Advanced Tactical Fighter

In 1981, USAF began forming requirements for a new air superiority fighter intended to replace the capability of the F-15 Eagle. In May 1981 a request for information (RFI) for the Advanced Tactical Fighter (ATF) was published by the Air Force Aeronautical Systems Division (ASD), followed by another RFI for the ATF propulsion systems in June. Design concepts were provided by defense contractors. The common areas among the concepts were stealth, STOL and supercruise.[3] It was envisioned that the ATF would incorporate emerging technologies including advanced alloys and composite material, advanced fly-by-wire flight control systems, higher power propulsion systems, and low-observable, or stealth technology.[4]

Diagram of several designs submitted for request for information (RFI).

In September 1983, study contracts were awarded to seven airframe manufacturers for further definition of their designs. By late 1984, ATF requirements had settled on a fighter with a maximum takeoff weight of 50,000 pounds (23,000 kg), a mission radius of 800 miles (1,300 km), supercruise speed of Mach 1.4–1.5 and the ability to use a 2,000 feet (610 m) runway.[5] A request for proposals (RFP) for the fighter's engine, called the Joint Advanced Fighter Engine (JAFE), was released in May 1983. Pratt & Whitney and General Electric received contracts for the development and production of prototype engines in September 1983.[6]

A request for proposals (RFP) for the fighter was issued in September 1985.[4][7] The RFP would see some changes after its first release; in December 1985, stealth requirements were drastically increased and in May 1986, the Air Force changed the RFP so that final selection would involve flying prototypes.[N 1][8] Additionally, the U.S. Navy, under the Navalized Advanced Tactical Fighter (NATF) program, eventually announced that it would use an ATF derivative to replace its F-14 Tomcat.[9] In July 1986, proposals were provided by Boeing, General Dynamics, Lockheed, Northrop, and McDonnell Douglas.[1] Two contractors, Lockheed and Northrop were selected in October 1986 to undertake a 50-month demonstration/validation phase, culminating in the flight test of two technology demonstrator prototypes, the YF-22 and the YF-23. Under terms of agreements between Lockheed, General Dynamics, and Boeing, the companies agreed to participate in the development jointly if only one company's design was selected. Northrop and McDonnell Douglas had a similar agreement.[10]

During the demonstration/validation phase of development, the USAF focused on system engineering, technology development plans, and risk reduction over point aircraft designs. This was reflected in the prototyping goals, where both the YF-22 and YF-23 were to be "best-effort" vehicles 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 the ability of contractors to meet predicted performance. Both contractor teams conducted performance and cost trade studies and presented them in system requirement reviews (SRRs) with the USAF. This enabled the USAF to adjust ATF requirements and delete ones that were significant weight and cost drivers while having marginal operational value. Because of the added weight for thrust vectoring/reversing nozzles and related systems on the F-15 S/MTD research aircraft, the Air Force changed the runway length requirement to 3,000 feet (910 m) and removed the thrust reversers on the ATF in late 1987.[11][12] As avionics was a significant cost driver, side-looking radars were deleted, and the dedicated infrared search and track (IRST) system was downgraded from requirement to goal. The ejection seat requirement was downgraded from a fresh design to the existing McDonnell Douglas ACES II. Despite efforts by the contractor teams to rein in weight, the takeoff gross weight estimate was increased from 50,000 lb (22,700 kg) to 60,000 lb (27,200 kg), resulting in engine thrust requirement increasing from 30,000 lbf (133 kN) to 35,000 lbf (156 kN) class.[13]

Two examples of each prototype were built for the Demonstration-Validation phase: one with General Electric YF120 engines, the other with Pratt & Whitney YF119 engines.[4][14] The first YF-23 made its maiden flight on 27 August 1990 and the first YF-22 first flew on 29 September 1990.[15] Flight testing began afterwards and added the second aircraft for each competitor in late October 1990.[16] The first YF-23 with P&W engines supercruised at Mach 1.43 on 18 September 1990 and the second YF-23 with GE engines reached Mach 1.72 on 29 November 1990.[16][17] The YF-22 with GE engines achieved Mach 1.58 in supercruise.[18] Flight testing continued until December 1990. Following flight testing, the contractor teams submitted proposals for ATF production.[16]

The production F-22 Raptor.

Following a review of the flight test results and proposals, the Air Force announced the Lockheed YF-22 with Pratt & Whitney engines as the competition winner for full-scale development, or engineering and manufacturing development (EMD), on 23 April 1991.[19] While both designs met or exceeded all performance requirements, the YF-23 was stealthier and faster, but the YF-22 was more agile.[20] The US Navy had begun considering a version of the ATF called Navy Advanced Tactical Fighter (NATF) in 1986.[21] It has been speculated in the aviation press that the YF-22 was also seen as more adaptable to the NATF.[22] The Navy abandoned NATF by 1992.[23]

The Lockheed team was awarded the EMD contract to develop and build the Advanced Tactical Fighter in August 1991. The YF-22 was modified into the production F-22 Raptor version, which first flew in September 1997 and entered service in December 2005.[24] The Northrop YF-23 design was later considered by the company for modification as a bomber,[19] but the proposals have not come to fruition.[25]

• Goodall, James C. "The Lockheed YF-22 and Northrop YF-23 Advanced Tactical Fighters". America's Stealth Fighters and Bombers, B-2, F-117, YF-22, and YF-23. St. Paul, Minnesota: MBI Publishing Company, 1992. ISBN 0-87938-609-6.
• Jenkins, Dennis R. and Tony R. Landis. Experimental & Prototype U.S. Air Force Jet Fighters. North Branch, Minnesota: Specialty Press, 2008. ISBN 978-1-58007-111-6.
• Miller, Jay. Lockheed Martin F/A-22 Raptor, Stealth Fighter. Hinckley, UK: Midland Publishing, 2005. ISBN 1-85780-158-X.
• Pace, Steve. F-22 Raptor. New York: McGraw-Hill, 1999. ISBN 0-07-134271-0.
• Sweetman, Bill. YF-22 and YF-23 Advanced Tactical Fighters. St. Paul, Minnesota: Motorbooks International Publishing, 1991. ISBN 0-87938-505-7.