A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets by dropping bombs. The hallmarks of a fighter are its small size, speed and maneuverability.
Many fighters have secondary ground-attack capabilities, and some are dual-roled as fighter-bombers. Consequently, the term "fighter" is sometimes extended colloquially to include dedicated ground-attack aircraft.
Fighters are the primary means by which armed forces gain air superiority over their opponents in battle. Since at least World War II, achieving and maintaining this air superiority has been a key component of victory in warfare, particularly conventional warfare (as opposed to guerrilla warfare). The purchase, training and maintenance of a fighter fleet therefore consumes a substantial proportion of the defense budgets of modern armed forces.
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| An A-10 Thunderbolt II, F-86 Sabre, P-38 Lightning and P-51 Mustang fly in formation during an air show at Langley Air Force Base, Virginia. The formation displays two generations of U.S. Air Force fighter aircraft, and an attack aircraft (the A-10). |
Piston engine fighters
World War I
The word "fighter" was first used to describe a two-seater aircraft with sufficient lift to carry a machine gun and its operator as well as the pilot. The first such "fighters" belonged to the "gunbus" series of experimental gun carriers of the British Vickers company which culminated in the Vickers F.B.5 Gunbus of 1914. The main drawback of this type of aircraft was its lack of speed. It was quickly realized that an aircraft intended to destroy its kind in the air needed at least to be fast enough to catch its quarry.
Fortunately another type of military aircraft already existed, which was to form the basis for an effective "fighter" in the modern sense of the word. It was based on the small fast aircraft developed before the war for such air races as the Gordon Bennett Cup and Schneider Trophy. The military scout airplane was not expected to be able to carry serious armament, but rather to rely on its speed to be able to reach the location it was required to "scout" or reconnoiter and then return quickly to report – while at the same time making itself a difficult target for anti-aircraft artillery or enemy gun-carrying aircraft. British scout aircraft in this sense included theSopwith Tabloid and Bristol Scout; French equivalents included the light, fast Morane-Saulnier N.
In practice, soon after the actual commencement of the war, the pilots of small scout aircraft began to arm themselves with pistols, carbines, grenades, and an assortment of improvised weapons with which to attack enemy aircraft. It was inevitable that sooner or later means of effectively arming "scouts" would be devised. One method was to build a "pusher" scout such as the Airco DH.2, with the propeller mounted behind the pilot. The main drawback was that the high drag of a pusher type's tail structure meant that it was bound to be slower than an otherwise similar "tractor" aircraft. The other approach was to mount the machine gun armament on a tractor-type airplane in a manner that enabled the gun to fire outside the arc of the propeller.
Only two configuration options were practical initially for tractor aircraft. One involved having a second crew member added behind the pilot to aim and fire a swivel-mounted machine gun at enemy airplanes. However, this limited the area of coverage chiefly to the rear hemisphere, and the inability to effectively coordinate the pilot's maneuvering with the gunner's aiming, which reduced the accuracy and efficacy of the gunnery. This option was chiefly employed as a defensive measure on two seater reconnaissance aircraft from 1915 on. The alternative configuration mounted a gun on the upper wing to fire over the propeller arc. While more effective for offensive combat, since the pilot could move and aim the guns as a unit, this placement made determining the proper aim point more difficult. Furthermore, this location made it nearly impossible for a pilot to maneuver his aircraft and have access to the gun's breech – a very important consideration, given the tendency of early machine guns to jam – hence this was a stopgap solution. Nevertheless, a machine gun firing over the propeller arc did have some advantages, and was to remain in service from 1915 (Nieuport 11) until 1918 (Royal Aircraft Factory S.E.5). The British Foster mounting was specifically designed for this kind of application.
The need to arm a tractor scout with a forward-firing gun whose bullets passed through the propeller arc was evident even before the outbreak of war, and its approach motivated inventors in both France and Germany to devise a practical synchronization gear that could time the firing of the individual rounds to when the propeller was not in the way. Franz Schneider, a Swiss engineer, had patented such a device in Germany in 1913, but his original work was not followed up. French aircraft designer Raymond Saulnier patented a practical device in April 1914, but trials were unsuccessful because of the propensity of the machine gun employed to hang fire due to unreliable ammunition.
In December 1914, French aviator Roland Garros asked Saulnier to install his synchronization gear on Garros' Morane-Saulnier Type L. Unfortunately the gas-operated Hotchkiss machine gun had a firing cycle which caused the bullet to leave the weapon too late to effectively and consistently synchronize the gunfire with a spinning propeller. Because of this, the propeller blades were armored, and Garros' mechanic, Jules Hue, fitted metal wedges to the blades to protect the pilot fromricochets. Garros' modified monoplane was first flown in March 1915 and he began combat operations soon thereafter. Firing 8 mm (.323 in) solid copper bullets, Garros scored three victories in three weeks before he himself was shot down on 18 April and his airplane – along with its synchronization gear and propeller – was captured by the Germans.
However, the synchronization gear (called the Stangensteuerung in German, for "pushrod control system") devised by the engineers of Anthony Fokker's firm was the first gear to attract official sponsorship, and this would make the pioneeringFokker Eindecker monoplane a feared name over the Western Front, despite its being an adaptation of an obsolete pre-war French Morane-Saulnier racing airplane, with a mediocre performance and poor flight characteristics. The first victory for the Eindecker came on 1 July 1915, when Leutnant Kurt Wintgens, flying with the Feldflieger Abteilung 6 unit on the Western Front, forced down a Morane-Saulnier Type L two-seat "parasol" monoplane just east of Luneville. Wintgens' aircraft, one of the five Fokker M.5K/MG production prototype examples of the Eindecker, was armed with a synchronized, air-cooled aviation version of the Parabellum MG14 machine gun, which did not require armored propellers. In some respects, this was the first "true" fighter victory of military aviation history.
The success of the Eindecker kicked off a competitive cycle of improvement among the combatants, building ever more capable single-seat fighters. The Albatros D.I of late 1916, designed by Robert Thelen, set the classic pattern followed by almost all such aircraft for about twenty years. Like the D.I, they were biplanes (only very occasionally monoplanes or triplanes). The strong box structure of the biplane wing allowed for a rigid wing that afforded accurate lateral control, which was essential for fighter-type maneuvers. They had a single crew member, who flew the aircraft and also operated its armament. They were armed with two Maxim-type machine guns – which had proven much easier to synchronize than other types – firing through the propeller arc. The gun breeches were typically right in front of the pilot's face. This had obvious implications in case of accidents, but enabled jams (to which Maxim-type machine guns always remained liable) to be cleared in flight and made aiming much easier.
The use of metal in fighter aircraft was pioneered in World War I by Germany, as Anthony Fokker used chrome-molybdenum steel tubing (a close chemical cousin tostainless steel) for the fuselage structure of all his fighter designs, and the innovative German engineer Hugo Junkers developed two all-metal, single-seat fighter monoplane designs with cantilever wings: the strictly experimental Junkers J 2 private-venture aircraft, made with steel, and some forty examples of the Junkers D.I, made with corrugated duralumin, all based on his experience in creating the pioneering Junkers J 1 all-metal airframe technology demonstration aircraft of late 1915.
As collective combat experience grew, the more successful pilots such as Oswald Boelcke, Max Immelmann, andEdward Mannock developed innovative tactical formations and maneuvers to enhance their air units' combat effectiveness and accelerate the learning – and increase the expected lifespan – of newer pilots reaching the front lines.
Allied and – until 1918 – German pilots of World War I were not equipped with parachutes, so most cases of an aircraft catching fire, or structurally breaking up in flight were fatal. Parachutes were well-developed by 1918, and were adopted by the German flying services during the course of that year (the famous "Red Baron" was wearing one when he was killed), but the allied command continued to oppose their use, on various grounds
World War II
Aerial combat formed an important part of World War II military doctrine. The ability of aircraft to locate, harass, and interdict ground forces was an instrumental part of the German combined-arms doctrine, and their inability to achieve air superiority over Britain made a German invasion unfeasible. German Field Marshal Erwin Rommel noted the effect of airpower: "Anyone who has to fight, even with the most modern weapons, against an enemy in complete command of the air, fights like a savage against modern European troops, under the same handicaps and with the same chances of success."
During the 1930s, two different streams of thought about air-to-air combat began to emerge, resulting in two different approaches to monoplane fighter development. In Japan and Italy especially, there continued to be a strong belief that lightly armed, highly maneuverable single-seat fighters would still play a primary role in air-to-air combat. Aircraft such as the Nakajima Ki-27,Nakajima Ki-43 and the Mitsubishi A6M Zero in Japan, and the Fiat G.50 and Macchi C.200 in Italy epitomized a generation of monoplanes designed to this concept.
The other stream of thought, which emerged primarily in Britain, Germany, the Soviet Union, and the United States was the belief that the high speeds of modern combat aircraft and the g-forces imposed by aerial combat meant that dogfighting in the classic World War I sense would be impossible. Fighters such as the Messerschmitt Bf 109, the Supermarine Spitfire, the Yakovlev Yak-1 and the Curtiss P-40 Warhawk were all designed for high level speeds and a good rate of climb. Good maneuverability was desirable, but it was not the primary objective.
The 1939 Soviet-Japanese Battle of Khalkhyn Gol (11 May-31 August 1939),[2] and the subsequent initial German invasion of Poland the following day,[3] were too brief to provide much feedback to the participants for further evolution of their respective fighter doctrines. During the Winter War, the greatly outnumbered Finnish Air Force, which had adopted the German finger-four formation, bloodied the noses of Russia's Red Air Force, which relied on the less effective tactic of a three-aircraft delta formation.
Rocket-powered fighters
The first rocket-powered aircraft was the Lippisch Ente, which made a successful maiden flight in March 1928.[7] The only pure rocket aircraft ever to be mass-produced was the Messerschmitt Me 163 in 1944, one of several German World War II projects aimed at developing rocket-powered aircraft.[8] Later variants of the Me 262 (C-1a and C-2b) were also fitted with rocket powerplants, while earlier models were fitted with rocket boosters, but were not mass-produced with these modifications.[9]
The USSR experimented with a rocket-powered interceptor in the years immediately following World War II, the Mikoyan-Gurevich I-270. Only two were built.
In the 1950s, the British developed mixed-power jet designs employing both rocket and jet engines to cover the performance gap that existed in turbojet designs. The rocket was the main engine for delivering the speed and height required for high-speed interception of high-level bombers and the turbojet gave increased fuel economy in other parts of flight, most notably to ensure the aircraft was able to make a powered landing rather than risking an unpredictable gliding return. The Saunders-Roe SR.53 was a successful design and was planned to be developed into production when economics forced curtailment of most British aircraft programs in the late 1950s. Furthermore, rapid advancements in jet engine technology had rendered mixed-power aircraft designs like Saunders-Roe's SR.53 (and its SR.177 maritime variant) obsolete. The American XF-91 Thunderceptor (which was the first U.S. fighter to exceed Mach 1 in level flight) met a similar fate for the same reason, and no hybrid rocket-and-jet-engine fighter design has ever been placed into service. The only operational implementation of mixed propulsion was Rocket-Assisted Take Off (RATO), a system rarely used in fighters.
First generation subsonic jet fighters (mid-1940s to mid-1950s)
Main article: First generation jet fighter
The first generation of jet fighters comprises the initial, subsonic jet fighter designs introduced late in World War II and in the early post-war period. They differed little from their piston-engined counterparts in appearance, and many employed unswept wings. Guns remained the principal armament. The impetus for the development of turbojet-powered aircraft was to obtain a decisive advantage in maximum speed. Top speeds for fighters rose steadily throughout World War II as more powerful piston engines were developed, and had begun approaching the transonic flight regime where the efficiency of piston-driven propellers drops off considerably.
The first jets were developed during World War II and saw combat in the last two years of the war. Messerschmitt developed the first operational jet fighter, the Me 262. It was considerably faster than contemporary piston-driven aircraft, and in the hands of a competent pilot, was quite difficult for Allied pilots to defeat. The design was never deployed in numbers sufficient to stop the Allied air campaign, and a combination of fuel shortages, pilot losses, and technical difficulties with the engines kept the number of sorties low. Nevertheless, the Me 262 indicated the obsolescence of piston-driven aircraft. Spurred by reports of the German jets, Britain's Gloster Meteor entered production soon after and the two entered service around the same time in 1944. Meteors were commonly used to intercept the V-1 "buzz bomb", as they were faster than available piston-engined fighters. By the end of the war almost all work on piston-powered fighters had ended. A few designs combining piston and jet engines for propulsion – such as the Ryan FR Fireball – saw brief use, but by the end of the 1940s virtually all new combat aircraft were jet-powered.
Despite their advantages, the early jet fighters were far from perfect, particularly in the opening years of the generation. Their operational lifespans, especially for their gas turbine powerplants, could be measured primarily in hours; the engines themselves were fragile and bulky, and power could be adjusted only slowly. Many squadrons of piston-engined fighters were retained until the early-to-mid 1950s, even in the air forces of the major powers (though the types retained were the best of the World War II designs). Innovations including ejector seats and all-moving tailplanes were introduced in this period.
The Americans were one of the first to begin using jet fighters post-war. The Lockheed P-80 Shooting Star (soon re-designated F-80) was less elegant than the swept-wing Me 262, but had a cruise speed (660 km/h [410 mph]) as high as the combat maximum of many piston-engined fighters. The British designed several new jets, including the iconic de Havilland Vampire which was sold to the air forces of many nations.
The British transferred the technology of the Rolls-Royce Nene jet engine to the Soviets, who soon put it to use in their advanced Mikoyan-Gurevich MiG-15 fighters which were the first to introduce swept wings in combat, an innovation first proposed by German research which allowed flying much closer to the speed of sound than straight-winged designs such as the F-80. Their top speed of 1,075 km/h (668 mph) proved quite a shock to the American F-80 pilots who encountered them over Korea, along with their armament of two 23 mm cannons and a single 37 mm cannon compared to machine guns. Nevertheless, in the first jet-versus-jet dogfight in history, which occurred during the Korean War on 8 November 1950, an F-80 (as the P-80 had been redesignated) intercepted two North Korean MiG-15s near the Yalu River and shot them down.
The Americans responded by rushing their own swept-wing F-86 squadrons to battle against the MiGs which had similar trans-sonic performance. The two aircraft had different strengths, but were similar enough that the superior technology such as a radar ranging gunsight and skills of the veteran United States Air Force pilots allowed them to prevail.
The world's navies also transitioned to jets during this period, despite the need for catapult-launching of the new aircraft. Grumman's F9F Panther was adopted by the U.S. Navy as their primary jet fighter in the Korean War period, and it was one of the first jet fighters to employ anafterburner. The de Havilland Sea Vampire was the Royal Navy's first jet fighter. Radar was used on specialized night fighters such as the F3D Skyknight which also downed MiGs over Korea, and later fitted to the F2H Banshee and swept wing F7U Cutlass and F3H Demon as all-weather / night fighters. Early versions of Infra-red (IR)air-to-air missiles (AAMs) such as the AIM-9 Sidewinder and radar guided missiles such as the AIM-7 Sparrow which would be developed into the 21st century were first introduced on swept wing subsonic Demon and Cutlass naval fighters.
Second generation jet fighters (mid-1950s to early 1960s)
The development of second-generation fighters was shaped by technological breakthroughs, lessons learned from the aerial battles of the Korean War, and a focus on conducting operations in a nuclear warfare environment. Technological advances in aerodynamics, propulsion and aerospace building materials (primarily aluminium alloys) permitted designers to experiment with aeronautical innovations, such as swept wings, delta wings, and area-ruledfuselages. Widespread use of afterburning turbojet engines made these the first production aircraft to break the sound barrier, and the ability to sustain supersonic speeds in level flight became a common capability amongst fighters of this generation.
Fighter designs also took advantage of new electronics technologies that made effective radars small enough to be carried aboard smaller aircraft. Onboard radars permitted detection of enemy aircraft beyond visual range, thereby improving the handoff of targets by longer-ranged ground-based warning and tracking radars. Similarly, advances in guided missile development allowed air-to-air missiles to begin supplementing the gun as the primary offensive weapon for the first time in fighter history. During this period, passive-homing infrared-guided (IR) missiles became commonplace, but early IR missile sensors had poor sensitivity and a very narrow field of view (typically no more than 30°), which limited their effective use to only close-range, tail-chase engagements. Radar-guided (RF) missiles were introduced as well, but early examples proved unreliable. These semi-active radar homing (SARH) missiles could track and intercept an enemy aircraft "painted" by the launching aircraft's onboard radar. Medium- and long-range RF air-to-air missiles promised to open up a new dimension of "beyond-visual-range" (BVR) combat, and much effort was placed in further development of this technology.
The prospect of a potential third world war featuring large mechanized armies and nuclear weapon strikes led to a degree of specialization along two design approaches: interceptors, such as the English Electric Lightning and Mikoyan-Gurevich MiG-21F; and fighter-bombers, such as the Republic F-105 Thunderchief and the Sukhoi Su-7B. Dogfighting, per se, was de-emphasized in both cases. The interceptor was an outgrowth of the vision that guided missiles would completely replace guns and combat would take place at beyond visual ranges. As a result, interceptors were designed with a large missile payload and a powerful radar, sacrificing agility in favor of high speed, altitude ceiling and rate of climb. With a primary air defense role, emphasis was placed on the ability to intercept strategic bombers flying at high altitudes. Specialized point-defense interceptors often had limited range and little, if any, ground-attack capabilities. Fighter-bombers could swing,[citation needed] between air superiority and ground-attack roles, and were often designed for a high-speed, low-altitude dash to deliver their ordnance. Television- and IR-guided air-to-surface missiles were introduced to augment traditional gravity bombs, and some were also equipped to deliver anuclear bomb.
Third-generation jet fighters (early 1960s to circa 1970)
The third generation witnessed continued maturation of second-generation innovations, but it is most marked by renewed emphases on maneuverability and traditional ground-attack capabilities. Over the course of the 1960s, increasing combat experience with guided missiles demonstrated that combat would devolve into close-in dogfights. Analog avionics began to be introduced, replacing older "steam-gauge" cockpit instrumentation. Enhancements to improve the aerodynamic performance of third-generation fighters included flight control surfaces such as canards, powered slats, and blown flaps. A number of technologies would be tried for Vertical/Short Takeoff and Landing, but thrust vectoring would be successful on the Harrier jump jet.
Growth in air combat capability focused on the introduction of improved air-to-air missiles, radar systems, and other avionics. While guns remained standard equipment (early models of F-4 being a notable exception), air-to-air missiles became the primary weapons for air superiority fighters, which employed more sophisticated radars and medium-range RF AAMs to achieve greater "stand-off" ranges, however, kill probabilities proved unexpectedly low for RF missiles due to poor reliability and improvedelectronic countermeasures (ECM) for spoofing radar seekers. Infrared-homing AAMs saw their fields of view expand to 45°, which strengthened their tactical usability. Nevertheless, the low dogfight loss-exchange ratios experienced by American fighters in the skies over Vietnam led the U.S. Navy to establish its famous "TOPGUN" fighter weapons school, which provided a graduate-level curriculum to train fleet fighter pilots in advanced Air Combat Maneuvering (ACM) and Dissimilar Air Combat Training (DACT) tactics and techniques.
This era also saw an expansion in ground-attack capabilities, principally in guided missiles, and witnessed the introduction of the first truly effective avionics for enhanced ground attack, including terrain-avoidance systems. Air-to-surface missiles (ASM) equipped with electro-optical (E-O) contrast seekers – such as the initial model of the widely used AGM-65 Maverick – became standard weapons, and laser-guided bombs(LGBs) became widespread in effort to improve precision-attack capabilities. Guidance for such precision-guided munitions (PGM) was provided by externally mounted targeting pods, which were introduced in the mid-1960s.
It also led to the development of new automatic-fire weapons, primarily chain-guns that use an electric engine to drive the mechanism of a cannon; this allowed a single multi-barrel weapon (such as the 20 mm Vulcan) to be carried and provided greater rates of fire and accuracy. Powerplant reliability increased and jet engines became "smokeless" to make it harder to visually sight aircraft at long distances.
Dedicated ground-attack aircraft (like the Grumman A-6 Intruder, SEPECAT Jaguar and LTV A-7 Corsair II) offered longer range, more sophisticated night attack systems or lower cost than supersonic fighters. With variable-geometry wings, the supersonic F-111 introduced the Pratt & Whitney TF30, the first turbofan equipped with afterburner. The ambitious project sought to create a versatile common fighter for many roles and services. It would serve well as an all-weather bomber, but lacked the performance to defeat other fighters. The McDonnell F-4 Phantom was designed around radar and missiles as an all-weather interceptor, but emerged as a versatile strike bomber nimble enough to prevail in air combat, adopted by the U.S. Navy, Air Force and Marine Corps. Despite numerous shortcomings that would be not be fully addressed until newer fighters, the Phantom claimed 280 aerial kills, more than any other U.S. fighter over Vietnam.[11] With range and payload capabilities that rivaled that of World War II bombers such as B-24 Liberator, the Phantom would became a highly successful multirole aircraft.
Fourth generation jet fighters (circa 1970 to mid-1990s)
Fourth-generation fighters continued the trend towards multirole configurations, and were equipped with increasingly sophisticated avionics and weapon systems. Fighter designs were significantly influenced by the Energy-Maneuverability (E-M) theory developed by Colonel John Boyd and mathematician Thomas Christie, based upon Boyd's combat experience in the Korean War and as a fighter tactics instructor during the 1960s. E-M theory emphasized the value of aircraft specific energy maintenance as an advantage in fighter combat. Boyd perceived maneuverability as the primary means of getting "inside" an adversary's decision-making cycle, a process Boyd called the "OODA loop" (for "Observation-Orientation-Decision-Action"). This approach emphasized aircraft designs that were capable of performing "fast transients" – quick changes in speed, altitude, and direction – as opposed to relying chiefly on high speed alone.
E-M characteristics were first applied to the F-15 Eagle, but Boyd and his supporters believed these performance parameters called for a small, lightweight aircraft with a larger, higher-lift wing. The small size would minimize drag and increase the thrust-to-weight ratio, while the larger wing would minimize wing loading; while the reduced wing loading tends to lower top speed and can cut range, it increases payload capacity and the range reduction can be compensated for by increased fuel in the larger wing. The efforts of Boyd's "Fighter Mafia" would result in General Dynamics' (now Lockheed Martin's) F-16 Fighting Falcon.
The F-16's maneuverability was further enhanced by its being designed to be slightly aerodynamically unstable. This technique, called "relaxed static stability" (RSS), was made possible by introduction of the "fly-by-wire" (FBW) flight control system (FLCS), which in turn was enabled by advances in computers and system integration techniques. Analog avionics, required to enable FBW operations, became a fundamental requirement and began to be replaced by digital flight control systems in the latter half of the 1980s. Likewise, Full Authority Digital Engine Controls (FADEC) to electronically manage powerplant performance were introduced with the Pratt & Whitney F100 turbofan. The F-16's sole reliance on electronics and wires to relay flight commands, instead of the usual cables and mechanical linkage controls, earned it the sobriquet of "the electric jet". Electronic FLCS and FADEC quickly became essential components of all subsequent fighter designs.
Other innovative technologies introduced in fourth-generation fighters include pulse-Doppler fire-control radars (providing a "look-down/shoot-down" capability), head-up displays (HUD), "hands on throttle-and-stick" (HOTAS) controls, and multi-function displays (MFD), all of which have become essential equipment. Composite materials in the form of bonded aluminum honeycomb structural elements and graphite epoxy laminate skins began to be incorporated into flight control surfaces and airframe skins to reduce weight. Infrared search-and-track (IRST) sensors became widespread for air-to-ground weapons delivery, and appeared for air-to-air combat as well. "All-aspect" IR AAM became standard air superiority weapons, which permitted engagement of enemy aircraft from any angle (although the field of view remained relatively limited). The first long-range active-radar-homing RF AAM entered service with the AIM-54 Phoenix, which solely equipped the Grumman F-14 Tomcat, one of the few variable-sweep-wing fighter designs to enter production. Even with the tremendous advancement of Air to Air missiles in this era, internal guns were standard equipment.
Another revolution came in the form of a stronger reliance on ease of maintenance, which led to standardisation of parts, reductions in the numbers of access panels and lubrication points, and overall parts reduction in more complicated equipment like the engines. Some early jet fighters required 50 man-hours of work by a ground crew for every hour the aircraft was in the air; later models substantially reduced this to allow faster turn-around times and more sorties in a day. Some modern military aircraft only require 10 man-hours of work per hour of flight time, and others are even more efficient.
Aerodynamic innovations included variable-camber wings and exploitation of the vortex lift effect to achieve higher angles of attack through the addition of leading-edge extension devices such as strakes.
Unlike interceptors of the previous eras, most fourth-generation air-superiority fighters were designed to be agile dogfighters (although the Mikoyan MiG-31 and Panavia Tornado ADV are notable exceptions). The continually rising cost of fighters, however, continued to emphasize the value of multirole fighters. The need for both types of fighters led to the "high/low mix" concept which envisioned a high-capability and high-cost core of dedicated air-superiority fighters (like the F-15 and Su-27) supplemented by a larger contingent of lower-cost multi-role fighters (such as the F-16 and MiG-29).
Most fourth-generation fighter-bombers, such as the Boeing F/A-18 Hornet and Dassault Mirage 2000, are true multirole warplanes, designed as such from the start. This was facilitated by multimode avionics which could switch seamlessly between air and ground modes. The earlier approaches of adding on strike capabilities or designing separate models specialized for different roles generally became passé (with the Panavia Tornado being an exception in this regard). Dedicated attack roles were generally assigned either to interdiction strike aircraft such as the Sukhoi Su-24 and Boeing F-15E Strike Eagle or to armored "tank-plinking" close air support (CAS) specialists like the Fairchild-Republic A-10 Thunderbolt II and Sukhoi Su-25.
A typical US Air Force fighter wing of the era might contain a mix of: one air superiority squadron (F-15C), one strike fighter squadron (F-15E), and two multirole fighter squadrons (F-16C).[12]
Perhaps the most novel technology to be introduced for combat aircraft was "stealth", which involves the use of special "low-observable" (L-O) materials and design techniques to reduce the susceptibility of an aircraft to detection by the enemy's sensor systems, particularly radars. The first stealth aircraft to be introduced were the Lockheed F-117 Nighthawk attack aircraft (introduced in 1983) and the Northrop Grumman B-2 Spirit bomber (which first flew in 1989). Although no stealthy fighters per se appeared amongst the fourth generation, some radar-absorbent coatings and other L-O treatments developed for these programs are reported to have been subsequently applied to fourth-generation fighters.
4.5th generation jet fighters (1990s to the present)
The end of the Cold War in 1991 led many governments to significantly decrease military spending as a "peace dividend". Air force inventories were cut, and research and development programs intended to produce what was then anticipated to be "fifth-generation" fighters took serious hits; many programs were canceled during the first half of the 1990s, and those which survived were "stretched out". While the practice of slowing the pace of development reduces annual investment expenses, it comes at the penalty of increased overall program and unit costs over the long-term. In this instance, however, it also permitted designers to make use of the tremendous achievements being made in the fields of computers, avionics and other flight electronics, which had become possible largely due to the advances made in microchip and semiconductortechnologies in the 1980s and 1990s. This opportunity enabled designers to develop fourth-generation designs – or redesigns – with significantly enhanced capabilities. These improved designs have become known as "Generation 4.5" fighters, recognizing their intermediate nature between the 4th and 5th generations, and their contribution in furthering development of individual fifth-generation technologies.
The primary characteristics of this sub-generation are the application of advanced digital avionics and aerospace materials, modest signature reduction (primarily RF "stealth"), and highly integrated systems and weapons. These fighters have been designed to operate in a "network-centric" battlefield environment and are principally multirole aircraft. Key weapons technologies introduced include beyond-visual-range (BVR) AAMs; Global Positioning System (GPS)-guided weapons, solid-state phased-array radars; helmet-mounted sights; and improved secure, jamming-resistant datalinks. Thrust vectoring to further improve transient maneuvering capabilities have also been adopted by many 4.5th generation fighters, and uprated powerplants have enabled some designs to achieve a degree of "supercruise" ability. Stealth characteristics are focused primarily on frontal-aspect radar cross section (RCS) signature-reduction techniques including radar-absorbent materials (RAM), L-O coatings and limited shaping techniques.
"Half-generation" designs are either based on existing airframes or are based on new airframes following similar design theory as previous iterations; however, these modifications have introduced the structural use of composite materials to reduce weight, greater fuel fractions to increase range, and signature reduction treatments to achieve lower RCS compared to their predecessors. Prime examples of such aircraft, which are based on new airframe designs making extensive use of carbon-fibre composites, include the Eurofighter Typhoon, Dassault Rafale, and Saab JAS 39 Gripen.
Apart from these fighter jets, most of the 4.5 generation aircraft are actually modified variants of existing airframes from the earlier fourth generation fighter jets. Such fighter jets are generally heavier and examples include the Boeing F/A-18E/F Super Hornet which is an evolution of the 1970s F/A-18 Hornet design, the F-15E Strike Eaglewhich is a ground-attack/multi-role variant of the Cold War-era F-15 Eagle, the Sukhoi Su-30MKI and the Sukhoi Su-30MKK which are further developments of the Su-30fighter and the MiG-29M and MiG-35, upgraded versions of the 1980s MiG-29. The Su-30MKI, Su-MKK and MiG-35 use two- and three-dimensional thrust vectoringengines respectively so as to enhance maneuvering. The Chengdu J-10B incorporates an Active Electronically Scanned Array (AESA) radar for reduced cross section and DSI and IRST and vertical stabelisers fitted under the wings. Planned upgrades to the JF-17 Thunder are expected to also incproprate a AESA radar and reduced cross section measures. Most 4.5 generation aircraft are being retrofitted with AESA radars and other state-of-the art avionics such as electronic counter-measure systems and forward looking infrared.
4.5 generation fighters first entered service in the early 1990s, and most of them are still being produced and evolved. It is quite possible that they may continue in production alongside fifth-generation fighters due to the expense of developing the advanced level of stealth technology needed to achieve aircraft designs featuring very low observables (VLO), which is one of the defining features of fifth-generation fighters. Of the 4.5th generation designs, only the Super Hornet, Strike Eagle, and the Rafale have seen combat action.
The United States Government defines 4.5 generation fighter aircraft as those that "(1) have advanced capabilities, including— (A) AESA radar; (B) high capacity data-link; and (C) enhanced avionics; and (2) have the ability to deploy current and reasonably foreseeable advanced armaments."[13][14]
Fifth generation jet fighters (2005 to the present)
The fifth generation was ushered in by the Lockheed Martin/Boeing F-22 Raptor in late 2005. Currently the cutting edge of fighter design, fifth-generation fighters are characterized by being designed from the start to operate in a network-centric combat environment, and to feature extremely low, all-aspect, multi-spectral signatures employing advanced materials and shaping techniques. They have multifunction AESA radars with high-bandwidth, low-probability of intercept (LPI) data transmission capabilities. The Infra-red search and track sensors incorporated for air-to-air combat as well as for air-to-ground weapons delivery in the 4.5th generation fighters are now fused in with other sensors for Situational Awareness IRST or SAIRST, which constantly tracks all targets of interest around the aircraft so the pilot need not guess when he glances. These sensors, along with advanced avionics, glass cockpits, helmet-mounted sights (not currently on F-22), and improved secure, jamming-resistant LPI datalinks are highly integrated to provide multi-platform, multi-sensor data fusion for vastly improved situational awareness while easing the pilot's workload.[15] Avionics suites rely on extensive use of very high-speed integrated circuit (VHSIC) technology, common modules, and high-speed data buses. Overall, the integration of all these elements is claimed to provide fifth-generation fighters with a "first-look, first-shot, first-kill capability".
The AESA radar offers unique capabilities for fighters (and it is also quickly becoming a sine qua non for Generation 4.5 aircraft designs, as well as being retrofitted onto some fourth-generation aircraft). In addition to its high resistance to ECM and LPI features, it enables the fighter to function as a sort of "mini-AWACS," providing high-gain electronic support measures (ESM) andelectronic warfare (EW) jamming functions.
Other technologies common to this latest generation of fighters includes integrated electronic warfare system (INEWS) technology, integrated communications, navigation, and identification (CNI) avionics technology, centralized "vehicle health monitoring" systems for ease of maintenance, fiber optics data transmission, stealth technologyand even hovering capabilities.
Maneuver performance remains important and is enhanced by thrust-vectoring, which also helps reduce takeoff and landing distances. Supercruise may or may not be featured; it permits flight at supersonic speeds without the use of the afterburner – a device that significantly increases IR signature when used in full military power.
A key attribute of fifth-generation fighters is very-low-observables stealth. Great care has been taken in designing its layout and internal structure to minimize RCS over a broad bandwidth of detection and tracking radar frequencies; furthermore, to maintain its VLO signature during combat operations, primary weapons are carried in internal weapon bays that are only briefly opened to permit weapon launch. Furthermore, stealth technology has advanced to the point where it can be employed without a tradeoff with aerodynamics performance, in contrast to previous stealth efforts. Some attention has also been paid to reducing IR signatures, especially on the F-22. Detailed information on these signature-reduction techniques is classified, but in general includes special shaping approaches, thermoset and thermoplastic materials, extensive structural use of advanced composites, conformal sensors, heat-resistant coatings, low-observable wire meshes to cover intake and cooling vents, heat ablating tiles on the exhaust troughs (seen on the Northrop YF-23), and coating internal and external metal areas with radar-absorbent materials and paint (RAM/RAP).
The expense of developing such sophisticated aircraft is as high as their capabilities. The U.S. Air Force had originally planned to acquire 650 F-22s, but now only 187 will be built. As a result, its unit flyaway cost (FAC) is around US$150 million. To spread the development costs – and production base – more broadly, the Joint Strike Fighter (JSF) program enrolls eight other countries as cost- and risk-sharing partners. Altogether, the nine partner nations anticipate procuring over 3000 Lockheed Martin F-35 Lightning II fighters at an anticipated average FAC of $80–85 million. The F-35, however, is designed to be a family of three aircraft, a conventional take-off and landing (CTOL) fighter, a short take-off and vertical landing (STOVL) fighter, and a Catapult Assisted Take Off But Arrested Recovery (CATOBAR) fighter, each of which has a different unit price and slightly varying specifications in terms of fuel capacity (and therefore range), size and payload.
Other countries have initiated fifth-generation fighter development projects, with Russia's Sukhoi PAK FA and Mikoyan LMFS. In October 2007, Russia and India signed an agreement for joint participation in a Fifth-Generation Fighter Aircraft Program (FGFA), which will give India responsibility for development of a two-seat model of the PAK-FA. In December 2010, it was discovered that China is developing the 5th generation fighter Chengdu J-20.[16] The J-20 took its maiden flight in January 2011 and is planned to be deployed in 2017-19 time frame.[17] India is also developing its own indigenous fifth generation aircraft named Medium Combat Aircraft. Japan is exploring their technical feasibility to produce fifth-generation fighters.
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