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

Key Information

In the 1980s, the USAF began looking for a replacement for its F-15 fighter aircraft to more effectively counter emerging threats such as the Soviet Union's advanced Su-27 and 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 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 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[N 1] 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

[edit]
Main article: Advanced Tactical Fighter

Concept definition

[edit]

American reconnaissance satellites first spotted the advanced Soviet Su-27 and 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 F-15 Eagle and F-16 Fighting Falcon.[1] US tactical airpower was further threatened by new Soviet systems such as the A-50 airborne warning and control system (AWACS) revealed in 1978 and more advanced surface-to-air missile systems.[2] 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 materials, lightweight alloys, advanced flight-control systems, more powerful engines, and stealth technology.[3]

19 designs for the concept jets with annotations of features and specifications
Diagram of several designs submitted for ATF RFI, showing the comparatively small sizes of Northrop's initial designs

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.[4] 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-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.[5] Northrop's response was a Mach 2+ fighter design designated N-360 with delta wings, a single vertical tail, and twin engines with thrust vectoring nozzles and thrust reversers.[6][7] Around this time, the SPO also became aware of the very low radar cross section (RCS) results from the Air Force's "black world" innovations such as the Have Blue/F-117 ("Senior Trend"), Tacit Blue, and the Advanced Technology Bomber (ATB) program (which resulted in the B-2, or "Senior Ice"); consequently, the SPO increasingly emphasized stealth for survivability and combat effectiveness while still requiring fighter-like speed and maneuverability.[8]

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.[9] 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 planform shape, and the High Stealth Fighter (HSF) that balanced stealth and maneuverability with diamond wings, all-moving V-tail "ruddervators" (or butterfly tails), engine exhaust troughs, and aligned edges.[7][10] 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 edges) and canopy with their continuously curved, Gaussian surfaces. 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.[9][11]

Demonstration and validation

[edit]
Three metal models of the concept fighter jets
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.

By November 1984, concept exploration had allowed the SPO to narrow its requirements and release the Statement of Operational Need, which called for a 50,000 lb (22,700 kg) takeoff weight fighter with stealth and excellent kinematics, including prolonged supersonic flight without the use of afterburners, or supercruise; mission radius was expected to be 500 nautical miles (580 mi; 930 km) mixed subsonic/supersonic or 700–800 nautical miles (806–921 mi; 1,300–1,480 km) 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.[12] 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.[13] 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 ($86.4 million in 2024). 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 F-14 Tomcat and called for the procurement of 546 aircraft.[14][15]

Model of an early version of the YF-23 design on top of a wood holder
Northrop's DP110 submission for Dem/Val RFP, which was similar to the eventual YF-23

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.[16] 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 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.[17][18] Northrop's HSF design was refined into DP110, which was its submission for the Dem/Val RFP.[7]

In July 1986, proposals for Dem/Val were submitted by Lockheed, Boeing, General Dynamics, McDonnell Douglas, Northrop, Grumman and North American Rockwell; the latter two dropped out of the competition shortly thereafter.[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.[20]

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.[17][18] Both teams were awarded $691 million in FY 1985 dollars (~$1.71 billion in 2024) and given 50 months for demonstration and validation, culminating in the flight-test of their prototypes. Pratt & Whitney and General Electric had also been contracted to develop the engines, designated YF119 and YF120 respectively, for the ATF engine competition.[21] 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.[N 2][22]

Design refinement

[edit]
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 F/A-18 Hornet.[23] As well as the government contract awards, the team also invested $650 million (~$1.48 billion in 2024) combined into their ATF effort; General Electric and Pratt & Whitney, the two engine companies, also invested $100 million (~$228 million in 2024) each.[24] 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.[25] 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.[26][27] 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 C-131 Samaritan named the Total In Flight Simulator (TIFS).[28]

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.
Top view of the YF-23 (DP117K), showing the diamond wings and separation between the forward fuselage and engine nacelles

Throughout Dem/Val, the SPO conducted System Requirements Reviews (SRR) where it reviewed results of performance and cost 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 2,000 feet (610 m), which meant the use of thrust reversers on their engines. In 1987, the USAF changed the runway length requirement to 3,000 feet (910 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.[29][30] The number of internal missiles (with the 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 60,000 lb (27,200 kg) while engine thrust increased from 30,000 lbf (133 kN) class to 35,000 lbf (156 kN) class.[31]

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 Westinghouse/Texas Instruments phased-array radar and a Martin Marietta infrared search and track (IRST).[N 3][23][32] 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.[31]

Fighter jet with red hourglass identifier painted at center top
The red hourglass painted on the YF-23 PAV-1 for its maiden flight

Formally designated as the YF-23A, the first aircraft (serial number 87-0800), Prototype Air Vehicle 1 (PAV-1), was rolled out on 22 June 1990.[33] PAV-1 took its 50-minute maiden flight on 27 August with chief test pilot Alfred "Paul" Metz at the controls.[34][N 4] The second YF-23 (serial number 87-0801, PAV-2) made its first flight on 26 October, piloted by Jim Sandberg.[36] The first YF-23 was painted charcoal gray and was nicknamed "Gray Ghost". The second prototype was painted in two shades of gray and nicknamed "Spider".[37] 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 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.[37] When Northrop management found out about the marking, they had it removed.[38]

[edit]

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 canards. DP527 was determined to be the best solution.[39] 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.[40] A wind tunnel test model of DP527, tested for 14,000 hours, was donated (with canards removed) by Boeing St. Louis (formerly McDonnell Douglas)[N 5] in 2001 to the Bellefontaine Neighbors Klein Park Veterans Memorial in St. Louis, Missouri.[42]

Design

[edit]
Front view of jet aircraft showing curving exterior. The ruddervator tail is V-shaped.
A front view of PAV-1 87–0800 showing the curving exterior of the design

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, supercruise, stealth, and ease of maintenance.[43] Owing to its continual maturation from the initial 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-ruling to reduce wave drag, and all-moving V-tails, or "ruddervators".[44] 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 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.[45] The cockpit had a center stick and side throttles.[46]

Rear view of the YF 23, the two tile lined exhaust channels can be seen at the center, between the V tails
A rear view of a YF-23, showing its tile-lined exhaust channels

It was powered by two turbofan engines, with each in a separate engine nacelle with S-ducts to shield engine axial compressors from radar waves, on either side of the aircraft's spine.[47] 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 Detroit Diesel Allison, were built from a porous material called "Lamilloy" and "transpiration cooled" from engine bleed air to dissipate heat.[11][N 6] Unlike the YF-22, the YF-23 did not use thrust vectoring.[29] The YF-23's propulsion and aerodynamics, designed to minimize drag at transonic and supersonic speeds, enabled it to cruise efficiently at over Mach 1.5 without afterburners.[48]

A close up shot of the YF-23's S-duct engine air intake located below the right wing
YF-23 S-duct engine air intake with the porous suction panel in front

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 wing flaps and ailerons on one side and lowering them on the other provided roll. The V-tail fins were angled 50 degrees from the vertical. Pitch was mainly provided by rotating these V-tail fins in opposite directions so their front edges moved together or apart. Yaw was primarily obtained by rotating the tail fins in the same direction. Test pilot Paul Metz stated that the YF-23 had superior high AoA performance to legacy aircraft, with trimmed AoA of up to 60°.[49][50] Deflecting the wing flaps down and ailerons up on both sides simultaneously provided for aerodynamic braking.[51][52] 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 F-15E Strike Eagle.[11][36][53]

Production F-23

[edit]
Cross section drawing of the F-23 intended for production
Cutaway drawing of the EMD F-23 design (DP231)

The proposed production F-23 configuration (DP231 for the F119 engine and DP232 for the F120 engine) for full-scale development, or 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 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 70 ft 5 in (21.46 m) and 14 ft 8 in (4.47 m) respectively; wingspan remained about the same at 43 ft 7 in (13.28 m) with the same wing area of 950 sq ft (88.26 m2).[N 7] 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.[N 3] 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 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.[54]

NATF-23

[edit]
3D schematic of the naval F-23 design with its label at bottom right
Perspective CAD drawing of NATF-23 DP527, showing the drastic departure from the YF-23's HSF configuration

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 aircraft carrier operations as well as the Navy's greater emphasis on long range sensors, weapons, and loiter time for fleet air defense.[56][N 8] 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 carriers, and two-dimensional thrust vectoring nozzles instead of SERNs.[57] 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 advanced air-to-air missiles (AAAM) as well as potentially the AGM-88 HARM and 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 48 ft (14.63 m) wingspan and 17 ft 5 in (5.31 m) height, and a larger wing area of 1,050 sq ft (97.55 m2); overall length was reduced to 62 ft 8.5 in (19.11 m), the same as the F-14. Folded wingspan would be 23 ft 4 in (7.11 m). Like the Air Force version, the NATF-23 had both single-seat and two-seat variants.[40][39]

Proposed revival

[edit]
The manufacturer's concept art of the F-23 design repurposed as a supersonic bomber with regional range
Northrop Grumman concept art of the FB-23 "Rapid Theater Attack" regional bomber

In 2004, Northrop Grumman[N 1] proposed an F-23-based bomber called the FB-23[N 9] "Rapid Theater Attack" (RTA) to meet a USAF solicitation for an interim regional bomber, for which the Lockheed Martin FB-22 and Boeing B-1R were also competing.[59][60] 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 100 ft (30 m) in overall length, to fulfill the bomber role with a combat radius of over 1,600 nautical miles (1,840 mi; 2,960 km) and internal payload of 10,000 lb (4,540 kg). 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.[61][58] 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.[62][63] The USAF has since moved on to the Next-Generation Bomber and Long Range Strike Bomber program.[64]

In 2018, Northrop Grumman responded to a Japan Air Self-Defense Force (JASDF) solicitation for industry partners to assist with the development of its 5th/6th generation (F-X) fighter. There was speculation that the company could offer a modernized version of the F-23 to the JASDF. Lockheed Martin offered an airframe derived from the F-22, but Japan did not select these proposals due to cost and industrial work-share concerns.[65][66]

Operational history

[edit]

Evaluation

[edit]
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 two YF-23s flying over the Mojave Desert. They were nicknamed "Gray Ghost" (background), and "Spider" (foreground).

The first YF-23, with Pratt & Whitney engines, supercruised at Mach 1.43 on 18 September 1990, and the second, with General Electric engines, reached over Mach 1.6 on 29 November 1990, topping out at Mach 1.72.[N 10] By comparison, the YF-22 achieved Mach 1.58 in supercruise.[68] The YF-23 was tested to a top speed of Mach 1.8 with afterburners and achieved a maximum angle-of-attack of 25°.[49] The maximum speed is classified, though sources state a speed greater than Mach 2 at altitude in full afterburner.[69][70] The aircraft's weapons bay was configured for weapons launch, and used for testing weapons bay acoustics, but no missiles were fired; Lockheed fired AIM-9 and AIM-120 missiles successfully from its YF-22 demonstration aircraft. 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.[71] The two YF-23s flew 50 times for a total of 65.2 hours.[72] The tests demonstrated Northrop's predicted performance values for the YF-23.[61] Both designs met or exceeded all performance requirements; the YF-23 was stealthier and faster, but the YF-22 was more agile.[73][67]

Lockheed Martin's YF-22 is at the center of the picture and the YF-23 "Spider" is at its left
A YF-22 in the foreground with a YF-23 in the background

The two contractor teams submitted evaluation results and their PSC proposals for full-scale development in December 1990,[61] and on 23 April 1991, Donald Rice, the Secretary of the Air Force announced that the YF-22 team was the winner.[74] 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),[N 6] and were considered to have more effective program management.[76][74][61] 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.[77][78]

Following the competition, both YF-23s were transferred to NASA's Dryden Flight Research Center at Edwards AFB, California, without their engines.[79][11] 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.[79] 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.[79][76]

Aircraft on display

[edit]
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
PAV-1 restoration work at the USAF Museum
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
YF-23 "Gray Ghost" on display at the USAF Museum, 2023
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.
YF-23 "Spider" on display at the Western Museum of Flight, 2017

Specifications (YF-23A)

[edit]
YF-23 3-view drawing from Northrop/McDonnell Douglas
The YF-23 painted charcoal gray, the "Gray Ghost", pictured flying
YF-23 PAV-1 in flight

Data from Pace,[82] Sweetman,[83] Winchester,[11] Metz & Sandberg,[69] Aronstein & Hirschberg[70] (note, some specifications are estimated)

General characteristics

  • Crew: 1
  • Length: 67 ft 5 in (20.55 m)
  • Wingspan: 43 ft 7 in (13.28 m)
  • Height: 13 ft 11 in (4.24 m)
  • Wing area: 950 sq ft (88 m2)
  • Empty weight: 29,000 lb (13,154 kg) contractor weight (without engines)
  • Gross weight: 64,000 lb (29,030 kg) takeoff, 51,320 lb (23,280 kg) combat weight
  • Powerplant: 2 × Pratt & Whitney YF119-PW-100N or General Electric YF120-GE-100N afterburning turbofans, 23,500 lbf (105 kN) thrust each (YF120) dry, 30,000 or 35,000 lbf (130 or 160 kN) with afterburner

Performance

  • Maximum speed: Mach 2.2, 1,452 mph (1,262 kn; 2,337 km/h) at high altitude
  • Supercruise: Mach 1.72, 1,135 mph (986 kn; 1,827 km/h) at altitude[N 10]
  • Range: 2,400 nmi (2,800 mi, 4,500 km) ferry
  • Combat range: 700–800 nmi (810–920 mi, 1,300–1,500 km)
  • Service ceiling: 65,000 ft (19,800 m)
  • g limits: +7.1 g (highest tested)
  • Wing loading: 67.4 lb/sq ft (329 kg/m2) (54 lb/sq ft at combat weight)
  • Thrust/weight: 1.09 (1.36 at combat weight)

Armament
None as tested but provisions made for:[11]

See also

[edit]

Aircraft of comparable role, configuration, and era

Related lists

Notes

[edit]

Citations

[edit]
  1. ^ Rich & Stanley 1984, p. 7.
  2. ^ Aronstein, Hirschberg & Piccirillo 1998, pp. 37–39.
  3. ^ Miller 2005, p. 11.
  4. ^ Metz 2017, pp. 10–12.
  5. ^ Sweetman 1991a, pp. 10–13.
  6. ^ Chong 2016, pp. 226–227.
  7. ^ a b c Metz 2017, pp. 28–29.
  8. ^ Aronstein, Hirschberg & Piccirillo 1998, pp. 45–58.
  9. ^ a b Metz 2017, pp. 23–24.
  10. ^ Chong 2016, pp. 233–234.
  11. ^ a b c d e f g Winchester 2005, pp. 198–199.
  12. ^ Aronstein, Hirschberg & Piccirillo 1998, pp. 70–78.
  13. ^ Aronstein, Hirschberg & Piccirillo 1998, pp. 82–85.
  14. ^ Williams 2002, p. 5.
  15. ^ Aronstein, Hirschberg & Piccirillo 1998, pp. 87–88.
  16. ^ Metz 2017, p. 25.
  17. ^ a b Hehs 1998.
  18. ^ a b Metz 2017, p. 22.
  19. ^ Miller 2005, pp. 13–14, 19.
  20. ^ Goodall 1992, p. 94.
  21. ^ Jenkins & Landis 2008, pp. 233–234.
  22. ^ a b Aronstein, Hirschberg & Piccirillo 1998, pp. 88–89.
  23. ^ a b Metz 2017, p. 31.
  24. ^ Aronstein, Hirschberg & Piccirillo 1998, p. 164.
  25. ^ Metz 2017, p. 20.
  26. ^ Metz 2017, pp. 26–27.
  27. ^ a b Chong 2016, pp. 237–238.
  28. ^ Metz 2017, pp. 40–41.
  29. ^ a b Miller 2005, p. 23.
  30. ^ Sweetman 1991a, pp. 23, 43.
  31. ^ a b Aronstein, Hirschberg & Piccirillo 1998, pp. 106–108.
  32. ^ Aronstein, Hirschberg & Piccirillo 1998, pp. 113–114.
  33. ^ Flight International 1990, p. 5.
  34. ^ Goodall 1992, p. 99.
  35. ^ a b Miller 2005, p. 39.
  36. ^ a b Jenkins & Landis 2008, p. 237.
  37. ^ a b Western Museum of Flight 2015.
  38. ^ Goodall 1992, p. 120.
  39. ^ a b c Chong 2016, pp. 238–239.
  40. ^ a b Metz 2017, pp. 74–79.
  41. ^ a b Chong 2016, pp. 258–259.
  42. ^ St. Louis Post-Dispatch 2001, p. 100.
  43. ^ Flight International & 15 November 1986, p. 10.
  44. ^ Metz 2017, p. 84.
  45. ^ Goodall 1992, pp. 108–115, 124.
  46. ^ Metz 2017, pp. 92–93.
  47. ^ a b c Sweetman 1991a, pp. 42–44, 55.
  48. ^ a b National Museum of the US Air Force.
  49. ^ a b Defense Daily, 14 January 1991.
  50. ^ Metz 2022.
  51. ^ Sweetman 1991a, pp. 34–35, 43–45.
  52. ^ Metz 2017, p. 99.
  53. ^ Metz 2017, p. 114.
  54. ^ a b Metz 2017, pp. 67–73.
  55. ^ Aronstein, Hirschberg & Piccirillo 1998, p. 181.
  56. ^ United States Government Accounting Office 1990.
  57. ^ Simonsen 2016.
  58. ^ a b Metz 2017, pp. 80–83.
  59. ^ Hebert 2004.
  60. ^ Flight International, 13 July 2004.
  61. ^ a b c d Miller 2005, pp. 38–39.
  62. ^ Quadrennial Defense Review Report, p. 46.
  63. ^ Hebert 2006.
  64. ^ Majumdar 2011.
  65. ^ Mizokami 2018.
  66. ^ Mainichi Shimbun, 4 October 2018.
  67. ^ a b Sweetman 1991a, p. 55.
  68. ^ Goodall 1992, pp. 102–103.
  69. ^ a b Metz & Sandberg 2015.
  70. ^ a b Aronstein, Hirschberg & Piccirillo 1998, p. 136.
  71. ^ Miller 2005, pp. 36, 39.
  72. ^ Norris 1991.
  73. ^ Goodall 1992, p. 110.
  74. ^ a b Jenkins & Landis 2008, p. 234.
  75. ^ Northrop Corporation v. General Motors Corporation and Allison Engine Company, Inc.
  76. ^ a b Landis 2022.
  77. ^ Williams 2002, p. 6.
  78. ^ Miller 2005, p. 76.
  79. ^ a b c d NASA Dryden Flight Research Center.
  80. ^ Static Displays.
  81. ^ Northrop YF-23A "Black Widow II".
  82. ^ Pace 1999, pp. 14–15.
  83. ^ Sweetman 1991a, p. 93.

Bibliography

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Northrop YF-23

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The Northrop YF-23, officially designated the YF-23A and nicknamed the Black Widow II, was an advanced prototype stealth fighter aircraft developed jointly by Northrop and McDonnell Douglas for the United States Air Force's Advanced Tactical Fighter (ATF) program during the late 1980s and early 1990s. Intended as a fifth-generation replacement for the F-15 Eagle to counter evolving Soviet threats, it emphasized low-observability stealth design, supercruise capability without afterburners, and high maneuverability. Two prototypes were constructed: Prototype Air Vehicle 1 (PAV-1, serial 87-0800) and PAV-2 (serial 87-0801), with PAV-1 rolling out on June 22, 1990, and achieving its first flight on August 27, 1990, followed by PAV-2's debut on October 26, 1990. The ATF program originated from a 1981 U.S. request for information, with Northrop-McDonnell Douglas selected as one of two finalists in October 1986 alongside the Lockheed-Boeing-General Dynamics team developing the YF-22. The YF-23 featured a distinctive diamond-shaped wing planform, a flattened fuselage for reduced radar cross-section, and twin tail fins canted outward to minimize infrared signatures, powered by either YF119 or engines each providing approximately 35,000 pounds of thrust. During testing at , the prototypes demonstrated speeds up to Mach 1.6, a top speed of Mach 1.8 with afterburners, and exceptional with a maximum angle-of-attack of 25 degrees, while qualifying for air refueling early in the program; together they completed 50 sorties, with flight testing ending in December 1990 (PAV-1 on November 30, PAV-2 on December 18). Unlike the YF-22, the YF-23 omitted thrust-vectoring nozzles to prioritize stealth and weight reduction, achieving a single-seat layout inspired by the F-15E with advanced multi-purpose displays and for superior . In the 1991 downselect, the YF-23 lost to the YF-22—later the F-22 Raptor—primarily due to the Lockheed team's higher technical ratings, lower perceived development risks, and stronger program management, despite the YF-23's edge in stealth performance and the fact that both met ATF requirements. No production variants were authorized; both prototypes are preserved: PAV-1 (painted as the "Gray Ghost") at the National Museum of the U.S. Air Force and PAV-2 at the Western Museum of Flight. The YF-23's innovative design influenced subsequent stealth aircraft concepts and remains a notable "what if" in aviation history for its pioneering integration of supercruise and low observability.

Background and Development

Origins of the Advanced Tactical Fighter Program

In the late 1970s, the United States Air Force identified a pressing need for a new air superiority fighter to counter emerging Soviet threats, particularly the advanced Mikoyan MiG-29 and Sukhoi Su-27 interceptors, which posed significant risks to American tactical airpower in potential European conflicts. This requirement stemmed from assessments that existing aircraft like the F-15 Eagle would become obsolete by the mid-1990s, necessitating a successor capable of maintaining air dominance through superior speed, maneuverability, and stealth characteristics. By 1979, Air Force studies emphasized the urgency of developing such a platform to address the evolving aerial threat environment, building on lessons from Vietnam-era engagements and Cold War intelligence on Soviet aviation advancements. The (ATF) program evolved from earlier U.S. initiatives in the 1970s, including the Fighter Experimental (FX) program, which led to the F-15, and the Lightweight Fighter (LF) prototype competition that produced the YF-16 and YF-17 designs, ultimately resulting in the F-16 Fighting Falcon. These programs highlighted the balance between cost, performance, and , informing the ATF's emphasis on affordability alongside advanced capabilities. By the early , follow-on efforts like the Advanced Fighter Technology Integration (AFTI) and Highly Maneuverable Aircraft Technology (HiMAT) programs provided critical data on systems and , paving the way for the ATF's more ambitious goals. The ATF program was formally established in November 1981 when the Defense Resources Board approved the Mission Element Need Statement, marking it as a in the Fiscal Year 1983 budget cycle. Initial milestones included a issued in May 1981 to industry contractors and the award of seven concept exploration contracts in September 1983 to teams led by , , , Lockheed, McDonnell Douglas, Northrop, and Rockwell. This phase focused on defining requirements for a post-2000 fighter with enhanced survivability and multirole potential. By 1986, the program advanced to the Demonstration/Validation (Dem/Val) phase following congressional appropriations that supported development, with total through 1987 reaching approximately $557 million and an additional $537 million requested for 1988. On October 31, 1986, the awarded Dem/Val contracts valued at $691 million each to the Northrop/McDonnell Douglas team and the Lockheed/McAir (with and ) team, initiating a five-year effort to build and fly prototypes for competitive evaluation. These awards, part of a broader $9.6 billion development , were approved amid congressional to ensure cost controls, reflecting the program's semi-secretive nature and strategic priority for mid-1990s deployment.

YF-23 Concept Formation and Design Phase

In October 1986, the U.S. Air Force selected Northrop as the prime contractor for one of two Demonstration/Validation (Dem/Val) phase contracts under the (ATF) program, with McDonnell Douglas serving as the principal partner responsible for , , and development. The Northrop/McDonnell Douglas team was awarded a valued at approximately $691 million to refine and demonstrate key technologies for the YF-23 prototype, focusing on integrating stealth, , and high maneuverability. This partnership leveraged Northrop's expertise in low-observable designs and McDonnell Douglas's experience in advanced and structures. The YF-23 concept drew heavily from Northrop's prior stealth research, particularly the Tacit Blue demonstrator program of the early , which validated curved surfaces and buried engine inlets to reduce reflections and infrared signatures. Key influences included an emphasis on low observability derived from these efforts, evolving ATF requirements from initial "reduced cross-section" goals to full low-observability standards that incorporated without afterburners for extended range and lower detectability. The diamond-wing planform was selected to optimize low observability by aligning leading and trailing edges to scatter waves effectively, minimizing returns across multiple aspects while supporting supersonic performance. During the 1986-1989 Dem/Val phase, the team conducted extensive testing and (CFD) simulations to validate aerodynamic stability, feasibility at Mach 1.4-1.6 without afterburners, and overall configuration viability. A subscale model underwent rigorous evaluation, accumulating thousands of hours to refine efficiency and drag reduction, confirming the design's potential for sustained supersonic dash while maintaining low infrared emissions. Iterative refinements prioritized stealth over conventional control surfaces, leading to the adoption of a pure tailless configuration with canted ruddervators for pitch and yaw control, rejecting early canard proposals that would have increased frontal cross-section. This evolution balanced aerodynamic challenges—such as reduced stability—with systems, ensuring the YF-23 achieved superior low-observability compared to initial concepts while meeting ATF maneuverability thresholds.

Prototype Construction and Initial Flights

The two YF-23 prototypes, designated Prototype Air Vehicle 1 (PAV-1, serial number 87-0800) and Prototype Air Vehicle 2 (PAV-2, serial number 87-0801), were assembled at Northrop's facility in , as part of the program's demonstration/validation phase. Construction emphasized the realization of the aircraft's diamond-shaped wing planform and integrated stealth features derived from earlier concept designs. PAV-1, powered by Pratt & Whitney YF119 engines, completed assembly and was rolled out on June 22, 1990, followed by PAV-2, equipped with General Electric YF120 engines, in October 1990. Prior to , both prototypes underwent extensive ground evaluations at , including engine run-ups, high-speed taxi tests reaching up to 120 knots, and verification of cross-section signatures in anechoic chambers to confirm low-observability performance. These ground tests ensured structural , systems integration, and compliance with stealth requirements before airborne operations commenced. PAV-1's rollout ceremony was held on June 22, 1990, at the Edwards test facility, marking the transition from fabrication to flight preparation. PAV-1 achieved its on August 27, 1990, piloted by Northrop chief Alfred "Paul" Metz, lasting 51 minutes and reaching a top speed of Mach 0.4 during the low-speed handling assessment from . This initial focused on basic airworthiness, control surface responsiveness, and system validation, with the aircraft demonstrating stable behavior throughout. PAV-2 followed with its first flight on October 26, 1990, under the control of Jim Sandberg, initiating parallel evaluations of the alternative propulsion system. Early flight testing prioritized envelope expansion, achieving supersonic speeds up to Mach 1.43 by late September 1990 on PAV-1, while assessing handling qualities and the inherent stability of the diamond-wing configuration under various flight regimes. These objectives included verifying low-speed maneuverability, high-angle-of-attack recovery, and overall pilot workload, with the prototypes exhibiting agile and predictable responses that required minimal control inputs. By November 1990, joint formation flights between PAV-1 and PAV-2 had begun, further refining stability data and paving the way for advanced performance trials.

Competition Evaluation and Downselection

The Advanced Tactical Fighter (ATF) fly-off competition took place at Edwards Air Force Base, California, spanning flight testing from late 1990, with formal evaluation concluding in December 1990 ahead of the final decision. This phase pitted the Northrop/McDonnell Douglas YF-23 against the Lockheed/Boeing/General Dynamics YF-22, focusing on critical performance metrics including stealth characteristics, supercruise capability (sustained supersonic flight without afterburners), maneuverability, and maintainability to determine suitability for full-scale development. The two YF-23 prototypes conducted 50 flights during the evaluation, logging a total of 65.2 flight hours across sorties that demonstrated key capabilities. The YF-23 exhibited an advantage in stealth, achieving a lower cross-section (RCS) than the YF-22 through its flattened diamond-wing planform and serpentine engine inlets that reduced reflections from multiple aspects. It also validated performance by sustaining Mach 1.6 without engagement on its second prototype during November 1990 testing, minimizing detectability while meeting range and speed requirements. assessments highlighted the YF-23's features, such as removable wing sections for engine access, which promised reduced workload compared to more complex alternatives. On April 23, 1991, Secretary of the Donald B. Rice announced the downselection of the YF-22 for engineering and manufacturing development, citing the Lockheed team's demonstrated superior close-in maneuverability—enhanced by thrust-vectoring nozzles—as a key differentiator in scenarios. The decision also reflected concerns over the YF-23's higher projected production costs and greater technical risks in scaling up its innovative but unproven , despite the Northrop design's strengths in stealth and speed. USAF evaluators expressed higher confidence in Lockheed's program management and timeline adherence, prioritizing a balanced fighter capable of both beyond-visual-range engagements and agile within-visual-range combat.

Design Features

Airframe, Aerodynamics, and

The Northrop YF-23 featured a diamond-wing configuration with outward-canted vertical stabilizers optimized for stealth and high-speed performance, with a leading-edge sweep of 40 degrees to minimize reflections and enhance supersonic stability. The measured 67 feet 5 inches in length and had a of 43 feet 6 inches, incorporating a blended wing-body design that integrated the with the wings to reduce aerodynamic drag and eliminate protuberances that could increase detectability. This configuration, lacking traditional vertical stabilizers, relied on a low-aspect-ratio wing planform to facilitate efficient while maintaining structural integrity under high dynamic pressures. Stealth was a core design priority, achieved through a combination of shaping, materials, and inlet/exhaust treatments to achieve a very low frontal cross-section (RCS). The was coated with radar-absorbent materials (RAM) that absorbed incoming waves, while serpentine angled upward and inward shielded the faces from frontal illumination, preventing direct line-of-sight reflections. Exhaust systems employed diamond-shaped nozzles integrated into a serrated beavertail with submerged ventral troughs, which dispersed heat and reduced both and signatures from the rear aspect. Aerodynamic control was managed without to preserve stealth and weight margins, using trailing-edge elevons on the wings for pitch and roll authority. Yaw and additional roll were provided by ruddervators—large, all-moving surfaces at approximately 45 degrees—operating in conjunction with differential thrust from the twin engines and split drag devices for enhanced maneuverability at high speeds. This system enabled stable at Mach 1.25 without in early flight tests, demonstrating the airframe's inherent low-drag characteristics and for agile handling. The YF-23's empty weight was approximately 29,000 pounds, achieved through extensive use of composite materials comprising about 50% of the to minimize structural mass and thermal emissions. These composites, combined with an innovative cooling system for exhaust gases, significantly reduced the aircraft's by dissipating engine heat efficiently across cooled surfaces.

Avionics, Cockpit, and Armament Integration

The Northrop YF-23 prototypes incorporated a quad-redundant digital flight to ensure stability and control in the aircraft's inherently unstable tailless design. This system utilized advanced actuators, including small, high-power units for the thin-wing flaperons and two-stage direct-drive actuators for the large tailerons, enabling effective handling across low-speed maneuvers and supersonic flight regimes exceeding Mach 1. Integrated with inertial capabilities, the fly-by-wire setup supported precise vehicle management without traditional mechanical linkages, drawing from prior Northrop developments like the Tacit Blue demonstrator's air data sensing technologies. The cockpit design emphasized pilot efficiency and , drawing from the F-15E Strike Eagle layout with two 5-by-5-inch multifunction color displays (MPCDs) on the main instrument panel for presenting flight, navigation, and systems data. A (HUD) projected critical information onto the pilot's forward view, while an innovative "accel-decel" allowed speed-based control rather than direct management, reducing workload during complex missions. The raised canopy structure further enhanced visibility over the long, diamond-shaped , providing a broad field of regard for threat detection and targeting. The suite in the YF-23 prototypes focused on risk reduction for the program, delivering strong performance data during despite the aircraft's role as an and demonstrator without full production mission systems. A scaled version of the active electronically scanned array (AESA) , jointly developed by and , was planned for integration to enable long-range target detection and tracking with low-probability-of-intercept emissions. Supporting this, a mission data processor facilitated preliminary from , , and electronic warfare inputs, prioritizing stealthy operations in contested environments. Armament integration emphasized internal carriage to preserve the aircraft's low-observable profile, with the forward fuselage accommodating a single deep weapons bay split by a centerline bulkhead for structural reinforcement. This bay was configured to hold up to four air-to-air missiles on staggered launchers or two missiles alongside a 1,000-pound-class bomb, such as a GBU-32 JDAM, for precision strikes. Provisions existed for a 20 mm cannon in a side-fuselage fairing, though no live-fire testing occurred during the prototype phase; the airframe's design accommodated these elements without compromising aerodynamic or stealth characteristics.

Propulsion Systems and Performance Characteristics

The Northrop YF-23 prototypes were powered by twin YF119-PW-100 augmented engines, each providing approximately 35,000 lbf (156 kN) of with . These low-bypass engines were designed to enable sustained supersonic flight without use, a key requirement of the program. One prototype (PAV-2) utilized the competing YF120-GE-100 engines for comparative testing, but the YF119 configuration represented the primary propulsion setup evaluated by Northrop. The YF119 engines facilitated supercruise capability, with the prototypes demonstrating sustained supersonic speeds of approximately Mach 1.58 at 40,000 feet during . The design targeted a cruise speed of Mach 1.6 for operational efficiency, allowing the to maintain high subsonic-plus velocities without the fuel penalty and of afterburners. Maximum speed reached approximately Mach 2 during envelope expansion tests, while the service ceiling was 65,000 feet. Performance metrics included an internal capacity of 24,000 pounds, supporting an unrefueled range of 750-800 nautical miles. The resulting was approximately 1.36 at combat weight with , contributing to agile handling within the stealth-optimized . The fixed-geometry inlets featured an innovative system using perforated "gauzing" panels to divert slow-moving air away from the engine faces, reducing cross-section while ensuring stable supersonic without traditional diverter plates or variable ramps. This design precursor to later diverterless supersonic inlets (DSI) enhanced stealth integration with propulsion efficiency.

Variants and Proposals

Production F-23 Enhancements

The proposed production version of the YF-23, designated F-23A, would have incorporated several key enhancements to refine the prototype's stealth and performance capabilities while addressing operational requirements for the (ATF) program. These included further reductions in cross-section (RCS) through refined shaping, such as serrated leading edges on the intakes, building on the baseline YF-23's low-observable design features. Additionally, the nose section would have been redesigned to integrate an advanced () comparable to the , enabling enhanced multi-target tracking and low-probability-of-intercept operations without compromising stealth. To extend operational range beyond the prototype's capabilities, the F-23A was planned to feature conformal fuel tanks integrated into the , minimizing drag and maintaining the aircraft's aerodynamic profile while supporting missions requiring greater . Cost projections for the production F-23A emphasized affordability within ATF program constraints. Furthermore, the design anticipated lower lifecycle costs compared to the F-15 Eagle, primarily due to stealth features that reduced maintenance needs for radar-absorbent materials (RAM) and overall detectability. Manufacturing for the F-23A would have leveraged the Northrop-McDonnell Douglas partnership, with Northrop's Palmdale facility responsible for the airframe's aft section and , and McDonnell Douglas handling the wings and forward fuselage in . The program aimed to produce up to 750 units, with full-rate production targeted to achieve initial operational capability in the early and completion around , aligning with USAF timelines. Optional enhancements included thrust-vectoring nozzles for improved maneuverability at high angles of attack, drawing from 2D nozzle technologies evaluated in related designs, though the baseline prioritized stealth over agility. Improvements to RAM durability were also proposed, incorporating more robust, heat-resistant coatings for exhaust areas to enhance longevity in sustained operations.

NATF-23 Naval Variant Development

In the late , the U.S. Navy initiated the Naval Advanced Tactical Fighter (NATF) program as a carrier-capable of the Air Force's (ATF) effort, aiming to develop a multi-role stealth aircraft to replace the aging F-14 Tomcat for air superiority missions while also providing enhanced strike capabilities to succeed the A-6 Intruder in attack roles. The program sought to leverage the ATF prototypes, including Northrop and McDonnell Douglas's YF-23, to achieve high commonality in engines, radars, and while adapting the design for naval operations. Northrop and McDonnell Douglas proposed the NATF-23 as their entry, building on the YF-23's advanced stealth and aerodynamic features to evaluate it against the incumbent F-14 for carrier-based service. Studies focused on necessary adaptations for use, such as folding wings to facilitate storage on deck, reinforced to withstand catapult-assisted launches and arrested recoveries, and a strengthened to handle carrier landing stresses. The design incorporated twin vertical tails to improve low-speed control during carrier approaches, resulting in an increased empty weight due to these structural enhancements. The NATF program advanced through 1991 with conceptual evaluations, but rising costs and inter-service disagreements over requirements led to its cancellation in 1991-1992. The Navy shifted priorities to the A/F-X (Advanced Fighter/Attack) program, which was itself terminated in 1993 amid budget constraints, ultimately selecting the F/A-18E/F Super Hornet as the F-14 replacement with expanded multi-role capabilities. No prototypes of the NATF-23 were constructed, leaving the effort as a brief exploration of adapting fifth-generation technology for naval aviation.

Post-Competition Revival Concepts

Following the conclusion of the competition in 1991, explored derivative concepts based on the YF-23 design to meet emerging U.S. requirements for multi-role platforms. In the mid-2000s, the company proposed the F/B-23A Rapid Theater Attack aircraft as a stealthy variant, featuring a notional unrefueled range of 2,500 miles, a 10,000-pound capacity, and sustained at Mach 1.6; this concept was developed in direct response to competing proposals for an F/B-22 derivative. During the early 2010s, amid ongoing evaluations for next-generation air dominance, positioned elements of the YF-23's and stealth features as a foundational influence for its Next Generation Tactical Aircraft (NGTA) concept, aimed at replacing aging F-15C/D models and supplementing the F-22 fleet. This proposal incorporated sixth-generation advancements, including enhanced low-observability, more powerful engines for extended , upgraded , and optionally manned configurations to enable integration with unmanned collaborative combat aircraft (drones) for manned-unmanned teaming operations. The and saw renewed interest in YF-23 revival discussions, particularly after the F-22 production was capped at 187 aircraft in 2009 due to escalating costs exceeding $150 million per unit, prompting debates on leveraging legacy stealth designs for programs like the (NGAD). As of November 2025, no formal U.S. government program has advanced a direct YF-23 resurrection, though analysts highlight its superior radar cross-section and speed as potential assets for modern threats. Reviving the YF-23 faced significant hurdles, including the obsolescence of 1990s-era tooling and data, which would necessitate full-scale redevelopment of , , and materials to meet current standards—potentially costing billions in a manner comparable to NGAD's estimated $20 billion development phase. Additionally, post-merger industry consolidation between Northrop and in 1994, alongside broader defense sector mergers, complicated access and collaborative development, as government-funded ATF data rights remained fragmented and subject to proprietary restrictions.

Testing and Operational Assessment

Flight Testing Program Details

The flight testing program for the Northrop YF-23 prototypes was conducted at , California, beginning in August 1990 and concluding in December 1990, prior to the downselect phase of the competition. The two prototypes, designated Prototype Air Vehicle 1 (PAV-1, nicknamed "Black Widow II") and Prototype Air Vehicle 2 (PAV-2, nicknamed "Gray Ghost"), underwent a series of evaluations focused on , , handling qualities, and stealth integration, with pilots accumulating experience across multiple s to validate design predictions. PAV-1, powered by YF119 engines, completed its on August 27, 1990, lasting 50 minutes under the control of chief Paul Metz; this initial included checks on stability, control surfaces, and basic systems performance. PAV-2, equipped with engines, followed with its first flight on October 26, 1990, piloted by Jim Sandberg, marking the start of comparative engine testing between the two configurations. Together, the prototypes logged 50 flights totaling 65.2 hours, encompassing envelope expansion, performance verification, and systems integration without the installation of full operational or to prioritize validation. Key milestones included air refueling qualification achieved during PAV-1's fourth flight in September 1990, enabling extended test durations, and supersonic envelope exploration by the fifth flight. capability—sustained supersonic flight without afterburners—was demonstrated early, with PAV-1 reaching Mach 1.43 at approximately 30,000 feet on September 18, 1990, followed by PAV-2 achieving Mach 1.6 on November 29, 1990, during a formation flight with PAV-1 that also served as a photographic evaluation. Weapons bay door operations were tested in ground and limited flight configurations to assess acoustics and deployment mechanics, confirming low-observable compatibility for internal armament carriage, though no live launches occurred. The highest speed attained was Mach 1.8 by PAV-1 during a surge and flutter test on November 30, 1990. PAV-1 completed its on November 30, 1990. The program wrapped with PAV-2's final on December 18, 1990, a nearly two-hour mission evaluating high-altitude performance. Testing was not without challenges, including a issue during PAV-2's that required immediate post-flight inspection and adjustments, though it did not delay subsequent significantly. On PAV-1's 16th flight on October 30, 1990, the windscreen shattered due to aerodynamic pressures at Mach 1.5, but safely recovered the aircraft for landing. Early PAV-2 flights encountered propulsion anomalies, such as a left sub-idle condition on the second and fuel tank overpressurization on the third due to a line blockage, both resolved through interventions without compromising the overall schedule. preceded flights, with high-speed runs reaching 120 knots by August 11, 1990, to verify and control responses; post-flight, limited slow-speed runs continued into early 1991 to maintain airworthiness during storage. These efforts, supported by extensive pre-flight simulations, ensured the YF-23 met or exceeded projected handling and stealth thresholds within the compressed timeline.

Comparative Evaluation Against YF-22

The Northrop YF-23's design emphasized a flatter profile and diamond-like planform, resulting in a lower cross-section (RCS) compared to the , which provided an edge in stealth performance during the (ATF) competition. This configuration minimized returns from multiple aspects, though exact RCS figures remain classified. In contrast, the YF-22 incorporated thrust-vectoring nozzles that enhanced its agility in simulated scenarios, allowing for superior post-stall recovery and close-combat effectiveness despite its slightly higher RCS. In terms of agility and speed, the YF-23 prioritized high-speed, beyond-visual-range (BVR) intercepts, demonstrating capability at approximately Mach 1.6 with engines and reaching a top speed of Mach 1.8 during testing. This enabled sustained supersonic flight without afterburners, ideal for long-range engagements. The YF-22, however, excelled in close-range maneuvers, achieving 9g turns and up to 60-degree angles of attack, which showcased its thrust-vectoring advantages in within-visual-range combat simulations. The YF-23 demonstrated strong reliability in the competition phase, completing 50 flights totaling 65.2 hours across its two prototypes without major in-flight aborts, contributing to a high generation rate. The YF-22 experienced occasional handling issues during early testing, though both designs ultimately met ATF reliability thresholds. Pilot evaluations highlighted the YF-23's smooth ride quality and overall handling, with Paul Metz—who flew both prototypes—describing it as equal or superior to the YF-22 in flying qualities and control harmony.

Post-Program Analysis and Lessons Learned

Following the 1991 downselect in the (ATF) program, where the was chosen over the Northrop YF-23, post-program reviews highlighted potential shortcomings in the evaluation process. Analyses indicated that the placed greater emphasis on the competing team's demonstrated capabilities and delivery confidence, rather than solely on technical performance metrics, despite both prototypes meeting core requirements for stealth, , and integration. Key lessons from the ATF competition underscored the challenges in balancing stealth imperatives with demands in next-generation fighter requirements. The YF-23 design philosophy prioritized very low observable (VLO) stealth features, such as its diamond-shaped planform and aft deck configuration for suppression, over extreme maneuverability, aligning with evolving USAF specifications that increasingly valued in contested . In contrast, the selected YF-22 incorporated thrust-vectoring nozzles to enhance dogfighting , reflecting a perceived need for versatility in beyond-visual-range engagements. This trade-off debate influenced subsequent acquisition strategies, emphasizing the need for flexible requirements to avoid over-optimizing for one attribute at the expense of overall mission effectiveness. Insights from technical discussions and designer interviews in the revealed the prototype's advanced signature management techniques, such as transpiration cooling in the exhaust area to minimize thermal detectability from multiple angles. These disclosures provided insights into superior all-aspect stealth performance compared to early competitors, informing stealth shaping and materials integration in later programs like the F-35 Joint Strike Fighter. Cost-benefit assessments post-selection suggested the YF-23's streamlined and reduced maintenance-intensive features, like non-thrust-vectoring engines, could have yielded lower life-cycle operating s relative to the F-22, though exact projections varied amid evolving threat assessments and production scaling. Broader ATF retrospectives, including those from the , stressed the importance of stable industrial partnerships and realistic concurrency in development to mitigate cost growth seen in stealth-heavy programs.

Preservation and Legacy

Fate of the Prototypes

Flight testing of the two YF-23 prototypes concluded in December 1990, ahead of the Advanced Tactical Fighter competition's downselect in April 1991, with PAV-2 completing its final flight on December 18 and PAV-1 on December 30. Both aircraft, PAV-1 (87-0800, "Gray Ghost") and PAV-2 (87-0801, "Spider"), were then placed in flyable storage at Edwards Air Force Base, California, where PAV-1 underwent three additional low-speed taxi tests in January 1991. They remained in outdoor storage adjacent to the B-2 Spirit test facility at Edwards until December 1, 1993, during which time no further flight activity occurred. On December 1, 1993, the U.S. Air Force transferred both prototypes to NASA's (now ) at . Upon transfer, the aircraft had no engines installed, as these had been removed prior to handover; PAV-1 was originally powered by two YF119 turbofans, while PAV-2 used two engines, the latter of which was selected to power the production F-22 Raptor. briefly evaluated the prototypes for potential use in research programs, including a planned strain gage loads study for one , but ultimately declined to pursue any or extensive modifications due to lack of and shifting priorities. The prototypes remained in non-flyable storage at Dryden through 1996, with no research activities conducted. PAV-2 was placed on long-term loan to the Western Museum of Flight in October 1995, while PAV-1 remained in storage until its transfer to the National Museum of the United States Air Force in 2000, marking the end of their active program involvement; to safeguard sensitive technologies, components were not fully reassembled during this transition, though no formal partial disassembly for security was documented beyond standard storage protocols.

Surviving Aircraft on Display

The two surviving YF-23 prototypes are preserved as static displays in public museums, offering visitors insight into the Advanced Tactical Fighter program's innovative stealth technology. YF-23A PAV-1 (serial number 87-0800), nicknamed "Gray Ghost," is on exhibit at the National Museum of the United States Air Force in Dayton, Ohio, following its transfer in 2000 via C-5 Galaxy aircraft after post-program storage. Acquired that year, it underwent restoration completed in 2008, resulting in a full static display with original markings and two Pratt & Whitney YF119-PW-100 engines installed for presentation in the indoor Research & Development Gallery, where it is protected in a climate-controlled environment and accessible to the public during museum hours. YF-23A PAV-2 (serial number 87-0801) resides at the Western Museum of Flight in , on long-term loan from since its delivery in October 1995, with the airframe undergoing preliminary repairs at Northrop Grumman's Hawthorne facility before formal restoration at the museum after its relocation to in 2010. This prototype features two engines and is presented outdoors under protective cover, open to visitors with general admission. Both aircraft were relocated from storage at NASA's Dryden Flight Research Center without engines initially, as no further flight research was pursued, and sensitive internal components had been removed post-competition; as of , no flyable restorations are planned owing to technological obsolescence and preservation priorities focused on static . High-resolution photographs and scale models of the prototypes are widely available through official museum websites and aviation archives.

Influence on Modern Aircraft Design

The YF-23's innovative fixed-geometry air inlets, which utilized boundary layer control systems with gauzing panels to manage airflow without moving parts, significantly advanced stealth inlet technology by minimizing radar cross-sections from forward aspects while enabling stable supersonic performance. This approach addressed longstanding challenges in integrating stealth with high-speed aerodynamics, paving the way for subsequent designs. Although the production F-22 adopted caret-style fixed inlets derived from broader Advanced Tactical Fighter (ATF) program testing, the YF-23's concepts directly informed the planned Engineering and Manufacturing Development (EMD) version of the F-23, which would have incorporated diverterless supersonic inlets (DSI) with sawtooth edges—similar to those later implemented on the F-35 Lightning II for enhanced stealth and reduced drag. The diamond-shaped wing planform of the YF-23, optimized for low observability by deflecting radar returns away from the source, also echoed in later unmanned stealth platforms, such as the RQ-170 Sentinel's tailless configuration that prioritizes radar cross-section reduction through geometric shaping. The YF-23's demonstration of capability, achieving Mach 1.6 without afterburners using the General Electric YF120 engines, provided critical data that refined engine tuning for sustained supersonic flight in stealth environments. These tests, part of the ATF competition, validated the YF120 and Pratt & Whitney YF119 engines' performance, directly influencing the F-22 Raptor's final powerplants by confirming thrust-to-weight ratios and thermal management needs for operational up to Mach 1.5. For long-range stealth bombers like the B-21 Raider, the YF-23's emphasis on fuel-efficient high-altitude cruise in a low-observable contributed to efficiency goals, integrating ATF-derived propulsion technologies to balance range, stealth, and speed without compromising signature control. Lessons from the ATF program, including the YF-23's focus on pure air superiority, prompted a strategic shift in U.S. requirements toward multi-role platforms to address post-Cold War fiscal constraints and diverse threats. The YF-23's specialized design highlighted the risks of single-mission optimization, influencing the Joint Strike Fighter (JSF) program's emphasis on affordability and versatility to replace multiple legacy aircraft like the F-16 and A-10 across services. This evolution is evident in the F-35's requirements, which incorporated ATF stealth and advancements but prioritized multi-role ground attack and coalition interoperability over dedicated air dominance. Internationally, the YF-23's stealth technologies have been rumored to influence Japan's F-X program through Northrop Grumman's partnerships. In 2018, Northrop proposed designs potentially drawing from YF-23 concepts for the F-3, aiming to provide advanced low-observable features amid U.S. export restrictions on the F-22. While specific tech transfers remain unconfirmed, Northrop's involvement offered a range of stealth and options, supporting the F-3's development as a for the mid-2030s.

Technical Specifications

General Characteristics

The Northrop YF-23 was a single-seat designed for the U.S. Air Force's program, accommodating one pilot in its . Its featured a of 67 ft 5 in (20.5 m), a wingspan of 43 ft 6 in (13.3 m), and a height of 13 ft 11 in (4.2 m), contributing to its sleek, diamond-shaped configuration optimized for stealth and aerodynamics. The wing area measured approximately 900 sq ft (84 m²), providing the necessary lift for its intended high-speed, high-altitude operations. The aircraft's empty weight was 29,000 lb (13,200 kg), while its loaded weight reached approximately 51,320 lb (23,300 kg) when configured for typical missions. It carried 17,000 lb (7,700 kg) of internal fuel, enabling extended range without external stores that could compromise its low-observability profile. Propulsion came from two afterburning turbofans: either or , each delivering approximately 35,000 lbf (156 kN) of thrust. The prototypes included internal weapons bays capable of carrying up to six air-to-air missiles, maintaining stealth by avoiding external stores. Specifications are approximate and include proposed features for production variants, as the prototypes were technology demonstrators.
CharacteristicSpecification
Crew1 (pilot)
Length67 ft 5 in (20.5 m)
Wingspan43 ft 6 in (13.3 m)
Height
Wing area~900 sq ft (84 m²)
Empty weight29,000 lb (13,200 kg)
Loaded weight~51,320 lb (23,300 kg)
Internal fuel17,000 lb (7,700 kg)
Powerplant2 × YF119-PW-100 or General Electric YF120 afterburning turbofans, ~35,000 lbf (156 kN) thrust each
HardpointsInternal bays for up to 6 missiles; no external stores on prototypes

Armament and Avionics

The Northrop YF-23 prototypes incorporated a prototype system with low-probability-of-intercept (LPI) modes to minimize emissions and enhance in contested environments. This design allowed for air-to-air and air-to-ground targeting while maintaining a reduced signature compared to traditional mechanically scanned arrays. The suite featured an integrated defensive aids system (DAS) that included a (RWR) for threat detection and prioritization, along with automated chaff and dispensers to counter radar-guided and infrared-seeking missiles. Additionally, the system supported a secure for off-board targeting, enabling cooperative engagement with other platforms to share sensor data and extend the engagement envelope without compromising stealth. Armament provisions centered on internal weapons bays to preserve low observability, with capacity for four medium-range air-to-air missiles in the primary configuration or two short-range missiles for close-in combat. A single 20 mm M61A2 Vulcan , with approximately 480 rounds of ammunition, was planned for installation in a low-observable fairing along the starboard side to support dogfighting and strafing roles. Countermeasures emphasized passive and active defenses, including provisions for towed radar decoys to lure away incoming radar-guided threats and systems to disrupt heat-seeking missiles through laser-based jamming. These elements integrated with the overall DAS to provide layered protection, allowing the YF-23 to operate in high-threat scenarios while relying on stealth as the primary survivability feature.

Performance Metrics

The Northrop YF-23 exhibited exceptional high-speed performance during its flight test program, tested to a maximum speed of Mach 1.8 (1,180 mph; 1,900 km/h) with afterburners engaged, with the absolute maximum speed classified but estimated around Mach 2. The design emphasized efficient supersonic flight, enabling at Mach 1.6 (1,050 mph; 1,690 km/h) without use, which reduced and extended range during missions. Range capabilities supported long-endurance operations, with a ferry range of approximately 1,090 nmi (1,250 mi; 2,020 km) with air refueling and a radius of 500 nmi (580 mi; 930 km) using internal fuel alone. These figures highlighted the YF-23's strategic reach, prioritizing internal fuel to maintain stealth while allowing for air refueling to extend operational flexibility. The 's service ceiling reached 65,000 ft (20,000 m), providing superior altitude advantages for beyond-visual-range engagements. Maneuverability was enhanced by structural limits of +9 g to -3 g, a of 45,000 ft/min, a of 1.09 when loaded, and of approximately 57 lb/sq ft (278 kg/m²), contributing to agile handling in simulated scenarios despite the absence of .

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