15.16 Turboprop Engines Flashcards
What are some advantages of a turboprop engine?
Provide the best specific fuel consumption of any gas turbine engine and perform efficiently from sea level to height over 6000 m
How much power can a turboprop engine extract?
95%
Where does this turboprop power get used?
to drive the propeller/reduction gearbox, compressor, and engine accessories, while the remainder of the energy is used as residual thrust
What are the advantages of a free power turbine?
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 are free power turbine engines connected?
With gas flow between the gas generator and free power turbine
How are direct coupled turbine engines connected?
Mechanically to the compressor and reduction gear box
How are forward motions produced?
By the exhaust gases passing through the additional turbine stages
How does a turboprop engine maintain a constant speed?
Propeller pitch and fuel flow must be coordinated to maintain a constant speed
At normal operating conditions what should the propeller and engine speed both be?
Constant
What is the function of the reduction gear assembly?
To reduce high rpm from the engine to a propeller rpm that can be maintained without exceeding max propeller tip speed
How is reduction achieved?
Through a series of spur and epicyclic gears
What are spur gears used for?
Smaller reductions
What are epicyclic gears used for?
Target high torque reduction
What are the gears made of?
Quality alloy steel forging
What are the two main types of reduction gears?
Parallel spur gear type and epicyclic type