the servo ram
centerline, provides electrical feedback signals to the
The stabilizer shifting mechanism, shown in figure
AFCS. Mechanical feedback is provided by the
16-7, consists of a shift sector and its linkage, plus
differentiating lever, as in the manual mode. When
cable that runs from the flap drive gearbox and the
operating in the series mode, control surface
rudder cam shift mechanism. A spin recovery cylinder
displacement is not reflected at the control stick.
is also attached to the shifting mechanism, and
PARALLEL MODE.In this mode, stabilizer
provides an alternate method of shifting the stabilizer
and rudder from the "clean" configuration to the
movement is controlled by input signals from the
AFCS alone. Both series and parallel mode solenoid
"dirty," or increased throw configuration.