15.16 Flashcards
turboprop best for operating at what speed
483-725kmh / 300-450mph
What height is turboprop good for
6000m / 20000ft +
In cruising what makes turboprop better then turbo jet
Propulsion efficiency is constant in turboprop whereas it increases in turbojet as airspeed increases
How much power can turboprop extract
95%
What’s the core engine known as in turboprop
Gas generator or producer
Produces high velocity gases that provide energy to drive the power turbine
What connection is there in a free power turbine and gas generator
No mechanical connection only a gas flow connection
Advantages of free power turbine
Vibration not directly transmitted to the gas generator
Easier to start , especially in cold weather
Propeller held at low rpm during taxing
Can use a propeller brake to stop propeller movement during aircraft loading when shutdown not desired
How are gear-direct coupled turbines different to free power
Extra discs that are mechanically connected to compressor and reduction gearbox
Why does the propeller pitch and fuel flow need to be coordinated
So if fuel flow changes then propeller pitch must change to maintain a constant speed
What’s the function of the reduction gear assembly
Reduce high rpm from the engine to a propeller rpm
Needs to be maintained without exceeding the maximum propeller tip speed (SoS)
When would you use an epicyclic gear
Larger high torque reductions
2 types of reduction gears
Parallel spur and epicyclic
Advantage and disadvantage of straight cut parallel spur gear
Easy to cut and have lowest frictional losses
Very noisey
Helical cut parallel spur gear advantage and disadvantage
Quieter
Less efficient in transmission of power
What gear wheel does a epicyclic reduction gear use
Planet gears
How is epicyclic reduction gear ratio calculated
Dividing number of driven teeth by number is of driving teeth
What direction does the propeller shaft drive in rotating annulus
Opposite direction of rotation to the power turbine shaft
What direction does the propeller shaft drive in a fixed annulus
Same direction of rotation as the power turbine shaft
What speed does the propeller rotate in fixed annulus
At a speed dependent on the reduction gear ratio
What does the fadec system control
Engine and propeller
What shape is the spinner
Cone-shaped configuration that mounts on the propeller and encloses he some and barrel to reduce drag
What does the feathering system do
Feathers propeller when engine is shut down and unfeather if engine needs to be started
On multi-engine aircraft where is the lever for number one engine
On the left
What uses a single thrust lever
Gear couple engine
What lever does a turbo propeller engine use
Dual lever if it has a free turbine
What does the thrust lever do
Schedule fuel flow from idle - takeoff
Blade angle from 20 to -20 degrees (BETA / ground operating range)
What does the control lock do
Ensures aircracft control surfaces do not flutter excessively on the ground with the engines running
What does the propeller lever do
Selects the required rpm by applying or releasing pressure on the governor control spring
What does overspeed cause
Extreme stress to the propeller and engine and can lead to rapid and total failure
How low can reduction gearing be
Low as 1:22
One revolution = 22 engine rotations
What is the feathering angle
90 degrees to the plane of rotation
Blade chord is in line with the airflow
What does the automatic drag limiting system do
Feathers the propeller if the oil supply fails to avoid it from windmilling
When does a propeller overspeed governor activate
Propeller speed exceeds 105% governor dumps oil pressure to increase blade angle
What’s the governor a safety device for
Operate if normal propeller governor and fuel control overspeed governor fail to contain the engine speed
What happens in turbine shaft failure
Mechanical system in place to immediately shut off the engine-metered fuel supply in event of turbine shaft failure
