TM 1-1520-238-T-7
11–20
11–2.
LOCATION AND DESCRIPTION OF MAJOR COMPONENTS (cont)
11–2
e. Directional Flight Control System.
The directional flight control system (fig. 11–5) consists of the pilot
and CPG directional pedals, two LVDTs, two SPADs, feel spring and magnetic brake assemblies, the directional
mechanical control linkage, the directional servocylinder, the tail rotor swashplate assembly, pitch change links,
drive links, and the fork assembly.
(1) Pilot and CPG Directional Pedals.
The pilot and CPG directional pedals, located at the floor
centerline in each crew station, provide directional (yaw) control of the helicopter. They are made of aluminum
alloy and incorporate brake pedal control linkage and a reach adjust mechanism.
(2) LVDTs.
The directional LVDTs, attached to the fuselage and to a riveted arm on the SPAD, generate
electrical signals that are proportional to the amount of cyclic stick movement. The LVDT sends a signal to the
DASEC proportional to its movement.
(3) SPADs.
The directional SPADs, attached to a bracket that is mounted on the fuselage bulkhead aft
and below the foot pedal assemblies, activate the fly-by-wire BUCS system if the mechanical flight controls are
jammed and the shear pin is severed. The SPAD incorporates a mechanical cam lock, switch, and shear pin that
fits into a slot on one of the bellcranks and locks the input and output bellcranks together as a single unit.
(4) Feel Spring and Magnetic Brake Assemblies.
The feel spring and magnetic brake assemblies,
attached to the fuselage and a riveted arm assembly of the pilot’s SPAD (one directional feel spring and magnetic
brake assembly), provide trim for both crew stations.
(a) The feel spring assembly, a spring loaded device, overrides the magnetic brake when locked by
moving the cyclic stick against the spring.
(b) The magnetic brake assembly disengages to enable tracking of the cyclic stick position and
reengages to lock the new trim position.
(5) Directional Mechanical Control Linkage.
The directional mechanical control linkage is transmitted
through the lower part of the fuselage, left of the centerline, to the aft side equipment bay, then along the top of
the aft fuselage and tail boom section, then up the leading edge side of the vertical stabilizer to the directional
servocylinder. Movement of the directional pedals is transmitted to the tail rotor assembly for anti-torque (yaw)
and directionally controlled flight of the helicopter.
(6) Directional Servocylinder.
The directional servocylinder, horizontally mounted on top of the tail rotor
gearbox on the vertical stabilizer, provides hydraulic power to assist the directional movements of the directional
mechanical control linkage.
(7) Tail Rotor Swashplate Assembly.
The tail rotor swashplate assembly, mounted on the tail rotor
gearbox static support, receives and transmits control inputs from the directional pedals to the tail rotor blades via
the tail rotor pitch change links. The swashplate assembly consists of a stationary swashplate, a rotating
swashplate, an annular double-roll ball bearing assembly, and two sleeve bearings.
(a) The stationary swashplate receives push-pull input from the bellcrank which is attached to the
directional servocylinder and the stationary swashplate.
(b) The rotating swashplate, mounted to the double-roll ball bearing assembly above the stationary
swashplate, transmits control inputs received from the stationary swashplate to the tail rotor blades via the pitch
change link assemblies.
