Editing Convair F-106 Delta Dart (section)

===Background===
The F-106 was the ultimate development of the USAF's [[1954 interceptor]] program of the early 1950s.<ref name="knaack p159">Knaack 1978, p. 159.</ref> The initial winner of this competition had been the [[Convair F-102 Delta Dagger|F-102 Delta Dagger]], but early versions of this aircraft had demonstrated extremely poor performance, being limited to flying at subsonic speeds and relatively low altitudes.<ref name="knaack p166167">Knaack 1978, pp. 166-167.</ref> During the testing program the F-102 underwent numerous changes to improve its performance, notably the application of the [[area rule]] to the fuselage shaping and a change of engine, and the dropping of the advanced MX-1179 [[fire control system]] and its replacement with a slightly upgraded version of the MX-1 already in use on subsonic designs. The resulting aircraft became the F-102A, and in spite of being considered barely suitable for its mission, the Air Force sent out a production contract in March 1954, under which the first deliveries were expected during the following year.<ref name="knaack p164">Knaack 1978, p. 164.</ref><ref>Converse 2012, p. 241.</ref>

By December 1951, the Air Force had already turned its attention to a further improved version, which was initially referred to as the F-102B. The main planned change was the replacement of the F-102A's [[Pratt & Whitney J57]] (which had itself replaced the original J40<ref name="knaack p163">Knaack 1978, p. 163.</ref>) with the more powerful [[Wright J67]] (a [[Bristol Olympus]] [[licensed production|produced under license]]).<ref name="knaack p207">Knaack 1978, p. 207.</ref> By the time this engine would be available, the MX-1179 was expected to be available, and thus it was selected as well. The intended result would be the "ultimate interceptor" that the USAF had originally sought.<ref name="knaack p207208">Knaack 1978, pp. 207-208.</ref> However, while initial work on the Olympus design appeared to go well, by August 1953 Wright was already a full year behind schedule in development. Continued development did not resolve problems with the engine, and in early 1955 the Air Force approved the switch to the [[Pratt & Whitney J75]].<ref>{{cite web |title = History of the 'F-106 Delta Dart' |url = http://www.f-106deltadart.com/history.htm |website = F-106DeltaDart.com |publisher = Convair Aircraft Plant San Diego, CA |access-date = 17 June 2014 |url-status = live |archive-url = https://web.archive.org/web/20140722114037/http://www.f-106deltadart.com/history.htm |archive-date = 22 July 2014}}</ref><ref name="knaack p208"/>

The J75 was somewhat larger than the J57 in the F-102A, and had greater {{clarification needed span|text=mass flow.|reason=What is "mass flow"?  Appropriate link or reliable citation, please.|date=May 2024}} This demanded changes to the inlets to allow more airflow, and led to the further refinement of using a somewhat shorter [[intake ramp|variable-geometry inlet duct]] to allow the intakes to be tuned to best performance across a wide range of supersonic speeds. The fuselage grew slightly longer, and was cleaned up and simplified in many ways. The wing was slightly enlarged in area, and a redesigned vertical tail surface was used. The engine's two-position afterburner exhaust nozzle was also used for idle thrust control, held open to decrease thrust by 40%, resulting in slower taxiing and less brake wear.<ref>Flight Manual F-106A and F-106B T.O. 1F106A-1 page 1-22 "Idle thrust control switch".</ref>