A Tiltrotor was a helicopter with the vertical lift capability of a conventional helicopter and the speed and range of an airplane. The most famous was the V-22 Osprey.
(Note: The background section of this page uses most of the same words as Terra Futura's page on conventional helicopters to save time.)
The concept of a helicopter originated with Leonardo da Vinci in the 1480s. Along with other flying machines, the helicopter took a while to be successful. The word helicopter was originally a French word derived from Greek. Helicopters were built throughout the early 20th century. However, it was not until 1942 that Igor Sikorsky built the first successful helicopter. With the advent of the R-4, helicopters entered mass production. The R-4 was the only helicopter used in World War II. With the advent of the turboshaft engine, more and more helicopters were being produced. They were larger, faster, and had a higher performance. But there was a problem. The rotor blades caused the helicopter to torque. A tail-rotor was used to stop that. Soon, however, more advanced designs would come.
Tech Level: 10
Tiltrotors had been a concept since the 1930s. However, it was not until the 1980s that tiltrotors entered commercial use. The V-22 began development in 1981. Its first flight was in 1989. Testing began. The V-22 Osprey was finally brought into service in 2007. (Hence, the Tech Level.) There was a problem though. 6 accidents since introduction were caused by a hazardous transition phase. There were two ways to solve this problem. One of them was a mono tiltrotor aircraft.