SP Guide Publications puts forth a well compiled articulation of issues, pursuits and accomplishments of the Indian Army, over the years

— General Manoj Pande, Indian Army Chief

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— Admiral R. Hari Kumar, Indian Navy Chief

My compliments to SP Guide Publications for informative and credible reportage on contemporary aerospace issues over the past six decades.

— Air Chief Marshal V.R. Chaudhari, Indian Air Force Chief

Aero Engines - The Hype & the Hyper

Issue: 05-2009By Air Marshal (Retd) V.K. Bhatia, New Delhi

Today, practically all the frontline fighters of the world use turbofan jet engines. For tomorrow, one concept fast gaining momentum is that of HYPERSONIC flight.

Wright brothers Orville and Wilbur are credited with making the first controlled, heavierthan-air flight. To power the aircraft, they had specially commissioned their bicycle workshop mechanic, Charlie Taylor, to build a matching low-weight engine, mostly of the light metal aluminum. On December 17, 1903, with the first flight of Wright Flyer 1, they not only made aviation history but also set the trend for designers and manufacturers of aero engines to build products in sync with the requirements of the aircraft. Sensibly, this trend has continued during the entire span of the rapidly changing aviation scenario, but most unfailingly, in the field of military aviation.

Aero engines per force have to be extremely reliable, lightweight, powerful, fuel-efficient, easily maintainable and capable of operating at high altitudes as also at high speeds. Initially, automobile engines were suitably modified and used on aircraft, but soon a new breed of aero engine manufacturers sprang up to cater for the specific needs of designers and manufacturers of aircraft. Various types of piston-engines with different cylinder positions, such as inline, rotary, radial and v-shaped, were tried out. But in their quest to fly faster and higher, especially the fighter aircraft, designers hit a dead end with the propeller-driven, piston-engined aircraft, because with the propeller-tips reaching the speed of sound, the aircraft speed had to remain in the vicinity of 500 mph. It was realised that if aircraft performance was ever to increase, a way would have to be found to improve the design of the piston engine—or, alternatively, a wholly new type of power plant would have to be developed. The latter proved to be an easier option with the advent of the gas turbine engine, commonly called a jet engine, which, as the events unfolded, ushered in a revolution in aviation almost as vital as the first heavierthan-air flight by the Wright Brothers.

Jet Pips the Piston
By the middle of the 1950s, jet engines had been propelled to centre stage as power plants of choice for all combat aircraft. Piston-engines were confined to powering transport, liaison and other special duty aircraft. Even here, improvements in the turboprop (jet engine with propeller) pushed the piston out of the mainstream. The speed advantages of the jet engines were so alluring that by the next decade, all large civilian aircraft were also jet powered. But it was not till the late 1970s, when, with the advent of high bypass jet engines, fuel efficiency was so optimised as to herald the era of fast, safe and economical travel for the general public.

Meanwhile, eruption of Cold War resulted in an unprecedented arms race, which also gave catalytic push to ever faster airplanes flying at high speeds at the extremes of atmospheric boundaries. Who can forget the highly complex Pratt & Whitney J58-P4. A pièce de résistance, the J58-P4 was especially designed to power the US spy plane, the trisonic SR-71 Blackbird. Sharing the limelight was its counterpart, the Tumansky R 15(B) engine extraordinaire, used to power the matching Russian MiG-25 Mach 3 high-altitude aircraft for both interception and strategic reconnaissance roles.

Cut to the Present
While jet engines continued to evolve and were perfected as the mainstay for powering military combat aircraft, other engines were also being improved upon for use on various other types of aerial platforms. Mach 3 fighters and their engines may have lost some relevance after the arrival of space-based and near space platforms, but there are other fields where technological advancements offer capabilities to match emerging requirements. While advanced models of turbojets are being used for jet fighters, turboshafts are being further honed to power the new breed of helicopters. Similarly, while advanced technologies are being used in the field of turboprop engines, predominantly for military transports; piston-engines are shaping up for special platforms such as the Unmanned Aerial Vehicles.

Practically all the frontline fighters of the world use turbofan jet engines, fitted with a combination package of fan plus axial-flow compressors in varying numbers. All have afterburners for augmented thrust. Most are leaning towards vectored thrust to be able to impart much greater manoeuvrability to the combat platforms. In this category come the engines fitted on the Lockheed Martin F-22A Raptor (F119-PW-100), the Russian Su-30 MKI (AL-35F), being operated by the Indian Air Force (IAF) and the RD-33 MK thrust-vectoring engines being proposed for the MiG-35. A few are also incorporating super-cruise capability (see table).

Novel Designs
Lockheed Martin F-35 Lightning-II:
A somewhat novel engine design technology has been incorporated in powering the under development US Fifth Generation stealth F-35 JSF (Joint Strike Fighter). Two different engines are being developed for the F-35: the Pratt & Whitney F135 and the General Electric/Rolls-Royce F136 with stealth and supercruise capabilities. In addition, the Short Take-off & Vertical Landing (STOVL) version uses the innovative LiftSystem, patented by Lockheed Martin and built by Rolls-Royce. Different from the preceding generation of STOVL designs (such as the Harrier), the LiftSystem is composed of a lift fan, driveshaft, clutch, two roll posts and a three Bearing Swivel Module. The latter is a thrust vectoring nozzle which allows the main engine exhaust to be deflected downwards at the tail of the aircraft. The lift fan near the front of the aircraft provides the counter-balancing thrust. Roll control during slow flight is achieved by diverting pressurised air through wing-mounted thrust nozzles called Roll Posts.
Airbus A400M Military Transport: After lengthy deliberations and intense competition, Airbus selected the somewhat unique engine TP400-D6 from EuroProp International (ITP, MTU, Rolls-Royce and Snecma) for it’s under development four-engined A400M Future Large Aircraft programme. Each engine provides (13,000 shp) thermodynamic power de-rated to (11,000 shp) for take-off. Engine has a threeshaft configuration, an offset gearbox and dual-channel Full Authority Digital Engine Control with propeller control. Each engine sports an eight-blade FH386 composite curved propeller, capable of full reversal of pitch enabling the aircraft to back up at MTOW (2 deg/1 deg slope on concrete/soft surface). The uniqueness lies in the fact that the engines are handed, with one of each wing pair rotating in opposite direction to the other, offering reduction in torque and elimination of asymmetric airflow over wing. This down between engine configuration also improves asymmetric handling in the event of one of the engines becoming inoperative.