An Autogyro is an aircraft utilizing a rotary wing to produce lift instead of fixed wings like in more conventional airplanes. Unlike a helicopter that has a rotor powered by an on-board power train, an autogyro’s rotor turns purely because of the aerodynamic forces working in on it. These aerodynamic forces are generated by a separate source of propulsion. Think of it like a conventional aircraft, except the wings are replaced by a rotor.
Instead of the air rushing past the wing of a fixed-wing aircraft and generating lift, it rushes through the rotor, causing it to spin. This is called autorotation. Below are two vector diagrams explaining autorotation and powered rotors in more technical terms:
Vector Diagram of Autogyro’s autorotation:
Verctor diagram of Helicopter’s powered rotor:
Now that you know the basics of autorotation, it is easy to understand the advantages and disadvantages of an autogyro when compared to fixed-wing aircraft or helicopters. Autogyros have two distinct advantages, the first being flying low and slow, safely. Autogyros cannot stall and only lose altitude as apposed to fixed wing aircraft. The second is the ability to land and take-off from shorter runways. Autogyros need very little space to land and can stop dead in the right conditions and with the right pilot. Taking-off also does not require a lot of runway, especially if you have a powerful autogyro with a proper pre-rotation system. The pre-rotation system is key when talking about short take-offs in autogyros as it spins the rotor before the take-off run, adding energy and shortening the runway length needed to break ground.