Basic Gas Turbine Flashcards
What is the functional difference between a turboprop and a turboshaft
the turboshaft is a variation of the turbo prop except that the “free” turbine in the turbo shaft will drive something other than a propeller gearbox. Turbo shaft engines are mainly used in helicopters
How is a free power turbine characterised?
It is mechanically independent of other spools of the engine
What are the advantages of a free turbine propulsion system?
- Easier to start due to much lower propeller drag
- Gas generator shaft and propeller shaft can assume their optimum speeds independent of each other
- Design flexability
- Stop the propeller of the helicopter while the engine is still running
Why does a free turbine turboprop engine require a smaller starter motor
- Lower propeller drag
- only high pressure turbine and compressor needs to be rotated on start
what is the section called that includes the compressor and turbine
A spool
Why do some turbine engines have multiple spools?
For efficiency so that each one can operate at its desired optimum RPM
In a twin spool turbine engine, which are the high pressure and low pressure stages of the compressor and turbine?
- The first stage compressor/last stage turbine are low pressure
- The second stage compressor and first stage turbine are high pressure
Within an engines spool, what drives the intermediate pressure compressor?
The intermediate pressure turbine
What are the advantages of a triple spool over a twin spool by pass engine?
- Shorter and lighter
- Better range/Fuel consumption
What are the ideal characteristics of a turbine engine intake?
To deliver air to the compressor evenly at a higher than ambient pressure
What is the shape formed by the duct of an intake on a turbofan powered subsonic aircraft and why?
-Divergent duct, for subsonic flow increases static pressure and reduces velocity essentially converting kinetic energy to pressure energy (dynamic to static)
What is RAM effect?
The pressurisation of the air entering the intake caused by the aircrafts forward speed
What is the most common type of intake on turbofan engines?
the Pitot type
What is the disadvantage of using a divergent intake duct?
Seperation of the boundary layer on the duct walls
What is the disadvantage of a long intake duct
too much drag, with a resulting loss of efficiency
