Anyone living near an airport will testify to the ferocious sound of airplanes taking off and landing. It can be deafening very close to the runway and still very disruptive at a distance. But thanks to a European Union research project, those thundering flyovers could be muffled, sparing the eardrums of people under the flight paths.
Aircraft noise has been an issue for years, and it has been partially addressed through efficient acoustic design rules and noise reduction technologies in the engines. But until recently, very little could be done to soften the sounds from the airframe itself, which is an unexpectedly powerful noise source when aircraft are approaching to land.
The TIMPAN project (Technologies to IMProve Airframe Noise), looked at ways of reducing the din by focusing on two areas that are responsible for about half of the total aircraft noise in approach and landing situations: landing gear components and high-lift devices such as flaps and slats.
“We were very proud because we were able to meet our mid-term target of reducing airframe noise by 5 dB compared to the state-of-the-art designs from 2000,” says TIMPAN’s project coordinator Jean-François Piet, who heads airframe, propeller and jet noise activities for Airbus.
The TIMPAN landing gear is a great achievement, reducing noise levels substantially. Piet says much of the credit for its approach goes to Constantin Sandu, an aerospace engineer based in Bucharest, Romania, who was brought in to take part in the project. “He had an unusual background, and his proposals were initially met with scepticism,” says Piet. “But he was very innovative and thought completely out-of-the-box. Being part of the TIMPAN consortium meant he could brain-storm with other partners. And we were all delighted when we saw his idea actually work.”
Testing a quarter-scaled landing gear model in a wind tunnel, TIMPAN experimented with a number of modifications to the bogies, wheel spacing, leg-doors and brake fairings. But the main breakthrough came when the researchers took advantage of the pan-European links and followed up on Sandu’s ideas. That meant putting mesh materials around specific parts of the landing gear. They found that the meshes reduced the speed and turbulence of the flow impinging downstream components, dramatically lowering noise levels.
The mesh concept is one of the two patents TIMPAN has filed for landing gear low-noise technologies, and the results are already being used to research the design of landing gears for future aircraft.
TIMPAN also was able to reduce the noise around the slotted slats that account for most of the noise on high-lift systems of large aircraft. Using an aero-acoustic optimisation process (acoustics and aerodynamics computations), the project tested various configurations and found that an optimal slat setting could cut slat noise by up to 3.5 dB.
The TIMPAN technologies are still being further developed within current EU research programmes, and it may yet be a while before it is fitted on airplanes. But Piet says he hopes they will be applied in one of the forthcoming Airbus jet airliners.
Project acronym: TIMPAN
Participants: France (Coordinator), Germany, United Kingdom, France, Belgium, Netherlands, Romania