15.12 - Air Systems Flashcards
What is tapped air from engines referred to as?
Parasite air flows - they reduce the total thrust or torque of the engine
Where is parasite airflow tapped from in a turbine engine?
The HP compressor
How is the exhaust cooled?
By an insulation blanket and by a cooling film.
What is another purpose of the cooling airflow for the engine compartment?
Removes flammable vapours
By what effect are the accessories cooled on the ground?
Venturi-effect. Ram air during flight
Why is a film of oil used between two flexing shafts rather than an abradable lining?
Oil does not produce as much friction as an abradable lining
How does a thread-type seal work?
It contains a threaded surface (like a barrel of a shotgun) and air from the compressor is fed out, repelling any oil that tries to escape
Where would you find a ring-type seal?
They are used to seal bearing chambers; except in hot areas where oil degradation due to heat can lead to the ring seizing in its housing and not freely moving when the shaft comes into contact with it.
When would you replace a carbon seal?
At major overhauls.
What is active clearance control (ACC)?
Comprising of a cooling manifold, bleed air cools the turbine casing and reduces the blade tip clearance as necessary
The engine shafts are experiencing axial loads in the forward direction of the compressor, and rear direction on the turbine. How is this carried?
By the location bearing - it carries the difference between both forward and rearward axial loads throughout the engine thrust range
What is the purpose of the pressure balance system?
It reduces the force exerted on the compressor thrust bearing
How does a thermal wing de-icing system derive it’s air from the engine?
Through a pressure regulating shut-off valve (PRSOV)
What happens to thrust and EGT when air is taken from the compressor for air conditioning or anti-icing?
Thrust decreases and EGT increases
What is bleed air pressure and shut-off cock pressure?
45 psi
