15.16 Turbo prop engine Flashcards
what is a turbo prop engine coupled with a propellor the most efficient for?
speeds 300 - 450 mph
how much power can a turbo prop engine extract from the engine?
as much as 95 %
what is the principle of gas coupled/ free turbine engines?
the turbine driving the propellor is only connected via the gas flow
what advantages doe the gas coupled/ free turbine have?
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.
how does a direct coupled turbine differ?
they have additional turbines which are directly connected to the compressor and reduction gearbox and can transfer more power
why would an integrated propellor control system be necassary?
to adjust propellor pitch for power requirements in a direct coupled turbine
wha is the function of an integrated propellor control system?
to maintain a constant speed condition
what is the function of reduction gears in turbo prop engines?
to reduce high engine RPM to a propellor RPM
what gears are used in a reductio gear box in turboprop engines and what are their functions?
spur gears = for smaller reductions
epicyclic gears = large high torque reductions
what does a helical gear arrangement give?
quieter operation
what are the advantages of straight cut gears?
lowest friction losses and easy to cut
why must a ball or tapered bearing be used?
the axial loading of helical gears
what effects reduction ratio on epicyclic reduction gears?
driven teeth by driving teeth not number of planet gears
what are the two formats of annulus gears?
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
what is alpha range?
in flight = an efficient or flexible way to operate the power of the engine
what is the beta range?
ground handling or reversing = can give zero or negative thrust
what is the feathering system?
it feathers the propellor when the engine is shut down in flight which can be undone to restart
what is used to control the propellor and engine in flight in modern engines?
FADEC
when might a single lever control be used in a turbo prop engines?
in gear coupled engines where the fuel and propellor control are interconnected
when might dual lever controls be used on a turboprop engine?
when it utilises a free turbine system
there will be a power lever and propellor lever
what is the function of the propellor control unit?
govern max RPM of the engine in single lever systems
what is the function of the thrust lever?
The thrust lever will schedule fuel flow from idle to the take-off range. When the thrust lever is retarded from idle to reverse
what is Beta control?
changing the blade angle to be not in the flight configuration
what is the function of the propellor lever?
directly connected to the PCU and gives the required RPM by applying or releasing pressure on the governor control spring
what is the function of the control lock?
prevents excessive fluttering of control surfaces on the ground with engines running
what is the purpose of the ADLS automatic drag limiting system?
if negative torque is detected the auto feather system receives a signal which causes blades to move to the feather position
what is pitch locking?
prevents the pitch from going to a lower angle but can ber moved through pump pressure to a higher angle
what is the function of the propellor overspeed governor?
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
what occurs in the event of turbine shaft failure?
a mechanical system which immediately shuts off engine metered fuel supply in the event of turbine shaft failure to avoid catastrophic failure
