15.16 Turbo-Prop Engines Flashcards
At what speed range is a turboprop engine the most efficient?
Between 300 to 450 mph (483-725km/h)
How much energy can a turboprop engine extract from the total power produced to drive the propeller?
95% of the power
In a turboprop engine, what is the core part commonly known as?
The gas generator or the gas producer
What is a gas coupled or free power turbine?
A turbine which has no mechanical connection between the gas generator and the free power turbine
What are the advantages of a free power turbine?
- vibrations are not directly transmitted
- easier to start
- propeller can be held at low RPM for taxiing etc (reducing wear and lower noise)
- a propeller brake can be used when engine shut down is not required but propeller movement is required to be stopped
What is the problem with a direct coupled turbine?
There must be a complex control system that adjusts propeller blade angle (pitch)
How does a direct coupled turbine differ from a free power turbine?
It is mechanically connected via a reduction gear to the propeller
For turbo-prop engines, how is the intake lip designed?
Large lip radius preventing flow separation
What is the disadvantage of a turboprop engine?
The intake lip can ingest FOD
How is FOD prevented from entering a turboprop engine?
There is a movable vane which creates a severe directional change to the air, but not the high momentum particles which means they can be ejected
What is important about the lubrication for reduction gears?
The viscosity of the oil is higher than comparable turbo-jet engines due to the heavier loads imposed on the gears
What is different about reduction gears in turbo-prop engines compared to ones fitted to piston engines?
They have much higher reduction ratios than ones fitted to piston engines
What type of material are reduction gears made from?
They are machined from high quality alloy-steel forgings
What is a disadvantage of spur gears on turboprop engines?
They would be very bulky and noisy for the amount of reduction necessary
To overcome the problems with spur gears, what type of gears are used?
Spur Epicyclic reduction gears which output on the same axis as the input shaft
Where are Bevel Epicyclic gears used?
On piston engines - due to weight and dimension required
What is the advantage of using helically cut gears?
They reduce noise and vibrations whilst providing a means of measuring torque
What is the advantage of Compound Spur Epicyclic gears?
It consists of high speed and low speed gear train which gives greater speed reduction without larger components
What is a rotating annulus gear?
The propeller rotates in the opposite direction to the engine
What is a fixed annulus reduction gear?
The rotation of the propeller and engine are the same
What is the advantage of using a single lever control (throttle and propeller speed control) for a turboprop engine?
The engine can establish the correct RPM, fuel flow and blade pitch angle.
What does a twin lever control consist of, for a turboprop engine?
It consists of a power lever and a separate propeller conditioning lever
What overspeed devices are used in a free power turbine?
An engine governor and an overspeed governor which can be re-datumed for ground test purposes
