Propeller Owner’s Manual
147
DESCRIPTION AND OPERATION
61-00-47
Page 2-10
Rev. 17 Sep/20
1. Description of Propellers and Systems
A. Feathering and Reversing Propellers HC-E(4,5)( )-3( ) Series
Refer to Figure 2-1, Figure 2-2, Figure 2-3, Figure 2-4,
Figure 2-5, Figure 2-6, and Figure 2-6.1. The propellers
described in this section are constant speed, feathering,
and reversing. They use a single oil supply from a governing
device to hydraulically actuate a change in blade angle. The
propellers have four or five blades and are used primarily on
Pratt & Whitney turbine engines.
A two piece aluminum hub retains each propeller blade on a
thrust bearing. A cylinder is attached to the hub and contains
a feathering spring and piston. The hydraulically actuated
piston transmits linear motion through a pitch change rod
and fork to each blade to result in blade angle change.
While the propeller is operating the following forces are
constantly present: 1) spring force, 2) counterweight force,
3) centrifugal twisting moment of each blade and 4) blade
aerodynamic twisting forces. The spring and counterweight
forces attempt to rotate the blades to higher blade angle
while the centrifugal twisting moment of each blade is
generally toward lower blade angle. Blade aerodynamic
twisting force is generally very small in relation to the other
forces and can attempt to increase or decrease blade angle.
Summation of the propeller forces is toward higher pitch (low
RPM) and is opposed by a variable force toward lower pitch
(high RPM). The variable force is oil under pressure from a
governor with an internal pump that is mounted on and driven
by the engine. The oil from the governor is supplied to the
propeller and hydraulic piston through a hollow engine shaft.
Increasing the volume of oil within the piston and cylinder will
decrease the blade angle and increase propeller RPM.
Decreasing the volume of oil will increase blade angle and
decrease propeller RPM. By changing the blade angle, the
governor can vary the load on the engine and maintain
constant engine RPM (within limits), independent of where
the power lever is set. The governor uses engine speed
sensing mechanisms that permit it to supply or drain oil as
necessary to maintain constant engine speed (RPM).
