Chapter 12: Starting System Flashcards
4 sub system that needs to be started almsot simultaneously to start engine
air, fuel, oil, ignition supply
what are the soruces of supply to start engine
APU
GPU
other running engine
what power is needed to start an engine
pneumatic, electric
how long is the starting process?
10 seconds
how does the starter motor help start the engine?
starter motor runs main gear box > rotates HP shaft
what is the self-sustaining speed for twin spool engine?
40-50% N2 RPM
what is a hung start?
engine not reaching self sustaining speed
requirements of ignition system
1) igniting low temp lean fuel/air mixture which is at high speeds
2) in-flight relighting
3) prevent engine flameout
4) operate even when spark plug foul
5) safety (prevent electrocution)
what is spark plug fouling?
foreign material accumulating at tip of igniter
what are the pneumatic and electrical supply for?
pneumatic: spin starter motor
electrical: powering EEC and ignition units
types of gas turbine engine starter
1) Air turbine starter (turbofan)
2) cartridge (fighter)
3) electric motor starter (turboshaft/prop)
how does cartridge air starter work?
cartridge ignited by applying voltage > cartridge generate gas > rotation done by gas
what is a starter control valve?
on/off valve allowing air supply to starter motor
manual overridden switch to open valve for troubleshooting
controlled by EEC
components of ignition system
1) ignition unit
2) igniter plug
3) high tension leads
4) circuit breakers
5) air cooling tubes
safety precautions when handling ignition problem
1) shut down engine and let it cool for 10 mins
2) pull all relevant circuit breakers
3) wear high temp resistant gloves
4) ground tension ignition leads
common starting problems
1) low duct pressure
2) no rotation (no rpm)
3) start valve solenoid failure
4) no ignition/fuel flow/oil pressure
5) hung start
6) hot start
what is a hung start?
engine accelerates to some intermediate RPM below self sustaining speed without increasing or decreasing
reason for hung start
not enough energy or power to accelerate the engine
troubleshooting hung start
engine shut down, restart from beginning after letting it cool down
what is hot start?
when EGT goes above limit as a result of rich fuel/air ratio
how can hot start be anticipated?
greater than normal initial fuel flow
how to troubleshoot hot start?
dry motor till EGT is below 100degC and retry
what is dry motoring?
starting engine without fuel
