M15.12 Flashcards
What are the 3 subsystems of the air system?
Compressor control system
Clearance control system
Engine cooling system
What controls all the sub systems?
The hydro mechanical fuel control unit
What’s the main function of the compressor control system?
To protect engine compressor against stall and surge
How do compressor bleed vanes prevent stall and surge?
By bleeding off air in critical operation components
How do variable stator vanes protect against stall and surge?
By controlling airflow into compressor
What are start bleed valves?
Improve engine start and acceleration
What is the purpose of the clearance control system?
Optimise tip clearance
Where is the clearance control system found?
At HP and LP turbines
What are active clearance control valves controlled by?
Either:
Hydro mechanical fuel control unit
Or
FADEC system
The clearance control system doesn’t use cooling air, what does it use instead?
Warm air to heat the rotor
What does the external cooling system do?
Supply’s cold air into the cavities between engine cowling and engine cases
What does the internal cooling system do?
Covers all airflow below the engine rotors and at the bearing compartments
As well as cooling what is internal air also used for?
Sealing
Where is internal cooling important?
Areas of engine turbine
What does airflow escape from?
Exhaust nozzle
The gas loads in the compressors and turbines result in what?
Opposite axial forces on the rotor bearings
What components does the external cooling system cool?
Engine case
All components in the fan
What cools the fan compartment?
RAM air
What cools the core compartment?
Fan air
What type of ventilation cools the core compartment when the engines are running?
Positive ventilation
After shut down why is the engine able to bend?
And what is this called?
Because of the different expansion between the upper and lower zones
It’s called bowed rotor
What can bowed rotor lead to?
Hung starter
What is done to reduce the risk of hung starter?
There is a waiting time between engine shut down and engine start
How does the engine cool after shut down?
By convection
