Aircraft engine makers flying into a brighter future

The Sunday Times
February 8, 2009
Quieter planes with lower emissions are set for take-off
Dominic O’Connell

VISITORS to the Farnborough air show are used to loud noise, but this was different. A high-pitched buzz throbbed across the Hampshire airfield, prompting spectators to put down their Pimms and crane their necks at the aircraft soaring above them.
It looked like an ordinary commercial airliner – but there was something odd about its engines. One was conventional, while the other had two rows of curved propellers protruding hedgehog-like from the rear. This was the source of the unnerving howl.
The unducted fan, as the banshee powerplant was called, flew at Farnborough 21 years ago. It was a prototype from General Electric, the US aero-engines group, which claimed it would use much less fuel than standard designs. It never made it into production, and was pushed into the footnotes of aviation history by falling fuel prices and noise worries.
Until now, that is. Last year the National Aeronautics and Space Administration asked GE to resurrect and update the design. Trials start in Cleveland, Ohio, next month with the same test rig used 20 years ago. Nasa had kept it, just in case.
GE’s leap back to the future is indicative of the scramble for greater fuel economy and lower emissions that is gripping the industry. The big players – Rolls-Royce, GE, Pratt & Whitney and France’s Snecma – are spending hundreds of millions of pounds a year on research and development, driven by the long-term prospect of high oil prices and harsh scrutiny of aviation’s contribution to green-house-gas emissions.
It is a costly, high-stakes game. The group that places its technology bets wrongly risks being marginalised. The prize, on the other hand, is considerable, with industry leaders forecasting a new generation of planes that use 50% less fuel and are quieter than the best aircraft flying today.
All the big players are constantly tweaking their current products to squeeze out more efficiency. Mark King, president of commercial aero-space at Rolls-Royce, points out that the new version of its Trent engine is 15% more efficient than the 1995 original.
The next big leap, however, will come with the replacement of the workhorses of commercial aviation, the Airbus A320 and Boeing 737. New planes were expected around 2013, but are not now likely until around 2020, by which time some radical new engines should be ready to fly.
Undeterred by the delay, Pratt & Whitney, part of the American industrial conglomerate United Technologies Corporation (UTC) is pressing ahead with its “geared turbofan” (GTF). The new engine was shown in public for the first time last week in Toulouse, France, where it has been undertaking flight trials with Airbus. Pratt has spent over $1 billion (£684m) and two decades on the engine, which will go into service in 2013 on planes built not by Airbus or Boeing, but by Bombardier of Canada and Japan’s Mitsubishi.
The secret of the GTF is a gear-box that slows down the fan at the front of the engine. This lets the high-temperature gas turbine at its heart run faster and more efficiently than on a conventional turbofan. Pratt claims the GTF will cut fuel burn by up to 15%, with a corresponding reduction in carbon-dioxide emissions. It makes even greater claims on noise, claiming a 50% decrease, which translates into more than 70% in noise-affected areas around airports. Pratt said airlines using the engines could save over $1.5m a year per plane.
Bob Saia, the executive in charge of the programme, is not fazed by the postponement of the new Airbus and Boeing planes, saying: “It gives us time to work on a second generation of engines.”
GE and Rolls-Royce have turned their backs on the GTF, claiming they can get similar savings from improved standard turbofans. They are both working on new versions of the unducted fan that howled over Farnborough – now called the “open rotor” engine.
King said tests with a one-sixth scale model indicated the noise problem could be fixed and he expected open rotor to bring fuel savings of about 30%.
Rick Kennedy of GE said its new powerplant would be ready by 2020.
Pratt doesn’t dispute the greater fuel savings offered by the design, but says noise and other practicalities led it to pursue the geared fan instead.
King said Rolls-Royce was encouraging aircraft makers to take a broad approach to cut carbon and fuel use. “We are taking a fundamental look at the problem by talking to plane makers about what their next products will look like. We want to lead thinking in the sector.”