What rotorcraft term describes a rotorcraft that, for its horizontal motion, depends principally on engine-driven rotors?

• A. Gyrodyne
• B. Gyroplane
• C. Helicopter
• D. Idle Thrust

Answer: (C)

The key idea is how forward motion is produced in rotorcraft. If the horizontal motion comes mainly from the thrust of an engine-driven main rotor, the aircraft is a helicopter. In a helicopter, the same powered rotor that provides lift is tilted to create forward thrust, so the engine directly drives the rotor that moves the aircraft forward. A gyroplane, by contrast, has a rotor that is not driven by the engine for forward flight; it uses a propeller to push the plane forward while the rotor autorotates. A gyrodyne uses the powered rotor primarily for takeoff and hover, but in forward flight the propulsion that actually moves the aircraft comes from a separate source, not from the engine-driven rotor. Idle thrust isn’t a rotorcraft type describing how forward motion is produced. So the term that best fits a rotorcraft whose horizontal motion is principally from engine-driven rotors is a helicopter.