Super-quiet over the distance

All-embracing simulation model for cabin acoustics

Customer aspirations as regards VIP aircraft have become steadily more ambitious over the last few years. Whereas many private aircraft owners used to be primarily focused on visual aspects of the interior and the layout, today other factors such as the sound level inside the cabin, the weight, fuel consumption and hence the range of the aircraft play a critical role. The problem arises basically from the fact that the use of extra insulating materials adds to the weight of an aircraft, cutting down the distance it can fly. It is the job of engineers in Lufthansa Technik's VIP & Executive Jet Solutions unit in Hamburg to reconcile these interacting factors in the design of the aircraft configuration.

Under the "AkuKon" research and development project, which has been running since April 2009 and is scheduled to continue into March 2013, new acoustic concepts are being developed for economically and ecologically improved aircraft configurations. Before any tailored acoustics concepts can be created it is essential to analyze existing deficiencies in acoustic insulation and to thoroughly evaluate new approaches to noise attenuation. The idea behind the project is to sustainably develop an all-embracing simulation model for the cabin acoustics of VIP aircraft. With the aid of computer-aided simulations it will be possible in the future to not only make the optimal use of insulating materials but also improve and shorten development processes, minimize installation costs and increase aircraft range through targeted weight distribution and reduction.

As the basis for its calculations Lufthansa is drawing firstly on measurement data obtained for VIP cabin installations over the last few years. Further sources are measurement data gathered on a test Boeing 737 and the investigation of insulation material parameters in the test laboratory. Ray tracing, a method that enables sound levels to be calculated at selected locations, for example at the seats, is used to simulate sound propagation inside the cabin. On this project Lufthansa Technik is working with competent innovation partners EADS Deutschland GmbH, Novicos GmbH, the Hamburg University of Technology (TUHH), the Helmut Schmidt University and the University of Applied Sciences (HAW) in Hamburg. On top of this the Federal Ministry of Education and Research is providing financial support for the AkuKon research and development project.

Building on the results of earlier research projects (AkuKab), the AkuKon project is developing a calculation model to determine accurately the level of sound in the cabin. In this way it is possible to accurately calculate in advance the sound level at any position in the cabin, taking into account the influence of all the available input parameters. The calculations are currently focusing on the main sound sources and the modeling of the wall mounting. For this purpose all the usable materials and their combinations are measured acoustically and compared with one another. The results are then compared with in-flight measurements obtained on board converted VIP aircraft. In this way discrepancies between the simulation and the original cabin can be identified.

Engineers are already familiar with many parameters that would improve the acoustics in VIP cabins. These relate to both the interior design and the use of quite specific materials and surfaces. On top of this, additional sound insulation is provided in VIP aircraft in the form of acoustically optimized lining elements and furniture, along with other noise attenuation kits for acoustically optimizing the primary insulation. In this way between 0.6 and 1.8 tons of additional sound insulating material is required to finish the cabin of a medium-range VIP aircraft. In the case of the VIP cabin of a widebody aircraft the extra weight can amount to as much as two to four tons. Because this significantly greater weight increases fuel consumption and thus comes at the expense of range, today many VIP aircraft have auxiliary tanks installed to compensate for the weight-induced loss of performance.

The development of a computer-assisted simulation model to optimize the cabin acoustics will help significantly to improve and shorten the development process. Not only will this further reduce the installation costs, but above all it will enhance the efficiency of all the acoustic measures in relation to the weight and range of VIP aircraft. With the results of the AkuKon research and development project Lufthansa Technik will be able to further extend its lead in the area of VIP cabin installations for medium-range and widebody aircraft.