DESIGN Of F~22 RAPTOR

DESIGN Of F~22 RAPTOR

Overview

F-22 flying with its F119-PW-100 engines on full afterburner during testing

The F-22 Raptor is a fifth-generation fighter that is considered fourth generation in stealth aircraft technology by the USAF. It is the first operational aircraft to combine supercruise, supermaneuverability, stealth, and sensor fusion in a single weapons platform. The Raptor has clipped delta wings with a reverse sweep on the rear, four empennage surfaces, and a retractable tricycle landing gear. Flight control surfaces include leading and trailing-edge flaps, ailerons, rudders on the canted vertical stabilizers, and all-moving horizontal tails; these surfaces also serve as speed brakes.

The aircraft's dual Pratt & Whitney F119-PW-100 afterburning turbofan engines are closely spaced and incorporate pitch-axis thrust vectoring nozzles with a range of ±20 degrees; each engine has maximum thrust in the 35,000 lbf (156 kN) class.The F-22's thrust to weight ratio in typical combat configuration is nearly at unity in maximum military power and 1.25 in full after burner.Maximum speed without external stores is estimated to be Mach 1.82 during supercruise and greater than Mach 2 with afterburners.

The F-22 is among only a few aircraft that can supercruise, or sustain supersonic flight without using fuel-inefficient afterburners; it can intercept targets which subsonic aircraft would lack the speed to pursue and an afterburner-dependent aircraft would lack the fuel to reach.The Raptor's high operating altitude is also a significant tactical advantage over prior fighters.The use of internal weapons bays permits the aircraft to maintain comparatively higher performance over most other combat-configured fighters due to a lack of aerodynamic drag from external stores. The F-22's structure contains a significant amount of high-strength materials to withstand stress and heat of sustained supersonic flight. Respectively, titanium alloys and composites comprise 39% and 24% of the aircraft's structural weight.

The F-22 is highly maneuverable at both supersonic and subsonic speeds. Computerized flight control system and full authority digital engine control (FADEC) make the aircraft highly departure resistant and controllable. The Raptor's relaxed stability and powerful thrust-vectoring engines enable the aircraft to turn tightly and perform very high alpha (angle of attack) maneuvers such as the Herbst maneuver (J-turn) and Pugachev's Cobra. The aircraft is also capable of maintaining over 60° alpha while having some roll control.

The Raptor's aerodynamic performance, sensor fusion, and stealth work together for increased effectiveness. Altitude, speed, and advanced active and passive sensors allow the aircraft to spot targets at considerable ranges and increase weapons range; altitude and speed also complement stealth's ability to increase the aircraft's survivability against ground defenses such as surface-to-air missiles.

Avionics

Key avionics include BAE Systems EI&S AN/ALR-94 radar warning receiver (RWR),^[Lockheed Martin AN/AAR-56 infrared and ultraviolet Missile Launch Detector (MLD) and Northrop Grumman AN/APG-77 active electronically scanned array (AESA) radar. The MLD features six sensors to provide full spherical infrared coverage. The RWR is a passive radar detector with more than 30 antennas blended into the wings and fuselage for all-round coverage. Tom Burbage, former F-22 program head at Lockheed Martin, described it as "the most technically complex piece of equipment on the aircraft." The range of the RWR (250+ nmi) exceeds the radar's, and can cue radar emissions to be confined to a narrow beam (down to 2° by 2° in azimuth and elevation) to increase stealth. Depending on the detected threat, the defensive systems can prompt the pilot to release countermeasures such as flares or chaff. According to Bill Sweetman, experts had said the ALR-94 can be used as a passive detection system capable of searching targets and providing enough information for a radar lock on.

The AN/APG-77 AESA radar

The AN/APG-77 radar features a low-observable, active-aperture, electronically scanned array that can track multiple targets under any weather conditions. Radar emissions can also be focused to overload enemy sensors as an electronic-attack capability. The radar changes frequencies more than 1,000 times per second to lower interception probability and has an estimated range of 125–150 miles, though planned upgrades will allow a range of 250 miles (400 km) or more in narrow beams. Radar information is processed by two Raytheon Common Integrated Processor (CIP)s, each capable of processing up to 10.5 billion instructions per second. In a process known as sensor fusion, data from the radar, other sensors, and external systems is filtered and combined by the CIP into a common view, reducing pilot workload.However, upgrading the aircraft's avionics was reportedly very challenging due to their highly integrated nature.

The F-22's ability to operate close to the battlefield gives the aircraft threat detection and identification capability comparative with the RC-135 Rivet Joint, and the ability to function as a "mini-AWACS", though the radar is less powerful than those of dedicated platforms. The F-22 can designate targets for allies, and determine whether two friendly aircraft are targeting the same aircraft. This radar system can sometimes identify targets "many times quicker than the AWACS".The IEEE 1394B bus developed for the F-22 was derived from the commercial IEEE 1394 "FireWire" bus system. In 2007, the F-22's radar was tested as a wireless data transceiver, transmitting data at 548 megabits per second and receiving at gigabit speed, far faster than the Link 16 system.

The F-22's software has some 1.7 million lines of code, the majority involving processing radar data.^] Former Secretary of the USAF Michael Wynne blamed the use of the DoD's Ada for cost overruns and delays on many military projects, including the F-22. Cyberattacks on subcontractors have reportedly raised doubts about the security of the F-22's systems and combat-effectiveness. In 2009, former Navy Secretary John Lehman considered the F-22 to be safe from cyberattack, citing the age of its IBM software.

Cockpit

Cockpit of the F-22, showing instruments, head up display and throttle top (lower left)

The F-22 has a glass cockpit with all-digital flight instruments. The monochrome head-up display offers a wide field of view and serves as a primary flight instrument; information is also displayed upon six color liquid-crystal display (LCD) panels.The primary flight controls are a force-sensitive side-stick controller and a pair of throttles. The USAF initially wanted to implement direct voice input (DVI) controls, but this was judged to be too technically risky and was abandoned. The canopy's dimensions are approximately 140 inches long, 45 inches wide, and 27 inches tall (355 cm x 115 cm x 69 cm) and weighs 360 pounds.

The F-22 has integrated radio functionality, the signal processing systems are virtualized rather than as a separate hardware module. There have been several reports on the F-22's inability to communicate with other aircraft, and funding cuts have affected the integration of the Multifunction Advanced Data Link (MADL).Voice communication is possible, but not data transfer.

The integrated control panel (ICP) is a keypad system for entering communications, navigation, and autopilot data. Two 3 in × 4 in (7.6 cm × 10.2 cm) up-front displays located around the ICP are used to display integrated caution advisory/warning data, communications, navigation and identification (CNI) data and also serve as the stand-by flight instrumentation group and fuel quantity indicator.The stand-by flight group displays an artificial horizon, for basic instrument meteorological conditions. The 8 in × 8 in (20 cm × 20 cm) primary multi-function display (PMFD) is located under the ICP, and is used for navigation and situation assessment. Three 6.25 in × 6.25 in (15.9 cm × 15.9 cm) secondary multi-function displays are located around the PMFD for tactical information and stores management.

The ejection seat is a version of the ACES II (Advanced Concept Ejection Seat) commonly used in USAF aircraft, with a center-mounted ejection control.The F-22 has a complex life support system, which includes the on-board oxygen generation system (OBOGS), protective pilot garments, and a breathing regulator/anti-g (BRAG) valve controlling flow and pressure to the pilot's mask and garments. The pilot garments were developed under the Advanced Technology Anti-G Suit (ATAGS) project and are to protect against chemical/biological hazards and cold-water immersion, counter g-forces and low pressure at high altitudes, and provide thermal relief. Suspicions regarding the performance of the OBOGS and life support equipment have been raised by several mishaps, including a fatal crash.

Armament

AIM-120 AMRAAM (right) fitted in a weapons bay of an F-22

The Raptor has three internal weapons bays: a large bay on the bottom of the fuselage, and two smaller bays on the sides of the fuselage, aft of the engine intakes.The main bay can accommodate six LAU-142/A launchers for beyond-visual-range missiles and each side bay has an LAU-141/A launcher for short-range missiles. Four of the launchers in the main bay can be replaced with two bomb racks that can each carry one 1,000 lb (450 kg) or four 250 lb (110 kg) bombs.Carrying armaments internally maintains the aircraft's stealth and minimizes additional drag. Missile launches require the bay doors to be open for less than a second, during which hydraulic arms push missiles clear of the aircraft; this is to reduce vulnerability to detection and to deploy missiles during high speed flight.

Front fuselage detail of an F-22

The F-22 can also carry air-to-surface weapons such as bombs with Joint Direct Attack Munition (JDAM) guidance and the Small-Diameter Bomb, but cannot self-designate for laser-guided weapons. Internal air-to-surface ordnance is limited to 2,000 lb. An internally mounted M61A2 Vulcan 20 mm rotary cannon is embedded in the right wing root with the muzzle covered by a retractable door to maintain stealth. The radar projection of the cannon fire's path is displayed on the pilot's head-up display.

F-22 with external weapons pylons

The F-22's high cruise speed and altitude increase the effective ranges of its munitions, with the aircraft having 50% greater employment range for the AIM-120 AMRAAM than prior platforms. While specifics are classified, it is expected that JDAMs employed by F-22s will have twice or more the effective range of legacy platforms. In testing, an F-22 dropped a GBU-32 JDAM from 50,000 feet (15,000 m) while cruising at Mach 1.5, striking a moving target 24 miles (39 km) away.
While the F-22 typically carries weapons internally, the wings include four hardpoints, each rated to handle 5,000 lb (2,300 kg). Each hardpoint can accommodate a pylon that can carry a detachable 600-gallon (2,270 L) external fuel tank or a launcher holding two air-to-air missiles; the two inboard hardpoints are "plumbed" for external fuel tanks. The use of external stores degrades the aircraft's stealth and kinematic performance; after releasing stores the external attachments can be jettisoned to restore those characteristics.A stealthy ordnance pod and pylon was being developed to carry additional weapons in the mid-2000s.

Stealth

For stealth, the F-22 carries weapons in internal bays. The doors for the center and side bays are open; the six LAU-142/A AMRAAM Vertical Eject Launchers (AVEL) are visible.

The F-22 was designed to be highly difficult to detect and track by radar. Measures to reduce radar cross-section include airframe shaping such as alignment of edges, fixed-geometry serpentine inlets that prevent line-of-sight of the engine faces from any exterior view, use of radar-absorbent material (RAM), and attention to detail such as hinges and pilot helmets that could provide a radar return. The F-22 was also designed to have decreased radio emissions, infrared signature and acoustic signature as well as reduced visibility to the naked eye.The aircraft's flat thrust vectoring nozzle reduces infrared emissions to mitigate the threat of infrared homing ("heat seeking") surface-to-air or air-to-air missiles.Additional measures to reduce the infrared signature include special paint and active cooling of leading edges to manage the heat buildup from supersonic flight.

Compared to previous stealth designs like the F-117, the F-22 is less reliant on radar-absorbent materials, which are maintenance-intensive and susceptible to adverse weather conditions. Unlike the B-2, which requires climate-controlled hangars, the F-22 can undergo repairs on the flight line or in a normal hangar. The F-22 features a Signature Assessment System which delivers warnings when the radar signature is degraded and necessitates repair.The F-22's exact radar cross-section (RCS) is classified; however, in 2009 Lockheed Martin released information indicating it has an RCS (from certain angles) of −40 dBsm – equivalent to the radar reflection of a "steel marble". Effectively maintaining the stealth features can decrease the F-22's mission capable rate to 62–70%.

The effectiveness of the stealth characteristics is difficult to gauge. The RCS value is a restrictive measurement of the aircraft's frontal or side area from the perspective of a static radar. When an aircraft maneuvers it exposes a completely different set of angles and surface area, potentially increasing radar observability. Furthermore, the F-22's stealth contouring and radar absorbent materials are chiefly effective against high-frequency radars, usually found on other aircraft. The effects of Rayleigh scattering and resonance mean that low-frequency radars such as weather radars and early-warning radars are more likely to detect the F-22 due to its physical size. However, such radars are also conspicuous, susceptible to clutter, and have low precision.Additionally, while faint or fleeting radar contacts make defenders aware that a stealth aircraft is present, reliably vectoring interception to attack the aircraft is much more challenging. According to the USAF an F-22 surprised an Iranian F-4 Phantom II that was attempting to intercept an American UAV, despite Iran's claim of having military VHF radar coverage over the Persian Gulf.

Operational history

Designation and testing

An F-22 refuels from a KC-135 during testing; the attachment on the back top is for a spin recovery chute

The YF-22 was originally given the unofficial name "Lightning II", after the World War II Lockheed P-38 Lightning fighter, which persisted until the mid-1990s when the USAF officially named the aircraft "Raptor". The name "Lightning II" was later given to the F-35. The aircraft was also briefly dubbed "SuperStar" and "Rapier".In September 2002, USAF changed the Raptor's designation to F/A-22, mimicking the Navy's McDonnell Douglas F/A-18 Hornet and intended to highlight a planned ground-attack capability amid debate over the aircraft's role and relevance. The F-22 designation was reinstated in December 2005, when the aircraft entered service.

Flight testing of the F-22 began in 1997 with Raptor 4001, the first EMD jet, and eight more F-22s would participate in the EMD and flight test program.Raptor 4001 was retired from flight testing in 2000 and subsequently sent to Wright-Patterson Air Force Base (AFB) for survivability testing, including live fire testing and battle damage repair training. EMD F-22s have been used for testing upgrades, and also as maintenance trainers. The first production F-22 was delivered to Nellis AFB, Nevada, in January 2003.

In May 2006, a released report documented a problem with the F-22's forward titanium boom, caused by defective heat-treating. This made the boom on roughly the first 80 F-22s less ductile than specified and potentially shortened the part's life. Modifications and inspections were implemented to the booms to restore life expectancy.

In August 2008, an unmodified F-22 of the 411th Flight Test Squadron performed in the first ever air-to-air refueling of an aircraft using synthetic jet fuel as part of a wider USAF effort to qualify aircraft to use the fuel, a 50/50 mix of JP-8 and a Fischer–Tropsch process-produced, natural gas-based fuel.In 2011, an F-22 flew supersonic on a 50% mixture of biofuel derived from camelina.

Introduction into service

An F-22 fires an AIM-120 AMRAAM

In December 2005, the USAF announced that the F-22 had achieved Initial Operational Capability (IOC).During Exercise Northern Edge in Alaska in June 2006, in simulated combat exercises 12 F-22s of the 94th FS downed 108 adversaries with no losses.In the exercises, the Raptor-led Blue Force amassed 241 kills against two losses in air-to-air combat, with neither loss being an F-22. During Red Flag 07-1 in February 2007, 14 F-22s of the 94th FS supported Blue Force strikes and undertook close air support sorties. Against superior numbers of Red Force Aggressor F-15s and F-16s, 6–8 F-22s maintained air dominance throughout. No sorties were missed because of maintenance or other failures; a single F-22 was judged lost against the defeated opposing force.F-22s also provided airborne electronic surveillance.

The Raptor achieved Full Operational Capability (FOC) in December 2007, when General John Corley of Air Combat Command (ACC) officially declared the F-22s of the integrated active duty 1st Fighter Wing and Virginia Air National Guard 192d Fighter Wing fully operational.This was followed by an Operational Readiness Inspection (ORI) of the integrated wing in April 2008, in which it was rated "excellent" in all categories, with a simulated kill-ratio of 221–0.

Deployments

An F-22 from Elmendorf AFB, Alaska, intercepting a Russian Tupolev Tu-95 near American airspace

F-22 fighter units have been frequently deployed to Kadena Air Base in Okinawa, Japan. In February 2007, on the aircraft's first overseas deployment to Kadena Air Base, six F-22s of 27th Fighter Squadron flying from Hickam AFB, Hawaii, experienced multiple software-related system failures while crossing the International Date Line (180th meridian of longitude). The aircraft returned to Hawaii by following tanker aircraft. Within 48 hours, the error was resolved and the journey resumed. In early 2013, F-22s were involved in U.S.-South Korean military drills.

In November 2007, F-22s of 90th Fighter Squadron at Elmendorf AFB, Alaska, performed their first NORAD interception of two Russian Tu-95MS "Bear-H" bombers. Since then, F-22s have also escorted probing Tu-160 "Blackjack" bombers.The first pair of F-22s assigned to the 49th Fighter Wing became operational at Holloman AFB, New Mexico, in June 2008. In 2014, Holloman F-22s and their support personnel were reassigned to the reactivated 95th Fighter Squadron at Tyndall AFB.

Secretary of Defense Gates initially refused to deploy F-22s to the Middle East in 2007. The type made its first deployment in the region at Al Dhafra Air Base in the UAE in 2009. In April 2012, F-22s have been rotating into Al Dhafra Air Base, less than 200 miles from Iran; the Iranian defense minister referred to the deployment as a security threat. In March 2013 the USAF announced that an F-22 had intercepted an Iranian F-4 Phantom II that approached within 16 miles of an MQ-1 Predator flying off the Iranian coastline.

An F-22 of the 43d Fighter Squadron alongside an F-15 Eagle of the 27th Fighter Squadron, 2005

 In June 2014, F-22s from the 199th Fighter Squadron of the Hawaii Air National Guard were deployed to Malaysia to participate in the Cope Taufan 2014 exercise conducted by the USAF Pacific Air Forces and Royal Malaysian Air Force.

On 22 September 2014, F-22s performed the type's first combat sorties during the American-led intervention in Syria; a number of aircraft dropped 1,000-pound GPS-guided bombs on Islamic State targets in the vicinity of Tishrin Dam. Combat operations by F-22s are planned to continue into the foreseeable future. While some missions involve striking targets, the F-22's main role is intelligence, surveillance and reconnaissance (ISR) gathering. By January 2015, the F-22 accounted for three percent of Air Force sorties during Operation Inherent Resolve. General Mike Hostage of ACC said that it performed "flawlessly" during this deployment. Between September 2014 and July 2015, F-22s flew 204 sorties over Syria, dropping 270 bombs at some 60 locations. On 23 June 2015, a pair of F-22s performed the aircraft's first close air support (CAS) mission after receiving a short-notice request for airstrikes in close proximity to friendly forces.

An F-22 refueling prior to combat operations in Syria, September 2014

In late 2014, the USAF was testing a rapid deployment concept involving four F-22s and one C-17 for support, first proposed in 2008 by two F-22 pilots. The goal was for the type to be able to set up and engage in combat within 24 hours. Four F-22s were deployed to Spangdahlem Air Base in Germany in August and Lask Air Base in Poland and Amari Air Base in Estonia in September 2015 to train with NATO allies.

On 19 August 2016, two F-22s intercepted two Syrian Su-24 strike aircraft over Hasakah, Syria, following SyAAF attacks on U.S.-backed Kurdish forces in and around the city.

Maintenance and training

F-22 aircraft were available for missions 62% of the time on average in 2004 and 70% in 2009. The rate was at 63% in 2015. Early on, the F-22 required more than 30 hours of maintenance per flight hour and a total cost per flight hour of $44,000; by 2008 it was reduced to 18.1, and 10.5 by 2009; lower than the Pentagon's requirement of 12 maintenance hours per flight hour. When introduced, the F-22 had a Mean Time Between Maintenance (MTBM) of 1.7 hours, short of the required 3.0; in 2012 this rose to 3.2 hours. By 2013, the cost per flight hour was $68,362, over three times as much as the F-16. In 2014, the F-22 fleet required 43 maintenance man-hours per flight hour.

Each aircraft requires a month-long packaged maintenance plan (PMP) every 300 flight hours.The stealth system, including its radar absorbing metallic skin, account for almost one third of maintenance. The canopy was redesigned after the original design lasted an average of 331 hours instead of the required 800 hours. F-22 depot maintenance is performed at Ogden Air Logistics Complex at Hill AFB, Utah.

In January 2007, the F-22 reportedly maintained 97% sortie rate, flying 102 out of 105 tasked sorties while amassing a 144-to-zero kill ratio during "Northern Edge" air-to-air exercises in Alaska. According to Lieutenant Colonel Wade Tolliver, squadron commander of the 27th Fighter Squadron, the stealth coatings of the F-22 are more robust than those used in earlier stealth aircraft, being less sensitive to weather and wear and tear. However, rain caused "shorts and failures in sophisticated electrical components" when F-22s were posted to Guam.

To reduce operating costs and lengthen the F-22's service life, some pilot training sorties are performed using flight simulators, while the T-38 Talon is used for adversary training. DoD budget cuts led to F-22 demonstration flights being halted in 2013 before resuming in 2014. In 2012, it was reported that the F-22's maintenance demands have increased as the fleet aged, the stealth coatings being particularly demanding.

Operational problems

Operational problems have been experienced and some have caused fleet-wide groundings. Critically, pilots have experienced a decreased mental status, including losing consciousness. There were reports of instances of pilots found to have a decreased level of alertness or memory loss after landing. F-22 pilots have experienced lingering respiratory problems and a chronic cough; other symptoms include irritability, emotional lability and neurological changes. A number of possible causes were investigated, including possible exposure to noxious chemical agents from the respiratory tubing, pressure suit malfunction, side effects from oxygen delivery at greater-than-atmospheric concentrations, and oxygen supply disruptions. Other problems include minor mechanical problems and navigational software failures. The fleet was grounded for four months in 2011 before resuming flight, but reports of oxygen issues persisted.

In 2005, the Raptor Aeromedical Working Group, a USAF expert panel, recommended several changes to deal with the oxygen supply issues. In October 2011, Lockheed Martin was awarded a $24M contract to investigate the breathing difficulties. In July 2012, the Pentagon concluded that a pressure valve on flight vests worn during high-altitude flights and a carbon air filter were likely sources of at least some hypoxia-like symptoms. Long-distance flights were resumed, but were limited to lower altitudes until corrections had been made. The carbon filters were changed to a different model to reduce lung exposure to carbon particulates. The breathing regulator/anti-g (BRAG) valve, used to inflate the pilot's vest during high G maneuvers, was found to be defective, inflating the vest at unintended intervals and restricting the pilot's breathing. The on-board oxygen generating system (OBOGS) also unexpectedly reduced oxygen levels during high-G maneuvers. In late 2012, Lockheed Martin was awarded contracts to install a supplemental automatic oxygen backup system, in addition to the primary and manual backup. Changes recommended by the Raptor Aeromedical Working Group in 2005 received further consideration in 2012; the USAF reportedly considered installing EEG brain wave monitors on the pilot's helmets for inflight monitoring.
New backup oxygen generators and filters have been installed on the aircraft. The coughing symptoms have been attributed to acceleration atelectasis, which may be exacerbated by the F-22's high performance; there is no present solution to the condition. The presence of toxins and particles in some ground crew was deemed to be unrelated. On 4 April 2013, the distance and altitude flight restrictions were lifted after the F-22 Combined Test Force and 412th Aerospace Medicine Squadron determined that breathing restrictions on the pilot were responsible as opposed to an issue with the oxygen provided.

Variants

• YF-22A – pre-production technology demonstrator for ATF demonstration/validation phase; two were built.
• F-22A – single-seat production version, was designated F/A-22A in early 2000s.
• F-22B – planned two-seat variant, but was canceled in 1996 to save development costs.
• Naval F-22 variant – a carrier-borne variant of the F-22 with variable-sweep wings for the U.S. Navy's Navy Advanced Tactical Fighter (NATF) program to replace the F-14 Tomcat. Program was canceled in 1993. Former SoAF Donald Rice has called the possibility of the naval variant the deciding factor for his choice of the YF-22 over the YF-23.

Derivatives

The FB-22 was a proposed medium-range bomber for the USAF. The FB-22 was projected to carry up to 30 Small Diameter Bombs to about twice the range of the F-22A, while maintaining the F-22's stealth and supersonic speed. However, the FB-22 in its planned form appears to have been canceled with the 2006 Quadrennial Defense Review and subsequent developments, in lieu of a larger subsonic bomber with a much greater range.

The X-44 MANTA, or multi-axis, no-tail aircraft, was a planned experimental aircraft based on the F-22 with enhanced thrust vectoring controls and no aerodynamic surface backup. The aircraft was to be solely controlled by thrust vectoring, without featuring any rudders, ailerons, or elevators. Funding for this program was halted in 2000.