Module 15.16 Turboprop engines Flashcards
Is a turboprop engine fuel efficient?
Yes
How does the turbine section differ on a turbo prop?
More turbines
How much power can a turboprop extract to rotate the propeller?
95%
What is the only connection between the gas generator and the free power turbine?
Gas flow
On an engine with a free power turbine, how can the engine be used as a APU?
Putting the propeller brake on
How do Gear/Direct-Coupled turbine engines differ from free power engine turbine engines?
More turbine discs which remain mechanically connected
Because the propeller is driven directly by the engine, what adjusts the propeller pitch for the power requirements?
Integrated propeller control system
Under normal conditions propeller speed and engine speed are what?
Constant
To maintain a constant speed condition what must be co-ordinated?
Propeller pitch and fuel flow
What is the purpose of the reduction gear assembly?
To reduce high rpm from the engine to a propeller rpm that can be maintained without exceeding the maximum propeller tip speed
What are the two main reduction gear systems?
- Parallel spur gear type
- Epicyclical type
For high torque reductions what gear system is used?
Epicyclic gears
What does the reduction ratio depend on?
Relationship between the size of the driving and fixed gear
Why is the oil for the gear systems of higher viscosity than turbo-jet engine oil?
Heavier loads imposed on the gears
What is the advantage of parallel spur gears?
Mechanically simple
What two types of spur gears are used?
Straight cut or helical
What can be said about straight cut spur gears?
Easier to cut, low friction losses but are extremely noisy
What do helical gear teeth allow for?
More gradual onset of torque changes, quieter but less efficient transmission
What gear in the planetary gear system is driven by the power shaft?
Sun gear
In the planetary gear system what is the gear ratio not affected by?
Number of planet gears
How is the reduction ratio calculated?
Driven teeth/driving teeth
What is another name for the annulus?
Ring gear
Which direction does a fixed annulus rotate?
Same rotation direction as the power shaft
Which direction does a rotating annulus rotate?
Opposite rotation direction as the power shaft
What is alpha range?
Efficient and flexible means of using engine power in flight
When would beta range be used?
Ground handling or reversing
To control both the engine and the propeller what do most modern turboprop engines utilise?
Dual FADEC
When is the feathering system used?
In flight when the engine is shut down
Can the propellers be unfeathered during flight to restart the engine?
Yes
Is there propeller stops on a turboprop engine?
No as it is a direct coupled engine
What does the throttle quadrant include?
Integrated engine and propeller controls
What engines can be fitted with a single thrust lever?
Gear-coupled
What governs the maximum rpm of the engine in single lever control?
Propeller Control Unit (PCU)
When is dual lever controlled used?
Turboprop engines with a free turbine
What is each lever for in dual lever controls?
- Power lever
- Propeller control lever
What does the thrust lever control?
Fuel flow from idle to take off range
What does the thrust lever schedule when the lever is moved from idle to reverse?
Fuel flow and the blade angle
‘BETA’ or ‘Ground operating range’
In the beta range, what does the control unit do to the oil pressure?
Change from ‘flight fine’ to ‘ground fine’
What is the propeller lever connected directly to?
PCU
How does the PCU select the required rpm for the propeller?
Applying or releasing pressure on the governor control spring
When does the propeller lever not influence blade angle?
In beta range
What is the purpose of the control lock?
Ensure control surface do not flutter when on the ground
What can overspeed cause?
Rapid and total failure in flight
What angle do centrifugal forces try to reduce the blade angle to?
Zero
Why are the centrifugal forces changing the blade angle not desirable?
Windmilling will occur
What angle is the feathering angle?
90° to the plane of rotation
The action of propeller feathering is carried out by what?
Automatic Drag Limiting System (ADLS)
When must the propeller be feathered?
If oil supply to the propeller fails
When is the electrical feathering pump energised?
Negative torque detected
What are two backup locking mechanisms?
Mechanical and hydraulic
If oil pressure fails what will the mechanical pitch lock move under?
Spring force, to drain oil holding the locks out of engagement
What movement do pitch locks allow?
Allow the piston to move to a coarser pitch but NOT a finer pitch
How is the shuttle valve moved in the hydraulic pitch lock system?
Under spring pressure
What does the propeller overspeed governor do?
If the propeller speed exceeds 105% it will dump oil pressure to the return, causing the blade angle to increase
In the event of turbine shaft failure what does the mechanical system do?
Shut off the engine metered fuel supply
What are the 3 methods of stopping overspeed?
- Pitch locking
- Overspeed governor
- Turbine shaft mechanical system
