Engines are front and centre once more as the driving force behind advances in aviation as the industry struggles with soaring fuel costs and mounting environmental concerns.
The year ahead will see flight tests of new fuels as manufacturers and operators seek alternatives that can reduce costs and cut emissions. There will be progress on engines to power the next generation of single-aisle airliner. But how quickly new fuels and engines emerge, and how radically they differ from those of today, will depend on whether customers keep up the pressure for dramatic improvements in fuel burn and emissions.
During 2007, more airlines called for airframe and engine manufacturers to develop a new generation of narrowbody aircraft offering 15-20% lower fuel burn and equivalent cuts in carbon emissions. Mitsubishi and Bombardier have responded first, selecting Pratt & Whitney's Geared Turbofan to power the 70/90-seat MRJ and 110/130-seat CSeries, both planned to enter service in 2013.
Launch decisions on both aircraft are expected in 2008, with the 12% lower specific fuel consumption claimed for the GTF a major plank in marketing efforts. Flight trials of the GTF demonstrator engine will begin in May 2008, on P&W's Boeing 747 testbed, after completion of the ground testing that started in November 2007.
Launch of the GTF or either or both of the MRJ and CSeries will set the agenda for debate on powerplants for the next-generation narrowbodies, although key engine architecture selections are not expected before 2009. They are paced by the airframers, and Boeing now says it expects to make a launch decision on a 737 replacement by mid-2009.
International Aero Engines is weighing competing proposals from its shareholders, including P&W's GTF and an advanced two-shaft turbofan from Rolls-Royce. CFM International partners General Electric and Snecma are developing technology for both an advanced turbofan and an open-rotor engine, with choice between these architectures planned before the decade's end.
CFM and R-R believe advanced turbofans can deliver a 15% lower sfc than today's CFM56 and V2500 by 2015, enough to achieve a 20% reduction in fuel burn when combined with airframe advances. P&W says the same for GTF. But if airlines want deeper cuts, open rotors may be the only option.
Under Europe's Clean Sky joint technology initiative, which begins in January 2008, R-R and Snecma plan to run open-rotor demonstrators in 2012, but these will be subscale propulsor tests. CFM believes the acoustic and installation challenges to be overcome mean an open-rotor engine would not be available before 2018.
Decisions on new fuels will come earlier. Work on alternative fossil fuels set the pace, but interest in biofuels accelerated during 2007. Key flight demonstrations planned for 2008 could lead to earlier-than-anticipated availability of second-generation bio-jet fuels derived from sustainable feedstocks.
Development of "drop-in" replacements for oil-based jet fuel has been given impetus by the US Air Force, which ended 2007 with the cross-country demonstration flight of a Boeing C-17 airlifter using synthetic fuel. This is a step towards the USAF's goal of having all its aircraft fleets qualified to use a blend of conventional JP-8 and synthetic Fischer-Tropsch jet fuel by 2011, in a bid to reduce its dependence on foreign oil.
The potential environmental benefits of gas-to-liquid synthetic jet fuel are being researched by Airbus, Rolls-Royce, Shell and four Qatar-based organisations including Qatar Airways. Synthetic jet fuel produced from natural gas using the F-T process burns more cleanly and has higher energy density, reducing fuel burn, says R-R.
Work on bio-jet fuels advanced rapidly in 2007, with two key flight demonstrations planned for 2008. Virgin Atlantic Airways, Boeing and General Electric plan to fly a CF6-80C2-powered 747-400 using biofuel in one engine, while Air New Zealand, Boeing and Rolls-Royce plan a similar trial in an RB.211-powered 747-400.
Neither will involve an approved bio-jet fuel, and synthetic F-T fuels remain the near-term drop-in alternatives to Jet-A, but offer little environmental benefit. Proponents hope the demonstrations will spur commercial development and production of biofuels suitable for use in aircraft.
Leading fractional-ownership operator NetJets, operating a fleet of more than 600 business jets, launched a climate initiative in 2007 that includes sponsoring the next-generation jet fuel project at Princeton University and the University of California, Davis. This centres on producing an ultra-low-emissions fuel from a combination of coal and biomass.
In military propulsion, the highlight willbe the start of testing of Lockheed Martin's first short take-off and vertical landingF-35B Joint Strike Fighter. Powered by the Pratt & Whitney F135, the F-35B is due to begin hover-pit testing by February and flight testing in May.
After US Congress in 2007 overturned efforts by the Department of Defense to cancel development of the alternative JSF powerplant, the F136, partners General Electric and Rolls-Royce will work towards a first run of the final product configuration engine early in 2009. Early international F-35 customers could make engine decisions in 2008.