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Challenging evolution

WHEN THE US Air Force began defining its requirement for an air-superiority fighter to replace the McDonnell Douglas F-15, the world was a very different place. The Soviet Union still existed and Iraq was just a minor Middle Eastern power. The major regional conflict had not yet replaced superpower confrontation as the principal threat to US interests overseas.

When the requirement was formally identified in 1981, the F-15 had been in service for just six years, but the Air Force was looking ahead to the threat posed by advanced Soviet fighters, backed by integrated air-defences and able to reach out to strike allied aircraft at their bases. When the F-22 enters service in 2004, the F-15 will have been operational for almost 30 years - but the threat its replacement was conceived to counter is unlikely to have materialised.

Instead, the threat is likely to be another Gulf war or Korean conflict, or some other regional crisis that cannot be predicted or prepared for today. Although conceived to excel on the superpower battlefield, the F-22 will be a crucial player in coalition warfare, the Air Force argues, its lethality and survivability guaranteeing US forces the overwhelming air dominance required to minimise casualties.

 

 

CONCEPT DEFINED

When Advanced Tactical Fighter (ATF) concept-definition studies were launched in 1983, certain basic requirements were already clear, among them stealth, supercruise and range - stealth and supercruise to reduce the range and reaction time of hostile air-defences and, together with range, to extend air superiority deep into enemy airspace. Agility was considered essential, but a short take-off and landing requirement was dropped to save cost and weight.

Cost was already a major concern and, in 1986, the Air Force restructured the planned demonstration/validation phase into a "fly-before-buy" evaluation of two rival ATF designs. Dem/val became a means to determine what capability could be afforded within the $35 million flyaway-cost goal, as well as to reduce the technical risk before entering development.

Lockheed was one of seven companies that responded to the dem/val request for proposals, but in June 1986 it signed a teaming agreement with competitors Boeing and General Dynamics (GD) under which the winner would lead a three-company effort, with costs shared essentially equally. In October 1986, Lockheed was selected to build the YF-22 and Northrop, which had earlier teamed with McDonnell Douglas, to build the YF-23.

 

Prototypes assembled

Lockheed's Skunk Works led the dem/val effort and assembled the two prototypes, the first of which was flown in September 1990. As prime contractor, Lockheed was responsible for weapon-system integration, as well as building the forward fuselage; Boeing provided the wing and aft fuselage, and led avionics prototyping; and GD supplied the mid-fuselage and tail, and led systems development.

Dem/val was more than just an opportunity to fly competing prototypes. The contractor teams built avionics testbeds, proved the materials and processes planned for production and conducted key technology demonstrations in support of their bids for the ATF development programme. The Air Force's decision was to be based not on a "fly-off" between the YF-22 and YF-23 prototypes, but on an evaluation of the competing development proposals backed by the results from dem/val.

Lockheed's team took full advantage of the dem/val phase. In more than 90h flying with two YF-22A prototypes, the team demonstrated a still-classified supercruise speed exceeding Mach 1.5, manoeuvred at 60í angle-of-attack with thrust vectoring and launched both AIM-9 and AIM-120 missiles from the aircraft's weapons bays. Externally, the prototypes closely resembled the proposed development configuration, while internally they demonstrated the flat-panel cockpit displays, digital flight-controls and electronic subsystem-controls planned for the production aircraft.

Additionally, the team modified a Boeing 757 into a flying laboratory to demonstrate the integrated avionics in flight, supported by a ground laboratory able to demonstrate sensor performance. Crucially, the team was able to use these laboratories to validate its software algorithms for sensor fusion, the key to its concept for the F-22 "pilot-vehicle interface".

Development bids were submitted in December 1990, after both teams had flown prototypes powered by the rival Pratt & Whitney YF119 and General Electric YF120 engines. All four engine/airframe combinations met the ATF requirement, but in April 1991 the Air Force selected the F119-powered F-22, saying that it offered better capability at lower cost and with lesser risk.

The Lockheed/Boeing/GD team was awarded a $9.55 billion contract for F-22 engineering and manufacturing development (EMD) in August 1991, while P&W received a separate, $1.4 billion contract to develop the F119. At that time, 11 flight-test aircraft were planned, including two F-22B two-seaters. Today, nine development aircraft are being built, all single-seat F-22As, while the Air Force production requirement has been cut from 648 F-22A/Bs to 438 aircraft, all single seaters.

 

CHANGING REQUIREMENT

The original ATF requirement was for 750 aircraft, and the US Navy at one time was interested in 550 Naval ATF variants. The Navy dropped its interest before EMD award, to concentrate on the General Dynamics/McDonnell Douglas A-12 Avenger II Advanced Tactical Aircraft. After cancellation of the troubled A-12 programme, a derivative of the F-22 was proposed to meet the Navy's A/F-X requirement, but this was ultimately cancelled.

Flight testing of the YF119-powered YF-22 was resumed in October 1991, to gather additional loads and environment data for use in design of the F-22. Flight testing continued until April 1992, when the aircraft was damaged in an accident. The YF-22 had been flown for just over 100h when it crashed. Although no longer flightworthy, the damaged prototype was modified to represent the production F-22, and the aircraft is being used as a pole model to test antenna performance.

The first of a series of schedule changes came in January 1993, when budget cuts forced the programme to be rephased. This reduced the number of development aircraft from 11 to nine, still including two F-22B tandem-seat trainers, and the number of F119 flight-test engines from 33 to 27. Development of the two-seater was formally deferred by the Air Force in July 1996, to save money, but the number of development and production aircraft remained unchanged.

In January 1997, the programme was again restructured, leading to the cancellation of four pre-production verification (PPV) F-22s, which had been intended to bridge the gap between development and low-rate initial production (LRIP) aircraft. This reduced the number of planned production F-22s to 438. At the same time, LRIP was stretched from four to five years and the number of aircraft to be produced during this phase reduced to 70. The PPV aircraft were to have been used for initial operational test and evaluation. Instead the last two EMD and first two LRIP aircraft will be used.

 

CONFIGURATION CHANGES

There have been several design changes since award of the EMD contract, principally to reduce weight and radar cross-section (RCS). In March 1994 it was announced that the F-22's RCS was not meeting the specification, largely as a result of fitting doors and panels on the underside of the aircraft to provide maintenance access. The problem was uncovered by using new computer-modelling tools and was overcome by combining access panels and reducing the number of drain holes on the bottom of the aircraft.

Lockheed Martin began testing a full-scale pole model of the F-22 at its Helendale, California, RCS test-range in November 1996. Programme general-manager Tom Burbage says that results show that the aircraft is meeting or exceeding its radar-signature specification.

In April 1995, the Lockheed Martin/Boeing team was awarded a 24-month Air Force contract to explore derivatives of the F-22. The study was later curtailed, after the team had looked at missions such as precision strike, electronic reconnaissance and suppression of enemy air-defences. Burbage still anticipatess F-22 derivatives will emerge once production is under way. He believes the F-22, with its stealth and precision, is the only aircraft that can perform the deep-targeting mission for long-range missiles, such as those to be carried by the Navy's planned Arsenal Ship.

There is also the potential for development of export derivatives on the F-22. Several countries have been briefed on the aircraft, but no licence to sell the aircraft has yet been granted. Israel and South Korea are thought to be among the countries most interested in the F-22. Lockheed Martin/Boeing believes that export sales of 12 F-22s annually, in addition to the 48 aircraft a year now planned for the US Air Force, could substantially reduce production costs.

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