Military & Aerospace

Contours of a Sixth-Generation Fighter Aircraft
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Issue Vol. 35.4 Oct-Dec 2020 | Date : 09 Feb , 2021

F-35

The air combat that took place during Pakistan Air Force (PAF) riposte on March 27, 2019, as a response to the Indian Air Force’s (IAF) Balakot strikes, rekindled interest in fighter aircraft technologies and air combat capabilities. Combat aviation has not only become the most preferred means of prosecution of war, it has seen the fastest growth of technology. World War II featured fighter combat on a larger scale than any other conflict to date. As technology grew, the pilot was not just flying the aircraft accurately and safely, but was also a weapon systems manager and operator. After the advent of jet age, aviation community started classifying jet fighters by “generations”. There are no official definitions and they just represent stages in the development of fighter design, performance capabilities and technological evolution. Most air forces currently operate fourth-generation aircraft. There are a few fifth-generation aircraft flying and the sixth-generation aircraft are on the drawing boards and technologies are evolving.

The current pace of research is driven by an assessment that development of a successor to the current fifth-generation fighters will take many decades and is better started sooner rather than later. Countries such as the United States (US) already have years of experience of developing and flying sixth-generation fighters. There are others that have skipped or given up on their attempt to build fifth-generations jets, and would rather focus on tomorrow’s technologies. France, Germany and the United Kingdom, are developing the sixth-generation Future Combat Air System (FCAS) and the BAE Systems Tempest fighters. Russia is still developing and simultaneously deploying the Su-57 stealth fighter and is talking about the conceptual sixth-generation MiG-41 interceptor. Japan is contemplating the F-3 sixth-generation stealth jet. China has begun inducting the J-20 fifth-generation and the second J-31 is still evolving. Meanwhile, India is still refining the technology for the manufacture of fourth and fifth-generation aircraft and evolving the Advanced Medium Combat Aircraft (AMCA).

Initial Fighter Aircraft Generations

The first generation of jet fighters comprised the initial, sub-sonic jet fighter designs introduced late in World War II, many had un-swept wings and only guns as the principal armament. American F-86 Sabre and Soviet MiG-15s were first with swept wings and near transonic performance. Grumman F9F Panther was the first aircraft with an afterburner engine. Early versions of Infra-Red (IR) Air-to-Air Missiles (AAM) and radar guided missiles came up in 1950s. The second generation fighters evolved by mid 1950s and had better aerodynamic design (Swept and Delta wings), propulsion systems (afterburner) and used aluminum alloys and were able to break the sound barrier. Radars became small enough to be carried aboard smaller aircraft and greatly aided the pilot in target acquisition and weapon aiming. IR missiles became commonplace. Radar-guided (RF) missiles were introduced with the capability of Beyond-Visual-Range (BVR) combat. BVR allowed building the concept of the interceptor. However, based on experience in Korea and Vietnam, the third-generation aircraft that came around mid-1960s believed that combat would still devolve around close-in dogfights using IR missiles.

Analog avionics began replacing the older cockpit instrumentation and started taking over part of the pilot functions. Flight Control surfaces such as canards, slats and blown flaps greatly improved turning performance. Thrust vectoring evolved for Harrier vertical and short take-off and landing. Medium-range RF AAMs gave greater “stand-off” ranges. New techniques for Electronic Counter Measures (ECM) were introduced. US Navy established its famous TOPGUN fighter weapons school. Advanced Air Combat Manoeuvering (ACM) and Dissimilar Air Combat Training (DACT) began. Terrain avoidance radar made it possible to fly at very low level at night. Air-to-Surface Missiles and Laser Guided Bombs (LGB) increased stand-off weapon delivery distances. Power-plant reliability increased and jet engines became “smokeless” to make it harder to sight aircraft at long distances. Variable-geometry wings were introduced on aircraft such as the F-111 and MiG-23. Very high speeds of aircraft necessitated development of ejection seats for safe exit during emergency. Ejection seats are nowadays designed for use at zero-speed on ground. Quick response G-suits allow sustaining higher ‘G’ forces.

Fourth Generation Plus

Fourth-generation fighters strengthened the trend towards multi-role configurations. Concept of ‘energy-manoeuverability’ impacted aircraft designs that required performing ‘fast transients’ – quick changes in speed, altitude and direction – as opposed to relying mostly on high speed. It called for small lightweight aircraft with higher thrust-weight ratio. Thus the F-16, MiG-29 and Mirage-2000 evolved. Fly-By-Wire (FBW) flight controls became possible due to advances in computers and system integration and this allowed relaxed static stability flight and in turn agility. Analog systems began to be replaced by digital flight control systems in the late 1980s. Likewise, Full Authority Digital Engine Controls (FADEC) to electronically manage power-plant performance was introduced. Both allowed carefree manoeuvering by the pilot. Pulse-Doppler fire-control-radars added Look-down/Shoot-down capability. Head-up Displays (HUD), Hands-On-Throttle-And-Stick (HOTAS) controls and Multi-Function Displays (MFD) allowed better situational awareness and quicker reaction.

Composite materials such as bonded aluminum honeycomb structures and graphite epoxy laminate skins helped reduce aircraft weight. Improved maintenance design and procedures reduced aircraft turnaround time between missions and generated more sorties. Another novel technology was stealth using special ‘low-observable’ materials and aircraft design techniques to reduce detect-ability by the enemy’s sensors, particularly radars. The first real stealth designs were Lockheed F-117 Nighthawk attack aircraft in 1983, and the Northrop Grumman B-2 Spirit in 1989. Military budget cuts after the Cold War and high funding requirements of the fifth-generation fighter, resulted in a term called the 4.5 generation fighters in the period between 1990s and 2005. This sub-generation saw advanced digital avionics, newer aerospace materials, modest signature reduction and highly integrated systems and weapons. These fighters operated in network-centric environment.

Key technologies introduced included BVR AAMs; GPS-guided weapons, solid-state phased-array radars, Helmet-Mounted Sights (HMS), and improved secure, jamming-resistant data-links. A degree of super-cruise ability (supersonic without afterburner) was introduced. Stealth characteristics focused on front-aspect Radar Cross Section (RCS) reduction through limited shaping techniques. Eurofighter Typhoon, Dassault Rafale and Saab JAS 39 Gripen were in this category. Many fourth-generation aircraft were also upgraded with new technologies. Su-30MKI and Su-35 featured thrust vectoring engine nozzles to enhance manoeuvering capability. Most of these are still being produced and evolving. It is quite possible that these may continue in production alongside fifth-generation fighters due to the expense of developing the advanced levels of technology. 4.5 generation fighter aircraft are now expected to have AESA radar, high capacity data-link, enhanced avionics, and ability to deploy advanced armaments.

Fifth Generation Fighters

The fifth generation was ushered in by the Lockheed Martin/Boeing F-22 Raptor in late 2005. This aircraft was 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 multi-function AESA radars with high-bandwidth low-probability of intercept. IRST and other sensors are fused in for Situational Awareness and to constantly track all targets of interest around the aircraft’s 360-degree bubble. Avionics suites rely on extensive use of Very High-Speed Integrated Circuit (VHSIC) technology and high-speed data buses. Integration of all these elements is claimed to provide fifth-generation fighters with a “first-look, first-shot, first-kill capability”. In addition to its high resistance to ECM, they can function as a “mini-AWACS”. Integrated electronic warfare system, integrated Communications, Navigation and Identification (CNI), centralised vehicle ‘health monitoring’, fibre-optic data-transmission and stealth are important features. Manoeuver performance is enhanced by thrust-vectoring, which also helps reduce take-off and landing distances. Super-cruise is inbuilt. Layout and internal structures minimise RCS over a broad bandwidth of frequencies. To maintain low signature, primary weapons are carried in internal weapon bays.

Stealth technology has now advanced to where it can be employed without a trade-off with aerodynamics performance. Signature-reduction techniques include special shaping approaches, 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 and coating internal and external metal areas with radar-absorbent materials and paints. These aircraft are very expensive. F-22 costs around $150 million. Lockheed Martin F-35 Lightening II fighters will cost on average $85 million due to large scale production. Other fifth-generation fighter development projects include Russia’s Sukhoi PAK FA, now SU-57. India is also developing the AMCA. China’s fifth-generation fighter Chengdu J-20 is flying since January 2011 and combat units started inducting in early 2018. The Shenyang J-31 first flew in October 2012. The programme has received government funding and is being sought after by both the People’s Liberation Army Air Force (PLAAF) and the People’s Liberation Army Navy (PLAN).

Light Vs Heavy Stealth Fighters

There is a continued decision conflict about light vs heavy fighters. Light aircraft are relatively simple; they feature a high thrust-to-weight ratio, high manoeuverability, high reliability and lower cost. Modern single-engine light fighters include F-16, JAS-39 Gripen and Tejas LCA. Larger fighters provide the opportunity for more technology, longer range radars and heavier weapons, but are much more expensive and often unaffordable. Future stealth aircraft will have to have the capability of penetrating ‘anti-access/area-denial’ bubbles after eliminating the proliferating air defence systems such as the S-400. Low Radar Cross-Sections (RCS) will be a must. The stealth may be neutralised by advanced sensor technology, and therefore, jamming, electronic warfare and infrared obscuring defences will be important. As airbases and aircraft carriers become more vulnerable to missile attacks, warplanes will need to be able to fly longer distances and carry more weapons. That would mean a larger plane. Within-Visual-Range aerial dogfights would be rare, so it may be sensible to trade off manoeuverability for high sustainable speeds and a greater payload.

Fighters such as the F-35 and F-22 may be stealthy but their support assets like aerial tankers and AWACS are not. It is time to create low observable tankers, transports, bombers and AEW&C, as these will be targeted. The new stealth bomber designs could be adopted for a stealth tanker role. It will also give ability to insert Special Operations teams deep behind enemy lines via a stealthy high-altitude penetrating transport.

Unmanned or Optionally Manned Fighters

Unmanned Aircraft technologies are already proven and it is clearly emerging that the future is unmanned. The world is at a real time of transition. Dual use optionally manned aircraft are under development. Unmanned aircraft are already taking off and landing by themselves including on the moving aircraft carrier (Northrop Grumman X-47B). Autonomous air refueling has been tested. Lockheed Martin’s UCLASS drone ‘Sea Ghost’ looks rather like a stealth bomber and is expected to carry 1,000-pound class weapons. The USAF has already modified F-4s and F-16s to fly them remotely. In France, Dassault leads a multi-nation delta-wing UCAV ‘Neuron’ of the size of Mirage 2000. The UK has a Strategic Unmanned Air Vehicle (SUAVE) programme ‘Taranis’. This will be a supersonic autonomous stealth bomber with inter-continental range. The US is also working on a Strike Bomber that is likely to be optionally manned. Sixth-generation concepts are, therefore, advancing the idea of an optionally-manned aircraft. The optional manning may help ease the final transition to an unmanned fighter force.

Drones – and Drone Swarms

In October 2016, two FA-18 Super Hornets deployed 103 Perdix drones in a test. Supported by AI, the drones swarmed down like locusts over a designated target point. Kamikaze drones have already been used in action and it is easy to see how relatively small and cheap drones could become a particularly terrifying weapon. Inexpensive and expendable networked drones may prove far more difficult to defend against than a small number of costly and well-protected weapons platforms and missiles. Larger, faster, sensor-bearing and weapons carrying drones could still be complementing the sixth-generation fighters.

Evolving Technologies

Today, technologies are offering enhanced capabilities that are driving operational employment and tactics. Gallium Nitride (GaN) is a semiconductor material that is more efficient, easier to cool, and improves reliability for radars. The Passive Aero-elastic Tailored (PAT), a uniquely designed composite wing that will be lighter, more structurally efficient and have flexibility compared to conventional wings. This wing will maximise structural efficiency, reduce weight and conserve fuel. Hypersonic cruise, fuel cell technologies, hybrid sensors, improved human-machine interface using data analytics and bio-mimicry, combination of materials, apertures and radio frequencies that ensure survival in enemy territory are under development. Things will be built faster, better and more affordably, using 3D printing yet ensuring quality and safety standards. Additive 3D manufacture creates a world with spare parts on demand, faster maintenance and repairs, more effective electronics and customised weapons. The development of a hypersonic aircraft would forever change the ability to respond to conflict. Nano-materials will control sizes, shapes and compositions and significantly reduce weight and cost, even while we create stronger structures for air and spacecraft.

Data Fusion, Artificial Intelligence and Cyber Security

Artificial Intelligence (AI), smart structures and hybrid systems will dictate the future. Demand for streaming high-quality data requires bandwidth, which involves innovating sensor/processing systems. The data fusion will be deepened by integrating sensors on different platforms, including satellites and drones deployed alongside jet fighters. Network-centric payload processing units enable onboard data fusion prior to sending to digital links. While some fourth-generation fighters incorporated a back-seat Weapon Systems Officer to support the overloaded pilot, the fifth-generation stealth fighters had to be single-seaters. AI will support aircraft systems management and determine which data should be presented to the pilot. Sensor fusion and optional manning would mean heavy reliance on data-links and networks. These could be disrupted by jamming. Thus, sixth-generation avionics would have to be resilient and have the capability to jam adversary systems.

Future Weaponry

Future weaponry would utilise scramjets for the production of faster missiles that reach hypersonic speeds at which a missile could not be stopped by conventional air defence technology. The USAF is developing a new air-to-air missile, dubbed the Small Advanced Capabilities Missile (SACM) for 2030 and beyond. SACM would promise an improved solid rocket motor having synergised control enabled by combined aero, attitude control and thrust vectoring. The missile will have improved ‘high off bore sight’ for rear hemisphere kills and ‘lower cost per kill’. The missile would also incorporate energy optimising guidance, navigation and control. The Miniature Self-Defence Munitions (MSDM) will enhance future platforms self-defence capability, without impacting the primary weapon payload. A sixth-generation missile could replace AMRAAM. A survivable, long-range missile with combined air-to-air and air-to-ground capabilities is being evolved. It will be multi-band, broad spectrum – which aids it in survivability and reaching the target. Very long range Beyond-Visual-Range (BVR) missiles will be the game changers. The Air-to-Air Missiles such as the Meteor and the Chinese PL-15 can not only be fired at long ranges, but also have high no escape zones.

Directed Energy Weapons (DEW)

DEW and lasers, for defensive and offensive effects at the speed of light will shape sixth-generation fighters. New aircraft will have both expendable and reusable weaponry (lasers). The solid-state laser systems defensively create a sanitised sphere of safety around the aircraft, shooting down or critically damaging incoming missiles and approaching aircraft. They will even attack traditional targets on the ground with pinpoint precision or shoot down ballistic missiles. Swarms of drones and missiles could threaten or over-saturate an advanced stealth jet’s offensive and defensive capabilities. Lasers or microwaves can be fired quickly, precisely and unendingly provided there is sufficient electric power onboard. Lower-powered lasers will be used for disrupting or damaging enemy sensors and seekers – mid-powered for neutralising air-to-air missiles and high-powered for destroying aircraft and ground targets.

Future Pilot Support Systems

On-board Oxygen (OBOX) generation already obviates the need for carrying oxygen cylinders and increases endurance. Light-weight helmets with visor displays for integrated information from all sensors for weapon cueing and shoot command and providing a 360-degree situational awareness would become a standard feature in future fighters, possibly removing cockpit instrument panels. Research is being done for contact lens-mounted displays that could focus information from drones and satellites directly into eyeballs and helmets that could enable to communicate telepathically. Next-generation helmets will pick up vibrations from the skull and transmit sound directly into the head instead of using traditional microphone-earpiece combine. Voice activated commands for multiple aircraft functions will be a reality. Secure data-links aided commands will allow radio silence. To fit the contours, flexible display screens would be of easy to bend synthetic material other than glass.

US Sixth-Generation Fighter Programmes

The USAF and the US Navy (USN) have been defining their own requirements of a sixth-generation fighter. Currently, the US has two projects. The USAF’s ‘Penetrating Counter-Air’ requires a long-range stealth fighter to escort stealth bombers. The USN is pursuing a similar programme called the Next Generation Air Dominance, to complement the smaller Lockheed F-35. The timelines for aircraft in development such as the F/A-XX programme are now around 2030 to 2035. So far, Boeing, Lockheed-Martin, and Northrop-Grumman have unveiled sixth-generation concepts.

The US Department of Defense (DoD) began the sixth-generation fighter quest in October 2012. The Defence Advanced Research Projects Agency (DARPA) began a study to try to bridge the USAF and USN concepts. Next-generation fighter efforts will initially be led by DARPA under the “Air Dominance Initiative” to develop prototype X-plane. The USAF has announced that it will pursue “a network of integrated systems disaggregated across multiple platforms” rather than a “sixth generation fighter” in its Air Superiority 2030 plan. Dubbed the “Next Generation Tactical Aircraft/Next Gen TACAIR”, the USAF seeks a fighter with “enhanced capabilities in areas such as reach, persistence, survivability, net-centricity, situational awareness, human-system integration and weapons effects. The future system will have to counter adversaries equipped with next generation advanced electronic attack, sophisticated integrated air defence systems, passive detection, integrated self-protection, Directed Energy Weapons, and cyber attack capabilities. It must be able to operate in the anti-access/anti-denial environment that will exist in the 2030 to 2050 timeframe. The USAF and USN have common approach on the engine using the Adaptive Versatile Engine Technology for longer ranges and higher performance. The newer engines could vary their bypass ratios for optimum efficiency at any speed or altitude. That would give an aircraft a much greater range, faster acceleration and greater subsonic cruise efficiency. The engine manufacturers involved are General Electric (GE) and Pratt & Whitney (P&W).

The USAF intends to follow a path of risk reduction by prototyping, technology demonstration and systems engineering work before creation of an aircraft actually starts. The sixth-generation has strike capability not as just an aircraft, but a system of systems including communications, space capabilities, stand-off, and stand-in options. The USAF fighter, maybe larger, resembles a bomber more than a small, manoeuverable traditional fighter. A significantly larger fighter can rely on enhanced sensors, signature control, networked situational awareness and very-long-range weapons to complete engagements before being detected or tracked. Larger planes would have greater range that would enable them to be stationed further from a combat zone, have greater radar and IR detection capabilities and carry bigger and longer-range missiles. It would include stealth against low or very high frequency radars like those of the S-400 missile system, which would mean airframe with no vertical stabilizers. Lockheed Martin’s Skunk Works division has revealed a conceptual next-generation fighter design which calls for greater speed, range, stealth and self-healing structures. Northrop Grumman is looking at a supersonic tail-less jet.

Other Sixth-Generation Programmes

France and Germany have awarded a Joint Concept Study (JCS) contract to Dassault Aviation and Airbus for the Future Combat Air System (FCAS) programme. The baseline concept is an optionally manned Next Generation Fighter (NGF) and a System of Systems approach with associated next generation services. The BAE Systems Tempest is a proposed stealth fighter aircraft concept to be designed and manufactured in the United Kingdom (UK) for the Royal Air Force. It is being developed by a consortium consisting of the UK Ministry of Defence, BAE Systems, Rolls-Royce, Leonardo and MBDA and is intended to enter service from 2035 replacing the Eurofighter Typhoon. Approximately $2.66 billion will be spent by the British government on the project by 2025. BAE Systems is planning to approach India for collaboration for the design and manufacture of the Tempest. This aircraft could be optionally manned and have swarming technology to control drones. It will incorporate AI deep learning and possess DEWs. Tempest will feature an adaptive cycle engine and virtual cockpit shown on a pilot’s helmet-mounted display.

China is still evolving its J-20 and J-31. Some Chinese sixth generation aircraft (J-XX) is referred to as Huolong (Fire Dragon). But as on date, China has serious limitations in respect of radar, avionics and engine technologies. China planned to field it in the 2025 to 2030 timeframe. In Russia, work is on for its sixth-generation aircraft Mikoyan MiG-41. Japan’s Mitsubishi F-3 sixth-generation fighter would be based on concept of aircraft informed, intelligent and instantaneous, technologies for which are under testing on the Mitsubishi X-2 Shinshin test-bed aircraft. Given the enormous expenses and effort devoted to working out the kinks in the fifth-generation, the sixth-generation fighter programmes are still conceptual. Many technologies are under development in parallel. At the earliest, sixth-generation fighters may be visible in the 2030s or 2040s and may see further conceptual changes by then.

Summary of Sixth Generation Characteristics

Increased speed and range; advanced modular design with primary aircraft components with the ability to be swapped within hours to optimise for the mission requirements and easing the introduction of future upgrades; single-seat-only cockpits with training occurring mostly in simulators; optionally manned with the same airframe capable of conducting remote controlled or AI-controlled missions; controlling a swarm of drones acting in both a defensive and reconnaissance role for the controlling fighter. Battlefield data fusion with the aircraft acting as a network node capable of receiving and relaying data to multiple other platforms such as other aircraft, ground vehicles or satellites and processing that data onboard to dynamically generate new target lists or update mission parameters on the fly. Increased-range stand-off weapons with the drones conducting reconnaissance within enemy airspace and supplying targeting data to the fighter which remains safely outside enemy airspace. Greater electrical power generation to enable equipping DEWs such as a laser CIWS; virtual cockpit helmet-mounted display allowing the pilot 360-degree vision and doing away with cockpit displays; use of Adaptive Versatile Engine Technology. The sixth-generation strike capability with a system of systems which includes communications, space capabilities, stand-off and stand-in options; larger platforms with greater range, greater radar and IR detection capabilities and carry bigger and longer-range missiles.

Action India

India is still evolving technologies for the design of the LCA. India’s fifth generation aircraft, the AMCA is still on the drawing board and may require foreign help for many technologies. There are a handful of major aircraft engine manufacturers in the world. China and India are still evolving their engine design and manufacturing abilities. India has been dependent on Russian, French and American engines for long. India also needs help in AESA radars, EW systems, modern weapons, actionable AI and other advanced avionics. For India, it would perhaps be best to take a collaborative approach and use economic muscle, and go for a higher number of military systems requirements to seek Transfer of Technology. India needs to think ahead lest it gets left behind again.

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The views expressed are of the author and do not necessarily represent the opinions or policies of the Indian Defence Review.

About the Author

Air Marshal Anil Chopra

Air Marshal Anil Chopra, commanded a Mirage Squadron, two operational air bases and the IAF’s Flight Test Centre ASTE

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