Module 17.3 Propeller Pitch Control Flashcards
What must the engine produce little of when shutting down?
Drag
What is done to the propellers to reduce drag when shutting down?
Moved into the feathered position.
Why is reverse thrust used?
To shorten the distance on landing.
What is done to the propeller blades to produce reverse thrust?
They are turned into reverse pitch.
What is disc braking?
What does this cuase?
Where the blades are moved to a very fine (low) pitch on landing.
This causes a negative angle of attack and a braking force.
What is power ON braking?
Where the blades are moved so that the blade angle becomes negative and offers resistance to rotation.
This allows power to be applied to obtain a proportional and controllable braking force.
What is BETA range?
Propeller pitch control on ground.
What is Negative (Reverse) Pitch used for?
power-on braking and manoeuvring.
What is ALPHA range?
The constant speed range in flight.
What is Max Fine Pitch used for?
Rapid acceleration during take-off.
What is Coarse (High) Pitch used for?
High forward speed.
What can propeller pitch not be selected between?
Max coarse pitch and feather.
What can the pitch mechanism be categorised as?
Moving piston
Moving cylinder
What is a moving piston pitch change mechanism?
A piston is attached to the propeller blade lugs and moves within a cylinder.
What is a moving cylinder pitch change mechanism?
The cylinder is attached externally to the propeller blade and moves in response to the pressure felt on one side of a fixed piston.
What is a single acting propeller?
Oil pressure changes the pitch in one direction only.
Movement in the opposite direction is the result of spring force and the torsion moments of the blades
How do single acting propellers for single engine aircraft work?
Oil pressure moves the blades in the direction of high (coarse) pitch and the spring moves it towards low pitch.
What position are the blades in after shutdown on a Single Acting Propellers for Single Engine Aircraft?
The lowest (fine) pitch stop position.
On Single Acting Propellers for Single Engine Aircraft, what is an advantage of the lowest (fine) pitch stop position?
It’s optimal for restarting the engine.
How do single acting propellers for multi-engine aircraft work?
Oil pressure moves the blades in the direction of low (fine) pitch. The springs and torsional moments of the blades, move the blades towards high (coarse) pitch.
If the propeller blade turns towards low (fine) pitch because of centrifugal force, what is needed?
A counterweight must be attached to the blade root.
What is a double acting propeller?
Oil pressure changes pitch in both directions.
What is a propeller governor?
A device that responds to a change in engine RPM by directing oil under pressure to the propeller hydraulic cylinder or releasing oil from the hydraulic cylinder.
What condition is the propeller governor operating in when the engine is operating at the RPM set by the pilot?
Neutral “on speed”
During neutral “on speed”, the centrifugal force acting on the flyweights is…
Balanced
If the the propeller control lever (conditioning lever) is moved forwards to a new selected speed, what happens in the propeller governor?
More tension is exerted on the speeder spring, overcoming the centrifugal force on the flyweights and forcing the pilot valve down.
If the the propeller control lever (conditioning lever) is moved rearwards to a new selected speed, what happens in the propeller governor?
Tension is released n the speeder spring allowing the centrifugal force on the flyweights to lift the pilot valve up.
What is needed in an under-speed condition?
Higher propeller RPM.
What is needed in an over-speed condition?
Lower propeller RPM.
What is done by the pilot to feather the propeller?
The control in the cockpit is moved against the low-speed stop.
What does moving the control in the cockpit against the low-speed stop do?
Causes the governor to hold the pilot valve in the decrease RPM position regardless of the action of the governor flyweights.
How else can feathering be accomplished?
By pulling the engine emergency shutdown handle or switch to the shutdown position.
What is the Automatic (Auto-Coarsening) Feathering system used to do?
To provide automatic operation of the feathering system.
When is the automatic feathering system used?
During take-off and cruise.
In the event of an engine failure what is overridden?
The centrifugal flyweights
What does the auto feather system provide?
Automatically initiated propeller feathering, and good operating engine power up trim following an engine failure during take-off.
When auto feather selected to ‘ON’?
Take-off only.
Where is the auto-feather switch light located?
Engine instrument panel.
What pitch must the propeller be in to restart the engine?
A fine (low) pitch.
Why are some systems equipped with an unfeathering accumulator?
To provide a reserve of pressure.
What is the accumulator charged through during normal operating?
A non-return valve
How is unfeathering done when required?
By moving the power lever to a higher RPM position and releasing the pressure stored in the accumulator.
What type of engines are fitted with centrifugal latches?
Engines with a single-acting propeller.
Where is oil pressure when a single-acting propeller engine is shut down?
Trapped in the cylinder.
What do centrifugal latches prevent?
The propeller blades from being forced towards the coarse pitch by the spring.
When is up trim triggered?
When torque of the local engine falls below 25%.
How do centrifugal latches work?
By mechanically locking the piston in the fine (low) pitch position when the engine is not rotating.
What are centrifugal latches engaged by?
Spring pressure at low RPM.
What are centrifugal latches released by?
Centrifugal force as RPM increases.
What is the blade angle changed by in Beta Mode?
Directly by the power lever.
At what overspeed percentage will overspeed governor operate at?
104 to 106% Np
What does the propeller governor do to reduce overspeed?
Operates and returns oil from the propeller dome back into the reduction gearbox.
What is used to control propeller overspeed up to 102 to 103% Np?
The constant speed unit (CSU).
At what overspeed percentage do the flyweights open a bleed air link allowing pressurised air to leak into ambient air.
At 106 to 107% Np and above.
