Over the decades, the military aviation industry has developed a bewildering array of advanced engines, each claiming to be of superior performance. However, as engines become more powerful, environmental concerns are correspondingly growing. Apart from raw power, military aero engine designers will increasingly need to pay attention to green parameters.

When it comes to military aircraft, whether meant for high-intensity combat or air transport, there’s a premium on performance. And the power plant is the very heart of performance. But for sheer power, look no further than the Pratt & Whitney F135. It is an afterburning turbofan specially developed for the keenly-awaited Lockheed Martin F-35 Lightning II. The F-35 is a family of stealthy, single-engine, fifth generation, multi-role fighter, under development in the United States. While the F-35A is a conventional take off and landing variant, the F-35B is a short take off and vertical-landing aircraft, and the F-35C is a carrier-based option. The same F135—claimed to be the world’s most powerful fighter engine—will power all three F-35 variants.

The F135 is derived from the Pratt & Whitney F119-PW-100 that powers the US Air Force’s (USAF) battle-proven F-22 Raptor. It has a thrust of 43,000 lbf (191.3 kN) with afterburner and 28,000 lbf (128.1 kN) dry. It is a two-shaft engine featuring a three-stage low pressure (LP) fan and a sixstage high pressure (HP) compressor. The hot section has a short annular combustor with a single-stage HP turbine unit and a two-stage LP turbine. The F135 has approximately 40 per cent fewer parts than legacy engines, which contributes to its improved reliability. It includes advanced prognostics and health management systems. All line-replaceable components can be removed and replaced using a set of six common hand tools.

The futuristic F135 engine originally had a close competitor—an engine designated the F136 and produced by the Fighter Engine Team (FET) comprising GE Aviation and Rolls-Royce. The F136 has a twin-spool, counter-rotating, low aspect ratio, axial flow compressor, an annular combustor, and an axial flow, counter-rotating turbine. Its claimed maximum thrust range is 40,000 lbf. Lagging behind the F135 in development, this capable engine is now in the doldrums—a victim of massive cuts in the US defence budget. But so high are the stakes that the FET recently sought the Pentagon’s permission to resume development of the F136, offering to spend a cool $100 million of their own money for the purpose.

Fighter Duels

In India, the hardware headlines have been dominated by the planned acquisition of 126 medium multi-role combat aircraft (MMRCA) for the Indian Air Force (IAF). The longrunning MMRCA saga began with six contestants but four were dropped after failing to meet technical requirements, leaving only two aircraft—the Eurofighter Typhoon and the Dassault Rafale—in contention for the $10.4 billion deal that could be inked by December.

The front-running Typhoon’s twin EJ200 engines are manufactured by EuroJet Turbo GmbH consortium which comprises Rolls-Royce, MTU, Avio and ITP. These powerful turbofan engines, aided by the aircraft’s excellent aerodynamics, reportedly allow it to super-cruise (i.e. to cruise supersonically without the use of reheat) at between 1.2 and 1.5 Mach for long periods. The EJ200 is a lightweight engine with high strength and high temperature capability. It is a twin-shaft, afterburning turbofan, with three LP and five HP compressor stages, powered by two singlestage turbines (LP and HP). Rather unusually for an advanced turbofan, the fan lacks variable camber inlet guide vanes (IGV). The combustor is annular with air-spray injectors. Engine control is by an integrated full authority digital engine control (FADEC) system. Each EJ200 has a dry thrust of 13,500 lbf (60 kN) while the thrust with afterburner is 20,250 lbf (90 kN).

The Typhoon’s fierce rival, the French Rafale, also has twin engines—Snecma M88-2 turbofans. Each engine has a dry rating of 11,250 lbf (50 kN) while the thrust with afterburner is 17,000 lbf (75.6 kN). The M88-2 comprises a three-stage LP compressor with IGV, an annular combustion chamber, singlestage HP and LP turbines, a radial afterburner chamber, variable-section convergent flap-type nozzle and FADEC. It was designed with easy maintainability and reduced operating costs in mind. It consists of twenty-one modules for interchange and replacement repairs without the need for recalibration.

Then there are the four “also-rans” of the MMRCA shoot out, beginning with the F-16 Fighting Falcon. Lockheed Martin offered India the customised F-16IN Super Viper, which is based on the F-16E/F Block 60. It has one enhanced highthrust engine, the General Electric F110-GE-132A which can produce 32,500 lbf (144 kN) maximum thrust. This engine is derived from GE’s highly successful F110 engine family that powers the bulk of F-16C/Ds worldwide.

The other American offering, the Boeing F/A-18E/F Super Hornet has twin General Electric F414-GE-400 turbofans, each with dry thrust 14,000 lbf (62.3 kN) and thrust with afterburner 22,000 lbf (97.9 kN). Sweden’s contender was the Saab JAS 39 Gripen IN, an India-specific version of the Gripen NG, fitted with a single GE Aviation/Volvo Aero F414G engine. India’s own Tejas Mk II light combat aircraft is planned to be powered by one GE F414-GE-INS6 engine.

Lastly, the Russian Mikoyan MiG-35 has twin Klimov RD-33MK afterburning turbofans with dry thrust 11,900 lbf (53.0 kN) each and thrust with afterburner 19,800 lbf (88.3 kN) each. The RD-33MK is the latest version of the RD-33 and is seven per cent more powerful than the baseline model. The engines can be fitted with vectored-thrust nozzles, which enable the MiG-35 to remain controllable for sustained periods in zero-speed and “negative-speed” (tailforward) situations without angle-of-attack limitations.