15.16 Flashcards
What speed range is turbo prop and GTE ac engines said to be the most efficient
300-450mph (483 to 725kmh)
What distance from sea level are turboprop engines said to provide the best fuel consumption of GTE and to be the most efficient
6000 metres (20,000+ ft)
What percentage of total power can the turbo prop extract to drive the compressor, reduction gear box and other engine accessories and what’s the rest used for
95%
Residual thrust
What’s the difference between a free turbine and a direct coupled turbine, turbo prop engine?
Free turbines aren’t mechanically connected
What’s the advantages of a free power turbine
Vibration is not directly transmitted to the gas generator from the propeller/ reduction gearbox.
• Engine is easier to start, especially in cold weather.
• The propeller can be held at low rpm during taxiing, giving low noise and low blade erosion.
• A propeller brake can be used to prevent propeller movement during aircraft loading when engine shut down is not desired, for example, the gas generator can be utilised as an APU.
Why do turbo prop inlets have large radius
To prevent separation at inlet lip due to directional changes
What’s used in turboprop engines to help reduce FOD ingested into the engines
Particle separators
Are reduction gears in turbo prop engines compared to reduction gears in piston engines higher or lower
Higher
Why’s the viscosity of the oil used to lubricate reduction gearboxes in turbo prop engines than the oil used in turbo jet systems
As the loads imposed on gears in turbofan are heavier
What’s a disadvantages of using normal spur gears in reduction gear systems
Excessively bulky, noisy and propellor and turbines shafts would be offset
^^would impose gyroscopic forces on the drive systems and present problems with intake design
What was created as a result of the poor performance of spur gears and what’s it do
Epicyclic spur gear
Allows output on the same axis as the input shaft
How’s the reduction gear ratio found on bevel epicyclic gears
Number of teeth on fixed gear divided by number of teeth on fixed gear plus number of teeth in driving gear
What type of arrangement is bevel epicyclic gears in gearboxes only suitable on
Piston engines due to the weight and dimensions required to provided the reduction ratios needed for a turbo-prop engine.
What’s a benefit of the helical cuts on spur epicyclic gears
Can reduce noise and vibration whilst also providing a means of measuring torque
What does the two stages of gearing on compound spur epicyclic gears provide
Greater speed reduction without resorting to larger components
