Module 17.2 Propeller Construction Flashcards
How are wooden propellers constructed?
With several layers of wood bonded with a waterproof resin glue.
What is the most common wood used?
Birch
What is a “blank”?
When at least 5 layers of wood are laid down and glued together.
How long is the “blank” allowed to rest for?
A week
Why is the “blank” allowed to rest for a week?
To allow the equal distribution of moisture through all the layers.
After moisture has equally distributed through all the layers, what is the “blank” now called?
A white
Where is the cotton fabric sheathing applied and what does it do?
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.
What is done to the cotton fabric sheathing applied to the tip?
It’s doped
Why is the cotton fabric sheathing applied to the tip doped?
To protect it from deterioration by the weather and the sun’s ultraviolet (UV) rays.
Why is a protective metal tipping strip is rebated into the leading edge of the propeller?
To prevent damage from small stones during ground operations.
Why are small holes drilled in each propeller blade tip?
To release moisture and allow the wood to breathe.
What final coating paint is used on wooden propellers and what does this do?
Polyurethane paint which provides mechanical and UV ray protection.
What is the advantage of composite propellers over metal ones?
Lighter and stronger.
What is used to limit lightening strike damage to composite propellers?
Metal foil mesh incorporated on the surface.
If a composite propeller has a metal spar, what is it made from?
Titanium, aluminium alloy or stainless steel
Where does the spar run in a composite propeller with a metal spar?
Through the centre of the blade.
What is constructed around the metal spar
The fibreglass, kevlar or carbon fibre shell.
What does the spar in a propeller do?
Absorbs the centrifugal forces and bending loads.
What does the shell of a composite propeller do?
Give the propeller torsional rigidity.
What is the surface of a composite propeller protected by and what does this do?
Polyurethane paint which serves as protection against erosion and static charge.
What do composite propellers with no metal spar comprise of?
Carbon fibre components in the blade that form the hollow spar.
For composite spars without a metal spar, what is the hollow spar filled with?
Polyurethane foam
What are metal propellers constructed from?
Aluminium alloy or steel.
What material is most widely used for propellers?
Aluminium
How is the weight of steel propeller blades kept to a minimum?
They’re hollow
What is each blade divided into?
Stations
How are blade stations numbered?
From 1 onward in six-inch increments (15 cm) or the number of inches from the root of the blade toward its tip.
Where is the ‘master station’ identified?
In the propeller section of the maintenance manual
How can the ‘master station’ be marked on a blade?
A line drawn across the blade face.
What is a fixed pitch propeller?
A propeller where the blade angle (pitch) cannot be changed.
How is the pitch in a fixed pitch propeller determined?
In accordance with the purpose it will be used for.
What type of pitch is needed for steep climbing and towing?
Low (fine) pitch
What type of pitch is needed for a more gradual climb and cruising flight?
Higher (coarse) pitch
What are the two disadvantages of fixed pitch propellers?
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.
What is a controllable pitch propeller?
A propeller where the pilot can change the pitch of the blades in flight irrespective of the aircraft operating conditions.
What two controls are there for aircraft equipped with a controllable-pitch propeller?
Throttle control
Propeller control
What is a constant speeding propeller?
A propeller that is designed to automatically change its blade pitch to allow to maintain a constant RPM.
What mechanism is used to allow a constant speed propeller to work.
A constant speed unit.
What do constant speed units consist of?
A speeder spring and a set of fly weights.
Describe how the blade pitch is changed in a constant speed unit?
Oil is carried through a pilot valve under pressure in response to an under or over speed condition.
What happens to the fly weights if the propeller exceeds the preselected RPM?
They are forced outward.
What happens to the fly weights if the propeller under-speeds?
They swing inward.
What changes the tension on the speeder spring in a constant speed unit?
Over-speed or under-speed.
What are the three type of shaft?
Tapered Shaft
Splined Shaft
Flanged Shaft
What mates with the engine shaft taper?
The hub’s inverse taper.
What is used to secure the propeller to the engine in a tapered shaft?
A retaining nut that screws onto the engine shaft and presses the tapers together.
In a tapered shaft, how is the drive transmitted?
Through a key that is seated in slots in both the engine shaft and propeller hub.
What type of shaft is used for propellers with high output engines?
Splined shafts
When using a splined shaft, how is the propeller shaft connected to the engine crank shaft?
By reduction gearing.
The sizes of splined shafts are identified by what?
An SAE (Society of Automotive Engineers) number.
What type of shaft is used on most reciprocating and turboprop engines?
A flanged shaft
Why are spinners mounted?
For better aerodynamics, protection for the hub and aesthetics.
What are spinners manufactured from?
Aluminium alloy or glass fibre composites.
What is the spinner attached to?
The spinner backplate (or spinner bulkhead).
What should be done if there are cracks in the blade recesses or in the spinner mounting?
The parts should be replaced.
If a repair is permitted how should it be done?
Drilling to stop the crack.
