17.2 Construction Methods and Materials Flashcards
What can propellers be made from?
- wood
- metal
- composite
What is the most common wood used for propeller construction?
Birch
How many layers of wood are laid down to form a propeller?
Minimum of 5
What is a (White)?
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
What are the wooden layers bonded with?
Waterproof resin glue (aero-glue)
What is used to reinforce the strength of the thin wooden sections at the tip?
A cotton fabric sheathing is applied to the outer 12-15 inches of the tip to reinforce strength
What is rebated in to the leading edge of the propeller to prevent damage from small stones during ground operations?
A protective metal tipping strip
What is used to secure the tipping to the blade?
Countersink screws at the thicker ends of the blade and copper rivets near the tip
Why are 3 #60 (0.04-1.016mm) size holes 3/16 inch deep drilled in to each tip?
To release any moisture and allowing the wood to breathe
Why are some propellers coated with plastic instead of doped cotton fabric before the metal tipping is applied?
For added strength
Some types of propellers have a finishing coat of polyurethane paint, what is the purpose for this?
Provides mechanical and UV ray protection
What is a lag screw or coach bolt?
A heavy duty wood screw with a square or hexagonal head which is driven by a wrench
(Designed for metal to timber connections)
Why would metal propeller blades used?
With aircraft with greater engine power
Constructed from aluminium or steel
What are the most widely used material of propellers in the industry?
Aluminium
Why are aluminium propellers used?
More durable than wood because thinner more more efficient aerofoils may be constructed with out sacrificing structural integrity
Better cooling us also had
How are aluminium propellers finished?
The blade surfaces are finished by plating, chemical etching and or painting. Anodising is the most commonly used finishing process
When would steel propellers be used?
They are not very common and are used on some older aircraft or some transport aircraft
What is the advantage of hollow steel blades?
Reduced weight
What are attached to composite blades to protect from impact damage?
Nickel or stainless steel erosion sheets
What is a split hub?
A propeller hub is manufactured in two halves which are bolted together around a widened blade root
What are split rings?
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
What are split collars?
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
What are threaded blade retainers?
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
When would the tapered crankshaft propeller to engine attachment be used?
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
When would the flanged shaft propeller to engine attachment be used?
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
When would the splined shaft propeller to engine attachment be used?
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
Why are spinners used?
For better aerodynamics, as a mechanical protection for the hub and for aesthetic reasons
How Are spinners manufactured?
In one piece from spun aluminium alloy or glass fibre composites
What are spinner repairs limited to?
Sometimes stop drilling is allowed for cracks but usually damaged spinners are replaced
What is a blank?
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)
