HAMBURG, 25 November 2018 – Aircraft noise is a frequent nuisance, especially for residents in the neighbourhoods of large airports. Although the problem is far from solved (this fully silent MIT prototype won’t really fly commercially for the next decades), in recent years, much has changed for the better. Thanks to aerodynamic refinements and more modern, quieter engines, modern commercial aircraft are much quieter than their predecessors. As part of the LNATRA (Low Noise Advanced Technology and Research Aircraft) project, researchers at DLR (German Aerospace Center) have now developed and tested further devices that make a modern commercial aircraft quieter. They used the DLR research aircraft D-ATRA, an Airbus A320, which DLR uses for a wide range of test and research tasks.

Reduce aircraft noise by upgrading

The aim of LNATRA was the development of devices with which aircraft in service can be upgraded. It often takes a long time for a quieter generation of aircraft to replace its louder predecessors. Upgrades such as those tested by DLR scientists on test flights at Cochstedt Airport in September 2018 offer short or medium-term solutions.

  • DLR's Airbus D-ATRA is het grootste onderzoeksvliegtuig in Europa. Het is gestationeerd op de onderzoeksluchthaven Braunschweig en is sinds 2008 in gebruik.

In addition to the engine noise, the flow noise of the air flowing around the aircraft is responsible for the volume. This flow noise is, in fact, the louder part of the aircraft noise. Wherever the air flows past corners and edges, flaps, openings and gaps, small vortices of air and thus noise are created. Extended landing gear and landing flaps are among these sources of noise, as are antennas, tank cap openings and screw nuts on the landing gear, for example.

An Airbus becomes quiet

So the scientists worked out a solution for each of these sources. These were then mounted on the experimental Airbus D-ATRA before the actual flight tests. His engines were given new outlets with a special edge pattern. The many gaps and passages between the landing gear struts were covered with cover plates. Technicians also installed specially developed fairings between the wheels. The large gaps between the trailing edge of the wing and the flap, which are created when the flaps extend, were also covered with panels. “We have implemented a total of ten noise reduction measures in recent years,” reports project manager Michael Pott-Pollenske from the DLR Institute of Aerodynamics and Flow Technology in Braunschweig. “In particular, we expect audible improvements from the fairings on the landing gear and the innovative thrusters on the engines. But the filling of the gap between the wing and the rear flaps and the modification of the side edge of the flaps will also play a role.”

Evaluation of the flight tests

If you live near an airport, don’t start the celebration too soon. It remains to be seen when these solutions will find their way into commercial aviation. First, DLR scientists have to evaluate the results of their flight tests. They have extensive comparative data at their disposal because last year they already tested noise-reducing approach procedures with the A320 D-ATRA at Cochstedt Airport. They will now compare the results of these tests with those of the September 2018 tests. This will allow them to see which devices have the best effect.

Similar devices have been used in civil aviation for some time. Special “hush kits” can be used to reduce the noise of older engines. 17 years ago, DLR itself developed a vortex generator that reduces the annoying sounds at the filler cap opening of an A320 and is now installed in every new aircraft.

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