WEBVTT - How do jet engines start?

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<v Speaker 1>Welcome to brain Stuff from how stuff works dot com

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<v Speaker 1>where smart Happens. Hi Am Marshall Brain with today's question,

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<v Speaker 1>how do they start jet engines? On airplanes? A jet

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<v Speaker 1>engine has two sets of veins that are connected together

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<v Speaker 1>by a shaft. The hot gases produced by the burning

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<v Speaker 1>fuel drive one set of veins in exactly the same

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<v Speaker 1>way that the wind turns a windmill. These veins are

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<v Speaker 1>at the back of the engine and the hot exhaust

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<v Speaker 1>casts are blowing against them to spin them. Those veins

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<v Speaker 1>then connect to a shell aft which goes towards the

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<v Speaker 1>front of the engine to spin the turbans compressor veins,

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<v Speaker 1>so when the exhaust veins are spinning, the compressor veins

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<v Speaker 1>are also spinning and compressing the air that comes into

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<v Speaker 1>the engine. The starting process normally uses an electric motor

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<v Speaker 1>to spin that main turbine shaft. The motor has bolted

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<v Speaker 1>to the outside of the engine, and it uses gears

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<v Speaker 1>and another shaft to connect to that main shaft. The

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<v Speaker 1>electric motor spins the main shaft until there's enough air

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<v Speaker 1>blowing through the compressor and the combustion chamber to light

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<v Speaker 1>the engine. Fuel starts flowing in an igniter similar to

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<v Speaker 1>a spark plug ignites the fuel. Then fuel flow is

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<v Speaker 1>increased to spin the engine up to its normal operating speed.

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<v Speaker 1>If you've ever been at an airport and watched a

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<v Speaker 1>big engine start up on a jet, you know that

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<v Speaker 1>the blades start rotating slowly. You can see them spinning

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<v Speaker 1>at the front of the engine. The electric star motor

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<v Speaker 1>does that. Then you can hear a pop and see

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<v Speaker 1>smoke come out the back of the engine as the

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<v Speaker 1>fuel first starts to ignite. Then the engine spins up

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<v Speaker 1>and starts producing thrust. On smaller turbine engines, especially home

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<v Speaker 1>built models, another way to start the engine is to

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<v Speaker 1>simply blow air through the air intake with a hair

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<v Speaker 1>dryer or a leaf blower. This technique has the same

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<v Speaker 1>effect of getting air moving through the combustion chamber, but

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<v Speaker 1>it doesn't require the complexity or weight of an attached

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<v Speaker 1>starter motor. Besides the starter shaft, most big jet engines

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<v Speaker 1>include another output shaft for driving things like electrical generators,

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<v Speaker 1>air conditioning compressors, and so on needed to operate the

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<v Speaker 1>plane and keep it comfortable. This shaft can connect to

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<v Speaker 1>the main turbine shaft at the same point the starter does,

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<v Speaker 1>or somewhere else on the shaft. Do you have any

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<v Speaker 1>ideas or suggestions for this podcast? If so, please send

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<v Speaker 1>me an email at podcast at how stuff works dot com.

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