The first mode is the manual mode. Its
The sensor functions in the same manner as
primary purpose is to aid the pilot in manually
the ball in a turn-and-bank indicator. The ball
positioning the control surfaces. Control surfaces
gives a visual indication of slip or skid resulting
on large aircraft are much too large to move
from lateral acceleration. The sensor provides a
unaided. On smaller high-speed aircraft, the high
signal output of this condition. Figure 8-26 shows
air pressure makes it nearly impossible to move
a diagram of the forces acting on the aircraft in
the controls unaided. In the manual mode of
a turn. Refer to this figure as you read this section.
operation, the hydraulic booster package is
In a coordinated turn, the vertical and lateral
connected between the pilot's control stick
forces resolve into a vector perpendicular to the
and the control surface. It provides hydraulic
span of the aircraft. When the aircraft is turning
assistance to the pilot in much the same manner
with the two forces in balance, the ball is centered;
that power steering aids the driver of a car or
the pendulum in the sensor gives a null output.
truck.
When the aircraft bank angle is too large for
the turn rate, the balance is upset (fig. 8-26, view
Mode two of the hydraulic booster package
B). The ball moves away from the center toward
uses electrical signals from the AFCS to move the
the inside of the turn, and the pendulum moves
flight control surfaces. In this mode, the booster
the synchro rotor from the center null position.
package connects the AFCS to the control surface
The rotor displacement produces a signal with
and provides the muscle to move the surface.
magnitude proportional to the displacement angle
Synchro devices on the boost package provide
and signal polarity corresponding to the direction
feedback signals to the AFCS (fig. 8-27).
of displacement. The unbalanced condition results
from a sideways accelerating force, causing the
The surface position transmitter sends the
aircraft to slip toward the inside of the turn.
AFCS a signal representing the amount and
direction of control surface displacement from the
When the aircraft is insufficiently banked for
streamline position. This signal acts as a follow-
the turn, an acceleration acts toward the outside
up to prevent overshoot of the controls. Also,
of the turn (fig. 8-26, view C). The ball in the
it serves to return the control surface to the
turn-and-bank indicator moves from the center,
trimmed condition as the original signal returns
and the pendulum in the dynamic vertical sensor
to zero.
is displaced from null in the direction cor-
responding to the ball. This gives a signal whose
The modulating piston is displaced only when
polarity is opposite to that of the signal when the
the control surface is in motion. The position of
aircraft was in a slip. The signal is fed to the
the modulating piston is monitored to sense the
rudder channel for right or left rudder to
control surface rate of movement. This action
coordinate the turn. Since the pendulum is
generates a signal to dampen control surface
unaffected by transients, the rudder adjustment
movement.
is on a comparatively long-term basis.
Hydraulic load sensors determine the amount
of pressure the AFCS is applying to the control
Hydraulic Components
surface so the pilot can properly trim the aircraft
before disengaging the AFCS. If the aircraft is
Hydraulic systems provide the physical power
not properly trimmed and the control pressure is
to move the flight control surfaces. All electro-
suddenly relieved, the control surface moves
hydraulic (AFCS) actuators work in the same
rapidly, causing sudden aircraft movement.
manner. A brief discussion of electrohydraulics
is presented in the following paragraphs.
Some aircraft use both manual and AFCS
modes simultaneously. Aircraft stabilization is
provided from the AFCS, while the pilot manually
ELECTROHYDRAULIC SERVO ACTUA-
controls the aircraft. All flight control systems
TORS. --Electrohydraulic servo actuators
have a method of disconnecting the booster
(hydraulic booster packages) are discussed in
package. This method gives the pilot manual
chapter 4 of this TRAMAN. Modern aircraft use
control of the flight control surfaces if the booster
several types of actuators, with each booster
malfunctions or failure of the hydraulic system
actuator having at least two modes of operation--
occurs.
manual mode and electrical signals.
