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Speaker 1: Welcome to brain Stuff from how stuff works dot com

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Speaker 1: where smart Happens. Hi. I'm Marshall Brain with today's question.

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Speaker 1: When an acrobatic airplane flies upside down, how does the

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Speaker 1: fuel get to the engine? Gravity is one of those

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Speaker 1: amazing things. It's constant and we take it completely for granted.

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Speaker 1: For example, the fuel system in any normal car or

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Speaker 1: airplane depends on gravity to position and move the fuel

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Speaker 1: in the fuel tank. A high wing monoplane would stall

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Speaker 1: almost immediately if you tried to fly it upside down.

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Speaker 1: Gravity draws the fuel from the fuel tanks in the

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Speaker 1: wings down to the engine. So how does an aerobatic

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Speaker 1: plane fly upside down and get fuel from the gas

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Speaker 1: tank to the engine. One technique is called a flop tube.

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Speaker 1: It's a tube with a weight on it that literally

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Speaker 1: flops around inside the fuel tank. When you fly upside

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Speaker 1: down or sideways, the fuel and the tank shifts, but

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Speaker 1: the tube follows the fuel and flops into position. There's

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Speaker 1: one other technique that's used on some airplanes. It's a

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Speaker 1: small extra fuel tank located near the pilot's feet. When

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Speaker 1: the plane is right side up, fuel flows down into

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Speaker 1: this tank. Then, when the plane flies upside down. This

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Speaker 1: tank is above the engine and it provides the fuel

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Speaker 1: by gravity. Be sure to check out our new video podcast,

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