15.16 Turboprop Engines Flashcards
(30 cards)
What is the main benefit of a turboprop engine in the 300-400 mph speed range?
It has the best specific fuel consumption and high propulsive efficiency.
What is a gas generator in a turboprop engine?
The engine core that produces high-energy gases to drive the turbine.
How is a free-power turbine connected to the gas generator?
Only through the gas flow—there is no mechanical connection.
Name two advantages of free-power turbines.
Low noise at taxi, easier cold starts.
What distinguishes gear-coupled turbines from free turbines?
They use extra turbine stages that are mechanically linked to both the compressor and propeller.
Why do gear-coupled turbines need a complex control system?
To coordinate propeller pitch and fuel flow for constant RPM.
Why is a reduction gearbox needed in turboprop engines?
To reduce turbine RPM to a lower RPM suitable for propeller speed.
So the propeller tip doesn’t exceed the speed of sound
What gear types are commonly used in reduction gearboxes?
Parallel spur gears and epicyclic gears.
What is an advantage of straight-cut spur gears?
Low frictional loss and simple to cut.
What is a disadvantage of helical gears?
They produce axial loads that require special bearings.
In a fixed annulus epicyclic system, which way does the propeller rotate?
In the same direction as the turbine shaft.
In a rotating annulus system, which way does the propeller rotate?
In the opposite direction of the turbine shaft.
Why are bearings used in reduction gears?
To support shafts and carry loads (especially side and axial loads from gears).
What types of bearings are used?
Ball bearings and tapered roller bearings (for helical gear axial loads).
Whats a single lever control system?
One elver adjusts both fuel flow and propeller speed
Whats a dual lever control system?
One power lever
One propeller lever
What does the power lever control in a dual-lever turboprop system?
Fuel flow during flight and both fuel and blade angle in the Beta (ground) range.
What does the propeller lever control?
Propeller RPM during flight by adjusting the governor pressure.
What is the Beta range used for?
Ground operations such as taxiing and reverse thrust.
Which engines typically use dual lever controls?
Free turbine turboprop engines
Whats the function of the overspeed governor?
To prevent the propeller from exceeding safe RPM limits.
Whats the function of the control lock?
Prevents aircraft control surface flutter on ground
What role does FADEC play in modern turboprops?
It provides automatic control of both the engine and propeller.
When does propeller or engine overspeed occur?
When oil pressure is lost, centrifugal force twists the propeller blades to reduce pitch
Flat blades means more air hits them and the propeller spins freely (windmilling
