Aircraft noise

About: Aircraft noise is a research topic. Over the lifetime, 3051 publications have been published within this topic receiving 32039 citations.

Noise transmission and control for a light, twin-engine aircraft

Abstract: One of the dominant source-path combinations for cabin noise in light twin-engine aircraft is propeller noise being transmitted through the fuselage sidewall. This source-path was investigated and candidate sidewall add- on treatments were installed and tested using both an external sound source and the propeller in ground static engine runs. Results indicate that adding either mass or stiffness to the fuselage skin would improve sidewall attenuation and that the honeycomb stiffness treatment provided more improvement at most frequencies than an equal amount of added mass. It is proposed that double-wall construction in conjunction with skin stiffening should provide a good weight-efficient combination for the aircraft studied. NE of the principal source-path combinations of cabin noise in light, twin-engine aircraft is propeller noise transmitted through the fuselage sidewall. Improved methods of controlling this cabin noise are needed to provide a comfortable passenger environment, while at the same time controlling aircraft weight and fuel consumption. Lighter weight noise control methods are needed to replace traditional approaches which have relied largely on relatively heavy damping and mass treatments. A number of approaches have been investigated for reducing cabin noise for this type of aircraft. Flight tests indicated interior noise can be reduced about 3.5 dB(A) by a reduction of engine rpm in an aircraft with variable pitch propellers.1 Design of propeller configurations is being in- vestigated as a means of reducing the noise generated at the source.2 Theoretical prediction methods for sidewall noise transmission have been developed to aid the search for noise- resistant sidewall structures. Theoretical analysis of interior noise transmission has included mechanical analogy models, rigid-stiffener/flexible-panel models, and more complex flexible-stiffener/flexible-panel models. 3"5 The analyses have been compared with laboratory test data for verification and have been used to examine a number of candidate noise control treatments including variations of skin thickness, stiffener stiffness, and structural damping, and addition of damping, mass, and honeycomb panel stiffening. Previous work has not included evaluation of candidate noise control treatments in an experimental situation using an actual aircraft. Such studies are needed to evaluate and compare candidate treatments, and to guide further development of noise control treatments. The purpose of this paper is to describe an experimental program of evaluation of three noise control treatments. The work is focused on added stiffness in the form of honeycomb panels. Also, two mass treatments are included for comparison. The tests were carried out using a light twin-engine aircraft (Fig. 1). Can- didate treatments were developed using the aircraft with a horn noise source in the laboratory. The performance of the stiffness treatment was verified using ground static runs of the aircraft engines. The laboratory portion of this investigation is described in Ref. 6.

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.

Structural-acoustic response, noise transmission losses and interior noise levels of an aircraft fuselage excited by random pressure fields

Abstract: : A theoretical and empirical study of the structural-acoustic response and sound transmission properties of fuselage structures is described. The external fluctuating pressure environments discussed are boundary layer turbulence, jet noise and reverberant acoustic fields. In order to investigate the complete behavior of the fuselage, equivalent structural models are analyzed whose combined characteristics represent the complex fuselage structure throughout the entire frequency response range of interest. The structure and interior sound field are treated throughout as a coupled dynamic system whose response is describable in terms of the system's normal modes. Prediction methods are developed for structural responses, noise reduction and internal acoustic fields of untreated and acoustically treated fuselage structures. The results of this study have been programmed for computer solution, thus allowing the significant parameters affecting sound transmission to be determined. In addition to the computer programs, empirical design charts are presented for carrying out pre-design estimates of the external fluctuating loads due to boundary layer turbulence and jet noise and overall noise reduction of typical acoustic treatments.