Module 17.2 Propeller construction

Question 1

What is the most commonly used wood propeller construction?

Answer 1

Birch

Question 2

What forms a blank?

Answer 2

At least 5 layers of wood glued together

Question 3

Why is the blank left for a week after being roughly shaped?

Answer 3

Equal moisture distribution

Question 4

After the blank has been left for a week what is it now referred to as?

Answer 4

A white

Question 5

A cotton fabric sheathing is then applied to the outer 12 to 15 in (30 to 38 cm) of the tip, for what purpose?

Answer 5

Reinforce the strength of the thin sections at the tip

Question 6

What is done to the fabric to protect it?

Answer 6

Doped

Question 7

To prevent damage what is rebated onto the leading edge?

Answer 7

Protective metal strip

Question 8

What metals are used to protected the LE?

Answer 8

Brass, stainless steel, monel (nickel/copper alloy) or terneplate (steel coated with a lead/tin alloy).

Question 9

How is the tipping secured in thick blade sections?

Answer 9

Countersunk screws

Question 10

Where are copper rivets placed?

Answer 10

Near the tip

Question 11

How are the rivets safetied?

Answer 11

Solder

Question 12

What is the purpose of drilling small holes in the tip?

Answer 12

Release moisture and allow the wood to breathe

Question 13

Some propellers have a final coating of polyurethane paint for which purpose?

Answer 13

Mechanical and UV protection

Question 14

How are wooden controllable pitch propellers secured to the metal sleeve?

Answer 14

Using lag screws

Question 15

What are the methods of securing the propeller to the engine?

Answer 15

• Splined
• Tapered
• Forged steel hub
• Bolted

Question 16

What LE protection do composite propellers have?

Answer 16

Nickel or CRES

Question 17

How can Composite blades with a spar be constructed?

Answer 17

Spar, coated in fibreglass, kevlar or carbon fibre shell with foam or honeycomb in front and behind the spar.

Question 18

What loads does the spar absorb?

Answer 18

Centrifugal forces and bending loads

Question 19

What does the composite shell give the propeller?

Answer 19

Torsional rigidity

Question 20

What is on the inner and outer surface of the LE?

Answer 20

Heating element - inner
Metal guard - outer

Question 21

How is the blade surface protected? (composite)

Answer 21

Conducting polyurethane paint

Question 22

What purpose does the paint coat serve? (composite)

Answer 22

Erosion protection and prevents it from being statically charged

Question 23

How are composite blades without a metal spar constructed?

Answer 23

Two carbon fibre components in the blade that form the spar. Hollow core filled with foam

Question 24

What is used to horizontally balance the blade?

Answer 24

Lead wool in a hollow balancing tube

Question 25

How is the lead wool retained in place?

Answer 25

Use of a rubber plug

Question 26

What are the two different types of metal propeller?

Answer 26

Aluminium alloy or steel

Question 27

What type of propeller has better cooling properties for reciprocating engines?

Answer 27

Aluminium alloy

Question 28

Are steel propellers commonly used?

Answer 28

No, not really anymore

Question 29

How do you make steel blades lighter?

Answer 29

Hollowed out

Question 30

How big is a blade station?

Answer 30

6 inches

Question 31

How are the blade stations numbered?

Answer 31

From root to tip

Question 32

Where is the master reference station on a fixed pitch propeller?

Answer 32

75% from centre of rotation

Question 33

Where is the master reference station on a variable pitch propeller?

Answer 33

50 to 75% from the centre of rotation

Question 34

What is the master reference station also a reference point for?

Answer 34

Where most of the thrust of the blade acts

Question 35

Can the pilot control the angle of a fixed pitch propeller?

Answer 35

No

Question 36

What are the two types of controllable pitch propellers?

Answer 36

- Two position (high or low pitch) - Variable pitch

Question 37

How does the propeller control regulate engine RPM?

Answer 37

Manipulating blade angle

Question 38

Why is it necessary to change the blade angle?

Answer 38

To maximise the blade angle

Question 39

In older systems how is blade angle manipulated?

Answer 39

Crank handle which drives a pinion gear through a cable

Question 40

A constant speed propeller is what?

Answer 40

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

Question 41

How does a constant speed unit work?

Answer 41

Principle of centrifugal force and incorporates a speeder spring edna set of fly weights

Question 42

How is constant speed maintained?

Answer 42

Constant speed unit or governor

Question 43

In an engine overspeed condition what occurs to the piston? (Constant Speed Unit Governor)

Answer 43

Flyweights separate and piston rises. Allowing oil pressure to be directed to the propeller to push it to a coarser angle

Question 44

In an engine underspeed condition what occurs to the piston? (Constant Speed Unit Governor)

Answer 44

Flyweights come closer and piston sinks. Allowing oil pressure to leave the propeller to allow the blade to move to a finer blade angle

Question 45

What occurs at normal speed? (Constant Speed Unit Governor)

Answer 45

Hydraulic lock

Question 46

What are three types of shafts?

Answer 46

- Tapered shaft - Splined shaft - Flanged shaft

Question 47

How is the drive transmitted in a tapered shaft?

Answer 47

Key that is seated

Question 48

When are splined shafts used?

Answer 48

High output radial engines

Question 49

Why is one end of the splined shaft threaded?

Answer 49

To accommodate the hub nut

Question 50

How may the propeller shaft be connected to the engine crankshaft?

Answer 50

Large aircraft - Reduction gearbox Small aircraft - extension of crankshaft

Question 51

When are flanged shafts used?

Answer 51

Modern turboprop and reciprocating

Question 52

What does a flanged shaft have for synchronisation?

Answer 52

Index pins

Question 53

Why are spinners mounted?

Answer 53

- Protection - Aerodynamics - Aesthetics

Question 54

What loads are extremely high on the spinner?

Answer 54

Dynamic loads

Question 55

How may cracks be stopped on a spinner?

Answer 55

Stop drilling

Question 56

On spinner installation, it must be ensure that there is no what?

Answer 56

Noticeable wobble