Module 15.16 Turboprop Engines Flashcards
What speed range are turboprop engines most efficient at?
483 to 725 km/h (300 to 450 mph).
At what height are turbo prop engines most efficient at?
6000 metres (20 000 ft)
What percentage of the total power produced to the components can the engine extract?
95%
What is the core engine commonly known as?
The gas generator/producer.
What does the gas generator do?
Produces high-velocity gases that provide the energy to drive the power turbine.
What is a gas coupled/free-power turbine engine?
An engine with no mechanical connection between the gas generator and the free-power turbine.
What are the advantages of gas-coupled/free-power turbine engines?
Vibration is not directly transmitted to the gas generator.
Engine is easier to start due to only needing to drive the gas generator.
How does a gear/direct coupled turbine engine differ from a free-turbine one?
The addition of extra turbine discs which remain mechanically connected to the compressor and reduction gearbox.
As the propeller is driven directly by the engine, what is needed?
An integrated propeller control system.
What adjusts the propeller pitch for the power requirements of the engine.
The propeller control system.
Why must propeller pitch and fuel flow be coordinated?
To maintain a constant speed condition.
If fuel flow changes, then the propeller pitch must change.
What does the reduction gear assembly do?
Reduces high rpm from the engine to a propeller rpm that can be maintained.
What type of gear is used for small reductions?
Spur gears
What type of gear is used for high torque reductions?
Epicyclic gears
What are the larger shafts supported by?
Ball bearings
What do the ball bearings supporting the larger shafts do?
Absorb and transmit all loads imposed on them to the casing.
What are the two main types of reduction gears?
Parallel spur gear
Epicyclic
What are the two types of spur gear?
Straight-cut or helical
What is the disadvantage to straight-cut spur gears?
Very noisy
What is the advantage to helical-cut spur gears?
More gradual onset of torque making it quiet.
What is a fixed annulus and rotating annulus epicyclic gear?
Fixed - ring (outer) gear does not move.
Rotating - ring (outer) gear moves.
What must the propellor do to its blades if oil supply to the propeller fails?
It must feather them.
What happens if the torque indication system senses negative torque?
A signal is sent to the auto-feather system.
What happens if propeller speed exceeds 105%?
A separate governor will dump oil pressure to the return. This will cause the blade angle to increase until the overspeed condition ceases.
What is the governor?
A safety device designed to operate if the normal propeller governor and the fuel control overspeed governor fail to contain the engine speed.
What do modern turboprop engines now utilise to control the engine and propeller?
Dual Full Authority Digital Engine Control (FADEC) system
What is the spinner assembly?
A cone-shaped configuration that mounts on the propeller and encloses the dome and barrel.
What does the feathering system do?
Feathers the propeller when the engine is shut down in flight.
Can the propeller be unfeathered during flight?
Yes
What type of turboprop engine will use a single thrust lever?
Gear-coupled engines.
What does the single thrust lever control?
Fuel flow and propeller rpm.
What happens if a single lever control system is moved forward?
Increase in fuel flow and propeller rpm.
What does the Propeller Control Unit (PCU) do?
Controls the maximum rpm of the engine.
What happens when propeller rpm rises to a predetermined level?
The fuel control unit will take over and control the rise in rpm.
What type of turboprop engine will use a dual thrust lever?
Free-turbine engines.
What do the separate levers in a dual-lever system do?
One for power (fuel flow) and the other for propeller control (rpm).
What happens when the fuel lever goes from idle to reverse?
It changes fuel input and the blade angle.
What angle do the propeller blades go to when the thrust lever is in reverse?
From +20° to -20°.
When the propeller blades go from +20° to -20°, what is this called?
‘BETA’ or “ground operating range”.
What happens when the thrust lever is moved into ‘Beta Range’?
A control unit changes the propeller blade angle. It’s fined below the ‘flight fine’ pitch into ‘ground fine’.
What controls the degree of the propeller fining off into reverse?
Position of the thrust control lever in the Beta range.
What is the propeller lever connected to?
The Propeller Control Unit (PCU).
What does the propeller lever do?
Selects the required rpm.
What does the control lock do?
Ensures the aircraft control surfaces do not flutter excessively on the ground with the engines running.
Is the viscosity of the turboprop oil higher or lower in comparison to oil used for turbojet engines?
Why?
It’s higher due to having heavier loads imposed on the gears.
What is done in the event of a turbine shaft failure?
The fuel supply is immediately shut off.
Which type of gearbox will cause the propeller to turn in the opposite direction to the engine?
Epecyclic reduction gearbox with a rotating annulus?
