Powerplant Chapter 03 Flashcards

Turbine Engines

1
Q

Explain the main difference and advantage of turbofan over turbojet engines.

A

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.

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2
Q

Name the major components in a gas turbine engine.

A

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

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3
Q

What determines the amount of airflow through a turbine engine?

A

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

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4
Q

Name the two types of compressors commonly used in turbine engines.

A

Axial and centrifugal flow compressors.

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5
Q

Name two different methods for attaching turbine engine rotor blades to the rotor disks.

A

Dovetail-type root -or- Bulb-type root -or- Fir tree-type root.

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6
Q

What is a split compressor system?

A

Also called dual or twin spool compressors, these are connected to the turbine section with two rotor shafts, one inside the other.

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7
Q

What are the different types of combustion chambers used in turbine engines?

A

Can, annular, can-annular, and reverse flow annular.

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8
Q

What prevents the combustion chambers from burning?

A

Cooling air along the inside of the liner.

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9
Q

What is the purpose of the interconnecting tubes attached between can-type combustion chambers?

A

For flame propagation during start.

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10
Q

What functions do axial flow turbine nozzles perform?

A

They direct the mass airflow to drive the turbine rotor at a specific angle.

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11
Q

How is thermal stress relieved on a turbine disc?

A

By directing bleed air onto the face of the disk, or by the grooves being cut in the disk.

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12
Q

What are carbon seals used for in turbine engines?

A

They are used as oil seals for the rotor shaft bearings.

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13
Q

What is shaft horsepower?

A

It is an indication of the torque developed by a turboprop or turboshaft engine.

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14
Q

What is the principal advantage of AC current over DC current?

A

They provide ground electrical or pneumatic power for aircraft systems when the engines are not running.Pneumatic power can be used for engine starting, ground heating or air conditioning, and anti-icing. Many APUs may also be used as an emergency source of inflight electrical power.

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15
Q

Name the main components of a typical APU.

A

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

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16
Q

When is the greatest demand place on an APU?

A

When supplying bleed air.

17
Q

Where does an APU gets its fuel supply?

A

From one of the aircraft’s main fuel tanks.

18
Q

At what speed does a gas turbine APU operate and how is this speed maintained?

A

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.

19
Q

What is used to prevent a heavily loaded APU from exceeding its maximum EGT?

A

A load control valve modulates the pneumatic load to maintain EGTs within limits.

20
Q

How is an APU shut down and why is this procedure used?

A

After the APU 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 APU is abruptly shut down without any cooling down period, damage could occur as a result of thermal shock.

21
Q

What powers the variable inlet guide vanes used on some APUs to regulate compressor intake airflow?

A

Fuel pressure.

22
Q

What is fan blade shingling?

A

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

23
Q

When a turbofan or turbojet engine is shut down, what should a mechanic listen for during shutdown?

A

Any rubbing sound, or other unusual noises from the engine.

24
Q

How is an APU generally started?

A

With its own electrical starter and battery power.