Propeller Owner’s Manual
147
DESCRIPTION AND OPERATION
61-00-47
Page 2-14
Rev. 17 Sep/20
B. Feathering Propellers HC-E5A-2 Model
Refer to Figure 2-7. The propeller described in this section is
constant speed and feathering. It utilizes a single oil supply
from a governing device to hydraulically actuate a change in
blade angle. This propeller has five blades and is 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 usually very small in relation to the other
forces and can attempt to increase or decrease blade angle.
The 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 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).
