Tiltrotor

A tiltrotor is an aircraft that generates lift and propulsion by way of one or more powered rotors (sometimes called proprotors) mounted on rotating shafts or nacelles usually at the ends of a fixed wing. Almost all tiltrotors use a transverse rotor design, with a few exceptions that use other multirotor layouts. Tiltrotor design combines the VTOL capability of a helicopter with the speed and range of a conventional fixed-wing aircraft. For vertical flight, the rotors are angled so the plane of rotation is horizontal, generating lift the way a normal helicopter rotor does. As the aircraft gains speed, the rotors are progressively tilted forward, with the plane of rotation eventually becoming vertical. In this mode the rotors provide thrust as a propeller, and the airfoil of the fixed wings takes over providing the lift via the forward motion of the entire aircraft. Since the rotors can be configured to be more efficient for propulsion (e.g. with root-tip twist) and it avoids a helicopter's issues of retreating blade stall, the tiltrotor can achieve higher cruise speeds and takeoff weights than helicopters. A tiltrotor aircraft differs from a tiltwing in that only the rotor pivots rather than the entire wing. This method trades off efficiency in vertical flight for efficiency in STOL/STOVL operations. The first work in the direction of a tilt-rotor (French "Convertible") seems to have originated ca. 1902 by the French-Swiss brothers Henri and Armand Dufaux, for which they got a patent in February 1904, and made their work public in April 1905. Concrete ideas of constructing vertical take-off and landing (VTOL) aircraft using helicopter-like rotors were pushed further in the 1930s. The first design resembling modern tiltrotors was patented by George Lehberger in May 1930, but he did not further develop the concept. In World War II, Weserflug in Germany came up with the concept of their P.1003/1 around 1938, which was tilting to the top with part of the wings but not the full wings, so it may be in between tilt-rotor and tilt-planes.