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I understand that the power extracted from the turbine is used to drive the compressor which sucks and squeezes air sent to the combustion chamber, and the cycle continues.

But initially the compressor has to suck in air! What drives it at this stage before the turbine takes over?

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Turbine engines are spun up to idle speed using a starter. This is typically in the form of an electric motor for smaller turbine engines and APUs and pneumatic powered starters for large turbine engines. Once the gas core is spun up to a minimum speed, typically around 12-20% maximum core speed, fuel is introduced and ignited, causing a self sustaining combustion and the engine core spins up to its idle speed, typically about 50% - 60% maximum speed, before the starter cuts out. Care has to be taken not to introduce fuel to the engine prior to reaching these speeds as the engine can overheat during startup and be seriously damaged (this is about the only disadvantage of aviation gas turbines).

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  • $\begingroup$ You don't really have to worry about screwing up a start with FADEC engines. Most of them now you just push a button and away it goes. $\endgroup$ – John K Dec 31 '19 at 13:21
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    $\begingroup$ IF your aircraft is power by wire, that is. $\endgroup$ – Carlo Felicione Dec 31 '19 at 13:37
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    $\begingroup$ @JohnK Still, if you want to know how it works, How are turbine engines started? gives a really helpful overview and How is bleed air used to start a jet engine? shows what "pneumatic powered starters" are. $\endgroup$ – PerlDuck Dec 31 '19 at 13:46
  • $\begingroup$ Not to worry; I'm well acquainted with starting systems. My point is the disadvantage of crew member being able to ruin an engine starting it is eliminated with FADEC. $\endgroup$ – John K Dec 31 '19 at 13:49
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    $\begingroup$ And even then, you’d better closely supervise the process, since, if it goes wrong, you only have seconds to bring the engine to idle cutoff before it overheats. $\endgroup$ – Carlo Felicione Dec 31 '19 at 13:50

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