One promising development that is supported by a European Union research programme is the open rotor engine that can propel an aircraft with up to 35% more efficiency than the conventional jets used today.
But there’s a huge drawback: the counter-rotating propellors, which look like a twin set of twisted fan blades, are noisy. Researchers who tested similar engines more than 30 years ago had to shelve plans for commercial development in part because of their ear-piercing sound.
The open rotor technology is symbolic of the challenges faced by both policymakers and the airlines in trying to solve one environmental problem without creating another. The drive for the use of biofuels in aviation has, for instance, spurred concerns amongst environmentalists that when the impact of production is included, plant fuels do little to reduce greenhouse gas emissions.
What is clear is the need to improve efficiency to reduce the costs of complying with EU emissions rules and to meet aviation industry commitments to cut carbon emissions to 50% of 2005 levels by mid-century.
“Operational efficiency is the Number One thing to improve profitability and competitiveness,” Ray Conner, the new president of Boeing’s commercial airplanes division, told journalists at the Farnborough International Airshow in Britain on Monday.
Lighter and more streamlined
In trying to meet those goals, aircraft manufactures have turned to lighter and more durable metals like titanium, sleeker aircraft designs, slimmer seats and even low-energy lightbulbs to save fuel. But above all, engines have to do more with less.
Backed by the EU-aviation industry Clean Sky partnership to promote greener flying, companies like Snecma, a division of France’s Safran Group, and Britain’s Rolls-Royce are testing open rotor engines to ensure that they are safe - and quiet.
They are part of the growing technology field aimed at improving efficiency and lowering aviation emissions as the industry grows in the decades ahead. Already, revolutions in engine technology, streamlined wing and fuselage design and lighter component parts have helped reduce fuel use by 30% since 1990, according to Sustainable Aviation, an industry organisation in Britain.
Environmental concerns alone are not driving changes - many European and American airlines are struggling to squeeze out profits as passenger numbers level off in turbulent economic times, and cutting fuel cost is a quick way to bring down expenses. They are also concerned about long-term stability of fossil fuel supplies as global demand for passenger travel grows.
A boom market
Both Europe’s Airbus and Boeing, the leading American aircraft maker, project a surge in production in the next 40 years, driven by growing passenger numbers in emerging countries and the need for airlines in the traditionally dominant markets of Europe and the United States to replace older, less efficient airplanes.
Boeing’s newly published Current Market Outlook projects that world airlines will need 34,000 new aircraft by 2031, up from 19,890 in service today and more than five times the number of passenger aircraft in service in 1977.
The US market research firm Forecast International, in a reported released at the Farnborough air show, estimates that 14,655 new large airliners will be needed over the next decade, with Airbus and Boeing battling for much of that market.
More economical aircraft are not the only way to lift profits while lower pollution. Europe’s plans to consolidate national air traffic control systems would reduce flight delays and improve environmental performance - although the EU’s signature programme to improve traffic management, the Single European Sky, appears to be well off target.
Aviation industry officials have told EurActiv that the European Commission is likely to propose a revamp of the Single European Sky as early as next year, in effect conceding that the earlier plans were too ambitious.
Meanwhile, passenger airlines continue to look to their suppliers for innovations to boost efficiency. Lighter but more durable metals like titanium used in engines, landing gear and fittings have helped reduce aircraft weight. Arch-rivals Airbus and Boeing say the newest versions of their traditional workhorse aircraft - the A320neo and Boeing 737 Max - will deliver double-digit improvements in efficiency.
Engine for the future
But technologies like the open rotor are not likely to show up on aircraft anytime soon. Aircraft would have to be re-engineered and designed to accommodate their rear-mounted propellers. Their use would also be limited to single-aisle aircraft rather than the larger, continent-hopping jets that emit more carbon gases.
And solving the noise problem could take time. Aside from the research taking place in Europe, the US space agency NASA, in a report released last year, concluded that despite efficiency advantages of open-rotor technology, noise presented a significant setback with current technology.
Safety issues also remain a concern. Ian Lane, who heads the stress methods and expertise for Airbus in Britain, says aircraft would have to be redesigned to handle the impact of flying fragments should an engine break apart in flight - a rare but not unprecedented occurrence.
Still, he says design changes in future models can be made to ensure safety and the efficiency of open rotors.
“Our customers need reliable aircraft that work today. We don’t force technology on a customer. But, he said at an innovation exhibition at Farnborough, “every new airframe is an opportunity to incorporate new technologies.”