Hartzell HC-E3YR-7 Owner's Manual page 59

(3) During propeller operation 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. Spring and
counterweight forces attempt to rotate the blades to higher
blade angles while the centrifugal twisting moment of
each blade is generally toward lower blade angles. Blade
aerodynamic twisting force is generally very small in
relation to the other forces and can attempt to increase or
decrease blade angle based on blade design. 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 supply of oil will move the
propeller pitch to a lower blade pitch (higher RPM), the
drain of oil will move the propeller pitch to a higher blade
pitch (lower RPM) and no change of oil will maintain the
current blade pitch (no change of RPM).
(4) Figure 2-3 shows an example of the different oil pressures
in the propeller piston at different blade pitches between
low pitch and high pitch. The orientation of the oil
pressures required for opposing the propeller internal
force (spring) is a slope that has a higher value at low
pitch and is lower at high pitch. Two slopes are shown
(between low pitch and high pitch) and are parallel. The
upper line represents the required oil pressure from the
governor when blade pitch is decreasing and the lower
line represents the required oil pressure from the governor
when blade pitch is increasing. The separation between
the two lines is because of friction involved in moving the
propeller pitch change components. In the installation
chapter it will be necessary to understand this relationship
to properly set the pressure control unit to a pressure
attenuation value that will permit the governor to reach
an oil pressure slightly above the low pitch pressure and
within the range labeled as preloaded reversing spring.
DESCRIPTION AND OPERATION
Propeller Owner's Manual
136
61-00-36
Page 2-11
Rev. 2 Feb/17