Turbine Engine Types Flashcards
Compare the working cycle of a turbine engine and a piston engine
Piston engines create thrust by use of a propellor which accelerates a relatively large volume of air rearwards but relatively slowly.
turbine engines accelerate a relatively small amount of air but do so quickly.
Both use expansion of gas to produce thrust but the piston engine does this by rotation a prop while turbine engine converts the expansion of air directly into thrust by accelerating that air.
Describe the comparative advantages of turbine engines versus piston engines for aircraft propulsion (3)
Turbine is continuous.
Piston engine has to transfer an up and down motion into rotary motion, turbine doesn’t. Meaning its more efficient at creating thrust as it can extract more work from the fuel.
Piston engines have surges or spikes of pressure as the fuel-air is burnt, turbine operates at constant pressure.
Describe a turboprop
Turbine provides power to turn a propellor. Core of the engine is same concept as turbojet but power produced is delivered to a reduction gearbox connected to propellor.
Describe fixed turbine - direct drive turboprop.
DDTP engine, the prop is connected via reduction gearbox to the same turbines and shaft that turn compressor creating a linkage.
Fuel and propellor pitch controls are interconnected and governed so that excess turbine speed doesn’t overspeed prop.
Describe fixed turbine - compounds compressor turboprop.
Same as direct drive but has two spools each independent of the other spinning at different RPM.
Describe a free turbine turboprop
Most common type of turboprop which utilises a turbine to drive the propellor. Independent from the rest of the engine it allows engine to be started but prop to remain stationary.
Describe a turbojet.
Original type of jet turbine. Almost all air enters the intake is compressed, burnt in the combustion chambers and then expands and increases in speed as it flows past turbine and exits at exhaust.
As it flows past the turbine it rotates driving the compressor.
Difference in velocity of air entering the engine and exiting it, provides thrust.
Describe a turbo shaft
A gas turbine engine that delivers power to a shaft that drives something not a propellor (heli rotors)
Describe a turbofan
The core turns the fan at the front of the engine and all air enters the engine past the fan but most of the air bypasses the core of the engine.
The bypass air isn’t compressed as much as that air which goes through the core, but is accelerated to a much faster speed producing thrust.
Describe a geared turbofan
Using a reduction gearbox between the fan and low pressure spool, fan and spool rotate at different speeds improving efficiency.
Improved as less stages are needed to be used and as low pressure turbines can spin faster.
What’s a spool
A compressor-shaft-turbine combo.
E.g Turbojet is a single spool turbine engine, as it only has one shaft running through the centre of the engine.
As exhaust gases pass over the turbine wheel they cause it to rotate and as the turbine wheel is connected to the shaft and compressor they also turn.
What’s a twin spool.
A twin spool is a spool when turbofans are used as there needs to be a seperate spool to rotate the fan.
Single spool would rotate too fast for fan to be efficient.
What’s a triple spool
Three spool. Only used for turbo fan engines.
Shafts connect low, intermediate and high pressure spools. The low pressure spool is connected to the fan with each spool spinning at diff speeds.
Identify engines that fall into either the thrust producing or torque producing category.
Thrust producing engines are Turbojets and Turbofans.
Torque producing engines are Turboprops and Turboshafts.
