17.3 Propeller Pitch Control

Question 1

What are the categories of constant speed propellers?

Answer 1

Hydraulic,
Mechanical,
Electrical.

Question 2

What is disc braking?

Answer 2

Some propellers move their blades to a very fine pitch on landing.
Creating a negative AOA.(not blade angle).

Question 3

What is power ON braking?

Answer 3

Reverse pitch.
Blade angle becomes negative.

Question 4

What happens in the event of engine failure?

Answer 4

Feathering as CTM tries moves the blades to a fine pitch.

Question 5

How is CTM prevented?

Answer 5

Feathering.
Blade angle to 90 degrees.

Question 6

What is the BETA range?

Answer 6

Pilot controls the pitch on the ground.

Question 7

When is negative pitch used?

Answer 7

for power-on braking and manoeuvring.

Question 8

When is ground fine pitch used?

Answer 8

For engine starting and discing braking.

Question 9

When is MAX fine pitch used?

Answer 9

For rapid acceleration during take-off, allowing a shorter take-off run

Question 10

When is coarse pitch used?

Answer 10

For high forward speed.

Question 11

Describe a moving piston?

Answer 11

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

Question 12

What is the motive power used in a moving piston?

Answer 12

Oil pressure.

Question 13

Describe a moving cylinder?

Answer 13

Cylinder is attached to the propeller blades and moves in response to pressure felt on one side of a fixed piston.

Question 14

How does a single acting propeller work on single engine aircraft?

Answer 14

Oil pressure moves the blades to a high pitch.
Spring moves it towards low pitch.

Question 15

On single acting propellers on single engine aircraft, what blade position makes it easier to restart?

Answer 15

Lowest fine pitch, windmilling.

Question 16

How does a single acting propeller work on multi engine aircraft?

Answer 16

Oil pressure moves the blade angle to a low pitch,
Springs move the blade angle to a high pitch.

Question 17

On single acting propellers on multi engine aircraft, what occurs if an engine fails?

Answer 17

Decreasing oil pressure moves in the high pitch direction = Feathering.

Question 18

Why does CTM occur?

Answer 18

Due to distribution of propeller blade mass.

Question 19

What’s the problems with propeller low pitch in flight?

Answer 19

Windmilling.
Overspeed.
Produce high drag.

Question 20

How are CTMs overcome?

Answer 20

Spring and the Counterweights to drive the blades to a higher pitch.

Question 21

Describe double acting propellers?

Answer 21

Oil pressure leads to pitch change in both direction.

Question 22

Where are double acting propellers used?

Answer 22

On larger propellers.

Question 23

What is a propeller governor?

Answer 23

Engine RPM sensing device and high pressure oil pump.

Question 24

How does the govenor respond to change in engine RPM?

Answer 24

By directing oil under pressure to the propeller hydraulic cylinder or by releasing oil from the hydraulic cylinder.

Question 25

What are the other names of the Constant Speed Unit (CSU)?

Answer 25

Propeller Control Unit (PCU) Propeller governor.

Question 26

What does a spur gear type pump provide?

Answer 26

Positive operating pressure for the system.

Question 27

What is a pilot valve used for?

Answer 27

To control oil flow to and from the pitch change mechanism.

Question 28

When is the govenor operating at on-speed conditions?

Answer 28

When the engine is operating at the RPM set by the pilot.

Question 29

How does the tension change with speed conditions?

Answer 29

Under speed = exerts more tension on the speeder spring. Over speed = exerts less tension on the speeder spring.

Question 30

On counterweight type propellers, what provides a full coarse limit?

Answer 30

Fixed feather stop.

Question 31

On counterweight type propellers, what limits the negatives blade angle?

Answer 31

Fixed full reverse stop

Question 32

In electrical control, how is electrical power supplied?

Answer 32

Through a slip ring and and a brush assembly.

Question 33

How does electrical control work?

Answer 33

A reversible electric motor drives a bevel gear through a high reduction ratio gear.

Question 34

In electronic control system, what is a crosstalk facility between lanes used for?

Answer 34

To compare and share info with the opposite engine ECU.

Question 35

How does electronic control differ from the electric control?

Answer 35

Uses a ECU instead of a govenor unit with oil. Uses a 2 stage servo valve.

Question 36

Where does ECU receive demands from?

Answer 36

Pilot.

Question 37

How is the correct metered oil supply produced?

Answer 37

An output signal is sent to the torque motor on the servo valve.

Question 38

When oil pressure is routed to the piston, what happens?

Answer 38

It pushes the piston forward, overcoming the spring pressure and the counterweight forces, turns the blades to a finer angle.

Question 39

What happens when the oil line is opened to return?

Answer 39

The spring and counterweight forces will push the piston back towards coarse.

Question 40

What is manual feathering?

Answer 40

Propeller is feathered by moving the control in the cockpit against the low-speed stop.

Question 41

How can feathering be initiated?

Answer 41

By depressing the feathering button actioning the auxiliary pump. Pulling the engine emergency shutdown handle.

Question 42

When an engine fails, how does the automatic feathering work?

Answer 42

An electric feathering pump runs, driving the propeller to the feather position. Automatically overriding the centrifugal forces.

Question 43

What happens when you depress the feathering button?

Answer 43

Actions the auxiliary pump.

Question 44

What is up trim?

Answer 44

When an engine fails, the operating engine increases power by 10% to compensate for the failed engine.

Question 45

When is the up trim triggered?

Answer 45

Torque of local engine falls below 25%. Propeller RPM falls below 80%. PLA is in the rating decent. Maximum take off power is not set.

Question 46

What is unfeathering done by?

Answer 46

The unfeathering accumulator.

Question 47

What does the unfeathering accumulator provide?

Answer 47

A reserve of pressure.

Question 48

What do centrifugal latches do?

Answer 48

Locks the blade in low pitch in case of a leakage.

Question 49

Where are centrifugal latches used?

Answer 49

Only on single acting propellers.

Question 50

What are the advantages of beta range?

Answer 50

Reduce landing roll. Reduce brake wear. Improve manoeuvrability on ground. Allow reversing of aircraft during taxiing.

Question 51

What are the disadvantages of the beta range?

Answer 51

Reduce engine cooling when in reverse pitch. Increased blade damage. Complicated control system.

Question 52

In beta mode, how is the blade angle changed?

Answer 52

Directly with the power lever.

Question 53

Where is the first prop overspeed backup?

Answer 53

In the primary propeller govenor.

Question 54

What range does the normal govenor work in?

Answer 54

102-103%

Question 55

In what range does the overspeed govenor work in?

Answer 55

104-106%

Question 56

What happens at 106-107% Np and above?

Answer 56

Main govenor opens a bleed air link allowing pressurised air to leak

Question 57

What aircraft have an additional overspeed protection device?

Answer 57

Those powered by a PT6A engine.