Pitch rate and lateral acceleration inputs improve
provides pitch stability augmentation to comple-
the dynamic response of the aircraft, especially
ment the SAS system for additional redundancy.
in gusty air conditions. The pitch rate input
The stabilator system is completely independent
supplements the dynamic stability provided by the
of the other two AFCS subsystems except for
SAS and DAFCS. The lateral accelerometer input
common airspeed sensors, lateral accelerometers,
decouples the aircraft pitch response with changes
and pitch rate gyros. The stabilator control system
in tail rotor lift caused by changes in airflow on
is a completely automatic fly-by-wire control
the canted tail induced with sideslip.
system with a manual backup slew control. The
If a malfunction of the stabilator system
primary purpose of the stabilator control system
occurs, the pilot can manually position the
is to stop undesirable noseup attitudes. The
stabilator with the manual slew switch. The
noseup attitude is caused by rotor downwash
manual slew switch bypasses the stabilator
impinging on the horizontal stabilator during
amplifier automatic mode, applying power
low-speed flight and transition to a hover.
directly to the actuators through relays in the
The stabilator panel contains an automatic
amplifiers. A stabilator position indicator aids the
control (AUTO CONTROL) switch, a TEST push
pilot in positioning the stabilator to any position
button, and a manual slew (MAN SLEW) switch.
between the stabilator travel limits. However,
The AUTO CONTROL switch is used to engage
total travel is restricted if the malfunction is an
the automatic mode or to reset the stabilator if
actuator failure. Stabilator travel is restricted to
it should fail. The pilot can manually position the
35 degrees if an actuator fails in the full-down
stabilator to any position within the stabilator
position; 30 degrees if an actuator fails in the
limits by moving the MAN SLEW switch. The
full-up position. The stabilator control rate is
TEST push button is used to check the automatic
limited to 6 degrees per second.
mode fault detector.
The following is a description of the com-
Two electric jackscrews, working in series,
ponents of the stabilator system. To understand
position the stabilator. Each actuator provides
the system, you will need to know what these
one-half the input to position the stabilator and
components do.
is controlled by a separate and redundant
stabilator amplifier. The stabilator travels from
AIRSPEED TRANSDUCER. --The stabi-
40 degrees trailing edge down for hover and
lator position program is a function of four sensor
low-speed flight below 30 knots to 8 degrees
inputs. Each function has dual sensors for
trailing edge up for cruise and maneuvering
fail-safe operation. Airspeed for the No. 1
flight. Four inputs are required to position the
stabilator system is sensed by the airspeed
stabilator--airspeed, collective stick position,
transducer. It connects into the ATO pitot static
lateral acceleration, and pitch rate.
system and produces a dc output voltage that is
Each stabilator amplifier receives these
proportional to airspeed.
four inputs, but they receive the inputs from
independent sensors. The DAFCS computer
AIR DATA TRANSDUCER. --An air data
monitors each of these sensors for malfunctions,
transducer accomplishes airspeed sensing in the
and the stabilator control system monitors and
No. 2 stabilator system. The air data transducer
compares the position of the two actuators. Any
system malfunction caused by a difference
connects into the pilot's pitot static system. It
produces dc output voltages proportional to
between the two stabilator actuator positions
airspeed, altitude, and altitude rate. Airspeed data
results in the stabilator remaining in the last
is used by the stabilator system and AFCS
position. A malfunction also causes an automatic
computer. Altitude and altitude rate are applied
power shutdown to both actuators, an aural tone
to the pilot, and a STABILATOR caution light
to the DAFCS computer only for altitude hold
illuminating. The shutdown threshold between the
and depart modes of operation.
two stabilator actuator positions is 10 degrees for
LATERAL ACCELEROMETERS. --There
airspeeds less than 50 KIAS and 4 degrees for
airspeeds greater than 120 KIAS with a linear
are two lateral accelerometers--No. 1 and No 2.
variation between 50 KIAS and 120 KIAS.
They each produce a dc output signal proportional
to helicopter lateral acceleration. Each accel-
The airspeed input aligns the stabilator with
erometer dc signal goes to its related stabilator
the main rotor downwash during slow-speed
flight. The collective stick position input decouples
amplifier, where it is conditioned. The filtered
lateral acceleration signal is used to position the
aircraft pitch attitude with collective position.
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