Editing Convair XF-92 (section)

==Operational history==
[[File:USAF XF-92A.jpg|thumb|Convair XF-92A in flight with bare metal scheme]]

In April 1948 the XF-92A was shipped to [[Rogers Dry Lake|Muroc Dry Lake]] (later to become [[Edwards AFB]]). Early tests were limited to taxiing, although a short hop was made on 9 June 1948. The XF-92A's first flight was on 18 September 1948 with Convair test pilot Ellis D. "Sam" Shannon at the controls. On 21 December 1948 Bill Martin began testing the aircraft for the company. After 47 flights totaling 20 hours and 33 minutes, the aircraft was turned over to the USAAF on 26 August 1949,<ref name="Yenne 2009, p. 29">Yenne 2009, p. 29.</ref> with the testing being assigned to [[Frank Kendall Everest Jr.|Frank Everest]] and [[Chuck Yeager]].<ref name=baugher/>

On 13 October 1949 Yeager became the first Air Force pilot to fly the XF-92A.<ref name="Yenne 2009, p. 29"/> On his second flight he dove the aircraft in a 4&nbsp;g [[split-S]] dive, reaching Mach&nbsp;1.05 for a brief time.<ref name=GlobalSec>[http://www.globalsecurity.org/military/systems/aircraft/f-92.htm "XF-92A Dart."] ''globalsecurity.org.'' Retrieved: 3 July 2011.</ref> When approaching for landing on this flight he continued to pull the nose higher and higher in order to slow the forward speed to avoid the problems from his first attempt. Surprisingly, the aircraft simply wouldn't stall; he was able to continue raising the nose until he reached 45&nbsp;degrees [[Aircraft principal axes#Transverse axis (pitch)|pitch]], flying under control in that attitude to a landing at {{convert|67|mi/h|km/h|abbr=on}}, {{convert|100|mi/h|km/h|abbr=on}} slower than Convair had managed.

In 1951, the XF-92A was refitted with an Allison J33-A-29 engine with an afterburner, offering a thrust of {{convert|7500|lbf|abbr=on}}. The re-engined XF-92A was flown by Yeager for the first time on 20 July 1951. However, there was very little improvement in performance. In addition, there were maintenance problems with this engine and only 21 flights were made during the next 19 months.<ref name=baugher/> A final engine change was made to the {{convert|5400|lbf|abbr=on}} J33-A-16.

On 9 April 1953, [[Albert Scott Crossfield|Scott Crossfield]] began a series of flights on behalf of NACA. These tests revealed a violent pitch-up tendency during high-speed turns, often as much as 6&nbsp;g, and on one occasion 8&nbsp;g. The addition of [[wing fence]]s partially alleviated this problem. Crossfield flew 25 flights in the XF-92A by 14 October 1953.<ref>Yenne 2009, p. 30.</ref> After the aircraft's last flight the nose gear collapsed as Crossfield taxied off the lake bed; the aircraft was retired.<ref>Yenne 2009, p. 31.</ref>

None of the pilots had much good to say about the design. Yeager commented "It was a tricky plane to fly, but ... I got it out to 1.05 Mach." Crossfield was more direct, saying "Nobody wanted to fly the XF-92. There was no lineup of pilots for that airplane. It was a miserable flying beast. Everyone complained it was underpowered."<ref>DiGregorio, Barry E. [http://www.historynet.com/air_sea/flight_technology/3037311.html?showAll=y&c=y "Aviation History: Interview with Frank K. 'Pete' Everest Who Flew A Bell X-2 To Record Speed of Mach 3."] {{webarchive|url=https://web.archive.org/web/20070930210331/http://www.historynet.com/air_sea/flight_technology/3037311.html?showAll=y&c=y |date=2007-09-30 }} ''Aviation History,'' July 1998. Retrieved: 3 July 2011.</ref><ref>[http://www.nasa.gov/centers/dryden/news/FactSheets/FS-080-DFRC.html "NASA Fact Sheets: XF-92A."] {{Webarchive|url=https://web.archive.org/web/20141025161712/http://www.nasa.gov/centers/dryden/news/FactSheets/FS-080-DFRC.html |date=2014-10-25 }} ''NASA.'' Retrieved: 11 June 2011.</ref>

===Influence===
[[File:Convair XF-92A accident front.jpg|thumb|right|Landing accident, 1953]]

The delta wing's thin airfoil cross section, low weight and structural strength made it a good candidate for a supersonic airplane. The large surface area of 425&nbsp;ft<sup>2</sup> (39&nbsp;m<sup>2</sup>) gave a low [[wing loading]] which in turn led to good low-speed performance. Very slow landing speeds could be achieved, at the cost of extremely nose-high landing angles and the resulting poor visibility. The combination of good high-speed and low-speed characteristics was very difficult to achieve for other [[planform (aeronautics)|planform]]s. Although the XF-92 itself was not liked, the design concept clearly had promise and the delta wing was used on several Convair designs through the 1950s and 1960s.

Of particular interest to aircraft designers was the unexpectedly good low-speed behavior Yeager had noticed on his second flight. The aircraft continued to remain controllable at very high [[angle of attack|angles of attack]] (alpha), where a conventional layout would have stalled. The reason for this turned out to be the unexpected creation of a large [[vortex]] over the top of the wing, generated by the airflow between the fuselage and leading edge of the wing at high alpha. The vortex became "attached" to the upper surface of the wing, supplying it with air moving at speeds much greater than the aircraft's forward speed. By controlling the flow in this critical area, the [[performance envelope]] of the delta could be greatly expanded, which led to the introduction of [[canard (aeronautics)|canard]]s on most delta-wing designs in the 1960s and 1970s. More recently [[leading edge extension]]s have become common on most fighter aircraft, creating the vortex over a more conventional wing planform.