2.37.4 Trim Feel.
Use of the pilot FORCE TRIM REL switch
in the force trim off position with the heli-
copter on the ground is not authorized.
Inflight operation with the pilot FORCE
TRIM REL switch in the force trim off
position is authorized when briefed and
the force trim off selection is acknowl-
edged by both crewmembers.
Either crewmember can trim the cyclic and pedal controls.
A lateral, longitudinal, and directional trim feel magnetic
brake and spring assembly is incorporated into each con-
trol system. Setting the pilot FORCE TRIM REL switch to
the on position will engage the magnetic brakes in the lon-
gitudinal, lateral, and directional flight controls. The spring
assemblies will hold the cyclic stick and directional pedals
in trim. Movement of the cyclic or directional controls, by
either the pilot or CPG, with FORCE TRIM REL switch on,
will cause the spring assemblies to compress and provide
feel to the controls. When control pressure is released, the
controls will return to their trimmed position. Retrimming is
accomplished by a TRIM pushbutton on the CPG cyclic
stick or by a FORCE TRIM REL switch on the pilot cyclic
stick grip. Pressing the button or pressing up on the switch
releases the magnetic brake and allows the springs to
travel to the new control position. Additionally, this action
also allows the SAS actuators to recenter, if necessary.
Releasing the button or switch will then allow the magnetic
brake to engage and hold the springs at the new position.
The pilot may press the FORCE TRIM REL switch to the
full down position to disable trim feel entirely.
For the CPG, trim feel is lost in the affected axis when
the respective SPAD shear pin is broken or if mechanical
linkage severance has occurred between the pilot and
With the pilot FORCE TRIM REL switch in the down posi-
tion, the ATTD/HOVER HOLD and SAS actuator center-
ing capabilities of the DASE are inoperative. The capabili-
ties will return when the switch is returned to the center
position. The full down position of the pilot FORCE TRIM
REL switch may be used momentarily to unlatch the mag-
netic latch of the ATTD/HOVER HOLD switch on the ASE
control panel (fig 2-27). The DASE capabilities of the pilot
FORCE TRIM REL switch remain unaffected in the event
of a trim system failure such as with the magnetic brake or
spring capsule. Trim feel is operable throughout all ranges
of cyclic stick or pedal travel. The trim system receives 28
vdc from the emergency dc bus through the TRIM circuit
breaker on the pilot overhead circuit breaker panel.
2.37.5 Flight Control Servos.
The four primary flight
control servos are tandem units that use hydraulic pres-
sure from both the primary and utility hydraulic systems.
The primary and utility sides of the servos are indepen-
dent of each other which provides redundancy in the ser-
vos. If one hydraulic system fails, the remaining system
can drive the flight control servos. If both systems fail si-
multaneously during flight, either crewmember can use
stored accumulator hydraulic pressure to provide limited
hydraulics for safe landing. Section VI contains a detailed
description of the emergency hydraulic system. The pri-
mary side of each flight control servo has two electrohy-
draulic solenoid valves. One responds to DASE computer
signals for stability augmentation.
The second electrohydraulic solenoid valve responds to
DASE computer inputs for BUCS.
2.37.6 Digital Automatic Stabilization Equipment
The DASE augments stability and enhances
maneuverability of the helicopter. DASE includes and/or
controls the following: stability and command augmenta-
tion in pitch, roll, and yaw; attitude hold; heading hold;
hover augmentation; turn coordination; and the BUCS.
Major components include an ASE control panel (fig
2-27), a DASE computer, eight linear variable differential
transducers (LVDT), two 26 vac transformers, and four
hydraulic servo actuators.
a. DASE Computer.
The DASE computer receives
28 vdc from the No. 3 essential dc bus through the ASE
BUCS circuit breaker and a stepped down 26 vac refer-
ence voltage from the No. 1 essential ac bus through the
ASE AC circuit breaker. Both circuit breakers are on the
pilot overhead circuit breaker panel. The DASE computer
automatically disengages a mistrack of more than 35%
and lights the ASE FAIL indicator on both caution/warning
panels; concurrently, the PITCH, ROLL, and YAW
switches on the ASE control panel will drop to OFF. The
squat switch on the left main landing gear disables the
YAW CAS function during ground taxi to prevent overcon-
trol of the helicopter. The YAW channel circuitry in the
DASE computer receives sideslip data from the air data
sensor which provides turn coordination above 60 KTAS.