Autorotation is the name given to the generation of lift by the main rotor even though no power is being provided to the rotor by an engine. Gyrocopters have an un-powered main rotor so they rely continuously on autorotation as their source of lift. Autorotation is a complex phenomenon involving the balance of opposing aerodynamic forces along the rotor's blades. Generally, however, it is the portion of the blade nearer the hub that provides the aerodynamic force tending to increase rotational speed, and the portion toward the blade tip that provides the preponderance of the lifting force.

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