17.2 Propeller Construction

Question 1

Where is wood often used?

Answer 1

Fixed pitch propellers.

Question 2

What is the most commonly used wood?

Answer 2

Birch.

Question 3

How is a blank formed?

Answer 3

At least 5 layers of wood are laid down and glued together.

Question 4

How long is blank left to rest for and what does it become?

Answer 4

A week.
Then it’s known as a White.

Question 5

What is the purpose of fabric doping?

Answer 5

Protects it from deteriorating by the weather and suns UV rays.

Question 6

What protects the propeller LE for damage?

Answer 6

A metal tipping strip.

Question 7

What metals are used?

Answer 7

Brass, stainless steel, Monel, terneplate.

Question 8

How is the metal tipping strip secured to the blade?

Answer 8

Using countersunk screws at the thick blade section,
Copper rivets near the tips,
All are safe tied in place with solder.

Question 9

Why are small holes drilling at each tip?

Answer 9

Release moisture and allow wood to breathe.

Question 10

What can some propellers coated in instead of dope?

Answer 10

Coated in plastic

Question 11

What does the final coating of polyurethane paint provide?

Answer 11

Provides mechanical and UV ray protection.

Question 12

How are the propellers mounted on the engine crankshaft?

Answer 12

Splined crankshaft,
Tapered crankshaft,
Forged steel hub,
Or bolted.

Question 13

What propellers are taking over from metal blades?

Answer 13

Composite propellers.

Question 14

What is bonded to composite LEs to protect from impact damage?

Answer 14

Nickel or stainless steel erosion shields.

Question 15

What metal can the spar on composite propellers be made from?

Answer 15

Titanium, aluminium alloy or stainless steel.

Question 16

What is the shell over the metal spar and filling material made off?

Answer 16

Fibreglass, Kevlar or carbon fibre.

Question 17

What is the filling material in composite propellers with a metal spar?

Answer 17

Low density foam or honeycomb.

Question 18

What forces do the metal spar and shell absorb in composite propellers?

Answer 18

Spar absorbs centrifugal forces and bending loads.
Shell gives the necessary torsional rigidity.

Question 19

What is the purpose of the coat of conducting polyurethane paint on the LE surface?

Answer 19

Protects against erosion and prevents against static charging.

Question 20

What do composite blades without a metal spar comprise off?

Answer 20

2 carbon fibre components.
Hollow centre filled with polyurethane foam.
Composite shell.

Question 21

What allows for minor adjustments in composite blades without a metal spar while the blade is horizontally balanced?

Answer 21

Lead wool placed in the hollow balancing tube.

Question 22

How is the lead wool retained in place?

Answer 22

Using a rubber plug.

Question 23

What are metal propellers made from?

Answer 23

Aluminium alloy or steel.

Question 24

What are the most widely used propeller material?

Answer 24

Aluminium.

Question 25

Why is aluminium better than wooden propellers?

Answer 25

More durable. Better engine cooling. Require less maintenance, reducing operating costs.

Question 26

What is the most common finishing process of metal propellers?

Answer 26

Anodising.

Question 27

Where are steel propellers found?

Answer 27

Older aircraft.

Question 28

How are steel propellers made lighter?

Answer 28

Hollowing them out.

Question 29

How far apart are blade stations?

Answer 29

6 inches 15cm.

Question 30

How are blade stations numbered?

Answer 30

From root to tip.

Question 31

What is the master section also a reference point for?

Answer 31

Where the most thrust is produced.

Question 32

What are the types of controllable and variable pitch propeller?

Answer 32

Only 2 positions, (high and low pitch). Or ones can be adjusted to any pitch angle

Question 33

What 2 devices do controllable pitch propellers have?

Answer 33

Throttle control. Propeller control.

Question 34

What does throttle control do?

Answer 34

Controls power output of the engine.

Question 35

What does propeller control do?

Answer 35

Regulates engine RPM and in turn propeller RPM.

Question 36

Why are controllable pitch propellers best?

Answer 36

Result in most efficient performance.

Question 37

How is constant speeding propeller achieved?

Answer 37

By a Constant Speed Unit or a govenor.

Question 38

What is a constant spending propeller?

Answer 38

Design that automatically changes blade pitch to maintain constant RPM.

Question 39

What principle do Constant Speed Units work off and incorporate?

Answer 39

Work off Centrifugal force, Incorporate a speeder spring and a set of fly weights.

Question 40

How are flyweights positioned in over speed conditions?

Answer 40

Outwards.

Question 41

How are flyweights positioned in under speed conditions?

Answer 41

Inwards.

Question 42

What is the purpose of the Constant Speed Unit Govenor?

Answer 42

To perfectly match blade angle to engine power output.

Question 43

What happens in under speed conditions?

Answer 43

Flyweight move inwards, Pilot valve goes down, Blade angle would decrease, allow the oil pressure to leave the propeller.

Question 44

What happens in over speed conditions?

Answer 44

Flyweights move outwards, Pilot valve goes up, Blade angle increases by directing oil to the propeller.

Question 45

Where is a tapered shaft found?

Answer 45

Small, older low powered piston engines.

Question 46

How is drive transmitted in a tapered shaft?

Answer 46

Through a key that is seated in slots machined in the engine shaft and propeller hub.

Question 47

How may the propeller shaft be connected to the engine crankshaft in a splined shaft?

Answer 47

Reduction gearing.

Question 48

In smaller engines how does the splinted shaft differ?

Answer 48

The propeller shaft is simply an extension of the engine crankshaft. There is no reduction gearing.

Question 49

Where is a flanged shaft used?

Answer 49

On most reciprocating and turboprop engines.

Question 50

Why do some flanges have index pins in the propeller flanges?

Answer 50

So the propeller can only be installed in 1 position for synchronising and/or synchrophasing.

Question 51

Why are spinners mounted?

Answer 51

For better aerodynamics, Mechanical protection for hub, Aesthetic reasons.

Question 52

Why is there a support at the front end of the hub?

Answer 52

For centering purpose.

Question 53

What can be said about spinner repairs?

Answer 53

They are limited.

Question 54

Describe the dynamic loads on the spinner.

Answer 54

Extremely high.

Question 55

What must be ensured on spinner installation?

Answer 55

No noticeable wobble is present.