US Patent 9951690 Low noise aeroengine inlet system

An aeroengine has an inlet system which includes at least one deformable wall disposed adjacent a peripheral wall of an inlet duct and a plurality of acoustic cells attached to a back side in fluid communication through respective holes in the at least one deformable wall with an inlet duct air flow. The at least one deformable wall selectively forms part of the peripheral wall of the inlet duct when in an undeployed position and selectively forms a curved profile projecting into the inlet duct to reduce line-of-sight noise propagation through the inlet duct.