F-22 Raptor  |
American fighter aircraft that uses stealth technology. It is an air superiority fighter, but is equipped for ground attack, electronic warfare, and signals intelligence roles as well. The United States Air Force considers the F-22 a critical component of the US strike force. Faced with a protracted development period, the aircraft was variously designated F-22 and F/A-22 during the three years before formally entering US Air Force service in December 2005, as the F-22A. Lockheed Martin Aeronautics is the prime contractor and is responsible for the majority of the airframe, weapon systems and final assembly of the F-22. Along with Lockheed Martin, partner Boeing Integrated Defense Systems provides the wings, aft fuselage, avionics integration, and all of the pilot and maintenance training systems. The F-22 is claimed by several sources to be the world’s most effective air superiority fighter. The US Air Force claims that the F-22 cannot be matched by any known or projected fighter aircraft. Air Marshal Angus Houston, chief of the Australian Defence Force, and former head of the Royal Australian Air Force, said in 2004 that the "F-22 will be the most outstanding fighter plane ever built." Characteristics
F-22 Raptor displaying its F119-PW-100 engines on full afterburner
The F-22 is a fifth-generation fighter that is considered a fourth-generation stealth aircraft by the USAF. Its dual afterburning Pratt & Whitney F119-PW-100 turbofans incorporate thrust vectoring, but in the pitch axis only, with a range of ±20 degrees. The maximum thrust is classified, though most sources place it at about 35,000 lbf (156 kN) per engine. Maximum speed, without external weapons, is estimated to be Mach 1.72 in supercruise mode; as demonstrated by General John P. Jumper, former US Air Force Chief of Staff, when his Raptor exceeded Mach 1.7 without afterburners on 13 January 2005. With afterburners, it is "greater than Mach 2.0" (1,317 mph, 2,120 km/h), according to Lockheed Martin; however, the Raptor can easily exceed its design speed limits, particularly at low altitudes, with max-speed alerts to help prevent the pilot from exceeding them. Former Lockheed Raptor chief test pilot Paul Metz stated that the Raptor has a fixed inlet; but while the absence of variable intake ramps may theoretically make speeds greater than Mach 2.0 unreachable, there is no evidence to prove this. Such ramps would be used to prevent engine surge, but the intake itself may be designed to prevent this. Metz has also stated that the F-22 has a top speed greater than 1,600 mph (Mach 2.42) and its climb rate is faster than the F-15 Eagle due to advances in engine technology, despite the F-15's thrust-to-weight ratio of about 1.2:1, with the F-22 having a ratio closer to 1:1.The US Air Force claims that the F-22A cannot be matched by any known or projected fighter. 
Aircraft wing planform shapes: a KC-10 Extender (top) refuels an F-22 Raptor
The true top-speed of the F-22 is largely unknown to the general public, as engine power is only one factor. The ability of the airframe to withstand the stress and heat from friction is a further, key factor, especially in an aircraft using as many polymers as the F-22. However, while some aircraft are faster on paper, the internal carriage of its standard combat load allows the aircraft to reach comparatively higher performance with a heavy load over other modern aircraft due to its lack of drag from external stores. It is one of only a handful of aircraft that can sustain supersonic flight without the use of afterburner augmented thrust (and its associated high fuel usage). This ability is called supercruise. The F-22 is highly maneuverable, at both supersonic and subsonic speeds. The F-22's thrust vectoring nozzles allow the aircraft to turn tightly, and perform extremely high alpha (angle of attack) maneuvers such as the Herbst maneuver (or J-turn), Pugachev's Cobra, and the Kulbit, though the J-Turn is more useful in combat. The F-22 is also capable of maintaining a constant angle of attack of over 60°, yet still having some control of roll. During June 2006 exercises in Alaska, F-22 pilots demonstrated that cruise altitude has a significant effect on combat performance, and routinely attributed their altitude advantage as a major factor in achieving an unblemished kill ratio. AvionicsThe F-22's avionics include BAE Systems E&IS (formerly Sanders Associates) radar warning receiver (RWR) AN/ALR-94, and the Northrop Grumman AN/APG-77 Active Electronically Scanned Array (AESA) radar. The AN/APG-77 is possibly the most capable radar in active service, with both long-range target acquisition and low probability of interception of its own signals by enemy aircraft. The AN/ALR-94 is a passive receiver system capable of detecting the radar signals in the environment. Composed of more than 30 antennae smoothly blended into the wings and fuselage, it is described by the former head of the F-22 program at Lockheed Martin Tom Burbage as "the most technically complex piece of equipment on the aircraft." With greater range (250+ nmi) than the radar, it enables the F-22 to limit its own radar emission which might otherwise compromise its stealth. As the target approaches, AN/ALR-94 can cue the AN/APG-77 radar to keep track of its motion with a narrow beam, which can be as focused as 2° by 2° in azimuth and elevation. The AN/APG-77 AESA radar, designed for air-superiority and strike operations, features a low-observable, active-aperture, electronically-scanned array that can track multiple targets in all kinds of weather. The AN/APG-77 changes frequencies more than 1,000 times per second to reduce the chance of being intercepted. The radar can also focus its emissions to overload enemy sensors, giving the aircraft an electronic-attack capability. The radar’s information is processed by two Raytheon Common Integrated Processor (CIP)s. Each CIP operates at 10.5 billion instructions per second and has 300 megabytes of memory. Information can be gathered from the radar and other onboard and offboard systems, filtered by the CIP, and offered in easy-to-digest ways on several cockpit displays, enabling the pilot to remain on top of complicated situations. The Raptor’s software is composed of over 1.7 million lines of code, most of which concerns processing data from the radar.The radar 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. The F-22 has several unique functions for an aircraft of its size and role. For instance, it has threat detection and identification capability along the lines of that available on the RC-135 Rivet Joint. While the F-22's equipment isn't as powerful or sophisticated, because of its stealth, it can be typically hundreds of miles closer to the battlefield, which often compensates for the reduced capability. The F-22 is capable of functioning as a "mini-AWACS." Though reduced in capability compared to dedicated airframes such as the E-3 Sentry, as with its threat identification capability, the F-22's forward presence is often of benefit. The system allows the F-22 to designate targets for cooperating F-15s and F-16s, and even determine if two friendly aircraft are targeting the same enemy aircraft, thus enabling one of them to choose a different target.It is often able to identify targets hundreds of times faster than accompanying dedicated AWACS. The F-22's low probability of intercept radar is being given a high-bandwidth data transmission capability, to allow it to be used in a "broadband" role to permit high-speed relaying of data between friendly transmitters and receivers in the area. The F-22 can already pass data to other F-22s, resulting in considerably reduced radio "chatter." The IEEE-1394B data bus, developed for the F-22, was derived from the commercial IEEE-1394 bus system, often used on personal computers. The bus was subsequently deployed on the derivative F-35 Lightning II fighter. Armament
An F-22 releases a JDAM from its internal bay while flying at supersonic speed
The Raptor is designed to carry air-to-air missiles in internal bays to avoid disrupting its stealth capability. Launching missiles requires opening the weapons bay doors for less than a second, while the missiles are pushed clear of the airframe by hydraulic arms. The aircraft can also carry bombs such as the Joint Direct Attack Munition (JDAM) and the new Small-Diameter Bomb (SDB). The Raptor carries an M61A2 Vulcan 20 mm rotary cannon, also with a trap door, in the right wing root. The M61A2 is a last ditch weapon, and carries only 480 rounds; enough ammunition for approximately five seconds of sustained fire. Despite this, the F-22 has been able to use its gun in dogfighting without being detected, which can be necessary when missiles are depleted. As other air forces upgrade capabilities in the areas of air-to-air and air-to-ground munitions, one key aspect of the Raptor must be kept in mind. Its very high sustained cruise speeds, and operational altitude (something that is often ignored), add tremendously to the effective range of both air-to-air and air-to-ground munitions. Indeed, these factors could provide a strong rationale as to why the USAF has not pursued long-range, high-energy air-to-air missiles such as the MBDA Meteor. However the USAF plans to procure the AIM-120D AMRAAM, which will have a significant increase in range compared to the AIM-120C. The launch platform, in this case, provides the additional energy to the missile. This speed and altitude characteristic also helps improve the range of air-to-ground ordnance. While specific figures remain classified, it is expected that JDAMs employed by F-22s will have twice or more the effective range of munitions dropped by legacy platforms. In testing, a Raptor dropped a 1,000 lb (450 kg) JDAM from 50,000 feet (15,000 m), while cruising at Mach 1.5, striking a moving target 24 miles (39 km) away. The SDB, as employed from the F-22, should see even greater increases in effective range, due to the improved lift to drag ratio of these weapons. While in its air-superiority configuration, the F-22 carries its weapons internally, though it is not limited to this option. The wings are capable of supporting four detachable hardpoints. Each hardpoint is theoretically capable of handling 5,000 lb (2,300 kg) of ordnance. However, use of external stores greatly compromises the F-22's stealth, and has a detrimental effect on maneuverability, speed, and range. As many as two of these hardpoints are "plumbed", allowing the usage of external fuel tanks. The hardpoints are detachable in flight allowing the fighter to regain its stealth once these external stores are exhausted. Currently, there is research being conducted to develop a stealth ordnance pod and hardpoints for it. Such a pod would comprise a stealth shape and carry its weapons internally, then would split open when launching a missile or dropping a bomb. Both the pod and hardpoints could be detached when no longer needed. This system would allow the F-22 to carry its maximum ordnance load while remaining stealthy, albeit at a loss of maneuverability. However, there is concern over this program as external carriage of fuel tanks has shown more stress placed on the wings than originally anticipated. StealthAlthough several recent Western fighter aircraft are less detectable on radar than previous designs using techniques such as radar absorbent material-coated S-shaped intake ducts that shield the compressor fan from reflecting radar waves, the F-22A design placed a much higher degree of importance on low observance throughout the entire spectrum of sensors including radar signature, visual, infrared, acoustic, and radio frequency. The stealth of the F-22 is due to a combination of factors, including the overall shape of the aircraft, the use of radar absorbent material (RAM), and attention to detail such as hinges and pilot helmets that could provide a radar return. However, reduced radar cross section is only one of five facets that designers addressed to create a stealth design in the F-22. The F-22 has also been designed to disguise its infrared emissions to make it harder to detect by infrared homing ("heat seeking") surface-to-air or air-to-air missiles. Designers also addressed making the aircraft less visible to the naked eye, controlling radio transmissions, and noise abatement.The Raptor has an under bay carrier made for hiding heat from missile threats, like Surface-to-air missiles. The F-22 apparently relies less on maintenance-intensive radar absorbent material and coatings than previous stealth designs like the F-117. These materials caused deployment problems due to their susceptibility 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.[36] Furthermore, the F-22 has a warning system (called "Signature Assessment System" or "SAS") which presents warning indicators when routine wear-and-tear have degraded the aircraft's radar signature to the point of requiring more substantial repairs. The exact radar cross section of the F-22 remains classified. General characteristics
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© 2008 Farrhad A