control system computer and the SAS and
remove long term rate signals and applies a
BOOST shutoff valves.
correction signal to the pitch SAS servo valve. The
servo valve controls hydraulic pressure to the SAS
NO. 1 LATERAL ACCELEROMETER. --
actuator. The SAS actuator provides mechanical
The accelerometer provides lateral acceleration to
movement of the flight controls, producing
rotor head movement opposing the sensed pitch
the SAS amplifier via the No. 1 stabilator
rate.
amplifier for the turn coordination function of
The SAS 1 roll channel provides dynamic
SAS 1.
stability and limited roll stability for the
helicopter's roll axis. A roll attitude signal is
NO. 1 PITCH RATE GYRO. --The gyro
provided to the SAS amplifier from the ATO's
provides pitch rate to the SAS amplifier via the
Attitude. Heading Reference system. The SAS
No. 1 stabilator amplifier for the pitch dynamic
stability function. The pitch rate gyros are also
amplifier limits this signal and uses it with a roll
rate signal from an internal roll rate gyro. The
part of the stabilator control system.
amplifier applies the resultant correction signal
to the roll SAS servo valve. This servo valve
SAS ACTUATORS. --The SAS actuators, on
controls the actuator, which positions the flight
the pilot-assist servos, convert electrical signals
from the analog SAS 1 and digital SAS 2 to
controls to oppose the sensor inputs.
mechanical motion to move the flight controls.
The SAS 1 yaw channel provides dynamic
The actuators are electrohydraulic, operating
stability for the helicopter's yaw axis and turn
coordination. At airspeeds of less than 50 knots,
from pressure supplied by the No. 2 transfer
the No. 1 stabilator amplifier provides a +12 to
module, applied through the SAS shutoff valve.
+15 VDC airspeed switch discrete. The discrete
When the SAS/BOOST HYD switch is pressed,
power is removed from the SAS shutoff valve,
inhibits No. 1 lateral acceleration and roll rate
signals in the SAS amplifier. The discrete controls
opening the valve. Opening the valve allows the
the internal yaw rate gyro in the SAS amplifier
actuators to move with signals applied from SAS
as the yaw channel sensor. When sensing a yaw
1, SAS 2, or both. With pressure removed from
rate, the SAS amplifier processes it to remove long
the actuators, a spring-loaded device locks the
term yaw rate signals. It then develops a short
actuator piston in center position. Each actuator
term correction signal and applies it to the yaw
output piston connects to linkage. When the
SAS servo valve. The servo valve controls the
actuator piston becomes locked, it forms a fixed
actuator, which moves the flight controls to
pivot point on one end of the linkage. This allows
oppose the yaw rate.
the linkage to move with stick, pedal, or trim
inputs.
At speeds below 50 knots, the airspeed
transducer is applied to stabilator amplifier No.
1 and sent to SAS 1 amplifier (discrete signal).
SAS AMPLIFIER. --The SAS amplifier con-
This discrete signal allows the yaw SAS amplifier
tains the No. 1 roll and yaw rate gyro power
and flight controls to use the internal yaw rate
supplies and processing circuitry for SAS 1. The
outputs of the internal roll and yaw rate gyros are
gyro. Above 50 knots, the SAS amplifier recieves
used by SAS 1 and the digital automatic flight
a 12 to 15 VDC airspeed switch discrete from
the No. 1 stabilator amplifier. This enables filtered
control system computer. The amplifier processes
No. 1 lateral acceleration and roll rate to sum with
rate and proportional signals. Amplifier outputs
the yaw rate signal. Airspeed discrete from No.
operate the SAS actuators on the pilot-assist servo
1 stabilator amplifier is inhibited for this situation
assembly.
(above 50 knots). Airspeed discrete is not removed
from SAS amplifier.
NO. 1 STABILATOR AMPLIFIER. --The
The AFCS consists of many components. To
No. 1 stabilator amplifier provides filtered lateral
understand the entire system, you need to know
acceleration and pitch rate signals and an airspeed
what each component does. The following
discrete to the SAS amplifier. The stabilator
discussion describes the components that make
amplifier is part of the stabilator control system.
up the AFCS.
Stabilator System
AFCS POWER SWITCHING ASSEMBLY.--
The AFCS power switching assembly provides
The stabilator system optimizes trim attitudes
for cruise, climb, and autorotation. Also, it
power switching for the digital automatic flight
