The progress of the F-22 fighter program

Bill Sweetman, Jane’s International Defense Review (March 1, 1997)

Late in May, Lockheed Martin test pilot Paul Metz is due to take the F-22A fighter up on its maiden flight from Dobbins Air Force Base, Georgia, next to Lockheed Martin's Marietta plant. It will be a long-awaited milestone in what has become the US Air Force's (USAF's) most important program of the 1990s, and possibly one of the most significant programs in its history. The Pentagon is currently preparing the Quadrennial Defense Review (QDR), the second-term follow-on to the 1993 bottom-up review of US military plans. The 1993 review cut the planned number of F-22s from 648 to 442: there is a risk that the QDR will further reduce this. Congress fears a `tactical aircraft train-wreck': a situation in which increasing expenditures on the F-22, the US Navy's (USN's) F/A-18E/F and the Joint Strike Fighter (JSF) reach a point where it is impossible to retain all three programs. The F-22 is the most prominent of these programs and the most tempting target for budget-trimmers. Annual cuts imposed by Congress and the Pentagon have already delayed the program and increased its costs. Further cuts will be more expensive in the long run, while building fewer aircraft at a lower rate will increase its unit costs. The USAF's defense of the F-22 is far-reaching and fundamental. In the latest revision of its post-Soviet doctrine, air and space superiority is listed as the primary USAF `core competency'. Air and space superiority is intended to provide US forces with freedom of action, while preventing hostile aircraft and missiles from

interfering with US operations and denying them sanctuaries where they can operate. "Too many people fail to understand how the country depends on air dominance," Air Combat Command chief Gen Richard Hawley remarked at an Air Force Association symposium in Orlando in January. "How long will information from Rivet Joint and Joint STARS be available if those aircraft are threatened by long-range AAMs {air-to-air missiles} launched from sanctuaries protected by surface-to-air missiles {SAMs}? Will we be able to sustain precision attack operations against adversary fighters? Will ground forces be able to maneuver as they did in Operation `Desert Storm' if the enemy's reconnaissance aircraft can see them?" The USAF's case is that air supremacy is an unstated pre-requisite for US military operations. Consider that the US Army spends relatively little on its own air defense, mainly using SAMs to defend fixed targets or to deal with `leaker' aircraft. The USN's air defenses are designed for blue-water operations. Joint forces rely on force multipliers such as the Airborne Warning and Control System (AWACS) and Joint STARS, carried on vulnerable transports. To put it bluntly: what did more for the ground forces in the 1990-91 Gulf War - the USAF's control of the air, or USN deep-attack missions? F-15s have shot down 96 adversaries with zero losses in air combat. However, the USAF argues that a more lethal and

survivable replacement is needed to counter the proliferation of advanced fighters and SAM systems. Two factors support the need for a fighter which outclasses the threat, rather than matching it (as an improved F-15 could). First, US and allied forces in-theater are likely to be outnumbered in the early stages of a conflict, as they arrive and establish their bases. Second, the US public and political leaders expect quick success and minimal losses. A balanced assessment of the F-22's capabilities and the status of the program suggests that it should win the approval of the QDR and Congress. However, as Hawley said: "If the facts are allowed to speak, the outcome will not be in doubt. At this juncture, I'm not sure that will happen." While Hawley remarked that many people do not understand the F-22's mission, however, he could also have added that few people understand its capabilities either.

The F-22 represents the greatest one- generation advance in fighter-aircraft capability in 50 years. It brings about the greatest increase in sustained speed since the advent of the jet, flying most of its missions at speeds that other fighters attain only in short sprints, and accelerating and maneuvering at speeds where today's fighters are working hard to fly in a straight line. It will equal and probably surpass the agility of any other fighter, including the Su-35. It embodies all-aspect, wide-bandwidth radio-frequency (RF) and infrared (IR) stealth. Its integrated avionics and sensor-fused displays are a generation in advance of anything known to be under test elsewhere. The F-22's basic shape was devised in three hectic months in 1987, after Lockheed decided that the design with which it had won a place in the USAF's demonstration/validation (dem/val) program was both technically and competitively unacceptable.

The fundamental challenge was to reconcile the demands of stealth, supersonic cruise and agility. Stealth influences the shape and angle of all external surfaces, and requires that all weapons and fuel be carried internally, demanding an airframe of much greater volume than an equivalent non-stealthy design. Supersonic cruise requires low supersonic drag, which usually implies slenderness and thin wing and tail sections, which are not inherently compatible with large volume. Agility is achieved through a large wing span and area and effective controls: this is hard to reconcile either with the need for a small, thin wing for supercruise, or with the fact that the best tail for a stealth aircraft is no tail at all. The initial goal was a fighter with a 22.5-tonne clean take-off weight, but that proved impossible, and the F-22 tips the scales at 27 tonnes. In general layout, the F-22 is a moderately swept (42) delta of a kind that has not been seen since the Javelin and Skyray of the 1950s: little of the F-22's mass lies behind the line of the trailing edge. The wing and body are highly blended - one-third of the total wingspan lies between the wing attachment points - making room for the weapons bays and much of the fuel. The delta wing combines ample volume and a low thickness/chord ratio for supersonic drag with enough area to meet

maneuverability requirements, and still fits in standard NATO aircraft shelters. It is structurally efficient and stiff. At high g loadings, the ailerons deflect upwards to off-load the thinner outer sections. The wing is more sophisticated than it looks; large leading-edge flaps and complex camber make it more efficient at low speed and high alpha (angle of attack) than earlier deltas.

The F-22 was designed to reach extreme angles of attack while remaining under full control: the objective was `carefree abandon' handling, allowing the pilot to exploit a very large alpha/airspeed envelope without overstressing the aircraft or causing it to depart from controlled flight. Another goal was to avoid stability and control deficiencies that would require limits on the angle of attack. The F-22 is designed to be immune from deep stalls and to recover from high alpha, post-stall conditions with both engines flamed out.

According to test pilot Metz, the first F-22A will fly with a set of flight control system (FCS) laws that address the full flight envelope and all configurations. Although testing will be incremental (as always), the prototype YF-22 and wind-tunnel experience suggests that no major changes will be necessary. Thrust vectoring is not used to expand the envelope. At low airspeeds, vectored thrust gets the F-22 from one maneuver state to another more quickly, but the aircraft is controllable in any part of the envelope without it and can always recover with a failed engine. The same benefits could have been achieved with conventional controls, but it would have meant increasing the size of the tails by 30 per cent and adding 180kg to the empty weight. Given that the two-dimensional (2-D) nozzles were needed to meet stealth requirements, thrust vectoring added only 13-22kg to the aircraft. The nozzles vector only in pitch, but they make the F-22 more nimble in roll because, with the vectoring system operational, the horizontal tails can be exploited more fully for roll control.

The four-tail configuration was selected because it provides adequate stability and linear control response in pitch, roll and yaw over a wide speed and alpha range. The verticals are located well forward, so that even at high alpha they are not blanketed by vortices from the body, and stability and rudder effectiveness are retained. The horizontal tails are carried on booms projecting aft of the nozzles, and their root leading-edges fit into cut- outs in the flaperons.

The FCS runs the horizontal tails, the rudders, the vectoring nozzles, the wing surfaces (flaperons, ailerons and leading-edge flaps) and even the nosewheel steering. There are no speedbrakes: for in-flight deceleration, the flaperons go down, the ailerons deflect up and the rudders move outwards. On the ground, the entire trailing edge deflects up to spoil the wing lift.

Almost 17,000h of wind tunnel testing were performed during the engineering and manufacturing development program, involving 23 models in 15 facilities. The

basic program was completed in mid-1995, but a further 900h of work on GBU-32 and AIM-9X weapons release will be completed this year. No significant changes have been made as a result of tunnel tests.

The F-22's stealth design clearly evolved from that of the F-117, with a preponderance of flat, canted surfaces and a sharp chine line from the nose to the wingtips. Better modeling and testing techniques have allowed the designers to incorporate some curvature in the surfaces. In the now-familiar manner, surfaces and edges are aligned with one another; large openings such as the landing gear and weapon bay doors have serrated edges, aligned with the wing and tail edges; and small apertures are diamond- or rhombus-shaped. Gaps between control surfaces are delicately sculpted to avoid 90 angles as they move.

The object is to concentrate radar reflections in a small number of lobes, using pre-flight and onboard mission- planning software to minimize the time during which any lobe `dwells' on a known or detected RF threat. A basic difference between the F-117 and the F-22 is that radar absorbent material (RAM) is not applied to the entire aircraft, but selectively to edges, cavities and surface discontinuities. Lockheed Martin builds all the edges of the aircraft, which probably consist of wide-band radar-absorbent structures. Heat-resistant ceramic-matrix RAM is likely to be used on the exhaust nozzles.

The radome is a `bandpass' type which reflects signals at all frequencies except the precise wavelengths used by the F-22 radar. Radar cross-section (RCS) problems were discovered during early full-scale model tests. There was no single reason for the failure to meet the specification: rather, the problem was traced to the difficulty of maintaining tolerances in a large number of apertures and serrations. The result was a detailed redesign of the surface of the aircraft. Access panels and drain holes were eliminated or combined, and some serrated edges were modified with fewer, larger teeth. Recent tests of a modified RCS pole model have indicated that the problem is solved.

The F-22 structure includes less composite material than the designers planned, but the weight goal - 25 per cent lighter than an all-aluminum airframe - was achieved through the selective use of high-strength, high- stiffness composites and the large-scale use of titanium, which makes up 41 per cent of the airframe weight. Composites account for only 25 per cent, mostly in the wings and tails where their stiffness is valuable.

The heart of the structure is the mid-body section, built by Lockheed Martin Tactical Aircraft Systems in Fort Worth. It incorporates the four weapon bays, the main landing gears and the complex inlet ducts (see picture on left). The mid-body accomodates much of the fuel. Apart from the discrete bays for the missiles, landing gear, gun and environment control system, the mid-body is plumbed and

sealed as set of integral fuel tanks. An onboard inert gas generating system produces nitrogen, which is pumped into the tanks to reduce the risk of explosion from battle damage. The mid-body also accommodates much of the fuel. Apart from discrete bays for the missiles, landing gear, gun and environmental control system, the mid-body is plumbed and sealed as a set of integral fuel tanks. Nitrogen produced by an on-board inert gas generating system is pumped into the tanks to reduce the risk of explosion from battle damage. Attached to the mid-body are the forebody, accommodating the cockpit and avionics, which is built by Lockheed Martin in Marietta; and the wings, aft fuselage, engine bay and the tailbooms, built by Boeing. Five massive titanium bulkheads in the mid-body absorb most of the structural loads. The largest measures just under 4m between the wing attachment points and 1.8m from top to bottom, and is produced as the world's largest titanium forging by Wyman-Gordon, weighing 2,975kg. Some 95 per cent of its mass is removed during machining, leaving a 149kg finished part. The widest of the forgings measures 4.62m from tip to tip. The mid-body and rear fuselage include some unusual structural features. The inlet lip and the fittings that support the wing and rudder are hot isostatic process (HIP) castings, made from titanium alloy powder formed under very high pressure. HIP was originally developed for disks in engines, but is used to form highly loaded, rigid, complex-shaped components with a minimum parts count. The tailbooms are electron-beam welded titanium: the aft fuselage is 67 per cent titanium because of high temperatures. Carbonfiber/bismaleimide (BMI) composite is the primary material in the wings. BMI replaced the thermoplastic- matrix composite used in the YF-22 because it was stronger and less expensive. Thermoplastics had previously been tougher and more damage-tolerant than BMI, but improved BMI resins became available during dem/val. Thermoplastics tolerate higher temperatures than BMI, so the change to BMI in the EMD aircraft meant a reduction in maximum Mach number, from 2.0 to 1.8. The wings incorporate sine-wave spars - in which the web is an undulating curve - produced by a resin-transfer moulding (RTM) process developed by Boeing and Dow/United Technologies. In the RTM process, dry carbonfiber fabric is laid up in a mould and BMI resin is injected at high pressure. RTM provides better yields and lower costs for relatively small, complex parts. One in four of the spars is still made from titanium, a change made after live-fire damage-tolerance tests. Alliant TechSystems provides two of the largest carbonfiber/epoxy components on the aircraft: the 2.8m horizontal tail pivot shafts. The tape-wound shaft is up to 490 plies thick and blends from a long cylinder (on the aircraft side) to a flattened, sweptback spar buried in the tail. A few thermoplastic-matrix composites are still used - the largest components are the landing gear and weapon-bay doors, where damage tolerance is important. Weight has been an issue, but Lockheed Martin disputes that it has been out of control and says the projected empty mass is now lower than it was in 1994. There is no weight specification for the F-22: the requirement is written in terms of performance. As a result, some weight growth has been accepted at the expense of

small changes in performance.

The totally frameless Sierracin canopy is unique. Most canopy specifications require near-perfect optics only in the forward field of view, but the F-22 will have a helmet-mounted sight and therefore needs `zone 1 quality' throughout. The F-22 canopy is made from two 9.5mm sheets of polycarbonate, sandwiched between two sheets of optical glass, fusion-bonded in an autoclave, and drape-formed over a canopy blank at 400C. Birdstrike protection remains an issue. The F-22 canopy is not as inherently tough as the multi-layer F-16 canopy. Although the F-22 canopy can withstand a 450kt birdstrike, the impact initiates a wave through the canopy which, at its lowest point, strikes the head-up display (HUD) combiner, sending fragments into the pilot's face. HUD supplier GEC Avionics is working with Lockheed Martin on designs for a collapsible combiner.

The size and cycle of the F-22's Pratt &Whitney F119-PW-100 engines was driven by the supercruise requirement. Although the F119 is similar in size to the F100, with a roughly similar airflow (about 125kg/s), it has a very different cycle. The F119's bypass ratio is 0.2:1 or less, versus 0.7:1 for the F100, so its core handles at least 50 per cent more air. Although the thrust of the F119 is officially quoted as `in the 155kN class', information obtained by IDR suggests that the actual thrust may be more than 170kN with full augmentor, implying an intermediate (non- augmented) rating of 113kN. This is compatible with statements that at supersonic speed, on dry thrust, the F119 generates twice as much power as the F100-PW-200. The F119 has not been shown in public, but General Electric has exhibited the rival F120 in partly disassembled form, mounted alongside an F110 - the difference in the size of the core blading was considerable. These are huge engines, capable of delivering 180kN without afterburning when fitted with a larger fan for the Boeing JSF design. The F119 has completed a formal qualification program at the USAF's Arnold Engine Development Center (AEDC) in Tennessee, and initial flight release has been obtained. By late January, the first two flight-test engines had been delivered to Marietta, and preparations were being made for engine runs. Results have been good, says program manager Walt Bylciw, and the engine's early developmental troubles (which necessitated an extensive redesign of the turbine and some other fine-tuning) are behind it. The F119 has a three-stage fan, a six-stage compressor and single-stage low- and high-pressure turbines. Each has fewer blades than an F100 stage, so in all the F119 has 40 per cent fewer aerofoils. The counter- rotating shafts eliminate a stator between the turbine stages, saving weight, reducing the engine's length and cutting the requirement for cooling air. Integrally bladed disks are used throughout the fan and compressor; the hollow first stage blades are made separately and joined to the disk by linear friction welding, a technique in which the blade is rubbed so hard against the disk that it bonds to it. Early in the design process, Pratt &Whitney engineers joined operational USAF F-15 maintainers on the flight- line. As a

result, the designers selected a small set of wrenches, ratchets and sockets and built the engine so that all exterior maintenance could be carried out with those tools, and restricted themselves to a few types of clips and fasteners. Virtually all the engine's plumbing is accessible without removing the engine itself, and all lines are color-coded. The F-22 inlets are fixed-geometry, one of many ways in which the USAF's decision to forgo a high-Mach capability (seldom used on the F-15) saved time, weight and money. Boundary-layer turbulence is controlled by drawing air through pores in the duct wall, and the air is dumped overboard through exhaust grills and a bleed door. Each inlet duct has a larger bypass door just ahead of the compressor face, which can open during rapid deceleration. The philosophy of the design is that no doors are open except during maneuvers or engine transients. The vectoring nozzles can divert the full augmented thrust 20 upwards or downwards in a second. Two- dimensional nozzles are necessary for stealth in both the RF and IR bands: the edges of a 2-D nozzle can be aligned with the other edges of the aircraft, and its shape tends to flatten the exhaust plume and promote mixing with the ambient air. In a twin-engine aircraft, too, a 2-D nozzle helps to provide a smooth, low-drag aft-body shape. The nozzles are largely made of burn-resistant Alloy C titanium and incorporate a sophisticated internal cooling system. The F-22's main armament comprises six AIM-120C Advanced Medium-Range Air-to-Air Missiles (AMRAAMs). Three missiles are carried in each of the ventral bays, which are covered by bi-fold doors. The AIM-120C was designed for internal carriage on the F-22, with clipped wing and tail surfaces. Its performance is virtually identical to earlier AMRAAMs and it will be the standard version for all USAF fighters. The AIM-120s will be propelled from the weapon bays by pneumatic/hydraulic AMRAAM Vertical Ejector Launcher units. The side bays will each hold one GM-Hughes AIM-9X Sidewinder, carried on the AIM-9 Trapeze Launcher (ATL), a mechanically extending rail incorporating an exhaust plume deflector. The ATL will be extended automatically as the F-22 nears the point of achieving launch parameters on the target, allowing the IR seeker to lock on before launch. A General Dynamics M61A2 20mm cannon, a lighter version of the M61 with longer, composite-wrapped barrels and a redesigned breech, is mounted above the right wing root. The muzzle opens on to a shallow trench in the fuselage, covered by a side-hinged door. The F-22 carries 480 rounds of ammunition in a linear feed system aft of the weapon bays. In 1994, the USAF asked Lockheed to develop an air-to-surface capability for the F-22, and the lower weapon bays have been modified to accommodate the 450kg McDonnell Douglas GBU-32 Joint Direct Attack Munition (JDAM). The F-22 can carry two each of JDAMs, AMRAAMs and AIM-9s. JDAM is guided by a GPS/inertial system, with a specified circular error probable (CEP) of 13m. Development of a programmable seeker to provide a 3m CEP, equivalent to a laser-guided bomb, is due to start in 2002. A synthetic aperture radar (SAR) mode is being added to the F-22's radar for air-to-surface operations. Other weapons have been studied for the F-22, but not funded. The aircraft could carry a pair of Wind Corrected Munitions

Dispenser (WCMD) weapons for use against area targets. A compact version of the HARM missile is under study for the F-22. New and much smaller weapons are developed for production early next century and are particularly attractive for the F-22. Examples include an operational derivative of the Miniaturized Munitions Technology small hard- target weapon, eight of which would fit inside the F-22, and the Low-Cost Autonomous Attack System, a miniature cruise missile capable of detecting, identifying and destroying military vehicles. When stealth is not critical, the F-22 can carry up to 2,270kg of external stores on each of four underwing pylons. For ferry flights, each of these can accommodate a 600-gallon (2,270-liter) fuel tank and a pair of AMRAAMs, reducing the need for tanker and cargo support. However, none of the F-22's attributes could be exploited properly without the fighter's least visible element: its avionics system. It is revolutionary, in part because it has to be. The F-22 brings new complexities to the fighter mission. The air battle will unfold much more quickly in front of the pilot, because of the fighter's greater speed. The F-22 relies on its stealth for protection against hostile air defenses, but stealth can be compromised by emissions from its own systems. Stealth gives the pilot a new set of variables to consider; the F-22 is more stealthy against some radars than others, and its RCS changes according to the radar's bearing. Stealth imposes limitations on sensor design and operation. "I have to minimize power, and bury all my apertures," said avionics team leader Marty Broadwell. "If I don't do it this way {that is, the integrated and fused approach used on the F-22}, I can't see anything." Metz looks at the problem from a slightly different angle: "If you look at history, very few fighter pilots are effective," he said. In the Second World War, only 21 per cent of fighter pilots made kills and about one in six of these (3.6Eper cent of the total) became aces. During the 1950- 53 Korean War, the 4.8 per cent of pilots who became aces made 38 per cent of the total kills. "What if we can increase the ratio of pilots who make kills from one in five to one in two, or three?" said Metz. The implications in terms of force effectiveness are clear. Metz outlined three principles in the F-22 design which are intended to accomplish that goal. One of these is to eliminate `housekeeping' tasks through automation and self-test. Launching the F-22 is a matter of inserting a Data Transfer Module cartridge - which sets up the displays according to the pilot's preferences - switching the battery on, holding the auxiliary power switch in the on/start position and setting the throttles to idle. The engines start automatically and the avionics run through their diagnostic routines, and within a classified but extremely short time the fighter is ready to go. The second principle is the `carefree abandon' flying qualities which relieve the pilot from worrying about the flight envelope or possible departure. The third principle, and the driving force behind much of the avionics design, is to `maximize information and minimize data'.

The F-22's sensors and displays meet this challenge in three basic, inter-related ways: sensor fusion. Combining data from all different sensors to display one

target on the screen and relieving the pilot of the need to monitor and compare different displays; sensor management. In normal operation, the pilot does not control the sensors. This is done automatically according to the tactical situation; and emission control (EMCON). One of the tasks of the sensor management system is to keep electronic emissions at the lowest possible level. The F-22 cockpit is dominated by four large active-matrix liquid crystal display screens. There are no dedicated back-up instruments: these are hosted on smaller monochrome LCD panels. The GEC holographic HUD is designed so that the bulk of the optical system is located behind the panel, allowing the central 203mm{2} Tactical Situation Display (TSD) to be moved upward and making room for three 152x152mm screens left, right and below. The architecture behind the displays is revolutionary. In the traditional sense, the F-22 has no radar, electronic- warfare (EW) system, or communications, navigation and identification (CNI) systems. Instead, like the displays, they are peripherals serving the fighter's GM-Hughes Common Integrated Processor (CIP), which consists of two banks of 32-bit liquid-cooled computer modules housed in the forward fuselage. The entire system runs on 1.7 million lines of code hosted by the CIP. Fiberoptic high-speed databuses link the sensors to the CIPs and the CIPs to the displays. A practice sortie in Lockheed's concept demonstrator - a medium-fidelity, security-approved simulator - shows how the system works from the pilot's viewpoint. The pilot's main sources of information in the beyond-visual- range fight are the TSD and the screens on either side: the left for defense, and the right for attack. These both take a sub-set of the data on the TSD and add more detail to it. All the screens use the same symbology and the same perspective: `God's eye-view', with the F-22's track pointing up the center of the screen. The symbols are `dual-coded' - as far as possible, they differ both in shape and color. This makes them easy to distinguish and ensures that the displays will be workable if the pilot has to wear laser-protective goggles. Other F-22s in the formation are represented by blue circles, and other friendlies by green circles. Each symbol has a vector line which shows its direction and approximate speed. As the practice mission proceeds, four yellow squares appear at the top of the TSD. This symbol indicates that identification is incomplete. The targets were probably detected by an AWACS and transmitted to the F-22 by the Joint Tactical Information Distribution System. All the pilots in the formation will see the same displays. As well as a datalink that can import information from AWACS, the F-22 is fitted with an Intra-Flight Data Link (IFDL) which can transfer system and target information among F-22s. The IFDL operates at low power and in an RF band which attenuates rapidly in the atmosphere, so it is difficult for an adversary to detect or track.

The F-22's Northrop Grumman/Texas Instruments APG-77 radar could identify the targets, but it will not do so to begin with. The F-22's sensor management and EMCON functions divide the airspace around the fighter into concentric zones. In the outer zone, targets are not close enough to be a threat, and the system will not

break radar silence to identify them. As they get closer and enter the `situational awareness' zone, the system is programmed to identify and track them. The next zone is defined as that within which the F-22 pilot has the option to engage or avoid the threat. The inmost zone is bounded by the range of the threat's missiles. In each case, the system uses the radar only as much as is necessary to maintain a track. As the target gets closer, the radar will revisit it more often. In the simulated engagement, one of the targets gives the game away by using radar. The F-22's Lockheed- Sanders ALR-94 EW sensor suite "does not compare with anything out there today - it's vastly superior," remarks a Lockheed engineer. It can determine the target's bearing and, to some extent, its range. CIP software compares the incoming radar signal with other target data. Its source correlates with the unidentified targets being tracked by AWACS, so it is placed in the same `track file'. The software selects the highest-quality data from each sensor to build the display. The target symbols change to red triangles - hostiles. The CIP computes the detection envelope of the hostile's radar against the F-22 at its current bearing. It appears on the defense screen as a blue cone emanating from the target. The CIP will do the same for any SAM radars, placing a circle around them on the defensive display. If the F-22 turns to present its more reflective side or rear to the radar, the envelope will expand visibly. The pilot can choose whether to risk detection or change course. As the targets enter the engage-or-avoid zone, the F-22 pilot steers a cursor over them and presses a bar on the throttle. This activates a `shoot list': the targets are placed in order of priority and tracked for engagement. The targets may be divided among the formation using the IFDL, and only one radar at a time need be used for tracking. Targets on the shoot list are represented by numbered circles. The pilot can override the shoot list. It is one of a number of techniques pioneered by the USAF Pilot's Associate. One of the goals of Pilot's Associate was `adaptive aiding' in which automation would be there to help the pilot in high-workload situations, but would not take over against the pilot's wishes. The objective is to help the pilot make good decisions quickly, rather than automating the decision process. Similarly, the defensive screen will show countermeasure and maneuver options against an imminent threat. The target formation appears in a larger scale on the right-hand attack display. On the left of the screen is an altitude display. On the right, the targets appear on a range scale, compressed to one dimension, which shows the maximum range of the F-22's missiles and the lethal envelope of the target's missiles. The F-22 pilot can use that information to decide whether to fire as soon as possible - and break away earlier - or whether to allow the range to close and give the target less chance to escape. The shoot-list function selects and arms missiles. A `SHOOT' cue appears on the attack display and HUD when the target is within range. Once the missile is in the air, the system steps to the next target. The within-visual- range (WVR) fight has not been ignored. The HUD - regarded as a primary flight display, for the first time on a US fighter - uses a combination of US-type symbology, emulating vertical-tape displays, and counter-pointer symbols. The F-22 will enter service

with the Joint Helmet-Mounted Cueing System (JHMCS) and AIM-9X missile for off- boresight engagements. (Elbit/Kaiser and Honeywell/GEC teams are competing to produce JHMCS.) The displays and datalink will be important in WVR. Simulations have shown that the datalink reduces ambiguous voice calls. It also means that a target that is within the radar envelope of one aircraft in the formation is visible on the displays of all of them. Another technology which may well be added to the F-22 is three-dimensional (3-D) sound. The F-22 has a Bose audio system to provide active noise reduction, and research is showing that 3-D audio provides a very accurate and reliable bearing and elevation cue.

The F-22 display system has been extensively simulated since the late 1980s, including many real-time sorties using multiple interlinked dome displays. The results, says Lockheed Martin, show that the F-22 system is intuitive and easily learned, and raises the performance level of an inexperienced pilot. Lockheed engineers say that it would not be easy to emulate the F-22 avionics system on an existing aircraft. The system works, they say, because the barriers between the different sensors have been broken down.

The most powerful sensor is the APG-77. Its active-array antenna consists of nearly 2,000 finger-sized transmit and receive modules (produced by Texas Instruments) embedded in a fixed array. The cost of these modules has been the critical issue in the radar's design since the USAF decided to aim for an active-array radar in the Advanced Tactical Fighter program in the early 1980s. They have entered production for several programs and the USAF is satisfied that the APG-77 will be affordable. A pair of the EMD modules weighs a mere 15g and puts out over 4W of power.

The modular design of the APG-77 antenna and power supply eliminates the cause of many radar failures. The APG-77 is also expected to be extremely agile, and capable of changing the direction, power and shape of the radar beam very rapidly to acquire target data while minimizing the chance that its signals will be intercepted or tracked.

The F-22 could be described as bristling with CNI and EW antennas if any of them had been visible. The 30- plus apertures are all flush with the surface of the aircraft, including large-aperture arrays in the wing leading edges. The EW system includes azimuth and elevation arrays to provide 3-D target data. Windows for the electro-optical Missile Launch Detection system are located around the forward fuselage, and four dispensers for flare, chaff and active radar decoy cartridges are installed in the lower wing surfaces.

An IR search and track (IRST) system was part of the original ATF requirement. It was deleted during dem/val, but the Avionics Directorate of the USAF Wright Laboratories has continued its development with Lockheed Martin as the

contractor, and space, weight, power and cooling provisions for IRST are still on the aircraft. A low-observable IRST window for the F-22 was tested for stealth and durability last year. IRST is valuable for raid assessment, because of its high angular resolution. It is also useful against tactical ballistic missiles, and it can double as a thermal imaging system for ground attack.

The F-22 is the first USAF fighter in many years to have a specially developed life support system. It includes the HGU-86P helmet, developed by Helmets Integrated Systems of the UK. The anti-g garment covers more of the body than earlier g-suits and can exert pressure on more of the body's blood supply. The oxygen mask and counter-pressure vest are designed for positive-pressure breathing and are controlled by a breathing regulator and anti-g garment (BRAGG) valve which reacts to the rate of g onset.

Research at the USAF's Brooks Laboratory in San Antonio has shown that positive- pressure breathing, the smart valve and improved anti-g suit increase g tolerance, reduce the risk of g-induced loss of consciousness and allow the pilot to sustain g with less physical strain and fatigue (an important factor in sustaining high sortie rates).

Positive-pressure breathing also provides altitude protection. USAF fighters are normally limited to 50,000ft because, if power and cockpit pressure are lost, the pilot will lose consciousness before the aircraft descends into thicker air. The F-22 life-support ensemble has been chamber-tested to 66,000ft and its emergency oxygen system will function long enough to reach lower altitudes. The life-support system includes an air-cooling garment underneath the g-suit and counter- pressure vest, and optional suits that protect the pilot from chemical and biological agents and cold water immersion. Up and halfway The F-22's first flight marks only the mid-point between the start of EMD and the fighter's entry into service. Nine EMD aircraft are being built. The first three (4001-4003) are dedicated to airframe and engine testing and weapon release clearances. The second of these is due to fly in April next year and the third the following September. They will have non-standard displays, no mission avionics and simpler, flight-test-dedicated communications equipment. Conducting the first flight at Marietta was cheaper than disassembling the completed prototype and transporting it to Edwards AFB, which had been considered. A mission control center has been set up at Marietta, and the first flights have been rehearsed extensively using the pilot-and-hardware- in-the-loop simulator in Fort Worth. Lockheed Martin plans a physical rehearsal of the first flight, using an F-15 escorted by F-16 chase aircraft. After eight flights, the F-22 will be ferried to Edwards AFB non-stop, with inflight refueling. In July last year, the USAF deferred development of the F-22B two-seater to save money and eliminated two F- 22Bs from the test program. This was not a `painless' decision, says Metz, but the fighter's carefree handling and straightforward flying

qualities should make it easy and safe to fly, while recording devices and the debriefing functions built into the Boeing-developed training system allow a pilot's performance to be reviewed on the ground. The fourth to ninth aircraft (4004-4009) will fly between April 1999 and May 2000, and are all dedicated to avionics testing. The plan calls for all these aircraft to be kept identical: as new hardware and software is available, all the aircraft will be retrofitted at the same time. Software and hardware will be released in blocks. The first three test aircraft will fly with Block 0, which includes the inertial reference system, the stores management system and the displays. The first major milestone in avionics testing is Block 1, which includes radar and CNI. Altogether, comments Broadwell, Block 1 includes almost half the lines of code in the final system, and its successful completion will prove a number of principles. "If we survive Block 1, we'll know a lot about software integration, and we'll know how to debug the system. We won't be wrestling functional and infrastructure issues at the same time." With radar and CNI, too, Block 1 will demonstrate the first elements of sensor fusion. Block 1 will be available for testing almost a year before F-22 4004 is ready, and will fly first aboard the Boeing- built Flying Test Bed (FTB), a modified 757 airliner fitted with the APG-77, other sensors, CIPs and displays. If the FTB tests go well, Broadwell hopes that the F-22 test aircraft can be updated quickly to the Block 2 configuration, which adds radar modes and some EW functions and should be available in mid-1999. Block 3, originally planned as the final pre-initial operating capability (IOC) release of the software, should be released in April 2000 and includes all EW functions. It will be followed in late 2000 by Block 3.1, which includes provision for JDAM. Although the task of developing such a radical system is not trivial, Broadwell believes that solid progress is being made. "We surprised a lot of people," he said, by keeping the current total of 1.7 million software lines of code (SLOC) relatively close to the 1.3 million SLOC that was predicted in December 1990. "If we can hold the growth to 25 per cent we'll amaze the world." Every piece of hardware intended for the system has been built and is working in the laboratory, including a complete radar array, which is looking out over the airport at Northrop Grumman's Baltimore plant and is linked to a CIP. Software development so far has stayed on track, and the Block plan is mostly cumulative: "When you add a block in CNI, you add a function. When you add a block in radar, you add modes. It's done, and it doesn't change." Flight tests should confirm that the F-22's `conservative' looks belie its performance. Details are classified: however, the immense thrust should provide remarkable acceleration and speed. A chart published in 1991 shows that the F-22 is slightly faster on intermediate power than an F-15C on full burner, when both aircraft have eight AAMs on board. (The speeds are probably around Mach 1.6-1.7.) "We expect that this will be one of the things that surprises the air force," said Metz. "If you don't know what you're doing, you'll be supersonic." Unlike most fighters, too, the F-22 achieves its highest rate of climb at supersonic speed. It is almost as fast with afterburner as without. The augmentors will be used

mainly for acceleration and supersonic maneuvering. Metz believes that the "afterburner will generally not be required", and that when it is used it will be in bursts of seconds and tens of seconds, at the outside. The principal breakthrough in terms of straight-line performance is supercruise. The USAF has stated that "about 30 minutes in a one-hour mission" can be flown at supersonic speed, three to six times the supersonic endurance of any fighter using augmentors. On a typical mission, the F-22 can sustain supersonic speed for most of the time that it is over hostile territory. Supersonic endurance varies with speed: a supercruising F-22 may vary its speed between Mach 1.1 to Mach 1.5-plus according to the tactical situation. Supercruise has many tactical advantages. A faster aircraft retains engagement control: if its pilot chooses to fight, the adversary cannot run, and if the F-22 pilot disengages, the adversary cannot sustain the pursuit. The F-22 can maneuver around a slower adversary to engage it from the rear, and enters the fight with greater energy and overtaking speed. Supersonic speed goes along with a higher altitude capability: both shrink the lethal envelope of SAMs. First-look, First-Shot

The F-22's reduced head-on RCS is claimed to guarantee a first-look, first-shot advantage against any contemporary fighter radar. However, where the F-22 differs from any other air-combat fighter is in the importance placed on all-round RCS, which is described as being in the same order as the slower and less agile F-117 and B-2. All-round stealth is aimed primarily at the SAM threat. Stealth and supercruise are synergistic: the aim is not to be invisible, but to reduce detection range to the point where the system cannot complete an engagement against a fast-flying target before the range begins to increase.

The philosophy of `balanced observables' mandated that the F-22's IR signature be reduced so that IR and radar sensors would have a similar detection range. The most prominent source of IR radiation from an aircraft is its exhaust plume. On the F-22, plume radiation is reduced by minimal afterburner use, the 2-D nozzles and bypass mixing. Much of the remaining IR signature comprises reflected solar IR radiation and emissions caused by skin friction heat. IR-absorbent paint reduces solar reflection; it is analogous to normal paint except that it absorbs in the IR band. Friction heat cannot be absorbed by paint, but coatings have been developed that change the emissivity of a surface: that is, they make it less efficient at emitting IR. To some extent, coatings may also be able to shift the wavelength of the emitted IR energy into wavebands which attenuate most rapidly in the atmosphere. Heat from electronics and other systems can cause IR emissions. The F-22's specialized environmental control system stores peak heating loads in heat sinks and removes it from the aircraft through air-to-fuel heat exchangers. The F-22's visual signature will be managed by a new camouflage scheme, an overall grey with darker, soft-edged areas on the wings, body and tail. The base color is intended to match the luminance of the sky at typical combat altitudes and extreme

visual range, while the darker patches send mixed signals to the eye or to an electro-optical seeker with an edge-recognition algorithm. Metz prefers not to be drawn into the debate over the value of the low-airspeed, high-alpha maneuvers demonstrated by the Sukhoi Su-37 at the Farnborough air show last September, or by the X-31. Some pilots believe that the ability to fire a short-range AAM in almost any direction, by changing the fighter's body angle independently of its flightpath, will be critical in future combats. Others disagree vehemently, arguing that post- stall maneuvers kill so much airspeed that they are `suicidal' in a many-on-many fight. Whatever the outcome of the debate, the F-22 should be able to acquit itself well, with a very large flight envelope that is actually usable in combat. (At least some spectacular air-show maneuvers have involved disabling safety-related limiters.) Alphas to 60 were demonstrated in the YF-22 program, and some roll maneuverability was retained at that extreme pitch angle. The acual in-service alpha limit has not been released. However, the fact that 60 was demonstrated in flight tests, and the F-22 fuel system simulator is built to emulate 60 alphas, suggests that the fighter will indeed be designed to attain 60 in service - more than twice the service limit of any other fighter. At alphas of 15 and above, the F-22 rolls at least twice as fast as the F-15, and the gap widens until the F-15 hits its roll limit of 30 alpha. Maximum pitch rates are up to twice as fast as the F-16. The F-22's pitch rate is so fast that it is inhibited by a soft stop in the aft movement of the sidestick. Pulling the stick through the stop overrides a limit in pitch acceleration, and it is considered best for the pilot to be aware that the F-22 is about to respond very fast and that the BRAGG valve will respond in turn. The F-22 pilot who decides that the tactical situation warrants high-alpha, low-speed maneuvering may be reassured by the fighter's controllability and thrust-to-weight ratio. The F-22 should be able to end a maneuver rapidly when required, and will accelerate quickly to a safer combat speed. The fighter will be evaluated against `actual and simulated adversary aircraft' during its flight-test program, Metz states. "It will be a great air-show airplane, too," he added. The F-22 is claimed to have more than twice the range of the F-15C at subsonic speed, with a greater margin when the mission includes supersonic flight. Such numbers have to be treated with caution. In this case, the comparison is probably based on a full missile load and internal fuel only. The F-22's internal fuel load is greater than that of an F-15C with three 2,300-liter tanks, and it has much less drag, so it should have a greater combat radius on a similar mission profile. Despite its remarkable capabilities, the F-22 should not be a hard-to-maintain, exotic aircraft. Every part of the aircraft has been designed by an integrated product team that includes engineers and specialists in production and maintenance, and the goal is an aircraft that requires one-third as many maintenance hours per flight hour as the F-15. Built-in test equipment replaces off-board test equipment, and more items are designed to be replaced on the flight-line rather than repaired in an intermediate-level shop on the base. A 24-aircraft unit of F- 22s requires only eight C-141B-loads of equipment for a 30-day deployment, versus 18 for the same number of F-15s. It requires half

as many people to support the F-22 as are needed for the same number of F-15s. So far, developmental problems have been minor, with the exception of the turbine redesign, and program managers note that pre-flight testing and tight configuration control have unearthed problems before rather than after first flight - when there has been time to solve them at reasonable cost. The main cause of delays has been funding. Since the EMD program started, budget cuts have moved the first flight from August 1995 to May 1997, and have IOC from 2001 to 2004. These actions have made the F-22 more expensive. The total program cost - development, 438 aircraft, spares, ground equipment and construction - stands at US$73.5Ebillion. Much of this total includes 10 years or more of projected inflation, and it has increased as IOC has slipped. Lockheed Martin's development contract for the airframe was estimated late last year at US$12 billion. A review last year showed that costs were likely to rise more than predicted, because defense industry costs are expected to rise faster than the government-wide inflation rate on which the Pentagon's budgets are based. The Pentagon has responded by slowing initial production and adding a US$1.45 billion reserve to the EMD program. This is expected to fund investments in production and program changes (such as the early procurement of some avionics components) that will reduce costs in the future, and includes the integration of the AIM-9X and JHMCS. The total EMD cost, including Lockheed Martin and Pratt &Whitney contracts, and work done by the USAF, now seems likely to exceed US$17 billion including the sums already spent or committed. The projected average flyaway price of the F-22 is now US$71 million in 1996 dollars. (This price includes a fully-equipped aircraft but no spares or weapons.) Some of the added investments being made now, and other proposals made by the contractors - including multi-year procurements - are intended to ensure that this number continues to track the budgeted rate of inflation, rather than with defense industry costs. Lockheed Martin managers argue that export sales would reduce the cost of the F-22 to the Pentagon, and the sooner the better. Department of Defense policy precludes final contracts until initial operational test and evaluation is complete, in 2001-02, but that does not prevent Lockheed Martin from briefing export customers. The company planned to do this at the Farnborough air show, but the Pentagon withheld permission until the cost picture became clearer. USAF Deputy Chief of Staff Gen Tom Moorman noted in January that "I have no doubt that the F-22 will be released for export, and we have some authority to do that now."

An executive committee co-chaired by the US Under Secretary of Defense for Aquisition and Technology Paul Kaminski and Gen Joe Ralston, vice-chair of the Joint Chiefs of Staff, is reviewing the security issues raised by the possible export of a stealthy aircraft. Some of the stealth features of the F-22 are `modular' in nature and could be selectively removed or downgraded for export.

Potential customers include F-15 operators such as Israel, Japan and Saudi Arabia.

South Korea is considering a high-end fighter to complement the F-16, and Lockheed Martin is looking at the possibility of selling small `silver bullet' F-22 fleets to operators of modern but non-stealthy fighters; even Eurofighter members are not ruled out. Granted that cost definitions are fraught with a lack of international consistency, the F-22's flyaway cost of US$71 million does not appear widely different from the US$50 million to US$60 million figures recently quoted (by the German government audit office) for the Eurofighter, as well as those for Rafale. Eurofighter's claim, repeated at Farnborough, that its aircraft is "less than half the price" of the F-22 appears to rest on a comparison between a flyaway cost and a unit program cost.

Lockheed Martin executives appear reasonably confident that the F-22 will survive the QDR and this year's budget deliberations. Production may be cut to 300-350 aircraft, but it would not materially affect the program until 2008 - three US elections and at least two presidents hence. Both Lockheed and the USAF caution against deeper cuts, partly because experience with AWACS and similar `force multiplier' assets is showing that the limiting factor may be the ability to sustain and retain essential people for small, high-value forces that spend months on end away from home. This year is pivotal for the F-22. If it survives the QDR, it is likely to survive through the tenure of the administration, and by 2001 it should be well established: but by making the air superiority mission and the need for the F-22 its top priorities in the QDR, the USAF is nailing its colors to the mast. If the F-22 does not survive, and the F/A-18E/F emerges unscathed, the USAF will not see another new aircraft before the JSF arrives in 2010. It will be a victory for the advocates of sea-based airpower, and a setback for the concept of an independent air arm. The continuation of the F-22 program, however, would be the starting point for a new, more forward-thinking airpower doctrine for the 21st century. Illustration Caption: Photograph: An artist's rendition of a visual range confrontation. The F-22 in the picture has pursued two adversary aircraft to low altitude, destroying one (the `fireball' at the top right of the picture), and has launched one of its six AIM-120C air-to-air medium range missiles at the remaining enemy fighter. The visible camouflage scheme is one indication that the US Air Force has not ignored the certainty of visual-range combat (the retention of a 20mm cannon and 480 rounds of ammunition being another). Lockheed Martin Photograph: The F-22 team is using a unique vertical modular tooling process for assembly of the mid-fuselage, which incorporates the four weapon bays, the main landing gears and the inlet ducts. Made of carbonfiber/epoxy, the ducts curve sharply upwards and inwards to mask the engine faces from radar, changing section smoothly from rhomboidal to circular, and their inner contours must be smooth and accurate to maintain their stealth characteristics. Lockheed Martin Graphic: F-22 versus surface-to-air missile attack. A conventional fighter is detected at point A. The SAM system projects its track and launches towards intercept point B. The missile retains enough energy to counter target maneuvers.

The stealthy F-22, by comparison, is flying equally close to the SAM system, but is not detected until point C. The missile will take longer to reach its altitude because the slant range is greater. Coupled with the F-22's greater speed, this means that the first possible intercept point is D - a low-energy, long-range tail chase against a target at the limits of the system's tracking range. A moderate supersonic `jink' at D runs the missile out of energy. Source: Lockheed Martin Photograph: The F-22 canopy is approximately 3.5m long, 1m wide and 0.7m tall, and weighs about 160kg. This test canopy will be mounted on the rocket-powered multi-axis seat ejection vehicle, and launched along rails to simulate canopy jettison and seat firing in an aircraft traveling at various speeds. Lockheed Martin Photograph: Pratt &Whitney's F119-PW- 100 twin-spool augmented turbofan engine was selected to power the F-22 in April 1991. The first production engine is due in late 1999. Pratt &Whitney Photograph: An air-to-surface capability has been developed for the F-22. The aircraft's lower weapon bays have been modified to carry two McDonnell Douglas GBU-32 1,000 lb (450kg)-class Joint Direct Attack Munitions. The GBU-32 is a near-precision standoff weapon guided to its target by means of an inertial measurement unit updated inflight with data from Global Positioning System satellites. In this artist's rendition, an F-22 pilot releases both GBU-32 bombs against an enemy airfield's surface-to-air missile site. Photograph: The tactical display system that will provide unsurpassed situation awareness for F-22 pilots. The defense display on the left gives pilots the information they will need to protect themselves against threats. The display in the middle provides an overall situation awareness and navigation information, while on the right is the target attack display. Boeing Photograph: Boeing has modified a 757 airliner into a flying avionics testbed for the F-22. Modifications include installing a wing shape geometrically identical to the F-22 on the crown of the fuselage. This sensor wing will include F-22 electronic warfare and communication, navigation and identification sensors. There are also various apertures to replicate F-22 antennas, and the F-22 forward fuselage structure housing a prototype radar.