AUTOMATIC FEATHERING. --The auto-
Each power lever controls the propeller blade
pitch and engine fuel flow through hydro-
matic feathering system performs its function by
mechanical linkages. If a power lever is below 28
energizing the feathering button holding coil
degrees and the blade pitch angle is above 10
(pulling in the feathering button). This occurs
when the autofeather arming switch is in the
degrees, the pitchlock reset valve solenoid
ARMED position and the engine loses power,
(fig. 5-24) activates, resetting pitchlock up to 109
which results in a large decrease in propeller
percent RPM.
As the power levers advance above 34 degrees
thrust. This system is for use during takeoff only,
into the flight-idle range, the flyweight propeller
and it functions above 602 coordinator
governor assumes propeller pitch control. This
setting. Only one propeller will feather auto-
matically.
governor increases or decreases blade pitch to
maintain 100 percent RPM by directing fluid
Autofeather Arming Switch. --There is an
through the feather valve. The temperature
datum system controls proper engine temperature
autofeather ARMED-OFF switch on the auto-
operation.
feather and RPM control panel. It provides the
When ready for takeoff, the pilot places
control for the autofeather system. During normal
operations and when the switch is in the ARMED
the AUTOFEATHER switch in the ARMED
position, all power plants have autofeather
position. As the power levers advance beyond 60
protection. With the switch in the ARMED
degrees, the number 3 power lever switches close
to the HIGH POWER position. If a propeller's
position and electrical power to the power lever
quadrant, autofeather arming switches close and
thrust drops below 500 pounds, the thrust-
the autofeather armed lights illuminate. Both the
sensitive switch closes. This energizes the
autofeather relay. Power goes through the
arming switch and power lever quadrant switch
(activated at 60 degrees) must close before the
autofeather relay contacts to energize the feather
thrust-sensitive signal device can cause propeller
s w i t c h pull-in and hold-in solenoid. The
autofeathering.
autofeather relay loses its power from the feather
switch, but the feather switch remains energized
Autofeather System Indicators. --Four green
through a holding circuit. Power runs from the
indicator lamps, one for each propeller, illuminate
energized feather switch through the contacts of
to show the arming of each individual propeller
the feather cutout relay to the feather pump power
autofeathering circuit. The lights are on the pilot's
relay, to the feather pump motor. Power also goes
overhead control panel. Also, should a propeller
to the feather valve solenoid through the feather
autofeather, its light will remain on and the others
cutout relay. The feather valve solenoid moves the
will go out.
feather valve, which ports oil to increase pitch,
causing the propeller to feather. The fail-safe-type
UNFEATHERING ON THE GROUND. --
fuel control relay activates by power from the
The propeller is unfeathered by holding the
feather switch, causing the engine fuel shutoff
valve to close.
feathering button in the unfeather position. The
As the propeller feathers, the beta cam switch
air start switch (in the propeller) limits the blade
angle decrease to 45 degrees. For further blade
closes when the blade angle goes past 74 degrees.
angle decrease, you hold the pressure cutout
The feather motor cutout switch closes when the
propeller reaches full feather and the oil pressure
override button in.
increases. This completes a circuit that causes the
PROPELLER CONTROL OPERATION
feather cutout relay to energize, de-energizing the
feather valve solenoid. Besides cutting out the
In this section, you will read about a typical
feather pump power relay, the energized feather
propeller control operation. Before the operation
cutout relay maintains its own holding circuit.
is presented, you are given the following con-
This completes the autofeathering cycle.
When shutting down the engine with the
ditions:
EMERGENCY ENGINE SHUTDOWN handle,
The engines are running.
power from the emergency engine shutdown relays
is directed to the feather switch pull-in and hold-in
The engines are operating in the taxi range
solenoid. Each emergency shutdown handle has
two switches and two relays to make sure the
(power levers between 0 degree and 34
electrical systems energize. The engine is shutdown
degrees on the coordinator).
