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CPL Prep > Basic Gas Turbine > Flashcards

Basic Gas Turbine Flashcards

1
Q

TGT stands for what?

A

Turbine Gas Temperature

Measured in the turbine exhaust

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2
Q

How many ignitiors are present on most typical turbine engines?

A

Two

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3
Q

When starting a modern turbine engine, what is introduced last?

A

Fuel

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4
Q

What are the cons of an Axial Flow compressor system?

A

More complex design, engineering maintenance & costly
Vulnerable to Foreign Object Damage

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5
Q

What factors will reduce the thrust available from a turbine engine?

A
  • High humidity
  • High temperature
  • Low pressure
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6
Q

The purpose of rotor blades in a turbine engine is to…..?

A

Increase the kinetic energy of the air

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7
Q

Symptoms of a compressor stall includes what?

A
  • Rapidly rising turbine temp
  • Fluctuating fuel flow
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8
Q

How does the temp, density, pressure & velocity of a gas flow vary through a convergent duct at subsonic speed?

A

Temp, density & pressure reduce.

Velocity increases.

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9
Q

What is the purpose of a turbine shaft?

A

To attach the turbine disc to the drive compressor

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10
Q

What is the function of an oil relief valve?

A

To maintain oil supply to the engine if the oil filter or cooler gets blocked

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11
Q

What is the function of nozzle guide vanes?

A

To accelerate the velocity of combustion gas flow & present it to the first stage turbine at the correct angle of attack.

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12
Q

Turbine starters, otherwise known as nozzle guide vanes do what?

A

Sit prior to the turbine disc & increase the velocity of the combustion gas & reduce pressure

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13
Q

Divergent shape in the exhaust cone before convergence does what?

A

Slows air down to reduce energy losses to skin friction

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14
Q

The difference in temp, pressure, & velocity of air before it enters the compressor vs after does what?

A

Temp & pressure increase

Velocity slightly decreases

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15
Q

An advantage of a centrifugal compressor over an axial flow

A

Lighter

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16
Q

What are the advantages of a centrifugal compressor over an axial flow compressor?

A
  • Cheaper & easier to manufacture
  • More robust
  • Better handling of FOD
  • Relatively lower in weight
17
Q

What are disadvantages of using compressor bleed valves to prevent stalls & surges at low RPM?

A
  • Decreased mass airflow through engine.
  • Decreased thrust for a given setting.
  • Raises EGT due to less cooling air flowing through combustion chamber.
18
Q

The starter motor can be discontinued when?

A

Once self sustaining RPM is reached

19
Q

What are the cons of a centrifugal compressor?

A
  • Large frontal area = more drag.
  • Cannot have more than 2 stages due to energy losses between stages.
  • Poor acceleration leading to surging, stalling & choking.
20
Q

In an axial flow compressor, one purpose of the stator vanes in compressor are?

A
  • Decrease velocity
  • Prevent swirling
  • Boost pressure
  • Straighten airflow
21
Q

Turbine assemblies increase in diameter towards the rear of the engine, why?

A

To increase the torque from the assemblies.

22
Q

During the start sequence of a turbine engine, if there was insufficient fuel flow, what sort of abnormal start is most likely to occur?

A

Hung start

23
Q

Bleeding air is taken from where & what functions does it supply?

A
  • Pressurisation of cabin
  • Anti + de-icing
  • Heating of fuel
  • Sealing
  • Cooling
24
Q

The compressor ratio of an Axial Flow compressor is a function of what?

A

Number of compressor stages

25
Q

Axial flow compressor are designed to do what?

A

So that the pressure rises in both the rotor & stator blades

26
Q

What instrument is sued to set power on a turbo-prop aircraft?

A

Torque gauge

27
Q

What are the pros of an Axial Flow compressor?

A
  • Smaller frontal area = less drag.
  • Can provide a high compression ratio without large losses of efficiency.
  • Quick acceleration.
  • More stages can be added together to obtain a higher compression ratio.
28
Q

What is Specific Fuel Consumption?

A

Measure of the efficiency of an engine.

Fuel flow
/
Thrust

29
Q

What is a stage?

A

5 stage compressor

A paring of a rotor & stator.

5 rotors + 5 stators

30
Q

How does tenp, density, pressure & velocity of a gas flow vary through a divergent duct at subsonic speeds?

A

Temp, density & pressure increase.

Velocity decreases.

31
Q

Fluctuating core RPM & fluctuating fuel flow could be indications of what?

A

Compressor stall

CPL Prep (10 decks)

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