The autogiro was for many years the most reasonable alternative to the helicopter as a means of vertical flight. Because the rotor is not powered, the autogiro does not have to contend with torque (the tendency of the aircraft to turn in the opposite direction of the rotor) and thus avoided many of the control problems that impeded the development of the helicopter. The autogiro’s rotor is designed so that a blade set at a low positive angle of pitch will rotate automatically as long as an airstream is kept flowing through the rotor (autorotation). As the autogiro is propelled ...(100 of 4382 words)