electrically driven). An externally mounted ac
When speeder-spring force is equal to the
electric motor drives the two common shafted
flyweight centrifugal force, the pilot valve centers
auxiliary pumps. Two hydraulic fluid sumps are
in the pitch change sleeve to block pitch change
contained in the pump housing assembly. One is
hydraulic pressure from the propeller dome. Any
a pressurized sump with a capacity of 6 quarts.
change in the engine speed will change the out-
The other is an atmospheric sump with a capacity
ward position of the flyweight. The flyweight
of 4.5 quarts. A pressure cutout switch located
shifts the pilot valve to direct pitch change
in the pump housing serves to terminate the
hydraulic pressure to the dome.
action of the auxiliary pumps. This action occurs
Constant-speed governing is blocked out in the
when the feather blade angle is reached.
ground handling range. The propeller blade angle
The three mechanically driven gear-type
is coordinated with the position of the power
pumps are the main pump, the main scavenge
lever. Interaction of the cams on the alpha and
pump, and the standby pump. The electrical
beta shaft control the position of the pilot valve
pumps are the auxiliary scavenge pump and the
in the speed servo governor. When the power lever
feather pump. The feather pump is used for static
is moved, a cam on the alpha shaft positions the
ground operations. It also serves to complete the
pilot valve to obtain a corresponding blade angle.
feather operation in flight. An electrical motor-
As the blade pitch changes, a cam on the beta
driven pump is needed since the output pressure
shaft returns the pilot valve to a position that will
of the mechanically driven pumps is reduced in
maintain the blade pitch at the angle scheduled
proportion to the decaying propeller rpm.
by the power lever,
Rigging pin holes are located on the valve
VALVE HOUSING ASSEMBLY.-- The
housing assembly for rigging the valve housing
valve housing assembly is considered the brains
to the propeller assembly and power lever.
of the propeller system. It mounts to the upper
Adjustments are provided to set the mechanical
part of the pump housing assembly, forming the
governor speed and the reverse and ground
propeller control assembly. The valve housing
handling blade angles.
assembly is the most complex assembly of the
propeller system. Major units of the valve housing
PROPELLER MAINTENANCE
assembly are the speed servo governor assembly,
In today's Navy, comprehensive and sys-
flyweights, speeder spring, pilot valve, feather
tematic means of maintaining a multiengined pro-
valve, feather solenoid valve, main and standby
peller system is essential. You, as an Aviation
regulating valves, high-pressure relief valve, beta
Machinist's Mate, must know the procedures for
and speed-setting lever assembly, alpha and beta
day-to-day maintenance. You must know the pro-
pinion shafts, linkage support assembly, and the
cedures for removal and installation of a pro-
electrical branch cable.
peller, rigging, adjustment, and troubleshooting
The two ranges of operation controlled
of propeller systems. You should also be familiar
through the valve housing assembly are the
with the procedures for propeller balancing and
governing range and the taxi range. The governing
leakage test requirements. The modern-day pro-
range is commonly called the alpha or the flight
peller system is a complex and durable system,
range. The taxi range is commonly called the beta
and, with proper maintenance, a highly reliable
scheduling or the ground handling range. All
aircraft system.
primary propeller operations, except for feather-
ing and unfeathering the propeller, are determined
NOTE: The information noted here is
by the position of the pilot valve in the speed servo
general. Refer to applicable technical
governor. Hydraulic fluid for blade angle change
instructions for the specific methods used
operation is pumped from the pressurized sump
on a particular model of propeller.
by the main pump (and standby pump if needed)
to the pilot valve chamber.
Propeller Inspection
Flyweights are geared to the propeller shaft.
Inspect the blades daily for any gouges, nicks,
This causes their rotation to develop centrifugal
force in direct relation to the engine speed. The
scratches, or gross damage. If the propeller has
centrifugal force extends the flyweights outward
struck any object (static or rotating), inspect the
blades carefully for damage. For example, yellow
and pushes the pilot valve toward the increased
paint marks on a blade indicate that the propeller
pitch position. This movement of the pilot valve
could have possible damage from hitting a piece
opposes the speeder-spring force, which pushes
the pilot valve toward the decrease pitch position.
of support equipment.
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