Module 17.2 Propeller Construction

Question 1

How are wooden propellers constructed?

Answer 1

With several layers of wood bonded with a waterproof resin glue.

Question 2

What is the most common wood used?

Answer 2

Birch

Question 3

What is a “blank”?

Answer 3

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

Question 4

How long is the “blank” allowed to rest for?

Answer 4

A week

Question 5

Why is the “blank” allowed to rest for a week?

Answer 5

To allow the equal distribution of moisture through all the layers.

Question 6

After moisture has equally distributed through all the layers, what is the “blank” now called?

Answer 6

A white

Question 7

Where is the cotton fabric sheathing applied and what does it do?

Answer 7

To the outer 12 to 15 in (30 to 38 cm) of the tip to reinforce the strength of the thin sections at the tip.

Question 8

What is done to the cotton fabric sheathing applied to the tip?

Answer 8

It’s doped

Question 9

Why is the cotton fabric sheathing applied to the tip doped?

Answer 9

To protect it from deterioration by the weather and the sun’s ultraviolet (UV) rays.

Question 10

Why is a protective metal tipping strip is rebated into the leading edge of the propeller?

Answer 10

To prevent damage from small stones during ground operations.

Question 11

Why are small holes drilled in each propeller blade tip?

Answer 11

To release moisture and allow the wood to breathe.

Question 12

What final coating paint is used on wooden propellers and what does this do?

Answer 12

Polyurethane paint which provides mechanical and UV ray protection.

Question 13

What is the advantage of composite propellers over metal ones?

Answer 13

Lighter and stronger.

Question 14

What is used to limit lightening strike damage to composite propellers?

Answer 14

Metal foil mesh incorporated on the surface.

Question 15

If a composite propeller has a metal spar, what is it made from?

Answer 15

Titanium, aluminium alloy or stainless steel

Question 16

Where does the spar run in a composite propeller with a metal spar?

Answer 16

Through the centre of the blade.

Question 17

What is constructed around the metal spar

Answer 17

The fibreglass, kevlar or carbon fibre shell.

Question 18

What does the spar in a propeller do?

Answer 18

Absorbs the centrifugal forces and bending loads.

Question 19

What does the shell of a composite propeller do?

Answer 19

Give the propeller torsional rigidity.

Question 20

What is the surface of a composite propeller protected by and what does this do?

Answer 20

Polyurethane paint which serves as protection against erosion and static charge.

Question 21

What do composite propellers with no metal spar comprise of?

Answer 21

Carbon fibre components in the blade that form the hollow spar.

Question 22

For composite spars without a metal spar, what is the hollow spar filled with?

Answer 22

Polyurethane foam

Question 23

What are metal propellers constructed from?

Answer 23

Aluminium alloy or steel.

Question 24

What material is most widely used for propellers?

Answer 24

Aluminium

Question 25

How is the weight of steel propeller blades kept to a minimum?

Answer 25

They're hollow

Question 26

What is each blade divided into?

Answer 26

Stations

Question 27

How are blade stations numbered?

Answer 27

From 1 onward in six-inch increments (15 cm) or the number of inches from the root of the blade toward its tip.

Question 28

Where is the 'master station' identified?

Answer 28

In the propeller section of the maintenance manual

Question 29

How can the 'master station' be marked on a blade?

Answer 29

A line drawn across the blade face.

Question 30

What is a fixed pitch propeller?

Answer 30

A propeller where the blade angle (pitch) cannot be changed.

Question 31

How is the pitch in a fixed pitch propeller determined?

Answer 31

In accordance with the purpose it will be used for.

Question 32

What type of pitch is needed for steep climbing and towing?

Answer 32

Low (fine) pitch

Question 33

What type of pitch is needed for a more gradual climb and cruising flight?

Answer 33

Higher (coarse) pitch

Question 34

What are the two disadvantages of fixed pitch propellers?

Answer 34

Maximum propeller efficiency is possible only at one predetermined RPM and airspeed. The power available at take off is reduced because of the lower RPM.

Question 35

What is a controllable pitch propeller?

Answer 35

A propeller where the pilot can change the pitch of the blades in flight irrespective of the aircraft operating conditions.

Question 36

What two controls are there for aircraft equipped with a controllable-pitch propeller?

Answer 36

Throttle control Propeller control

Question 37

What is a constant speeding propeller?

Answer 37

A propeller that is designed to automatically change its blade pitch to allow to maintain a constant RPM.

Question 38

What mechanism is used to allow a constant speed propeller to work.

Answer 38

A constant speed unit.

Question 39

What do constant speed units consist of?

Answer 39

A speeder spring and a set of fly weights.

Question 40

Describe how the blade pitch is changed in a constant speed unit?

Answer 40

Oil is carried through a pilot valve under pressure in response to an under or over speed condition.

Question 41

What happens to the fly weights if the propeller exceeds the preselected RPM?

Answer 41

They are forced outward.

Question 42

What happens to the fly weights if the propeller under-speeds?

Answer 42

They swing inward.

Question 43

What changes the tension on the speeder spring in a constant speed unit?

Answer 43

Over-speed or under-speed.

Question 44

What are the three type of shaft?

Answer 44

Tapered Shaft Splined Shaft Flanged Shaft

Question 45

What mates with the engine shaft taper?

Answer 45

The hub's inverse taper.

Question 46

What is used to secure the propeller to the engine in a tapered shaft?

Answer 46

A retaining nut that screws onto the engine shaft and presses the tapers together.

Question 47

In a tapered shaft, how is the drive transmitted?

Answer 47

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

Question 48

What type of shaft is used for propellers with high output engines?

Answer 48

Splined shafts

Question 49

When using a splined shaft, how is the propeller shaft connected to the engine crank shaft?

Answer 49

By reduction gearing.

Question 50

The sizes of splined shafts are identified by what?

Answer 50

An SAE (Society of Automotive Engineers) number.

Question 51

What type of shaft is used on most reciprocating and turboprop engines?

Answer 51

A flanged shaft

Question 52

Why are spinners mounted?

Answer 52

For better aerodynamics, protection for the hub and aesthetics.

Question 53

What are spinners manufactured from?

Answer 53

Aluminium alloy or glass fibre composites.

Question 54

What is the spinner attached to?

Answer 54

The spinner backplate (or spinner bulkhead).

Question 55

What should be done if there are cracks in the blade recesses or in the spinner mounting?

Answer 55

The parts should be replaced.

Question 56

If a repair is permitted how should it be done?

Answer 56

Drilling to stop the crack.