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Speaker 1: Welcome to brain Stuff from how stuff works dot com
Speaker 1: where smart Happens. Hi Am Marshall Brain with today's question,
Speaker 1: how do they start jet engines? On airplanes? A jet
Speaker 1: engine has two sets of veins that are connected together
Speaker 1: by a shaft. The hot gases produced by the burning
Speaker 1: fuel drive one set of veins in exactly the same
Speaker 1: way that the wind turns a windmill. These veins are
Speaker 1: at the back of the engine and the hot exhaust
Speaker 1: casts are blowing against them to spin them. Those veins
Speaker 1: then connect to a shell aft which goes towards the
Speaker 1: front of the engine to spin the turbans compressor veins,
Speaker 1: so when the exhaust veins are spinning, the compressor veins
Speaker 1: are also spinning and compressing the air that comes into
Speaker 1: the engine. The starting process normally uses an electric motor
Speaker 1: to spin that main turbine shaft. The motor has bolted
Speaker 1: to the outside of the engine, and it uses gears
Speaker 1: and another shaft to connect to that main shaft. The
Speaker 1: electric motor spins the main shaft until there's enough air
Speaker 1: blowing through the compressor and the combustion chamber to light
Speaker 1: the engine. Fuel starts flowing in an igniter similar to
Speaker 1: a spark plug ignites the fuel. Then fuel flow is
Speaker 1: increased to spin the engine up to its normal operating speed.
Speaker 1: If you've ever been at an airport and watched a
Speaker 1: big engine start up on a jet, you know that
Speaker 1: the blades start rotating slowly. You can see them spinning
Speaker 1: at the front of the engine. The electric star motor
Speaker 1: does that. Then you can hear a pop and see
Speaker 1: smoke come out the back of the engine as the
Speaker 1: fuel first starts to ignite. Then the engine spins up
Speaker 1: and starts producing thrust. On smaller turbine engines, especially home
Speaker 1: built models, another way to start the engine is to
Speaker 1: simply blow air through the air intake with a hair
Speaker 1: dryer or a leaf blower. This technique has the same
Speaker 1: effect of getting air moving through the combustion chamber, but
Speaker 1: it doesn't require the complexity or weight of an attached
Speaker 1: starter motor. Besides the starter shaft, most big jet engines
Speaker 1: include another output shaft for driving things like electrical generators,
Speaker 1: air conditioning compressors, and so on needed to operate the
Speaker 1: plane and keep it comfortable. This shaft can connect to
Speaker 1: the main turbine shaft at the same point the starter does,
Speaker 1: or somewhere else on the shaft. Do you have any
Speaker 1: ideas or suggestions for this podcast? If so, please send
Speaker 1: me an email at podcast at how stuff works dot com.
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