Engines 9: Accessory, Starter, and Ignition Systems Flashcards
What are the different ways that aircraft accessories be driven?
Air-driven
Mechanically-driven
Where does the air for air-driven accessories come from?
Compressor bleed air
What are some air-driven accessories?
AC units
Cockpit/Cabin pressurization
Engine Anti-ice
Other accessories
What is interstage bleed air used for?
Only used for compressor stability; doesn’t drive any components
What percentage of airflow is used as bleed air to drive accessories?
About 1-4%
How are mechanically-driven accessories driven?
With a mechanical, geared drive that is attached to the main shaft that connects the turbine to the compressor
Accessory drive gear box
What are some mechanically driven accessories?
Generators
Alternators
Hydraulic pumps
What is the purpose of the starting system?
To accelerate the engine until the turbine is producing enough power to continue the engine acceleration itself
List the steps of the starting cycle in order.
- Starter achieves sufficient compressor rpms
- Ignition is activated
- Fuel is added
Why does the starter stay on after the engine reaches self-accelerating speed?
To decrease the potential of an abnormal start by reaching normal idle rpm faster
What is a normal start?
A rapid increase in internal turbine temperature within limits
What are the different types of abnormal starts?
Hot start
Hung start
False start
Wet start
What is a hot start?
When you exceed the max allowable turbine temperature during start
What is a hung start?
When turbine temperature continues to rise and compressor rpms stabilizes below normal
“Hung is hot, false is not.”
What is a false start?
When compressor rpms stabilizes below normal and turbine temperature remains within limits
“Hung is hot, false is not.”
