of the propeller system. The dome assembly
As we discuss the propeller assembly, refer to
is mounted on the front barrel shelf and
figure 8-14.
held in position by the dome retaining nut.
The principal components of this pitch-changing
BARREL ASSEMBLY.-- The propeller barrel
mechanism are the rotating cam, the stationary
assembly serves several functions. It retains the
cam, the piston assembly, and the low pitch stop
four propeller blades and also supports the dome
assembly. The low pitch stop assembly is screwed
assembly and the propeller control assembly.
into the lever sleeve bushing at the front of the
Engine torque is transmitted to the propeller by
dome.
the barrel assembly, which mounts and secures
to the front of the reduction gearbox propeller
Preformed packings are used throughout the
shaft.
dome assembly for internal leakage control and
The barrel assembly is a split type; the front
to seal the piston assembly in order to separate
and rear barrel sections are manufactured and
the inboard and outboard hydraulic pressure
balanced as a matched pair. These sections are
necessary for blade movement. Shims are used to
kept together throughout the service life of the
establish the proper clearance between the rotating
propeller. The high centrifugal blade loads are
cam and the blade segment gears. The dome
carried by the barrel shoulders and lips at each
assembly is mounted in position on the front
blade position.
barrel shelf. It is held in place by the dome
A machined integral extension on the rear
retaining nut that is locked in place by a special
barrel half is splined internally and has seats at
head screw.
both ends. The front and rear cones are beveled
The low pitch stop assembly screws into the
to match the extension seats for centering and
dome assembly. It sets the desired low pitch
securing the propeller on the propeller shaft. The
stop blade angle. In the flight range of operation,
extension is splined externally for driving pumps
the low pitch stop lever assembly prevents
in the propeller control assembly. A propeller hub
the propeller blade angle from going below
nut locks the barrel assembly to the reduction
13 degrees. In the ground range, extra high
gearbox propeller shaft. The propeller hub nut has
hydraulic fluid pressure actuates the low pitch
a flange on its inboard end that butts against the
front cone.
stop assembly, allowing the piston to move
further outboard. This turns the blades from the
low pitch stop position towards the reverse blade
BLADE ASSEMBLY.-- The broad, light-
angle.
weight propeller blade is forged from a solid
aluminum alloy, which gives it the strength
necessary to obtain the high thrust capability at
PITCHLOCK REGULATOR ASSEMBLY.--
low aircraft speeds. The blade butt is partially
The propeller pitchlock regulator assembly
hollow to allow for installation of the blade
mounts within the propeller barrel and is splined
bushing and blade balancing assembly. Propeller
to the propeller hub nut. The pitchlock regulator
balancing is discussed in the balancing section of
assembly directs hydraulic pressure to the out-
this chapter.
board and inboard sides of the dome piston. It
The blade shank has a molded fairing that is
also serves as a safety feature by preventing a
composed of a plastic foam material covered with
decrease in blade angle, by pitchlocking, under
a nylon reinforced neoprene material. The heater
certain conditions. Pitchlock occurs if hydraulic
assembly is bonded to the leading edge of the
control pressure is lost or during an overspeed of
fairing. It contains the necessary blade deicer
103 to 103.5 percent.
elements to prevent ice buildup on the blade
The pitchlock regulator assembly contains two
assembly. Blade heater element damage, involving
ratchet rings that are spring-loaded together, but
cut or broken heater wires because of weather
corrosion or foreign object damage (FOD) strikes,
are held apart by hydraulic pressure. One ratchet
ring is splined to the rotating cam of the dome
can be repaired if no more than four wires are
assembly. The other ratchet ring is splined to the
damaged. If more than four wires are damaged,
propeller rear barrel half and does not rotate. If
the heater assembly must be replaced. The
hydraulic pressure is lost, the ratchet rings come
purpose of the blade fairing (cuff) is to streamline
together, and their teeth mesh to prevent a
and direct the airflow to the engine intake.
decreased blade angle. This is referred to as pitch-
lock, and can only occur between approximately
DOME ASSEMBLY.-- The propeller dome
15 to 60 degrees of blade angle. Pitchlock is
assembly is the blade angle changing mechanism
8-14
