TURBOPROP Flashcards
What is the simplest form of reduction gear?
Spur gear.
What speed is the turbo-prop engine proved to be the most efficient at?
480-725 km/h (30 - 450 mph)
What altitude do turbo-prop engines perform well at?
6000m above sea level (20 000 ft)
How much of the total power can a turbo-prop engine extract?
95% to drive the propeller/reduction gearbox, compressor and accessories.
(Remaining used as residual fuel)
What is the core engine commonly known as in a turbo-prop aircraft?
Gas generator or gas producer
How is a gas coupled/free power turbine designed?
There is no mechanical connection between the gas generator and the free power turbine.
(Only common connection is gas flow)
What are the advantages of free power turbine engines?
- vibration not transmitted to propeller/gearbox
- engine start easier in cold
- propeller held at low rpm during taxi
- propeller brake used to prevent propeller movement (gas gen can be used as APU)
How do gear/direct coupled turbines differ from the free power turbine engines?
Gear/direct has extra turbine discs which maintain connected to the compressor and reduction gearbox
Why do gear/coupled turbines generate increased power forwards?
Exhaust gases passing through the additional turbine stages
If fuel flow changes on a gear/coupled turbine, what else must change to remain a constant speed?
Propeller pitch
Why must a turbo-prop inlet lip be of a large radius?
Due to Relatively low air speeds and high engine speeds to separation of airflow due to severe directional changes.
What method is used to reduce compressor blade erosion?
Particle separators on the inlets
What high quality forging are the gears made from in reduction gear boxes?
Alloy-steel
What viscosity is oil in turbo prop reduction gear system in comparison to a turbo-jet engine?
Much thicker as they take higher loads as the system is much heavier.
Why do propellers use SPUR EPICYCLIC gears for reduction gears?
Normal spur gears would be too noisy and bulky to provide such a large reduction.
(Output drive on same axis as input shaft)
What are bevel epicyclic (planet) gears only good on?
Piston engines because of weight and dimension required to provide reduction ratios.
How is reduction ratio found on bevel epicyclic gears?
Number of teeth
What can helically cut gears do?
Reduce noise and vibration whilst also providing a means of measuring torque.
What is a compound spur epicyclic good for?
Greater speed reduction without making components bigger.
How do the shafts move in a compound spur epicyclic gear?
Tend to move axially.
How does a rotating annulus make the propeller rotate?
In the opposite direction to the engine.
What is a 2 stage spur reduction gearbox made from?
Magnesium alloy.
How is the temperature of gas flow into the turbine in a turbo prop controlled?
Varying fuel flow.
How is the mass of gas flow into the turbine controlled on a turbo prop engine?
Varying engine speed through through a variable pitch propeller.
What is the propeller conditioning level for on a twin lever?
Set the propeller rpm in a constant speed mode.
How do over speed safety devices protect the propeller?
First instance to coarsen the blade angle.
If fails, reduce engine power.
(Engine governor, free power turbine governer, an over speed governer)
