Tejas is the smallest light combat aircraft in its class designed to meet the stringent requirements of a multi role combat aircraft . A modern airborne weapon system like the Tejas combines the best of aerodynamics, structures, sensors, avionics and weapon system designs. The sleek aerodynamic designs of the compound tail less data plan form results in high lift to drag ratio , which coupled with high thrust levels provided by GE 404 IN-20 engines gives Tejas, high performance to match other contemporary aircraft in its class. The other important feature of Tejas is its agility and exceptionally good flying qualities, which is the result of unsuitable aerodynamics augmented by state of the art quarduplex digital fly by wire fight control system . Tejas has a very high percentage of composites in its structures. Compared to the conventional metal structure, composites have very high strength to weight ratio as well as very low radar cross section which makes it very difficult to be detected by enemy aircraft and ground radars.
Tejas is equipped with a number of modern and powerful sensors such as multimode radar and laser designation pod. These when integrated with an array of weapons such as air to air missiles, conventional and laser guided bombs which are carried on the eight hard points makes Tejas a very potent airborne weapon system. In addition, the rear warning radar (RWR), modern electronic warfare (EW) suit and information friend or foe (IFF) system provides Tejas the required survivability features in the contemporary battle scenario. Information overload is the flip side of complex system which is made user friendly through clever pilot-vehicleinterface (PVI) design. This is achieved through the modern open architecture based avionics system which effectively integrates the on-board systems, sensors, and weapon to provide the required controls as well as status and warning information on the multifunction displays (MFDs) of the Tejas all glass cockpit as well as the helmet mounted display and sighting (HMDS) integrated on the aircraft.
Any system is exploitable to its full potential only if it is operable and maintainable in the harsh and unforgiving field conditions. Tejas systems have been ruggedised to withstand extreme environments ranging from the summer of Nagpur to the freezing winter of Leh . Maintainability features include built-in tests (BIT) and flight fault report (FFR) generated by all the computer controlled systems on board as well as easy accessibility to the line replaceable units (LRUs). The excellent PVI and maintainability features of Tejas are the result of user involvement from the early stage of design, development and testing.
Challenges in Technology
Development: Tejas story is the story of aerospace technology development in the country; and the project had to face and overcome unprecedented challenges. They are briefly indicated below:
Huge technology Gap: The only other indigenous fighter programme India ever undertook was HF 24 (Marut), which was of 1960 vintage . Accordingly, Tejas programme had the twin objectives of developing a state of the art combat aircraft for over Services and to bridge the four decades of Technology gap in the process- a tall order indeed! Indigenisation was the third dimension added to make picture more complex.
Technology Denial Regime: Tejas was designed and developed at a time when sensitive technologies of the west were denied to India. We would recall that following the Pokhran nuclear tests, Indian scientists and engineers were literally thrown out of the premises of their collaborators abroad. It took years before we could retrieve our own development and testing equipments from there. But, in every challenge there are opportunities and Tejas team effectively utilized this opportunity to develop these complex systems on our own.
Large number of organisations and work centres: Tejas truly became a national programme. This is borne out by the fact that a large number of work centres spread across the length and breath of the nation are involved in one way or other in the design, development and testing of Tejas systems . These include DRDO, CSIR Labs, PSUs, Private industries, certification agencies (CEMILAC, DGAQA) as well as educational institutions. Coordinating and integrating such a large number of work centres with varied organisational cultures was one of the biggest challenges faced and over come by innovative technology management which is briefly covered in the next section.
Technology Management
Features of the innovative technology management approach adopted by the Tejas programme are too many to be listed here. However, a few salient ones are briefly discussed below:
National Team Concept: ADA formed various national teams to develop critical technologies. These are National Control Law team for design and development of the critical control laws (CLAW) of the quadruplex digital fly by wire flight control system, National wing team to develop composite structures and the National Flight Test Centre for the safety critical flight test technology. These national teams were formed by pooling in national resources from all available avenues.
Effective review mechanisms: Tejas project has developed and perfected very effective and efficient review mechanisms. These include preliminary design reviews (PDR) critical design reviews (CDRs) at systems levels and weekly monthly, quarterly and annual reviews at project level with participation and over sight from several levels in the hierarchy, including users. Quarterly Empowered Committee in chaired by the Chief of the Air Staff while General Body is chaired by honorable Raksha Mantri.
Quality Assurance and Systems Effectiveness Group (QA&SEG): ADA was seized of the fact that ‘quality’ is not incidental but will need to be built in the design. This dictum was the driver for the formation of QA&SEG group of ADA which is tasked to design and integrate ‘quality’ in every system, while enhancing its effectiveness to the maximum.
Independent Verification and Validation (IV&V): Tejas is one of the most software intensive systems ever developed in the country and IV&V is a process developed on the project which ensures that the maximum member of software ‘bugs’ are caught and eliminated very easily in the stage of design. The effectiveness of IV&V has been nationally acknowledged and replicated on other important national programmes.
Challenges in Testing and Certification
The objective of ‘Development Testing’ is to prove and improve design. Testing takes place at component level, subsystem level, system level on different test rigs and platforms, in the final integrated form on the aircraft. One hundred percent testing of a massive and complex system is neither possible nor viable. Accordingly, how much and how to test is a challenging and tough call that needs to be jointly addressed by the designers, technology manages and certification agencies. Tejas flight test programme faced and overcame some of the toughest and unprecedented challenges which are briefly discussed below:
Large number of ‘new’ technologies to be proven on one prototype: When the first Tejas prototype technology demonstrator (TD-1) got airborne for the first time on 04 Jan 2001, it created aviation history of sorts in that it was probably the first time that a prototype got airborne with so many unproven technologies on board. The very objective of the technology demonstration phase in the development was to prove and demonstrate these technologies. These were quadruplex Digital fly by wire flight control system without any analogue or mechanical back up, composite structure, all glass cockpit with-multifunction displays and micro processor based general systems. Technology Demonstration phase was successfully completed with 212 test flights on the initial prototypes. There after, the project graduated to prototype vehicle (PV) and Limited Series Production (LSP) variants for development and testing in the Initial Operational Clearance (IOC) phase.
Flight Test Technology Gap: For want of worthwhile development programmes in the intervening four decades, there was a perceptible technology gap in the area of flight test as well. These were in the form of lack of expertise, infrastructure and qualified, trained and experienced test, instrumentation and analysis personnel. High technology and lack of expertise in testing is a potentially dangerous combination which was the biggest challenges faced by the test team at the formative stages.
Risk mitigation and management
Assessment and management of risk within acceptable limits is the single most important task of any flight test organisation. The following methodologies were effectively used in managing risk in development flight testing.
Formation of National Flight Test Centre (NFTC):
NFTC was formed in 1994 by none other than Dr. APJ Abdul Kalam, the then Scientific Advisor to Raksha Mantri and Director General ADA, spear heading the Tejas programme. NFTC was the result of an understanding among ADA, HAL and IAF to pool in all the available expertise and resources under one umbrella.
Cautious step by step build up approach: From the very beginning, a cautious step by step build up approach was adopted to mitigate risk. Starting from a very benign condition, flight test progressed towards the flight envelope limits backed by detailed analysis and simulation. Even the flight test infrastructures in terms of the state of the art static as well as mobile telemetry were built up progressively.
Safe, effective and efficient flight test process: During the course of the project, NFTC has developed, and put in place a safe, effective and efficient flight test process which is well documented in fight test operations manual. Following are a few high lights of the flight test process followed at NFTC.
- Conduct of flight test from the telemetry by the test Director who is a qualified flight test engineer, supported by system specialists and safety pilot monitoring systems performance and safety parameters in real time.
- Efficient and effective flight/data briefing and debriefing sessions. n Effective coordination with all agencies involved in flight test, such as hangar, designers, certification agencies, Air Traffic Control (ATC) Met, search and rescue, medical etc.,
- First flight readiness and safety reviews
- Data base to track progress of flight test (Test points) and issues arising out of flight test (Request for action – RFA)
- Well structured method of training and grading test crew. NFTC is also in the process of developing a software system (TejTESCT) for automation and optimization of flight test process for use in the ongoing testing as well as on future programmes.
Active participation in the design and development process: Flight test is an integral part of the design and development team. Their direct roles involve handling quality (HQ) evaluation and pilot-vehicle interface (PVI) design. HQ evaluation and fine tuning starts on HQ simulators and later on the aircraft in different phases of flight. PVI design is perfected through several iterations on cockpit evaluation facility (CEF). Very experienced service test pilots and flight test engineers on the project also provide the vital operational orientation for the programme.
Programme Management: Tejas programme has been one of the most efficiently managed in terms of both time and cost. Given the historical background of huge technology gap and lack of infrastructure, to design, develop and test a fourth generation combat aircraft, the programme was managed very efficiently starting with technology demonstration phase, through proto vehicle development and establishing production line delivering eight limited series production (LSP) aircraft. A few salient programme milestones are given below:
- Full scale engineering development (FSED) phase – I for technology demonstrator was approved in April 1993 and was completed in March 2004 without any cost overruns.
- FSED phase – II was approved in November 2001, comprising of development of three proto vehicles and establishing production lines for delivering eight LSP aircraft. The initial operational clearance was achieved in January 2011. By December 2010, Indian Air Force placed orders for forty aircraft. Final operational clearance of Tejas Mk-I is scheduled to be achieved by 2012.
- Government of India has approved funding in 2009 for FSED phase-III for design and development of Tejas Mk-II variant with higher thrust engines and other upgrades to obviate obsolescence. The above time lines are comparable with any other fighter aircraft development of similar class and similar scope, involving technology demonstration, building the technology gap and building specialised infrastructure for the industry.
Conclusion
10 January 2011 was a red-letter day in the history of Indian Aviation. On that day the honorable Raksha Mantri, Sri AK Antony handed over the service documents of Tejas to the IAF Chief, Air Chief Marshal PV Naik at a glittering ceremony held at HAL Bangalore, marking the initial operation clearance of the aircraft in to the Indian Air Force. Release to Service was based on certification by Centre for Military Airworthiness and Certification (CEMILAC), backed up by data from over 1500 successful test fights spread across 11 prototypes; which has proven the reliability and safety the aircraft beyond doubt. This indeed was a proud moment for the entire nation in general and for ‘Team Tejas’ in particular. Jai Hind
—Dr P S Subramanyam, is a Distinguished Scientist, and Programme Director (Combat Aircraft) & Director (ADA) . Wg Cdr (Retd) P K Raveendran, SC is Sc/Engr ‘G’Group Director (Flight Test) National Flight Test Centre, ADA
