Hartzell HC-D2X20-3 Owner's Manual page 44

C. General Description (Control)
(1) 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 controlled
from a governor or is engine oil that is pilot controlled
through a valve. The variable oil force (oil supply) is
supplied under pressure to the hydraulic cylinder and
piston on the face of the engine case encircling the
splined engine shaft and propeller. 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. Changing blade angle will vary the load on the
engine and result in a change of engine and propeller
RPM. On constant speed installations the governor will
maintain a constant RPM (within limits) independent of
where the throttle is set. On a manually controlled
propeller the pilot selects a blade angle through a cable
attached to a valve on the hydraulic cylinder and piston to
select a higher or lower RPM, as desired. The manually
controlled valve will allow engine oil under pressure to
enter the piston and cylinder cavity, or will allow oil to
leave the piston and cylinder cavity and return to engine
drain.
(2) Reverse blade angle operation is only available on a
manually controlled propeller model. The governed
propeller model covered by this manual is not reversible.
DESCRIPTION AND OPERATION
Propeller Owner's Manual
140
61-00-40
Page 2-6
Nov/02