Chapter 3 - Turbine Engines - Oral Questions Flashcards
Explain the main difference and advantage of turbofan over turbojet engines?
A turbofan engine uses a fan to bypass some air around the engine core and to provide thrust. The advantage is that this provides additional thrust without increasing fuel flow
Name the major components in a gas turbine engine?
Air inlets, compressor section, combustion section, turbine section, exhaust section, gearbox and accessory section
What determines the amount of airflow through a turbine engine?
The 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 engine rotor blades to the rotor disks?
Dovetail-type root or Bulb-type root or Fir tree-type root
What is a split compressor system?
Also called dual or twin 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 air flow 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 grooves being cut 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 shaft horsepower?
It is an indication of the torque developed by a turboprop or turbo shaft engine
Name the components of a typical APU
A small power turbine for power and bleed air , and a electrical generator
When is the greatest demand placed on APU?
When supplying bleed air
How is an APU generally started?
With its own electrical starter and battery power
Where does the APU get its fuel supply?
From one of the aircraft’s main tanks
At what speed does a gas turbine APU operate and how is this speed maintained?
At or near its rated speed regardless of electrical or pneumatic loads imposed. The APU fuel control automatically adjusts the fuel flow to maintain the rated speed
What is used to prevent a heavy loaded APU from exceeding its maximum EGT?
A load control valve modulates the pneumatic load to maintain EGTs within limits
How is an APU shut down and why is this procedure used?
After the APU is unload by closing the bleed air valve, and it is run 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 APU is abruptly shut down without any cooling down period, damage could occur as a result of thermal shock
What powers the varible inlet guide vanes used on some APUs to regulate compressor intake airflow?
Fuel pressure
What is fan shingling?
It is the overlapping of the midspan shrouds of the fan blade
When a turbofan or turbojet engine is shut down, what should a mechanic listen for during coastdown?
Any rubbing sound or other unusual noise from the engine
