Showing papers on "Aircraft noise published in 1981"

Helicopter rotor trailing edge noise

Abstract: A two dimensional section of a helicopter main rotor blade was tested in an acoustic wind tunnel at close to full-scale Reynolds numbers to obtain boundary layer data and acoustic data for use in developing an acoustic scaling law and testing a first principles trailing edge noise theory. Results were extended to the rotating frame coordinate system to develop a helicopter rotor trailing edge noise prediction. Comparisons of the calculated noise levels with helicopter flyover spectra demonstrate that trailing edge noise contributes significantly to the total helicopter noise spectrum at high frequencies. This noise mechanism is expected to control the minimum rotor noise. In the case of noise radiation from a local blade segment, the acoustic directivity pattern is predicted by the first principles trailing edge noise theory. Acoustic spectra are predicted by a scaling law which includes Mach number, boundary layer thickness and observer position. Spectrum shape and sound pressure level are also predicted by the first principles theory but the analysis does not predict the Strouhal value identifying the spectrum peak.

Aircraft Noise and Children: Longitudinal and Cross-Sectional Evidence on Adaptation to Noise and the Effectiveness of Noise Abatement

Abstract: Longitudinal and cross-sectional data on effects of aircraft noise on elementary school children are presented as evidence for the effects of community noise on behavior. To examine the generality of previous laboratory findings in a naturalistic setting, the study assesses the impact of noise on attentional strategies, learned helplessness, performance on cognitive tasks, and blood pressure. Children were tested on the same measures twice, with a 1-year interval between sessions. A previous article reported cross-sectional findings from the first testing session. In the present article, longitudinal data are used to determine whether children adapt to the aircraft noise over the 1-year period and to assess the effectiveness of noise abatement interventions introduced in a number of noiseimpacted classrooms. Additional cross-sectional data from the original testing session are also presented to provide further information on the utility of noise abatement. In general, there was little evidence for adaption to noise over the 1-year period. Noise abatement had small ameliorative effects on cognitive performance, children's ability to hear their teachers, and school achievement. The implications of the study for understanding the relationship between noise and behavior and resulting policy implications are discussed.

Nonlinear Propagation of Aircraft Noise in the Atmosphere

Abstract: Carefully controlled tests of aircraft noise propagation have shown instances of anomalously low attenuation (deficiencies in excess of 10 dB over 500 m) for frequencies in the range 5-10 kHz. These results have been explained with the aid of a statistical theory of finite-amplitude noise propagation. Detailed analysis of recordings from one test has provided a direct check on the nonlinear theory. Results from several different tests have been incorporated in a statistical model, which allows the nonlinear distortion of aircraft noise spectra to be estimated as a function of distance, level, spectrum shape, and atmospheric conditions. Preliminary results show encouraging agreement with the anomalous data.

Direct comparison of community response to road traffic noise and to aircraft noise

Abstract: Previous efforts to synthesize information on community responses to various noise sources have been forced to rely on a variety of surveys conducted in different countries over a number of years. Comparability of both the noise measurements and the questions asked has been limited, and has of necessity relied on professional judgment. Data collected recently around Toronto International Airport provide a direct comparison of response to two sources, based on 673 interviews of persons exposed to a variety of levels of both aircraft and road traffic noise. The results of that analysis do not support the assumption that response to these two noise sources is the same. For the same value of Ldn, a greater percentage of the sample is highly annoyed by aircraft noise than by road traffic noise. Possible reasons for this contradiction of the results of a previous synthesis of noise surveys are discussed.

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.

Wing Effect on Jet Noise Propagation

Abstract: Jet aircraft with engines under the wings may produce higher flyover noise levels than similar aircraft with other engine mounting arrangements. To determine the cause of higher flyover noise of such aircraft, an experimental investigation was performed in an anechoic chamber. Basic experimental apparatus consisted of an ASME 15.24 cm (6 in.) diameter converging nozzle and a wing section which corresponded to the horizontal projection area of a portion of a wing of a typical jetliner. Results of this experiment indicate that the presence of the wing in the vicinity of the jet enhances the noise produced by the jet alone. This noise enhancement may be attributed to two sources. The boundary layer generated on the surface of the wing as the result of entrainment of the air into the region between the wing and the jet is believed to be responsible for the low-frequency noise enhancement. Reflection of jet noise incident on the wing surface contributes to enhancement of noise primarily at high frequency. The jet is found to have considerable effect on noise enhancement at high frequency where strong refraction effects on sound waves occur. The substantial enhancement of high-frequenc y noise measured in planes at oblique angles to the wing surface may require consideration in aircraft noise prediction and design. Based on static test results, it appears that the wing effect may increase the sideline noise levels of aircraft during takeoff.

Handbook of aircraft noise metrics

Abstract: Information is presented on 22 noise metrics that are associated with the measurement and prediction of the effects of aircraft noise. Some of the instantaneous frequency weighted sound level measures, such as A-weighted sound level, are used to provide multiple assessment of the aircraft noise level. Other multiple event metrics, such as day-night average sound level, were designed to relate sound levels measured over a period of time to subjective responses in an effort to determine compatible land uses and aid in community planning. The various measures are divided into: (1) instantaneous sound level metrics; (2) duration corrected single event metrics; (3) multiple event metrics; and (4) speech communication metrics. The scope of each measure is examined in terms of its: definition, purpose, background, relationship to other measures, calculation method, example, equipment, references, and standards.

Computer program to predict aircraft noise levels

Abstract: Methods developed at the NASA Lewis Research Center for predicting the noise contributions from various aircraft noise sources were programmed to predict aircraft noise levels either in flight or in ground tests. The noise sources include fan inlet and exhaust, jet, flap (for powered lift), core (combustor), turbine, and airframe. Noise propagation corrections are available for atmospheric attenuation, ground reflections, extra ground attenuation, and shielding. Outputs can include spectra, overall sound pressure level, perceived noise level, tone-weighted perceived noise level, and effective perceived noise level at locations specified by the user. Footprint contour coordinates and approximate footprint areas can also be calculated. Inputs and outputs can be in either System International or U.S. customary units. The subroutines for each noise source and propagation correction are described. A complete listing is given.

Propeller Light Aircraft Noise at Discrete Frequencies

Abstract: In-flight measurements are analyzed to study the acoustic field of a propeller-driven light aircraft. The separation of noise sources is achieved by examination of the influence on the acoustic field of the propeller and the engine. At high rotational speed, the propeller is the dominant source. Evaluating then the field due to steady/unsteady loading on the blades, one concludes that the former are acoustically the most efficient. The analysis of flyover noise measurements, using an original signal processing (Doppler effect compensation) enhances the results.

Effects of noise frequency on performance and annoyance for women and men.

Abstract: Effects of noise frequencies on both performance on a complex psychomotor task and annoyance were investigated for men (n = 30) and women (n = 30). Each subject performed a complex psychomotor task for 50 min in the presence of low-frequency noise, high-frequency noise, or ambient noise. Women and men learned the task at different rates. Little effect of noise was shown. Annoyance ratings were subsequently obtained from each subject for noises of various frequencies by the method of magnitude estimation. High-frequency noises were more annoying than low-frequency noises regardless of sex and immediate prior exposure to noise. Sex differences in annoyance did not occur. No direct relationship between learning to perform a complex task while exposed to noise and annoyance by that noise was demonstrated.

Community sensitivity to changes in aircraft noise exposure

Abstract: Interviews were conducted in the vicinity of Burbank Airport during a four month period during which a counterbalanced series of changes in aircraft noise exposure occurred due to runway repairs. Another interview was undertaken approximately one year after completion of the initial runway repairs. Noise measurements were made in conjunction with administration of a brief questionnaire to a near exhaustive sample of residents in four airport neighborhoods. The magnitude and direction of change of annoyance with aircraft noise exposure corresponded closely to the actual changes in physical exposure. Estimates were made of time constants for the rate of change of attitudes toward aircraft noise.

Design guide for shipboard airborne noise control

Abstract: After discussing noise criteria, an outline of a shipboard noise control plan is given to assist the designer in formulating approaches to meet the criteria. Guidelines on acoustical design practices are then presented. The major part of the Guide deals with noise prediction procedures, using a source-path-receiver approach. Information on noise control treatments is provided.

A Comprehensive Bibliography of Literature on Helicopter Noise Technology

Abstract: : This bibliography, covering the period 1975 through calendar 1980, also provides, abstracts on literature that appear to make a significant contribution to the field of helicopter noise technology. The helicopter is recognized as a complex noise generator, with significant contributions from the rotors, the engine and the gearbox. Progress continues to be made in the noise areas of: (a) Formulations, math models and analytical procedures; (b) Noise prediction methodology; (c) Noise reduction techniques; and (d) Subjective response to helicopter noise. The body of information, data and knowledge has use in many applications, including the reduction of helicopter noise in a cost effective manner and in minimizing annoyance to the civil populace.

Annoyance by aircraft noise and fear of overflying aircraft in relation to attitudes toward the environment and community.

Abstract: If, as has been suggested, expressions of annoyance attributable to aircraft noise may reflect, in part, fear of aircraft overflights and possible crashes, then residents of areas where crashes have occurred should express more annoyance. To test this hypothesis, 50 residents of an Albany, New York area where an aircraft crash producing fatalities recently occurred, and 50 residents of a comparable nearby area without such a history, were asked to respond to a "Quality of Life" questionnaire. Among the items were some designed to test annoyance by noise and fear of aircraft overflights. It was predicted that those in the crash area would express more fear and would more often identify aircraft as a noise source. Factor analysis and discriminant analysis results sustained these hypotheses. A near-replication was carried out in Louisville, Kentucky; results were much the same. For the crash-area groups there was association of aircraft fear and noise annoyance responses; this was true to an apparently lesser extent for non-crash-area groups. The greater annoyance of crash groups by aircraft community noise apparently does not carry over to assessment of aircraft noise in the laboratory. Language: en

Subjective field study of response to impulsive helicopter noise

Abstract: Subjects, located outdoors and indoors, judged the noisiness and other subjective noise characteristics of flyovers of two helicopters and a propeller driven airplane as part of a study of the effects of impulsiveness on the subjective response to helicopter noise In the first experiment, the impulsive characteristics of one helicopter was controlled by varying the main rotor speed while maintaining a constant airspeed in level flight The second experiment which utilized only the helicopters, included descent and level flight operations The more impulsive helicopter was consistently judged less noisy than the less impulsive helicopter at equal effective perceived noise levels (EPNL) The ability of EPNL to predict noisiness was not improved by the addition of either of two proposed impulse corrections A subjective measure of impulsiveness, however, which was not significantly related to the proposed impulse corrections, was found to improve the predictive ability of EPNL

An operations manual for the Spinning Mode Synthesizer in the Langley Aircraft Noise Reduction Laboratory

Abstract: The need for a dependable and controllable noise source and the consequent development of the Spinning Mode Synthesizer (SMS) is discussed Configuration of the SMS incorporated into the flow duct facility is reported Turbofan noise is composed of a series of fundamental acoustical modes, which are produced by acoustic drivers equispaced circumferentially around the flow duct Pressure field is compared to an ideal result in an optimization algorithm, adjusting driver settings until system error is minimized The following items are included: operating instructions, a detailed description of the system, and a user's guide to data acquisition packages available

Statistical estimation of correlation for nonstationary aircraft noise

Abstract: Based on the acoustic radiation theory for a moving source, the estimation of the correlation function of a nonstationary acoustic signal is considered. We obtain an estimator for the acoustic correlation, which is shown to be unbiased and consistent. The estimation procedure can be applied to an aircraft noise measurement, where the reflected wave can be eliminated.

Acoustic facilities for human factors research at NASA Langley Research Center: Description and operational capabilities

Abstract: A number of facilities were developed which provide a unique test capability for psychoacoustics and related human factors research. The design philosophy, physical layouts, dimensions, construction features, operating capabilities, and example applications for these facilities are described. In the exterior effects room, human subjects are exposed to the types of noises that are experienced outdoors, and in the interior effects room, subjects are exposed to the types of noises and noise-induced vibrations that are experience indoors. Subjects are also exposed to noises in an echo-free environment in the anechoic listening room. An aircraft noise synthesis system, which simulates aircraft flyover noise at an observer position on the ground, is used in conjunction with these three rooms. The passenger ride quality apparatus, a device for studying passenger response to noise and vibration in aircraft, or in other vehicles, is described.

A shock wave approach to the noise of supersonic propellers

Abstract: To model propeller noise expected for a turboprop aircraft, the pressure ratio across the shock at the propeller tip was calculated and compared with noise data from three propellers At helical tip Mach numbers over 10, using only the tip shock wave, the model gave a fairly good prediction of the noise for a bladed propeller and for a propeller swept for aerodynamic purposes However for another propeller, which was highly swept and designed to have noise cancellations from the inboard propeller sections, the shock strength from the tip over predicted the noise In general the good agreement indicates that shock theory is a viable method for predicting the noise from these supersonic propellers but that the shock strengths from all of the blade sections need to be properly included

Sources, control, and effects of noise from aircraft propellers and rotors

Abstract: Recent NASA and NASA sponsored research on the prediction and control of propeller and rotor source noise, on the analysis and design of fuselage sidewall noise control treatments, and on the measurement and quantification of the response of passengers to aircraft noise is described. Source noise predictions are compared with measurements for conventional low speed propellers, for new high speed propellers (propfans), and for a helicopter. Results from a light aircraft demonstration program are considered which indicates that about 5 dB reduction of flyover noise can be obtained without significant performance penalty. Sidewall design studies are examined for interior noise control in light general aviation aircraft and in large transports using propfan propulsion. The weight of the added acoustic treatment is estimated and tradeoffs between weight and noise reduction are discussed. A laboratory study of passenger response to combined broadband and tonal propeller-like noise is described. Subject discomfort ratings of combined tone broadband noises are compared with ratings of broadband (boundary layer) noise alone and the relative importance of the propeller tones is examined.

Engine isolation for structural-borne interior noise reduction in a general aviation aircraft

Abstract: Engine vibration isolation for structural-borne interior noise reduction is investigated A laboratory based test procedure to simulate engine induced structure-borne noise transmission, the testing of a range of candidate isolators for relative performance data, and the development of an analytical model of the transmission phenomena for isolator design evaluation are addressed The isolator relative performance test data show that the elastomeric isolators do not appear to operate as single degree of freedom systems with respect to noise isolation Noise isolation beyond 150 Hz levels off and begins to decrease somewhat above 600 Hz Coupled analytical and empirical models were used to study the structure-borne noise transmission phenomena Correlation of predicted results with measured data show that (1) the modeling procedures are reasonably accurate for isolator design evaluation, (2) the frequency dependent properties of the isolators must be included in the model if reasonably accurate noise prediction beyond 150 Hz is desired The experimental and analytical studies were carried out in the frequency range from 10 Hz to 1000 Hz

Upper Surface Blowing Noise of the NASA Ames Quiet Short-Haul Research Aircraft

Abstract: An experimental study of the propulsive-lift noise of the NASA-Ames quiet short-haul research aircraft (QSRA) is described. Comparisons are made of measured QSRA flyover noise and model propulsive-lift noise data available in references. Developmental tests of trailing-edge treatments were conducted using sawtooth-shaped and porous USB flap trailing-edge extensions. Small scale parametric tests were conducted to determine noise reduction/design relationships. Full-scale static tests were conducted with the QSRA preparatory to the selection of edge treatment designs for flight testing. QSRA flight and published model propulsive-lift noise data have similar characteristics. Noise reductions of 2 to 3 dB were achieved over a wide range of frequency and directivity angles in static tests of the QSRA. These noise reductions are expected to be achieved or surpassed in flight tests planned by NASA in 1980.

Noise Transmission and Attenuation for Business Aircraft

Abstract: This paper describes analytical studies applicable for estimating the effects of noise transmission into light aircraft and commuter type aircraft. The propeller noise and turbulent boundary layer noise are considered. The analytical model described uses modal methods and incorporates flat stiffened panels for flat sided sidewalls and curved stiffened panels for cylindrical enclosures. The numerical results include noise attenuation with add-on treatments and the sensitivity of the transmitted noise to the discrete stiffening of the sidewall panels.

Flight test of a pure-tone acoustic source. [aircraft noise]

Abstract: A unique experiment involving static and flight testing of a pure‐tone acoustic source has been conducted. The objectives of the experiment were: to determine if a 4‐kHz tone radiated by the source in flight and mixed with broadband aircraft flyover noise, could be measured on the ground with a high degree of statistical confidence; to determine how well a flight‐to‐static tone radiation pattern comparison could be made to the static radiation pattern; and to determine if there were any installation effects on the radiation pattern due to the flight vehicle. Narrow‐band acoustic data were measured and averaged over eight microphones to obtain a high statistical confidence. The flight data were adjusted to an equivalent static condition by applying corrections for retarded time, spherical spreading, atmospheric absorption, ground impedance, instrumentation constraints, convective amplification, and the Doppler shift. The flight‐to‐static results are in excellent agreement with the measured static data. No ...

Resident annoyance response to aircraft noise events

Abstract: In a study conducted in the vicinity of Salt Lake City International Airport, community residents reported their annoyance with individual aircraft flyovers during rating sessions conducted in their homes. Annoyance ratings were obtained at different times of the day. Aircraft noise levels were measured, and other characteristics of the aircraft were noted by trained observers. Metrics commonly used for assessing aircraft noise were compared, but none performed significantly better than A-weighted sound pressure level. A significant difference was found between the ratings of commercial jet aircraft and general aviation propeller aircraft, with the latter being judged less annoying. After the effects of noise level were accounted for, no significant differences were found between the ratings of landings and takeoffs. Aircraft noise annoyance reactions are stronger in lowered ambient noise conditions. This is consistent with the theory that reduced nighttime and evening ambient levels could create different reactions at different times of day. After controlling for ambient noise in a multiple regression analysis, no significant differences were found between the ratings of single events obtained during the three time periods: morning, afternoon, and evenings.

Turboprop cargo aircraft systems study

Abstract: The effects of using advanced turboprop propulsion systems to reduce the fuel consumption and direct operating costs of cargo aircraft were studied, and the impact of these systems on aircraft noise and noise prints around a terminal area was determined. Parametric variations of aircraft and propeller characteristics were investigated to determine their effects on noiseprint areas, fuel consumption, and direct operating costs. From these results, three aircraft designs were selected and subjected to design refinements and sensitivity analyses. Three competitive turbofan aircraft were also defined from parametric studies to provide a basis for comparing the two types of propulsion.

Minimum noise impact aircraft trajectories

Abstract: Numerical optimization is used to compute the optimum flight paths, based upon a parametric form that implicitly includes some of the problem restrictions. The other constraints are formulated as penalties in the cost function. Various aircraft on multiple trajectores (landing and takeoff) can be considered. The modular design employed allows for the substitution of alternate models of the population distribution, aircraft noise, flight paths, and annoyance, or for the addition of other features (e.g., fuel consumption) in the cost function. A reduction in the required amount of searching over local minima was achieved through use of the presence of statistical lateral dispersion in the flight paths.