Two Crossing Rotors | Syncropter

This is K-MAX, an anxiety machine, also known as a synchropter, or, intermeshing-rotor helicopter, which is a synchronized twin-rotor, turning in opposite directions.

This technology was developed by German Anton Flettner in the 1930s.
But what's the magic that prevents the blades from colliding?
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Note 1: This video is an adaptation of a video from my Brazilian Portuguese channel called "Integrando Conhecimento".
Note 2: "The appearance of U.S. Department of Defense (DoD) visual information does not imply or constitute DoD endorsement."