Bell XV-3

The Bell XV-3 (Bell 200) is an American tiltrotor aircraft developed by Bell Helicopter for a joint research program between the United States Air Force and the United States Army in order to explore convertiplane technologies. The XV-3 featured an engine mounted in the fuselage with driveshafts transferring power to two-bladed rotor assemblies mounted on the wingtips. The wingtip rotor assemblies were mounted to tilt 90 degrees from vertical to horizontal, designed to allow the XV-3 to take off and land like a helicopter but fly at faster airspeeds, similar to a conventional fixed-wing aircraft. The XV-3 was first flown on 11 August 1955. The first prototype use three blade rotors, and had issue with flutter crashing two months after its first flight. Tests were conducted on the second prototype with 2-blade rotors and flew successfully. Although it was limited in performance compared to later types, the aircraft successfully demonstrated the tiltrotor concept, accomplishing 110 transitions from helicopter to airplane mode between December 1958 and July 1962. The XV-3 program ended when the remaining aircraft was severely damaged in a wind tunnel accident on 20 May 1966. The data and experience from the XV-3 program were key elements used to successfully develop the Bell XV-15, which later paved the way for the V-22 Osprey. The remaining prototype survived to the 21st century when it was restored by Bell, with a two-year restoration that included engineers that worked on the XV-3 originally. It was then transferred to the National Museum of the United States Air Force in Dayton, Ohio, where it was put on display.

Summary from Wikipedia, photo via Wikimedia Commons, licensed under CC BY-SA.