Noise-free cabins are certainly a key factor in airline passenger comfort. Under the BRAIN project, European researchers have developed new mathematical models which enable cabin soundproofing to be incorporated in the initial aircraft design stage. A technology which has applications for other modes of transport, too.
Airlines don't opt for a particular type
of aircraft on the grounds of its speed or fuel consumption alone.
Passenger comfort is increasingly a factor, and noise-free cabins
play an important part in ensuring a high-quality flight.
Noise pollution of this kind is especially difficult to control, mainly because of engine vibration. Soundproofing adds to the weight of the aircraft and the active noise control system (loudspeakers generating sound waves which tend to cancel out the unwanted decibels) is not 100% satisfactory.
Researchers and industrialists
An early European project, ASANCA, had brought together researchers from seven aeronautics institutes to investigate this problem. Among them was Peter Göransson, director of the Department of Acoustics and Structural Dynamics at the Aeronautical Research Institute of Sweden (FFA). Eager to pursue the research, Göransson relaunched the partnership in 1992. Four institutes signed up, followed by new participants, including a number of industrialists. The major European airframe manufacturers were to supervise the research and supply fuselages for the tests. Christened BRAIN (Basic Research in Aircraft Interior Noise), the project quickly secured the backing of the European Community.
The aim of BRAIN is to develop new mathematical models which can be used to predict the level of noise inside a cabin. Up until then, the efforts put into soundproofing the aircraft fuselage had been undertaken without the benefit of a rigorous, scientific method for incorporating the impact of equipment due to be added on later; also, the research into limiting noise pollution - based on in situ experiments - lacked sufficiently sophisticated simulation tools. The work done under the BRAIN project made it possible to develop these tools and to incorporate far more sophisticated "anti-noise" parameters, tailored to real flying conditions.
The researchers studied every aspect of the way noise is conducted through all the structures and the various materials used to insulate the fuselage - and devised new methods of predicting sound propagation. Their task was not an easy one: "We were hampered by a lack of computer power because even the fastest workstations are barely adequate for this kind of research," explains Peter Göransson. "The models which we have developed are designed for future aircraft, and hence for future computers!"
Improved comfort, lower costs
The simulation models developed by the BRAIN researchers nevertheless make it possible to predict noise pollution more accurately - to within 3 dB. Not only do they reduce interior noise, they also lead to significant time savings in the design, development and production of new models of aircraft, and help reduce the weight of the planes. Overall cost savings are estimated at about 10%.
"We couldn't have achieved these results if we'd each been working on our own. The partnership with aircraft manufacturers was a key factor in the progress that we've made," concludes the director of the FFA. Moreover, the project has exceeded its original objective. Although the models developed by BRAIN are primarily of interest to the aircraft industry, they could also be adapted to other modes of transport, and not only terrestrial - cars, trains, ships - but also for use in space. Thus, the European Space Agency (ESA) is already using the findings of the research carried out under the BRAIN project to design the manned modules of the future.