15.16 Turboprop Engines

Question 1

What is a turboprop engine known as?

Answer 1

A gas generator/ producer engine.

Question 2

How can a gas coupled/ free power turbine be identified?

Answer 2

There are no mechanical connections between the gas generator and the free power turbine.

Question 3

What are the advantages of a gas couple/ free power turbine?

Answer 3

Vibration isn’t directly transmitted to the gas generator.

Engine is easier to start.

Propellor can be held at low rpm=low noise + blade erosion.

Propellor brake can be used during loading= engine can be used as an APU.

Question 4

How does a gear/direct coupled turbine differ from a free power turbine?

Answer 4

It has extra turbine discs.

Question 5

What does the gear/direct coupled turbine do?

Answer 5

Transmitter increased power forwards.

Question 6

In a gear/ direct coupled turbine, because the propeller is driven by the engine what is necessary?

Answer 6

Complex integrated propeller control system.

Question 7

How is constant speed achieved in a gear/ direct coupled turbine?

Answer 7

Propeller pitch and fuel flow are coordinated.

Question 8

For small reductions, what gears are used?

Answer 8

Spur gears.

Question 9

For larger high torque reductions, what gears are used?

Answer 9

Epicyclic gears.

Question 10

How is oil viscosity different than a turbo jet engine?

Answer 10

It is higher, due to heavier loads been imposed on gears.

Question 11

What are the 2 main types of reduction gears?

Answer 11

Parallel spur.

Epicyclical.

Question 12

What are the advantage and disadvantage of straight cut parallel gears?

Answer 12

+ Lowest friction losses

• But noisy.

Question 13

When may heavy duty bearings be required?

Answer 13

When torque changes create high loading on gear teeth.

Question 14

What are the advantages of helical parallel gears?

Answer 14

Allow gradual onset of torque changes,

Quieter

Question 15

What is the disadvantage of helical parallel gear?

Answer 15

Less efficient power transmission.

Question 16

What is an annulus also known as?

Answer 16

Ring gear.

Question 17

In a fixed annulus system, which way does the propeller spin?

Answer 17

Same direction as power turbine shaft.

Question 18

In a rotating annulus system, which way does the propeller spin?

Answer 18

Oppositely to the power turbine shaft.

Question 19

What is flight range known as?

Answer 19

Alpha range.

Question 20

What is ground handling range known as?

Answer 20

Beta range.

Question 21

When is the feathering system used?

Answer 21

When an engine shut downs in flight.

Question 22

Can propellers be unfeathered in flight?

Answer 22

Yes, to restart the engine.

Question 23

Where is single lever control used ?

Answer 23

On gear coupled engines.

Question 24

What makes up a single lever control?

Answer 24

An integrated fuel and propeller control unit.

And a PCU.

Question 25

Where is Dual lever control used?

Answer 25

With free power turbines.

Question 26

What is the purpose of the thrust lever?

Answer 26

Schedules fuel flow.

Question 27

What is the BETA/ ground operating propeller angle range?

Answer 27

+20 to -20 degrees.

Question 28

Where is the propeller lever operated?

Answer 28

In flight.

Question 29

What is the purpose of control locks?

Answer 29

Ensure control surfaces don’t flutter on ground with engines running.

Question 30

What system prevents propeller windmilling?

Answer 30

Automatic Drag Limiting System (ADLS)

Question 31

What is the feathering angle of ADLS?

Answer 31

90

Question 32

What is the purpose of ADLS?

Answer 32

Prevents propeller from driving engine in case of oil supply failure.

Question 33

What powers ADLS?

Answer 33

Feathering pump

Question 34

Where does the feathering pump get its oil supply from?

Answer 34

Draws oil from engine tank

Question 35

What are the 3 over speed safety devices?

Answer 35

Pitch locking.
Propeller over speed govenor.
Turbine shaft failure.

Question 36

What is the purpose of pitch locking?

Answer 36

Prevents propeller moving to a fine pitch angle.

Question 37

How does pitch locking work?

Answer 37

It moves under spring force when oil supply fails.

Question 38

What does the propeller over speed govenor do?

Answer 38

Dumps oil pressure to return if propeller speed exceeds 105%

Question 39

What happens in the event of turbine shaft failure?

Answer 39

Engine fuel supply is immediately shut down.