Leonardo Da Vinci was probably the first person to conceive a machine that would use vertical lift to produce flight. Even at the time, when he made a miniature of what he variously called an aerial screw or air gyroscope, he mused that this contraption would have to wait for a power source with a much more favorable power to weight ratio than a human being. His dream would eventually be realized in the development of the helicopter, but before that, we had the autogyro.

Also known as a gyroplane, a pure autogyro is simply a flying machine where the lift is provided not by a fixed wing or wings, but by unpowered (usually, hence the name which means self spinning) rotor blades mounted above the fuselage on a vertical shaft and the forward motive force is provided by a propeller. The forward motion spins the rotor blades through an aerodynamic phenomenon called autorotation. Most autogyros power the rotors for takeoff by diverting power from the main engine. This allows them to take off from very short runways or rooftops as they can sort of jump in the air before starting their forward motion. Once aloft the rotor shaft can be disconnected and autorotation takes over. They are very manouverable and can rise and fall steeply but they can't rise vertically like a helicopter. They are also not very fast or fuel efficient. Though they can't hover, it is impossible to stall them and they can land vertically even without power which makes them extremely safe.

The autogyro was invented and first flown successfully by Juan de la Cierva y Codorníu, a Spanish engineer. Though he had been working on the design of an autogyro since 1920, his C4 design first flew with de la Cierva at the controls in January 9th, 1923. The C4 owed its success to the use of hinged rotor blades that would allow the pilot to adjust the pitch of the blade. The C4 however, still had fixed wings to provide control surfaces. His C11 did away with the progressively vestigial wings of intervening designs and introduced the rotor powered 'jump start' maneuver. He registered the trademark Autogiro, fine tuned his designs over the years and licensed them to a number of manufacturers from his design and management facilities in England, the Cierva Autogiro Company. Amelia Earhart, the first woman ever to fly an autogyro, achieved the then record altitude of 18,415 feet in April 8 1931.

The autogyro enjoyed a brief period of popularity and interest as an observational platform and mail transport. In 1936 de la Cierva died in a fixed wing aircraft accident* and the Focke-Wulf Fw 61, the first practical helicopter saw the light of day, almost completely eclipsing the autogyro.

Autogyros have found many small niches through the years. Most famously, small, light unpowered autogyros were used by Germany in World War II as observational platforms towed by submarines, the Focke-Wulf Fa-330 Bachstelze (Wagtail). In the heat of battle German subs would often submerge without retrieving the unfortunate pilots. Inspired by the Fa-330, Igor Bensen produced an unpowered gyro in 1950 and later a powered version which established a strong foothold in the sport aviation field. Bensen's designs use a rear mounted propeller as many other ultra-light aircraft do.

* ironically the airplane in which he was flying stalled due to the loss of a motor and plummeted to the ground shortly after take off at Croydon airport. If he had been in an autogyro, he would have slowly descended to safety and perhaps he would have gone on to perfect the helicopter and not Igor Sikorsky.
Autogiros/Historia,http://www.aviacionulm.com/autogiroshistoria.html, 9/16/2004
Autogyro,http://en.wikipedia.org/wiki/Autogyro, 9/16/2004
The contributions of the autogyro,http://www.centennialofflight.gov/essay/Rotary/autogiro/HE3.htm, 9/16/2004
Autogiro,http://www.centennialofflight.gov/essay/Dictionary/autogyro/DI8.htm, 9/16/2004
Evolution of Helicopter Flight,Professor J. Gordon Leishman,http://www.flight100.org/history/helicopter.html, 9/16/2004

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