Noise Reduction Assessments and Preliminary Design Implications for a Functionally-Silent Aircraft

Abstract

Aircraft noise is a major inhibitor of the growth of air transport. Airports in key locations are operating at full capacity and the noise in the vicinity of airports is so intrusive that local communities object to any further expansion. A functionallysilent aircraft is aimed at reducing 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. There are two technical aspects to be dealt with in reducing aircraft community noise: propulsion system noise and airframe noise. The work presented focuses on both aspects for noise during take-off, approach and landing. The main objectives of this paperare to (1)investigatethe technologicalbarriersand requirements for a functionally-silent aircraft, (2) assess the potential noise reductions of selected low-noise concepts for such aircraft, and (3) delineate design implications and airframe/propulsion system configurations for a silent aircraft. The theme of the technical approach 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 silent aircraft. A noise reductionassessment frameworkis developedto explore the necessary technologies. The design study and acoustic analysis is based on an aerodynamically clean blended-wingbody type airframe configuration. Results from the noise assessment studies are discussed and preliminary design implications for a silent aircraft are given. 1 Introduction - Vision & Goals Where airports serving desirable regions in Europe and the UnitedStates havesought to relievecapacity constraints andease delays through expansion, local communities have resisted, citing the disruptive intrusions and economic dislocations caused by aircraft noise. The term Silent Aircraft refers to an aircraft sufficiently quiet that, outside of the airfield perimeter, the contribution of aircraft noise to the general noise environment of a well-populated community is less than other sources. Such aircraft would enable an expansion in air transportation by creating opportunity for new airports and allowing increases in operating hours at existing sites.