Air Systems Flashcards
What are the 3 types of air systems
Compressor
Clearance
Engine cooling
What does the compressor control system do
Protect compressor against stall and surge
How are air sub-systems controlled
By hydro-mechanical fuel control unit of FADEC system
What does variable bleed vanes do
Bleed air from LP compressor into fan discharge duct which protects the LP compressor against stall and surge
What components protect against stall and surge
Variable bleed vanes and variable stator vanes
Why does the HPC surge at low rotor speeds
The forward stages deliver too much air to the aft stages
What does the variable stator vanes optimise
Optimise efficiency of compressor at high power settings
What does the bleed valve improve at the HPC
improves engine start and acceleration
What are start bleed valves used for
Start sequence
What does the clearance control system do
Optimise tip clearing in turbines and compressors
What does clearance control systems match
Match expansion of stator case with expansion of engine rotor
What does passive clearance do
Continuous cooling airflow
What is active clearance
Use cooling air control valves to optimise tip clearance by controlling quantity of air going to turbine case
How are active clearance valves controllled
Hydro mechanical fuel control unit or FADEC
What air does a compressor clearance control system use
Warm air to hear rotor
Why is warm air used to heat rotor
Warm air increases the expansion on compressor rotor which decreases tip clearance
Where does external cooling system supply air to
Cavaties between engine cowlings and cases
What air does the external cooling system use
Ram air from fan & fan air from core
Where does the internal air system cover
All airflow below the engine rotors around the bearing compartment
What is the internal air system used for
Internal cooling and sealing purposes
What’s the tasks of the internal air system
Internal sealing
Pressure balancing
Internal cooling
What does pressure balancing do
Minimises axial loads on rotor bearings
What direction does compressor gas loads push rotors
Fwd direction
What direction do turbine loads push rotor
In aft direction
What prevents flammable vapours collecting in the engine compartment
External cooling system
What does the naca air inlet do
Picks up ram air as aircraft moves
Where is the naca air inlet
Lower part of fan cowl
What is bowed rotor
After engine shutdown engine can bend due to different expansion
What can a bowed rotor lead to
Hung start or rotor wear
How is bowed rotor prevented
Minimum wait time between engine shut down and start
How is engine cooler after shut down
Cooled by convection
