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Jet engines have a little spiral painted on the center of the turbine. You’ve probably seen them while boarding or from your window seat. They’re not just cool designs, they’re actually an important safety measure. See, the human eye can’t tell how fast a jet engine is spinning, and any other pattern won’t be detectable. A spiral, though, warns people that the jet is spinning and they shouldn’t get close or they’ll be sucked in. Once ground crew can see the spiral shape, they know it’s safe to approach.

Full story at YouTube.

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