Bell X-5
      The Bell X-5 was the world's first airplane to vary the sweepback of its wings in flight. It was built to prove the theory that by increasing the sweepback of an airplane's wings after takeoff, a higher maximum speed could be obtained, while still retaining low takeoff and landing speed and higher rate of climb with the wings swept forward.  It was based on the German Messerschmitt P.1101 discovered and captured by American troops at the end of World War II,
      Two X-5's were constructed (USAF serial numbers 50-1838 and 50-1839), both were flown from Edwards AFB. The X-5's variable sweep wing could be adjusted in flight from 20 to 60 degrees.   The first example was flown by the Air Force, and crashed on October 13, 1953, killing the pilot (USAF test pilot Major Raymond Popson). The other X-5 was flown by the NACA. Notable pilots that flew the X-5 include Neil Armstrong, Gen. Albert Boyd, Scott Crossfield, and Joseph Walker. The X-5 was retired from service in 1955, and is now on display at the USAF museum in Dayton, Oh.
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