Propeller Owner's Manual
115N
DESCRIPTION AND OPERATION
61-00-15
Page 2-23
Rev. 24 Dec/20
3. 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 maintains the propeller system RPM. The
governor is set for a specific RPM via the cockpit propeller
control, which 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 2-5. 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 2-6. 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 2-7. 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.
