Turbine engines Flashcards
Explain the main difference and advantage of a turbofan engine over a turbojet engine
A turbofan engine uses a fan to bypass some air around the engine core to provide thrust. The advantage is that this provides an increase in thrust without an increase in fuel flow
Name the major components in a gas turbine engine
Air inlet, compressor section, combustion section, turbine section, exhaust section, gearbox and accessory section
What determines the amount of airflow through a turbine engine?
Forward speed of the aircraft, compressor speed and air density
Name the two types of compressors commonly used in turbine engines
Axial and centrifugal flow compressors
Name two different methods for attaching turbine rotor blades to the main turbine rotor disc
Dove tail, bulb or fir tree type root
What is a split compressor system?
Also called twin or dual spool compressors, these are connected to the turbine section with two rotor shafts, one inside the other
What are the different types of combustion chambers used in turbine engines?
Can, annular, can-annular and reverse flow annular
What prevents the combustion chambers from burning?
Cooling air along the inside of the liner
What is the purpose of the interconnecting tubes attached between can type combustion chambers?
For flame propagation during start
What functions do axial flow turbine nozzles perform?
They direct the mass airflow to drive the turbine rotor at a specific angle
How is thermal stress relieved on a turbine disc?
By directing bleed air onto the face of the disc or by cutting grooves in the disc
What are carbon seals used for in turbine engines?
They are used as oil seals for the rotor shaft bearings
What is a shaft horsepower?
It is an indication of the torque developed by a turboprop or turboshaft engine
Name the main components of a typical a.p.u
A small turbine for power and bleed air and an electrical generator
When is the greatest demand placed on an a.p.u?
When supplying bleed air
How is an a.p.u generally started?
With its own electrical starter and battery power
Where does the a.p.u get it’s fuel supply?
From one of the aircraft’s main fuel tanks
At what speed does a gas turbine a.p.u operate and how is the speed maintained?
At or near its rated speed regardless of electrical or pneumatic loads imposed. The a.p.u fuel control automatically adjusts the fuel flow to maintain the rated speed
What is used to prevent a heavily loaded a.p.u from exceeding it’s maximum egt?
A load control valve modulates the pneumatic load to maintain egts within limits
How is an a.p.u shut down and why is this procedure used?
After the a.p.u is unloaded by closing the bleed air valve, it is run for a specified amount of time to allow the egt to cool and stabilize. This cool down period is typically three minutes. If a heavily loaded a.p.u is abruptly shut down without any cool down period, damage could occur as a result of thermal shock
What powers the variable inlet guide vanes used on some a.p.us to regulate compressor intake airflow?
Fuel pressure
What is fan blade shingling?
It is the overlapping of the mid-span shrouds of the fan blade
When a turbofan or turbojet engine is shut down, what should a mechanic listen for during coast down?
Any rubbing sound or other unusual sounds coming from the engine
