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AIRPLANE MAINTENANCE MANUAL
PROPELLER DESCRIPTION AND
OPERATION
The propeller is a single-acting unit in
which hydraulic pressure opposes the
forces of springs and counterweights to
obtain the correct pitch for engine load.
Hydraulic pressure urges blades toward
low pitch (increasing rpm), while springs
and counterweights urge blades toward
high pitch (decreasing rpm).
propeller owner's manual for more explicit
details.
The source of hydraulic pressure for
operation is oil from the engine lubricating
system, boosted in pressure by the
governor gear pump, and supplied to the
propeller piston through the beta tube
(beta
tube
supplied
manufacturer). The flow of oil through the
governor and the propeller does not
interfere with engine lubrication.
The propeller is designed to operate in two
modes of operation – governor mode and
beta mode.
Governor mode. Oil is metered to and
from the propeller (by the governor control
valve
as
positioned
increasing and decreasing blade angle
(changing pitch) as required when the
propeller speed control setting is altered,
or to control and stabilize engine speed
with varying power conditions or flight
altitudes with a fixed speed setting.
Beta mode.
The pilot may select beta
mode
for
ground
operation.
In the beta mode, the
aircraft/engine
mechanical
repositions a sleeve on the beta tube to
allow high pressure oil to reach the
propeller piston and move the blades
toward reverse pitch. In beta mode the
engine automatically, by controlling fuel
flow, develops power output to correspond
with the pitch setting (determined by the
pilot).
Cockpit procedure for normal constant
Effective: 03/26/2010
THRUSH AIRCRAFT INC - MODEL S2R-G10
See the
by
engine
by
flyweights),
reversing
or
taxi
linkage
speed operation, starting, stopping and
ground run-up is consistent with standard
practice for this type propeller.
In-flight loss of oil pressure, whether due to
system failure or pilot manipulation of the
feather control, will cause the blades to
move to the feathered position.
electric, hydraulic, unfeathering pump is
required to un-feather the propeller.
The propeller hub cavity is partially filled
with turbine oil which is sealed in the hub
and isolated from engine oil.
provides
lubrication
protection to blade bearings and other
internal parts.
The propeller is equipped with a start lock
mechanism which prevents the blades
from going to full feather on engine shut-
down.
The mechanism operates in
response to the centrifugal force acting on
rotating weights.
designed to engage a fixed stop and limit
piston movement in the direction of
increasing blade angle during engine shut-
down.
During all flight operations, the
weights are in a disengaged position and
offer
no
resistance
Unfeathering or reversing of the propeller.
PROPELLER REMOVAL –
McCauley
Remove upper half of nose bowl.
Remove spinner and spinner fillets. Mark
location of parts. (Note number of shims
under the plastic spinner support.)
Remove beta tube retainer plug assembly
and beta tube.
* NOTE *
Beta tube retainer plug cannot be
removed with McCauley propeller in
feathered position.
assembly with propeller on start
locks.
* NOTE *
The
This oil
and
corrosion
The mechanism is
to
feathering,
Remove plug
4-5
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