Sound-Transmission Measurements on Composite and Metal Fuselage Panels for Different Boundary Conditions

Abstract

†In the framework of the EU-project FACE, sound transmission measurements have been performed by NLR and KTH on a curved and stiffened composite fuselage panel and an aluminium panel with the same structure. Both panels consist of a part with axial stiffeners and a part, suitable for mounting windows, without these stiffeners. The main goals of the measurements are to provide experimental data for validation of numerical models, and experimental determination of the effect of a.o. panel material on the sound transmission. At NLR, the panels have been suspended on springs, implementing well defined (free-free) boundary conditions, suppressing flanking noise adequately by a special designed panel support structure. At KTH, the panels have been clamped. In spite of the different boundary conditions, the TL data measured by KTH and NLR TL data show a good agreement for 200 Hz and higher frequencies. Due to the curvature and stiffening, the transmission loss of the panels is much lower than the mass law prediction. For frequencies above about 600 Hz, the transmission loss of the composite panel is significantly lower than that of the metal panel, despite its 6% larger mass. For the frequency band of 250 – 2000 Hz, the transmission loss of the window area of the composite panel is much (up to 5 dB) larger than for the stringer area. It seems that the stringers of the composite panel have some bad influence on the sound transmission loss and should be further investigated.