Autogyros are in essence, a hybrid- half airplane, half helicopter. A basic autogyro consists of an airframe with a rotor mounted on top, and a propeller mounted either on the front or the rear of the aircraft. An engine powers only the propeller.
The theory to autogyro flight is relatively simple. The rotor is free-spinning. It only turns when the motion of the aircraft forces relative wind to auto-rotate the rotor. A conventional plane flies by moving the wings through the air creating lift. An autogyro uses forward motion through the air to spin a rotor, creating lift!
A pilot maneuvers an autogyro through the air by manipulating three controls- a stick (called the cyclic), rudder and throttle. The Cyclic control tilts the rotor in different directions, providing nose up and nose down control (pitch) and rotation on the longitudinal axis (roll). The rudder pedals provide control on the vertical axis (yaw). By manipulation of the rudder, the pilot can yaw the nose of the Autogyro to the left or to the right. The throttle controls the power setting of the engine. Most autogyros also have a clutch that can momentarily rotate the main rotor while on the ground.
Autogyros have several advantages. They have amazing take-off performance. A mere 50 feet of runway, field or road, and you'll be flying! 15 feet of take off run are also not uncommon! Compared to fixed wing aircraft, they also have great low speed flight capabilities. They can fly at speeds as low as 15m.p.h, due to the fact that the surface that is providing lift is rotating and does not stall. An autogyro is also much simpler in design than a helicopter, meaning less cost to operate, maintenance, and a lowering of the number of components that can fail, resulting in greater reliability. Autogyros also operate at faster speeds than helicopters, especially considering that the faster helicopters are turbine powered, while autogyros are usually piston powered. A higher speed is achieved because in a helicopter, the rotor must provide both thrust and lift, while in an autogyro, the rotor only provides lift, thrust being accounted for by the propeller. In an autogyro, engine failure too is relatively simple. The aircraft will just descent slowly towards the ground.
Now that all of that has been said, who was the mastermind that invented these amazing machines? It all goes down to basically one man, the Spaniard Juan de la Cierva. He first began work on the project in 1919, but the first autogyro didn't fly until January 9th 1923. Although functional, Cierva's designs still needed improvement. One notable effect, due to the rigidity of the rotor, was a strong gyroscopic effect. This would try to tilt the aircraft as soon as it tried to move. Throughout the next decades, other engineers continued to refine the design of the autogyro.