17.6 Propeller Maintenance Flashcards
What is blade tracking?
The ability of one blade to follow the other in the same plane of rotation
What are the two main methods for checking a blades tracking?
Flat bench method
Block or pointer method
How does the flat bench method work?
Requires a smooth board, move the tip fore and aft through its small range making small marks the lines should not be separated by more than 3mm
What is the block or pointer tracking method?
Place a solid object couple of inches off the ground next to the tip so it touches it rotate the propeller slowly to determine if the next blade tracks the same point within 1/16 inches of each other
What is a crack?
is an irregular shaped separation within a material, usually visible as a narrow opening at a surface
What is a debond?
is a separation of the metal erosion shield from the composite material in the blade
What is a delamination?
is an internal separation of the layers of composite material
What is a depression?
is a surface area where the material has been compressed, but not removed, by contact with a sharp object
What is a distortion?
is an alteration of the original shape or size of a component
What is an exposure?
is a condition in which material is left open to the action of the elements
What is a gouge?
is a small surface area from which material has been removed by contact with a sharp object
What is impact damage?
occurs when the propeller blade or hub assembly strikes or is struck by an object
What is a scratch?
is a removal of paint and a small amount of material not exceeding (0.5 mm)
What is a nick?
small indent or notch, not deeper than 0.5 mm
What is a split?
is a delamination of a composite blade extending to the blade surface, normally found near the trailing edge or tip
What is a dent?
hollow or mark left by impact, blow or pressure
What is erosion?
is a gradual wearing away or deterioration due to the action of air contaminations (sand, dust, etc.)
What is corrosion?
is a gradual wearing away due to a chemical action
Where does fatigue usually occur?
Fatigue failures normally occur within a few inches of the blade tip
What is visual inspection?
The primary defence against early failure of propellers. When inspecting propellers, it is necessary to use touch and other senses, as well as visual cues
What is a tap test?
Composite blades are inspected for delaminations and debonds by tapping the blade or cuff (if applicable) with a metal coin, if a change in sound is heard you know there is damage
What is penetrant inspection?
Fluorescent penetrant is far superior to non-fluorescing penetrant (visible dye penetrant), particularly for detecting small surface cracks on propeller blades
What is an ultrasonic inspection?
Ultrasonic inspection uses specialised equipment to send, receive, and process sound waves to detect flaws on or below the surface of the component being tested
What is an eddy current inspection?
Eddy current inspection uses specialised equipment to generate and measure an electric field that detects flaws at or slightly below the surface of the component being inspected
What is magnetic particle inspection?
Magnetic particle inspection is conducted at an appropriately approved maintenance facility. It is useful for finding cracks, inclusions, and imperfections at or near the surface of ferrous parts
What is erosion?
The loss of material from blade surface by the action of small particles such as sand or water and is usually present on the leading edge close to the tip
What do composite blades have to try prevent erosion?
An erosion strip
What is external corrosion?
External corrosion on metal blades, hubs, and other components poses a serious problem
What is internal corrosion?
Internal corrosion may exist where moisture may collect in internal cavities such as hubs, blade clamps, and pitch control mechanisms
What are the three types of metal corrosion?
Surface corrosion
Pitting
Inter granular corrosion
What is surface corrosion?
The loss of surface metal due to chemical or electro-chemical action with visible oxidation products usually having a contrasting color and texture to the base metal
What does pitting look like?
Pits consist of visible corrosion cavities extending inward from the metal surface
Where does intergranular corrosion occur?
In grain boundaries
Why does intergranular corrosion occur?
The presence of intergranular corrosion may be the result of the continued presence of moisture such as under a decal, in a fastener hole, or where the anodise and paint protective barriers have been lost
What is impact damage?
Damage from FOD can include a broad spectrum of damage, from no visible damage, in composite blades, to a small nick, to severe ground impact damage
What are wood and composite propellers susceptible to?
Internal damage from small stone strikes that can create delamination or micro cracks
What can moisture cause?
The expansion of existing cracks and delaminations
What can propeller roughness be caused by ?
- Bent blades
- Blades out of track due to an improper mounting of the propeller on the engine shaft
- Imbalance
- Propeller loosely mounted on the engine shaft
- Blade angles between blades out of tolerance with respect to each other
- Spinner imbalance due to improper mounting or to dirt, snow or ice inside the shell
What are the three different types of balancing ?
- Static balancing
- Dynamic balancing
- Aerodynamic balancing
What is static and dynamic imbalance caused by ?
Unequal mass distribution
Why is aerodynamic balancing carried out ?
To ensure that each blade delivers an equal amount of thrust
When might dynamic balancing be carried out ?
When an aircraft has large or fast running propellers
When will a body capable of rotating about a fixed point be in static balance ?
When it’s centre of gravity lies on the axis of rotation
When a body is in static balance, when spun, where will it stop ?
In a random position
Where will static balancing be Carried out ?
Either at the manufacturer, overhauled or an approved propeller repair facility
What planes are checked during static balancing ?
Horizontal and vertical planes
What is dynamic balancing ?
Balancing the propeller to reduce the moment of imbalance
What should dynamic balancing be carried out on ?
A running engine
What is the aim of dynamic balancing ?
To eliminate vibrations
Why isn’t dynamic balancing carried out on small propellers ?
Their centre of gravity is too small
Why might a propeller that isn’t totally aerodynamically balanced cause vibrations ?
Total thrust, being off centre rotates with the propeller, causing vibrations
What causes aerodynamic imbalance ?
Blades being a different shape, causing different amounts of lift
What can make vibration due to aerodynamic imbalance worse ?
Increasing pitch and thrust
Blades can be aerodynamically balanced in two ways, what are these ?
Thrust, indicated by ACFT
Torque, indicated by ACFQ
When is aerodynamic necessary ?
For propellers with high performance
What should the reference point for aerodynamic balancing be ?
The master blade
What is the aerodynamic balancing process known as ?
Blade indexing
What is a universal blade protractor used for ?
Used to measure the propeller blade angle at a specific blade station to determine if the propeller is properly adjusted
What is built into the universal blade protractor to ensure more accurate readings ?
A spirit level
Where is the blade angle referenced from ?
From the propeller plane of rotation
Where is the propeller plane of rotation in reference to the crankshaft centreline ?
Ninety degrees to the crankshaft centreline
What are examples of static checks ?
-flight fine pitch stop
Auto coarsening
Manual feather
Autofeather
Unfeather
What are static checks ?
Certain checks in the propeller and control system can be carried out without the need of an engine run
When are static checks normally carried out ?
Prior to an engine run
What are the two subcategories of piston engines?
- normally aspirated engines
- supercharged engines
What is the power output in relation to in piston engines ?
Manifold air pressure
What is reference RPM ?
When your manifold pressure reads 0 boost, the RPM must reed the reference RPM
How should the propeller be adjusted when testing with Reference RPM ?
Fine pitch
How should the aircraft face when doing engine runs ?
Into the wind
How is engine power measured in a turboprop?
Shaft horse power
Why are performance checks carried out ?
To ensure the continued safe operation of the propeller/ engine
What is the relationship that is commonly monitored during performance checks ?
Torque ,rpm ,fuel flow and EGT
What is the relationship that is commonly monitored during performance checks ?
Torque ,rpm ,fuel flow and EGT
When must anti icing be on when doing an engine run ?
If the temperature is below 10°C and there is visible moisture in the air
