Concept development In 1981, the USAF began forming requirements for the ATF, eventually codenamed "
Senior Sky". In May, a
request for information (RFI) to the aerospace industry was published by the USAF
Aeronautical Systems Division (ASD), followed by another RFI for the ATF propulsion systems in June. In response, a number of aerospace
defense contractors provided design concepts for analysis by the ASD, which released their final report in December 1982. During this time, the ASD also established an internal ATF Concept Development Team (CDT) in October 1982 to manage concept development studies. As the ATF was still early in its requirements definition, including whether the aircraft should be focused on air-to-air or air-to-surface, there was great variety in the RFI responses; the submitted designs generally fell into four concepts. •
Numbers Fighter (N): Lightweight, low-cost design trading lower individual capability for quantity. •
Supersonic Cruise and Maneuver (SCM): Approximately takeoff weight fighter with high maneuverability and
specific excess power at transonic and supersonic speeds. •
Subsonic Low Observable (SLO): An internal ASD concept that sacrificed fighter-like performance and speed for low
radar cross-section and
infrared signature. •
High-Mach/High-Altitude (HI): Large and fast missileer aircraft over at takeoff intended to operate well above Mach 2 and . Further analysis by ASD would indicate that the best air-to-surface concept was
SLO, while the best air-to-air concept was
SCM; neither
N nor
HI were rated highly, and responses from contractors also broadly agreed on avoiding either extremes of the quality-versus-quantity spectrum. Even with the variety of the submitted designs in the responses, the common areas among some or all the concepts were reduced observability, or
stealth (though not to the extent of the final requirements), short takeoff and landing (
STOL) and sustained supersonic cruise without afterburners, or
supercruise. It was envisioned that the ATF would incorporate emerging technologies to include advanced alloys and
composite material, advanced avionics and
fly-by-wire flight control systems, higher power propulsion systems, and low-observable, or stealth technology. By October 1983, the ATF Concept Development Team had become the System Program Office (SPO) led by Colonel Albert C. Piccirillo at
Wright-Patterson Air Force Base. After discussions with
Tactical Air Command (TAC), the CDT/SPO determined that the ATF should focus on air-to-air missions. The air-to-surface missions would be handled by the upgraded
F-111 variants, the upcoming
Dual-Role Fighter (DRF) (which would result in the
F-15E Strike Eagle) as well as the then-classified
F-117 Nighthawk ("
Senior Trend"), while the air-to-air threat from the new Soviet fighters and AWACS remained. Additionally, a multirole aircraft designed to effectively perform both air-to-air and air-to-surface missions was considered too costly; as with ASD and industry responses, TAC did not want the ATF to be at either extremes of the quality-versus-quantity spectrum. With the ATF's mission now focused on air-to-air, another round of requests were sent to the industry for concept exploration and study contracts were awarded to seven airframe manufacturers for further definition of their designs. The SPO also expected that avionics would be a major component of the ATF in light of rapidly advancing semiconductor technology; requests for advanced avionics components such as the integrated
electronic warfare system were sent out that November. During this time, the SPO took an increasing interest in stealth as results from classified
special access or "
black world" programs such as the
Have Blue/F-117,
Tacit Blue, and the Advanced Technology Bomber (ATB) program (which would result in the
B-2 Spirit, or "
Senior Ice") promised greatly reduced radar cross sections (RCS) that were orders of magnitude smaller than existing aircraft.
Request for proposals The
request for proposals (RFP) for demonstration and validation (Dem/Val) was issued in September 1985, with proposals initially to be due that December. The top four proposals, later reduced to two to reduce program costs, would proceed with Dem/Val. The RFP not only had the ATF's demanding technical requirements, but also placed great importance on
systems engineering, technology development plans, and risk mitigation; in fact, these areas were deemed more important than the aircraft designs themselves as contractors would later discover in their debriefs after Dem/Val selection. This was because the SPO anticipated that the ATF would need to employ emerging technologies beyond even the contemporary state-of-the-art and did not want a point aircraft design frozen at then-mature
technology readiness levels; as such, the SPO needed to evaluate its confidence in a contractor's ability to effectively and affordably develop new technology. Initially, there was no requirement for flying prototype air vehicles. The Dem/Val RFP would indeed see some changes after its first release that pushed the due date to July 1986; in December 1985, following discussions with Lockheed and Northrop, the two contractor teams with prior stealth experience from the
Have Blue/F-117 and ATB/B-2 respectively, all-aspect stealth requirements were drastically increased. Furthermore, the
Packard Commission, a federal commission by President
Ronald Reagan to study
Department of Defense procurement practices, had released its report in February 1986 and one of its recommendations was a "fly-before-buy" competitive procurement strategy that encouraged prototyping. The ATF SPO was pressured to follow the recommendations of the Packard Commission, and in May 1986, the RFP was changed so that final selections would involve flying prototypes. While Lockheed also had extensive prior stealth experience, their actual aircraft design was quite immature and only existed as a rough concept that would have to be extensively redesigned; instead, Lockheed primarily focused on systems engineering and
trade studies in its proposal, which pulled it ahead of Northrop's to take top ranking. The two teams, Lockheed-Boeing-General Dynamics and Northrop-McDonnell Douglas, were awarded $691 million
firm fixed-price contracts in FY 1985 dollars (~$ in ) and would undertake a 50-month Dem/Val phase, culminating in the flight test of two technology demonstrator prototypes, designated
YF-22 for Lockheed and
YF-23 for Northrop. Pratt & Whitney and General Electric would also receive $341 million (~$ in ) each for the development and prototyping of the competing engines (designated YF119 and YF120 respectively), and the JAFE propulsion effort would later be renamed ATF Engine (ATFE) and directly managed by the ATF SPO. During Dem/Val, the ATF SPO program manager was Colonel James A. Fain, while the technical director (or chief engineer) was Eric "Rick" Abell. The director of ATF requirements was Colonel David J. McCloud of TAC, and the draft System Operational Requirements Document (SORD), derived from the 1984 SON, was released in December 1987. In addition to the government contract awards, company investments during Dem/Val would amount to $675 million and $650 million (~$ and ~$ in ) for the Lockheed and Northrop teams respectively, not counting additional investments during prior phases or by subcontractors. Pratt & Whitney and General Electric would each invest $100 million as well (~$ in ). With the ATF system specification, the SPO had set the technical requirements without specifying the "how"; this was meant to give the contractor teams flexibility in developing the requisite technologies and offer competing methods. The
ejection seat requirement was downgraded from a fresh design to the existing McDonnell Douglas
ACES II. However, both contractor teams still found the takeoff gross weight goal unachievable, so this was increased to , resulting in engine thrust requirement increasing from class to class. Furthermore, Dem/Val would be extended several times to better mature technologies and reduce near-term budgets. used for testing the Lockheed team's avionics and later modified into the Flying Test Bed during full-scale development. Aside from advances in air vehicle and propulsion technology, the ATF would make a leap in terms of avionics performance with a fully integrated avionics suite that
fuses sensor information together into a common tactical picture, thus improving the pilot's situational awareness and reducing workload; the avionics were expected to make up about 40% of the ATF's flyaway cost. The avionics system was to employ the
PAVE PILLAR system architecture and leverage technology from the
Very High Speed Integrated Circuit program; software would primarily be written in
Ada. The avionics requirements were also the subject of SRRs and adjustments; as avionics was a significant cost driver,
side-looking radars were deleted, and the dedicated IRST system was downgraded from multicolor to single color before changing from requirement to goal and provision for future addition. Finally, two examples of each prototype air vehicles were built and flown for Dem/Val: one with
General Electric YF120 engines, the other with
Pratt & Whitney YF119 engines. Contractor teams made extensive use of analytical and empirical methods for their air vehicle designs, including
wind tunnel testing, RCS pole testing, and software for
computational fluid dynamics, RCS calculations, and
computer-aided design. Consistent with the SPO's willingness to give contractor teams the flexibility in determining how to achieve the ATF requirements, the flight test plans were created and executed by the teams themselves and the prototype air vehicles were not flown against each other for direct comparisons; neither the YF-22 nor YF-23 would share the same test points, which were set by their own teams to
demonstrate concept viability and validate engineering predictions. Noteworthy is the Lockheed team's complete redesign of their aircraft's entire shape and configuration in summer 1987 due to weight concerns, with prototype design freeze relatively soon afterwards resulting in the YF-22's shape being rather unrefined and immature. In contrast, the YF-23 was a continual refinement of Northrop's design concept even prior to Dem/Val proposal submission, with the configuration remaining largely the same throughout. Accurate artwork of the prototypes, which had been highly classified due to the stealth shaping, was first officially released in 1990 ahead of their public unveiling; the aforementioned Dem/Val extensions also pushed flight testing from 1989 to 1990. While the prototype air vehicle designs were frozen in 1988 in order to build the aircraft and begin flight tests by 1990, both teams continued to refine their F-22 and F-23 designs, or Preferred System Concepts, for full-scale development. The first YF-23 made its maiden flight on 27 August 1990 and the first YF-22 first flew on 29 September 1990. Flight testing began afterwards at
Edwards Air Force Base and added the second aircraft for each competitor in late October 1990. The first YF-22 with GE engines achieved Mach 1.58 in supercruise on 3 November 1990 and the second YF-22 with P&W engines also achieved Mach 1.43 on 27 December 1990. Maximum speed of both prototype designs in afterburner was in excess of Mach 2. Flight testing continued until December 1990 with the YF-22s accumulating 91.6 flight hours in 74 sorties while the YF-23s flew 65.2 hours in 50 sorties. Following flight testing, the contractor teams submitted their ATF full-scale development proposals on 31 December 1990. The teams' NATF designs, often referred to as "
NATF-22" and "
NATF-23" (they were never formally designated), were included in their proposals as well. ==Selection and full-scale development==