Synergy of stealth, super-cruise and information fusion for complete situational awareness are the attributes of fifth generation fighter aircraft. But with the fast emerging rival capabilities, the buzz for a manned sixth generation tactical aircraft, with more powerful capabilities is fast turning into clamour. One may not have to wait for long before it becomes a din.

If one were to classify modern advanced fighters in the order of performance, fifth generation fighter aircraft (FGFAs) would clearly lead the pack. They represent a class of their own. However, technologies involved are so advanced and resources required so substantial that so far only the United States has been able to field a state-ofthe-art operational fifth generation fighter in its F-22, the Raptor. The US is also in the lead to develop a smaller size joint strike fighter (JSF) F-35 Lightening II the other claimant to that pedigree and which is slated to form the backbone of not only the US Air Force (USAF) but also the US Navy in its carrier-borne avatar and a vertical take-off and landing (VTOL) version for the US marines. Technical complexity and high costs have encouraged like-minded nations to form consortia to share risks and costs. For the F-35, while the United States is the primary customer and financial backer, the United Kingdom, Italy, the Netherlands, Canada, Turkey, Australia, Norway and Denmark, have all contributed towards the development costs of the programme with individual acquisition plans.

Russia, which came on the scene more than a decade later, is testing its own FGFA —the PAK-FA—on its own. The programme has now evolved into a Russia-India joint venture with Sukhoi and the Hindustan Aeronautics Limited (HAL) sharing risks and costs.

Not to be outdone, China surprised the entire global military aviation community by launching the maiden flight early last year of its own version of fifth generation aircraft, code-named the J-20.

India too, in addition to the Indo-Russian joint PAK-FA programme, has its own FGFA programme in the form of medium combat aircraft (MCA), but it is still on the drawing board. Therefore, the number of countries which are engaged in developing their own fifth generation fighters remains limited.

Attributes of FGFA: A comparison

What are the characteristics and attributes that separate the FGFA from the other fighters and how do the current FGFAs compare with each other? Broadly the idea can be summed up as synergy of stealth, super-cruise and information fusion for complete situational awareness.

Stealth

Of all attributes, “stealth” or low observability is perhaps the most important defining characteristic of a FGFA. It is low visibility against the entire spectrum of sensors including radar, infrared, acoustic and even visual which yields a stealth fighter the edge that nullifies many other performance advantages that the adversary might enjoy. By outwitting all defences during the opening phases of the first Gulf War in 1991, F-117A Nighthawk (the first fighter with stealth as its predominant strength) brought home dramatically the exponential value addition of this attribute. However, in achieving low visibility, it had to sacrifice important performance parameters of speed and manoeuvrability, thus leaving a window of vulnerability, should it get detected. F-22 Raptor and other aircraft in the fifth generation stable have overcome this limitation to varying degrees. For example, in manoeuvre performance, a F-22 Raptor in dry power matches or exceeds F-15C in afterburner regime.

Low observability in FGFAs is achieved by a combination aerodynamic tailoring, usage of composite materials which help both in reducing weight as well as in radar reflectivity, shaping intake ducts to prevent radar echoes from the highly reflective compressor and turbine faces and a host of other techniques which helps to reduce its footprint. Earlier stealth designs (like the B-2 spirit bomber radar and Night Hawk F-117A) used absorbent materials and coatings extensively to absorb the incident radar energy. However, they were maintenance-intensive and required climate-controlled hangars to protect their stealth coatings. Aerodynamic refinements now have reduced reliance on this method of signature control. Weapons carriage on external pylons, a major contributor to the radar cross-section (RCS) of all fighters, has been replaced by provisioning of internal weapon bays, thus maintaining the sleek stealthy airframe lines except for brief moments of weapon release. Close attention to detail has resulted in a virtually noiseless aircraft with very little thermal, acoustic or radar signature.

For instance while the exact radar cross section of the F-22 in various aspects remains classified, in early 2009, Lockheed Martin revealed that from certain critical angles, Raptor’s signature was comparable to that of a “steel marble”.

It is obvious that some trade-off are necessary between what is required to enhance low observability mission requirements and even cost. F-22A design keeps it stealthy from all aspects as required in an air dominance fighter. F-35 Lightening II on the other hand has a very low radar profile from the front, is less stealthy viewed sideways and is least stealthy in the rear quarters. The Indo-Russian PAKFA, on the other hand, has been designed to be more manoeuvrable than the US fighters at the cost of making it less stealthy. One of the design elements that have such an effect is the leading edge vortex controller (LEVCON). Similarly, Canard surfaces and leading edge extensions increase radar cross-section (RCS). But the Chinese chose to retain canards on J-20 to enhance agility while scarifying some bit of its radar signature. A lot also depends on the main role envisaged for the aircraft. For example, while in the case of US F-22, the emphasis is on air dominance, in the case of the J-20, its main role appears to be long-range, stand-off attack capability against surface targets. Similarly, in the case of PAK-FA, emphasis appears to be on multi-role capability.

Super-Cruise: A desirable attribute of a FGFA is the capability for it to super-cruise i.e. transit in and out of combat zone at supersonic speeds but without the use of afterburner(s). This coupled with the other major attributes of stealth and data fusion and armed with air-to-air and air-to-surface weapons of appropriate stand-off ranges, it would have the unmatched capabilities of not only ‘first look’, ‘first shoot’ and ‘first kill’, but also ‘first scoot’ capability. The US F-35 JSF was purposely not designed to super-cruise but all other FGFAs including the Chinese J-20 have the capability to super-cruise.

Sensor Fusion/Situational Awareness

With ever more challenging mission requirements, fighter aircraft have gradually come to resemble sensor beds. A host of sensors operating at different wavelengths in the electromagnetic spectrum connect the pilot to his operating environment. In a first, Raptor’s design for example embeds passive sensors for various wavelengths all around the aircraft’s structure. This greatly improves the aircraft’s first detection ability, even with its radar switched off. In the emerging battlefield environment, fighter aircraft on a mission no longer hunt individually. They operate in a networked environment—receiving and sharing data with a variety of dispersed sources. The APG-77 active electronically scanned array (AESA) radar system of the F-22 functions as a Wi-Fi access point which can transmit data at 548 megabit/sec and receive in the gigabit/sec range. To put it in perspective, Link 16 still in use by the US and allied aircraft transfers data at just over one Mb/sec. The intention behind high speed of connectivity is to generate seamlessly a comprehensive all-round picture to enhance the pilot’s situational awareness. The flood of information spewed by multitude of sensors (all crucial to mission accomplishment) would overwhelm the pilot unless filtered, prioritised and presented appropriately in an easily digestible format. Powerful integration processors perform that crucial function. In the F-22, the AN/APG-77 phased array radar is the key to the Raptor’s integrated avionics and sensor capabilities.

However, while the sensor fusion capabilities in the F-22 are indeed impressive, it is the US F-35 JSF which is the epitome of a masterpiece to provide unmatched sensorfusion/situational awareness capability. The F-35 has been purposefully designed with synergy between sensors as a specific requirement, with the “senses” of the aircraft expected to provide a more cohesive picture of the reality around it, and be available in principle for use in any possible way and any possible combination with one another. All of the sensors feed directly into the main processors to support the entire mission of the aircraft. For example, the AN/APG-81 functions not just as multi-mode radar, but also as part of the aircraft’s electronic warfare system. As far as the Russian and Chinese designs are concerned, not much has been revealed about this segment, but it can be safely assumed that this aspect would definitely engage the designers’ attention, albeit to varying degrees (see Table for a comparison of the various important attributes of the already operational/under development FGFAs in the world).