autogiros

An autogiro, or autogyro, is a type of rotorcraft in which lift is produced by a freely turning rotor and thrust is provided by a separate engine-driven propeller. Because the rotor is not powered, its rotation is sustained by autorotation as the aircraft moves forward. Consequently, autogiros require forward airspeed for takeoff and landing and cannot hover like helicopters. The rotor typically spins due to airflow, and its blades are mounted on a hub with hinges that allow flapping and lead-lag motion to absorb changing loads.

Most autogiros also carry conventional stabilizing surfaces, including a tail assembly with a rudder and elevator. Some designs include small fixed wings to improve stability. Control is achieved with the usual aerodynamic surfaces for pitch and yaw, while the rotor continues to autorotate to provide lift as speed changes. A pre-rotation device may be used to spin the rotor up to operating RPM before takeoff.

History and development: The autogiro was developed in the 1920s by Spanish engineer Juan de la Cierva to address instability in early rotorcraft. Cierva’s designs demonstrated safe landings on engine loss and popularized the concept of autorotation. His licensed manufacturing sites produced machines such as the Pitcairn PCA-2 in the United States and various models elsewhere. Autogiros found roles in observation, aerial surveying, training, and light transport during the 1930s, before helicopters with powered rotors largely supplanted them.

Legacy: Today the term autogyro is often used for historic machines, while modern light rotorcraft that retain the unpowered-rotor principle are commonly called gyrocopters or autogyros. These contemporary designs emphasize light sport operation, safety features, and easier handling, but like their predecessors they rely on forward speed to maintain rotor RPM.