MD Helicopters CSP-900RMM-2, Техническое обслуживание и ремонт

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CSP − 900RMM − 2 MD Helicopters, Inc.
Rotorcraft Maintenance Manual
Page 2
Revision 31
62-00-00
4. Main Rotor Hub Assembly
The main rotor hub assembly mounts the main
rotor system to the static support mast and is
driven by the main rotor drive shaft.
The main rotor hub assembly consists of:
A. Upper and Lower Hub Halves
The rotor hub halves are machined, hardened
aluminum alloy. Rotor hub halves mount and
transmit drive force to the rest of the main rotor
system rotating components. Moisture contami­
nation and corrosion are prevented by neo­
prene and stainless steel spring seals.
B. Flexbeam
The flexbeam is attached between the rotor
blade and the main rotor hub. Flexing of the
beam allows rotor blades to move about the
feathering, flapping, and lead/lag axes without
the need for hinges. Flexbeams transfer driving
force from the hub to the rotor blades. The
flexbeams are a composite structure made of
laminated fiberglass. Flexbeam attachment
points are hardened stainless steel bushings
embedded in the laminate. An elastomeric
flexbeam bumper is bonded around the
flexbeam to reduce flexbeam deflections during
rotor starts and stops.
C. Hub Plate
A hardened steel hub plate is sandwiched
between the hub halves to absorb centrifugal
loads. The hub plate also separates the
lead/lag legs of the flexbeams into the upper
and lower hub halves.
D. Fretting Buffer
The fretting buffer has been removed from the
helicopter. It is not necessary and made it
more difficult to get a good seal around the
drive plate to main rotor hub joint.
E. Tapered Roller Bearing Set
The tapered roller bearing sets transfer flight
and static loads between the rotating and
non-rotating sections of the main rotor hub. The
upper bearing carries most of the load, and the
lower bearing acts as a follower, centering the
hub on the static mast of the helicopter. The
tapered roller bearing sets are located between
the upper hub half and the non-rotating
components of the main rotor installation.
F. Hub Liner
The hub liner is a stainless steel tube in the
center of the upper hub half that fits snugly
over the stationary support mast. During main
rotor hub installation a hub retaining nut is
threaded to the top of the stationary support
mast. The retaining nut presses the upper
bearing inner race against the bearing
pre-load shim, which presses the hub liner
against a machined shoulder on the stationary
mast. The lower bearing inner race is an
interference fit on the hub liner. The hub liner
also provides the inner contact surface for the
lower and center upper hub seals.
G. Drive Ring
The drive ring is a machined, hardened, and
anodized aluminum alloy two piece component.
The drive ring is attached to the upper hub half
by clamp up and to the lower hub half through
the striker plate brackets. The drive ring
provides drive through the scissors to the
rotating swashplate.
H. Grounding Brushes and Straps
The grounding brushes and straps are the
grounding path from the pitchcases to the
stationary support mast. The brushes are
located on the drive ring at the upper scissors
attachment point. The carbon brushes ground
the rotating hub assembly to the stationary
support mast through a groove at the bottom of
the hub liner. The straps (bonding jumpers)
provide positive bonding between the rotor
blade, pitchcases, and hub assembly.
I. Droop Stop
The droop stop limits the rotor blade droop
angle at low rotor speed. As the rotor blades
loose lift with reduced rotor speed, the droop
stop roller contacts the striker plate on the main
rotor hub. The droop stop roller is mounted to
the pitchcase by the axle and lower damper cap.
The striker plate is fixed to the rotor hub drive
ring by the droop stop striker support. The
droop stop striker plate and roller are made of
stainless steel. The inner diameter of the droop
stop roller is coated with molybdenum disulfide
and needs no lubrication.