Turbine Engine Types Flashcards
What are the main types of turbine engines? 4
Turboshaft, turboprop, turbojet, turbofan.
What is the definition of the bypass ratio of a turbofan engine?
The ratio of the mass of air bypassing the engine core, to the mass of the air passing through the engine core.
What is the main similarity between a turbine engine and reciprocating engine?
Both the turbine and reciprocating engines are internal combustion.
What is the main advantage of a turbine engine over reciprocating engine of the same power output?
The turbine engine has a much higher power to weight ratio than a reciprocating engine of a similar power output.
How does the combustion cycle of a turbine engine compare with that of a reciprocating engine?
A turbine engine combustion takes place at a near constant pressure, while in a reciprocating engine combustion takes place at near constant volume.
What is the functional differences between turboprop and a Turboshaft?
A turboprop engine has an output shaft which drives a gearbox for a propeller while a Turboshaft engine has an output shaft which drives a gearbox for something other than a propeller, e.g. a helicopter’s main rotor gearbox.
How is a free power turbine characterised?
It is mechanically completely independent of the other spools in the engine.
What are the advantages of a free turbine propulsion system? 4
- Easier to start.
- The spools can run at their optimum speeds, independent from each other.
- Design flexibility of layout.
- The ability to stop the propeller or helicopter rotors while the engine is still running.
Why does a free turbine turboprop engine require a smaller starter motor than direct-drive and compound turboprops?
Because only the high pressure turbine and compressor need to be rotated on start.
Which part of a turboprop engine usually powers the accessory gearbox?
The high pressure compressor (N2) section.
What drives the main drive gearbox in a free turboprop or Turboshaft?
The low pressure turbine(s).
What is the meaning of the term “spool”?
A spool is an independent compressor, shaft, turbine combination.
What is compressor/ turbine combination called?
A spool
Why do turbine engines have multiplayer spools?
So that each can operate closer to their design rpm.
In a twin spool turbine engine, which are the high pressure and low pressure stages of the compressor and turbine?
The first stage(s) of the compressor and the last stage(s) of the turbine are low pressure, while the last stage(s) of the compressor and the first stage(s) of the turbine are high pressure.
Within an engine’s spools, what drives the intermediate pressure compressor?
The intermediate pressure turbine.
Within an engine’s spools, what drives the low pressure compressor?
The low pressure turbine.
What is the description of a turbofan engine?
A fan/ low pressure compressor supplying supercharged (pressurised) air to the engine core and to the bypass duct. A ducted propeller, suitable for a powering high speed aircraft.
What is the ‘core’ of a turbofan engine comprised of? 4
The compressor, combustion chamber, turbine and exhaust section.
What is the bypass ratio if 20% of the intake air passes through the engine core?
4:1
In terms of bypass ratio, how does a pure turbojet compare to a turbofan?
A pure turbojet has no bypass air.
What percentage of bypass air passes through the compressor of a turbofan engine?
0%
Why is a turbofan engine more efficient than a turbojet engine?
Because turbofan accelerate a relatively larger amount of air a relatively lower amount.
Why are turbofan engines more resistant to FOD ingestion than pure turbojet engines?
Because the fan blades are bigger and stronger than the first stage compressor stages of the turbojet, and because most of the air bypasses the engine core.
What are the advantages of a twin spool over a triple spool bypass engine? 2
Lower cost.
Easier maintenance.
What are the advantages of a triple spool over a twin spool bypass engine? 2
Shorter and lighter.
Better range/ fuel consumption.
What is the name given to turbine engine which has propeller blades mounted radially from the low pressure turbine?
An aft fan turbojet.
What output is provided by an APU?
AC electrical power and bleed air.
What is the primary purpose of an APU?
To provide AC electrical power and pneumatic bleed on the ground, and in flight in the event of a main engine failure.
What section of an APU provides pneumatic bleed air for engine start?
The compressor
