In 1923 Juan de la Cierva (1895-1936) pioneered the first autogyro. These machines appear superficially similar to helicopters, but with a single unpowered rotor. Early autogyros were less maneuverable than helicopters and were unable to take off or descend vertically. The invention of the autogyro predated the helicopter and so paved the way for vertical flight. Autogyro rotors are not powered, unlike those of a helicopter, and thus work in a similar way to spinning "helicopter" seed pods such as those of the box elder tree, Acer negundo. These seeds are aerodynamically shaped to spin as they fall, allowing the seed to disperse much further; autogyro rotors autorotate in the same way.
The power or thrust of the autogyro comes from a powered propeller (or in later designs a jet engine) meaning that most do require some takeoff runway, but normally only tens of feet. As they can land in an equally small space, the autogyro had distinct advantages over airplanes as they are much more maneuverable and stable flying at low speeds, but can also fly faster than helicopters. The autogyro is also unable to "stall" in mid-air, making it considerably safer than other aircraft.
De la Cierva started developing his ideas for the autogyro around 1920, motivated partially by the frequent crashes that fixed-wing aircraft often suffered—especially at low speeds. The first successful autogyro flight was in 1923, in a machine called the C4. This was not a perfect machine by any means, but each time it stalled or there was a problem in mid-air, it was able to glide slowly back to earth on its autorotating blades.
