Bell X-5
A variable-sweep research aircraft built by Bell Aircraft Corporation for the U.S. Air Force and the NACA, developed from the captured Messerschmitt P.1101 to test changing wing sweep in flight. Two aircraft flew from 1951 to 1955: one was lost in a fatal spin accident in 1953, and the other made 122 NACA flights before going to the Air Force Museum in 1958.
Why It Mattered
The Bell X-5 was built to answer one question: could an aeroplane change its wings' sweep in flight, and what would that buy? NASA's fact sheet lays out the operational logic — wings spread for takeoff would cut both takeoff speed and the runway needed, then sweep back in the air to reduce drag and raise speed. For research, a single variable-sweep aircraft could stand in for a whole series of fixed-sweep experimentals, each of which returned data at only one wing angle. Wikipedia describes the X-5 as the first aircraft able to change the sweep of its wings in flight. The type's findings fed the variable-sweep generation that followed: NASA lists the F-111, the F-14 and the B-1 among the American aircraft that took up the feature from the 1960s onward.
Design Notes
The X-5 grew out of the captured Messerschmitt P.1101, a small jet whose wings could be reset on the ground to three fixed angles between 35 and 45 degrees, but which never flew. Bell's Robert Wood proposed in July 1948 that an enlarged derivative be built that could change its sweep in flight instead, and Air Force Headquarters approved the project on 4 February 1949 with the NACA's support. The two aircraft kept the German design's broad layout: a nose-mounted intake, a bubble canopy, an underslung engine and a boom-mounted tail. In flight the wings pivoted between 20 and 60 degrees, and as they swept they also slid about 27 inches forward on rails inside the fuselage, compensating for the shifting centre of gravity and centre of pressure. A full change took about 20 seconds; a hand crank covered electrical failure, and the aircraft could not land safely with more than 40 degrees of sweep.
Operational History
The first X-5, serial 50-1838, was delivered to Edwards Air Force Base on 9 June 1951 and flew 11 days later in the hands of Bell test pilot Jean "Skip" Ziegler. Ziegler worked the sweep mechanism in flight for the first time on the ninth flight, on 27 July, and Bell's 20-flight Phase I programme closed on 8 October 1951. The Air Force's Maj. Frank Everest then flew the aircraft six times across December 1951 and January 1952, after which it passed to the NACA on 8 January 1952. NACA pilot Joe Walker checked out the next day and led the research flying — stability and control at 45 and 60 degrees of sweep, gust response, tail loads, buffeting, even drag studies behind an F-80 and a B-29 and chase work for a B-47. Scott Crossfield and Walter P. Jones joined in April 1952; Jones flew eight times and Crossfield ten missions through 1954, with Walker the programme's main pilot into mid-1954. The type's spin behaviour was its dark side: Walker needed 18,000 feet to recover from a spin entered at 36,000 feet in October 1952, and Crossfield later called the aircraft a terrible spinner. The second X-5, flown by the Air Force, was lost on 13 October 1953 when Maj. Raymond Popson could not recover from a spin with the wings at 60 degrees. Stanley Butchart and John McKay took over the flying from June 1954, and the final NACA flight came on 25 October 1955, a checkout by new pilot Neil Armstrong that ended with a separated landing-gear door and the aircraft grounded.
Afterlife
NASA counts 122 NACA flights for the first X-5, a per-aircraft figure kept at that scope here rather than folded into a programme total. The verdict on the programme was mixed, NASA judges: the flights confirmed wind-tunnel predictions of drag reduction and performance gains from variable sweep, and the pilots found the concept gave a tactical edge, but the sliding mechanism itself proved impractical. The remedy came from NACA engineers at Langley, who moved the wings' pivot points outside the fuselage — the arrangement later swing-wing aircraft adopted. The surviving X-5 was sent to the Air Force Museum in March 1958; NASA's museum note names its home as the National Museum of the United States Air Force at Dayton, Ohio. Wikipedia adds that the aircraft is displayed in that museum's Research & Development Hangar.