Editing Lockheed YF-22 (section)

===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>