Editing Lockheed YF-22 (section)

===Concept definition===
In 1981, the U.S. Air Force (USAF) began exploring concepts and developing requirements for an [[Advanced Tactical Fighter]] (ATF) that would eventually become a new [[air superiority fighter]] to replace the [[McDonnell Douglas F-15 Eagle|F-15 Eagle]] and [[General Dynamics F-16 Fighting Falcon|F-16 Fighting Falcon]]. This was made more crucial by the emerging worldwide threats, including development and proliferation of [[Soviet Union|Soviet]] [[Mikoyan MiG-29|MiG-29 "Fulcrum"]] and [[Sukhoi Su-27|Su-27 "Flanker"]]-class fighter aircraft, [[Beriev A-50|A-50 "Mainstay"]] airborne warning and control system (AWACS), and more advanced surface-to-air missile systems. The ATF would take advantage of the new technologies in fighter design on the horizon including [[composite material]]s, lightweight [[alloy]]s, advanced avionics and flight-control systems, more powerful propulsion systems and [[stealth technology]].<ref name="YF F/S">{{Cite web|title=Fact sheet: Lockheed-Boeing-General Dynamics YF-22|publisher=U.S. Air Force|date=11 February 2009 |url=http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2382|access-date=18 June 2011|archive-url=https://web.archive.org/web/20120119223134/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2382|archive-date=19 January 2012}}</ref>

[[File:F-22 RFI.jpg|thumb|upright=1.25|Diagram of several designs submitted for ATF RFI. Note Lockheed's large CL-2016 design with inspiration from the SR-71 family.]]
The USAF sent out the ATF [[request for information]] (RFI) to the aerospace industry in May 1981 to explore what the future fighter aircraft could look like, and subsequently established a Concept Development Team (CDT) to analyze the results.<ref>Aronstein and Hirschberg 1998, p. 30.</ref> Eventually code-named ''"Senior Sky"'', the ATF at this time was still in the midst of requirements definition with both air-to-air and air-to-ground missions in consideration, and consequently there was substantial variety in the responses from the industry. Lockheed's initial concept was a particularly large aircraft called CL-2016, nicknamed "battlecruiser" for its size, that resembled its [[Lockheed SR-71 Blackbird|SR-71]]/[[Lockheed YF-12|YF-12]] with large [[delta wing]]s and engines mounted in nacelles spaced away from the fuselage and would have had similarly high operating speed and altitude as a missile platform (or "missileer" per Lockheed).<ref name="Hehs1998P1">Hehs 1998, Part 1.</ref><ref>Aronstein and Hirschberg 1998, pp. 39–42.</ref>

In 1983, the ATF Concept Development Team became the System Program Office (SPO) at [[Wright-Patterson Air Force Base]]. After discussions with aerospace companies and [[Tactical Air Command]] (TAC), the CDT/SPO narrowed the requirements to an air superiority fighter with outstanding kinematic performance in speed and maneuverability to replace the F-15.<ref>Sweetman 1991, pp. 10–13.</ref> Additionally, the SPO began to increasingly emphasize stealth for survivability, while still requiring fighter-like speed and maneuverability, due to the Air Force's experience from "[[black project|black world]]" projects such as the [[Lockheed Have Blue|''Have Blue'']]/[[Lockheed F-117 Nighthawk|F-117]] ("''Senior Trend''") and the Advanced Technology Bomber (ATB) program (which would result in the [[Northrop B-2 Spirit|B-2]], or "''Senior Ice''").<ref>Aronstein and Hirschberg 1998, pp. 45–58.</ref> With stealth becoming a core requirement, Lockheed's design team, led by Bart Osborne from its [[Skunk Works]] division at [[Burbank, California]], migrated away from its initial SR-71-like "battlecruiser" concept and instead began drafting a design that resembled the company's F-117. However, the faceted shape, resulting from Lockheed using the same "Echo" computer program that it had used to design the F-117, gave the design very poor aerodynamic performance that would be unsuitable for a fighter. Lockheed would perform poorly throughout the concept exploration phase, placing among the bottom of the competing contractors.<ref name="Hehs1998P1"/>