Bell X-2

The Bell X-2 was developed to provide a vehicle for researching flight characteristics at speeds and altitudes in excess of the capabilities of the Bell X-1 and D-558 II, while investigating aerodynamic heating problems in what was then called the "thermal thicket".https://archive.org/details/Aviation_Week_1957-10-21/page/n55?q=aviation+week+thicket+thermal p.112

The Bell X-2 had a prolonged development period due to the advances needed in aerodynamic design, control systems, materials that retained adequate mechanical properties at high temperature, and other technologies that had to be developed. Not only did the X-2 push the envelope of manned flight to speeds, altitudes and temperatures beyond any other aircraft at the time, it pioneered throttleable rocket engines in U.S. aircraft (previously demonstrated on the Me 163B during World War II) and digital flight simulation. The XLR25 rocket engine, built by Curtiss-Wright, was based on the smooth variable-thrust JATO engine built by Robert Goddard in 1942 for the Navy.{{cite book|last=Lehman|first=Milton|title=Robert H. Goddard|year=1963|publisher=Da Capo Press|location=New York|page=351}}

Providing adequate stability and control for aircraft flying at high supersonic speeds was only one of the major difficulties facing flight researchers as they approached Mach 3. For, at speeds in that region, they knew they would also begin to encounter a "thermal barrier", severe heating effects caused by aerodynamic friction. Constructed of stainless steel and a copper-nickel alloy called K-Monel, and powered by a liquid propellant (alcohol and oxygen) two-chamber Curtiss-Wright XLR25 2,500 to 15,000 lbf (11 to 67 kN) sea level thrust, continuously throttleable rocket engines, the swept-wing Bell X-2 was designed to probe the supersonic region.

File:X-2 After Drop from B-50 Mothership - GPN-2000-000396.jpg|alt=X-2 just after being dropped.|X-2 just after being dropped.

File:X-2 on ramp with B-50 mothership and support crew.jpg|alt=X-2, crew, B-50 mothership, and support equipment.|X-2, crew, B-50 mothership, and support equipment.

File:X-2 in flight.jpg|alt=The X-2 inflight.|The X-2's twin set of shock diamonds in the exhaust plume, characteristic of supersonic conditions from a two-chamber rocket engine.

Following a drop launch from a modified B-50 bomber, Bell test pilot Jean "Skip" Ziegler completed the first unpowered glide flight of an X-2 at Edwards Air Force Base on 27 June 1952. Ziegler and aircraft #2 (46-675) were subsequently lost on 12 May 1953, in an inflight explosion during a captive flight intended to check the aircraft's liquid oxygen system.{{cite news |url=http://www.astronautix.com/x/x-2.html|archive-url=https://web.archive.org/web/20160820123533/http://www.astronautix.com/x/x-2.html|url-status=dead|archive-date=August 20, 2016|title=X-2|work=astronautix.com|access-date=July 16, 2017}} A B-50 crew member, Frank Wolko, was also killed during the incident. The wreckage of the aircraft fell into Lake Ontario and was not recovered.Spaceplanes: From Airport to Spaceport, Matthew A. Bentley, P.11

Lt. Col. Frank K. "Pete" Everest completed the first powered flight in the #1 airplane (46-674) on 18 November 1955. By the time of his ninth and final flight in late July 1956 the project was years behind schedule, but he had established a new speed record of Mach 2.87 (1,900 mph, 3,050 km/h). About this time, the YF-104A was demonstrating speeds of Mach 2.2 or 2.3 in a fighter configuration. The X-2 was living up to its promise, but not without difficulties. At high speeds, Everest reported its flight controls were only marginally effective. High speed center of pressure shifts along with fin aeroelasticity were major factors. Moreover, simulation and wind tunnel studies, combined with data from his flights, suggested the airplane would encounter very severe stability problems as it approached Mach 3.Machat 2005, p. 42.

Captains Iven C. Kincheloe and Milburn G. "Mel" Apt were assigned the job of "envelope expansion" and, on 7 September 1956, Kincheloe became the first pilot ever to climb above 100,000 ft (30,500 m) as he flew the X-2 to a peak altitude of 126,200 ft (38,470 m). Just 20 days later, on the morning of 27 September, Apt was launched from the B-50 for his first flight in a rocket airplane. He had been instructed to follow the "optimum maximum energy flight path".{{Cite book |last=Petty |first=Chris |url=https://www.worldcat.org/oclc/1193585597 |title=Beyond Blue Skies: The Rocket Plane Programs that Led to the Space Age |publisher=University of Nebraska Press |year=2020 |isbn=978-1-4962-2355-5 |location=Lincoln, NE |pages=133–138 |oclc=1193585597}} With nozzle extenders and a longer than normal motor run, Apt flew an extraordinarily precise profile; he became the first man to exceed Mach 3, reaching Mach 3.2 (2,094 mph, 3,370 km/h) at 65,500 ft (19,960 m).Machat 2005, p. 37.

The flight had been flawless to this point, but shortly after attaining top speed, Apt attempted a banking turn while the aircraft was still above Mach 3 (lagging instrumentation may have indicated he was flying at a slower speed or perhaps he feared he was straying too far from the safety of his landing site on Rogers Dry Lake). The X-2 tumbled violently out of control and he found himself struggling with three sequential coupling modes, control coupling, inertial roll coupling and supersonic spinning.https://www.nasa.gov/centers/dryden/pdf/88484main_H-2106.pdf p.8 "Inertia coupling" and a subsonic inverted spinThe X-Planes X-1 To X-31, Jay Miller, New Revised Edition 1988, {{ISBN|0-517-56749-0}}, p. 26 had overtaken Chuck Yeager in the X-1A nearly three years before. Yeager, although exposed to much higher vehicle inertial forces, was able to recover. Apt attempted to recover from a spin, but could not. The rudder lock was still on in the attempted spin recovery. He fired the ejection capsule, which was itself only equipped with a relatively small drogue parachute. Apt was probably disabled by the severe release forces. As the capsule fell for several minutes to the desert floor, he did not exit so that he could use his personal parachute before ground impact, and was killed.Machat 2005, p. 43. The aircraft continued to fly in a series of glides and stalls before landing and breaking into three pieces (separate from the capsule). A proposal to salvage the aircraft and modify it for a hypersonic test program was not approved. The aircraft was scrapped.https://www.nasa.gov/centers/dryden/pdf/88484main_H-2106.pdf p.15

File:X-2 Accident 03 adjusted.jpg|alt=Crash site in the desert near Edwards Air Force Base.|Crash site in the desert near Edwards Air Force Base.

File:X-2 Accident 8201.jpg|alt=Two pieces of the X-2 at the crash site.|Two pieces of the X-2 at the crash site, {{convert|5|mi|km}} from where the escape capsule landed.

File:X-2 Accident 8181.jpg|alt=The X-2's escape capsule at the crash site.|The X-2's escape capsule at the crash site.

File:X-2 Accident 8189.jpg|alt=The cockpit of the X-2's escape capsule at the crash site.|The cockpit of the X-2's escape capsule at the crash site.

File:X-2 Wreckage (E56-2685) (cropped).jpg|alt=Wreckage from Captain Mel Apt's fatal crash in the X-2 (46-674).|Wreckage from Apt's fatal crash in the X-2.

The subsequent investigation into the X-2's fatal flight raised numerous contributing factors into the crash{{--}}largely focusing on Apt's decision to turn the aircraft while still above Mach 3. Some cited his lack of experience with rocket planes, but, as historian Chris Petty notes, "he had in fact flown the complex profile almost perfectly, but this, combined with additional seconds of thrust from the XLR25 [engine], had carried the X-2 well beyond the envelope of knowledge and into the uncertain stability predicted by the GEDA [Goodyear Electronic Differential Analyzer computer]." In short, Petty suggests that Apt did his job too well and may have been pushed to exceed Mach 3 by the AFFTC and conflicting priorities within it. Petty quotes Base commander General Stanley Holtoner: "I think that every supervisory guy from me on down has criticized himself, because if we had told this boy [Apt] to stop at a specific speed, this wouldn't have happened."

One point that became clear even before the investigation was that the X-2's escape mechanism was woefully inadequate. According to The New York Times reporting on the event, Everest had criticized the relatively new detachable capsule, maintaining that "some safety had been sacrificed in preference to delaying the X-2 flight tests while the escape mechanism was modified."{{Cite news |date=1956-09-28 |title=1,900-M.P.H. Rocket Plane Crashes and Kills Test Pilot |language=en |edition=Late City |volume=106 |page=1 |work=New York Times |url=http://timesmachine.nytimes.com/timesmachine/1956/09/28/86699646.html?zoom=16.06 |access-date=2021-05-11}} Another NACA research pilot, Scott Crossfield, described it more bluntly as a "way to commit suicide to keep from getting killed."{{Cite book |url=https://www.worldcat.org/oclc/51518730 |title=The Spoken Word: Recollections of Dryden History, the Early Years |publisher=US Government Printing Office |year=2003 |isbn=0-16-067752-1 |editor-last=Peebles |editor-first=Curtis |location=Washington, D.C. |page=84 |oclc=51518730}}

While the X-2 had delivered valuable research data on high-speed aerodynamic heat build-up and extreme high-altitude flight conditions (although it is unclear how much, as the unmanned Lockheed X-7 and IM-99 were among the winged vehicles operating at comparable or higher velocities in this era), this tragic event terminated the program before the National Advisory Committee for Aeronautics could commence detailed flight research with the aircraft. The search for answers to many of the riddles of high-Mach flight had to be postponed until the arrival three years later of the most advanced of all the experimental rocket aircraft, the North American X-15.

Two aircraft completed a total of 20 flights (27 June 1952 – 27 September 1956).

• 46-674: seven glide flights, 10 powered flights, crashed 27 September 1956, subsequently scrapped
• 46-675: three glide flights, destroyed 12 May 1953

File:X-2 3-view.svg

{{Aircraft specs

|ref=Concept Aircraft: Prototypes, X-Planes and Experimental AircraftWinchester 2005, p. 35.

|prime units?=imp

|crew=1

|length ft=37

|length in=10

|length note=

|span ft=32

|span in=3

|span note=

|height ft=11

|height in=10

|height note=

|wing area sqft=260

|wing area note=

|aspect ratio=

|airfoil= NACA 2S-(50) (05-50) (05-arc){{cite web |last1=Lednicer |first1=David |title=The Incomplete Guide to Airfoil Usage |url=https://m-selig.ae.illinois.edu/ads/aircraft.html |website=m-selig.ae.illinois.edu |access-date=16 April 2019}}

|empty weight lb=12375

|empty weight note=

|gross weight lb=

|gross weight note=

|max takeoff weight lb=24910

|max takeoff weight note=

|fuel capacity=

|more general=

|eng1 number=1

|eng1 name=Curtiss-Wright XLR25

|eng1 type=liquid-fuelled rocket engine

|eng1 lbf=15000

|eng1 note=at sea level

|max speed mph=2094

|max speed note=

|max speed mach=3.196

|cruise speed mph=

|cruise speed note=

|stall speed mph=

|stall speed note=

|never exceed speed mph=

|never exceed speed note=

|range miles=

|range note=

|combat range miles=

|combat range note=

|ferry range miles=

|ferry range note=

|endurance=

|ceiling ft=126200

|ceiling note=

|g limits=

|roll rate=

|glide ratio=

|climb rate ftmin=

|climb rate note=

|time to altitude=

|sink rate ftmin=

|sink rate note=

|lift to drag=

|wing loading lb/sqft=

|wing loading note=

|fuel consumption lb/mi=

|thrust/weight=

|more performance=

|avionics=

}}

{{Main|Aircraft in fiction#Bell X-2}}

{{Aircontent

|related=

|similar aircraft=

• Douglas D-558-2 Skyrocket

|lists=

• List of experimental aircraft
• List of rocket aircraft
• List of X-2 flights

|see also=

• Mach number

}}

{{Reflist}}

{{Refbegin}}

• Everest, Lt. Col. Frank and Guenther, John. Fastest Man Alive. New York, E. P. Dutton, 1958. {{LCCN|578998}}.
• Hallion, Dr. Richard P. "Saga of the Rocket Ships." AirEnthusiast Five, November 1977 – February 1978. Bromley, Kent, UK: Pilot Press Ltd., 1977.
• Machat, Mike. "Color Schemes of the Bell X-2." Airpower, Volume 35, no. 1 January 2005.
• Matthews, Henry. The Saga of the Bell X-2, First of the Spaceships. Beirut, Lebanon: HPM Publications, 1999.
• {{Cite book |last=Petty |first=Chris |url=https://www.worldcat.org/oclc/1193585597 |title=Beyond Blue Skies: The Rocket Plane Programs that Led to the Space Age |publisher=University of Nebraska Press |year=2020 |isbn=978-1-4962-2355-5 |location=Lincoln |pages=133–138 |oclc=1193585597}}
• {{Cite journal |last=Whitford |first=Ray |date=1997 |title=Lessons Learned from the Bell X-2 Program |url=https://www.jstor.org/stable/44650531 |journal=SAE Transactions |volume=106 |pages=1407–1421 |jstor=44650531 |issn=0096-736X}}
• Winchester, Jim. "Bell X-2." Concept Aircraft: Prototypes, X-Planes and Experimental Aircraft. Kent, UK: Grange Books plc, 2005. {{ISBN|978-1-84013-809-2}}.

{{Refend}}

{{Commons}}

• [https://history.nasa.gov/monograph31.pdf American X-Vehicles: An Inventory X-1 to X-50, SP-2000-4531 – June 2003; NASA online PDF Monograph]
• [https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-079-DFRC.html NASA Bell X-2 Starbuster Fact Sheet]
• [http://sites.google.com/site/rgoddardsite/ Robert H. Goddard's contribution to the X-2's XLR25 engine] {{Webarchive|url=https://web.archive.org/web/20090205053231/http://sites.google.com/site/rgoddardsite/ |date=2009-02-05 }}

{{Bell Aircraft}}

{{X-planes}}

{{Authority control}}

Category:Edwards Air Force Base

Category:Rocket-powered aircraft

X-02, Bell

X-2

Category:Low-wing aircraft

Category:Aircraft with retractable tricycle landing gear