Module 17.3 Propeller Pitch Control

Question 1

What must the engine produce little of when shutting down?

Answer 1

Drag

Question 2

What is done to the propellers to reduce drag when shutting down?

Answer 2

Moved into the feathered position.

Question 3

Why is reverse thrust used?

Answer 3

To shorten the distance on landing.

Question 4

What is done to the propeller blades to produce reverse thrust?

Answer 4

They are turned into reverse pitch.

Question 5

What is disc braking?

What does this cuase?

Answer 5

Where the blades are moved to a very fine (low) pitch on landing.

This causes a negative angle of attack and a braking force.

Question 6

What is power ON braking?

Answer 6

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.

Question 7

What is BETA range?

Answer 7

Propeller pitch control on ground.

Question 8

What is Negative (Reverse) Pitch used for?

Answer 8

power-on braking and manoeuvring.

Question 9

What is ALPHA range?

Answer 9

The constant speed range in flight.

Question 10

What is Max Fine Pitch used for?

Answer 10

Rapid acceleration during take-off.

Question 11

What is Coarse (High) Pitch used for?

Answer 11

High forward speed.

Question 12

What can propeller pitch not be selected between?

Answer 12

Max coarse pitch and feather.

Question 13

What can the pitch mechanism be categorised as?

Answer 13

Moving piston

Moving cylinder

Question 14

What is a moving piston pitch change mechanism?

Answer 14

A piston is attached to the propeller blade lugs and moves within a cylinder.

Question 15

What is a moving cylinder pitch change mechanism?

Answer 15

The cylinder is attached externally to the propeller blade and moves in response to the pressure felt on one side of a fixed piston.

Question 16

What is a single acting propeller?

Answer 16

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

Question 17

How do single acting propellers for single engine aircraft work?

Answer 17

Oil pressure moves the blades in the direction of high (coarse) pitch and the spring moves it towards low pitch.

Question 18

What position are the blades in after shutdown on a Single Acting Propellers for Single Engine Aircraft?

Answer 18

The lowest (fine) pitch stop position.

Question 19

On Single Acting Propellers for Single Engine Aircraft, what is an advantage of the lowest (fine) pitch stop position?

Answer 19

It’s optimal for restarting the engine.

Question 20

How do single acting propellers for multi-engine aircraft work?

Answer 20

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.

Question 21

If the propeller blade turns towards low (fine) pitch because of centrifugal force, what is needed?

Answer 21

A counterweight must be attached to the blade root.

Question 22

What is a double acting propeller?

Answer 22

Oil pressure changes pitch in both directions.

Question 23

What is a propeller governor?

Answer 23

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.

Question 24

What condition is the propeller governor operating in when the engine is operating at the RPM set by the pilot?

Answer 24

Neutral “on speed”

Question 25

During neutral "on speed", the centrifugal force acting on the flyweights is...

Answer 25

Balanced

Question 26

If the the propeller control lever (conditioning lever) is moved forwards to a new selected speed, what happens in the propeller governor?

Answer 26

More tension is exerted on the speeder spring, overcoming the centrifugal force on the flyweights and forcing the pilot valve down.

Question 27

If the the propeller control lever (conditioning lever) is moved rearwards to a new selected speed, what happens in the propeller governor?

Answer 27

Tension is released n the speeder spring allowing the centrifugal force on the flyweights to lift the pilot valve up.

Question 28

What is needed in an under-speed condition?

Answer 28

Higher propeller RPM.

Question 29

What is needed in an over-speed condition?

Answer 29

Lower propeller RPM.

Question 30

What is done by the pilot to feather the propeller?

Answer 30

The control in the cockpit is moved against the low-speed stop.

Question 31

What does moving the control in the cockpit against the low-speed stop do?

Answer 31

Causes the governor to hold the pilot valve in the decrease RPM position regardless of the action of the governor flyweights.

Question 32

How else can feathering be accomplished?

Answer 32

By pulling the engine emergency shutdown handle or switch to the shutdown position.

Question 33

What is the Automatic (Auto-Coarsening) Feathering system used to do?

Answer 33

To provide automatic operation of the feathering system.

Question 34

When is the automatic feathering system used?

Answer 34

During take-off and cruise.

Question 35

In the event of an engine failure what is overridden?

Answer 35

The centrifugal flyweights

Question 36

What does the auto feather system provide?

Answer 36

Automatically initiated propeller feathering, and good operating engine power up trim following an engine failure during take-off.

Question 37

When auto feather selected to 'ON'?

Answer 37

Take-off only.

Question 38

Where is the auto-feather switch light located?

Answer 38

Engine instrument panel.

Question 39

What pitch must the propeller be in to restart the engine?

Answer 39

A fine (low) pitch.

Question 40

Why are some systems equipped with an unfeathering accumulator?

Answer 40

To provide a reserve of pressure.

Question 41

What is the accumulator charged through during normal operating?

Answer 41

A non-return valve

Question 42

How is unfeathering done when required?

Answer 42

By moving the power lever to a higher RPM position and releasing the pressure stored in the accumulator.

Question 43

What type of engines are fitted with centrifugal latches?

Answer 43

Engines with a single-acting propeller.

Question 44

Where is oil pressure when a single-acting propeller engine is shut down?

Answer 44

Trapped in the cylinder.

Question 45

What do centrifugal latches prevent?

Answer 45

The propeller blades from being forced towards the coarse pitch by the spring.

Question 46

When is up trim triggered?

Answer 46

When torque of the local engine falls below 25%.

Question 47

How do centrifugal latches work?

Answer 47

By mechanically locking the piston in the fine (low) pitch position when the engine is not rotating.

Question 48

What are centrifugal latches engaged by?

Answer 48

Spring pressure at low RPM.

Question 49

What are centrifugal latches released by?

Answer 49

Centrifugal force as RPM increases.

Question 50

What is the blade angle changed by in Beta Mode?

Answer 50

Directly by the power lever.

Question 51

At what overspeed percentage will overspeed governor operate at?

Answer 51

104 to 106% Np

Question 52

What does the propeller governor do to reduce overspeed?

Answer 52

Operates and returns oil from the propeller dome back into the reduction gearbox.

Question 53

What is used to control propeller overspeed up to 102 to 103% Np?

Answer 53

The constant speed unit (CSU).

Question 54

At what overspeed percentage do the flyweights open a bleed air link allowing pressurised air to leak into ambient air.

Answer 54

At 106 to 107% Np and above.