Technology carries a certain momentum of its own. Despite very high costs and the considerable margin by which the US has already outpaced its nearest competitor, buzz for a ‘sixth-generation fighter’ dubbed ‘next generation tactical aircraft’ with even more powerful capabilities, is already audible.

If one were to seek a benchmark to separate modern advanced fighters from the rest of the pack, fifth-generation fighters (FGFAs) clearly lie on top of the heap. They represent a class of their own. However, the technologies involved are so advanced and the resources required so substantial that so far only the United States has been able to field an operational fifth-generation fighter in F-22, the Raptor. The United States Air Force (USAF) had originally intended to buy 750 aircraft with production beginning in 1994. However, both due to changed threat perception and even more significantly the prohibitively high cost, procurement target has gradually been whittled down to 187 units. The flyway cost of F-22 was $150 million ( Rs. 750 crore) per aircraft in 2009. Joint strike fighter (JSF-Lightening II), the other claimant to that pedigree and which is slated to form the backbone of the USAF, has had to tackle major technical and cost overrun issues. A US Government Accountability Office report of March 2010 states that the overall unit cost of an F-35A would be $112 million ( Rs. 560 crore) in 2010 money. Technical complexity and high costs have encouraged likeminded 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 agreed to contribute an overall $4.375 billion ( Rs. 21,875 crore) towards the development costs of the programme. Russia is testing its FGFA, the PAK-FA, on its own, but joint Sukhoi/HAL FGFA would be built on the same PAK-FA foundation—thus sharing risks and costs.

What are the attributes that separate the FGFA from the other fighters? Broadly the idea can be summed up as synergy of stealth, 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-117 A 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 manouverability, 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-15 C in afterburner regime.

Low observability in FGFAs is achieved by a combination of aerodynamic tailoring, usage of composite materials which help both in reducing weight as well as 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 and Night Hawk F-117A) used absorbent materials and coatings extensively to absorb the incident radar energy. However, they were maintenance-intensive and required climatecontrolled hangars to protect their stealth coatings. Aerodynamic refinements now have reduced reliance on this method of signature control. Weapons carriage on external pylons, which is a major contributor to the RCS of all fighters, have 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 tradeoffs 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. Similarly, Canard surfaces and leading edge extensions increase radar cross-section (RCS). But many designs choose to retain canards to enhance agility while sacrificing some bit of their radar signature.

Sensor Fusion

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, allied aircraft transfers data at just over 1 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’s AN/APG-77, AESA radar is the key to the Raptor’s integrated avionics and sensor capabilities. Two common integrated processors (CIPs), each with a signal processing capacity of more than 20 billion operations /sec (Bops) fuse, filter and present to the pilot in the cockpit in an easily digestible format the information gathered from the radar and other onboard and off board sources. The CIPs have built-in expansion potential of up to 50 Bops to accommodate inputs from additional sensors and systems as and when they become available for integration.