Bell X-1E (46-063)

Photograph: Bell X-1 (46-063) taken by Paul Cremin on 2 July 2013 at the NASA Armstrong Flight Research Center, California, USA taken with a Canon EOS 40D with Canon EF 17-85mm lens, f16, 1/500 sec, ISO 400.

The Bell X-1E on display at a jaunty angle outside the main headquarters building (Building 4800) at NASA's Armstrong Flight Research Center in Edwards, California, is the ultimate and final variant of the historic X-1 rocket-plane series. It represents a crucial bridge between the original generation of supersonic experimental aircraft and the high-hypersonic X-15 programme.

The X-1E did not start its life as a completely new airframe. It was originally built as the X-1-2 (serial number 46-063), a first-generation sister ship to Chuck Yeager's famous Glamorous Glennis (46-062).

By 1951, the National Advisory Committee for Aeronautics (NACA, NASA's predecessor) faced a data crisis. Multiple Mach 2 test aircraft (the X-1D and X-1-3) had been lost to catastrophic fuel-system explosions. Seeking a safer path to study sustained Mach 2 flight and aerodynamic heating, NACA chose to heavily rebuild the aging 46-063 airframe into a cutting-edge testbed.

NACA engineers drastically altered the aircraft, turning it into the X-1E:

• Ultra-Thin Wings: Built by the Stanley Aviation Company, the new wings were a mere 3⅛ inches thick at the root. They were embedded with over 200 pressure sensors and 343 strain gages to measure structural stress and friction heat.
• New Fuel System: Technicians replaced the dangerous high-pressure nitrogen propellant-feed spheres with a brand-new low-pressure turbopump system.

• Cockpit & Ejection Seat: The dangerous side-hatch entry was removed and replaced by an upward-opening canopy, providing the space needed to add an ejection safety seat.

Operating out of the High-Speed Flight Station (now Armstrong), the X-1E made 26 total flights between December 1955 and November 1958:

• The Pilots: Main project pilot Joe Walker flew 21 of the flights, and John "Jack" McKay flew the final 5.

• Performance Records: Joe Walker pushed the aircraft to its maximum speed of Mach 2.24 (1,450 mph) on 8 October 1957, and reached a peak altitude of 70,046 feet on 14 May 1958.

• Stability Upgrades: Flight tests revealed severe directional instability at high speeds. To correct this, engineers fixed two large ventral stabilizer fins onto the rear underside of the bullet-shaped fuselage.

The X-1E flew its 26th and final mission on 6 November 1958, piloted by Jack McKay to test a high-energy synthetic propellant blend known as "U-Deta".

During a routine post-flight X-ray inspection, technicians discovered a significant structural crack in the fuel tank wall. Because the revolutionary X-15 programme was already arriving to take over high-speed research, management decided that the repair costs were unwarranted. The X-1E programme was officially cancelled, and the remaining research goals were transferred to high-performance F-104 Starfighters.

Instead of being scrapped or sent away to a national museum, the historic rocket plane remained at Edwards Air Force Base. It was mounted on a pedestal directly in front of the centre's main building, where it continues to stand today as a monument to the dawn of the supersonic age.