M15.16 Turboprop Engines Flashcards
How gas coupled or free power turbine designed?
Designed so there is no mechanical connection between the gas generator and free power turbine. Only connection is both gas flow
Advantages of gas coupled turbines?
Engine is easier to start, especially in cold weather
Propeller can be held at low rpm during taxiing, giving low noise and low blade erosion
Describe a gear/direct coupled turbine?
Compared to free power turbine there is an addition of extra turbine discs. These transmit increased power forwards, generated by exhaust gases through additional extra turbine stages
If a gear/direct coupled turbine fuel flow changes, what must happen?
The propeller pitch must change to maintain a constant speed
What is the function of a reduction gear assembly?
Is to reduce the high rpm from the engine to a propeller rpm that can be maintain without exceeding maximum propeller tip speed
How is a reduction achieved in a reduction gear?
Through a series of both spur gears and epicyclic gears.
Smaller reductions will be achieved using spur gears
Larger achieved by epicyclic gears
The reduction ratio depends upon what relationship?
Relationship between the size of the driving and fixed gear
The gears in reduction gear box are machined by what?
High quality alloy steel forgings
Larger shafts in reduction gearbox are supported by what?
Ball bearings, designed to absorb and transmit all loads imposed on them to the casing
Two main types of reduction gears?
Parallel spur gear type
Epicyclical type
Advantage of parallel spur gears?
Advantage of being mechanically simple
Advantage of helical engagement in reduction gears?
Quieter
Describe epicyclic reduction gears?
Incorporates a sun gear wheel on the power turbine shaft that drives several planet gear wheels engaged with either a fixed or rotating ring gear
What is significant about the reduction gear ratio in epicyclic reduction gears?
It is unaffected by the number of planet gears or number of teeth
Modern turboprop use what to control both the engine and propeller?
A dual Full authority digital engine control (FADEC) system
Can a propeller be unfeathered during flight?
Yes, if engine needs to be started again
How are control leavers arranged on prop aircraft flight decks?
On single engine props it is mounted on the centre pedestal so both flight crew members can operate
On multi engine the left engine lever is on the left and right engine lever on the right
Describe a single lever control?
Fitted with single lever that controls both propeller controls and fuel, they are interconnected.
Propeller control unit (PCU) governs the max rpm of the engine.
When risen to a predetermined rpm level the fuel control unit takes over from PCU
Describe dual lever controls?
Used on turboprop with a free turbine
One lever is a power lever
Other is a prop control lever
Describe automatic drag limiting system (ADLS)?
If torque indication system senses a negative torque, a signal is sent to auto feather system
This energises the pitch increases solenoid and lifts a valve to pass oil pressure to control valve to force it fully up
This moves blades to feathered position.
What are the two backup locking systems for pitch locking?
Mechanical and hydraulic
How does a propeller overspeed governor work?
If propeller speed exceeds 105% a separate governor will dump oil pressure to the return
Thus causing blade angle to increase until overspeed condition ceases
What are the two main types of reduction gears available?
Parallel spur gear and epicyclical type
What is the function of the propeller control unit? (PCU)
It governs the max rpm of the engine
