ATRA flies over microphone array at Cochstedt Airport
During the flight tests for the Low Noise ATRA project, the A320 ATRA research aircraft flies over a microphone array at Magdeburg-Cochstedt Airport. Acoustic measurements were taken on the ground using a large-scale microphone array consisting of 30 microphones spread across an area of 120 by 340 metres.
A320 ATRA fly-past with noise reduction technologies
The aircraft was fitted with eight different noise reduction technologies for the flight tests, including new engine exhaust nozzles with specially designed edge profiles, porous materials along the edges of the landing flaps and partial fairings for the landing gear.
Analysis of test results shows that targeted modifications can reduce noise emissions from individual aircraft components by up to six decibels.
The simulation data highlights the 800-hertz one-third octave band, represented in colours ranging from blue to green to red, illustrating measured sound levels before and after noise-reduction features were installed.
DLR researchers have demonstrated that retrofitting aircraft can reduce noise levels by up to three decibels.
Initial tests using specialised technologies, such as modified engine exhausts and landing gear fairings, have yielded positive results.
The long-term goal is to make aviation quieter and more sustainable.
Focus: Aviation, aircraft noise reduction
Aircraft noise affects millions of people, particularly those living near airports. As part of the Low Noise ATRA (LNATRA) project, researchers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) have achieved promising results in the field of aviation noise pollution, demonstrating that targeted retrofits to existing aircraft can lead to measurable noise reduction.
Noise reduction of three decibels
The results of the DLR research are striking. "We were able to reduce noise at individual sources, such as the landing gear and the edges of the landing flaps, by up to six decibels," explains Michael Pott-Pollenske from the DLR Institute of Aerodynamics and Flow Technology. Overall, retrofitting measures led to a decrease in flyover noise of three decibels (dB). "For people on the ground, this corresponds to a perceived noise reduction of around 30 percent."
Brake covers and partial fairing on the main landing gear
Brake covers and fairings on the main landing gear were among the eight noise-reduction measures implemented on the ATRA research aircraft.
These findings are based on an in-depth analysis of flight tests conducted by DLR between 2016 and 2019, using the A320 Advanced Technology Research Aircraft (ATRA) at Magdeburg-Cochstedt Airport. The aircraft was fitted with eight different noise reduction technologies, including new engine exhaust nozzles with specially designed edge profiles, porous materials along the edges of the landing flaps and partial fairings for the landing gear.
Acoustic measurements were taken on the ground using a large-scale microphone array consisting of 30 microphones spread across an area of 120 by 340 metres. By combining this data with wind tunnel tests and computer simulations, researchers were able to validate their findings through precise comparisons with measurements from reference flights without retrofits in 2016.
This animation highlights noise sources on the wings of the DLR Airbus A320 ATRA, including areas such as the extended slats and outer flaps.
Animation: Visualisation of noise sources on the Airbus A320 ATRA
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Animation: Visualisation of noise sources on the Airbus A320 ATRA
This animation highlights noise sources on the wings of the DLR Airbus A320 ATRA, including areas such as the extended slats and outer flaps.
Reducing noise while balancing climate protection and costs
"Our results from flight tests, earlier wind tunnel experiments and simulations are in good agreement," explains project manager Michael Pott-Pollenske. "This confirms that our years of research into noise sources were well directed and that the transfer to real aircraft was successful." The findings are technically sound and have gained international recognition. "At a global level, only JAXA and NASA have achieved comparable results."
Despite these successes, noise reduction remains a challenge. Additional cladding and materials add weight to an aircraft, which can increase fuel consumption. "However, this effect can be offset by aerodynamic refinements," Pott-Pollenske adds, citing laminar flow technologies that decrease drag as one example.
Balancing climate protection with noise abatement remains a key priority in DLR's research. "Noise can be detrimental to health, which is why noise research remains a vital part of our work," Pott-Pollenske emphasises. "Our findings can make a significant contribution to making aviation quieter and more sustainable."
The results from LNATRA are already feeding into other projects, such as the ongoing 'LU(FT)² 2030' research initiative. This project expands the focus beyond aircraft as noise sources to consider how residents perceive noise. The goal is to increase the use of simulations, enabling the development and implementation of noise reduction measures more quickly, cost-effectively and efficiently. "By continuously refining our simulations, we will be able to design quieter aircraft digitally in the future," explains Pott-Pollenske. This approach allows sound radiation to be assessed via computer simulations, ensuring that noise protection is integrated into aircraft design from the outset.
Through this work, DLR is advancing aviation towards the EU Commission's target of reducing aircraft noise by 65 percent by 2050, compared to 2000 levels. The long-term vision is clear: the air traffic of the future must not only be climate-compatible but also quieter, and DLR’s researchers are convinced that noise reduction is both an achievable and worthwhile target.
