Showing papers on "Aircraft noise published in 1975"

Scaling loudness, noisiness, and annoyance of aircraft noise.

Abstract: The capacity of man to differentiate and scale aircraft noise with regard to three psychological attributes frequently encountered in social survey research on ambient noise was tested. Calibrated scales for the attributes evolved from the two‐step psychological scaling procedure employed. It was demonstrated that observers in carefully designed laboratory situations are able to use and produce scales of loudness, noisiness, and annoyance for aircraft noise. The relationships between the attributes were satisfactorily described by linear functions. In general, aircraft noise was judged to be more annoying than noisy and more noisy than loud. For all three attributes, the psychophysical relationships were best described by power functions with dB(A)max as the physical measure (exponents 0.21–0.24).Subject Classification: 65.50, 65.75.

Airframe noise - The next aircraft noise barrier

Abstract: Progress in quieting the commercial aviation fleet has been achieved by reducing the noise generated by jet engines. Recent tests have indicated that noise produced by airflow over aircraft surfaces (lifting surfaces, landing gear, flaps, and cavities) is only 8 to 10 EPNdB below certification requirements for current aircraft and will likely be a design consideration for aircraft of the future as engines become still quieter. This paper reviews the state of the art for understanding, predicting, and control of airframe noise. Levels and spectral content of the noise, correlation with important variables, and noise generation mechansims are discussed. The noise floors for future aircraft, the direction of research projects, and likely impact of this new technology on aircraft design are indicated.

An evaluation of the impact of aircraft noise on property values with a simple model of urban land rent

Abstract: The urban models of rent determination have concentrated mainly on the transportation-saving aspect, paying little attention to the amenity or disamenity aspect. The purpose of this paper is to modify the Mohring model so as to include a typical disamenity such as aircraft noise (Mohring 1961). While it is obvious that the rationale behind the determination of prices on the house and land market is complex, it is of great interest to concentrate on two phenomena-transportation savings and disamenity--and hold constant other variables when estimating. Estimations with a modified Mohring model are provided for the London airport case. Those estimations were calculated from two typical sample areas around London Heathrow airport, one being relatively "quiet" and the other, under the flight path, being noisy. /Author/

Prediction of airframe noise

Abstract: Methods of predicting airframe noise generated by aircraft in flight under nonpowered conditions are discussed. Approaches to predictions relying on flyover data and component theoretical analyses are developed. A nondimensional airframe noise spectrum of various aircraft is presented. The spectrum was obtained by smoothing all the measured spectra to remove any peculiarities due to airframe protrusions, normalizing each spectra by its overall sound pressure level and a characteristics frequency, and averaging the spectra together. A chart of airframe noise sources is included.

Aircraft noise prediction

Abstract: Aircraft noise prediction programs which are generally available are described. A background discussion including levels of acoustical sophistication and units of measure is also presented as an aid to understanding the requirements of an aircraft noise prediction system.

Interior noise levels of two propeller driven light aircraft

Abstract: The relationships between aircraft operating conditions and interior noise and the degree to which ground testing can be used in lieu of flight testing for performing interior noise research were studied. The results show that the noise inside light aircraft is strongly influenced by the rotational speed of the engine and propeller. Both the overall noise and low frequency spectra levels were observed to decrease with increasing high speed rpm operations during flight. This phenomenon and its significance is not presently understood. Comparison of spectra obtained in flight with spectra obtained on the ground suggests that identification of frequency components and relative amplitude of propeller and engine noise sources may be evaluated on stationary aircraft.

A Comprehensive Review of Helicopter Noise Literature

Abstract: : This report summarizes the state-of-the-art in helicopter noise. It includes a bibliography of reports on all components of helicopter noise including main rotor, tail rotor, engine and gearbox. Literature on helicopter noise reduction and subjective evaluation of helicopter noise were also included. Capsule summaries of important reports are included which describe the purpose of the report, summarizes the important results, compares the report with others on the same subject, and provides a critical evaluation of the work presented. It is concluded that the available prediction methodology provides a means for estimating helicopter sources on a gross basis. However, the mechanisms of noise generation are still not fully understood, although the experimental and theoretical tools are now available to conduct the definitive experiments and establish the mathematical models needed for accurate definition of helicopter noise generation mechanisms. Spectrum analyses of helicopter noise show that main rotor, tail rotor, and engine sources contribute significantly to annoyance. In cases where these sources have been heavily suppressed, gearbox noise will also appear as a significant contributor to annoyance. Therefore, quieter helicopters must include suppression of all of these components. For certification, the liter

Effects on sleep of noise from two proposed STOL aircraft

Abstract: Responses, both overt behavior and those measured by electroencephalograph, to noise by eight male subjects were studied for sixteen consecutive nights. Test stimuli were: (1) The simulated sideline noise of a short takeoff and landing aircraft with blown flaps; (2) the simulated sideline noise of a STOL aircraft of turbofan design; (3) the simulated takeoff noise of the blown flap STOL aircraft; and (4) a four second burst of simulated pink noise. Responses to each noise were tested at three noise intensities selected to represent levels expected indoors from operational aircraft. The results indicate that the blown flap STOL aircraft noise resulted in 8 to 10 percent fewer sleep disturbance responses than did the turbofan STOL aircraft when noises of comparable intensities from similar maneuvers were used.

The development of experimental techniques for the study of helicopter rotor noise

Abstract: The features of existing wind tunnels involved in noise studies are discussed. The acoustic characteristics of the MIT low noise open jet wind tunnel are obtained by employing calibration techniques: one technique is to measure the decay of sound pressure with distance in the far field; the other technique is to utilize a speaker, which was calibrated, as a sound source. The sound pressure level versus frequency was obtained in the wind tunnel chamber and compared with the corresponding calibrated values. Fiberglas board-block units were installed on the chamber interior. The free field was increased significantly after this treatment and the chamber cut-off frequency was reduced to 160 Hz from the original designed 250 Hz. The flow field characteristics of the rotor-tunnel configuration were studied by using flow visualization techniques. The influence of open-jet shear layer on the sound transmission was studied by using an Aeolian tone as the sound source. A dynamometer system was designed to measure the steady and low harmonics of the rotor thrust. A theoretical Mach number scaling formula was developed to scale the rotational noise and blade slap noise data of model rotors to full scale helicopter rotors.

Development of a new computer system for aircraft noise prediction

Abstract: The paper presents an overview of the activities of NASA's Aircraft Noise Prediction Office (ANOPO). The principal goal of ANOPO is to develop a comprehensive, user-oriented, Aircraft Noise Prediction Program (ANOPP). ANOPO's activities in support of ANOPP development are briefly discussed. They include acquisition, implementation, and evaluation of an in-house, interim collection of programs and implementation of a plan for acquiring, in the form of Key Technology Documents, state-of-the-art methodology for aircraft noise prediction. The paper is primarily devoted to a presentation of the general architecture and functional capability planned for ANOPP together with the rationale supporting major design decisions.

Review of aircraft noise propagation

Abstract: The current state of knowledge about the propagation of aircraft noise was reviewed. The literature on the subject is surveyed and methods for predicting the most important and best understood propagation effects are presented. Available empirical data are examined and the data's general validity is assessed. The methods used to determine the loss of acoustic energy due to uniform spherical spreading, absorption in a homogeneous atmosphere, and absorption due to ground cover are presented. A procedure for determining ground induced absorption as a function of elevation angle between source and receiver is recommended. Other factors that affect propagation, such as refraction and scattering due to turbulence, which were found to be less important for predicting the propagation of aircraft noise, are also evaluated.

Measurements and analysis of aircraft airframe noise

Abstract: Flyover measurements of the airframe noise of AeroCommander, JetStar, CV-990, and B-747 aircraft are presented. Data are shown for both cruise and landing configurations. Correlations between airframe noise and aircraft parameters are developed and presented. The landing approach airframe noise for the test aircraft was approximately 10 EPNdB below present FAA certification requirements.

Method of representation of acoustic spectra and reflection corrections applied to externally blown flap noise

Abstract: A computer method for obtaining a rational function representation of an acoustic spectrum and for correcting reflection effects is introduced. The functional representation provides a means of compact storage of data and the nucleus of the data analysis method. The method is applied to noise from a full-scale externally blown flap system with a quiet 6:1 bypass ratio turbofan engine and a three-flap wing section designed to simulate the take-off condition of a conceptual STOL aircraft.

A study of helicopter interior noise reduction

Abstract: The interior noise levels of existing helicopters are discussed along with an ongoing experimental program directed towards reducing these levels. Results of several noise and vibration measurements on Langley Research Center's Civil Helicopter Research Aircraft are presented, including measurements taken before and after installation of an acoustically-treated cabin. The predominant noise source in this helicopter is the first stage planetary gear-clash in the main gear box, both before and after installation of the acoustically treated cabin. Noise reductions of up to 20 db in some octave bands may be required in order to obtain interior noise levels comparable to commercial jet transports.

Factors affecting the noise from small propeller driven aircraft

Abstract: The factors affecting noise from small propeller driven airplanes are reviewed to quantify their affects where possible, and to indicate the potential for noise reduction. The main sources of external noise are noted to be the propellers and engines; the airframe being of less importance for both aural detection and community annoyance. Propeller noise is a strong function of tip speed and is affected adversely by nonuniform inflows. Reciprocating engine exhausts are noisier than those of comparably rated turboshaft engines, but their noise can be reduced by the use of flight certified exhaust mufflers. Presently, there are no generally accepted engineering methods for development of optimized propellers and exhaust muffler designs from weight and performance penalty standpoints. Flight demonstration results, however, suggest that required noise reductions for future certification should be possible with potentially small penalties.

A model and plan for a longitudinal study of community response to aircraft noise

Abstract: A new approach is discussed for the study of the effects of aircraft noise on people who live near large airports. The approach was an outgrowth of a planned study of the reactions of individuals exposed to changing aircraft noise conditions around the Dallas-Ft. Worth (DFW) regional airport. The rationale, concepts, and methods employed in the study are discussed. A critical review of major past studies traces the history of community response research in an effort to identify strengths and limitations of the various approaches and methodologies. A stress-reduction model is presented to provide a framework for studying the dynamics of human response to a changing noise environment. The development of the survey instrument is detailed, and preliminary results of pretest data are discussed.

Military Aircraft Noise

Abstract: Opportunities to reduce military aircraft noise without inhibiting mission capability are considered. Emphasis is placed on the need for a comprehensive military aircraft noise abatement program involving compatible land use in the vicinity of military airports, operational constraints, and procedures to reduce noise impact and source noise reduction. The military to civil transfer of aircraft and engine technology is discussed together with the effect of increasing civil noise constraints on this evolutionary practice. Research and development activities to reduce military aircraft noise at the source are highlighted and plans to incorporate noise reduction technology early in the development cycle of military engines are outlined. Recommended noise goals for military aircraft are presented.

Comparison of the Acoustic Characteristics of Large-Scale Models of Several Propulsive-Lift Concepts

Abstract: Wind-tunnel acoustic investigations were performed to determine the acoustic characteristics and the effect of forward speed on these characteristics of four propulsive lift concepts: the over-the-wing externally-blown jet flap (OTW), the under-the-wing externally-blown jet flap (UTW), the internally-blown jet flap (IBF), and the augmentor wing (AW). The data in this paper represent the basic noise generated by the powered-lift system without acoustic treatment, assuming all other noise sources, such as the turbofan compressor noise, have been suppressed. Under these conditions, when scaled to a 45,500 kg (100,000 Ib) aircraft, the OTW concept exhibited the lowest perceived noise levels because of dominant low-frequency noise and wing shielding of the highfrequency noise. The AW was the loudest configuration because of dominant high-frequency noise created by the high jet velocities and small nozzle dimensions. All four configurations emitted noise 10 to 15 PNdb higher than the noise goal of 95 PNdb at 153 m (500 ft). The AW is the only powered-lift concept which has shown the capability of acoustic suppression to this level. The effect of forward speed did not approach that expected from the relative velocity increments investigated. The dominant low-frequency noise of the OTW and UTW was reduced 2 db by an 80 knot free-stream velocity. The dominant high-frequency noise of the IBF and AW was unaffected by forward speed. Nomenclature OASPL = overall sound pressure level, db PNL = perceived noise level, PNdb SPL = sound pressure level, db referred to 2 x 10'5 N/m2 (0.0002 microbar) Vj = aver age isentropic jet exhaust velocity, m/sec (fps) V^ = freestream velocity, knots (fps) a = angle of attack with respect to wing chord plane, deg df = flap deflection with respect to wing chord plane, deg

Comparisons of variability in aircraft flyover noise measurements

Abstract: Data from controlled flight testing conducted for 11 aircraft noise certification programs under FAA FAR 36 show typical standard deviations for sets of EPNL and PNL values ranging from 08 to 14 dB Much greater variability was found in the noise levels measured near the approach path to runway 21R at Detroit Metropolitan Airport during two ten‐day periods of routine operations EPNL, SEL, and maximum A‐level data, classified in jet aircraft groups by number of engines (regardless of type), showed typical standard deviations ranging from 38 to 49 dB at the different ground measuring points Correlation of the Detroit noise data with slant distance gave moderately high correlation coefficients, with 95% prediction intervals about the regression lines varying from ±54 to ±95 dB The regression lines show quite good agreement, particularly in slope, with generalized noise level versus distance curves often used for noise exposure calculations Correlations between different noise measures were high, as

Community Noise Exposure Resulting from Aircraft Operations: Acquisition and Analysis of Aircraft Noise and Performance Data

Abstract: : This report is one of a series describing the research program undertaken by the Aerospace Medical Research Laboratory to develop procedures for predicting community noise exposure resulting from aircraft operations. This report outlines the acoustic measurement test conditions, the acoustic data reduction and interpretation procedures, and the type of aircraft performance information needed to obtain a noise data file for predicting the noise produced by aircraft operations. The procedures result in the descriptions of the noise of an aircraft in terms of the effective perceived noise level, the sound exposure level and several other noise measures. Level flight measurements and static engine noise tests are described, and are applicable to conventional fixed wing aircraft and helicopters.

Effect of temperature and humidity on aircraft noise propagation

Abstract: This report presents the results of a test program conducted to measure the effect of varying meteorological conditions on aircraft flyover noise levels. Detailed temperature and humidity data were obtained using an instrument system carried by a light aircraft. High and low altitude inversions as well as standard lapse rate atmospheres were investigated. Level flyovers were conducted, using a DC-9-10 aircraft operated at a thrust of 6,000 lbs., as a constant noise source. Measured noise levels varied up to 4 EPNdB depending upon the absorptive properties of the atmosphere. Several analysis procedures were investigated in an effort to correct noise data for weather conditions. Weather correction procedures based on single point meteorological data were inadequate to normalize, to reference conditions, the noise data for those conditions with non-uniform temperature and humidity profiles. A layered analysis procedure, however, normalized all flyover noise levels to those levels taken under near reference conditions. The layered analysis procedure incrementally adjusts the measured peak spectra based on the acoustic absorption in each increment. These results indicated that noise certification testing under non-uniform temperature and humidity conditions could, if allowed, be conducted provided that frequent and detailed meteorological data is available and the layered weather correction procedure is used.