The Long Haul
By Atul Chandra
The Gas Turbine Research Establishment (GTRE) is a premier Defence Research and Development Organisation (DRDO) lab entrusted with the critical task of designing and developing an operational gas turbine engine for the Tejas Light Combat Aircraft (LCA). While the road has been long and arduous, FORCE visited GTRE to get a better understanding of the challenges faced by the team and the milestones that have been achieved till date.
Kaveri Programme
The Gas Turbine Research Centre as it was called way back in 1959 consisted of a modest team of 10 engineers, scientists and 20 technicians entrusted with designing a centrifugal type gas turbine engine generating 1000 kg (2200 lb) of thrust. This engine ran for the first time on a test bed at Kanpur in 1961, by the end of that year the entire establishment moved to Bangalore and was renamed as Gas Turbine Research Establishment (GTRE). From that infant stage, today, GTRE has grown to house more than 1,250 technical personnel whose primary responsibility is to design and develop an aero gas turbine engine for military applications besides carrying out advanced research in subsystems for the same.
The project Design and Development of Kaveri Engine was sanctioned on 30 March 1989 is yet ongoing and has incurred an expenditure of more than Rs 3,000 crore.
The programme can in hindsight be termed as having been highly optimistic considering the fact there was a complete lack of knowhow ranging from design and development of a modern aero engine to technology and materials, not to mention a nonexistent vendor base capable of supplying high quality aero components on a consistent basis initially. However, aero engine development world over has always been a technology-intensive and time consuming task and the lessons that have been learnt so far are sure to be put to good use in the coming years. The effort has also resulted in numerous spinoffs over a variety of applications and the creation of a large knowledge pool with regards to gas turbine engines and associated sub systems.
The Kaveri is a twin spool, low bypass ratio, augmented turbofan generating a dry thrust of 52 kN (11,690 lb) and reheat thrust of 81 kN (18,210 lb) weighing approximately 1250 kg. A quick comparison with engines that the Kaveri must match by the time it enters service before the end of this decade is given below.
The Eurojet 200 and F414-GE-400 are already in a competition for the Tejas engine contract while Snecma will partner GTRE in the quest to develop a higher thrust variant of the Kaveri engine. The Eurojet 200 is a twin spool turbofan with an afterburner thrust of 20,000 lb and 13,500 lb without reheat weighing 1,000 kg. The GE F414-400 has a maximum reheat thrust of 22,000 lb and weighs 1,109 kg. The Snecma M-88-2 offers 17,000 lb of thrust with reheat and 11,250 lb without reheat and weighs 1977 lbs. However a Snecma brochure does say that improvements could increase the thrust to 20,000 lb.
Interestingly, while the General Electric (GE) engine powers the twin engine F/A 18 Super Hornet and the single engine Saab Gripen, the other two engines power twin engine fighters only. Also the GE and Snecma engines are used in fighters that also have naval variants in the Super Hornet and Rafale respectively unlike the Eurojet 200 which is used on the Eurofighter.
Challenges
According to director, GTRE, T Mohana Rao the, materials required for a gas turbine engine are extremely complex. They have to be light and strong at high temperatures. An exotic alloy called Ti-64 is used for the low pressure compressor and parts of the high pressure compressor. Another alloy is used for the high temperature sections at elevated temperatures of 900 degrees centigrade for the high pressure compressor blades. Titanium, super alloys and maraging steel, all form essential components of an aero engine and a lot of these materials were developed for the Kaveri programme along with DMRL Hyderabad and Midhani.Now we have 12 important alloys for air worthiness and use on aircraft that have been certified by Centre for Military Airworthiness and Certification (CEMILAC) and RCMA. This has taken a decade to develop and we used to import all these materials previously.
Some of the other crucial technologies that are required for a modern combat aero engine are single-piece bladed compressor disks (blisks), single crystal high pressure turbine blades, powder metallurgy disks, ceramic coatings and composite materials. These are essential to provide the high thrust, reliability and low weight demanded of present fighter engines. Many of these technologies are not available readily and the task of developing this type of technology in house has proved to be insurmountable. However, with the entry of Snecma one can expect the programme to have access to newer technologies.
Infrastructure
The most important benefit to have been realised out of developing the Kaveri engine has been the creation of invaluable infrastructure for the design, manufacture, testing and certification of a modern military aero engine.
Foreign Object Damage (FOD) Test Rig:
The FOD test rig is used to understand effects of different sized objects that are ingested by the engine at high speeds. The military requirement for an aero engine is that when an object weighing two lb impacts the rotating blades at 12,000 rpm and 0.4 Mach, then the engine should be able to recover 95 per cent of its thrust in five seconds. The Kaveri engine meets this specification. The force of that impact is equivalent to 20 tonne and one can only imagine the standards required to be met to keep an aero engine operating after such an impact. The rig has also been used for the Delhi Metro (to test the windscreen), NAL Saras programme, HAL 'Dhruv', IJT and LCA windshield testing.
Rapid Prototyping:
GTRE has developed an excellent rapid prototyping facility which can manufacture the required part in a few hours, which normally took a few months. This can then be used to conduct initial studies on the prototype and speed up the development process. Stereo lithography and fused deposition modelling using 3D CAD model data is undertaken here.
Spin Testing:
Another technology mastered by GTRE has been spin testing of rotors. For this, spin pits and all the associated testing equipment is available at GTRE. This equipment has also been used by HAL for cyclic spin testing of the Adour Low Pressure (LP) and High Pressure (HP) turbine rotors and has realised revenue of Rs 3.8 crore.
The overriding impression at GTRE was the impressive strides that have taken place in the creation of required infrastructure to design and develop our very own military aero engine. The Kaveri programme can now call on the knowledge garnered over the years, talented manpower, increased funding and entry of a foreign engine house to provide assistance. The vision of having the Tejas powered by the indigenous Kaveri engine towards the end of this decade may yet be realised.
We Are Going For An Upgraded Version of the Kaveri Engine Over The Next Two Years
Director, Gas Turbine Research Establishment, T. Mohana Rao
What is the status of the Kaveri engine as of now?
The Kaveri engine is undergoing ground testing now while the simulated flight testing has already been completed. The flying test bed trials are expected to start sometime in this month. The engine has completed about 2000 hours of ground testing so far and has been delivering the designed thrust as part of ground testing. The engine has also been fully certified for ground testing condition except for the flying test bed. Once flying trials are completed, it will be a major milestone for the project
What developments do you see taking place over the next few years with respect to the Kaveri engine?
The engine that has been developed at this stage will definitely have some utility. Once it is configured further, at some level, it will have a variety of applications ranging from aircraft to marine to power generation. We are going for an upgraded version of the Kaveri engine over the next two years. There is a lot of scope for us to design and develop a higher thrust class of engine and we are waiting for the contract with Snecma to go through. The requirements of the IAF will be the first priority for us while developing any type of higher thrust engine.
Can you mention any developments on the partnership with Snecma?
I would like to defer this question till such time as we sign the contract. Then we will come out with exactly what the benefits are. However, I can assure that this will be very beneficial for the country.
What are the benefits that have accrued from the Kaveri engine programme?
Firstly we are able to design a gas turbine engine today for a particular specification which was not possible two decades ago. The very fact that we are capable of developing an aero engine is the reason why other engine houses around the world are now prepared to join hands with us for jointly developing a higher level engine. Our design capability in this field is now well-established.
We have established all the facilities required to do the analysis for a gas turbine engine. An excellent material base has been created and the core materials for the engine have been certified to air worthy quality in coordination with Defence Metallurgical Research Laboratory (DMRL) and Mishra Dhatu Nigam (Midhani). There is also a certified Aeronautical Materials Test Laboratory (AMTL) in Hyderabad which is state-of-the-art and can cover the entire gamut of material testing required. Excellent infrastructure for manufacturing the Kaveri engine in house has also been made here at GTRE.
Five engine test beds for aero engines are in operation and can simulate conditions in Bangalore and elevated conditions up to two km altitude at a Mach No of 0.40 forward speed conditions. Two of these test beds have been internationally calibrated where the GE engine for the LCA has been tested. The calibration level has been set so that any international engine can be tested here and we can establish and declare the thrust.
We have also created a large vendor base both within and outside Bangalore who can manufacture, inspect and deliver precision aero components. The number of vendors has now reached 300 approximately and high quality routine parts can now be delivered to us by our vendors.
What is the update on the Kaveri marine engine for the Indian Navy?
The Kaveri marine engine is a spin off on the Kaveri engine. This was based on a requirement of the Indian Navy for 10-12 mw of power generation for naval applications. The Kaveri core engine has been used and we have developed one prototype which is undergoing tests at the naval dockyard in Vizag. BHEL will undertake manufacture of this marine engine once all development tests are complete. Marine engines need to last for 40,000 to 50,000 hours compared to aero engines which typically have a life of 2000 to 3000 hours. The marine environment also has creates very high vibrations and the challenge is to isolate these vibrations of 50-100 g to an acceptable 2-3g for the engine. The other challenges were the saturated salt environment with 100 per cent humidity and high inlet temperatures and corrosion. The engine has to work reliably despite all these factors.
Can you tell us more about the indigenously developed air turbine starter developed by GTRE?
The air turbine starter is a crucial technology that has been developed in house by GTRE. The Kaveri engine has to be started on ground using a pneumatic starter with high pressure air at around 4 atmospheres from a ground system being supplied to start the engine and get it to around 40 per cent speed after which we cut the starter. This starter was earlier supplied by Garret and due to sanctions the supplies were stopped as well as maintenance and repair of the starters had stopped. Hence, we had to develop a starter with a higher capacity as the capacity of the Garret starter was limited. We went ahead and jointly developed this with a Bangalore-based company called Turbotech. While the Garret starter was qualified for 500 starts our indigenously developed air turbine starter is giving more than 1000 starts before a major overhaul.
What is the relationship between GTRE and HAL?
HAL has been our manufacturing partner from day one. HAL Koraput has produced items like the fan disc for the Kaveri engine while the HAL engine factory is manufacturing the jet pipe and afterburners. In fact, whatever parts that HAL could develop and manufacture from a prototype level, they have done. They have been our preferred partners from the inception of the Kaveri engine programme. Wherever they have not been able to support us due to constraints of time or availability we have sought outside vendors. When the Kaveri engine will need to move to serial production then that task to manufacture it will go to HAL
What has been the learning for GTRE from the Kaveri engine programme?
We have been able to design, develop and manufacture our own aero engine. So far we have made nine Kaveri engines and four core engines. Testing has been going on extremely well. We did have a lot of problems related to design, strength and safety earlier, now almost 98 per cent of those problems are behind us. We started virtually from scratch two decades ago and did not have the knowhow to manufacture this type of product. This resulted in the time frame for development being long as a result of wrong expectations which further led to cost overruns. Any gas turbine engine would take around 25-30 years to develop and at a cost of Rs 15-20000crore. With all our limitations, we have taken 22 years with limited resources in materials, manpower and funds at the same time creating a substantial infrastructure which will be of use to the nation.
Developing of the required materials was an essential step for the Kaveri engine, followed by setting up the required design capability in house. This capability has to be audited and proven by engine houses from abroad. But no engine house from abroad came forward to help us in design enhancement and design audit. We had to go to Russia to Central Institute of Aviation Motors (CIAM) to help us in auditing of the design and make some course corrections.
Technologies like friction welding and inertia welding were not available initially but slowly due to advances in our own technology we may get access to such technology. Apart from this, other high technologies like BLISK (a combination of blade and disc) and high temperature thermal barrier coatings, among others, were not available to us. As a result, we had to make do with whatever technology was available with us at that time. We also learnt that for small orders for certain components, manufacturers abroad were not enthused and we were given low priority for these parts causing delays in their arrival.
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