History
Background
In the late 1970s and early 1980s, intelligence reports from American reconnaissance satellites indicated that the Soviet Union had developed jet fighter prototypes that would soon become significant threats. These aircraft, later identified as the Su-27 Flanker and the MiG-29, were reported to have flight characteristics comparable to the recently introduced F-15 Eagle and F-16 Fighting Falcon. Additionally, the Soviet Union developed a new AWACS testbed based on the IL-76 airframe, which eventually led to the creation of the Beriev A-50 “Mainstay” for airborne early warning and control roles. These advancements significantly reduced the effectiveness and survivability of low-altitude penetration missions by USAF strike fighters, especially when combined with the increasing lethality and sophistication of Soviet surface-to-air missile systems.
To counter these emerging threats, the US Air Force began to outline requirements for the Advanced Tactical Fighter (ATF) program in 1981 to replace the F-15. The ATF was envisioned to fulfill both air-to-air and air-to-ground missions. In May 1981, the Air Force released a request for information to several aerospace companies to explore potential solutions and develop the necessary features for the new fighter. Over time, the requirements were refined, with a greater emphasis on air-to-air missions for air superiority. By the end of 1984, the specifications were narrowed down to include a fighter with a takeoff weight of 50,000 lbs (22,700 kg), stealth capabilities, and exceptional kinematics. Key features included prolonged supersonic flight at Mach 1.5 without afterburners (known as supercruise), super maneuverability, and a combat radius exceeding 700 nautical miles (806 miles; 1,300 km). The unit flyaway cost was estimated at $35 million in 1985 dollars.
It became clear that the ATF would need to incorporate state-of-the-art technologies, such as advanced avionics, fly-by-wire flight control systems, higher-power propulsion systems, and stealth technology. These features would ensure the ATF maintained an advantage over Soviet air-to-air threats, particularly during offensive and defensive counter-air missions over Europe and Russia in a hypothetical conflict. This capability would also enhance the effectiveness of strike fighters conducting air interdiction missions against ground targets with minimal losses. In September 1985, a request for proposals for demonstration and validation was issued, with submissions initially due in December 1985 but later postponed to July 1986.
By July 1986, proposals were submitted by Boeing, General Dynamics, Grumman, Lockheed, Northrop, McDonnell Douglas, and North American Rockwell. Grumman and North American Rockwell withdrew shortly afterward. Lockheed and Northrop, both with prior stealth experience from the Have Blue/F-117 Nighthawk and ATB/B-2 Spirit programs, respectively, emerged as the leading contenders. Given the high risks and extensive investments required for the ATF program, the USAF encouraged teaming among contractors to develop the necessary technologies. Consequently, Lockheed, Boeing, and General Dynamics formed one team, while Northrop and McDonnell Douglas formed another. Notably, Northrop and McDonnell Douglas had previously collaborated on the F/A-18 Hornet.
On October 31, 1986, Lockheed and Northrop were selected as first and second place, respectively, and awarded contracts to develop their prototypes, the YF-22 and YF-23. Additionally, Pratt & Whitney and General Electric received contracts to develop competing engines, designated the YF119 and YF120, respectively. This set the stage for a competition between the two manufacturers to determine which engine would power the ATF aircraft.
YF-23 Design and Development
Northrop led the YF-23 program in collaboration with McDonnell Douglas. Responsibilities were evenly split, with Northrop constructing the aft fuselage and tail assembly in Hawthorne, California, and performing the final assembly at Edwards Air Force Base. McDonnell Douglas built the wings and forward fuselage in St. Louis, Missouri. Between 1986 and 1988, the YF-23 design underwent continuous refinement, drawing from Northrop’s DP110 High Stealth Fighter concept, which evolved into the DP117K design proposed for the ATF. McDonnell Douglas’s design influenced nonsignificantly for the final configuration. Construction began almost immediately to meet the competition’s tight deadlines, and Northrop unveiled its prototype during a rollout ceremony at Edwards AFB on June 22, 1990.
The YF-23 was larger than the F-15 and longer and more slender than the YF-22, measuring 7 feet (2.13 meters) longer. Its design blended stealthy shapes with aerodynamic efficiency to achieve a low radar cross-section without compromising performance. The aircraft featured diamond-shaped wings tapered symmetrically, with edges swept 40° front and back, a slimmer profile to reduce wave drag at transonic speeds, and all-moving ruddervators to provide roll and yaw capabilities. The cockpit was positioned high near the nose to provide the pilot with excellent visibility, while the nose was shaped with sharp chine edges to enhance high-angle-of-attack characteristics. A single large weapons bay was located on the underside of the fuselage between the nose and main landing gear, and the aerial refueling receptacle was centered on the spine of the forward fuselage. The YF-23 utilized a tricycle landing gear configuration with commercial off-the-shelf components, including an F-15 nose wheel and F/A-18 main landing gear parts, to keep costs low.
The YF-23 was inherently unstable but relied on a fly-by-wire system to provide artificial stability. Flight control surfaces were managed by a central computer system. Aileron rolls were controlled by raising wing flaps and ailerons on one side while lowering them on the other. Pitch control was achieved by rotating the ruddervators, or V-tail, in opposite directions, while yaw control involved rotating the tail fins in the same direction. Aerodynamic braking was accomplished by deflecting wing flaps down and ailerons up on both sides simultaneously.
The YF-23 was powered by two afterburning turbofan engines housed in separate nacelles with S-ducts to shield the engine axial compressors from radar waves. The trapezoidal fixed-geometry inlets featured a bleed system that absorbed the turbulent boundary layer using porous suction panels, which ducted air to vents and doors over the fuselage and wings. The aircraft employed single-expansion ramp nozzles (SERN), similar to those on the B-2 Spirit, where exhaust flowed through troughs lined with heat-abating tiles to reduce infrared signature detection from below. These tiles were transpiration-cooled using engine bleed air, providing active heat protection. Unlike the YF-22, the YF-23 did not use thrust vectoring to not increase weight, so it can increase stealth. Combined with its aerodynamic design, the propulsion system minimized drag at transonic and supersonic speeds, allowing it to enable supercruise at over Mach 1.5 without afterburners.
Flight Testing and Evaluation
When Northrop unveiled its first of two prototypes during a rollout ceremony at Edwards AFB on June 22, 1990, the aircraft, unofficially dubbed “Black Widow II”, bore the serial number 87-0800 and the official designation Prototype Air Vehicle 1 (PAV-1). It was powered by Pratt & Whitney YF119 engines, rated at 30,000 lbf (133 kN) thrust. Northrop began engine runs the following month, and the PAV-1 moved under its own power for the first time on July 7. Taxi tests were conducted at increasing speeds, culminating in a high-speed test reaching 120 knots on August 11. On August 27, 1990, the PAV-1 completed its maiden flight, lasting 50 minutes, from Edwards AFB, California. During this flight, the PAV-1 climbed so rapidly that an accompanying F-16 had to use afterburners to keep up, despite the YF-23 flying without afterburners.
Following the unveiling of the YF-22 prototype by Lockheed on August 28, the PAV-1 completed four additional flights by mid-September, including supersonic speed tests. It conducted in-flight refueling tests with a KC-135 on September 14 and achieved a supercruise speed of Mach 1.43 on September 18, 1990, the highest supercruise speed recorded for this YF-23. The second prototype, PAV-2 (87-0801), was rolled out on October 26, 1990, powered by General Electric YF120 engines, rated at 35,000 lbf (156 kN) thrust.
The two YF-23 prototypes were visually distinct: the PAV-1 was painted black and nicknamed “Spider”, while the PAV-2 was painted in two shades of gray and nicknamed “Gray Ghost”. Rumors suggest that the PAV-1 briefly featured a red hourglass marking on its ram air scoop, resembling the underside of a black widow spider, further reinforcing the unofficial nickname “Black Widow II”. However, Northrop management ordered the marking removed upon discovery.
Nevertheless, the PAV-2 completed its maiden flight on October 26, 1990, but its early flights were plagued by issues. During its second flight, the left engine entered a sub-idle condition and failed to accelerate, forcing the aircraft to land on a single engine. On November 21, the PAV-2 nearly suffered catastrophic damage during its third flight when a plugged air sense line caused the fuel tanks to overpressurize. Internal pressures reached critical structural limits, but ground control ordered an immediate landing, preventing serious damage. Those issues were thoroughly addressed, and the aircraft was cleared to continue the testing.
The two prototypes flew together only once during the test program, on November 29, 1990, when they flew in formation over the Mojave Desert. During this flight, the PAV-2 achieved a supercruise speed of Mach 1.6, surpassing the YF-22’s maximum supercruise speed of Mach 1.58. The PAV-1 reached a top speed of Mach 1.8 using afterburners, achieved a maximum angle of attack of 25°, and performed maneuvers at up to +7g. While the maximum speed remains classified, some sources claim the PAV-2 exceeded Mach 2 at an unspecified altitude with full afterburners.
Although the YF-23’s weapons bay was configured for missile launches and tested for acoustic performance, no missiles were ever fired, unlike the YF-22, which successfully launched AIM-9 and AIM-120 missiles.
The PAV-1 concluded its testing with a fast-paced combat demonstration, completing six flights in 10 hours by November 30, 1990. Flight testing for the PAV-2 continued into December. On December 18, the PAV-2 flew in formation with the first YF-22 for 15 minutes, the only time the two competing prototypes flew together. The final flight of the program occurred later that day when the PAV-2 completed a two-hour test flight. By the end of testing, the YF-23 had successfully matched Northrop’s predicted performance values. Both the YF-22 and YF-23 met or exceeded all performance requirements, with the YF-23 being stealthier and faster, while the YF-22 was more agile.
On April 23, 1991, the YF-22 team was announced as the winner of the ATF program. The Pratt & Whitney F119 engine was also selected to power the production F-22. The YF-22 was chosen due to its thorough evaluation, greater number of flight hours, lower cost, and higher reliability compared to the YF-23.
Epilogue
After the F-22 was selected for production, both YF-23 prototypes were stripped of government-furnished equipment, including usable avionics and engines, and placed in outdoor storage near the B-2 test facility at Edwards AFB. After nearly two years in storage, NASA acquired both prototypes on December 1, 1993, intending to conduct structural testing of composite airframes. However, funding shortages prevented these tests, and the aircraft remained in storage at various locations around NASA’s Dryden Flight Research Center.
Eighteen months later, NASA decided to transfer the prototypes to museums. The PAV-1 was moved to the National Museum of the United States Air Force in Dayton, Ohio, after a temporary display at the FFTC Museum at Edwards AFB in May 1995. The PAV-2 was disassembled and transported to the Western Museum of Flight, originally located in Hawthorne, California, but later relocated to Torrance, California. In 2000, the PAV-1 was disassembled and transported via C-5 Galaxy to the National Museum of the United States Air Force, where it remains on display in the Research and Development hangar.
Had the F-23 entered full-scale production, it would have differed significantly from the prototypes. The production version would have featured two tandem weapons bays in the lengthened forward fuselage: a forward bay for AIM-9 Sidewinder missiles and an aft main bay for AIM-120 missiles and bombs, replacing the single weapons bay. An M61 rotary cannon would have been installed on the left side of the forward fuselage. The F-23’s length and height would have increased slightly to 70 ft 5 in (21.46 m) and 14 ft 8 in (4.47 m), respectively, while the wingspan remained at 43 ft 7 in (13.28 m). Fuselage volume would have been expanded to accommodate additional avionics and fuel, with the nose and radome enlarged to house advanced sensors and mission systems, including an active electronically scanned array (AESA) radar. Like the F-22 team, the F-23 team selected the Westinghouse/Texas Instruments radar, which became the AN/APG-77. The F-23’s structure would have been further refined to enhance stealth capabilities.
