CYCLIC CONTROL – GENERAL
The cyclic control is a conventional metallic rod and bellcrank type. The
control is composed of a stick for pilot and copilot that make a common input
to a mixing unit. The collective control sticks are made of aluminium with a
control grip at the top. The pilot and copilot stick are connected together by a
torque tube. The sticks are connected to the floor using an attachment plate
containing a spherical bearing which is connected with a cross shaped,
stainless steel fitting to a torsion tube.
The pilot attachment plate contains a shaped flange used to limit pitch and
roll movements combination.
To statically balance the control linkage weight, springs are installed on the
stick cross-shaped fitting.
At the left end of the torque tube, the cross-shaped fitting allows for the
connection with rods to the longitudinal and lateral trim actuators.
From the right side the control is connected with a lower bellcrank
installation and then with rods that extend vertically to an upper bellcrank
installation.
Each lower bellcrank installation has a friction clamp (fixed friction) for
counteracting the output force of the series actuators, when the pitch/roll trim
actuators are declutched, thus ensuring the movement is translated to the
mixing unit.
At the upper bellcrank installation there is a compound linkage connection
which transmits the longitudinal and lateral control to the mixing unit. The
compound linkage connection incorporates dual-action bellcranks which
permit inputs from pilot and from dual linear actuators to be summed as a
series connection to move the mixing unit.
Limit stops are present in the upper bellcrank to limit the longitudinal and
lateral cyclic pitch to the limits of its envelope.
PITCH AND ROLL TRIM ACTUATORS
Pitch and roll trim actuators are installed in parallel with the cyclic stick below
LH forward cockpit floor. Trim actuators have full travel authority on the pitch
and roll control lines.
Trim actuators can be overridden by pilot commands via a spring-clutch.
Actuators are operated by pilot commands or by the AFCS. They convert the
command to a mechanical output.
PITCH AND ROLL DUAL LINEAR ACTUATORS
The pitch and roll linear actuators are installed in series with the rods of the
relevant mechanical linkages: one side of them is attached to the mixing unit
body, the other side is attached to a dual-action bellcrank located on the top
RH side of the forward frame of the cabin.
Pitch and roll dual linear actuators provide limited control inputs commanded
by the Autopilot.
Connection to the the pitch and roll control line linkages is achieved through
a dual-action bellcrank and an anchor spring which provides a safety
function in case the actuator gets disconnected: in this case the spring
reacts to the manual input as a pivot point to ensure the movement is
transferred to the mixing unit.
CYCLIC CONTROL – PRINCIPLE OF OPERATION
The cyclic control is a mechanical, dual linkage system, actuated by the
cyclic control sticks.
The cyclic torque tube interconnects pilot and copilot sticks: pitch inputs are
transferred by torquing the tube, roll inputs are transferred by pushing/pulling
the cyclic torque tube sideways.
The cyclic inputs are transmitted to the mixing unit via push-pull rods and
bellcranks; the mixing unit sends the cyclic inputs to the three main rotor
actuators.
The mechanical linkage also gives a connection to the pitch and roll trim
actuators and pitch and roll dual linear actuators controlled by the AFCS
(see chapter 22-00).