Definition
A rotorcraft whose rotor is normally driven by the engine for takeoff, hovering, and landing, but is allowed to autorotate during forward cruise flight, with forward thrust supplied by a separate propeller or jet. The rotor remains powered only enough to keep it turning at flight RPM; most of the cruise lift still comes from the rotor, but it is no longer the source of forward thrust.
Plain English
An aircraft that takes off and hovers like a helicopter, but flies forward like an airplane using a separate propeller for thrust while the rotor spins freely overhead to provide lift.
Context Anchor
Seen in rotorcraft category discussions, aircraft certification language, and comparisons between helicopters, gyroplanes, and other rotorcraft.
Derivation
From Greek 'gyros' meaning circle or turn, and 'dyne' from Greek 'dynamis' meaning power or force. The name reflects the design: a rotating wing that produces force, but with the power applied differently than in a conventional helicopter.
Why Pilots Care
Gyrodynes sit between helicopters and autogyros in the rotorcraft family. Knowing the distinction matters when reading certification rules, performance data, or accident reports, because the handling, power requirements, and flight envelope are not the same as a pure helicopter.
Intuition Check
Do not assume a gyrodyne is just another name for a gyroplane. A gyroplane’s main rotor is not normally engine-powered in flight, while a gyrodyne’s rotor is powered for takeoff, hovering, landing, and part of its forward flight.
Example Sentence 1
The gyrodyne lifted off vertically under rotor power, then transitioned to forward flight as the pusher propeller took over thrust duties.
Example Sentence 2
During forward flight the gyrodyne's rotor continued turning without engine drive, providing lift through autorotation.