15.16

Question 1

Where is a turboprop engine the most efficient power source?

Answer 1

From aircraft operating from 483 to 725 km/h (300 to 400 mph)

Question 2

What is the downside of the turboprop engine compared to the turbojet?

Answer 2

They are more complicated and heavier

Question 3

What type of engine has the best fuel consumption out of any turbine engine?

Answer 3

Turboprop

Question 4

How much of the total power produced is used?

Answer 4

95%

Question 5

In a turboprop engine what is the core engine commonly known as?

Answer 5

A gas generator or gas producer

Question 6

What does the core engine produce?

Answer 6

High-velocity gases that provide the energy to drive the power turbine

Question 7

What is special in regards to the gas generator and the free-power turbine?

Answer 7

There is no mechanical connection (Gas flow is the inly connection)

Question 8

What are the 4 advantages of a free-power turbine engine?

Answer 8

Vibration is not directly transmitted to the gas generator from the propeller/reduction gearbox
Engine is easier to start (especially in cold weather)
Propeller can be held at low rpm during taxi (low noise and blade erosion)
Propeller brake can be used to prevent propeller from turning so engine can be used as an APU

Question 9

How to gear/direct coupled turbines differ from free-power turbines?

Answer 9

The addition of extra turbine discs which remain mechanically connected to the compressor and reduction gearbox

Question 10

What adjusts the propeller pitch for the power requirements of the engine?

Answer 10

A complex integrated propeller control system

Question 11

What is the same at normal operating conditions?

Answer 11

The propeller speed and engine speeds are constant

Question 12

What must be coordinated to maintain a constant speed condition?

Answer 12

Propeller pitch and fuel flow

Question 13

What must change about the propeller when the fuel flow changes and why?

Answer 13

The propeller pitch to maintain a constant speed

Question 14

What is the function of the reduction gear assembly?

Answer 14

Reduce the high rpm from the engine to a propeller rpm

Question 15

What is important about the propeller rpm?

Answer 15

It must not exceed the maximum propeller tip speed (speed of sound)

Question 16

What is reduction achieved using?

Answer 16

Through a series of both spur gears and epicylic gears

Question 17

What will smaller and larger reductions be done by?

Answer 17

Smaller - Spur gears
Larger - Epicyclic gears prevent torque couples forming

Question 18

What does the reduction ratio depend on?

Answer 18

The relationship between the size of the driving and fixed gear

Question 19

What are the gears used in engine reduction gearboxes made of and why?

Answer 19

High-quality alloy-steel forgings because of the high stresses they endure

Question 20

What do ball bearings do in larger shafts?

Answer 20

Absorb and transmit all loads imposed on them to the casing

Question 21

What are the 2 ways reduction gearboxes are lubricated?

Answer 21

By the engine lubrication systems
Their own self-contained system

Question 22

Why is the viscosity of oil higher than that for a turbo-jet engine?

Answer 22

Because of the heavier loads imposed on the gears

Question 23

What are the 2 types of reduction gears?

Answer 23

Parallel spur gear type
Epicyclical type

Question 24

What is an advantage of a parallel spur gear?

Answer 24

They are mechanically simple

Question 25

What type of gears can a parallel spur gear be?

Answer 25

Straight-cut Helical

Question 26

What are the 2 advantages and 1 disadvantage of straight-cut gears?

Answer 26

They are easier to cut and have the lowest friction losses They are very noisy

Question 27

What do torque changes result in and what does this require?

Answer 27

High loading on the individual gear teeth either high sideways loads, requiring large heavy-duty bearings

Question 28

What is an advantage and disadvantage of helical gear?

Answer 28

Quieter But less efficient transmission

Question 29

How is an axial component on the helical gear handled?

Answer 29

Either a ball or tapered roller bearing

Question 30

What does an epicyclic arrangement incorporate?

Answer 30

A sun gear wheel on the power turbine shaft, driving several planet gears that are engaged with either a fixed or rotating ring gear or annulus

Question 31

Is the reduction gear ratio affected by the number of planet gears or number of teeth on them?

Answer 31

No

Question 32

What is a fixed annulus?

Answer 32

When the outer fixed gear ring or annulus is fixed stationary

Question 33

What is a rotating annulus?

Answer 33

When the arrangement rotates on fixed pinion shafts

Question 34

What direction does the ring gear connected to the propeller shaft turn?

Answer 34

The opposite direction of rotation to the power turbine shaft

Question 35

What is alpha range?

Answer 35

When the aircraft is in flight

Question 36

What is beta range?

Answer 36

When the aircraft is on ground

Question 37

What can the propeller provide when in beta range?

Answer 37

Zero or negative thrust

Question 38

What do modern turboprop engines utilise to control the engine and propeller?

Answer 38

A duel FADEC system

Question 39

What does FADEC stand for?

Answer 39

Full Authority Digital engine Control

Question 40

What is the spinner assembly and what does it do?

Answer 40

A cone-shaped configuration that mounts on the propeller and encloses the dome and barrel to reduce drag

Question 41

What does a turboprop engine have when it's shut down in flight?

Answer 41

A feathering system

Question 42

Can the propeller be unfeathered during flight if the engine needs to be started again?

Answer 42

Yes

Question 43

Where is the throttle quadrant located and why?

Answer 43

On the central pedestal in the flight deck, so both flight crew members can operate the levers

Question 44

What is on the throttle quadrant?

Answer 44

Integrated engine and propeller controls

Question 45

What is a single-lever control?

Answer 45

Both the fuel and propeller control units are interconnected (forward flow increases fuel flow and selects a higher rpm)

Question 46

What does the Propeller Control Unit (PCU) govern?

Answer 46

The maximum rpm of the engine

Question 47

What takes over from the PCU when the rpm has risen to s predetermined level?

Answer 47

The fuel control unit, which will inhibit the rise of rpm

Question 48

Where are duel-lever controls used?

Answer 48

Turbopropeller engine with a free turbine

Question 49

What are the 2 levers used for in a duel-lever control?

Answer 49

One is a power lever One is a propeller control lever

Question 50

What does a thrust lever do?

Answer 50

Schedule fuel flow from idle to take-off

Question 51

What does the thrust lever do when put into reverse?

Answer 51

Schedules fuel and the blade angle from +20 to -20 degrees

Question 52

What moves the blade angle?

Answer 52

Oil pressure

Question 53

What does a propeller lever do and what is it connected to?

Answer 53

Selects the required rpm by applying or releasing pressure on the governor control spring, it is connected directly to the PCU

Question 54

When does the propeller level operate/not operate the propeller?

Answer 54

Operates it in the normal constant speed range, but doesn't operate it when the propeller id in the beta range

Question 55

Where is a control lock located?

Answer 55

On the control quadrant

Question 56

What does a control lock ensure?

Answer 56

That the surfaces do not flutter excessively on the ground with the engines running

Question 57

What does overspeed cause?

Answer 57

Extreme stress to the propeller and the engine that can lead to rapid and total failure in flight

Question 58

How does the propeller balance engine power output?

Answer 58

By absorbing it by presenting the blades at an angle to the airflow (blades are not aligned with the plane of the propeller rotation)

Question 59

How does the blade angle change mechanism work?

Answer 59

It is hydraulically operated by the engine oil

Question 60

What would happen if the engine failed during flight due to centrifugal twisting motion?

Answer 60

The blades will try to return to a zero angle

Question 61

What does the blades being at a zero angle do?

Answer 61

Presents the blades as a negative angle of attack and the propeller will windmill to uncontrollable rpm, the propeller is now driving the engine

Question 62

What can the reduction gearing be as low as?

Answer 62

1:22, for every 1 spin of the propeller the engine will rotate 22 times

Question 63

What do we do to avoid the propeller making the aircraft uncontrollable?

Answer 63

The blades are set at 90 degrees (feathering angle) so there is no angle of attack so the propellers will stop rotating

Question 64

What does the solenoid do in a feathering system?

Answer 64

It lifts a valve to pass oil pressure to the control valve to force it fully up

Question 65

Where is the oil supply for the feathering pump drawn from?

Answer 65

The engine oil tank which remains filled even if the engine oil pressure is lost

Question 66

What are the 2 backup locking mechanisms?

Answer 66

Mechanical Hydraulic

Question 67

What happens if the oil pressure fails?

Answer 67

A shuttle valve in the mechanical pitch look will move under spring force ti drain the oil holding the locks out of engagement

Question 68

What do the locks engage to?

Answer 68

The racket teeth on the pitch change position which means the piston will be unable to move towards fine pitch but can move towards course pitch under the pump pressure

Question 69

What does the shuttle valve in the hydraulic pitch do?

Answer 69

Moves under spring pressure to block the oil return from the front of the piston

Question 70

What happens if the propeller speed exceeds 105% ?

Answer 70

A separate governor will dump oil pressure to the return causing the blade angle to increase until the overspeed ceases

Question 71

What is the governor?

Answer 71

A safety device designed to operate if the normal propeller governor and the fuel control overspeed governor fail to contain engine speed

Question 72

What does a mechanical system do if the turbine detaches from its shaft?

Answer 72

Immediately shuts off the engine-metered fuel supply