15.13 - Starting and Ignition Systems Flashcards
In order to start a gas turbine engine successfully what two criteria must be satisfied?
- The core engine (compressor, combustor and turbine) must be rotated up to a speed sufficient to provide adequate pressure airflow and fuel flow.
- An ignition system capable of lighting a relatively weak supply of fuel and to continue this until reliable self-sustaining operation is achieved.
What type of starter is most commonly used on Large Gas Turbine Engines?
Also which type is used for starting turboprops?
Large Gas Turbine Engines = Pneumatic (air turbine) starter motor
Turboprop = Electric starter motor
Describe the benefits of using a combined Starter/Generator?
Where are they used?
It is much lighter than two separate starter and generator components.
It is always permanently splined into the engine’s accessory drive train.
Used on corporate jets and some APU’s
What is the first step when starting and APU?
The first step in starting the APU is to turn battery switch ‘’ON’’
APU is usually started by an Electric starter motor powered exclusively by a separate battery.
What voltage must typically be induced in a high tension ignition plug to create ionisation of the air gap?
20,000 volts
List the 2 starting methods for a gas turbine engine?
- Electric starter motor (turbo-props)
- Pneumatic (air turbine) starter motor
Where are DC starter motors used on large aircraft?
'’Heavy duty’’ aircraft - older turboprop engines
Starter-generators are normally used on what type of engine?
Light Business Jets
- Compact / lightweight /2 seperate machines in 1
What is the main advantage of an air starter (what pressure is required)?
It’s main advantage is it’s high power to weight ratio - it weighs approx. 20% of the weight of a comparable electric starter.
Pressure = 30 to 45 psi from APU or ground pneumatic cart
What is the rotational speed of an air starter?
The rotational speed of an air starter is 60 - 80,000 RPMa
How is a manual start achieved?
Manual opening of the butterfly valve via an Allen key or spanner turned spindle is a common feature
List the 3 purposes of an ignition system?
To be able to ignite the fuel spray from the fuel burners at any point within the aircraft’s operational envelope including:
- ground start-up
- in flight relight
- Intermittent or low energy use during heavy precipitation to guard against flame-out
What part of an ignition system is normally air cooled?
Igniter Sleeve
What is the sequence for stripping an ignition system
- Pull and collar relevant circuit breakers
- Disconnect input lead
- wait interval detailed in manual
- Disconnect HT lead and ground (not to engine casing) to discharge capacitor systrem
