Editing Lockheed YF-12 (section)

===NASA testing===
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| title       = NASA Overview of the YF-12, circa 1974
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The initial phase of the test program included objectives aimed at answering some questions about implementation of the [[Rockwell B-1 Lancer|B-1]]. Air Force objectives included exploration of its use in a tactical environment, and how [[airborne early warning and control]] (AWACS) would control supersonic aircraft. The Air Force portion was budgeted at US$4&nbsp;million. The [[NASA]] tests would answer questions such as how engine inlet performance affected airframe and propulsion interaction, boundary layer noise, heat transfer under high Mach conditions, and altitude hold at supersonic speeds. The NASA budget for the 2.5-year program was US$14&nbsp;million (~${{Format price|{{Inflation|index=US-GDP|value=14000000|start_year=1982}}}} in {{Inflation/year|US-GDP}}).<ref>Drendel 1982, p. 6.</ref>

The YF-12 and SR-71 originally suffered from severe control issues that affected both the engines and the physical control of the aircraft. Wind testing at NASA Dryden and YF-12 research flights developed computer systems that nearly completely solved the performance issues. Testing revealed vortices from the nose chines interfering with intake air, which led to the development of a computer control system to open the forward bypass doors. A computer system to reduce [[unstart]]s was also developed. They also developed a flight engineering computer program called Central Airborne Performance Analyzer (CAPA) that relayed engine data to the pilots and informed them of any faults or issues with performance and indicated the severity of malfunctions.<ref name="nasa.gov">{{Cite web|url=https://www.nasa.gov/centers/dryden/about/Organizations/Technology/Facts/TF-2004-17-DFRC.html|title=NASA - NASA Dryden Technology Facts - YF-12 Flight Research Program|website=www.nasa.gov|language=en|access-date=2020-04-24|archive-date=12 September 2019|archive-url=https://web.archive.org/web/20190912045121/https://www.nasa.gov/centers/dryden/about/Organizations/Technology/Facts/TF-2004-17-DFRC.html|url-status=dead}}</ref>

Another system called Cooperative Airframe-Propulsion Control System (CAPCS) greatly improved the control of supersonic aircraft in flight. At such high speeds even minor changes in direction caused the aircraft to change position by thousands of feet, and often had severe temperature and pressure changes. CAPCS reduced these deviations by a factor of 10. The overall improvements increased range of the SR-71 by 7 percent.<ref name="nasa.gov"/>

Of the three YF-12As, AF Ser. No. 60-6934 was damaged beyond repair by fire at Edwards AFB during a landing mishap on 14 August 1966; its rear half was salvaged and combined with the front half of a Lockheed static test airframe to create the only [[Lockheed SR-71 Blackbird#Variants|SR-71C]].<ref>Landis and Jenkins 2005, pp. 62, 75.</ref><ref>Pace 2004, pp. 109–10.</ref>

YF-12A, AF Ser. No. 60-6936 was lost on 24 June 1971 due to an in-flight fire caused by a failed fuel line; both pilots ejected safely just north of Edwards AFB. YF-12A, AF Ser. No. 60-6935 is the only surviving YF-12A; it was recalled from storage in 1969 for a joint USAF/NASA investigation of supersonic cruise technology, and then flown to the [[National Museum of the United States Air Force]] at [[Wright-Patterson Air Force Base]] near [[Dayton, Ohio]] on 17 November 1979.<ref name=museum/>

[[File:YF-12C on ramp.jpg|thumb|YF-12C on ramp]]
A fourth YF-12 aircraft, the "YF-12C", was actually the second SR-71A (AF Ser. No. 61–7951). This SR-71A was re-designated as a YF-12C and given the fictitious Air Force Serial Number 60-6937 from an A-12 to maintain SR-71 secrecy. The aircraft was loaned to NASA for propulsion testing after the loss of YF-12A (AF Ser. No. 60–6936) in 1971. The YF-12C was operated by NASA until September 1978, when it was returned to the Air Force.<ref name=Land_Jenk_p49-55>Landis and Jenkins 2005, pp. 49–55.</ref>

The YF-12 had a real-field sonic-boom overpressure value between 33.5 and 52.7 N/m<sup>2</sup> (0.7 to 1.1&nbsp;lb/ft<sup>2</sup>) – below 48 was considered "low".<ref name="dugan">Dugan, James F. Jr. [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19730009312_1973009312.pdf "Preliminary study of supersonic-transport configurations with low values of sonic boom"], p. 18. [[NASA]] [[Lewis Research Center]], March 1973. Retrieved: March 2012. (PDF)</ref>