15.16 Turbo prop engine

Question 1

what is a turbo prop engine coupled with a propellor the most efficient for?

Answer 1

speeds 300 - 450 mph

Question 2

how much power can a turbo prop engine extract from the engine?

Answer 2

as much as 95 %

Question 3

what is the principle of gas coupled/ free turbine engines?

Answer 3

the turbine driving the propellor is only connected via the gas flow

Question 4

what advantages doe the gas coupled/ free turbine have?

Answer 4

Vibration is not directly transmitted to the gas generator from the propeller/reduction gearbox.
Engine is easier to start, especially in cold weather.
The propeller can be held at low rpm during taxiing, giving low noise and low blade erosion.
A propeller brake can be used to prevent propeller movement during aircraft loading when engine shutdown is not desired, for example, the gas generator can be utilised as an APU.

Question 5

how does a direct coupled turbine differ?

Answer 5

they have additional turbines which are directly connected to the compressor and reduction gearbox and can transfer more power

Question 6

why would an integrated propellor control system be necassary?

Answer 6

to adjust propellor pitch for power requirements in a direct coupled turbine

Question 7

wha is the function of an integrated propellor control system?

Answer 7

to maintain a constant speed condition

Question 8

what is the function of reduction gears in turbo prop engines?

Answer 8

to reduce high engine RPM to a propellor RPM

Question 9

what gears are used in a reductio gear box in turboprop engines and what are their functions?

Answer 9

spur gears = for smaller reductions
epicyclic gears = large high torque reductions

Question 10

what does a helical gear arrangement give?

Answer 10

quieter operation

Question 11

what are the advantages of straight cut gears?

Answer 11

lowest friction losses and easy to cut

Question 12

why must a ball or tapered bearing be used?

Answer 12

the axial loading of helical gears

Question 13

what effects reduction ratio on epicyclic reduction gears?

Answer 13

driven teeth by driving teeth not number of planet gears

Question 14

what are the two formats of annulus gears?

Answer 14

fixed = where the propellor shaft rotates in the same direction as the power turbine shaft
rotating = where the propellor shaft rotates in the opposing direction

Question 15

what is alpha range?

Answer 15

in flight = an efficient or flexible way to operate the power of the engine

Question 16

what is the beta range?

Answer 16

ground handling or reversing = can give zero or negative thrust

Question 17

what is the feathering system?

Answer 17

it feathers the propellor when the engine is shut down in flight which can be undone to restart

Question 18

what is used to control the propellor and engine in flight in modern engines?

Answer 18

FADEC

Question 19

when might a single lever control be used in a turbo prop engines?

Answer 19

in gear coupled engines where the fuel and propellor control are interconnected

Question 20

when might dual lever controls be used on a turboprop engine?

Answer 20

when it utilises a free turbine system
there will be a power lever and propellor lever

Question 21

what is the function of the propellor control unit?

Answer 21

govern max RPM of the engine in single lever systems

Question 22

what is the function of the thrust lever?

Answer 22

The thrust lever will schedule fuel flow from idle to the take-off range. When the thrust lever is retarded from idle to reverse

Question 23

what is Beta control?

Answer 23

changing the blade angle to be not in the flight configuration

Question 24

what is the function of the propellor lever?

Answer 24

directly connected to the PCU and gives the required RPM by applying or releasing pressure on the governor control spring

Question 25

what is the function of the control lock?

Answer 25

prevents excessive fluttering of control surfaces on the ground with engines running

Question 26

what is the purpose of the ADLS automatic drag limiting system?

Answer 26

if negative torque is detected the auto feather system receives a signal which causes blades to move to the feather position

Question 27

what is pitch locking?

Answer 27

prevents the pitch from going to a lower angle but can ber moved through pump pressure to a higher angle

Question 28

what is the function of the propellor overspeed governor?

Answer 28

if the propellor speed exceeds 105 % a governor will dump oil pressure to the return, this causes the blade angle to decrease until the condition ends

Question 29

what occurs in the event of turbine shaft failure?

Answer 29

a mechanical system which immediately shuts off engine metered fuel supply in the event of turbine shaft failure to avoid catastrophic failure