Tiltrotor - 'Copter and plane in one

This paper is concerned with a most unusual aircraft, called the Tiltrotor XV-15, which combines the versatility of the helicopter with the characteristics of a conventional aircraft. Two large, three-bladed propellers are mounted at the tips of the wings. For takeoff, the propellers and their engines are rotated 90 degrees, and the XV-15 can climb vertically into the air as a helicopter. When the vehicle is off the ground, propellers and engines rotate forward, and the lift is transferred from the propellers to the wings. As a conventional aircraft, the Tiltrotor can cruise for more than two hours. Operating as a vertical-takeoff aircraft, the XV-15 can fly twice as fast as a helicopter and deliver payloads on half the fuel when traveling distances greater than 185 kilometers. The results of the first three years of flight-testing are discussed, taking into account the relationship of rotor vibrations and/or air turbulence to resonance of a section of the Tiltrotor's wing.