Editing Lockheed YF-22 (section)

== Development ==
{{Main|Advanced Tactical Fighter}}

===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"/>

===Demonstration and validation===
[[File:Lockheed Faceted ATF.jpg|thumb|left|Early Lockheed ATF concept with faceted shape for stealth]]
By November 1984, the SPO had further narrowed the requirements and released the Statement of Operational Need (SON), with requirements calling for a {{convert|50000|lb|kg|-2|abbr=on}} takeoff weight fighter that places strong emphasis on stealth, maneuver, and supersonic cruise without afterburners, or [[supercruise]]; [[radius of action|mission radius]] was expected to be {{convert|500|nmi|mi km|sigfig=2}} mixed subsonic/supersonic or {{convert|700|-|800|nmi|mi km|sigfig=3}} subsonic.<ref name="SON_RFP">Aronstein and Hirschberg 1998, pp. 70–78.</ref> In September 1985, the Air Force sent out technical [[request for proposal]]s (RFP) to a number of aircraft manufacturing teams for demonstration and validation (Dem/Val). In addition to the ATF's demanding technical requirements, Dem/Val also placed a great deal of importance on [[systems engineering]], technology development plans, and risk mitigation. The top four proposals, later reduced to two to reduce program costs, would proceed with Dem/Val as finalists; there was initially no requirement for prototype air vehicles. At the time, the Air Force anticipated procuring 750 ATFs at a unit flyaway cost of $35&nbsp;million in [[fiscal year]] (FY) 1985 dollars (~${{Format price|{{Inflation|index=US-GDP|value=35000000|start_year=1985}}}} in {{Inflation/year|US-GDP}}).<ref name="Hehs1998P1"/><ref name="SON_RFP"/><ref>Aronstein and Hirschberg 1998, pp. 87–88.</ref> Furthermore, under Congressional pressure to combine efforts with the Air Force to reduce costs, the U.S. Navy joined the ATF program initially as an observer and eventually announced in 1988 that it would use a variant/derivative of the winning design to replace its [[Grumman F-14 Tomcat|F-14 Tomcat]] as the Navy Advanced Tactical Fighter (NATF); the service called for the procurement of 546 aircraft.<ref name=Williams_p5>Williams 2002, p. 5.</ref>

[[File:Lockheed Model 090P 300x172.jpg|thumb|Lockheed's submission for Dem/Val RFP, designated Configuration 090P]]
Having performed poorly during ATF concept exploration while also [[Lockheed Senior Peg|losing the ATB]] to [[Northrop Corporation|Northrop]] who had a curved surface design, Lockheed abandoned faceting in 1984 and began incorporating curved shapes and surfaces. Although its analytical tools were initially not able to calculate for such shapes, good empirical results from radar range testing at [[Helendale, California]], gave Lockheed confidence in designing a stealthy aircraft with smooth, curved surfaces, thus greatly improving its aerodynamic characteristics. As Lockheed gradually became able to analyze curved shapes,{{refn|A stealthy curved radome was the last challenge Lockheed overcame in early 1985.<ref name="Hehs1998P1"/>|group=N}} the final design submitted for Dem/Val, designated Configuration 090P, would have an arrowhead-like forward fuselage shape, swept [[trapezoidal wing]]s, four [[empennage]] tail surfaces, [[S-duct|S-shaped]] inlet ducts obscuring the engine face, and an internal rotary missile launcher.<ref name="Hehs1998P1"/> In addition to the change in aircraft design, Lockheed also shifted much more engineering talent and manpower to its ATF effort, appointing Sherman Mullin as the program manager, and had its draft proposals aggressively [[red team|red-teamed]] by a group led by retired Air Force general [[Alton D. Slay]].<ref>Mullin 2012, p. 13.</ref> The resulting proposal improvements were substantial, particularly the systems engineering volume.<ref>Mullin 2012, pp. 18–19.</ref>

The ATF RFP would see some alterations after its first release; the SPO drastically increased all-aspect stealth requirements in December 1985 after discussions with Lockheed and Northrop regarding their experiences with the ''Have Blue''/F-117 and ATB/B-2, and the requirement for flying technology demonstrator prototypes was added in May 1986 due to recommendations from the [[Packard Commission]], a federal commission by President [[Ronald Reagan]] to study [[Department of Defense]] procurement practices.<ref>Aronstein and Hirschberg 1998, pp. 82–85.</ref><ref>Mullin 2012, pp. 19–21.</ref> Seven companies submitted bids in July&nbsp;1986.{{refn|The seven bidding companies were Lockheed, Boeing, General Dynamics, McDonnell Douglas, Northrop, [[Grumman]], and [[Rockwell International|North American Rockwell]].<ref>Miller 2005, pp. 14, 19.</ref>|group=N}} Owing to the immense investments companies were expected to make on their own, teaming was encouraged by the SPO. Following proposal submissions, Lockheed, Boeing, and General Dynamics formed a team to develop whichever of their proposed designs was selected, if any. Northrop and McDonnell Douglas formed a team with a similar agreement.<ref>Goodall 1992, p. 94.</ref>

On [[Halloween|31&nbsp;October&nbsp;]]1986, Lockheed and Northrop, the two industry leaders in stealth aircraft, were selected as the first and second place respectively; Sherman Mullin would credit the Lockheed's top rank to their proposal's system engineering volume, an area other contractors had not emphasized. The two teams, Lockheed/Boeing/General Dynamics and Northrop/[[McDonnell Douglas]], were awarded $691&nbsp;million contracts in FY 1985 dollars (~${{Format price|{{Inflation|index=US-GDP|value=691000000|start_year=1985}}}} in {{Inflation/year|US-GDP}}) and would undertake a 50-month demonstration and validation phase, culminating in the flight test of the two teams' prototypes, the YF-22 and the [[Northrop YF-23|YF-23]]; [[Pratt & Whitney]] and [[General Electric]] had earlier been awarded contracts to develop the competing prototype propulsion systems with the designations [[Pratt & Whitney F119|YF119]] and [[General Electric YF120|YF120]] respectively.<ref name=Miller_p19-0>Miller 2005, pp.&nbsp;19–20.</ref><ref>Jenkins and Landis 2008, pp.&nbsp;233–234.</ref><ref name="Williams 2002, pp. 5–6">Williams 2002, pp.&nbsp;5–6.</ref> Because the requirement for flying prototypes was a late addition due to political pressure, the prototypes were to be "best-effort" vehicles not meant to perform a competitive flyoff or represent a production aircraft, but to demonstrate the viability of its concept and to mitigate risk.{{refn|The contractor teams were to give the SPO "sealed envelope" flight performance predictions against which their prototypes would be evaluated, rather than against each other.<ref>Aronstein and Hirschberg 1998, p. 137.</ref>|group=N}}<ref>Aronstein and Hirschberg 1998, pp. 87–88.</ref>

===Design evolution===
[[File:Lockheed Boeing General Dynamics DemVal Proposal 300x359.jpg|thumb|left|From top to bottom, ATF Dem/Val submissions from Lockheed, Boeing, and General Dynamics (not to scale)]]
Work would be divided roughly equally among the team.{{refn|The division of work was initially 35% Lockheed, 32.5% Boeing, and 32.5% General Dynamics.<ref>Miller 2005, p. 44</ref>|group=N}} Because Lockheed's submission was selected as one of the winners, the company assumed leadership of the program partners. It would be responsible for the forward fuselage, cockpit, and stealthy edge treatments at Burbank as well as final assembly at [[Palmdale]], [[California]]. Meanwhile, the wings and aft fuselage would be built by Boeing at [[Seattle]], [[Washington (state)|Washington]], and the center fuselage, weapons bays, tail and [[landing gear]] would be built by General Dynamics at [[Fort Worth, Texas|Fort Worth]], [[Texas]].<ref name="J&L p. 235"/> The team would also invest $675&nbsp;million (~${{Format price|{{Inflation|index=US-GDP|value=675000000|start_year=1988}}}} in {{Inflation/year|US-GDP}}) combined into their ATF effort during Dem/Val in addition to the government contract awards.<ref>Aronstein and Hirschberg 1998, p. 164.</ref> The partners brought their design experience and proposals with them. Boeing's design was large and long with a chin-mounted inlet, trapezoid wings, [[V-tail]] empennage surfaces (deemed sufficient due to the high operating speed), and palletized internal weapons. General Dynamics' design was smaller with fuselage and delta wings optimized for maneuver and supercruise, shoulder-mounted inlets, a large single vertical tail as the only empennage surface which compromised all-aspect stealth, and weapon bays in the center fuselage. However, much of the team's scrutiny fell on Lockheed's Configuration 090P, which was problematic due to being highly immature as a result of Lockheed's greater focus on systems engineering rather than a point design. Nevertheless, 090P was the initial starting point that the team worked to refine.<ref name="Hehs1998P2">Hehs 1998, Part 2.</ref>

Throughout Dem/Val, the SPO held System Requirement Reviews (SRR) with contractor teams and used the results of their performance and cost [[trade study|trade studies]] to develop the ATF system specifications and adjust or delete requirements that were significant weight and cost drivers while having marginal value.<ref>Mullin 2012, pp. 31–32.</ref> For instance, the requirement for eight internal missiles (represented by the baseline [[AIM-120 AMRAAM|AIM-120A]]){{refn|A clipped-fin variant of the AMRAAM, the AIM-120C, was eventually developed to increase the F-22's internal missile load back to eight.<ref>Aronstein and Hirschberg 1998, pp. 184–185.</ref>|group=N}} was reduced to six. The team continually refined the design, making extensive use of analytical and empirical methods such as wind tunnel testing (18,000 hours by the end of Dem/Val), pole testing at radar ranges, and [[computational fluid dynamics]] (CFD) and [[computer-aided design]] (CAD) software. By early 1987, the design had evolved into Configuration 095, which replaced the rotary launcher with a flatter weapons bay to reduce volume and drag, and the shapes of the forward fuselage and leading-edge root extensions were recontoured to reduce their planform area, preventing uncontrollable pitch-up moments. Around this time, the design had split into two families, the 500 prefix that represents the full system design – or Preferred System Concept (PSC) — to be carried forward for full-scale development and the 1000 prefix that represents the same external airfame shape but designed to be built as prototype air vehicles instrumented for flight testing; Configuration 095 thus became 595 and 1095 respectively.<ref name="Hehs1998P2"/>

[[File:F-22 design evolution 595 to 645 200x592.png|thumb|upright=0.66|From top to bottom, Configuration 595/1095, 614/1114, 632/1132 (YF-22 design), and 645 (EMD/production F-22 design)]]
By mid-1987, detailed weight analysis of Configuration 595/1095 revealed that it was overweight by {{convert|9000|lb|kg|-2|abbr=on}} even if it could still nominally meet maneuver parameters.<ref name="Hehs1998P2"/> With weight likely to increase and compromises not forthcoming, the team chose to completely start over with a new design in July 1987, with Lockheed bringing a new director of design engineering, Richard Cantrell.{{refn|Richard Heppe, president of [[Lockheed Corporation#Aeronautical Systems group|Lockheed California Company]], would also play a major role.<ref>Mullin 2019.</ref>|group=N}}<ref>Mullin 2012, p. 29.</ref> Various different layouts were explored and after an intensive three-month effort, the team chose a new design, Configuration 614/1114, as the starting point in late 1987 with shoulder-mounted inlets and diamond-like delta wings similar to General Dynamics' design, and four empennage tail surfaces; notably, the diamond-like delta's aerodynamic characteristics approached the original swept trapezoidal profile's while offering much lower structural weight due to the longer root chord. The design evolved through the rest of 1987 and into May 1988, when Configuration 632/1132 was frozen as the YF-22. Changes include the shapes of the empennage surfaces to diamond-like and recontouring of the fore and aft fuselage to reduce [[wave drag]] following the deletion of the [[thrust reverser]] requirement after another SRR;<ref name="Miller2005P19-24"/><ref>Mullin 2012, p. 30.</ref> the prototype [[thrust vectoring]] nozzles still retained some thrust reversing hardware provisions however, resulting in the prototype aft fuselage being bulkier than needed. Ultimately, the 50,000-lb takeoff weight still proved to be unachievable for both the Lockheed and Northrop teams, and was adjusted to {{convert|60000|lb|kg|-2|abbr=on}}, resulting in engine [[thrust]] increasing from {{convert|30000|lbf|kN|0|abbr=on|adj=on}} to {{convert|35000|lbf|kN|0|abbr=on|adj=on}} class.<ref>Aronstein and Hirschberg 1998, p. 119.</ref> While the YF-22 configuration was frozen at an immature state relatively soon after the redesign to begin construction of the prototypes, the team continued evolving the configuration and PSC design into the F-22 for full-scale development.<ref name="Hehs1998P2"/>

In addition to the advanced air vehicle and propulsion design, the ATF required an integrated avionics system for sensor fusion to increase the pilot's situational awareness and decrease workload; this demanded a leap in sensor and avionics capability. Avionics development was marked by extensive testing and prototyping and supported by ground and flying laboratories, with Boeing being responsible for avionics integration. As the YF-22 was a technology demonstrator for the airframe and engines, it would not have any of the mission systems avionics. Boeing would build the Avionics Ground Prototype (AGP) and also provide a [[Boeing 757#Government, military, and corporate|Boeing 757]] modified with the mission systems as a flying laboratory for avionics development; this aircraft would later be named the Flying Test Bed.<ref>Aronstein and Hirschberg 1998, pp. 104–121.</ref><ref name="f22_flight_test_update">{{cite journal |last1=Kohn |first1=Lt. Col. Allen E. |last2=Rainey |first2=Lt. Col. Steven M. |author-link2=Steven M. Rainey |journal=SETP 41st Symposium |date=9 April 1999 |publisher=[[Society of Experimental Test Pilots]] |url=http://fas.org/man/dod-101/sys/ac/docs/f-22-emd-paper.htm |title=F-22 Flight Test Program Update |archive-url=https://web.archive.org/web/20140717014716/http://fas.org/man/dod-101/sys/ac/docs/f-22-emd-paper.htm |archive-date=17 July 2014}}</ref> The SPO would similarly adjust avionics requirements as a result of SRRs with contractors. [[Side looking airborne radar|Side-looking radar]] and [[infrared search and track]] (IRST) were deleted from the baseline requirement and became provisions for potential future addition, and a $9&nbsp;million cap in FY 1985 dollars (~${{Format price|{{Inflation|index=US-GDP|value=9000000|start_year=1985}}}} in {{Inflation/year|US-GDP}}) for avionics per aircraft was placed by the SPO in 1989 on the baseline proposal for full-scale development.<ref name="Hehs1998P2"/>

Formally designated as the YF-22A, the first aircraft (PAV-1, [[United States military aircraft serials|serial number]] 87-0700, N22YF), with the GE YF120 engine,<ref>Williams 2002, p.&nbsp;5.</ref><ref name="YF-22 first flight">{{Cite journal|url=http://www.flightglobal.com/pdfarchive/view/1990/1990%20-%203086.html|title=YF-22 flies as ATFs head for deadline|journal=[[Flight International]]|location=London|publisher=Reed Business Information|issue=4237|volume=138|page=6|date=10–16 October 1990|access-date=23 June 2011|archive-url=https://web.archive.org/web/20110521184521/http://www.flightglobal.com/pdfarchive/view/1990/1990%20-%203086.html|archive-date=21 May 2011|issn=0015-3710}}</ref> was rolled out on 29&nbsp;August&nbsp;1990<ref name="J&L p. 235">Jenkins and Landis 2008, p.&nbsp;235.</ref><ref name="YF-22 rollout">Bailey 1990, p. 34.</ref> and first flew on 29&nbsp;September&nbsp;1990, taking off from Palmdale piloted by David L. Ferguson.<ref name="J&L p. 235"/><ref name=Goodall_p99>Goodall 1992, p.&nbsp;99.</ref> The second YF-22A (PAV-2, s/n 87-0701, N22YX) with the P&W YF119 made its [[maiden flight]] on 30&nbsp;October at the hands of chief test pilot Thomas A. Morgenfeld.<ref name="J&L p. 235"/> The aircraft was given the unofficial name "Lightning II" after Lockheed's [[World War II]]-era fighter, the [[Lockheed P-38 Lightning|P-38 Lightning]], which persisted until the mid-1990s when the USAF officially named the production F-22 "Raptor".<ref>{{Cite web|url=http://www.aerospaceweb.org/question/history/q0221.shtml |title=Military Aircraft Names |work=Aerospaceweb.org |access-date=26 September 2010 |archive-url=http://arquivo.pt/wayback/20091012134155/http://www.aerospaceweb.org/question/history/q0221.shtml |archive-date=12 October 2009 |url-status=dead }}</ref> The [[Lockheed Martin F-35 Lightning II|F-35]] later received the "Lightning II" name in 2006.<ref name="jsf_name_announcement">"{{Cite press release|url=http://www.jsf.mil/downloads/documents/JSF_F-35_2006_Inauguration%20Press%20Release.doc|title=Lockheed Martin Joint Strike Fighter Officially Named 'Lightning II'|publisher=Official Joint Strike Fighter program office|date=7 July 2006|access-date=23 June 2011|archive-url=https://web.archive.org/web/20060715214726/http://www.jsf.mil/downloads/documents/JSF_F-35_2006_Inauguration%20Press%20Release.doc|archive-date=15 July 2006}}</ref>

===Naval variant===
Because the NATF, which was to replace the F-14 Tomcat for the U.S. Navy, required a lower landing speed than the ATF for [[CATOBAR|aircraft carrier recovery]] while still attaining Mach 2-class speeds, the Lockheed team's NATF design group went through several configurations to arrive at a suitable design that would achieve acceptable characteristics for carrier operations. Boeing had advocated for a fixed-wing design while General Dynamics favored [[variable-sweep wing]]s. After an internal competition and extensive wind tunnel testing, the team chose to incorporate variable-sweep wings in August 1989. The design retained the thrust vectoring nozzles and four tails.<ref name="Mullin2012P38-39"/> The resulting aircraft would have been heavier, more complex, and more expensive than the Air Force ATF counterpart.<ref name="Miller2005p74">Miller 2005, p. 74.</ref> The Lockheed team would submit its NATF design along with its F-22 full-scale development proposal in December 1990, although the Navy would withdraw from the program shortly afterwards due to cost.<ref name="Mullin2012P38-39">Mullin 2012, pp. 38–39.</ref>