15.16 TURBOPROP ENGINES👌🏼

Question 1

Explain feathering system

Answer 1

• propeller can be feathered when engine is shut down in flight
• prevents propeller spinning if engine fails

Question 2

What do modern turboprop engines utilise to control both engine and propeller

Answer 2

• dual full authority digital engine control (FADEC)

Question 3

Can a turboprop aircraft be unfeathered

Answer 3

Yes

Question 4

Explain single-lever control

Answer 4

• gear coupled engines
  -Single lever that controls both fuel and propeller control

Question 5

Explain dual-lever turbines

Answer 5

• used on turboprop engines with free turbine
• one lever is power lever
• other is a propeller control lever

Question 6

Explain thrust lever

Answer 6

• schedule fuel flow from idle to takeoff range.
• schedules blade angle too

Question 7

What are the 2 main types of reduction gears

Answer 7

• parallel spur gear type
• epicyclical type

Question 8

What is ‘BETA’ or ‘ground operating range’

Answer 8

• when thrust lever is retarded from idle to reverse, thrust lever schedules fuel and blade angle

Question 9

Explain propeller lever

Answer 9

• connected directly to PCU and selects required rpm
• by a governor control spring

Question 10

Explain control lock

Answer 10

• ensure aircraft control surfaces do not flutter excessively when engines are running on ground

Question 11

What is the function of the reduction gear assembly

Answer 11

Reduce high rpm from the engine to a propeller tip speed (speed of sound)

Question 12

Smaller reductions are achieved by what gears

Answer 12

• spur gears

Question 13

Larger high torque reductions will use what gear

Answer 13

Epicyclic gears

Question 14

What must occur if the oil supply to the propeller fails

Answer 14

• feathered quickly to avoid windmilling

Question 15

If the torque indication system senses negative torque, a signal is sent where

Answer 15

Auto-feather system

Question 16

How many locking mechanisms are there in pitch locking

Answer 16

2
(One is mechanical) ( other is hydraulic)

Question 17

What keeps both locks open in pitch locking

Answer 17

Fine-pitch oil line pressure

Question 18

If engine (oil pressure) fails what occurs

Answer 18

• shuttle valve in mechanical pitch lock will move under spring force to drain the oil holding the locks out of engagement

Question 19

How are the locks engaged in pitch locking

Answer 19

• engage with ratchet teeth on the pitch change piston

Question 20

Simply explain pitch locking

Answer 20

• prevents overspeeding of propeller

Question 21

If a propeller speed exceeds 105% what occurs

Answer 21

• separate governor dumps oil pressure to return
• causes blade angle to increase until overspeed ceases

Question 22

What does the mechanical system do if the power turbine detaches from shaft

Answer 22

immediately shut off the engine metered fuel supply in the even of a turbine shaft failure

Question 23

Why is the viscosity of oil higher in a turbo prop engine

Answer 23

Due to heavier loads imposed on the gears

Question 24

Explain parallel spur gears

Answer 24

• mechanically simple
• straight-cut or helical

Question 25

Explain straight cut gears

Answer 25

• easier to cut, have lowest frictional losses
• very noisy

Question 26

Explain helical engagement of gear teeth

Answer 26

• quieter but less efficient transmission of power

Question 27

Explain epicyclic reduction gear

Answer 27

• incorporates sun gear wheel on power turbine shaft that drives serve real planet gear wheels
• engaged with fixed or rotating ring gear or annulus

Question 28

Turboprop is the most efficient power source for aircraft operating between what speed

Answer 28

• 483 to 725km/h
  (300 - 450mph)

Question 29

The engine can extract as much as —% of the total power produced

Answer 29

95

Question 30

How is the gas-coupled/free power turbine designed

Answer 30

• no mechanical connection between gas generator and free power turbine

Question 31

What are the advantages of free power turbine engine

Answer 31

• Less vibration
• engine easier to start (especially in cold)
• propeller can be held at low rpm (e.g. during taxiing) (gives low noise)
• propeller brake can be used to prevent propeller movement

Question 32

Explain gear/direct-coupled turbines

Answer 32

• Have extra turbines which remain mechanically connected

Question 33

In the direct-coupled turbines, at normal operating conditions, both propeller speed and engine speed are constant.

Answer 33

True