Northrop YF-23

{{short description|Prototype demonstrator aircraft for the US Air Force Advanced Tactical Fighter program}} {{redirect|YF-23|the Chinese rocket engine|YF-23 (rocket engine)}} {{featured article}}  {{Use dmy dates|date=May 2022}} {{Infobox aircraft |name = YF-23 |image = File:Ray Wagner Collection Image YF-23.jpg |caption = YF-23 flying over [[Edwards Air Force Base]] |alt = The first YF-23 prototype PAV-1, nicknamed "Black Widow", conducts test flights over Edwards Air Force Base |type = [[Stealth aircraft|Stealth]] [[fighter aircraft|fighter]] prototype [[Technology demonstration|Technology demonstrator]] |national_origin = United States |manufacturer = [[Northrop Corporation|Northrop]]/[[McDonnell Douglas]] |designer = |first_flight = 27 August 1990 |introduction = |status = Canceled, aircraft retired |primary_user = [[United States Air Force]] |more_users = |produced = 1989–1990 |number_built = 2 |program cost = |unit cost = |developed_from = |variants = }}

The '''Northrop–McDonnell Douglas YF-23''' is an American single-seat, [[twinjet|twin-engine]], [[Stealth aircraft|stealth]] [[fighter aircraft|fighter]] prototype [[technology demonstrator]] designed for the [[United States Air Force]] (USAF). The design team, with [[Northrop Corporation|Northrop]] as the prime contractor, was a finalist in the USAF's [[Advanced Tactical Fighter]] (ATF) demonstration and validation competition, battling the [[Lockheed Corporation|Lockheed]]-led [[Lockheed YF-22|YF-22]] team for full-scale development and production. Nicknamed "'''Black Widow II'''", two YF-23 prototypes were built.

In the 1980s, the USAF began looking for a replacement for its [[McDonnell Douglas F-15 Eagle|F-15]] fighter aircraft to more effectively counter emerging threats such as the [[Soviet Union]]'s advanced [[Sukhoi Su-27|Su-27]] and [[Mikoyan MiG-29|MiG-29]] fighters. Several companies submitted design proposals; the USAF selected proposals from Northrop and Lockheed for demonstration and validation. Northrop teamed up with [[McDonnell Douglas]] to develop the YF-23, and Lockheed, [[Boeing]], and [[General Dynamics]] developed the YF-22. The YF-23 was stealthier and faster, but less agile than its competitor. After a four-year development and evaluation process, the YF-22 team was announced as the winner in 1991 and developed the [[Lockheed Martin F-22 Raptor|F-22 Raptor]], which first flew in 1997 and entered service in 2005. The US Navy considered using a naval version of the ATF as an [[Grumman F-14 Tomcat|F-14]] replacement, but these plans were later canceled due to costs.

After flight testing, both YF-23s were placed in storage while various agencies considered plans to use them for further research, but none proceeded. In 2004, [[Northrop Grumman]]<ref name="NG" group=N/> used the second YF-23 as a display model for its proposed regional bomber aircraft, but this project was dropped because longer range bombers were required. The two YF-23 prototypes are currently displayed at the [[National Museum of the United States Air Force]] and the [[Western Museum of Flight]].

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

===Concept definition=== American reconnaissance satellites first spotted the advanced Soviet [[Sukhoi Su-27|Su-27]] and [[Mikoyan MiG-29|MiG-29]] fighter prototypes between 1977 and 1979, which caused concern in the US. Both Soviet models were expected to reduce the combat and maneuverability advantages of contemporary US fighter aircraft, including the newly introduced [[McDonnell Douglas F-15 Eagle|F-15 Eagle]] and [[General Dynamics F-16 Fighting Falcon|F-16 Fighting Falcon]].{{sfn|Rich|Stanley|1984|p=7}} US tactical airpower was further threatened by new Soviet systems such as the [[Beriev A-50|A-50]] [[airborne early warning and control|airborne warning and control system]] (AWACS) revealed in 1978 and more advanced [[surface-to-air missile]] systems.{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|pp=37–39}} In 1981, the USAF began developing requirements and discussing with the aerospace industry on concepts for an [[Advanced Tactical Fighter]] (ATF) with both air-to-air and air-to-ground missions in consideration. The ATF was to take advantage of emerging technologies, including [[composite material]]s, lightweight [[alloy]]s, advanced flight-control systems, more powerful engines, and [[stealth technology]].{{Sfn|Miller|2005|p=11}}

[[File:F-22 RFI.jpg|thumb|upright=1.25|Diagram of several designs submitted for ATF RFI, showing the comparatively small sizes of Northrop's initial designs|alt=19 designs for the concept jets with annotations of features and specifications]] The USAF released the ATF [[request for information]] (RFI) in May 1981 to the aerospace defense industry on possible features for the new fighter. Later code-named ''"Senior Sky"'', the ATF at this time was still in the midst of requirements definition, which meant that there was considerable variety in the responses from the aerospace companies. Northrop submitted three designs for the RFI, ranging from ultra low-cost, to highly agile, to low-observable missileer; all were on the smaller and lighter end of the response spectrum.{{Sfn|Metz|2017|pp=10–12}} In 1983, the ATF System Program Office (SPO) was formed at [[Wright-Patterson Air Force Base]] from the initial Concept Development Team (CDT). After discussions with aerospace companies and [[Tactical Air Command]] (TAC), the CDT/SPO made [[air superiority fighter|air-to-air combat]] the primary role for the ATF, which would replace the F-15 and emphasize outstanding kinematic performance with supersonic cruise and maneuver.{{Sfn|Sweetman|1991a|pp=10–13}} Northrop's response was a larger Mach 2+ design designated N-360 with [[delta wing]]s, a single vertical tail, and twin engines with [[thrust vectoring]] nozzles and [[Thrust reversal|thrust reversers]].{{Sfn|Chong|2016|pp=226–227}}{{Sfn|Metz|2017|pp=28–29}} Around this time, the SPO also became aware of the very low radar cross section (RCS) results from the Air Force's "[[black project|black world]]" innovations such as the [[Lockheed Have Blue|''Have Blue'']]/[[Lockheed F-117 Nighthawk|F-117]] ("''Senior Trend''"), [[Northrop Tacit Blue|''Tacit Blue'']], and the Advanced Technology Bomber (ATB) program (which resulted in the [[Northrop Grumman B-2 Spirit|B-2]], or "''Senior Ice''"); consequently, the SPO increasingly emphasized stealth for survivability and combat effectiveness while still requiring fighter-like speed and maneuverability.{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|pp=45–58}}

Northrop was able to quickly adapt to the ATF's increasing emphasis on stealth. Since October 1981, a small team of engineers under Robert Sandusky within its ATB/B-2 division had been working on stealth fighter designs. Sandusky later became the Northrop ATF's Chief Engineer, and fellow B-2 stealth engineer Yu Ping Liu was recruited in 1985 as the chief scientist.{{Sfn|Metz|2017|pp=23–24}} Three design concepts were studied: the Agile Maneuverable Fighter (AMF) similar to N-360 with two canted vertical tails and the best aerodynamic performance of the three but with minimal stealth, the Ultra Stealth Fighter (USF) that emphasized maximum stealth through edge alignment with only four RCS lobes and nicknamed "Christmas Tree" for its [[wing configuration|planform]] shape, and the High Stealth Fighter (HSF) that balanced stealth and maneuverability with [[diamond wing]]s, all-moving [[V-tail]] "ruddervators" (or butterfly tails), engine exhaust troughs, and aligned edges.{{Sfn|Metz|2017|pp=28–29}}{{Sfn|Chong|2016|pp=233–234}}{{refn|Despite its excellent stealth potential, USF (DP21/DP22) was unsuitable due to its aerodynamic qualities that made it uncontrollable beyond roughly 10° angle-of-attack.{{Sfn|Chong|2016|pp=233–234}}{{Sfn|Cummings|2025}}|group=N}} First emerging in 1983, HSF took many design cues from the B-2 to reduce its susceptibility to radar and [[infrared]] detection, and Liu's understanding of both radar signatures and aerodynamics lent itself to key design features, such as the shaping of the nose (nicknamed the "[[platypus]]" for the initial shape and pronounced [[Chine (aeronautics)|chine]] edges) and canopy with their continuously curved, [[Gaussian surface]]s. By 1985, HSF had evolved to be recognizably similar to the eventual YF-23 and emerged as the optimal balance of stealth and aerodynamic performance.{{Sfn|Metz|2017|pp=23–24}}{{Sfn|Winchester|2005|pp=198–199}}

===Demonstration and validation=== [[File:Northrop AMF USF HSF 300x245.jpg|thumb|left|From left to right, flat-plate models of Northrop's AMF, USF ("Christmas Tree"), and HSF design concepts. HSF was the preferred concept by 1985.|alt=Three metal models of the concept fighter jets]]

By November 1984, concept exploration had allowed the SPO to narrow its requirements and release the Statement of Operational Need, which called for a {{convert|50000|lb|kg|-2|abbr=on}} takeoff weight fighter with stealth and excellent kinematics, including prolonged supersonic flight without the use of [[afterburner]]s, 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. In September 1985, the USAF issued the [[request for proposal]] (RFP) for demonstration and validation (Dem/Val) to several aircraft manufacturers with the top four proposals, later cut down to two to reduce program costs, proceeding to the next phase; as well as the ATF's demanding technical requirements, the RFP also emphasized [[systems engineering]], technology development plans, and risk mitigation.{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|pp=70–78}} The RFP saw some changes after initial release; following the SPO's discussions with Lockheed and Northrop regarding their experiences with the F-117 and B-2, all-aspect stealth requirements were drastically increased in late 1985.{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|pp=82–85}} Although there was initially no requirement for the evaluation of prototype air vehicles, this 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. At this time, the USAF envisioned procuring 750 ATFs at a unit flyaway cost of $35 million in [[fiscal year]] (FY) 1985 dollars (${{Format price|{{Inflation|index=US-GDP|value=35000000|start_year=1985}}}} in {{Inflation/year|US-GDP}}). The US Navy under the Navy Advanced Tactical Fighter (NATF) program announced in 1988 that it would use a derivative of the ATF winner to replace its [[Grumman F-14 Tomcat|F-14 Tomcat]] and called for the procurement of 546 aircraft.{{Sfn|Williams|2002|p=5}}{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|pp=87–88}}

[[File:Northrop ATF DP110 300x258.jpg|thumb|Northrop's DP110 submission for Dem/Val RFP, which was similar to the eventual YF-23|alt=Model of an early version of the YF-23 design on top of a wood holder]] Northrop's early work on the HSF paid off for the Dem/Val RFP. By January 1986, the HSF evolved into Design Proposal 86E (DP86E) as a refined and well-understood concept through extensive [[computational fluid dynamics]] simulations, [[wind tunnel]] testing, and RCS pole testing and became Northrop's preference for its ATF submission.{{Sfn|Metz|2017|p=25}} Northrop's ability to design and analyze stealthy curved surfaces, stemming back to its work on ''Tacit Blue'' and the ATB/B-2, gave their designers an early advantage in combining stealth with aerodynamics, especially since Lockheed, the only other company with extensive stealth experience, had previously relied on faceting as on the F-117 and [[Lockheed Senior Peg|lost the ATB]] to Northrop as a result. That loss, along with the poor aerodynamic performance of their early faceted ATF concept, forced Lockheed to also develop designs and analysis methods with curved stealthy surfaces.{{sfn|Hehs|1998}}{{Sfn|Metz|2017|p=22}} Northrop's HSF design was refined into DP110, which was its submission for the Dem/Val RFP.{{Sfn|Metz|2017|pp=28–29}}

In July 1986, proposals for Dem/Val were submitted by Lockheed, Boeing, General Dynamics, McDonnell Douglas, Northrop, [[Grumman]] and [[Rockwell International|North American Rockwell]]; the latter two dropped out of the competition shortly thereafter.{{Sfn|Miller|2005|pp=13–14, 19}} As contractors were expected to make significant investments for technology development, companies forming teams was encouraged by the SPO. Following proposal submissions, Northrop and McDonnell Douglas formed a team to develop whichever of their proposed designs was selected, if any. Lockheed, Boeing, and General Dynamics formed a team with a similar agreement.{{Sfn|Goodall|1992|p=94}}

Lockheed and Northrop, the two industry leaders in stealth aircraft, were selected as the two finalists on 31 October 1986 for Dem/Val at first and second place, although the approaches to their proposals were markedly different. Northrop's refined and well-understood design proposal was a significant advantage, especially in contrast to Lockheed's immature design, but the Lockheed proposal's focus on systems engineering rather than a point aircraft design actually pulled it ahead.{{Sfn|Hehs|1998}}{{Sfn|Metz|2017|p=22}} Both teams were awarded $691 million in FY 1985 dollars (~${{Format price|{{Inflation|index=US-GDP|value=691000000|start_year=1985}}}} in {{Inflation/year|US-GDP}}) and given 50 months for demonstration and validation, culminating in the flight-test of their prototypes. The SPO designated YF-22 for Lockheed's aircraft and YF-23 for Northrop's. [[Pratt & Whitney]] and [[General Electric]] had also been contracted to develop the engines, designated [[Pratt & Whitney F119|YF119]] and [[General Electric YF120|YF120]] respectively, for the ATF engine competition.{{Sfn|Jenkins|Landis|2008|pp=233–234}} Because of the late addition of the prototyping requirement due to political pressure, the prototype air vehicles were to be "best-effort" machines not meant to perform a competitive flyoff or represent a production aircraft that meets every requirement, but to demonstrate the viability of its concept and 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.{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|pp=88–89}}|group=N}}{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|pp=88–89}}

===Design refinement=== [[File:McDonnell_Douglas_Advanced_Tactical_Fighter_Dem-Val_proposal.jpeg|thumb|right|Artwork of Northrop partner McDonnell Douglas' submission for Dem/Val RFP; this design had little influence on the YF-23.]]

As one of the winning companies for the Dem/Val proposals, Northrop was the program lead of the YF-23 team with McDonnell Douglas; the two had previously collaborated on the [[McDonnell Douglas F/A-18 Hornet|F/A-18 Hornet]].{{Sfn|Metz|2017|p=31}} As well as the government contract awards, the team also invested $650 million (~${{Format price|{{Inflation|index=US-GDP|value=650000000|start_year=1988}}}} in {{Inflation/year|US-GDP}}) combined into their ATF effort; General Electric and Pratt & Whitney, the two engine companies, also invested $100 million (~${{Format price|{{Inflation|index=US-GDP|value=100000000|start_year=1988}}}} in {{Inflation/year|US-GDP}}) each.{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|p=164}} Airframe fabrication was divided roughly evenly, with Northrop building the aft fuselage and [[empennage]] in [[Hawthorne, California]] and performing final assembly at [[Edwards Air Force Base]] and McDonnell Douglas built the wings and forward fuselage in [[St. Louis, Missouri]]. Manufacturing was greatly assisted by the use of [[computer-aided design]] software. The YF-23 design was largely a continual refinement from Northrop's DP110 HSF with little influence from McDonnell Douglas's design, which had swept trapezoidal wings, four empennage surfaces, and chin-mounted split wedge inlets and did not perform well for stealth.{{Sfn|Metz|2017|p=20}} The YF-23's design evolved into DP117K when it was frozen as the prototype configuration in January 1988, with changes including a sharper and more voluminous nose from the earlier "platypus" shape for better radar performance and a strengthened aft deck with lower drag shaping.{{Sfn|Metz|2017|pp=26–27}}{{Sfn|Chong|2016|pp=237–238}} Due to the complex surface curvature, the aircraft was built outside-in, with the large composite skin structures fabricated first before the internal members. To ensure precise and responsive handling characteristics, Northrop developed and tested the flight control laws using both a large-scale simulator as well as a modified [[Convair C-131 Samaritan|C-131 Samaritan]] named the Total In Flight Simulator (TIFS).{{Sfn|Metz|2017|pp=40–41}}

[[File:YF-23 top view.jpg|thumb|left|Top view of the YF-23 (DP117K), showing the diamond wings and separation between the forward fuselage and engine nacelles|alt=Top view of black jet aircraft, showing diamond wings, engine nozzles with exhaust trenches, and two-piece tail. The separation between the forward fuselage and engine nacelles is apparent.]] Throughout Dem/Val, the SPO conducted System Requirements Reviews (SRR) where it reviewed results of performance and cost [[trade study|trade studies]] with both the Lockheed and Northrop teams to develop the ATF system specifications and, if necessary, adjusted requirements and deleted ones that added substantial weight or cost with marginal value. The ATF was initially required to land and stop within {{convert|2000|ft|m}}, which meant the use of [[thrust reversal|thrust reversers]] on their engines. In 1987, the USAF changed the runway length requirement to {{convert|3000|ft|m}} and by 1988 the requirement for thrust reversers was no longer needed. This allowed Northrop to have smaller engine [[nacelle]] housings with the space between them filled in to preserve area ruling in subsequent design refinements for the F-23 full system design, or Preferred System Concept (PSC). As the YF-23 design (DP117K) had been frozen by then, the nacelles—nicknamed "bread loafs" for their flat upper surface—were not downsized on the prototypes.{{Sfn|Miller|2005|p=23}}{{Sfn|Sweetman|1991a|pp=23, 43}} The number of internal missiles (with the [[AIM-120 AMRAAM|AIM-120A]] AMRAAM as the reference baseline) was reduced from eight to six. Despite these adjustments, both teams struggled to achieve the 50,000-lb takeoff gross weight goal, and this was subsequently increased to {{convert|60000|lb|kg|-2|abbr=on}} while engine thrust increased from {{convert|30000|lbf|kN|0|abbr=on}} class to {{convert|35000|lbf|kN|0|abbr=on|adj=on}} class.{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|pp=106–108}}

Aside from advances in air vehicle and engine design, the ATF also required innovations in avionics and sensor systems with the goal of achieving [[sensor fusion]] to enhance situational awareness and reduce pilot workload. The YF-23 was meant as a demonstrator for the airframe and propulsion system design and thus did not mount any mission systems avionics of the PSC F-23. Instead, Northrop and McDonnell Douglas tested these systems on ground and airborne laboratories with Northrop using a modified [[BAC One-Eleven]] as a flying avionics laboratory and McDonnell Douglas building the Avionics Ground Prototype (AGP) to evaluate software and hardware performance and reliability; sensors evaluated include a [[Northrop Grumman Electronic Systems|Westinghouse]]/[[Texas Instruments]] phased-array radar and a [[Martin Marietta]] [[infrared search and track]] (IRST).<ref name="APG-77" group=N/>{{Sfn|Metz|2017|p=31}}{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|pp=113–114}} Avionics requirements were also the subject of SPO SRRs with contractors and adjusted during Dem/Val. For example, the IRST sensor was dropped from a baseline requirement to provision for future addition in 1989.{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|pp=106–108}}

[[File:YF-23 hourglass.png|thumb|The red hourglass painted on the YF-23 PAV-1 for its maiden flight|alt=Fighter jet with red hourglass identifier painted at center top]] Formally designated as the YF-23A, the first aircraft ([[United States military aircraft serials|serial number]] ''87-0800''), Prototype Air Vehicle 1 (PAV-1), was rolled out on 22 June 1990.{{sfn|Flight International|1990|p=5}} The first YF-23 was painted charcoal gray and was nicknamed "Gray Ghost". The second prototype (serial number ''87-0801'', PAV-2) was painted in two shades of gray and nicknamed "Spider".{{sfn|Western Museum of Flight|2015}} PAV-1 briefly had a red hourglass painted on its ram air scoop to prevent injury to ground crew. The red hourglass resembled the marking on the underside of the [[Latrodectus|black widow]] spider, further reinforcing the unofficial nickname "Black Widow II" given to the YF-23 because of its 8-lobe radar cross section plot shape that resembled a spider and as homage to the [[Northrop P-61 Black Widow]] of [[World War II]].{{sfn|Western Museum of Flight|2015}} When Northrop management found out about the marking, they had it removed.{{Sfn|Goodall|1992|p=120}}

===Naval variant=== A proposed naval variant of the F-23, sometimes known unofficially as the NATF-23 (the proposed naval variants were never formally designated), was considered as an [[F-14 Tomcat]] replacement for the U.S. Navy. The original HSF configuration of the F-23 was first considered with the initial DP500 design but would have had issues with flight deck space (it was to be no longer than the F-14), handling, storage, landing, and catapult launching, thus necessitating a different design. By 1989, the design was narrowed down to two possible configurations: DP533 with four tails and DP527 with two V-tails and [[Canard (aeronautics)|canards]]. DP527 was determined to be the better solution.{{Sfn|Chong|2016|pp=238–239}} The NATF-23 design was submitted along with the F-23 proposal for full-scale development, or engineering and manufacturing development (EMD), in December 1990. However, by late 1990 the Navy was already beginning to back out of the NATF program and fully abandoned it by FY 1992 due to escalating costs.{{Sfn|Metz|2017|pp=74–79}} A wind tunnel test model of DP527, tested for 14,000 hours, was donated (with canards removed) by [[Boeing Defense, Space & Security#Organization|Boeing St. Louis]] (formerly McDonnell Douglas){{refn|Boeing merged with McDonnell Douglas in 1997 under the former's name.{{sfn|Chong|2016|pp=258–259}}|group=N}} in 2001 to the [[Bellefontaine Neighbors]] Klein Park Veterans Memorial in St. Louis, Missouri.{{sfn|St. Louis Post-Dispatch|2001|p=100}}

==Design== [[File:YF-23 front.jpg|thumb|left|A front view of PAV-1 ''87–0800'' showing the curving exterior of the design|alt=Front view of jet aircraft showing curving exterior. The ruddervator tail is V-shaped.]]

The YF-23A was a prototype intended to demonstrate the viability of Northrop's ATF proposal, which was designed to meet USAF requirements for [[Survivability (military)|survivability]], supercruise, stealth, and ease of maintenance.{{sfn|Flight International|15 November 1986|page=10}} Owing to its continual maturation from the initial High Stealth Fighter (HSF) concept which it still greatly resembled, the YF-23's shaping was highly refined. It was an unconventional-looking aircraft, with diamond-shaped wings tapered symmetrically (edges swept 40° front and back), a profile with substantial [[area rule|area-ruling]] to reduce [[wave drag]], and [[Stabilator|all-moving]] V-tails, or "ruddervators".{{Sfn|Metz|2017|p=84}} The [[cockpit]] was placed high, near the nose of the aircraft, for good visibility for the pilot. The chiseled shape of the nose, with its sharp chine edges, generated vortices to improve high angle of attack (AoA) characteristics. The aircraft featured a [[Tricycle gear|tricycle landing gear]] configuration with a nose [[landing gear]] leg and two main landing gear legs. The [[aerial refueling]] receptacle was centered on the spine of the forward fuselage. A single large weapons bay was placed on the underside of the fuselage between the nose and main landing gear.{{Sfn|Goodall|1992|pp=108–115, 124}} The cockpit had a center stick and side throttles.{{Sfn|Metz|2017|pp=92–93}}

[[File:YF-23 exhaust.jpg|thumb|A rear view of a YF-23, showing its tile-lined exhaust channels|alt=Rear view of the YF 23, the two tile lined exhaust channels can be seen at the center, between the V tails]] It was powered by two [[turbofan]] engines, with each in a separate engine nacelle with [[S-duct]]s to shield engine [[axial compressor]]s from [[radar]] waves, on either side of the aircraft's spine.{{Sfn|Sweetman|1991a|pp=42–44, 55}} The fixed-geometry inlets were widely spaced and trapezoidal in frontal profile, with a bleed system to absorb the turbulent [[boundary layer]] by using porous suction panels in front of the inlet. The boundary layer air was then ducted to vents and doors over the fuselage and wings. Of the two aircraft built, the first YF-23 (PAV-1) had Pratt & Whitney YF119 engines, and the second (PAV-2) was powered by General Electric YF120 engines. The aircraft had single-expansion ramp nozzles (SERN) where, as on the B-2, the exhaust from the engines flowed through troughs in the aft deck lined with heat-abating tiles to shield the exhaust from [[infrared homing]] (IR) missile detection from below. The tiles, made by [[Allison Engine Company|Detroit Diesel Allison]], were built from a porous material called "Lamilloy" and "[[Transpiration cooling|transpiration cooled]]" from engine bleed air to dissipate heat.{{Sfn|Winchester|2005|pp=198–199}}<ref group=N name="aft_deck"/> Unlike the YF-22, the YF-23 did not use thrust vectoring.{{Sfn|Miller|2005|p=23}} The YF-23's propulsion and aerodynamics, designed to minimize [[aerodynamic drag|drag]] at [[transonic]] and [[supersonic]] speeds, enabled it to cruise efficiently at over Mach 1.5 without afterburners.{{sfn|National Museum of the US Air Force}}

[[File:Northrop McDonnell Douglas YF-23A PAV-1 87-0800 Black Widow II LEngineIntake R&D NMUSAF 25Sep09 (14414042127).jpg|thumb|left|YF-23 [[S-duct]] engine air intake with the porous suction panel in front|alt=A close up shot of the YF-23's S-duct engine air intake located below the right wing]] The YF-23 was statically unstable—having [[relaxed stability]]—and flown through [[fly-by-wire]] which provided artificial stability with the [[flight control surfaces]] controlled by a central management computer system. Raising the [[Flap (aircraft)|wing flaps]] and [[aileron]]s on one side and lowering them on the other provided [[Flight dynamics (aircraft)|roll]]. The V-tail fins were angled 50 degrees from the vertical. [[Flight dynamics (aircraft)|Pitch]] was mainly provided by rotating these V-tail fins in opposite directions so their front edges moved together or apart. [[Yaw (aviation)|Yaw]] was primarily obtained by rotating the tail fins in the same direction. Chief test pilot Alfred "Paul" Metz stated that the YF-23 had superior high AoA performance to legacy aircraft, with trimmed AoA of up to 60°.{{sfn|Defense Daily, 14 January 1991}}{{sfn|Metz|2022}} Deflecting the wing flaps down and ailerons up on both sides simultaneously provided for [[Air brake (aircraft)|aerodynamic braking]].{{Sfn|Sweetman|1991a|pp=34–35, 43–45}}{{Sfn|Metz|2017|p=99}} To keep prototyping costs low despite the novel design, some [[commercial off-the-shelf]] components were used, including an F-15 nose wheel, F/A-18 main landing gear parts, and the forward cockpit components of the [[McDonnell Douglas F-15E Strike Eagle|F-15E Strike Eagle]].{{Sfn|Winchester|2005|pp=198–199}}{{Sfn|Jenkins|Landis|2008|p=237}}{{Sfn|Metz|2017|p=114}}

===Production F-23=== [[File:EMD F-23 cutaway 304x196.jpg|thumb|Cutaway drawing of the EMD F-23 design (DP231)|alt=Cross section drawing of the F-23 intended for production]]

The proposed production F-23 configuration (DP231 for the F119 engine and DP232 for the F120 engine) for full-scale development, or [[Manufacturing readiness level#Definitions|Engineering & Manufacturing Development]] (EMD), represented the final refinement of the HSF concept and would have differed from the YF-23 prototypes in several ways. Rather than a single weapons bay, the EMD design would have had two tandem bays in the lengthened forward fuselage, with the forward bay designed for short range [[AIM-9 Sidewinder]] missiles and the aft bay for AIM-120 missiles and bombs. An [[M61 Vulcan|M61]] rotary cannon would be installed on the left side of the forward fuselage. The F-23's overall length and height were slightly increased to {{convert|70|ft|5|in|m|abbr=on|2}} and {{convert|14|ft|8|in|m|abbr=on|2}} respectively; wingspan remained about the same at {{convert|43|ft|7|in|m|abbr=on|2}} with the same wing area of {{convert|950|sqft|sqm|abbr=on|2}}.{{refn|70 ft 5 in was the length of DP231, while DP232 was {{convert|5|in|cm|abbr=on|1}} longer at {{convert|70|ft|10|in|m|abbr=on|2}} due to the slightly larger F120 engines, with a small additional notch (less ideal) in the fuselage and empennage trailing edge pattern; wingspan and height remained the same as DP231.{{Sfn|Metz|2017|pp=67–73}}|group=N}} Fuselage volume was expanded for avionics and more fuel, with the nose and radome enlarged to accept sensors and mission systems, including the [[active electronically scanned array]] (AESA) radar.{{refn|name="APG-77"|The F-22 team and F-23 team both chose the same Westinghouse/Texas Instruments radar, which eventually became the [[AN/APG-77]].{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|p=181}}|group=N}} The forward fuselage cross section was more squared off with the forebody chines less pronounced and raised to the same [[waterline]] height as the leading edge of the wing. The deletion of thrust reversers enabled the engine nacelles to have a smaller, more rounded cross-section, and the trough between them was filled in to preserve area-ruling. The edges of the exhaust trough's heat-abating lining in the aft deck were aligned with the planform sweep angles for stealth. The inlet design changed from the trapezoidal profile with suction panels to a serrated semicircular cowl with a [[inlet cone#Alternative shapes|conical compression bump]] acting as a fixed shock cone and the boundary layer control vents were simplified. The fuselage and empennage trailing edge pattern would also have fewer serrations and the engine thrust lines were toed in at 1.5° off center. The EMD proposal had both single-seat F-23A and two-seat F-23B variants.{{Sfn|Metz|2017|pp=67–73}}

===NATF-23=== [[File:NATF-23 DP527 300x233.jpg|thumb|[[Perspective (graphical)|Perspective]] CAD drawing of NATF-23 DP527, showing the drastic departure from the YF-23's HSF configuration|alt=3D schematic of the naval F-23 design with its label at bottom right]]

The naval NATF-23 variant (internally designated DP527), the schematics of which surfaced in the 2010s, differed significantly from the YF-23 due to the requirements of [[CATOBAR|aircraft carrier operations]] as well as the Navy's greater emphasis on long range sensors, weapons, and [[Loiter (aeronautics)|loiter]] time for fleet air defense.{{sfn|United States Government Accounting Office|1990}}{{refn|The DP527 drawings show the same F119 engines as the Air Force version, but the final powerplant may have been a modified variant with greater bypass ratio for improved fuel efficiency at the expense of supercruise performance.{{Sfn|Chong|2016|pp=238–239}}|group=N}} The diamond wings were placed as far back as possible, and the aircraft had ruddervators with a more vertical cant and serrations to reduce overall length, folding wing capability for flight deck storage, reinforced landing gear, tailhook and dihedral canted canards for increased maneuverability at low speeds to land on [[aircraft carrier]]s, and two-dimensional thrust vectoring nozzles instead of SERNs.{{sfn|Simonsen|2016}} The inlet design was also different, being a quarter circle serrated cowl and a conical compression surface, and closer to the centerline adjacent to the forward fuselage; the inlet was offset from the fuselage by a gap to bypass the boundary layer. The internal weapons bay was split into two compartments by a bulkhead along the centerline in the forward fuselage to strengthen the aircraft's keel and would have accommodated the Navy's planned [[AIM-152 AAAM|AIM-152]] advanced air-to-air missiles (AAAM) as well as potentially the [[AGM-88 HARM]] and [[Harpoon (missile)|AGM-84 Harpoon]]. The bay doors would carry AIM-9 missiles and an M61 rotary cannon would be installed in a fairing in the right wing. The NATF-23 had an increased {{convert|48|ft|m|abbr=on|2}} wingspan and {{convert|17|ft|5|in|m|abbr=on|2}} height, and a larger wing area of {{convert|1050|sqft|sqm|abbr=on|2}}; overall length was reduced to {{convert|62|ft|8.5|in|m|abbr=on|2}}, the same as the F-14. Folded wingspan would be {{convert|23|ft|4|in|m|abbr=on|2}}. Like the Air Force version, the NATF-23 had both single-seat and two-seat variants.{{Sfn|Metz|2017|pp=74–79}}{{Sfn|Chong|2016|pp=238–239}}

===Proposed revival=== [[File:FB-23_Concept_Art.png|thumb|Northrop Grumman concept art of the FB-23 "Rapid Theater Attack" regional bomber|alt=The manufacturer's concept art of the F-23 design repurposed as a supersonic bomber with regional range]]

In 2004, [[Northrop Grumman]]{{refn|name="NG"|group=N|Northrop acquired Grumman in 1994 to become Northrop Grumman.{{sfn|Chong|2016|pp=258–259}}}} proposed an F-23-based bomber called the FB-23{{refn|The "F/B-23" designation was also used.{{Sfn|Metz|2017|pp=80–83}}|group=N}} "Rapid Theater Attack" (RTA) to meet a USAF solicitation for an [[2037 bomber controversy|interim regional bomber]], for which the [[Lockheed Martin FB-22]] and [[Rockwell B-1 Lancer#Variants|Boeing B-1R]] were also competing.{{sfn|Hebert|2004}}{{sfn|Flight International, 13 July 2004}} The FB-23 would have a two-seat cockpit and a similar planform shape to the F-23, but considerably larger in all dimensions, about {{convert|100|ft|m|abbr=on|0}} in overall length, to fulfill the bomber role with a combat radius of over {{convert|1600|nmi|mi km|sigfig=3}} and internal payload of {{convert|10000|lb|kg|abbr=on|sigfig=3}}. The engines would also have round axisymmetric nozzles above the aft deck rather than each having a single wedge-shaped flap. The EMD F-23's semicircular inlet design with the conical compression bump was retained. Northrop Grumman modified the YF-23 PAV-2 to serve as a display model for its proposed interim bomber.{{Sfn|Miller|2005|pp=38–39}}{{Sfn|Metz|2017|pp=80–83}} The possibility of an FB-23 interim bomber ended with the 2006 [[Quadrennial Defense Review]], which favored a long-range strategic bomber with much greater range.{{sfn|Quadrennial Defense Review Report|p=46}}{{sfn|Hebert|2006}} The USAF has since moved on to the [[Next-Generation Bomber]] and [[Long Range Strike Bomber]] program.{{sfn|Majumdar|2011}}

In 2018, Northrop Grumman responded to a [[Japan Air Self-Defense Force]] (JASDF) solicitation for industry partners to assist with the development of its [[Fifth-generation jet fighter|fifth]]/[[Sixth-generation jet fighter|sixth generation]] ([[Mitsubishi F-X|F-X]]) fighter. There was speculation that the company could offer a modernized version of the F-23 to the JASDF. Meanwhile, [[Lockheed Martin Aeronautics|Lockheed Martin]] offered an airframe derived from the F-22. Ultimately, Japan did not move forward with these proposals due to cost and industrial work-share concerns.{{sfn|Mizokami|2018}}{{sfn|Mainichi Shimbun, 4 October 2018}}

==Operational history== ===Evaluation=== [[File:Northrop YF-23 DFRC.jpg|thumb|left|The two YF-23s flying over the Mojave Desert. They were nicknamed "Gray Ghost" (background), and "Spider" (foreground).|alt=The two YF-23 production models flying over a desert, the first one named "Gray Ghost" painted in charcoal gray is at the left of the second one named "Spider", painted light gray, which is in the immediate front]]

The first YF-23, PAV-1 with Pratt & Whitney engines, took its 50-minute [[maiden flight]] on 27 August 1990 with Paul Metz at the controls.{{Sfn|Goodall|1992|p=99}}{{refn|Metz later became the chief test pilot for the EMD/production F-22.{{sfn|Miller|2005|p=39}}|group=N}} The second YF-23, PAV-2 with General Electric engines, made its first flight on 26 October, piloted by Jim Sandberg.{{Sfn|Jenkins|Landis|2008|p=237}} PAV-1 supercruised at Mach 1.43 on 18 September 1990, while PAV-2 reached over Mach 1.6 on 29 November, topping out at Mach 1.72.{{refn|The YF-23 with the General Electric engines was officially stated to have been able to supercruise at over Mach 1.6, and estimates from General Electric engineers suggest that the top supercruise speed was as high as Mach 1.8.{{sfn|Sweetman|1991a|p=55}}{{sfn|Chong|2016|pp=237–238}}|group=N|name="supercruise_speed"}} By comparison, the YF-22 achieved Mach 1.58 in supercruise.{{Sfn|Goodall|1992|pp=102–103}} The YF-23 was tested to a top speed of Mach 1.8 with afterburners and achieved a maximum angle-of-attack of 25°.{{sfn|Defense Daily, 14 January 1991}} The maximum speed is classified, though sources state a speed greater than Mach 2 at altitude in full afterburner.{{sfn|Metz|Sandberg|2015}}{{Sfn|Aronstein|Hirschberg|Piccirillo|1998|p=136}} The aircraft's weapons bay was configured for weapons launch, and used for testing bay acoustics, but no missiles were fired; Lockheed fired AIM-9 and AIM-120 missiles successfully from the YF-22. PAV-1 performed a fast-paced combat demonstration with six flights over a 10-hour period on 30 November 1990. Flight testing continued into December.{{Sfn|Miller|2005|pp=36, 39}} The two YF-23s flew 50 times for a total of 65.2 hours.{{sfn|Norris|1991}} The tests demonstrated Northrop's predicted performance values for the YF-23.{{Sfn|Miller|2005|pp=38–39}} Both designs met or exceeded all performance requirements; the YF-23 was stealthier and faster, but the YF-22 was more agile.{{Sfn|Goodall|1992|p=110}}{{Sfn|Sweetman|1991a|p=55}}

[[File:YF-22 and YF-23.jpg|thumb|A YF-22 in the foreground with a YF-23 in the background|alt=Lockheed Martin's YF-22 is at the center of the picture and the YF-23 "Spider" is at its left]] The two contractor teams submitted evaluation results and their PSC proposals for full-scale development in December 1990,{{Sfn|Miller|2005|pp=38��39}} and on 23 April 1991, [[Donald Rice]], the [[United States Secretary of the Air Force|Secretary of the Air Force]] announced that the YF-22 team was the winner.{{Sfn|Jenkins|Landis|2008|p=234}} The Air Force also selected the Pratt & Whitney F119 engine to power the F-22 production version. The Lockheed and Pratt & Whitney designs were rated higher on technical aspects, considered lower risk (the YF-23 flew considerably fewer sorties and hours than its counterpart),{{refn|One particular risk area for the YF-23 and F-23 design was the aft deck heating from the engine exhaust, and the performance and cost of the "Lamilloy" exhaust liners for the troughs became the subject of lawsuits between Northrop and the material developer Allison.{{sfn|Northrop Corporation v. General Motors Corporation and Allison Engine Company, Inc.}}|group=N|name="aft_deck"}} and were considered to have more effective program management.{{sfn|Landis|2022}}{{Sfn|Jenkins|Landis|2008|p=234}}{{Sfn|Miller|2005|pp=38–39}} Aviation observers have speculated that Northrop's poor performance on the B-2 and [[AGM-137 TSSAM]] programs with cost overruns and delays contributed to the loss.{{Sfn|Chong|2016|pp=237–238}} Furthermore, it has been speculated in the aviation press that the Lockheed design was also seen as more adaptable as the basis for the Navy's NATF, but by FY 1992 the US Navy had abandoned NATF.{{Sfn|Williams|2002|p=6}}{{Sfn|Miller|2005|p=76}}

Following the competition, both YF-23s were transferred to NASA's [[Dryden Flight Research Center]] at Edwards AFB, California, without their engines.{{sfn|NASA Dryden Flight Research Center}}{{Sfn|Winchester|2005|pp=198–199}} NASA planned to use one of the aircraft to study techniques for the calibration of predicted loads to measured flight results, but this did not happen.{{sfn|NASA Dryden Flight Research Center}} Both YF-23 airframes remained in storage until mid-1996 when they were transferred to museums, with PAV-2 briefly serving as a display model for the proposed FB-23 regional bomber in 2004.{{sfn|NASA Dryden Flight Research Center}}{{sfn|Landis|2022}}

==Aircraft on display== {{multiple image | align = center | total_width = 750 | footer = | image1 = YF-23 in the restoration area of the usaf museum.jpg | alt1 = A YF-23 undergoing restoration at the US Air Force Museum, one other plane can be seen at top left, another at top right; jeeps, machines, benches, cables and a plaque can be seen | caption1 = PAV-1 restoration work at the [[National Museum of the United States Air Force|USAF Museum]] | image2 = PAV-1 Display.jpg | alt2 = The YF-23 painted in charcoal gray, the "Gray Ghost" is seen front and center, with a man walking in front of it at the bottom right of the image. Multiple other aircraft held at the museum can be seen behind it | caption2 = YF-23 "Gray Ghost" on display at the USAF Museum, 2023 | image3 = YF-23 PAV-2 "Spider" Static.jpg| alt3 = The YF-23 painted light gray, the "Spider", can be seen at the center with its labels. An unmarked fighter jet is at its left, and a Navy aircraft is to the right, marked VF-2, probably the squadron it belonged to. | caption3 = YF-23 "Spider" on display at the Western Museum of Flight, 2017 }}

* YF-23A PAV-1, Air Force serial number ''87-0800'', "Gray Ghost", registration number N231YF, is on display in the Research and Development hangar of the [[National Museum of the United States Air Force]] near [[Dayton, Ohio]].{{sfn|National Museum of the US Air Force}} * YF-23A PAV-2, AF ser. no. ''87-0801'', "Spider", registration number N232YF, was on exhibit at the [[Western Museum of Flight]] until 2004,{{sfn|NASA Dryden Flight Research Center}} when it was reclaimed by Northrop Grumman and used as a display model for an F-23-based regional bomber.{{Sfn|Miller|2005|p=39}} PAV-2 was returned to the Western Museum of Flight in 2010 and is on display after the museum's relocation at [[Zamperini Field]] in [[Torrance, California]].{{sfn|Static Displays}}{{sfn|Northrop YF-23A "Black Widow II"}}

{{Aircraft specs |ref= Pace,{{sfn|Pace|1999|pp=14–15}} Sweetman,{{sfn|Sweetman|1991a|p=93}} Winchester,{{sfn|Winchester|2005|pp=198–199}} Metz & Sandberg,{{sfn|Metz|Sandberg|2015}} Aronstein & Hirschberg{{sfn|Aronstein|Hirschberg|Piccirillo|1998|p=136}} (note, some specifications are estimated) |prime units?=kts  |crew=1 |length ft=67 |length in=5 |length note= |span ft=43 |span in=7 |span note= |height ft=13 |height in=11 |height note= |wing area sqft=950 |wing area note= |aspect ratio= |airfoil= |empty weight lb=29000 |empty weight note=contractor weight (without engines) |gross weight lb=64000 |gross weight note=takeoff, {{convert|51320|lb|kg|abbr=on}} combat weight |max takeoff weight lb= |max takeoff weight note= |fuel capacity= |more general=  |eng1 number=2 |eng1 name=[[Pratt & Whitney YF119]]-PW-100N ''or'' [[General Electric YF120]]-GE-100N |eng1 type=[[Afterburner|afterburning]] [[turbofan]]s |eng1 kn= |eng1 lbf=23500 |eng1 note=(YF120) |power original= |thrust original= |eng1 kn-ab= |eng1 lbf-ab=30000 or 35000  |max speed kts= |max speed note= |max speed mach=2.2, {{convert|1452|mph|kn km/h|0|abbr=on}} at high altitude |cruise speed kts= |cruise speed note=*'''Supercruise''': Mach 1.72, {{convert|1135|mph|kn km/h|0|abbr=on}} at altitude<ref group=N name="supercruise_speed"/> |stall speed kts= |stall speed note= |never exceed speed kts= |never exceed speed note= |minimum control speed kts= |minimum control speed note= |range nmi= |range km=4500 |range note=ferry |combat range mi= |combat range nmi=700–800 |combat range note= |ferry range nmi= |ferry range note= |endurance= |ceiling ft=65000 |ceiling m=19800 |ceiling note= |g limits=+7.1 ''g'' (highest tested) |roll rate= |climb rate ftmin= |climb rate note= |time to altitude= |wing loading lb/sqft=67.4 |wing loading note=(54 lb/sq ft at combat weight) |fuel consumption lb/mi= |thrust/weight=1.09 (1.36 at combat weight) |more performance=   |armament= None as tested but provisions made for:{{sfn|Winchester|2005|pp=198–199}} * 1 × 20 mm (0.79 in) [[M61 Vulcan]] cannon * 4 × [[AIM-120 AMRAAM]] or [[AIM-7 Sparrow]] medium-range [[air-to-air missile]]s{{sfn|Winchester|2005|pp=198–199}}{{sfn|Sweetman|1991a|pp=42–44, 55}} * 2 × [[AIM-9 Sidewinder]] short-range air-to-air missiles{{sfn|Sweetman|1991a|pp=42–44, 55}}

|avionics= }}

==See also== {{aircontent |similar aircraft= * {{annotated link|Lockheed YF-22}} |lists= * [[List of fighter aircraft]] * [[List of United States fighter aircraft]] }}

== Notes == {{reflist|group=N|50em}}

== Citations == {{reflist}}

== Bibliography == ===Books=== {{refbegin}} * {{cite book |first1=David C. |last1=Aronstein |first2=Michael J |last2=Hirschberg |last3=Piccirillo |first3=Albert C. |title=Advanced Tactical Fighter to F-22 Raptor: Origins of the 21st Century Air Dominance Fighter |location=Arlington, Virginia |publisher=AIAA ([[American Institute of Aeronautics & Astronautics]]) |year=1998 |isbn=978-1-56347-282-4}} * {{cite book |last=Chong |first=Tony |year=2016 |title=Flying Wings & Radical Things, Northrop's Secret Aerospace Projects & Concepts 1939-1994 |location=Forest Lake, Minnesota |publisher=Specialty Press |isbn=978-1-58007-229-8}} * {{cite book |last=Goodall |first=James C |chapter=The Lockheed YF-22 and Northrop YF-23 Advanced Tactical Fighters |url-access=registration |url=https://archive.org/details/americasstealthf00good/mode/1up?view=theater |title=America's Stealth Fighters and Bombers, B-2, F-117, YF-22, and YF-23 |location=St. Paul, Minnesota |pages=91–127 |publisher=Motorbooks International Publishing |year=1992 |isbn=9780879386092}} * {{cite book |last1=Jenkins |first1=Dennis R. |last2=Landis |first2=Tony R. |title=Experimental & Prototype U.S. Air Force Jet Fighters |location=North Branch, Minnesota |publisher=Specialty Press |year=2008 |isbn=978-1-58007-111-6}} * {{cite book |last=Metz |first=Alfred "Paul" |title=Air Force Legends Number 220. Northrop YF-23 ATF |location=Forest Lake, Minnesota |publisher=Specialty Press |year=2017 |isbn=9780989258371}} * {{cite book |last=Miller |first=Jay |title=Lockheed Martin F/A-22 Raptor, Stealth Fighter |location=Hinckley, UK |publisher=Midland Publishing |year=2005 |isbn=9781857801583}} * {{cite book |last=Pace |first=Steve |title=F-22 Raptor: America's Next Lethal War Machine |location=New York |publisher=McGraw-Hill |year=1999 |isbn=9780071342711}} * {{Cite book |last=Simonsen |first=Erik |title=A Complete History of US Combat Aircraft Fly-Off Competitions |publisher=Specialty Press |year=2016 |isbn=9781580072274 |chapter=Wings Over the Mojave Desert: The Advanced Tactical Fighter |location=Forest Lake, Minnesota |pages=171–192}} * {{cite book |last=Sweetman |first=Bill |author-link=Bill Sweetman |title=YF-22 and YF-23 Advanced Tactical Fighters |location=St. Paul, Minnesota |publisher=Motorbooks International Publishing |year=1991a |isbn=9780879385057}} * {{cite book |editor-last=Williams |editor-first=Mel |chapter=Lockheed Martin F-22A Raptor |title=Superfighters: The Next Generation of Combat Aircraft |location=London |publisher=AIRtime Publishing |year=2002 |isbn=9781880588536 |pages=4–6}} * {{cite book |editor-last=Winchester |editor-first=Jim |chapter=Northrop/McDonnell Douglas YF-23 |title=Concept Aircraft: Prototypes, X-planes, and Experimental Aircraft |location=Rochester, Kent, UK |publisher=Grange Books |year=2005 |isbn=9781840138092 |pages=192–201}} {{refend}}

===Articles and interviews=== {{refbegin}} * {{Cite journal |date=1991-01-14 |title=YF-23 would undergo subtle changes if it wins competition. |url=https://go.gale.com/ps/i.do?p=AONE&sw=w&issn=08890404&v=2.1&it=r&id=GALE%7CA9371744&sid=googleScholar&linkaccess=abs |journal=Defense Daily |language=English |volume=170 |issue=8 |pages=62–63 |via=Gale |ref={{sfnref|Defense Daily, 14 January 1991}}}} * {{Cite news |date=15 November 1986 |title=ATF procurement launches new era |url=http://www.flightglobal.com/pdfarchive/view/1986/1986%20-%203004.html |url-status=dead |archive-url=https://web.archive.org/web/20120724101828/http://www.flightglobal.com/pdfarchive/view/1986/1986%20-%203004.html |archive-date=24 July 2012 |work=[[Flight International]] |pages=10–11 |publisher=Reed Business Information |ref={{sfnref|Flight International|15 November 1986}}}} * {{Cite news |date= |title=YF-23 roll out marks ATF debut |url=http://www.flightglobal.com/pdfarchive/view/1990/1990%20-%201803.html |url-status=dead |archive-url=https://web.archive.org/web/20120724011217/http://www.flightglobal.com/pdfarchive/view/1990/1990%20-%201803.html |archive-date=2012-07-24 |access-date=2024-06-13 |work=[[Flight International]] |page=5 |publisher=Reed Business Information |series=27 June – 3 July 1990 |ref={{sfnref|Flight International|1990}}}} * {{Cite news |date=13 July 2004 |title=YF-23 re-emerges for surprise bid |url=http://www.flightglobal.com/pdfarchive/view/2004/2004-09%20-%201169.html |url-status=dead |archive-url=https://web.archive.org/web/20120723232009/http://www.flightglobal.com/pdfarchive/view/2004/2004-09%20-%201169.html |archive-date=23 July 2012 |work=[[Flight International]] |page=6 |ref={{sfnref|Flight International, 13 July 2004}}}} * {{cite web |last=Cummings |first=Darold |date=3 August 2025 |title="Christmas Tree" ATF fighter design |url=https://www.linkedin.com/posts/darold-cummings-6851b6b_after-the-youtube-video-the-yf-23-is-back-activity-7357630009794064385-WFqW?utm_source=li_share&utm_content=feedcontent&utm_medium=g_dt_web&utm_campaign=copy |publisher=LinkedIn |ref={{sfnref|Cummings|2025}}}} * {{cite magazine |last=Hehs |first=Eric |date=1998 |title=Design Evolution of the F-22, Part 1 |url=https://www.codeonemagazine.com/f22_article.html?item_id=179 |archive-url=https://web.archive.org/web/20240518062846/https://www.codeonemagazine.com/f22_article.html?item_id=179 |archive-date=18 May 2024 |magazine=Code One |publisher=Lockheed Martin}} * {{cite magazine|url=https://www.airandspaceforces.com/article/1104strike/|title=Long-Range Strike in a Hurry|last=Hebert|first=Adam J.|access-date=6 September 2009|date=November 2004|volume=87|issue=11|magazine=[[Air & Space Forces Magazine]]|archive-url=https://web.archive.org/web/20250614175702/https://www.airandspaceforces.com/article/1104strike/|archive-date=14 June 2025|url-status=live}} * {{cite magazine|url=https://www.airandspaceforces.com/article/10062018/|title=The 2018 Bomber and Its Friends|last=Hebert|first=Adam J.|date=October 2006|access-date=6 September 2009|magazine=[[Air & Space Forces Magazine]]|volume=89|issue=10|archive-url=https://web.archive.org/web/20250225150449/https://www.airandspaceforces.com/article/10062018/|archive-date=25 February 2025|url-status=live}} * {{cite report |url=https://www.afmc.af.mil/News/Article-Display/Article/2919261/flashback-northrop-yf-23-black-widow-ii/ |title=Flashback: Northrop YF-23 Black Widow II |author=Landis |first=Tony |date=1 February 2022 |publisher=Air Force Materiel Command History Office |archive-url=https://web.archive.org/web/20240523165544/https://www.afmc.af.mil/News/Article-Display/Article/2919261/flashback-northrop-yf-23-black-widow-ii/ |archive-date=23 May 2024 |url-status=live}} * {{cite news |date=4 October 2018 |title=Defense Ministry to develop own fighter jet to succeed F-2, may seek int'l project |url=https://mainichi.jp/english/articles/20181004/p2a/00m/0na/001000c |url-status=live |archive-url=https://web.archive.org/web/20190425170901/https://mainichi.jp/english/articles/20181004/p2a/00m/0na/001000c |archive-date=25 April 2019 |access-date=28 April 2019 |newspaper=[[Mainichi Shimbun]] |ref={{sfnref|Mainichi Shimbun, 4 October 2018}}}} * {{Cite web |last=Majumdar |first=Dave |date=23 January 2011 |title=U.S. Air Force May Buy 175 Bombers |url=http://www.defensenews.com/article/20110123/DEFFEAT04/101230303/U-S-Air-Force-May-Buy-175-Bombers |url-status=dead |archive-url=https://archive.today/20120904021628/http://www.defensenews.com/story.php?i=5520432 |archive-date=4 September 2012 |access-date=2024-06-13 |website=Defense News}} * {{Cite AV media |people=Metz, Alfred "Paul" |url=https://www.youtube.com/watch?v=OdFL6r-OszM |title=YF-23 Advanced Tactical Fighter (ATF) – Paul Metz (Part 1) |date=2022-01-04 |publisher="10 Percent True" – Tales from the Cockpit |access-date=2024-06-15 |ref={{sfnref|Metz|2022}} |archive-url=https://web.archive.org/web/20231111214116/https://www.youtube.com/watch?v=OdFL6r-OszM |archive-date=11 November 2023 |via=YouTube}} * {{Cite AV media |people=Metz, Alfred "Paul" |url=https://www.youtube.com/watch?v=HSeApmqE_z4 |title=YF-23 and F-22A – Paul Metz (Part 2) |date=2022-01-16 |publisher="10 Percent True" – Tales from the Cockpit |access-date=2024-06-15 |archive-url=https://web.archive.org/web/20231111144120/https://www.youtube.com/watch?v=HSeApmqE_z4 |archive-date=11 November 2023 |via=YouTube}} * {{cite AV media |url=https://www.youtube.com/watch?v=Vpkv1ErWIf8 |title=YF-23 DEM/VAL Presentation by Test Pilots Paul Metz and Jim Sandberg |date=27 August 2015 |publisher=Peninsula Seniors Production |location=Western Museum of Flight, Torrance, California |access-date=30 June 2020 |archive-url=https://web.archive.org/web/20231014142723/https://www.youtube.com/watch?v=Vpkv1ErWIf8 |archive-date=14 October 2023 |people=Metz, Alfred "Paul"; Sandberg, Jim |ref={{sfnref|Metz|Sandberg|2015}}}} * {{Cite web |last=Mizokami |first=Kyle |date=2018-07-09 |title=Now Northrop Grumman Wants to Build Japan's New Fighter Jet |url=https://www.popularmechanics.com/military/aviation/a22093705/northrop-grumman-japans-fighter-jet/ |url-status=live |archive-url=https://web.archive.org/web/20240523033655/https://www.popularmechanics.com/military/aviation/a22093705/northrop-grumman-japans-fighter-jet/ |archive-date=23 May 2024 |access-date=2024-06-13 |website=[[Popular Mechanics]] |language=en-US}} * {{Cite web |date=1996-01-20 |title=YF-23 Photo Gallery |ref={{sfnref|NASA Dryden Flight Research Center}} |url=http://www.dfrc.nasa.gov/gallery/photo/YF-23/index.html |url-status=dead |archive-url=https://web.archive.org/web/19970605022423/http://www.dfrc.nasa.gov/gallery/photo/YF-23/index.html |archive-date=5 June 1997 |access-date=2024-06-13 |website=NASA Dryden Flight Research Center}} * {{Cite news |last=Norris 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General Motors Corporation and Allison Engine Company, Inc. |vol=49A02-0205-CV-428 |reporter= |opinion= |pinpoint= |court=Court of Appeals of Indiana |date=27 April 2004 |url=https://caselaw.findlaw.com/court/in-court-of-appeals/1121429.html |archive-url=https://web.archive.org/web/20241212141942/https://caselaw.findlaw.com/court/in-court-of-appeals/1121429.html |archive-date=12 December 2024 |access-date=27 June 2025 |ref={{sfnref|Northrop Corporation v. General Motors Corporation and Allison Engine Company, Inc.}}}} * {{cite web |title=Northrop-McDonnell Douglas YF-23A Black Widow II |url=https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/195766/northrop-mcdonnell-douglas-yf-23a-black-widow-ii/ |archive-url=https://web.archive.org/web/20230530132209/https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/195766/northrop-mcdonnell-douglas-yf-23a-black-widow-ii/ |archive-date=30 May 2023 |work=National Museum of the U.S. Air Force |ref={{sfnref|National Museum of the US Air Force}}}} * {{Cite web |date=6 February 2006 |title=Quadrennial Defense Review Report |url=http://www.defenselink.mil/qdr/report/Report20060203.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070215031830/http://www.defenselink.mil/qdr/report/Report20060203.pdf |archive-date=15 February 2007 |access-date=2024-06-13 |website=U.S. Department of Defense |language=en-US |ref={{sfnref|Quadrennial Defense Review Report}}}} * {{Cite web |last1=Rich |first1=Michael |last2=Stanley |first2=William |date=April 1984 |title=Improving U.S. Air Force Readiness and Sustainability |url=https://www.rand.org/pubs/reports/2006/R3113.1.pdf |archive-url=https://web.archive.org/web/20230702172045/https://www.rand.org/content/dam/rand/pubs/reports/2006/R3113.1.pdf |archive-date=2 July 2023 |website=RAND Corporation}} * {{Cite news |title=Memorial Day's service will include unveiling of plane |url=https://www.newspapers.com/article/st-louis-post-dispatch-memorial-days-s/169329940/ |work=[[St. Louis Post-Dispatch]] |edition=Main |date=24 May 2001 |location=[[St. Louis, Missouri]] |page=100 |via=[[Newspapers.com]] |ref={{sfnref|St. Louis Post-Dispatch|2001}}}} * {{cite journal |last=Sweetman |first=Bill |author-link=Bill Sweetman |title=The Fighter They Didn't Want |journal=[[World Air Power Journal]] |year=1991b |location=London |publisher=Aerospace Publishing |volume=7 |pages=32–41 |issue=Autumn/Winter 1991 |isbn=9781874023135 |issn=0959-7050}} * {{cite report |url=https://www.gao.gov/assets/nsiad-90-54.pdf |title=Report to the Chairman, Committee on Armed Services, House of Representatives: Navy's Participation in Air Force's Advanced Tactical Fighter Program |date=March 1990 |publisher=United States Government Accounting Office |archive-url=https://web.archive.org/web/20240617092715/https://www.gao.gov/assets/nsiad-90-54.pdf |archive-date=17 June 2024 |ref={{sfnref|United States Government Accounting Office|1990}}}} * {{cite web |url=http://www.wmof.com/display.htm |title=Static Displays |url-status=dead |archive-url=https://web.archive.org/web/20190715211258/http://www.wmof.com/display.htm |archive-date=15 July 2019 |website=Western Museum of Flight |ref={{sfnref|Static Displays}}}} * {{cite web |url=http://www.wmof.com/yf23a.htm |title=Northrop YF-23A "Black Widow II" |website=Western Museum of Flight |archive-url=https://web.archive.org/web/20190715212432/http://www.wmof.com/yf23a.htm |archive-date=15 July 2019 |ref={{sfnref|Northrop YF-23A "Black Widow II"}}}} * {{Cite AV media |url=https://www.youtube.com/watch?v=iU8gWgz9n4U |title=YF-23 Walk Around and Design Features by Test Pilot Paul Metz |date=2015-09-06 |publisher=Peninsula Seniors Productions |place=Western Museum of Flight, Torrance, California |time=7:20 |access-date=2024-06-15 |archive-url=https://web.archive.org/web/20231121153354/https://www.youtube.com/watch?v=iU8gWgz9n4U |archive-date=21 November 2023 |via=YouTube |ref={{sfnref|Western Museum of Flight|2015}}}} {{refend}}

==External links== {{Commons }} * [https://web.archive.org/web/20120204045047/http://www.dfrc.nasa.gov/gallery/Photo/YF-23/HTML/EC94-42454-3.html YF-23 photos on DFRC/NASA site]

[[Category:McDonnell Douglas aircraft|F-023]] [[Category:Northrop aircraft|F-023]] [[Category:Stealth aircraft]] [[Category:1990s United States fighter aircraft|Northrop F-23]] [[Category:V-tail aircraft]] [[Category:Twinjets]] [[Category:Mid-wing aircraft]] [[Category:Aircraft first flown in 1990]] [[Category:Cancelled military aircraft projects of the United States]] [[Category:Aircraft with retractable tricycle landing gear]]