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Fourth-generation fighter

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File:USAF F15.jpg
A "fourth generation" F-15 Eagle.

Aircraft classified as fourth generation jet fighters are those in service approximately from 1980-2010, representing the design concepts of the 1970s. Fourth generation designs are heavily influenced by lessons learned from the previous generation of combat aircraft. Representative fighters include the "teen" series of American fighters (F-14, F-15, F-16, and F/A-18) and the Soviet MiG-29 and Su-27. The growing costs and the demonstrated success of multi-role aircraft such as the F-4 Phantom II gave rise to the popularity of multi-role fighters. Long-range air-to-air missiles, originally thought to make dogfighting obsolete, proved less influential than expected; designers responded with a renewed emphasis on maneuverability.

The rapid advance of microcomputers in the 1980s and 90s permitted rapid upgrades to the avionics over the lifetimes of these fighters, incorporating system upgrades such as AESA, digital avionics buses, and IRST. Because of the drastic enhancement of capabilities in these upgraded fighters and in new designs of the 1990s that reflected these new capabilities, the designation 4.5th generation is sometimes used to refer to these later designs. It is intended to reflect a class of fighters that are evolutionary upgrades to the 4th generation to incorporate integrated avionics buses and elements of stealth technology. A prime example of this generation is the F/A-18E/F Super Hornet, an upgrade of the 1970s Hornet design. While the basic aerodynamic features remain the same, the Super Hornet features improved avionics in the form of an all-glass cockpit, a solid-state AESA fixed-array radar, new engines, the structural use of composite materials to reduce weight, and a slightly modified shape to minimize its radar signature.


List of 4th generation fighters

4.5th generation

5th generation designs

The American F-22 Raptor, put into production in 2004, is often regarded as the first of a new generation of fighters, termed the fifth generation. The key design difference between the F-22 and preceding designs is an emphasis on stealth. The in-development Joint Strike Fighter has also been designed for stealth, and the F-22 has influenced the continued development of the 4th generation designs, and the shape of design work for other countries' long-term fighter development projects (for instance, the rumoured J-XX project, and the Russian Mikoyan Project 1.44). This article will discuss the Raptor and, to some extent, the JSF, as contemporaries of the later 4th generation designs.

Design considerations

Performance

Perfomance has traditionally been one of the most important design characteristics, as it enables a fighter to gain a favorable position to use its weapons while rendering the enemy unable to use his. 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 he is unable to aim or fire his weapons and his hot exhaust makes a good target for IR-guided missiles. At long range, while optimal positions are not so clear, it is nonetheless an advantage to intercept enemy aircraft before they reach their targets.

These two scenarios have competing demands - interception requires excellent linear speed, while WVR engagements require excellent turn rate and acceleration. Prior to the 1970's, 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 visually identify targets. Though improvments 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 a secondary emphasis on maneuverability, interceptors have been relegated to a secondary role in the fourth generation, with a renewed emphasis on maneuverability.

There are two primary contributing factors to maneuverability - the amount of power delivered by the engines, and the ability of the aircraft's control surfaces to translate that power into changes in direction. Air combat manoeuvering (ACM) involves a great deal of energy management, where energy is roughly the sum of altitude and airspeed. The greater energy a fighter has, the more flexibility it has to move where it wants. An aircraft with little energy is immobile, and a defenseless target. Note that power does not necessarily equal speed; while more power gives greater acceleration, the maximum speed of an aircraft is determined by how much drag it produces. Herein lies the tradeoff. Low-drag configurations have small, stubby, 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.

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 lifing 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

Table of thrust-to-weight ratio and wing loading
Thrust/
Weight
Ratio 		wing
loading
kg/m² 		notes
Rafale F2 1.13 304 5300 l fuel internal
Typhoon 1.18 300 4700 l fuel internal
F-2 0.89 430
MiG-29SM 1.13 411
Su-27
Su-30 1.10 414 Indian Su-30MKI has thrust vectoring
J-10 1.10 300 Proposed upgrade will have thrust vectoring
Gripen 0.94 341
F-22A 1.2 342 13000 l fuel internal and 2D thrust vectoring
F-35A 0.83 446

Notes:

  • values are at normal takeoff weight unless otherwise specified
  • some of the takeoff weights and thrust values are not officially available; there is some considerable guesswork involved.

Thrust vectoring

Thrust vectoring is a new technology being introduced to further enhance a fighter's turning ability. 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 technology has been fitted to the Mikoyan MiG-35, Sukhoi Su-30MKI, F-35, and F-22 Raptor. The U.S. explored fitting the technology to the F-16 and the F-15, but decided against implementing them. There is some indication that the Typhoon may eventually be refitted with thrust vectoring.

Supercruise

Supercruise is the ability of aircraft to cruise efficiently at supersonic speeds without the afterburner. Because of parasitic drag effects, fighters carrying external weapons stores encounter excessive drag near the speed of sound, making it impossible or prohibitively fuel-consuming to break the sound barrier. Though fighters easily break Mach 1 and 2 in clean configurations on afterburner, and the English Electric Lightning was able to break Mach 1 without the use of afterburner, these were academic exercises as they were not carrying combat loads.

With improvements to engine power output and careful aeronautical design of weapons stores, it is now possible for fighters to supercruise with combat loads. The Typhoon, and the (fifth-generation) F-22 are the only modern fighters with this ability. Dassault claims the Rafale to be able to supercruise but this claim has yet to be demonstrated. The Typhoon can supercruise at Mach 1.5 with a combat load of six missiles and no tanks, or Mach 1.3 with a full combat load. Though specifications have not been claimed, the F-22 is believed to have superior supercruise ability, owing to its internal weapons stores.

Avionics

Avionics is a catch-all phrase 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 sensors (Radar and IR sensors), 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 protected. Since many export aircraft have downgraded avionics, many buyers substitute domestically developed avionics, sometimes considered superior to the original. For example, the Sukhoi Su-30MKI sold to India, the F-15I and F-16I sold to Israel, and the F-15K sold to South Korea.

The primary sensor for all modern fighters is radar. The U.S. pioneered the use of solid-state AESA radars, which have no moving parts and are capable of projecting a much tighter beam and quicker scans. It is fitted to F-15C, the F/A-18E/F Super Hornet, and the block 60 (export) F-16, and will be used for all future American fighters. A European coalition GTDAR is developing an AESA radar for use on the Typhoon and Rafale, and it is unknown if Russia or China are developing airborne AESA radars. For the next generation F-22 and F-35, the U.S. will utilize 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.

In reaction to the increasing American emphasis on radar-evading stealth designs, the Soviet Union turned to alternate sensors. This drove them to emphasize 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 are essentially a TV camera in the IR wavelength, passively measuring the emitted IR radiation from targets. However, 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. IRST sensors have now become standard on Russian aircraft. With the exception of the F-14D, no Western fighters carry built-in IRST sensors for air-to-air detection, though the similar FLIR is often used to acquire ground targets. The next-generation F-22 and F-35 will both have built-in IRST sensors, though the latter's is intended for ground targets.

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 of the modern European and American aircraft are capable of sharing targeting data with allied fighters and from 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.


Cost

The per unit cost is difficult to accurately determine, as the amortization of a large development cost over a varying number of units produced can greatly vary the price. Moreover, the purchase price does not reflect lifetime costs of maintenance, parts, and training. A useful guide to costs come from export prices, which are widely reported, and represent a mix of the marginal cost of production plus some recouperation of development costs.

Figures are in USD unless otherwise specified.

Maintenance Demands

As militaries make growing use of Operations Research and other management techniques from the corporate world to examine the effectiveness of hardware, a growing emphasis is being placed on maintenance and reliability. A prime example of this is the F/A-18 Hornet. While unimpressive on paper compared to its contemporaries, it incorporated a low-maintenance design. As a result, its mean time between failure is three times greater than any other Navy strike aircraft, and requires half the maintenance time. These greatly elevated its sortie rate and made it more effective than aircraft that were superior in a 1 on 1 comparison but which were more often than not unavailable to fight.

Stealth technology

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 from 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 1960's, 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) and were much more difficult to detect on radar.

During the 1970's, 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, 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.

Recent American fighter aircraft development has focused on stealth, and the recently deployed F-22 is the first fighter designed from the ground up with a consideration for stealth. However, the stealthiness of the F-22 from angles other than head-on is not clear. The F-35 incorporates the same degree of stealth shaping, although its exposed rear turbine blades render it significantly less stealthy from the rear (the thrust vectoring nozzles of the F-22 also serve to conceal the turbine blades). Several late 4-th generation fighters have been given stealth shaping and other refinements to reduce their RCS, including the Super Hornet, Typhoon, and Rafale.

It should be noted that stealth is considered mainly in terms of lack of visibility to other airborne radars. Ground-based, lower-frequency radars are less affected by stealth features. The Australian Jindalee over-the-horizon radar project is reported to be able to detect the wake turbulence of an aircraft regardless of its stealth capabilities . It remains to be seen whether a similar system can be devised that is small enough to fit into aircraft, and is suitable for tracking rather than simply a warning. Loss of stealth advantages would make the F-35 particularly vulnerable.

There are some reports that the Rafale’s avionics, the Thales Spectra, includes "stealthy" radar jamming technology, a radar cancellation systems 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; the French system is hypothesised to interfere with detection without revealing that jamming is in operation. In effect, such a system could potentially offer stealth advantages similar in effect to, but likely less effective than, the F-22 and JSF. However, it is unclear how effective the system is, or even whether it is fully operational yet.

As well, research continues into other ways of decreasing observability by radar. There are claims that the Russians are working on "plasma stealth", . Obviously, such techniques might well remove some of the current advantage of the F-22 and JSF, but American defence research also continues unabated.

There are 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

Comparative Analysis

It's misleading to extrapolate comparisons regarding these fighters from the combat history, as fighters function in a combined arms environment in which many other factors, including CI (command, control, communications, computers, and intelligence) assets and pilot training determine success. For example, the undefeated records of the F-15 and F-16 should not be taken as unambiguous indicators of their superiority as airframes, as their combat action involved action by well-trained American and Israeli pilots with superior training and CI assets against poorly trained adversaries with much poorer CI assets.

However, for purchasing considerations, nations often consider comparative analyses of fighters to fill their specific mission requirements. Additionally, joint exercises are often revealing about the performance of fighters in a system, even as their validity is compromised by the inherent assumptions about the systems on either side.

DERA study

Britain’s Defence Evaluation and Research Agency (now split into QinetiQ and DSTL) did an evaluation (simulation based on the available data) comparing the Typhoon with some other modern fighters in how well they performed against an expected adversary aircraft, the Sukhoi Su-35. Due to the lack of information gathered on the 5th generation combat aircraft and the Su-35 during the time of this study it is not meant to be considered official.

The study used real pilots flying the JOUST system of networked simulators. Various western aircraft supposed data were put in simulated combat against the Su-35. The results were:

Aircraft Odds vs.
Su-35
Lockheed Martin/Boeing F-22 Raptor 10.1:1
Eurofighter Typhoon 4.5:1
Sukhoi Su-35 'Flanker' 1.0:1
Dassault Rafale C 1.0:1
J-10 1.0:1
McDonnell Douglas F-15C Eagle 0.8:1
Boeing F/A-18+ 0.4:1
McDonnell Douglas F/A-18C 0.3:1
General Dynamics F-16C 0.3:1

These results mean, for example, that in simulated combat, 4.5 Su-35s were shot down for every Typhoon lost. Missiles such as the KS-172 may be intended for large targets and not fighters, but their impact on a long range BVR engagement needs to be factored in.

The "F/A-18+" in the study was apparently not the current F/A-18E/F, but an improved version. All the western aircraft in the simulation were using the AMRAAM missile, except the Rafale which was using the MICA missile. This does not reflect the likely long-term air-to-air armament of Eurofighters (as well as Rafales), which will ultimately be equipped with the longer-range MBDA Meteor (while carrying the AMRAAM as an interim measure).

Details of the simulation have not been released, making it harder to verify whether it gives an accurate evaluation (for instance, whether they had adequate knowledge of the Sukhoi and Raptor to realistically simulate their combat performance). Another problem with the study is the scenarios under which the combat took place are unclear; it is possible that they were deliberately or accidentally skewed to combat scenarios that favoured certain aircraft over others; For instance, long-range engagements favour planes with stealth, good radar and advanced missiles, whereas the Su-35’s alleged above-average manoeuverability may prove advantageous in short-range combat. Nor is it clear whether the Su-35 was modeled with thrust vector control (as the present MKIs, MKMs have).

Eventually, we shall not forget that the DERA simulation was made in the mid 90s with limited knowledge about the Radar Cross Section, the ECM and the radar performances of the actual aircraft : indeed, at that time, the 4th/5th generation fighters were all at the prototype stage.

Exercise reports

File:F-15 Su30 Mir2000.jpg
Two IAF HAL Su-30 MK (rear) and two IAF Mirage 2000 fly with two USAF F-15 (middle of V-formation) during Cope India '04. The Su-30s scored a kill ratio of 9:1 over the F-15s during the air exercise.

Friendly air forces regularly practice against each other in exercises, and when these air forces fly different aircraft some indication of the relative capabilities of the aircraft can be gained.

Chinese J-10s have always overcome their Flankers in their exercises adding more mystery to the already little known about aircraft.

The results of an exercise in 2004 pitting USAF F-15 Eagles against Indian Air Force Su-30MKs, Mirage 2000s, MiG-29s and even the elderly MiG-21 have been widely publicised, with the Indians winning "90% of the mock combat missions" . Another report claims that the kind of systemic factors mentioned in the previous section were heavily weighted against the F-15s. According to this report, the F-15s were outnumbered 3-to-1. The rules of the exercise also allowed the Indian side the use of a simulated AWACS providing location information, and allowed them to use the full fire-and-forget active radar of simulated MBDA Mica and AA-12 missiles. The F-15s, by contrast, were not permitted to simulate the full range of the AMRAAM (restricted to 32 km when the full range is claimed in the report to be over 100km), nor to use the AMRAAM’s own radar systems to guide itself in fire-and-forget mode (rather relying on the F-15’s internal radar for the purpose). None of the F-15s were equipped with the latest AESA radars, which are fitted to some, but not all, of the USAF’s F-15 fleet.

It is worth noting that the USAF is currently lobbying hard for as large a complement as possible of the F-22 and F-35, and evidence that present USAF equipment is inferior to potential enemy fighters is a useful lobbying tool.

In June 2005, a Eurofighter pilot was reportedly able, in a mock confrontation, to avoid two pursuing F-15s and outmanoeuvre them to get into shooting position.

References

  • Kelly, Orr (1990). Hornet: the inside story of the F/A-18. Novato: Presido Press. ISBN 0-89141-344-8.
  • Shaw, Robert (1985). Fighter Combat:Tactics and Maneuvering. Annapolis: Naval Institute Press. ISBN 0870210599.
  • Sweetman, Bill (2001). "Fighter Tactics". Jane's International Defense Review. Jane's. Retrieved 2006-04-10.
  • Kopp, Carlo (2002). "Lockheed-Martin F-35 Joint Strike Fighter Analysis 2002". Air Power Australia. Retrieved 2006-04-10.