Acoustic challenges of the A400M for active systems

Harald Breitbach; Delf Sachau; Sten Böhme

doi:10.1117/12.658435

30 March 2006 Acoustic challenges of the A400M for active systems

Harald Breitbach, Delf Sachau, Sten Böhme

Proceedings Volume 6171, Smart Structures and Materials 2006: Industrial and Commercial Applications of Smart Structures Technologies; 617104 (2006) https://doi.org/10.1117/12.658435
Event: SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring, 2006, San Diego, California, United States

Abstract

In some types of aircraft tonal interior noise with high sound pressure level (up to 110 dB(A)) occurs at low frequencies (f < 500 Hz). Typical examples are propeller driven aircraft, for which the excitation frequencies are given by the blade passage frequency (BPF) and its higher harmonics. The high tonal noise levels at these frequencies can occur due to the fact that the blades' profiles are only optimized in terms of aerodynamics. The acoustic properties are usually not taken into account. In order to obtain an acceptable interior noise level, and to guarantee both work-safety and comfort in the aircraft interiors, passive methods are commonly used - e.g. adding material with high damping or vibration absorbing qualities. Especially when low frequency noise has to be reduced, adding material results in a lot of unwanted additional weight. In order to avoid this extra weight, the concept of active noise reduction (ANR) and tunable vibration absorber systems (TVA), which focus on the unwanted tonal noise, are a good compromise of treating noise and the amount of additional weight in aircraft design. This paper briefly discusses two different possible methods to reduce the low frequency noise. The noise reduction of tuned vibration absorbers (TVA) mounted on the airframe are nowadays commonly used in propeller driven aircraft and can be predicted by vibroacoustic finite element calculations, which is described in this paper. In order to abide to industrial safety regulations, the noise level inside the semi closed loadmaster area (LMA) must be reduced down to a noise level, which is even 8 dB(A) below the specified cargo hold noise level. The paper describes also the phases of development of an ANR system that could be used to control the sound pressure level inside the LMA. The concept is verified by experimental investigations within a mock up of the LMA.

Citation Download Citation

Harald Breitbach, Delf Sachau, and Sten Böhme "Acoustic challenges of the A400M for active systems", Proc. SPIE 6171, Smart Structures and Materials 2006: Industrial and Commercial Applications of Smart Structures Technologies, 617104 (30 March 2006); https://doi.org/10.1117/12.658435

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