moves faster. The direction of the pressure
static state (zero signal), dc flow through the
determines the direction of control surface
transfer valve coil is equal, and the plunger
movement.
mechanism remains in the centered position (with
If there is no pressure at the control wheel,
help from the centering springs).
Hydraulic pressure from the engagement valve
the main control valve centers (fig. 4-13). Trapped
flows to the top land on the hydraulic transfer
fluid holds the hydraulic actuator piston in
valve piston. Fluid also flows through a small
position.
The manual operation of the dual shutoff and
orifice to the bottom land of the same piston.
bypass valves is from the flight station. If there
Pressure to the bottom of the piston is regulated
is a loss of hydraulic pressure or a malfunction
by controlling the amount of fluid leaving the
modulated pressure chamber. If chamber pressure
in the boost system, the flight crew pulls
is 1,500 PSI and one drop of fluid leaves the
the handle. Operation of the valves shuts off
hydraulic pressure to the hydraulic actuating
chamber for every drop that enters, the pressure
piston and opens both working lines to each other.
remains constant. To increase pressure, an
This prevents hydraulic lock in the actuator piston
unbalanced dc voltage on the coil causes the
and allows control surface movement without the
plunger to block the return orifice for an instant
aid of the boost system.
so more fluid enters the chamber than leaves.
Trapped hydraulic pressure in the modulator
Conversely, an unbalanced dc signal from the
piston aids the mod piston centering spring in
AFCS computer that causes the plunger to rise
holding the piston centered. This allows positive
for an instant lowers chamber pressure.
With zero input signal from the AFCS
control of the main control valve by the control
lever.
computer, the transfer valve piston is in the
Upon AFCS engagement, the engagement
centered position (fig. 4-13). The pressure acting
valve ports hydraulic fluid to the hydraulic
on the smaller surface area of the piston's upper
transfer valve and to the engagement piston.
land and the modulated pressure acting on the
Movement of the engagement piston locks the
larger area of the piston's lower surface are in
control lever in its centered position and prevents
balance, keeping the piston centered.
mechanical inputs from the control wheels. This
With an electrical signal input, as shown in
piston can, however, be overpowered by about
figure 4-14, a higher pressure in the modulated
15 pounds of force on the control wheel, if
chamber causes the piston to raise. This action
necessary, in an emergency.
allows fluid to flow to another component of the
Electrical inputs from the AFCS computer
boost system. The larger the electrical signal input,
change to hydraulic fluid pressures in the
the more pressure difference on the piston;
hydraulic transfer valve, and the pressure controls
therefore, more fluid flow.
the modulator piston. The modulator piston
BOOSTER SYSTEM OPERATION. --The
changes the hydraulic pressure into linear
mechanical motion, which repositions the main
booster operates in two separate modes--manual
control valve. Movement of the main control
and AFCS. In the manual mode, control surface
valve ports hydraulic fluid to the actuator piston
deflection desired by the pilot starts by a lateral
to position the control surface and control wheel
movement of the control wheel (fig. 4-13). This
as previously described.
small movement of the control wheel transmits
Electrical devices on the booster provide
through the feel lever and feel rod to the control
information inputs to the AFCS. The modulator
lever. The control lever is free to move about its
piston linear transducer tells the AFCS the rate
pivot, and a centering spring holds the modulating
piston in place. Movement of the control lever
of control surface movement, and the surface
displaces the main control valve, porting fluid
position synchro transmitter provides position
information. Read chapter 8 for more information
from two hydraulic systems to the hydraulic
about automatic flight control system operation.
actuator piston. (The main control valve and
hydraulic actuator work identically, whether in
Landing Gear System
manual or AFCS modes.)
When the hydraulic actuator piston moves,
Most naval aircraft have hydraulically
actuated, electrically controlled, retractable
both the feel lever and the power arm position
landing gear. Normally, locking the landing gear
the control surface and the control wheel to the
in the retracted or extended position is automatic.
position the pilot selects. As the pilot applies more
Figure 4-15 is an electrical schematic of the
pressure to the control wheel, the control surface
