With its 10-strong fleet, which might rise to 16, the IAF is poised to be the giant plane’s largest overseas operator. Each C-17 is powered by four F117-PW-100 turbofan engines, manufactured by Pratt & Whitney.

This time next year, the Indian Air Force (IAF) base at Hindon on the outskirts of Delhi will be the proud home to a couple of Boeing C-17 Globemaster III strategic airlift aircraft, the vanguard of an eagerly awaited strategic air transport squadron. The C-17 Globemaster III will be the largest aircraft to enter the IAF inventory and perhaps its most flexible transport plane besides the Lockheed Martin C-130J Super Hercules. Six of these aircraft inducted by the IAF arrived at Hindon last year to form the 77 ‘Veiled Vipers’ Squadron. The Boeing C-17 advanced transport aircraft and their associated equipment contracted under a $4.1 billion ( Rs. 22,500 crore) deal that the Indian Government signed in June 2011 under the US Government’s foreign military sales (FMS) programme, are expected to be delivered by June 2015.

The C-17 attained initial operating capability in 1995 and since then has seen action in many theatres. It is truly a battle-proven beast of burden. It can carry a payload of 1,60,600 pounds and fly 2,400 nautical miles (4,440 km) un-refuelled. It also has in-flight refuelling capability. Its cruise speed is approximately 450 knots (833 km/h, 0.74 Mach). It would be natural for such a large aircraft (wingspan 51.8 m, length 53 m, height 16.8 m) to have ponderous ground-handling characteristics; yet it can take off and land on small austere runways as short as 3,000 feet (914 m) and just 90 feet (27.4 m) wide. Even on such narrow surfaces, it has the grace of a ballet dancer, being able to turn around using a three-point star turn and its excellent backing capability. The powerful thrust reverser system can back it fully loaded up to a two-degree slope.

War and Peace

The C-17 aircraft that the IAF will receive is designed equally to undertake routine peacetime airlift missions or a combat airdrop over an unsecured location under the cover of darkness or to provide urgently needed aid in a rapidly unfolding natural disaster. Boeing has already delivered 244 C-17s globally, including 28 to international customers. The US Air Force (USAF) including active National Guard and Reserve units has taken delivery of 216 planes. Such is the indispensability of the C-17 to USAF global operations that the lifespan of its fleet is expected to be shortened by five years, the result of very heavy utilisation and way above initial projections.

With its 10-strong fleet, which might rise to 16, the IAF is poised to be the giant plane’s largest overseas operator. The aircraft will be useful for strategic airlift and transporting outsize equipment to distant areas. The C-17’s 72.8-tonne maximum payload is a marked increase over the 45 to 47-tonne capacity of the IL-76, currently the country’s sole heavy-lift military transport aircraft and will greatly contribute to the IAF’s ambitious aim of tripling its lift capacity. India’s forces need the means to quickly transport large numbers of troops to counter any emerging threat on the northern, eastern or western borders as also to respond rapidly to terror tactics such as the 26/11 Mumbai attacks. The C-17 should prove invaluable in such situations.

Power on Demand

Each C-17 is powered by four F117-PW-100 turbofan engines, manufactured by Pratt & Whitney, a unit of United Technologies Corporation. Pratt & Whitney is a world leader in the design, manufacture and servicing of aircraft engines. It is currently making waves in the commercial aviation industry on account of its revolutionary new engine, the PurePower PW1000G with patented geared turbofan (GTF) technology. This new development in engine technology is destined to power the next generation of fuel efficient passenger aircraft. The company has a particularly enviable military track record, providing top-of-the-line engines to fighters such as the F-15 Eagle, F-16 Fighting Falcon, F-22 Raptor and F-35 Lightning II joint strike fighter. The 40,400 pound thrust F117-PW-100, with a unit cost in 2012 of $9.75 million ( Rs. 54 crore), is the military avatar of the commercial PW2000. The PW2000/PW 2037 is a series of high bypass turbofan engines powering the Boeing 757 twinjet. The F117 complements its commercial cousin’s reputation as the world’s leading mid-range thrust engine. Rather unusually for a military power plant, therefore, it minimises fuel burn and meets all current and anticipated commercial requirements for low engine noise and exhaust emissions.

The F117-PW-100 has a twin-spool, axial flow, single stage fan compressor with four low pressure (LP) and 12 high pressure (HP) stages. Its turbine has two LP and five HP stages and it has an annular combustor. The overall pressure ratio at maximum power is 30.8:1, thrust-to-weight ratio is 5.7:1, and bypass ratio is 5.9:1. A full authority digital electronic control (FADEC) with greater capacity delivers higher operational performance, lower fuel burn and improved maintenance diagnostics. Operating with two independent channels for control and redundancy, the FADEC system not only makes it easier for flight crews to manage engine control, but also renders the engine much more efficient.

A defining characteristic of the C-17 is the “externally blown flap” or “powered lift” system that enables the plane to make slow, steep approaches despite heavy cargo loads. With this system, the engine’s exhaust flow is directed below and through slotted flaps to augment the wing lift to roughly twice that of comparable transport planes. This allows much shorter take off runs and steeper descents on approach for landing. The latest F117 model, the reduced temperature configuration (RTC), uses technical and material advancements such as second generation single crystal turbine materials, improved cooling management and thermal barrier coatings to lower the operating temperatures.