Innovative aircraft design for step changes in noise reduction

Abstract

Low-noise integrated propulsion system concepts are proposed for functionally silent aircraft with the goal to reduce airframe and propulsion system noise by as much as 30 dB. Silent in this context means sufficiently quiet that the aircraft noise is less than that of the background noise in a typical well-populated environment. The theme of the technical approach for this multi-disciplinary problem is based on a systems view rather than an individual component view of the airframe and interacting propulsion system. Simple analytical modeling and existing semi-empirical noise prediction methods and scaling laws are used to predict the acoustic signature of low-noise airframe and propulsion system concepts envisioned for a functionally silent aircraft. The design study and acoustic analysis is based on an aerodynamically clean blended-wing-body-type airframe configuration. A distributed propulsion system is proposed to facilitate airframe boundary layer ingestion and to take advantage of shielding effects by embedding engines in the airframe. Ultra-high bypass ratio engines are necessary to reduce jet noise and multiple small engines or a multi-fan engine system is envisioned to enable integrating the propulsion system with the airframe. Results from the noise assessment studies are discussed and preliminary design implications for a functionally silent aircraft are given.