Fourth-generation jet fighter

American McDonnell Douglas F-15 Eagle

Fourth-generation jet fighter is a general classification of fighter aircraft in service from approximately 1980 to present day, and represent design concepts of the 1970s. Fourth-generation designs are heavily influenced by lessons learned from the previous generation of combat aircraft. Long-range air-to-air missiles, originally thought to make dogfighting obsolete, proved less influential than expected precipitating a renewed emphasis on maneuverability. Meanwhile, the growing costs of military aircraft in general and the demonstrated success of aircraft such as the F-4 Phantom II gave rise to the popularity of multirole fighters in parallel with the advances marking the so-called fourth generation.

During the period in question, maneuverability was enhanced by relaxed static stability, made possible by introduction of the fly-by-wire (FBW) flight control system (FLCS), which in turn was possible due to advances in digital 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.^[1]

The further advance of microcomputers in the 1980s and 1990s permitted rapid upgrades to the avionics over the lifetimes of these fighters, incorporating system upgrades such as Active Electronically Scanned Array (AESA), digital avionics buses and Infra-red search and track (IRST). Due to the dramatic enhancement of capabilities in these upgraded fighters and in new designs of the 1990s that reflected these new capabilities, the US government has taken to using the designation 4.5th generation to refer to these later designs. This is intended to reflect a class of fighters that are evolutionary upgrades of the 4th generation incorporating integrated avionics suites, advanced weapons efforts to make the (mostly) conventionally designed aircraft nonetheless less easily detectable, and trackable as a response to advancing missile and radar technology (see stealth technology).^[2][3] Inherent airframe design features exist, and include masking of turbine-blades and application of advanced sometimes radar-absorbent materials, but not the distinctive low-observable configurations of the latest aircraft, referred to as fifth-generation fighters or aircraft such as the F-22 Raptor and the F-35 Lightning II.

The United States defines 4.5 generation fighter aircraft as fourth generation jet fighters that have been upgraded with AESA radar, high capacity data-link, enhanced avionics, and "the ability to deploy current and reasonably foreseeable advanced armaments."^[4][5]

Design considerations

Performance

The Chengdu J-10A features a canard delta design and a quadruplex fly by wire system.

General performance has traditionally been the most important class of design characteristics, as it enables a fighter to gain a favorable position to use its weapons while rendering the enemy unable to use theirs. This can occur at long range (beyond visual range or BVR) or short range (within visual range or WVR). At short range, the ideal position is to the rear of the enemy aircraft, where it is unable to aim or fire weapons and the hot exhaust makes a good target for infrared-guided missiles. At longer BVR range, the probability of a successful missile intercept is improved by launch at high energy, kinetic (the aircraft's speed towards its target) and potential (altitude advantage). Being able to maneuver violently, and without losing energy meanwhile increases the chance of evading enemy missiles, or escape out of range of the likely return-fire.

These two scenarios have competing demands—interception requires excellent linear speed, while Within Visual Range or WVR engagements require excellent turn rate, while maintaining speed, rapid acceleration, and availability of control at low speeds and high angle of attack.

The HAL Tejas conducting an inverted pass shown here is an example of fly-by-wire controls.

Prior to the 1970s, a popular view in the defense community was that missiles would render WVR combat obsolete and hence maneuverability useless. Combat experience proved this untrue due to the poor quality of missiles and the recurring need to identify targets visually. Though improvements in missile technology may make that vision a reality, experience has indicated that sensors are not foolproof and that fighters will still need to be able to fight and maneuver at close ranges. So whereas the premier third-generation jet fighters (e.g., the F-4 and MiG-23) were designed as interceptors with only a secondary emphasis on maneuverability, interceptors have been relegated to a secondary role in the fourth generation, with a renewed emphasis on maneuverability. While the trade-offs involved in combat aircraft design are again shifting towards BVR engagement, the management of the advancing environment of numerous information flows in the modern battle-space, and low-observability, arguably at the expense of maneuvering ability in close-combat, the application of thrust vectoring provides a way to maintain it, especially at low speed.

There are two primary contributing factors to maneuverability—the amount of thrust delivered by the engines, and the ability of the aircraft's control surfaces to efficiently generate aerodynamic forces, and hence alterations in the plane's direction. Air-combat maneuvering (ACM) involves a great deal of energy management. The greater energy a fighter has, the more flexibility it has to move where it wants. An aircraft with little energy is immobile, and becomes a defenseless target. Note that available thrust does not necessarily equal speed; while it does give greater acceleration, the maximum speed of an aircraft is also determined by how much drag it produces. Herein lies one important trade-off. Low-drag configurations have small, often highly swept wings that disrupt the airflow as little as possible. However, that also means they have greatly reduced ability to alter the airflow to maneuver the aircraft.

An F-16 on a mission near Iraq in 2003

There are two rough indicators of these factors. A plane's turning ability can be roughly measured by its wing loading, defined as the mass of the aircraft divided by the area of its lifting surfaces. A highly loaded wing has little capacity to produce additional lift, and so has limited turning ability, whereas a lightly loaded wing has much greater potential lifting power. A rough measure of acceleration is a plane's thrust-to-weight ratio.

Fly-by-wire

The F/A-18 inverted above an F-14 shown here is an example of fly-by-wire control.

The fourth generation jet fighter defining point is fly-by-wire, like 4.5 is defined on AESA radar. YF-16 was the world’s first aircraft intentionally designed to be slightly aerodynamically unstable. This technique, called "relaxed static stability" (RSS), was incorporated to further enhance the aircraft’s performance. Most aircraft are designed with positive static stability, which induces an aircraft to return to its original attitude following a disturbance. However, positive static stability; the tendency to remain in its current attitude; opposes the pilot’s efforts to maneuver. On the other hand, an aircraft with negative static stability will, in the absence of control input, readily deviate from level and controlled flight.

An aircraft with negative static stability can therefore be made more maneuverable. At supersonic airspeed, a negatively stable aircraft can exhibit positive static stability due to aerodynamic center migration.^[1][6] To counter this tendency to depart from controlled flight—and avoid the need for constant minute trimming inputs by the pilot—the 4th gen aircraft has a quadruplex (four-channel) fly-by-wire (FBW) flight control system (FLCS). The flight control computer (FLCC), which is the key component of the FLCS, accepts the pilot’s input from the stick and rudder controls, and manipulates the control surfaces in such a way as to produce the desired result without inducing a loss of control. The FLCC also takes thousands of measurements per second of the aircraft’s attitude, and automatically makes corrections to counter deviations from the flight path that were not input by the pilot. Coordinated turn is also achieved in the same way, processing thousands of instructions per second to synchronize yawing and rolling to minimize sideslip drag in turns.^[7]

Thrust vectoring

MiG-29OVT all-aspect thrust vectoring engine view

Thrust vectoring is a technology introduced to further enhance a fighter's turning ability, introduced in Soviet fighters. By redirecting the jet exhaust, it is possible to directly translate the engine's power into directional changes more efficiently than via the plane's control surfaces. The Sukhoi Su-27 was the first aircraft to display publicly thrust vectoring for pitch (called 2D TVC), making the aircraft highly maneuverable, capable of near-zero airspeed at high angles of attack without stalling, and dynamic aerobatics at low speeds like Pugachev's Cobra. The TVC nozzles of the MKI are mounted 32 degrees outward to longitudinal engine axis (i.e. in the horizontal plane) and can be deflected ±15 degrees in the vertical plane. This produces a corkscrew effect, greatly enhancing the turning capability of the aircraft.^[8] The MiG-35 with its RD-33OVT engines with the vectored thrust nozzles allows it to be the first twin-engine aircraft with vectoring nozzles that can move in two directions (that is, 3D TVC). Other existing thrust vectoring aircraft, like the Su-30MKI and the F-22, have nozzles that vector in one direction.^[9] The technology has been fitted to the Sukhoi Su-47 Berkut and later derivatives. The U.S. explored fitting the technology to the F-16 and the F-15, but only introduced it on the F-22 Raptor.

Supercruise

Rafale features supercruise^[1]

Supercruise is the ability of aircraft to cruise at supersonic speeds without the afterburner.

Because of parasitic drag effects, fighters carrying external weapons stores encounter a vastly increased drag divergence near the speed of sound. This can prevent safe acceleration through the transonic regime, or make it too fuel-expensive to be effective on missions. Meanwhile, maintaining supersonic speed without (periodic) afterburner use saves large quantities of fuel too, increasing the range at which an aircraft can in reality still take advantage of its full performance.

According to the German Air Force the Typhoon can cruise at about Mach 1.2 without afterburner.^[10] The manufacturer claims that the maximum level speed possible without reheat is Mach 1.5.^[11][12] An EF T1 DA (Development Aircraft trainer version) demonstrated supercruise (1,21M) with 2 SRAAM, 4 MRAAM and drop tank (plus one tonne flight test equipment, plus 700 kg more weight for the trainer version) during the Singapore evaluation.^[13]

The Dassault Rafale can supercruise, in dry power, even with four missiles and a 1,250-liter belly drop tank and even in the naval version (Rafale M).^[14][15]

Avionics

F-15E cockpit

Avionics is a catch-all term for the electronic systems aboard an aircraft, which have been growing in complexity and importance. The main elements of an aircraft's avionics are its communication and navigation systems, sensors (Radar and IR), computers and data bus, and user interface. Because they can be readily swapped out as new technologies become available, they are often upgraded over the lifetime of an aircraft. Details about these systems are highly classified. Thus, many export aircraft have downgraded avionics, and buyers often replace them with domestically developed avionics, sometimes considered superior to the original. Examples are the Sukhoi Su-30MKI sold to India, the F-15I and F-16I sold to Israel, and the F-15K sold to South Korea.

Zhuk-AE AESA radar

The primary sensor for all modern fighters is radar. The U.S. fielded its first modified F-15Cs equipped with APG-63(V)2 AESA radars,^[16] which have no moving parts and are capable of projecting a much tighter beam and quicker scans. Later on, it was introduced to the F/A-18E/F Super Hornet and the block 60 (export) F-16 also, and will be used for future American fighters. A European coalition GTDAR is developing an AESA radar for use on the Typhoon and Rafale, and Russia has an AESA radar on its MIG-35 and their newest Su-27 versions. For the next-generation F-22 and F-35, the U.S. will use Low Probability of Intercept (LPI) capacity. This will spread the energy of a radar pulse over several frequencies, so as not to trip the radar warning receivers that all aircraft carry.

The OLS-30 is a combined IRST/LR device.

In response to the increasing American emphasis on radar-evading stealth designs, Russia turned to alternate sensors, with emphasis on infra-red search and track (IRST) sensors, first introduced on the American F-101 Voodoo and F-102 Delta Dagger fighters in the 1960s, for detection and tracking of airborne targets. These measure IR radiation from targets. As a passive sensor, it has limited range, and contains no inherent data about position and direction of targets - these must be inferred from the images captured. To offset this, IRST systems can incorporate a laser rangefinder in order to provide full fire-control solutions for cannon fire or for launching missiles. Using this method, German MiG-29 using helmet-displayed IRST systems were able to acquire a missile lock with greater efficiency than USAF F-16 in wargame exercises. IRST sensors have now become standard on Russian aircraft. With the exception of the F-14D (officially retired as of September 2006), no 4th-generation Western fighters carry built-in IRST sensors for air-to-air detection, though the similar FLIR is often used to acquire ground targets.

The Eurofighter Typhoon designated '4.5th generation' (beginning with Tranche 1 Block 5 aircraft,^[17] while previously build aircraft are being retrofited since spring 2007^[18]) and the F-35s will have built-in, PIRATE IRST sensors, a feature adopted early in the design, meanwhile beginning in 2012 the Super Hornet will also have an IRST.^[19]

The tactical implications of the computing and data bus capabilities of aircraft are hard to determine. A more sophisticated computer bus would allow more flexible uses of the existing avionics. For example, it is speculated that the F-22 is able to jam or damage enemy electronics with a focused application of its radar. A computing feature of significant tactical importance is the datalink. All modern European and American aircraft are capable of sharing targeting data with allied fighters and AWACS planes (see JTIDS). The Russian MiG-31 interceptor also has some datalink capability, so it is reasonable to assume that other Russian planes can also do so. The sharing of targeting and sensor data allows pilots to put radiating, highly visible sensors further from enemy forces, while using that data to vector silent fighters toward the enemy.

Stealth technology

Eurofighter Typhoon has a largely conventional configuration, but exhibits a substantially lower radar cross-section than its predecessors.

Stealth technology is an extension of the notion of visual camouflage to modern radar and IR detection sensors. While not rendering an aircraft "invisible" as is popularly conceived, stealth makes an aircraft much more difficult to discern among the sky, clouds, or distant aircraft, conferring a significant tactical advantage. While the basic principles of shaping aircraft to avoid detection were known at least since the 1960s, it was not until the availability of supercomputers that shape computations could be performed from every angle, a complex task. The use of computer-aided shaping, combined with radar-absorbent materials, produced aircraft of drastically reduced radar cross section (RCS) that were much more difficult to detect on radar. Meanwhile advances in digital flight control make potentially destabilizing, or control-complicating effects of shape alterations easier to compensate for.

During the 1970s, the rudimentary level of stealth shaping (as seen in the faceted design of the F-117 Nighthawk) resulted in too severe a performance penalty to be used on fighters. Faster computers enabled smoother designs such as the B-2 Spirit, and thought was given to applying the basic ideas to decrease, if not drastically reduce, the RCS of fighter aircraft. These techniques are also combined with methods of decreasing the IR, visual, and aural signature of the aircraft. While fighters designated 4.5th generation under the US-devised system incorporate some low-observable features, so-called fifth generation fighters have more clearly been designed with this as a very high priority. The inclusion of this as a criterion for the designation of "fifth generation" serves to illustrate the degree to which US manufacturers and their clients appear to assign value to this capability.

The JF-17 Thunder Block I features diverterless supersonic inlets, which hides the fan blades and subsequently reduces its frontal radar cross section.

There are some reports that the Dassault Rafale's avionics, the Thales Spectra, includes "stealthy" radar jamming technology, and systems for the active cancellation of RADAR analogous to the acoustic noise suppression systems on the De Havilland Canada Dash 8. Conventional jammers make locating an aircraft more difficult, but their operation is itself detectable, with missiles being designed more recently to endeavor to follow the jamming itself. The French system is hypothesized to interfere with detection without revealing that jamming is in operation.

Such a system ought in principle to be able to make an aircraft entirely invisible, were it to be feasible to actively mimic an undisturbed RADAR signature (canceling all reflections, and compensating for any RADAR shadow) however such a system would be incalculably difficult and is not envisaged. Meanwhile the real effectiveness of systems that allegedly exist is unknown.

Research continues into other ways of decreasing observability by radar. There are claims that Russian researchers are working on "plasma stealth".^[20] Obviously, such techniques might well remove some of the envisaged advantages held by fifth generation aircraft, adding to skepticism over the real value of the "generation" label, which seems to assume the superiority and uniqueness of particular design philosophies.

There are in any case ways to detect fighters other than radar. For instance, passive infra-red sensors can detect the heat of engines, and even the sound of a sonic boom (which any supersonic aircraft will make) can be tracked with a network of sensors and computers. However, using these to provide precise targeting information for a long-range missile is considerably less straightforward than radar.

Combat performance

The F-15 and F-16 have the first and second best known overall combat records of modern jet fighters. F-15s have a claimed combat record of 101 victories and zero losses in actual air to air combat.^[21] Such statistics may be of limited use in comparing aircraft since the quality of the opposition and other factors are not taken into account.

• 1982 Lebanon War, Israeli Air Force credited their F-15s and F-16s with 86 air-to-air kills, mostly of MiG-21s and MiG-23s, while suffering no air-to-air losses of their own.
• Iran–Iraq War, saw the first instance of employing 4th generation jet fighters in open war. Iran used F-14s and Iraq deployed MiG-29s, although there are no reports of the two aircraft types actually engaging each other.

• Gulf War of 1991
  • On 17 January 1991, the first night of the Coalition counteroffensive, an Iraqi MiG-25PD shot down a U.S. Navy F/A-18C (piloted by Lt Cdr Scott Speicher), which was lost 29 nautical miles (54 km) southeast of Baghdad.^[22][23][24]
  • USAF F-15 pilots shot down five Iraqi MiG-29s.^[25]

• On 8 October 1996, after the escalation over Imia/Kardak a Greek Mirage 2000 fired an R550 Magic and shot down a Turkish F-16D over the Aegean Sea. The Turkish pilot died, while the co-pilot ejected and was rescued by Greek forces.

• During the Kargil Conflict between India and Pakistan in 1999, the Indian Air Force used Dassault Mirrage 2000s to drop laser-guided bombs. MiG-29s were used extensively to provide fighter escort to the Mirage 2000s. The Mirages successfully targeted Pakistani camps and logistic bases in Kargil. Two Mirage squadrons flew a total of 515 sorties, and in 240 strike missions dropped 55,000 kg (120,000 lb) of ordnance. The Pakistan Air Force did not take active part allowing the IAF Mirages to fly at will.

• 1999 Kosovo War
  • A Dutch F-16 pilot shot down a Yugoslavian MiG-29 and a USAF F-16 pilot also shot down a MiG-29.^[26][27]
  • USAF F-15 pilots shot down four MiG-29s.^[26]

• Eritrean-Ethiopian War. In February 1999, according to some reports, Ethiopian Su-27 pilots shot down four Eritrean MiG-29s. Some of these sources claim that the Ethiopian planes were flown by Russian pilots, and the Eritrean planes by Ukrainians. (It is certainly true that local pilots were trained by instructors from those nations.^[28])

• In the Libyan civil war of 2011, the Belgian Air Component had six F-16 Fighting Falcon fighter jets. The Royal Canadian Air Force deployed seven (six front line, one reserve) CF-18 fighters. The Royal Danish Air Force participated with six F-16AMs; four F-16s used for offensive operations, and the remaining two in reserve. French Air Force, which realized 35% of NATO's strikes, participated in the mission with 18 Mirage 2000s and 19 Rafales. The Italian government committed four Italian Air Force Tornado ECRs for SEAD operations, supported by two Tornado IDS variants in an air-to-air refuelling role and four F-16 ADF fighters as escort. After the transfer of authority to NATO and the decision to participate in strike air-ground operations, the Italian government assigned four Italian Air Force Eurofighters and four Tornado ECRs for NATO use. The Royal Netherlands Air Force provided six F-16AM fighters, four F-16s were flying patrol over Libya, while the other two kept in reserve. The Royal Norwegian Air Force initially deployed six F-16AMs to Souda Bay Air Base. The Qatar Armed Forces contributed with six Mirage 2000-5EDA fighters; the Qatari aircraft were stationed in Crete. The Spanish Armed Forces sent six EF-18 fighters to participate in air control, maritime surveillance and to help prevent the inflow of arms to the Libyan regime. The Royal Swedish Air Force sent eight JAS 39 Gripens for reconnaissance. This was first time a Gripen participated in an international military operation. Sweden were the only country neither a member of NATO nor the Arab League that participated in the no-fly zone. The Turkish Air Force participated with six F-16s for aerial operations. The United Arab Emirates Air Force sent six F-16 and six Mirage 2000 fighters to join the mission. The Royal Air Force were participating with 16 Tornados and 10 Typhoons. The United States participated with both F-15 and F-16 fighters.^{[citation needed]}

Exercise reports

A Sukhoi Su-30MKI of the Indian Air Force

Different air forces regularly practice against each other in exercises, and when they fly different aircraft some indication of the relative capabilities of the aircraft can be gained.^[29]

During the "Cope India '04" exercise (2004), USAF F-15 Eagles were pitted against Indian Air Force Su-30MKs, Mirage 2000s, MiG-29s and aging MiG-21s. The results have been widely publicized with the IAF winning a majority of the mock combat, although the USAF fought at a numerical disadvantage, and both sides without AWACS support thereby restricting BVR combat.^[30][31]

The "Cope India 2005" exercise was conducted with teams that used a combination of United States and Russian-designed aircraft. The Christian Science Monitor (CSM) reported that “both the Americans and the Indians won, and lost.”^[32] According to the same article the Indian air force designed Cope 2005 in that the rules of engagement be that the forces fight within visual range, and both forces could not take advantage of their long range sensors or weapons.^{[citation needed]}

In July 2007, the Indian Air Force fielded the Sukhoi Su-30MKI during the Indra-Dhanush exercise with Royal Air Force's Eurofighter Typhoon. This was the first time that the two jets had taken part in such an exercise.^[33][34] The IAF did not allow their pilots to use the radar of the MKIs during the exercise so as to protect the highly-classified N011M Bars.^[35] RAF Tornado pilots were candid in their admission of the Su-30 MKI's superior manoeuvring in the air, just as they had anticipated, but the IAF pilots were also impressed by the Typhoon's agility in the air.^[36]

Aircraft

Active

Country	Manufacturer	Aircraft	Introduced	Variants
China	Chengdu	J-10	2003	J-10B
	Shenyang	J-11	1998	J-11B,J-15, J-16
	Xian	JH-7	1992	JH-7A,JH-7B
France	Dassault	Mirage 2000	1982	N/D
		Rafale	2000
India	HAL	Tejas	2013	Mk 1
Japan  United States	Mitsubishi	F-2	2000	F-2A/B
Pakistan  China	PAC Chengdu	JF-17 Thunder	2007
Russia	Mikoyan	MiG-31	1982
		MiG-29	1983	M, K
	Sukhoi	Su-27	1984	Su-30, Su-33, Su-34, Su-35
Sweden	Saab	JAS 39 Gripen	1997
Taiwan	AIDC	F-CK-1 Ching-kuo	1994
United Kingdom  Germany  Italy	Panavia	Tornado ADV	1985
United Kingdom  Germany  Italy  Spain	Eurofighter	Typhoon	2003
United States	Grumman	F-14 Tomcat	1974
	General Dynamics (Lockheed Martin)	F-16 Fighting Falcon	1978
	McDonnell Douglas (Boeing)	F-15 Eagle	1976	F-15E, F-15J
		F/A-18 Hornet	1983	F/A-18E/F Super Hornet

In development

•  Russia
  • Mikoyan MiG-35

•  South Korea
  • FA-50

•  United States
  • Boeing F-15SE Silent Eagle

Canceled

•  Argentina
  • FMA SAIA 90
•  France
  • Dassault Mirage 4000
•  Israel
  • IAI Lavi
  • IAI Nammer
•  People's Republic of China
  • Chengdu J-9
  • Shenyang J-13
•  Romania
  • IAR 95
•  South Africa
  • Atlas Carver
•  Russia -  Soviet Union
  • Mikoyan Project 1.44
  • Sukhoi Su-47
  • Yakovlev Yak-141
  • Yak-43
  • Yakovlev Yak-45
•  Russia- Iran
  • M-ATF
•  United States
  • Northrop YF-17
  • Northrop F-20 Tigershark
•  Yugoslavia
  • Novi Avion

See also

• List of fighter aircraft

References

Notes

Bibliography