AUTOMATIC TRIM. --Some AFCS systems
THEORY OF OPERATION
incorporate automatic trimming. When a signal
is present in the control channel, there is
The AFCS has three main control channels to
an unbalance in fluid pressure at the input
control movement of the aircraft about its axis.
to the hydraulic booster. The hydraulic load
These channels control the yaw (rudder), roll
sensor (fig. 8-28) detects this unbalance. Its
(aileron), and pitch (elevator). Each of the
signal is amplified and drives the trim servo-
control channels has similar functional equipment
groupings. The groupings include controls,
motor. The engagement clutch engages when
sensors, signal coupling circuits, AFCS servo
the AFCS is operating and the automatic
loops, and aircraft flight controls.
trim system is functioning properly. The slip
clutch allows the pilot to override the auto-
Each channel of the AFCS supplies control sig-
matic trim in case of a malfunction. Most
nals to the flight controls and receives error signals
from the sensors. The error sensors and the signal cou-
AFCS use autotrim in the pitch channel;
pling circuits in use in each control channel depend
however, it can be used for yaw and roll as
well.
on the mode of operation. The AFCS servo loops
Figure 8-27.-Hydraulic booster block diagram.
