17.2 Construction Methods and Materials

Question 1

What can propellers be made from?

Answer 1

• wood
• metal
• composite

Question 2

What is the most common wood used for propeller construction?

Answer 2

Birch

Question 3

How many layers of wood are laid down to form a propeller?

Answer 3

Minimum of 5

Question 4

What is a (White)?

Answer 4

The blank is roughly shaped and allowed to rest for a week to allow for the equal distribution of moisture throughout all of the layers

Question 5

What are the wooden layers bonded with?

Answer 5

Waterproof resin glue (aero-glue)

Question 6

What is used to reinforce the strength of the thin wooden sections at the tip?

Answer 6

A cotton fabric sheathing is applied to the outer 12-15 inches of the tip to reinforce strength

Question 7

What is rebated in to the leading edge of the propeller to prevent damage from small stones during ground operations?

Answer 7

A protective metal tipping strip

Question 8

What is used to secure the tipping to the blade?

Answer 8

Countersink screws at the thicker ends of the blade and copper rivets near the tip

Question 9

Why are 3 #60 (0.04-1.016mm) size holes 3/16 inch deep drilled in to each tip?

Answer 9

To release any moisture and allowing the wood to breathe

Question 10

Why are some propellers coated with plastic instead of doped cotton fabric before the metal tipping is applied?

Answer 10

For added strength

Question 11

Some types of propellers have a finishing coat of polyurethane paint, what is the purpose for this?

Answer 11

Provides mechanical and UV ray protection

Question 12

What is a lag screw or coach bolt?

Answer 12

A heavy duty wood screw with a square or hexagonal head which is driven by a wrench

(Designed for metal to timber connections)

Question 13

Why would metal propeller blades used?

Answer 13

With aircraft with greater engine power

Constructed from aluminium or steel

Question 14

What are the most widely used material of propellers in the industry?

Answer 14

Aluminium

Question 15

Why are aluminium propellers used?

Answer 15

More durable than wood because thinner more more efficient aerofoils may be constructed with out sacrificing structural integrity

Better cooling us also had

Question 16

How are aluminium propellers finished?

Answer 16

The blade surfaces are finished by plating, chemical etching and or painting. Anodising is the most commonly used finishing process

Question 17

When would steel propellers be used?

Answer 17

They are not very common and are used on some older aircraft or some transport aircraft

Question 18

What is the advantage of hollow steel blades?

Answer 18

Reduced weight

Question 19

What are attached to composite blades to protect from impact damage?

Answer 19

Nickel or stainless steel erosion sheets

Question 20

What is a split hub?

Answer 20

A propeller hub is manufactured in two halves which are bolted together around a widened blade root

Question 21

What are split rings?

Answer 21

The propeller hub is made from one piece and the blade root is inserted through a hole in the hub. A split ring is placed around the blade root, inside the hub, to secure the blade in position

Question 22

What are split collars?

Answer 22

This method is similar to the split hub. The blade root is repositioned over a trunnion incorporated on a solid hub. A two piece collar is then clamped around the hub and the blade root to secure the blade

Question 23

What are threaded blade retainers?

Answer 23

A method that uses threaded blade root rings which screw in to threads formed in the propeller hub. These are then torque loaded and locked in to position

Question 24

When would the tapered crankshaft propeller to engine attachment be used?

Answer 24

Usually found on older, low powered, piston engines

A key way is provided to ensure the correct positioning of the propeller hub to the crankshaft

Question 25

When would the flanged shaft propeller to engine attachment be used?

Answer 25

They are used on most horizontally opposed piston engines and some turbo props

A flange is formed on the front of the engine shaft to which the propeller is attached

Question 26

When would the splined shaft propeller to engine attachment be used?

Answer 26

Found on many types of engine including radial, in line and horizontally opposed piston engines as well as many turboprop engines

Master spline is incorporated to correct Positioning of the propeller assembly of the shaft

Question 27

Why are spinners used?

Answer 27

For better aerodynamics, as a mechanical protection for the hub and for aesthetic reasons

Question 28

How Are spinners manufactured?

Answer 28

In one piece from spun aluminium alloy or glass fibre composites

Question 29

What are spinner repairs limited to?

Answer 29

Sometimes stop drilling is allowed for cracks but usually damaged spinners are replaced

Question 30

What is a blank?

Answer 30

The minimum of 5 layers of wood that are laid down and glued together (when roughly shaped and left for a week to allow even moisture distribution, it becomes a white)