India’s Fighter Engine Dream
Vol 11 Issue 2 May - Jun 2017
An absorbing History of the Development of Aircraft Engines
Wednesday, May 24, 2017
Aircraft jet engine development remains a domain of the few. Most designers have kept their cards close to the chest. The main manufacturers of military jet engines today (and the aircrafts these engines power) are Pratt & Whitney (US; F-16, F-22), General Electric (US; B-1, B-2), Rolls-Royce (UK; Harrier), Tumansky (Soviet Union; Mig-25, Mig-29), Lyulka/Saturn (Russia; SU-27/30, SU-37), Turbo-Union (UK, Germany, Italy; Tornado), EuroJet (UK, Germany, Italy, Spain; Eurofighter Typhoon) and SNECMA (France; Mirage-2000, Rafale). Others nations, such as China, have been trying to develop engines based on designs of existing Aircraft engines. India initially took on the ambitious fighter engine ‘Kaveri’ for its Light Combat Aircraft (LCA) but could not reach the end state. It is now trying to tie-up with a foreign partner to recover the project.
Evolution of Fighter Jet Engines
By end of World War II the military aircraft started getting the gas turbine engines. The jet engine meant more power for less weight, lower frontal area permitting supersonic flight, far greater reliability, no cooling problems and safer kerosene-type fuels. Fighters and bombers soon switched to the turbojet. More powerful engines also meant improvements in take-off and climb performance. Initial engines had many stages of compressor and turbine blades. But over the years efficient compression and fuel burning have greatly reduced stages and thus the size and weight. Unlike the slim fighter engines, the civil and transport aircraft do not have any such restrictions. Therefore, separate technologies had to be developed for the two. Interestingly yet, the best-selling CFM56 has the core of a long-established military engine, the F101 used in the Rockwell B-1B Lancer. Another peculiar feature of fighter engines is the afterburner (Reheat), where in fuel is burnt in the jet-pipe downstream of the turbines. Supersonic aircraft have after burning engines in order to increase the energy in the jet so that, properly expanded in a special nozzle, it can be ejected at highly supersonic speed, in order to achieve the high flight Mach number. High afterburner use shortens engine life.
Super Cruise Engine Attributes
Current engines are fairly powerful and power augmentation is needed at best only during take-off or in close-combat. Super-cruise is the term for flying at sustained supersonic speed without the use of the afterburner. Modern fighters like the Lockheed Martin F-22 Raptor, Rafale, Eurofighter Typhoon, and F-35 can accelerate to supersonic speed without using augmentation and then sustain such a speed indefinitely in dry thrust. Super-cruise also reduces the IR (infrared) signature by some 75%, thus making aircraft safer from heat-homing AAM.
Russians were the first to research on fully variable nozzles with the ability to vector (point in different direction). Bristol Siddeley introduced unique nozzles for the Harrier V/STOL aircraft. Thrust reversers on most civil aircraft are a form of vectored thrust. The high manoeuvrability of the Su-27 and the many subsequent fighters from the Sukhoi stable extensively use thrust vectoring for the aerodynamics-defying high agility. Test Pilot Pugachev and his colleagues demonstrate the superb manoeuvrability during air shows. Eurofighter’s EJ200 engine is also likely to get thrust vectoring during first mid-life update.
Newer Fighter Engine Technologies
Fighter aircraft and airliners aspire to go faster at several times the speed of sound, (typically Mach 5) which at high altitude corresponds to 5310 km/h. Such speeds are possible only through ramjet engines. For a ramjet to start it requires the engine to be at an initial velocity. Statistically, the power available from a given size of engine has doubled roughly every 30 years; simultaneously the specific fuel consumption has consistently fallen. Unmanned fighters of the future would not only be smaller but also give the designer greater flexibility. The engine inlet can be positioned where the windscreen used to be, which most designers consider will give enhanced stealth characteristics, without affecting engine efficiency. Jet engine UAV (unmanned air vehicle) would almost certainly be single-engine. Smaller jet engines with low fuel consumption will increase endurance. Other jet engine stealth features are concealed intakes, kinked inlet duct or positioned above the fuselage. Propulsive nozzle with minimized thermal, visual and acoustic signatures. The Lockheed Martin F-117 Nighthawk nozzles are flattened slits in the trailing edge of the wing. A lot is being written about engine technologies such as electric-field propulsion, and electro-gravitics (or anti-gravity).
Gas Turbine Research Establishment
India’s serious aero gas turbine engine research began with setting up of the Defence Research & Development Organization (DRDO)’s Gas Turbine Research Establishment (GTRE) in Bangalore in 1959. As a spin-off GTRE also developed a few marine gas-turbines. In the early years GTRE developed India’s “first centrifugal type 10kN thrust engine; successfully upgraded of the reheat system of the Orpheus 703 engine; and the first attempt at a “demonstrator” gas turbine engine – GTX 37-14U - for fighter aircraft. GTX 35VS Kaveri Engine was intended to power production models of HAL Light Combat Aircraft (LCA) Tejas. The project kept getting unacceptably delayed and finally had to be abandoned. GTRE blamed the delays on many factors including non-availability of state of the art wind tunnel facility in India and the technology restrictions imposed by USA, both hurdles have since been cleared.
HAL Engine Manufacturing
Significant engine expertise is also available with HAL engine division, Bangalore which was set up in 1957 and has produced Orpheus turbo jet engines under licence from Rolls Royce, and overhauled Avon engines fitted on Canberra & Hunter aircraft. It is manufacturing Artouste engines for Chetak/Cheetah helicopters, Adour engines for Jaguar aircraft and Garrett engines for Dornier aircraft. HAL’s Engine Division also undertakes repair and overhaul of various military aero engines operated in India. It has the wherewithal for manufacturing modern engines. HAL is working closely with GTRE for Kaveri Engine. HAL has two engine related 50-50 joint ventures. The Snecma-HAL Aerospace Pvt Ltd to establish a Centre of Excellence for production of Precision Aero Engine components and assemblies as an Export Oriented Unit. The International Aerospace Manufacturing Private Ltd with Rolls-Royce to manufacture compressor rings, turbine blades and nozzle guide vanes. Sukhoi Engine Division at Koraput was established to Manufacture and Overhaul AL31FP engines. Division began overhaul of the SU-30 engine AL31FP Engines from 2007. In addition to Engines, they overhaul nearly 38 types of Rotables.
GTRE GTX-35VS Kaveri Engine
In 1986 DRDO was authorized to launch a program to develop an indigenous power-plant for the LCA. Full-scale development GTX-35VS Kaveri was authorized in April 1989 in what was then expected to be a 93-month program projected to cost US$56.8 million. The original plans called for 17 prototype test engines to be built. GTX-35VS Kaveri Engine was meant to be an afterburning turbofan which was first run in 1996. In 2002, it was known that the Kaveri had a tendency to “throw” turbine blades, which required securing blades from French engine maker SNECMA. Continuing development hold ups with the Kaveri resulted in the 2003 decision to procure the uprated F404-GE-IN20 engine for the eight pre-production Limited Series Production (LSP) aircraft and two naval prototypes. In mid-2004, the Kaveri failed its high-altitude tests in Russia, ending the last hopes of introducing it with the first production Tejas aircraft. This led the Indian Ministry of Defence (MoD) to order 40 more IN20 engines in 2005 for the first 20 production aircraft, and to openly appeal for international participation in completing development of the Kaveri. In February 2006, the ADA awarded a contract to SNECMA for technical assistance to identify Kaveri’s problems. However, the Kaveri program failed to satisfy the technical requirements and was officially delinked from the Tejas in September 2008. The engine remained over weight, did not have the required thrust and there were safety and reliability issues. In December 2009, Kaveri-Snecma JV tried a back-door entry for LCA with a possible engine an uprated derivative of the M88-2 engine that powers the French Rafale fighter.
The Kaveri program has attracted much criticism due to its ambitious objective, protracted development time, cost overruns, and the DRDO’s lack of clarity and openness and reluctance in admitting problems. Another criticism has been DRDO’s resistance to involve foreign engine manufacturers until the problems became too large to handle. In November 2014, Kaveri engine (GTX-35VS) program was abandoned. In July 2016, France offered to invest and revive India’s combat jet engine project, proposing a joint development plan that could see the Kaveri powering the LCA by 2020. In November 2016, DRDO confirmed that DRDO and France’s SNECMA have tied up to revive Kaveri Engine as part of the offsets deal for 36 Rafale jets.
Kaveri Design Features Ahead
The revived Kaveri will remain a low-bypass-ratio afterburning turbofan engine featuring a six-stage core high-pressure (HP) compressor and a three-stage low-pressure (LP) compressor. GTRE hopes to fit production Tejas aircraft with an axisymmetric, multi-axis thrust-vectoring nozzle to further enhance the LCA’s agility. The general arrangement of the Kaveri will be very similar to other contemporary combat engines, such as the Eurojet EJ200, GE-F414, and SNECMA M88. Achieving a fan an overall pressure ratio of 27:1 may give the Tejas super-cruise ability. There are also plans for a non-afterburning version for an advanced jet trainer. GTX-35VS Kaveri is also proposed to go on the indigenous Advanced Medium Combat Aircraft (AMCA). 52-kilonewton Ghatak, a Kaveri derivative is being developed to power India’s Unmanned Combat Air Vehicle DRDO’s AURA.
China’s Engine Program Approach
China is already making Chinese variants of the French SNECMA M53-P2 (Mirage 2000 engine), and the Russian Saturn AL-31 (Su-30 engine) to power Chinese J-20 fighters. The J-31 will have two Russian RD-93 engines which is also used on JF-17 Thunder with PAF. Aviation Industry Corporation of China (AVIC) in the meanwhile has made real progress in creating new heat-resistant alloys, the key technology in developing afterburning turbofan jet engines. China’s overall development and production of military aircraft is advancing rapidly, but the most critical and difficult-to-produce component is the engine. Still, the outcome and impact of these efforts remains uncertain. China has already spent huge amounts on engine development and is prepared to spend up to US$49 billion on jet engine development over the next two decades. China is hoping to come out with a reliable, mass-produced version of the WS-10 engine that may power the J-11B, J-15, and J-16 aircraft. China’s ability to series-produce an engine powerful and capable enough to give the J-20 true 5th-generation performance is perhaps a few years away. China’s current pursuit of Su-35 purchase agreement with Russia primarily reflects a desire to gain access to the latest NPO Saturn/Lyulka117S engine, for its J-20 stealth fighter, to try to reduce development time for Chinese engine programs.
The Way Ahead - India
Manufacturing jet engines is a complex process and requires much superior technology infrastructure. With their complex, esoteric technologies and demanding performance parameters, aero-engines represent the pinnacle of aerospace development. Alloys, powder metallurgy, and single crystal blades must all be mastered. The Jet engine turbine blades are made using a single crystal solidification method which is specialized. India is behind the development curve and hasn’t developed the necessary metallurgical abilities & infrastructure. India yet lacks the ability to produce modern turbine blades.
Till recently, India also lacked test facilities thus necessitating testing abroad. Positioning the many pipes running from inside of the engine to line replaceable units (LRUs) on the outside on the aircraft carrying hydraulic fluid, fuel, and lubricants without interference was a challenge. There are approximately 2,500 engine components that have to be part of the assembly. Tie-up with French defence equipment manufacturer Safran, for manufacturing aviation engines under the Make-in-India scheme is a good option. The plant could also manufacture parts for the Rafale fighter jets, 36 of which have been ordered. HAL and Safran Helicopter Engines have agreed to set up a support centre in India for national and international rotorcraft customers. The centre will provide maintenance, repair and overhaul (MRO) services for Safran TM333 and HAL Shakti engines that power HAL-built helicopters. With over 1,000 engines, including 250 TM333 and 250 Shakti, Indian Armed Forces are one of the largest operators of Safran-designed helicopter engines. Shakti is fitted to HAL’s ALH - advanced light helicopter (Dhruv) and has been selected to power HAL-designed light combat helicopter (LCH).
For India it is best to make initial engines through the joint-venture route and have an enforceable transfer of technology clause. India has to master metallurgy and manufacturing techniques, components and systems design, integration, and management as they are the most probable weak points holding back engine production. Mastering engine technologies has great growing civil aviation potential also. It will be a great leap for India if we get it right.