Structurally integrated constrained layer damping for noise reduction on sandwich and semi-monocoque helicopter structures

Abstract

The constrained layer effect is known as an efficient approach for noise attenuation on aircraft structures, being typically implemented by using add-on acoustic pads. This paper presents an integrative approach, with an elastomeric layer being interleaved within the primary structural arrangement, and its application on primary and secondary composite sandwich panels, as well as on composite and titanium semi-monocoque panels. These types of construction are representative for helicopter upper decks which are particularly involved within the acoustic loading on helicopter cabins. The acoustic performance of the undamped and damped panels is experimentally evaluated in terms of the sound transmission loss.