Chp 3 ( Air Systems) Flashcards
How are main shafts cooled?
Main shafts are cooled by compressor air fed through the bearing housing and into the hollow shaft.
How are main bearings cooled?
Main bearings are cooled by the lubricating oil.
What do oil/air seals use within the engine?
Oil/air seals use tapped air from the compressors.
Why does air migrate through the labyrinth seal?
The air, being at a greater pressure than the oil, migrates through the labyrinth seal preventing an oil loss.
What must be removed from the scavenge system?
The air that migrates through the labyrinth seal must be removed from the scavenge system.
What generates a thrust load on the supporting bearings?
The compressor blades, having aerofoil sections, generate a thrust load on their supporting bearings.
What subjects turbine spools to thrust?
The turbine spools are subjected to the thrust of the gas flow.
How is thrust loading reduced on bearings?
Tapped HP pressure air is fed onto the opposing face to reduce this loading.
How are combustion chamber components cooled?
A layer of air is imposed between the parts to be cooled and the hot gases.
How is the outer wall of the combustion chamber cooled?
A proportion of the cooler compressor delivered air is ducted between the outer wall and flame tube.
How is the flame tube protected from burning gases?
Compressor delivery air is progressively admitted through a series of annular slots throughout the length of the tube.
What is the limiting factor on gas turbine output?
The turbine entry temperature (TET) is the limiting factor on gas turbine output.
How is the temperature of turbine blades reduced?
Air is tapped from the compressor delivery air and fed through the hollow turbine blades to reduce their temperature.
What is the engine internal air system?
The engine internal air system is defined as airflow that does not directly contribute to the engine thrust.
What are the important functions of the internal air system?
The internal air system performs several important functions for safe and efficient engine operation, including sealing, ventilation, anti-icing, air pressure supply, pressure balancing, and internal cooling.
What are the internal functions of the air system?
Internal functions include:
- Sealing of bearings and labyrinth seals
- Ventilation (purge) of torch igniters
- Anti-icing
- Air pressure to the FCU
- Pressure balancing of HP and power turbines
- Internal cooling
What are the external functions of the air system?
External functions include:
- Cabin air conditioning
- Sand filter system
- Winch motor operation
- Cooling accessories
What is the purpose of internal cooling in the air system?
Various methods are used to cool components, and sometimes the same system may be required to cool more than one component.
What components are involved in the air system pathway?
Components include:
- LP Compressor
- HP Turbine
- HP Compressor
- LP Turbine
- Various bearings
- Air Transfer Ports
What is the purpose of external accessories in an engine?
External accessories, such as the starter/generator, produce considerable heat and usually require their own cooling system.
How is excess heat from friction in gears typically managed?
Excess heat due to friction in gears is normally conducted away by the lubricating oil.
What cooling method is often used for engine-mounted accessories?
Atmospheric air, ducted through intake louvres, is often used for cooling engine-mounted accessories.
What can cause ice formation on engine components?
Ice formation can occur on engine intakes and other components in low temperatures where water vapour is present, such as flying through clouds or during ground operation in foggy conditions.
What are the hazards associated with ice formation on engine components?
Ice changes the aerodynamic properties of components and presents a considerable FOD hazard if it breaks off and is ingested into the compressor.
What are the two forms of ice protection systems?
Ice protection systems usually take one of two forms: hot air or electrical.
How does a hot air system work for ice prevention?
In a hot air system, air is taken from the H.P. area of the compressor and ducted to areas that require ice removal or prevention.
What happens to the air used in a hot air system after it serves its purpose?
The air is then passed back into the air intake or vented overboard.
What is the purpose of electrical ice protection systems in turboprop and turboshaft engines?
They use heater mats made of conductors sandwiched between layers of neoprene or glass cloth impregnated with resin, bonded to the outer skin of the intakes or cowlings.
What do electrical ice protection systems consist of?
Electrical elements, glass cloth layers, continuously heated elements, intermittently heated elements, and a junction box.
What cockpit indications may a pilot see when anti-icing is switched on?
A slight rise in JPT (Jet Pipe Temperature) and a slight drop in Engine RPM.
