helicopter stability. This system is fast in response,
of less than 50 knots, attitude changes are
limited in authority, and operates without causing
commanded by changing the cyclic stick position.
The pilot can use the TRIM REL switch or the
movement of the flight controls. The outer loop
four-direction (beeper) TRIM switch to change
(AUTO PILOT) provides long-term inputs by
cyclic stick position. This causes the cyclic stick
trimming the flight controls to the position
required to maintain the selected flight regime.
to move, and the helicopter attitude to change
about 5 degrees per second. When cyclic move-
It can drive the flight controls throughout their
ment stops, the autopilot stabilizes the helicopter
full range of travel (100-percent authority). The
around the new stick position and attitude. Above
outer-loop drive rate is limited to 10 percent per
50 knots and bank angles less than 30 degrees,
second. Both inner and outer loops allow for
the system becomes airspeed sensitive in pitch.
complete pilot override through the normal use
Operating the four-direction TRIM switch causes
of the flight controls.
the cyclic stick to move and the helicopter to
The DAFCS computer processes incoming
change airspeed reference at 6 knots per second.
information from various sensors (fig. 8-32)
Because of variations in the pitot-static system
aboard the aircraft and stores this information in
during gusty conditions, integrated longitudinal
its memory. The central processing unit (CPU)
acceleration is used for short-term correction. The
uses the sensor information to compute required
airspeed sensor is used for long-term updates
correction signals. Inner-loop correction signals
through a 3-second filter.
go to the SAS actuators, and outer-loop signals
operate trim servos and actuators.
The roll channel autopilot holds roll attitude
of the helicopter. Attitude information is supplied
TRIM SYSTEM. --The parallel trim actuator
to the computer from the pilot's and copilot's
assemblies provide the flight control force
A/A24G vertical gyros. The command signal is
gradients and detent positions and the outer-loop
applied to roll SAS 1 and SAS 2 and the roll trim
autopilot control functions. The trim actuators
system. When the pilot actuates the four-direction
command full control authority in all four control
TRIM switch, the helicopter roll attitude will
channels, but are rate-limited to 10 percent per
change at about 6 degrees per second. In addition
second. Pressing the trim release switch (cyclic
to the attitude hold feature, the system includes
trim release, collective trim release, and pedal
an automatic wing-leveling capability. During
release) disengages the respective trim function
transitions from hover to airspeeds above 50
and allows free control motion. Releasing the trim
knots, this feature automatically retrims the
release switch re-engages trim. For yaw trim
aircraft from a left roll attitude in a hover to a
release above 50 knots, the pilot must press the
wings level attitude at 50 knots. After establishing
pedal microswitches and the cyclic trim switch.
a level attitude, the attitude hold feature maintains
Below 50 knots only the pedal microswitches have
that attitude until a new roll attitude is
to be pressed. The pilot can override the trim
commanded by the pilot.
control forces in all channels.
HEADING HOLD. --The yaw channel of the
AUTOPILOT. --The autopilot maintains
helicopter pitch and roll attitude, airspeed, and
autopilot provides the heading hold feature for
heading during cruise flight and provides a
hover and forward flight. It is engaged whenever
coordinated turn feature at airspeeds above 50
the AUTO PLT PBS is illuminated. Heading hold
knots. To engage the autopilot function, the pilot
is an outer-loop function, operating through the
presses the control panel SAS 1 or SAS 2 switches,
yaw trim actuator; therefore, it will only work
when the yaw trim is engaged. Releasing all pedal
TRIM switch, and then the AUTO PLT push
switches at a given heading synchronizes the
button. The autopilot may be disengaged by
trim system to the established heading. A
pressing the AUTO PLT push button or pressing
potentiometer in the yaw trim actuator applies a
the AFCS release button. The computer also
trim position feedback signal to the computer.
provides command signals to the trim actuators
This signal cancels the drive signal at the desired
to reposition the flight controls using the trim
system.
position, stopping the motor. The yaw autopilot
also uses a collective stick position sensor to hold
reference heading for yaw excursions caused by
ATTITUDE AND AIRSPEED HOLD. --
main rotor torque changes. The collective stick
Attitude and airspeed hold are engaged with
position sensor is controlled by an airspeed signal
AUTO PLT. In the pitch channel, at airspeeds
8-32
