There are actually brave souls around the world who build and fly their own jetpacks, most notably Yves Rossy, a Swiss pilot who created a flying wing powered by four small turbofan engines.

WSJ: Jetlev R200 Jetpack: Personal Flight, Beyond Bond

Turbines run most efficiently at high speeds, and fans at low speeds, so turbofan engines have to compromise between the two, because the engine's design requires them to turn at the same speed.

ECONOMIST: Monitor

Four turbofan jet engines, with afterburners, are each able to provide more than 30, 000-lbs of thrust.

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