15.16 turboprop engines

Question 1

what speed is turboprop efficient at

Answer 1

300-450mph

Question 2

how much power can be extracted by a turboprop

Answer 2

95%

Question 3

what is a gas coupled turboprop known as

Answer 3

free power turbine

Question 4

what is a free power turbine

Answer 4

no mechanical connection between gas generator and free power turbine

Question 5

pros of free power turbine

Answer 5

vibration reduced
easy to start
can be held at low rpm
propeller brake can be used

Question 6

what is difference between gear coupled turbine and free power turbines

Answer 6

gear coupled has extra turbine discs which are mechanically connected to compressor and reduction gearbox

Question 7

how is propeller pitch controlled in a direct coupled turbine

Answer 7

complex integrated propeller control system

Question 8

if fuel flow changes does propeller pitch change in a geared turbine engine?

Answer 8

yes
propeller pitch must change to maintain constant speed

Question 9

what is the function of a reduction gear

Answer 9

reduce the high rpm from the engine to a propeller rpm that can be maintained without exceeding the speed of sound on the propeller tip

Question 10

what type of gears are used in a reduction gearbox

Answer 10

spur gears and epicyclic gears

Question 11

for small reduction sin a reduction gearbox, what gear is used

Answer 11

spur gear

Question 12

for large reductions in a reduction gearbox, what gear is used

Answer 12

epicyclic

Question 13

what are the gears used in reduction gearboxes made from

Answer 13

high quality alloy steel forgings

Question 14

what lubrication system does reduction gearboxes utilise?

Answer 14

may be lubricated using engine lubrication system or their own self contained system

Question 15

pros of parallel spur gear

Answer 15

mechanical simple

Question 16

can turboprops be used for negative thrust

Answer 16

yes, the propeller can be operated to produce zero or negative thrust for ground handling and reversing

Question 17

what system does modern turboprop use to control engine and propeller

Answer 17

fadec

Question 18

when is feathering used

Answer 18

when engine is shut down in flight

Question 19

what governs the maximum rpm on a single lever control turboprop

Answer 19

propeller control unit (PCU)

Question 20

when the rpm rises to a predetermined level, what inhibits the rise of rpm. (pcu or fuel control unit)

Answer 20

fuel control unit

Question 21

which engines are dual lever controls usually used on

Answer 21

turboprop with a free turbine

Question 22

what is the purpose of power lever

Answer 22

schedule fuel flow from idle to take off range

Question 23

does power lever control the blade angle?

Answer 23

yes
- when power lever is retarded form idle to reverse, the blade angle changes to a -20 degree angle

Question 23

what is beta control do

Answer 23

a control unit on the reduction gear will select oil pressure to fine the blade angle below “flight fine pitch” into “ground fine pitch”.

Question 24

what does propeller connected to

Answer 24

directly connected to the PCU

Question 25

what does propeller lever do

Answer 25

selects the required rpm by applying or releasing pressure on the govenor control spring

Question 26

what is control lock

Answer 26

ensures that the aircraft control surfaces do not flutter excessively on the ground on the ground with the engines running

Question 27

if oil supply to propeller fails what happens

Answer 27

prop must be feathered to prevent windmilling

Question 28

how does propeller overspeed governor work

Answer 28

if propeller speed exceeds 105% a separate governor will dump oil pressure to the return.