SERVO CONTROLS
MAIN ROTOR SERVO ACTUATORS - GENERAL
There are three Main Rotor (MR) servo actuators: LEFT, RIGHT and
FORWARD (LH, RH and FWD).
Each main rotor servo actuator is a fixed body actuator comprising two
separate cylinder assemblies bolted together at the actuator center and
tandem pistons.
The upper piston is connected to the fixed swashplate; the lower end of the
cylinder is connected with a support to the MGB.
Each cylinder assembly has an integral flow distributor that contains a dual
concentric valve which provides the normal servo control and a jam tolerant
function.
The flow distributor assembly is controlled through an input lever which
receives the input from pilot's flight controls and through a feedback link
which is connected to the output piston.
The anti-jamming device consists of a inner and outer sleeve that are held in
place under the action of a spring. In case of a valve spool jam the force
required at the input lever to operate the main valve exceeds a preset value
thus compressing the spring and allowing the two sleeves to move relatively
to control the hydraulic fluid within the cylinder chambers.
The actuator is designed to operate normally with two hydraulic systems
(hydraulic system no.1 and hydraulic system no.2) which are completely
separated within the actuator.
In case of failure of one system, the level of performances with only one
hydraulic system operating ensures no degradation of handling qualities.
The indication system of the rotor flight controls is supplied by a pressure
switch installed on each actuator control-valve.
If the control spool of an actuator control-valve jams or moves abnormally,
the pressure switch will send an input to the indicating system which, in turn,
will generate a caution and a 1 SERVO or 2 SERVO message depending on
which system has had a jam.