Fourth-generation fighter jets have been operational since around 1980, represent 1970s design concepts. These designs were influenced by experiences with previous generations of combat aircraft.
Third-generation fighters focused mainly on interception, prioritizing speed and air-to-air missiles, often compromising maneuverability.
However, supersonic dogfights proved impractical, with combats quickly becoming subsonic and close-range, leaving these fighters vulnerable. This reality renewed interest in maneuverability for the fourth-generation fighter.
The rise of multirole combat aircraft also characterized this period, particularly due to the escalating costs of military aircraft and the success of models like the F-4 Phantom II.
Relaxed static stability enhanced maneuverability, facilitated by the advent of fly-by-wire (FBW) systems, enabled by advancements in digital computing and system-integration techniques.
By the late 1980s, analog avionics began giving way to digital flight-control systems, driven by the proliferation of microcomputers.
Advancements in the 1980s and 1990s allowed for continuous avionic upgrades, incorporating features such as active electronically scanned array (AESA) and infra-red search and track.
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Aircraft reflecting these enhancements are sometimes termed as 4.5 generation fighters, exhibiting evolutionary upgrades like integrated avionics suites and advanced armaments.
These upgrades aim to make these conventionally designed aircraft less detectable and trackable, responding to advancements in missile and radar technology.
However, they don’t incorporate the distinctive low-observable configurations found in fifth-generation fighters like the Lockheed Martin F-22 Raptor.
The United States categorizes 4.5-generation fighters as upgraded fourth-generation jets equipped with AESA radar, high-capacity data-link, advanced avionics, and the capacity to deploy advanced armaments.
Examples of such aircraft include the Boeing F/A-18E/F Super Hornet, CAC/PAC JF-17 block III, Chengdu J-10C, Dassault Rafale, Eurofighter Typhoon, HAL Tejas MK1A, Lockheed Martin F-16E/F/V Block 70/72, McDonnell Douglas F-15E/EX Strike Eagle/Eagle II, Mikoyan MiG-35, Mitsubishi F-2, Saab JAS 39E/F Gripen, Shenyang J-15B/J-16, and Sukhoi Su-30SM/Su-34/Su-35.
Fourth-Generation Fighter Performance Outcomes
Third-generation jet fighters like the F-4 and MiG-23 prioritized interception, with maneuverability as a secondary focus.
In contrast, fourth-generation fighters emphasize close-range dogfighting and maneuverability, with interception as a secondary role.
However, design trade-offs are increasingly favoring beyond visual range (BVR) engagement and low-observability over close combat maneuvering.
Despite this, thrust vectoring maintains maneuverability, particularly at low speeds. Enhanced maneuverability in fourth-generation models is due to high engine thrust, powerful control surfaces, and relaxed static stability (RSS).
Fly-by-wire technology enables RSS, allowing more effective air combat maneuvering and energy management under varied flight conditions.
The Hawker Siddeley Harrier first introduced thrust vectoring for vertical takeoff and landing. Pilots developed “viffing” to boost maneuverability. The Sukhoi Su-27 was the first to display enhanced maneuverability using thrust vectoring in pitch publicly.
This technology and a high thrust-to-weight ratio let it perform high angles of attack aerobatics like Pugachev’s Cobra without stalling.
The Sukhoi Su-30MKI’s three-dimensional TVC nozzles, mounted 32° outward, can create a corkscrew effect to enhance turning capability. The MiG-35 has RD-33OVT engines with vectored thrust nozzles, making it the first twin-engine to have 3D TVC.
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Unlike the MiG-35, aircraft like the F-22 have nozzles that vector in one direction. The technology also features in the Sukhoi Su-47 Berkut and its derivatives.
The U.S. explored this technology for the F-16 and the F-15 but only implemented it with the fifth-generation fighters.
Fly by Wire
Fly-by-wire describes the computer-controlled automation of flight control surfaces. Early fourth-generation fighters, like the F-15 Eagle and F-14 Tomcat, used electromechanical flight hydraulics. Later models extensively adopted fly-by-wire technology.
The General Dynamics YF-16 was designed to be aerodynamically unstable, pioneering relaxed static stability (RSS) to enhance performance.
Typically, aircraft have positive static stability, leading them to return to original attitudes after disturbances.
But, this stability opposes maneuvering efforts by pilots. Negative static stability allows an aircraft to deviate readily from controlled flight without control input.
It makes an unstable aircraft more maneuverable. Such aircraft necessitate computerized fly-by-wire systems to maintain their flight path.
Lastly, some derivatives, like the F-15SA Strike Eagle, have been upgraded to include fly-by-wire technology.
The principles of shaping aircraft to evade radar were known since the 1960s. However, radar-absorbent materials made such designs practical.
In the 1970s, early stealth technology created the faceted airframe of the Lockheed F-117 Nighthawk.
This aircraft’s design caused radar beams to reflect directionally, creating brief “twinkles”. Most detection systems considered these twinkles as noise.
Despite using digital FBW for stability and control, the aerodynamic penalties were substantial. Thus, the F-117 mainly undertook night ground-attack roles.
Stealth technology also aims to reduce infrared, visual, and acoustic signatures of aircraft.
4.5 The Next Generation
The term “4.5 generation” usually refers to advanced fighters developed since the 1990s. These exhibit some features of the fifth generation. Yet, they lack others. Thus, 4.5-generation fighters are generally less costly and less complex.
They also have shorter development times compared to true fifth-generation aircraft. However, they maintain advanced capabilities over original fourth-generation ones. These include advanced sensor integration and AESA radar.
Supercruise capability and supermaneuverability are also significant features. Additionally, they have broad multi-role capability and reduced radar cross-section.
Aircraft like the Dassault Rafale have introduced integrated IRST systems, including the optronique secteur frontal integrated IRST. The Eurofighter Typhoon features the PIRATE-IRST.
Even the Super Hornet has IRST, attached as a separate pod. Advances in materials and design have allowed smoother airframes and retrospective application of stealth technology to existing models.
Many 4.5 generation models incorporate low-observable features and prioritize reducing radar visibility. Models like the JF-17 and Chengdu J-10B/C employ diverterless supersonic inlet and other radar-evading technologies. The KAI KF-21 Boramae, a South Korean-Indonesian program, represents a typical ‘4.5th generation’ model in functionality.