Module 17.2 Propeller construction Flashcards
What is the most commonly used wood propeller construction?
Birch
What forms a blank?
At least 5 layers of wood glued together
Why is the blank left for a week after being roughly shaped?
Equal moisture distribution
After the blank has been left for a week what is it now referred to as?
A white
A cotton fabric sheathing is then applied to the outer 12 to 15 in (30 to 38 cm) of the tip, for what purpose?
Reinforce the strength of the thin sections at the tip
What is done to the fabric to protect it?
Doped
To prevent damage what is rebated onto the leading edge?
Protective metal strip
What metals are used to protected the LE?
Brass, stainless steel, monel (nickel/copper alloy) or terneplate (steel coated with a lead/tin alloy).
How is the tipping secured in thick blade sections?
Countersunk screws
Where are copper rivets placed?
Near the tip
How are the rivets safetied?
Solder
What is the purpose of drilling small holes in the tip?
Release moisture and allow the wood to breathe
Some propellers have a final coating of polyurethane paint for which purpose?
Mechanical and UV protection
How are wooden controllable pitch propellers secured to the metal sleeve?
Using lag screws
What are the methods of securing the propeller to the engine?
- Splined
- Tapered
- Forged steel hub
- Bolted
What LE protection do composite propellers have?
Nickel or CRES
How can Composite blades with a spar be constructed?
Spar, coated in fibreglass, kevlar or carbon fibre shell with foam or honeycomb in front and behind the spar.
What loads does the spar absorb?
Centrifugal forces and bending loads
What does the composite shell give the propeller?
Torsional rigidity
What is on the inner and outer surface of the LE?
Heating element - inner
Metal guard - outer
How is the blade surface protected? (composite)
Conducting polyurethane paint
What purpose does the paint coat serve? (composite)
Erosion protection and prevents it from being statically charged
How are composite blades without a metal spar constructed?
Two carbon fibre components in the blade that form the spar. Hollow core filled with foam
What is used to horizontally balance the blade?
Lead wool in a hollow balancing tube
How is the lead wool retained in place?
Use of a rubber plug
What are the two different types of metal propeller?
Aluminium alloy or steel
What type of propeller has better cooling properties for reciprocating engines?
Aluminium alloy
Are steel propellers commonly used?
No, not really anymore
How do you make steel blades lighter?
Hollowed out
How big is a blade station?
6 inches
How are the blade stations numbered?
From root to tip
Where is the master reference station on a fixed pitch propeller?
75% from centre of rotation
Where is the master reference station on a variable pitch propeller?
50 to 75% from the centre of rotation
What is the master reference station also a reference point for?
Where most of the thrust of the blade acts
Can the pilot control the angle of a fixed pitch propeller?
No
What are the two types of controllable pitch propellers?
- Two position (high or low pitch)
- Variable pitch
How does the propeller control regulate engine RPM?
Manipulating blade angle
Why is it necessary to change the blade angle?
To maximise the blade angle
In older systems how is blade angle manipulated?
Crank handle which drives a pinion gear through a cable
A constant speed propeller is what?
A propeller that is designed to automatically change its blade pitch to allow it to maintain a constant RPM
How does a constant speed unit work?
Principle of centrifugal force and incorporates a speeder spring edna set of fly weights
How is constant speed maintained?
Constant speed unit or governor
In an engine overspeed condition what occurs to the piston? (Constant Speed Unit Governor)
Flyweights separate and piston rises. Allowing oil pressure to be directed to the propeller to push it to a coarser angle
In an engine underspeed condition what occurs to the piston? (Constant Speed Unit Governor)
Flyweights come closer and piston sinks. Allowing oil pressure to leave the propeller to allow the blade to move to a finer blade angle
What occurs at normal speed? (Constant Speed Unit Governor)
Hydraulic lock
What are three types of shafts?
- Tapered shaft
- Splined shaft
- Flanged shaft
How is the drive transmitted in a tapered shaft?
Key that is seated
When are splined shafts used?
High output radial engines
Why is one end of the splined shaft threaded?
To accommodate the hub nut
How may the propeller shaft be connected to the engine crankshaft?
Large aircraft - Reduction gearbox
Small aircraft - extension of crankshaft
When are flanged shafts used?
Modern turboprop and reciprocating
What does a flanged shaft have for synchronisation?
Index pins
Why are spinners mounted?
- Protection
- Aerodynamics
- Aesthetics
What loads are extremely high on the spinner?
Dynamic loads
How may cracks be stopped on a spinner?
Stop drilling
On spinner installation, it must be ensure that there is no what?
Noticeable wobble
