Editing Bell X-1 (section)

==Variants==
Later variants of the X-1 were built to test different aspects of supersonic flight; one of these, the X-1A, with Yeager at the controls, inadvertently demonstrated a very dangerous characteristic of fast (Mach 2 plus) supersonic flight: [[inertia coupling]]. Only Yeager's skills as an aviator prevented disaster; later [[Mel Apt]] would lose his life testing the [[Bell X-2]] under similar circumstances.

[[File:Bell X-1A in flight.jpg|thumb|right|X-1A in flight]]

===X-1A===
('''Bell Model 58A''')
[[File:Bell X-1A.jpg|thumb|right|X-1A]]
Ordered by the Air Force on 2 April 1948, the '''X-1A''' (serial number 48-1384) was intended to investigate aerodynamic phenomena at speeds greater than Mach&nbsp;2 (681&nbsp;m/s, 2,451&nbsp;km/h) and altitudes greater than 90,000&nbsp;ft (27&nbsp;km), specifically emphasizing dynamic stability and air loads. Longer and heavier than the original X-1, with a stepped canopy for better vision, the X-1A was powered by the same Reaction Motors XLR-11 rocket engine. The aircraft first flew, unpowered, on 14&nbsp;February 1953 at Edwards AFB, with the first powered flight on 21&nbsp;February. Both flights were piloted by Bell test pilot [[Jean "Skip" Ziegler]].

After [[NACA]] started its high-speed testing with the [[Douglas Skyrocket]], culminating in [[Scott Crossfield]] achieving Mach&nbsp;2.005 on 20&nbsp;November 1953, the Air Force started a series of tests with the X-1A, which the test pilot of the series, [[Chuck Yeager]], named "Operation NACA Weep". These culminated on 12&nbsp;December 1953, when Yeager achieved an altitude of {{convert|74700|ft}} and a new airspeed record of Mach&nbsp;2.44 (equal to 1620&nbsp;mph, 724.5&nbsp;m/s, 2608&nbsp;km/h at that altitude). Unlike Crossfield in the Skyrocket, Yeager achieved that in level flight. Soon afterwards, the aircraft spun out of control, due to the then not yet understood phenomenon of [[inertia coupling]]. The X-1A dropped from maximum altitude to {{convert|25000|ft}}, exposing the pilot to accelerations of as much as 8g, during which Yeager broke the canopy with his helmet before regaining control.<ref>Young, Dr. Jim. [https://web.archive.org/web/20080215062652/http://www.af.mil/shared/media/document/AFD-080107-018.pdf "Major Chuck Yeager's Flight to Mach 2.44 In the X-1A"].   ''AFFTC History Office'', Edwards AFB. Retrieved 14 October 2009.</ref>

On 28 May 1954, Maj. [[Arthur W. Murray]] piloted the X-1A to a new record of {{convert|90440|ft}}.<ref name=Martin>Martin, Douglas |title=Arthur Murray. [https://www.nytimes.com/2011/08/05/us/05murray.html?src=recg "Test Pilot, Is Dead at 92"]. ''[[The New York Times]]'', 4 August 2011. Retrieved 6 August 2011.</ref>

The aircraft was transferred to NACA during September 1954, and subsequently modified. The X-1A was lost on 8 August 1955, when, while being prepared for launch from the [[Boeing B-50 Superfortress|RB-50]] mothership, an explosion ruptured the plane's liquid oxygen tank. With the help of crewmembers on the RB-50, test pilot [[Joseph A. Walker]] successfully extricated himself from the plane, which was then jettisoned. Exploding on impact with the desert floor, the X-1A became the first of many early X-planes that would be lost to explosions.<ref>Miller 2001, p. 21.</ref><ref>Thompson, Lance. [http://www.ufomind.com/area51/org/afftc/articles/airspace_9502.html "The X-Hunters"]. ''[[Air & Space]]'', February/March 1995, ISSN 0886-2257. Retrieved 12 March 2008.</ref>

===X-1B===
('''Bell Model 58B''')
[[File:Bell X-1B, NMUSAF, 2011.JPG|thumb|right|X-1B at the National Museum of the United States Air Force]]
The '''X-1B''' (serial 48-1385) was equipped with [[aerodynamic heating]] instrumentation for thermal research (more than 300 thermal probes were installed on its surface). It was similar to the X-1A except for having a slightly different wing. The X-1B was used for high-speed research by the U.S. Air Force starting from October 1954, prior to being transferred to the NACA during January 1955. NACA continued to fly the aircraft until January 1958, when cracks in the fuel tanks forced its grounding. The X-1B completed a total of 27 flights. A notable achievement was the installation of a system of small reaction rockets used for directional control, making the X-1B the first aircraft to fly with this sophisticated control system, later used in the [[North American X-15]]. The X-1B is now at the [[National Museum of the United States Air Force]], [[Wright-Patterson Air Force Base]] at [[Dayton, Ohio]], where it is displayed in the museum's Maj. Gen. Albert Boyd and Maj. Gen. Fred Ascani Research and Development Gallery.

===X-1C===
('''Bell Model 58C''')
The '''X-1C''' (serial 48-1387)<ref>Baugher, Joe. [http://www.joebaugher.com/usaf_serials/usafserials.html "USAAS-USAAC-USAAF-USAF Aircraft Serial Numbers – 1908 to Present."] ''USAAS/USAAC/USAAF/USAF Aircraft Serials,''20 January 2008. Retrieved: 12 December 2010.</ref> was intended to test armaments and munitions in the high transonic and supersonic flight regimes. It was canceled while still in the mockup stage, as the development of transonic and supersonic-capable aircraft like the [[North American F-86 Sabre]] and the [[North American F-100 Super Sabre]] eliminated the need for a dedicated experimental test vehicle.<ref>[http://www1.dfrc.nasa.gov/gallery/photo/X-1A/HTML/E-24911.html "Photo number E-24911: X-1A in flight with flight data superimposed."] {{webarchive |url=https://web.archive.org/web/20061207181208/http://www1.dfrc.nasa.gov/gallery/photo/X-1A/HTML/E-24911.html |date=December 7, 2006 }} ''NASA Dryden''. Retrieved: 14 October 2009.</ref>

===X-1D===
('''Bell Model 58D''')
The '''X-1D''' (serial 48-1386) was the first of the second generation of supersonic rocket planes. Flown from an [[Boeing B-50 Superfortress|EB-50A]] (s/n #46-006), it was to be used for heat transfer research. The X-1D was equipped with a new low-pressure fuel system and a slightly increased fuel capacity. There were also some minor changes of the avionics suite.

On 24 July 1951, with Bell test pilot Jean "Skip" Ziegler at the controls, the X-1D was launched over [[Rogers Dry Lake]], on what was to become the only successful flight of its career. The unpowered glide was completed after a nine-minute descent, but upon landing, the nose landing gear failed and the aircraft slid ungracefully to a stop. Repairs took several weeks to complete and a second flight was scheduled for mid-August. On 22 August 1951, the X-1D was lost in a fuel explosion during preparations for the first powered flight. The aircraft was destroyed upon impact after it was jettisoned from its EB-50A mothership.<ref name="X-1 fs">[http://www.nasa.gov/centers/dryden/news/FactSheets/FS-082-DFRC.html "Fact Sheet X-1."] ''NASA Dryden Fact Sheet''. Retrieved: 12 March 2008.</ref>

===X-1E===
('''Bell Model 44''')
[[File:Bell X-1-3 being mated with the motherplane.jpg|thumb|left|Bell X-1-3, aircraft #46-064, being mated to the B-50 mothership for a captive flight test on 9 November 1951. While being de-fueled after this flight it exploded, destroying itself and the B-50, and seriously burning Joe Cannon. X-1-3 had completed only a single glide-flight on 20 July.<ref>Miller 2001, p. 25.</ref>]]
The '''X-1E''' was the result of a reconstruction of the X-1-2 (serial 46-063), in order to pursue the goals originally set for the X-1D and X-1-3 (serial 46-064), both lost by explosions during 1951. The cause of the mysterious explosions was finally traced to the use of Ulmer leather<ref>Made by the Ulmer Company. James R. Hansen, "First Man" p. 134</ref> gaskets impregnated with [[tricresyl phosphate]] (TCP), a leather treatment, which was used in the [[liquid oxygen]] plumbing. TCP becomes unstable and explosive in the presence of pure oxygen and mechanical shock.<ref>[http://www.dfrc.nasa.gov/gallery/Photo/X-1A/HTML/E-24911.html "Photo X-1A (E-24911)."] {{webarchive |url=https://web.archive.org/web/20080920144335/http://www.dfrc.nasa.gov/gallery/Photo/X-1A/HTML/E-24911.html |date=September 20, 2008 }} ''NASA (Dryden Collections)''. Retrieved: 5 January 2016.</ref> This mistake cost two lives, caused injuries and lost several aircraft.<ref>Lockett, Brian. [http://www.air-and-space.com/edwards.htm  "Edwards Air Force Base History: Bell X-1 Explosions."] ''Goleta Air and Space Museum'', 3 July 1998. Retrieved: 5 January 2016.</ref>

[[File:Joe Walker X-1E.jpg|thumb|right|The X-1E, christened ''Little Joe'', with pilot Joe Walker]]
The changes included:

* A turbopump fuel feed system, which eliminated the high-pressure nitrogen fuel system used in '062 and '063. Concerns about metal fatigue in the nitrogen fuel system resulted in the grounding of the X-1-2 after its 54th flight in its original configuration.<ref name= "x-1e fs">[http://www.nasa.gov/centers/dryden/news/FactSheets/FS-083-DFRC.html "Fact sheet: X-1E."] ''NASA (Dryden Collections)''.  Retrieved: 5 January 2016.</ref>
* A re-profiled super-thin wing ({{convert|3+3/8|in|disp=or|abbr=out}} at the [[Wing root|root]]), based on the [[X-3 Stiletto]] wing profile, enabling the X-1E to exceed Mach 2.<ref>{{cite web |url=https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-083-DFRC.html |title=X-1E |publisher=NASA |date=7 August 2017 |access-date=6 November 2022}}</ref>
* A 'knife-edge' windscreen replaced the original greenhouse glazing, an upward-opening canopy replaced the fuselage side hatch and allowed the inclusion of an [[ejection seat]].
* The addition of 200 pressure ports for aerodynamic data, and 343 strain gauges to measure structural loads and aerodynamic heating along the wing and fuselage.<ref name = "x-1e fs" />

The X-1E first flew on 15 December 1955, a glide-flight controlled by USAF test pilot [[Joseph A. Walker|Joe Walker]]. Walker left the X-1E program during 1958, after 21 flights, attaining a maximum speed of Mach 2.21 (752&nbsp;m/s, 2,704&nbsp;km/h). NACA research pilot [[John B. McKay]] took his place during September 1958, completing five flights in pursuit of Mach 3 (1,021&nbsp;m/s, 3,675&nbsp;km/h) before the X-1E was permanently grounded after its 26th flight, during November 1958, due to the discovery of structural cracks in the fuel tank wall.