Chapter 3 Turbine engine

What is the main advantage of turbofan engines over turbojet engines?

A turbofan engine uses a fan to bypass some air around the engine core, providing additional thrust without increasing fuel flow.

What are the major components of a gas turbine engine?

Air inlet, compressor, combustion, turbine, exhaust, gearbox, and accessory section.

What factors determine the amount of airflow through a turbine engine?

The forward speed of the aircraft, compressor speed, and air density.

What are the two types of compressors commonly used in turbine engines?

Axial and centrifugal flow compressors.

What are two methods for attaching turbine engine rotor blades to the rotor disks?

Dovetail-type root, 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 types of combustion chambers are 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 interconnecting tubes 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 disk or by grooves being cut in the disk.

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 turboshaft engine.

What are the main components of a typical APU?

A small turbine for power and bleed air, and an electrical generator.

When is the greatest demand placed on an 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 fuel 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; the APU fuel control automatically adjusts the fuel flow.

What prevents a heavily 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 unloading by closing the bleed air valve, it is run for a specified time to allow the EGT to cool and stabilize.

What powers the variable inlet guide vanes on some APUs?

Fuel pressure.

What is fan blade shingling?

It is the overlapping of the midspan shrouds of the fan blade.

What should a mechanic listen for during coastdown of a turbofan or turbojet engine?

Any rubbing sound or other unusual noises from the engine.