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CAA Module 15 > Module 15.16 Turboprop engines > Flashcards

Module 15.16 Turboprop engines Flashcards

1
Q

Is a turboprop engine fuel efficient?

A

Yes

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2
Q

How does the turbine section differ on a turbo prop?

A

More turbines

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3
Q

How much power can a turboprop extract to rotate the propeller?

A

95%

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4
Q

What is the only connection between the gas generator and the free power turbine?

A

Gas flow

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5
Q

On an engine with a free power turbine, how can the engine be used as a APU?

A

Putting the propeller brake on

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6
Q

How do Gear/Direct-Coupled turbine engines differ from free power engine turbine engines?

A

More turbine discs which remain mechanically connected

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7
Q

Because the propeller is driven directly by the engine, what adjusts the propeller pitch for the power requirements?

A

Integrated propeller control system

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8
Q

Under normal conditions propeller speed and engine speed are what?

A

Constant

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9
Q

To maintain a constant speed condition what must be co-ordinated?

A

Propeller pitch and fuel flow

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10
Q

What is the purpose of the reduction gear assembly?

A

To reduce high rpm from the engine to a propeller rpm that can be maintained without exceeding the maximum propeller tip speed

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11
Q

What are the two main reduction gear systems?

A
  • Parallel spur gear type
  • Epicyclical type
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12
Q

For high torque reductions what gear system is used?

A

Epicyclic gears

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13
Q

What does the reduction ratio depend on?

A

Relationship between the size of the driving and fixed gear

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14
Q

Why is the oil for the gear systems of higher viscosity than turbo-jet engine oil?

A

Heavier loads imposed on the gears

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15
Q

What is the advantage of parallel spur gears?

A

Mechanically simple

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16
Q

What two types of spur gears are used?

A

Straight cut or helical

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17
Q

What can be said about straight cut spur gears?

A

Easier to cut, low friction losses but are extremely noisy

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18
Q

What do helical gear teeth allow for?

A

More gradual onset of torque changes, quieter but less efficient transmission

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19
Q

What gear in the planetary gear system is driven by the power shaft?

A

Sun gear

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20
Q

In the planetary gear system what is the gear ratio not affected by?

A

Number of planet gears

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21
Q

How is the reduction ratio calculated?

A

Driven teeth/driving teeth

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22
Q

What is another name for the annulus?

A

Ring gear

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23
Q

Which direction does a fixed annulus rotate?

A

Same rotation direction as the power shaft

24
Q

Which direction does a rotating annulus rotate?

A

Opposite rotation direction as the power shaft

25
Q

What is alpha range?

A

Efficient and flexible means of using engine power in flight

26
Q

When would beta range be used?

A

Ground handling or reversing

27
Q

To control both the engine and the propeller what do most modern turboprop engines utilise?

A

Dual FADEC

28
Q

When is the feathering system used?

A

In flight when the engine is shut down

29
Q

Can the propellers be unfeathered during flight to restart the engine?

A

Yes

30
Q

Is there propeller stops on a turboprop engine?

A

No as it is a direct coupled engine

31
Q

What does the throttle quadrant include?

A

Integrated engine and propeller controls

32
Q

What engines can be fitted with a single thrust lever?

A

Gear-coupled

33
Q

What governs the maximum rpm of the engine in single lever control?

A

Propeller Control Unit (PCU)

34
Q

When is dual lever controlled used?

A

Turboprop engines with a free turbine

35
Q

What is each lever for in dual lever controls?

A
  • Power lever
  • Propeller control lever
36
Q

What does the thrust lever control?

A

Fuel flow from idle to take off range

37
Q

What does the thrust lever schedule when the lever is moved from idle to reverse?

A

Fuel flow and the blade angle

‘BETA’ or ‘Ground operating range’

38
Q

In the beta range, what does the control unit do to the oil pressure?

A

Change from ‘flight fine’ to ‘ground fine’

39
Q

What is the propeller lever connected directly to?

A

PCU

40
Q

How does the PCU select the required rpm for the propeller?

A

Applying or releasing pressure on the governor control spring

41
Q

When does the propeller lever not influence blade angle?

A

In beta range

42
Q

What is the purpose of the control lock?

A

Ensure control surface do not flutter when on the ground

43
Q

What can overspeed cause?

A

Rapid and total failure in flight

44
Q

What angle do centrifugal forces try to reduce the blade angle to?

A

Zero

45
Q

Why are the centrifugal forces changing the blade angle not desirable?

A

Windmilling will occur

46
Q

What angle is the feathering angle?

A

90° to the plane of rotation

47
Q

The action of propeller feathering is carried out by what?

A

Automatic Drag Limiting System (ADLS)

48
Q

When must the propeller be feathered?

A

If oil supply to the propeller fails

49
Q

When is the electrical feathering pump energised?

A

Negative torque detected

50
Q

What are two backup locking mechanisms?

A

Mechanical and hydraulic

51
Q

If oil pressure fails what will the mechanical pitch lock move under?

A

Spring force, to drain oil holding the locks out of engagement

52
Q

What movement do pitch locks allow?

A

Allow the piston to move to a coarser pitch but NOT a finer pitch

53
Q

How is the shuttle valve moved in the hydraulic pitch lock system?

A

Under spring pressure

54
Q

What does the propeller overspeed governor do?

A

If the propeller speed exceeds 105% it will dump oil pressure to the return, causing the blade angle to increase

55
Q

In the event of turbine shaft failure what does the mechanical system do?

A

Shut off the engine metered fuel supply

56
Q

What are the 3 methods of stopping overspeed?

A
  • Pitch locking
  • Overspeed governor
  • Turbine shaft mechanical system

CAA Module 15 (18 decks)

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