Clean Sky: Aviation researchers test radical ideas in a conservative industry

A counter-rotor engine like this one being developed under the Clean Sky programme could be propelling aircraft within 20 years. [Timothy Spence]

This article is part of our special report Le Bourget 2015.

SPECIAL REPORT / European researchers foresee a time when people could travel across the globe in the equivalent’s of today’s hybrid cars – an airplane that uses fossil fuel when a burst of energy is needed, then switches to stored electricity while cruising to a landing.

It’s not quite Star Trek, but the corporations and academics involved in helping to design next-generation aviation technologies hope the ideas being thrown about today with the help of European Union funding will reduce fossil fuel consumption and curtail the noise impact of a steadily growing industry.

Some of that future is on display this week at the Paris Air Show. Many of the same companies involved in the EU’s Clean Sky research project are vying here to promote current technologies as the greenest ever.

Businesses involved in the collaborative programme also see a benefit beyond reducing the industry’s growing environmental footprint – future profits.

“This is an opportunity for European industry to gain competitiveness and technology,” Gerhard Ebenhoch of MTU Aero Engines, a German firm, explained in a Clean Sky briefing in Paris.

Billions of investment

Clean Sky was launched in 2008 with €1.6 billion in funding split by the partner firms and the European Commission. The second phase, launched in 2014, has a budget of €4 billion over a decade. Its mission is to achieve a 30% reduction in aviation carbon dioxide and nitrogen emissions and up to a 75% reduction in the industry’s noise footprint.

“One can easily translate all the investment into a benefit for society, either jobs in education, knowledge growth, as well as allowing people to fly,” said Axel Flaig, Airbus senior vice president for research and technology. The European aircraft maker is a partner in the Clean Sky along with some of Europe’s leading research centres and other aviation companies.

But achieving the Clean Sky goals will not be easy. Global commercial aviation is growing at a 5 percent annual clip and has managed to weather economic and political shocks of recent years.

It could take years to deploy some of the technologies developed over the programme’s first eight years. Other outcomes offer more incremental improvements in performance, including some passengers may never see, such as new power storage technologies that reduce fossil fuel use in aircraft operations.

For Airbus’ Flaig, who spoke to EURACTIV at the Paris Air Show, Clean Sky offers two especially promising technological developments – one in propulsion and the other in aerodynamic wing design.

The first is part of Clean Sky’s Sustainable and Green Engines (SAGE) project. Researchers have worked in recent years to develop open-rotor motors that tests suggest would lead to dramatic reductions in fuel use and emissions.

Snecma, a division of France’s Safran Group, and Britain’s Rolls-Royce have both developed open rotor concepts. The experimental engines feature counter-rotating propellers, giving them the ungainly appearance of an advanced food mixer.

Radical ideas

“It’s a very radical design,” said Flaig, who explained that propellers in general are more efficient than jet engines. The advantage of a double set of blades is that the air passing through the first set changes direction “and you still have energy in flow. When you have a counter-rotating propeller, you also remove this energy and this makes it more efficient.”

Researchers see additional efficiency by mounting these twin-blade engines on the back of the aircraft fuselage, thus reducing the wind drag that occurs with wing-mounted engines. Tests have shown the open rotors could cut emissions by 30 percent.

The SAGE project has had to overcome problems. The double set of blades made the engines heavy and noise, complicating the mission to develop quieter and more agile propulsion systems. Flaig says some of the early obstacles have been overcome and that testing could begin in another decade. If successful, airplanes with open rotor motors could begin appearing on the tarmac in the 2030s.

Another Clean Sky venture is closer to taking flight. Researchers involved in the Smart Fixed Wing Aircraft (SFWA) project applied laminar coatings to shortened wings of a long-range Airbus carrier to reduce wind drag, cutting the noise profile and reducing fuel consumption by 8 percent.

The stubbier wings are being fitted on an A340 and the plane could be ready for test runs in 2017, Flaig said.

Flaig says the possibilities for innovation are as unlimited as the sky. He points to a group of university students who developed the concept of imbedding rechargeable batteries in aircraft skins made of composite metals, opening the door to hybrid propulsion.

Still, bringing such ideas to the market could take a generation or more in an industry as cautious as aviation. As Jeff Hobday of Clean Sky partner Rolls-Royce Plc explained at the Clean Sky briefing: “We’re very risk averse and wisely so. So we have to be confident with the technology we are developing and the only way to do that is through flight and ground demonstrators.”

The aviation industry wants to save costs and cut their carbon emissions to comply with polices like the EU’s Emissions Trading System. The industry aims to improve fuel efficiency by an average of 1.5% per year in order to halve emissions by 2050 from 2005 levels.

Doing so won’t be easy with passenger traffic forecast to double in two decades. The Air Transport Action Group, a Geneva-based industry group, estimates that the number of people flying will rise from 2.7 billion today to 5.9 billion in 2030. That will require more than 45,000 aircraft, more than twice the number in service today.

The European Commission projects that global international aviation emissions will be around 70 percent higher in 2020 than in 2005. The airline industry has set a target of carbon-neutral growth by 2020 and wants to cut carbon emissions by 50 percent compared to 2005 levels by mid-century.

While carbon dioxide emissions from passenger airlines account for some 2% of the total, aviation emissions are growing at 6% to 7% per year in the EU, according to Friends of the Earth Europe, an environmental group. An Organisation for Economic Cooperation and Development transportation report shows that aviation carbon emissions in the EU-15 rose 85% from 1990-2007, a time of liberalisation and surging passenger traffic.

The US space agency NASA is also conducting research aimed at reducing the environmental footprint of aviation. The agency announced at the Paris Air Show that it had signed a deal with the German Aerospace Center (DLR) to collaborate on reducing noise.

The agreements were signed at by Jaiwon Shin, associate administrator in NASA's research arm, and Rolf Henke, DLR’s executive board member for aeronautics research.

“In recent years, we have brought our scientific strengths together in several projects, including joint research flights for more efficient and environment-friendly aircraft,” Henke said in a statement released by NASA. “We are now expanding this successful collaboration into the research areas of aircraft noise and rotor craft.”

“NASA and DLR have had a successful research relationship for many years now,” Shin said. “These agreements will ensure that productive collaboration continues as we work together solving challenges that will benefit a global aviation community and flyers worldwide.”

  • 2008-2014: Clean Sky 1
  • 2014:2024: Clean Sky 2
  • 5-21 June 2015: Paris Air Show [FR]
  • 2020: Aviation industry’s target date for achieving carbon-neutral growth
  • 2050: Aviation industry’s target date for achieving a 50 percent reduction in carbon emissions (from 2005 levels)

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