TurboFans Flashcards
A turbojet is the core component of what three turbine engines?
Turbofan
Turboprop
Turboshaft
In addition to the turbojet engine core what gets added on to make it a turbofan?
A big fan stuck on the front. An additional turbine at the end powers this fan.
A turbofan engine is the most modern variation of the basic turbine engine (the turbojet)
How does a turbofan work?
Incoming air passes through the fan. Some of it goes into the core but most of it goes out the edges as thrust.
The rest is the same as the basic turbojet.
How much more efficient are turbofans vs turboprops?
30-40%
What is engine Pressure Ratio (EPR)?
Its the ratio of the Turbine Outlet Pressure (out the back) to the Compressor Inlet Pressure (in the front)
A fancy way of saying how much thrust we’re producing.
What is the Bypass Ratio?
The amount of air going around the core turbine from the turbofan
What is a ‘hot start’?
When the fuel is injected into the burner before the compressor is spinning fast enough, the fuel can end up burning out of control.
This is because not enough pressure is in the engine to throw all the hot air out towards the back and through the turbine.
This will cause the fuel to burn in the burner area and can melt your engine fast.
What do you need to get a turbine engine started?
A good flow of air, typically up to 12% of the normal compressor speed, before introducing and igniting the fuel.
If you are parked into a tailwind you would need to face it into the wind before starting, as the air must be flowing in the right direction.
What is an APU used for?
To power up the ACs electrical system and to provide pneumatic pressure to spin up the compressors in the main engine(s) during startup.
Most big planes have a little jet hidden in the tail. The APU starts this, and the little jet generates enough power to bring the compressors up to speed in the main engines.
