17.3.2 Feathering and Reverse Pitch Flashcards
What is feathering in aviation?
Feathering is selected to prevent excessive drag and negative torque (windmilling) in the event of an engine failure.
How is feathering selected?
The selection of feathering is carried out manually but can also be activated automatically during certain flight phases if certain conditions are met.
What are the components of a basic propeller feathering system?
A basic propeller feathering system consists of a feathering pump, reservoir, a feathering time-delay switch, and a propeller feathering light.
How is the propeller feathered manually?
The propeller is feathered by moving the control in the cockpit against the low-speed stop, causing the pilot valve lift rod to hold the pilot valve in the decrease RPM position.
What initiates feathering in some propeller models?
On some models, feathering can be initiated by depressing the feathering button, which actions the auxiliary pump and feather solenoid.
What happens when the propeller is fully feathered?
When the propeller has been fully feathered, oil pressure builds up and operates a pressure cut-out switch, causing the auxiliary pump to stop.
How can feathering be accomplished besides manual control?
Feathering may also be accomplished by pulling the engine emergency shutdown handle or switch to the shutdown position.
What is automatic feathering?
Automatic feathering provides automatic operation of the feathering system during take-off and cruise.
What triggers the auto feather system?
In the event of an engine failure, the centrifugal flyweights are overridden, and the electric feathering pump runs to drive the propeller to the feather position.
When is auto feather selected ‘ON’?
Auto feather is selected ‘ON’ for take-off only, using the Auto-feather switch light on the engine instrument panel.
What conditions trigger up trim?
Up trim is triggered when the torque of the local engine falls below 25%, NP falls below 80%, or PLA is in the rating detent.
What happens when the torque of the local engine falls below 25%?
Auto feather is triggered from the armed state when the torque falls below 25% for at least three seconds.
What does the auxiliary feathering pump do?
The auxiliary feathering pump provides a backup source of oil pressure to the propeller pitch-change mechanism.
How can the auto feather system be disarmed?
The auto feather system can be disarmed by pushing OFF the auto feather switch light, retarding power levers to flight idle, or when engine torques drop below approximately 50%.
What is the function of centrifugal latches?
Centrifugal latches prevent unacceptable loads on the starter system by mechanically locking the piston in the fine pitch position when the engine is not rotating.
