M15.12 Air systems Flashcards
What are the three engine air subsystems?
The compressor control system
The clearance control system
The engine cooling system
What does the compressor control system do?
Protects the engine compressors against stall and surge as well as increasing efficiency
What does the clearance control system do?
Maintains tip clearance
Increases efficiency
What three typical subsystems are found in the compressor control system?
Variable bleed valves
Variable stator vanes
HP compressor bleed Valve system
How are the three main engine air subsystems controlled?
Either by the HMU or by the fadec
What do VBV’S do?
Control the amount of airflow into the HP compressor, usually installed in the fan frame behind the LP compressor
What two methods protect the HP compressor from stall and surge?
VBS’S
Variable stator vanes
The two combined methods prevent too much air entering the HP compressor, as well as increasing the efficiency of the compressor
What type of bleed valves can be found on some engines?
So called start bleed valves, only used for starting.
Found at the MID or AFT stages of the HP compressor
What is the purpose of clearance control?
To keep the blades of the turbine disks, and potentially the HP compressor, at an optimum clearance from the casing. the control system matches the expansion and keeps the gap small
What are the two types of clearance control systems?
Active and passive
Explain passive clearance control?
The flow rate of the air is fixed, so the system cannot meet the requirements of all operating speeds
Explain active clearance control?
The system can modulate the flow rate to meet the requirements of engine speed
How is the compressor clearance control system different than that of the turbine?
This system uses hot air instead of cold air to decrease the tip clearance
With the engine cooling system, What are the common tasks of the internal air system?
Internal sealing
Pressure balancing
Internal cooling
Where is the internal cooling air taken from?
Some points on the primary airflow at the engine compressors or turbine.
This are is first used for pressure balancing and then for cooling
Where is the air for bearing sealing taken from?
LP compressor - vents overboard through the hollow N1 shaft
How can the HP NGV and blades be cooled?
By HP compressor discharge air,
How is the first stage and rotor drum of the LP turbine cooled?
By HP turbine and bleed air from the IP stages of the HP compressor
How else may the rotor drum of the HP compressor be cooled?
Bleed air from the LP compressor
What other components can be cooled by the LP compressor bleed air?
The cavity under the combustion chamber and the aft part of the LP turbine rotor drum
What happens to internal cooling air when it is finished with?
Escapes into the nozzle of the engine
What is pressure balancing?
The forces acting on the shafts in the engine are effected by both the compressor sections forces and the turbine section forces. both forces work in opposition to each other. By using pressure balancing it is possible to relive the axial stresses on each spool
How is the fan compartment usually cooled?
by NACA ducts utilizing ram air, this is air is then discharged overboard
How is the core compartment cooled?
Is cooled by fan air picked up by the use of a fan discharge duct, this air is then ejected through the jet nozzle
