The Northrop/McDonnell Douglas YF-23 is an American single-seat, twin-engine, stealth fighter technology demonstrator prototype designed for the United States Air Force (USAF).

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.

Both Soviet models were expected to reduce the combat and maneuverability advantages of contemporary U.S. fighter aircraft, including the newly introduced F-15 Eagle and F-16 Fighting Falcon.

[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.

[3] The USAF released the ATF request for information (RFI) in May 1981 to several aerospace companies on possible features for the new fighter.

Eventually 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 industry responses.

[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.

[6][7] Around this time, however, the SPO would begin to also increasingly emphasize stealth for survivability and combat effectiveness due to 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 would result in the B-2, or "Senior Ice"); fighter-like speed and maneuverability were still required.

[9][11] 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.

[12] The RFP would see 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.

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.

[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.

[20] Lockheed and Northrop, the two industry leaders in stealth aircraft, were selected as finalists on 31 October 1986 for Dem/Val as first and second place, although the approaches to their proposals were markedly different.

[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.

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.

[31] 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.

The original HSF configuration of the F-23 was first considered but would have had issues with flight deck space, handling, storage, landing, and catapult launching, thus necessitating a different design.

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".

The chiseled shape of the nose, with its sharp chine edges, generated vortices to improve high angle of attack (AoA) characteristics.

[N 4] Fuselage volume was expanded for more fuel and avionics, with the nose and radome enlarged to accept sensors and mission systems, including the AESA radar.

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 inlet design changed from the trapezoidal profile with suction panels to a serrated semicircular with a compression bump and the boundary layer control vents were simplified.

[52] The naval NATF-23 variant (internally designated DP527), the schematics of which surfaced in the 2010s, was different in many ways 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.

[53][N 5] The diamond wings were located as far back as possible, and the aircraft had ruddervators with more serrations to reduce overall length, folding wing capability for flight deck storage, reinforced landing gear, tailhook and slightly canted canards for increased maneuverability at low speeds to land on aircraft carriers, and two-dimensional thrust vectoring nozzles instead of SERNs.

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.

[55][56] The FB-23 would have a two-seat cockpit and a similar planform shape as the F-23, but considerably larger in all dimensions to fulfill the bomber role with a combat radius of over 1,600 nautical miles (1,840 mi; 2,960 km).

[75] 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.

[75][76] Data from Pace,[79] Sweetman,[80] Winchester,[11] Metz & Sandberg,[66] Aronstein & Hirschberg[67] (note, some specifications are estimated)General characteristics Performance Armament None as tested but provisions made for:[11]