What speed range are turboprop engines most efficient in?
Approximately 300–450 mph (483–725 km/h).
Why are turboprops more fuel-efficient than turbojets at medium speeds?
They have superior propulsive efficiency and extract most engine power to drive the propeller.
What percentage of engine power is typically extracted by the turbine in a turboprop?
Up to 95%.
What is the gas generator in a turboprop engine?
The engine core that produces high-energy gas to drive the turbine.
What defines a free-power (gas-coupled) turbine?
There is no mechanical connection between the gas generator and power turbine.
One advantage of a free-power turbine during ground operations?
Allows low propeller RPM during taxi, reducing noise and wear.
What is a gear-coupled (direct-coupled) turboprop?
A turboprop where the turbine is mechanically connected to the compressor and gearbox.
Why is a reduction gearbox required in turboprop engines?
To reduce high turbine RPM to safe and efficient propeller RPM.
What is the reduction ratio of a PT6A-34 engine?
Approximately 15:1.
Which gear type is best suited for high torque and large reductions?
Epicyclic (planetary) gears.
What are the main components of an epicyclic gear system?
Sun gear, planet gears, and ring gear (annulus).
Difference between fixed and rotating annulus epicyclic gears?
Fixed annulus gives same rotation direction; rotating annulus reverses direction.
What is the alpha range of a turboprop propeller?
The in-flight operating range.
What is the beta range used for?
Ground operations including taxi and reverse thrust.
What system automatically feathers the propeller after engine failure?
The auto-feather or Automatic Drag Limiting System (ADLS).
Why is feathering important after an engine failure?
It prevents windmilling and reduces drag.
What happens to propeller blades if oil pressure is lost?
They move toward fine or zero pitch due to centrifugal twisting forces.
What is the function of a propeller overspeed governor?
To increase blade angle and reduce RPM if overspeed occurs.
At what RPM does the overspeed governor typically activate?
Around 105% RPM.
What protection exists for turbine shaft failure?
A mechanical fuel shutoff system that stops fuel flow immediately.
