Hartzell HC-D2MV20-3 Series, Owner'S Manual And Logbook

Page: 59 / 204

Propeller Owner's Manual
140
DESCRIPTION AND OPERATION
61-00-40
Page 2-19
Nov/02
4. Governors
A. Theory of Operation
(1) A governor is an engine RPM sensing device and high
pressure oil pump. In a constant speed propeller system,
the governor responds to a change in engine RPM by
directing oil under pressure to the propeller hydraulic
cylinder or by releasing oil from the hydraulic cylinder. The
change in oil volume in the hydraulic cylinder changes the
blade angle and returns the propeller system RPM to the
set value. The governor is set for a specific RPM via the
cockpit propeller control, that compresses or releases the
governor speeder spring.
(2) When the engine is operating at the RPM set by the
pilot using the cockpit control, the governor is operating
onspeed . Refer to Figure 2-6. In an onspeed condition,
the centrifugal force acting on the flyweights is balanced
by the speeder spring, and the pilot valve is neither
directing oil to nor from the propeller hydraulic cylinder.
(3) When the engine is operating below the RPM set by the
pilot using the cockpit control, the governor is operating
underspeed . Refer to Figure 2-7. In an underspeed
condition, the flyweights tilt inward because there is not
enough centrifugal force on the flyweights to overcome
the force of the speeder spring. The pilot valve, forced
down by the speeder spring, meters oil flow to decrease
propeller pitch and raise engine RPM.
(4) When the engine is operating above the RPM set by the
pilot using the cockpit control, the governor is operating
overspeed . Refer to Figure 2-8. In an overspeed
condition, the centrifugal force acting on the flyweights
is greater than the speeder spring force. The flyweights
tilt outward, and raise the pilot valve. The pilot valve
then meters oil flow to increase propeller pitch and lower
engine RPM.