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 1990s 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 of the 4th generation to incorporate integrated avionics suite, advanced weapons, and elements of stealth technology (but not true stealth).
A prime example of this generation is the F/A-18E/F Super Hornet, a growth version of the 1970s Hornet design. While the basic aerodynamic features are largely the same, the Super Hornet features improved avionics in the form of an all-glass cockpit, a solid-state AESA active phased array radar, new engines, the structural use of composite materials to reduce weight, a slightly modified shape to minimize its radar signature, and IRST.
These two scenarios have competing demands — interception requires excellent linear speed, while WVR engagements require excellent turn rate and acceleration. Prior to the 1970s, a popular view in the defence 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 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 maneuvering (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 defenceless 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 trade-off. 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 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.
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 and later derivatives, and F-22 Raptor. The U.S. explored fitting the technology to the F-16 and the F-15, but only introduced it on the F-22 Raptor.
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 F-22 can supercruise over 1.5 Mach. According to the German Luftwaffe the Typhoon can cruise at about Mach 1.2 without afterburner.The manufacturer claims on their Austrian publicity website that the maximum speed possible without reheat is Mach 1.5. Rafale's supercruise capabilities have been described as marginal with the current engine (the aircraft failed to demonstrate the capability during the Singapore evaluation). A EF T1 DA (Development Aircraft trainer version) demonstrate Supercuise(1,21M) with 2 SRAAM, 4 MRAAM and drop tank (plus one tonne flight test equiment, plus 700 kg more weight for the trainer version) during the Singapore evaluation.
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 future American fighters. A European coalition GTDAR is developing an AESA radar for use on the Typhoon and Rafale, Russia has an AESA radar on MIG-35 and the newest SU-27 versions. 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. To offset this, IRST systems can incorporate laser rangefinders in order to provide full fire-control solutions for cannon fire or launching missiles. 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 next-generation Eurofighter Typhoon (beginning with Tranche 1 Block 5 aircraft, while previously build aircraft are being retrofited since spring 2007), F-22 and F-35 will all have built-in IRST sensors. Beginning in 2012 the Super Hornet will also have an IRST.
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.
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.
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 4.5th generation fighters have been given stealth shaping and other refinements to reduce their RCS, including the Super Hornet, Eurofighter Typhoon, Rafale, and HAL Tejas.
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 F-35. However, it is unclear how effective the system is, or even whether it is fully operational yet.
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 F-35, 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.
During the "Cope India '04" exercise (2004), USAF F-15 Eagles were pitted against Indian Air Force Su-30MKs, Mirage 2000s, MiG-29s and elderly MiG-21. The results have been widely publicized, with the Indians winning "90% of the mock combat missions". 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.” However, it also noted “that in a surprising number of encounters — particularly between the American F-16s and the Indian Sukhoi-30 MKIs — the Indian pilots came out the winners. 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. The article goes on to state that a retired Indian Air Force General stated that: "The Sukhoi is a... better plane than the F-16." The USAF was said to be “most impressed by the MiG-21 Bisons and the Su-30 MKIs”.
In June 2005, a Royal Air Force Eurofighter trainer two seater was reportedly able, in a mock confrontation, to avoid two pursuing F-15E fighter-bombers and outmaneuver them, to get into a shooting position.
During Exercise "Northern Edge 2006" (a simulated war game), in Alaska (June 2006), the F-22 reportedly proved its mettle against as many as 40 U.S Air Force simulated "enemy aircraft" during simulated battles. The Raptor is claimed to have achieved a 108:0 kill ratio at that exercise.
In April 2006, during a DACT exercise a F/A-18F Super Hornet from VFA-11 was able to get a brief gun track on a F-22. However, it should be noted that the F/A-18F and F-22 were within the safety margin, and a full gun track and kill was not recorded.
An F-16C pilot assigned to the 64th Aggressor Squadron gained the first-ever F-22 simulated kill in Red Flag, February 2007. [94th commander] Lt. Col. Dirk Smith told AFM. However, the F-22 "killed" its attacker with a simulated missile launch while the F-16s'simulated missile was enroute to the F-22. In essence, the F-16 had to kill itself to score a kill on the F-22. While all of the above is alleged to have happened it should be noted the following:
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.
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|
|Sukhoi Su-35 'Flanker'||1.0:1|
|Dassault Rafale C||1.0:1|
|McDonnell Douglas F-15C Eagle||0.8:1|
|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 an older version of 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 maneuverability 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).
Additionally, 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.