This article is part of our special report Future of aviation: A quieter ride.
SPECIAL REPORT / As jet engines grow quieter, European researchers are turning to other parts of aircraft to reduce noise to spare those living near airports and to make the final moments before landing more comfortable for passengers. EURACTIV reports from the Paris Air Show.
Researchers working with financial support from the EU’s Clean Sky programme are experimenting with designs that could one day replace hinged flaps on aircraft wings, creating a continuous surface that would reduce noise and fuel consumption.
It could take years before such developments are ready for commercial use. But Martin Lehmann, a researcher at the Fraunhofer Institute in Germany, says “the first impressions are quite good” that “gapless” wings could one day improve the environmental footprint of aviation.
The research is part of a project financed by the EU’s Clean Sky Joint Technology Initiative, launched in 2008 to encourage public-private cooperation with a goal of cutting fuel consumption and reducing noise by 75%.
Today’s engines are on average 75% quieter than those produced at the start of the jet age 50 years ago, a result of steady technological improvements that along with more aerodynamic aviation designs have reduced the nuisance of flying for passengers and those living in the vicinity of airfields.
More traffic, more nuisance
Yet even if planes are quieter, the steady growth of air traffic means noise remains a political bombshell in Europe, which leads the world in noise-based flight restrictions. EU states are obliged to limit noise around airports under a 2002 regulation that is now being revamped to reflect the anticipated growth in the airline industry.
Engines are big noise culprits on take-off, when maximum power is needed to lift aircraft to their cruising altitude. But on approach to landing, it is mainly the turbulence that creates noise – wind blowing through gaps between the wing and flaps and whistling in the cavities where landing gear are stored.
One solution is designing an insulating cover that can pop into place when landing gear are lowered on the runway approach. Another is taking a lesson from birds, creating a smoother wing surface without the need for bulky flaps that pilots now need to manoeuvre their planes towards the runway.
Reducing or eliminating the gaps between the wing and the hinged flaps are technical challenges that Fraunhofer and other researchers in the Clean Sky Smart Fixed Wing Aircraft, or SFWA, project are working on.
“It’s a dream of aeronautical engineers from I don’t know how long,” Valerio Carli, who is also involved in the Fraunhofer’s public-private partnership, told EURACTIV at the Paris Air Show.
Eliminating hinges and flaps also reduces the plane’s weight, yielding fuel savings. Passengers have a gentler landing as well.
A breath away from quieter aviation
Researchers are experimenting with making wings more elastic to replace the need for hinges – creating what they call “gapless profiles.” Carli said the goal is to reduce noise levels by 10 decibels, equivalent to the sound of breathing, but a level that researchers say produces a significant reduction when combined with other technological advances and air-traffic management measures.
Some of the newest aircraft engines coming on the market produce noise equivalent to a food mixer or coffee grinder, or about 85 decibels.
The race is on to create ever quieter aircraft and to reduce noise pollution around airports. Industry officials say the noticeable benefits of replacing older fleets with quiet planes will gradually decline because of growing traffic.
There are 28,000 flights a day in Europe’s airspace and the European Commission estimates that the volume will grow by 50% before 2030, creating pressure to for more efficient air traffic flow and better environmental performance from airplanes.
Fraunhofer and its Clean Sky partners, which include leading aircraft and engine manufacturers, are not alone in trying to make airplanes as agile as a bird. Researchers at Cambridge University and the Massachusetts Institute of Technology in 2006 unveiled their concept of the post-2030 airplane, with flapless V-shape wings and rear-mounted engines.
The American space agency NASA has also designed a flap-free airplane with engines mounted on the top of the fuselage, to reduce the sound that reaches the ground even further.
For now, the Fraunhofer’s researchers say there are major design challenges ahead and are wary of guessing when their elastic wing concept might be available for commercial use. One challenge is reducing the physical stress on wings during descent. Another is finding the right materials that are strong but flexible.
Wing stress poses “a big problem” for the project, Fraunhofer’s Lehmann explained, adding that aeroelastic wings would most likely be used on smaller aircraft first rather than on transcontinental giants.