Showing papers on "Aircraft noise published in 1979"

Noise Component Method for Airframe Noise

Abstract: A method was developed for predicting aerodynamic noise radiated by an airframe. Separate contributions are calculated for the clean wing, horizontal tail, vertical tail, landing gear, leading-edge slats and flaps, and trailing-edge flaps. Each noise component is predicted using scaling laws appropriate to that component, with amplitudes matched to available data. Spectra calculated by this method, the NASA Aircraft Noise Prediction Program (ANOPP) total aircraft method, and the drag element method are compared with flyover noise data for a twin-propeller lightplane, a business jet, and a jumbo jet. from high bypass ratio turbofans with extensive inlet and exhaust acoustic suppression, at approach power setting. Future certification levels must be based on what can be achieved with economically viable airframes and propulsion systems. Thus it is necessary to understand the fundamental processes of airframe noise radiation. Several methods for predicting airframe noise were examined by NASA as part of the Aircraft Noise Prediction Program (ANOPP). Two airframe noise prediction methods, the total aircraft method for aircraft in the clean con- figuration, and the drag element method for all con- figurations, were recommended2 and were subsequently programmed by NASA Aircraft Noise Prediction Office. Verification by comparisons with measured airframe noise spectra have not been published for the total aircraft method and were available for only a few cases for the drag element method. More recently, a noise component method was developed for the Federal Aviation Administration under Contract DOT-FA76WA-3821.3 The purposes of this paper are to describe that method, including recent revisions, and to evaluate the validity of these several airframe noise prediction methods by comparisons between calculated and measured flyover noise spectra. NASA ANOPP Methods Two NASA ANOPP methods for calculating airframe noise were obtained from NASA within one computer program. Option 1 of that computer program is the total aircraft noise method developed by Hardin 2 for clean air- frames. It was derived from a regression analysis of measured peak OASPL for selected aircraft flyovers. These OASPL's

A summation and inhibition model of annoyance response to multiple community noise sources

Abstract: A model of annoyance due to combined noise sources was developed. The model provides for the summation of the subjective magnitudes of annoyance due to the separate noise sources and for the inhibition of the subjective magnitudes of each source by the presence of the other noise sources. The inhibition process is assumed to mathematically obey a power-group transformation. The results of an experiment in which subjects judged the annoyance of 15 minute sessions of combined aircraft and with several other models of combined source annoyance. These comparisons indicated that the model developed herein provides better qualitative and quantitative agreement with experimental responses than the other models. The application of the model to multiple community noises is discussed.

Large scale model measurements of airframe noise using cross-correlation techniques

Abstract: Cross-correlation techniques are used to measure the sound radiated by wing/flap airfoil configurations in the NASA-Ames 40 x 80 ft wind tunnel using a 6.7-m semispan model with three deployed flaps. The dominant source of flap noise is identified as the flap side edges, which exceeds that radiated by the midspan region by more than 10 dB. The turbulent surface eddies at the flap side edge have scales on the order of one-half the flap chord. The installation of flap actuator fairings at the flap side edge reduces the noise radiated from that location by 10 to 15 dB. The cross-correlation technique extracts airframe noise radiated by specific surface locations from the tunnel background noise, even when the noise is 25 dB higher than the measured airframe noise level.

Characteristics of propeller noise on an aircraft fuselage related to interior noise transmission

Abstract: Exterior noise was measured on the fuselage of a twin-engine, light aircraft at four values of engine rpm in ground static tests and at forward speeds up to 36 m/s in taxi tests. Propeller noise levels, spectra, and correlations were determined using a horizontal array of seven flush-mounted microphones and a vertical array of four flush-mounted microphones in the propeller plane. The measured levels and spectra are compared with predictions based on empirical and analytical methods for static and taxi conditions. Trace wavelengths of the propeller noise field, obtained from point-to-point correlations, are compared with the aircraft sidewall structural dimensions, and some analytical results are presented that suggest the sensitivity of interior noise transmission to variations of the propeller noise characteristics.

Assessment of airframe noise

Abstract: A component method of airframe noise prediction is used to predict levels of operational and proposed aircraft airframe noise to assess the contribution of airframe noise to community noise levels. This is done after first evaluating the prediction method using newly acquired detailed measurements from full-scale aircraft and models. In the course of the evaluation, modeling techniques of airframe noise sources are examined with attention to scaling. Finally, when used to predict approach airframe EPNLs, the levels fell about 10 EPNdB below current noise regulations and about 5 EPNdB below proposed noise regulations.

Engine-induced structural-borne noise in a general aviation aircraft

Abstract: Structural borne interior noise in a single engine general aviation aircraft was studied to determine the importance of engine induced structural borne noise and to determine the necessary modeling requirements for the prediction of structural borne interior noise. Engine attached/detached ground test data show that engine induced structural borne noise is a primary interior noise source for the single engine test aircraft, cabin noise is highly influenced by responses at the propeller tone, and cabin acoustic resonances can influence overall noise levels. Results from structural and acoustic finite element coupled models of the test aircraft show that wall flexibility has a strong influence on fundamental cabin acoustic resonances, the lightweight fuselage structure has a high modal density, and finite element analysis procedures are appropriate for the prediction of structural borne noise.

An acoustical study of the XV-15 Tilt Rotor Research Aircraft

Abstract: Acoustic data were obtained during a full-scale test of the XV-15 Tilt Rotor Research Aircraft in the Ames 40- by 80-Foot Wind Tunnel. The XV-15 has two 25-ft-diameter, three-bladed rotors at the tips of a 32-ft span wing. The rotors are used as lifting rotors, as propellers, and in various intermediate stages. Acoustic waveforms, dBA, and spectra as functions of different rotor conditions are presented and discussed. The noise level was found to be sensitive to change in rotor-disk angle of attack in the helicopter configuration. Much higher noise levels and harmonic contents were found in the helicopter mode than in the airplane mode. The measurements are compared with existing theoretical predictions which include wind-tunnel wall reflections.

Characteristics of the advanced supersonic technology AST-105-1 configured for transpacific range with Pratt and Whitney aircraft variable stream control engines

Abstract: Credence to systems weights and assurance that the noise study AST concept can be balanced were studied. Current titanium structural technology is assumed. A duct-burning turbofan variable stream control engine (VSCE), with noise reduction potential through use of a coannular nozzle was used. With 273 passengers, range of the AST-105-1 for a cruise Mach number of 2.62 is essentially transpacific. Lift-to-drag ratio is slightly higher than for previous AST configurations. It is trimmable over a center-of-gravity range of 4.7m (15.5 ft). Inherent high positive effective dihedral, typical of arrow-wing configurations in high-lift approach, would limit AST-105-1 to operating in crosswinds of 11.6 m/sec (22.4 kt), or less, with 75 percent of available lateral control. Normal power takeoff with cutback results in noise in excess of Federal Aviation Regulation Part 36 but less than for conventional procedure takeoff. Results of advanced (noncertificated) programmed throttle takeoff and approach procedures, not yet optimized, indicate that such can be an important additional method noise reduction.

A study of the prediction of cruise noise and laminar flow control noise criteria for subsonic air transports

Abstract: General procedures for the prediction of component noise levels incident upon airframe surfaces during cruise are developed. Contributing noise sources are those associated with the propulsion system, the airframe and the laminar flow control (LFC) system. Transformation procedures from the best prediction base of each noise source to the transonic cruise condition are established. Two approaches to LFC/acoustic criteria are developed. The first is a semi-empirical extension of the X-21 LFC/acoustic criteria to include sensitivity to the spectrum and directionality of the sound field. In the second, the more fundamental problem of how sound excites boundary layer disturbances is analyzed by deriving and solving an inhomogeneous Orr-Sommerfeld equation in which the source terms are proportional to the production and dissipation of sound induced fluctuating vorticity. Numerical solutions are obtained and compared with corresponding measurements. Recommendations are made to improve and validate both the cruise noise prediction methods and the LFC/acoustic criteria.

Effect of noise spectra and a listening task upon passenger annoyance in a helicopter interior noise environment

Abstract: The effects of helicopter interior noise on passenger annoyance were studied. Both reverie and listening situations were studied as well as the relative effectiveness of several descriptors (i.e., overall sound pressure level, A-weighted sound pressure level, and speech interference level) for quantifying annoyance response for these situations. The noise stimuli were based upon recordings of the interior noise of a civil helicopter research aircraft. These noises were presented at levels ranging from approximately 68 to 86 dB(A) with various gear clash tones selectively attenuated to give a range of spectra. Results indicated that annoyance during a listening condition is generally higher than annoyance during a reverie condition for corresponding interior noise environments. Attenuation of the planetary gear clash tone results in increases in listening performance but has negligible effect upon annoyance for a given noise level. The noise descriptor most effective for estimating annoyance response under conditions of reverie and listening situations is shown to be the A-weighted sound pressure level.

A computer program for detailed analysis of the takeoff and approach performance capabilities of transport category aircraft

Abstract: The takeoff and approach performance of an aircraft is calculated in accordance with the airworthiness standards of the Federal Aviation Regulations. The aircraft and flight constraints are represented in sufficient detail to permit realistic sensitivity studies in terms of either configuration modifications or changes in operational procedures. The program may be used to investigate advanced operational procedures for noise alleviation such as programmed throttle and flap controls. Extensive profile time history data are generated and are placed on an interface file which can be input directly to the NASA aircraft noise prediction program (ANOPP).

Advanced turbo-prop airplane interior noise reduction-source definition

Abstract: Acoustic pressure amplitudes and phases were measured in model scale on the surface of a rigid semicylinder mounted in an acoustically treated wind tunnel near a prop-fan (an advanced turboprop with many swept blades) model. Operating conditions during the test simulated those of a prop-fan at 0.8 Mach number cruise. Acoustic pressure amplitude and phase contours were defined on the semicylinder surface. Measurements obtained without the semi-cylinder in place were used to establish the magnitude of pressure doubling for an aircraft fuselage located near a prop-fan. Pressure doubling effects were found to be 6dB at 90 deg incidence decreasing to no effect at grazing incidence. Comparisons of measurements with predictions made using a recently developed prop-fan noise prediction theory which includes linear and non-linear source terms showed good agreement in phase and in peak noise amplitude. Predictions of noise amplitude and phase contours, including pressure doubling effects derived from test, are included for a full scale prop-fan installation.

High velocity jet noise source location and reduction. task 6. supplement. computer programs: engineering correlation (m*s) jet noise prediction method and unified aeroacoustic prediction model (m*g*b) for nozzles of arbitary shape

Abstract: This General Supplement Report documents two Computerized Jet Noise Prediction Techniques: the Engineering Method and the Unified Aeroacoustic Prediction Model. A complete description of the computer programs is provided, including examples of input preparation and output cases, plus a listing of the FORTRAN computer code. The comprehensive, empirical, jet noise prediction method has been developed by correlating extensive data from this program and available data from other published sources. The data were correlated by means of basic engineering principles and physical parameters. The resulting prediction method includes unsuppressed conical nozzles; multitube and multichute single- and dual-flow suppressed nozzles; and multitube/multichute nozzles with hardwall and treated sectors. A unified aerodynamic/acoustic prediction technique has also been developed for assessing the noise characteristics of suppressor nozzles. The technique utilizes an extension of Reichardt's method so as to provide predictions of a jet plume flow field. The turbulent fluctuations in the mixing regions of the jet are assumed to be the primary source of noise generation, as in Classical Theories of Jet Noise. The alteration of the generated noise by the jet plume itself as it propagates through the jet to the farfield is modeled utilizing the high-frequency shielding theory based on Lilley's equation. These basic modeling elements have been coupled together in a discrete volume-element formulation. The individual volume elements are assumed to be uncorrelated with each other, so that the total contribution to the farfield is simply the sum of the individual volume element contributions.

Technology Status of Jet Noise Suppression Concepts for Advanced Supersonic Transports

Abstract: In conducting technology studies for advanced supersonic transports, Douglas Aircraft Company of the McDonnell Douglas Corporation has found that the constraints of community noise dictate the engine cycle selection and nozzle design, and significantly affect the overall airplane configuration design. Since selection and development of an engine is probably the pacing item in any new program start, much activity is underway on definition of engine cycles, provisions for jet exhaust noise suppression, levels of suppression achievable, and the impact of each possible combination on overall airplane performance and technical risk. This paper presents one aircraft manufacturer's views on the technology status of three of the most promising exhaust nozzle designs meeting the noise constraints: the coannular, the coannular with plug, and the retractable mechanical suppressor. Each type is defined along with predicted operational characteristics. Theoretical and actual test performance, for both thrust loss and noise suppression, are summarized. Each of these three nozzles is combined with an appropriate engine, and is sized and integrated into a baseline Mach 2.2 supersonic transport to evaluate range performance. The current status of performance for the various suppression concepts is summarized.

Effects of duration and other noise characteristics on the annoyance caused by aircraft-flyover noise

Abstract: A laboratory experiment was conducted to determine the effects of duration and other noise characteristics on the annoyance caused by aircraft-flyover noise. Duration, doppler shift, and spectra were individually controlled by specifying aircraft operational factors, such as velocity, altitude, and spectrum, in a computer synthesis of the aircraft-noise stimuli. This control allowed the separation of the effects of duration from the other main factors in the experimental design: velocity, tonal content, and sound pressure level. The annoyance of a set of noise stimuli which were comprised of factorial combinations of a 3 durations, 3 velocities, 3 sound pressure levels, and 2 tone conditions were judged. The judgements were made by using a graphical scale procedure similar to numerical category scaling. Each of the main factors except velocity was found to affect the judged annoyance significantly. The interaction of tonal content with sound pressure level was also found to be significant. The duration correction used in the effective-perceived-noise-level procedure, 3 dB per doubling of effective duration, was found to account most accurately for the effect of duration. No significant effect doppler shift was found.

Aircraft Noise-Induced Building Vibrations

Abstract: The outdoor/indoor noise levels and associated vibration levels resulting from aircraft and nonaircraft events are recorded at 11 homesites, a historic building, and a school. In addition, limited subjective tests are conducted to examine the human detection/annoyance thresholds for building vibration and rattle caused by aircraft noise. Results include relationships between aircraft noise and building vibration and between vibration and human response. Comparisons of building vibration data with existing criteria for building damage and human response are also considered.

Validation of aircraft noise prediction program

Abstract: Predictions made with NASA's aircraft noise prediction program (ANOPP) were compared with flyover noise data. A data base of six flyover noise runs for the DC-10-40/JT9D-59A configuration was used. For all power settings, ANOPP consistently underpredicted the low frequency spectral levels, overpredicted high frequency spectral levels and, consequently, overpredicted the inlet and aft PNLT time histories.

Summary of noise reduction characteristics of typical general aviation materials

Abstract: The paper presents the results of a large number of systematic tests to determine noise reduction characteristics of general aviation materials. Effects of material type (metallic and composite), thickness, panel stiffening, vibration damping materials, sound absorption materials and pressurization on noise reduction are included. Several promising methods for reducing cabin interior noise in light airplanes are discussed based on the results.

Temporary threshold shift from transportation noise

Abstract: Temporary threshold shifts (TTS), induced by recordings of aircraft noise, road traffic noise, and interior railroad car noise, were examined to estimate the auditory effects of these typical environmental noises. The aircraft noise used was of a Boeing 747 landing, recorded adjacent to the end of a runway. Six hours of binaural exposure to the noise, presented every 2 min at a maximum A‐weighted level of 97 dB (slow response), developed a TTS2 at 4 kHz of 1.0±2.7 (SD) dB as the mean value for the 57 better ears of 19 subjects on three successive days. The road traffic noise was recorded on a road where traffic volume was 49.5 (26.8 heavy) vehicles per min, and the interior railroad car noise was in a car commonly utilized for commuting. These two noises, reproduced with duty cycles of 4 min 7 s and 3 min 4 s, respectively, induced, after 6 h of exposure, a TTS0.5 at 1.5 kHz and a TTS2 at 4 kHz of almost the same degree at each sound level (A weighted) of 75, 85, and 90 dB, in L 50. The TTS0.5 were 0.5, 2 and 3 dB, and the TTS2 were −0.5, 3.5, and 5.5 dB, on the average, for the better ears of three to four persons, which indicates especially that 75 dB for the road traffic noise and 70 dB for the interior railroad car noise are the maximum sound levels which may fail to develop significant TTS even at 4 kHz. The present results lead to the conclusion that affected populations may have TTS induced by road traffic noise but that little effect is likely due to aircraft noise or interior railroad car noise.

An Experimental Study of Propeller - Induced Structural Vibration and Interior Noise

Abstract: This paper presents results of tests conducted to study fuselage sidewall dynamics and their effects on the cabin interior noise of a twin-engine, propeller-driven, light aircraft. Data on the dynamic behavior were obtained by slowly sweeping the RPM of one of the engines while the aircraft was stationary on the ground. This technique allowed frequency response plots of the sidewall structural accelerations to be obtained. These accelerations are compared to similar results from a test using a mechanical shaker in order to evaluate the structural dynamic response caused by the harmonics of the propeller blade passage tone. The dynamic response of the fuselage sidewall is also discussed as a noise transmission mechanism. A second mechanism for noise transmission through the fuselage sidewall was investigated by opening the copilot's window. The results illustrate the complex nature of the noise transmission mechanisms and the importance of correctly assessing noise paths.

Variability of annoyance response due to aircraft noise

Abstract: An investigation was conducted to study the variability in the response of subjects participating in noise experiments. This paper presents a description of a model developed to include this variability which incorporates an aircraft-noise adaptation level or an annoyance calibration for each individual. The results indicate that the use of an aircraft-noise adaption level improved prediction accuracy of annoyance responses (and simultaneously reduced response variation).

XV-15 Tilt Rotor Research Aircraft - Program report

Abstract: This paper is a status report of the NASA/Army XV-15 Project. The basic tilt-rotor concept and the XV-15 Tilt-Rotor Research Aircraft are discussed and some results of full-scale wind-tunnel tests in the Ames 40- by 80-Foot Wind Tunnel are presented. Flight-test data are included to give preliminary performance, noise, and vibration data in hover and as far into transition flight as are available at the time of presentation. Information concerning vehicle aerodynamics and airloads obtained as a result of both wind-tunnel and flight tests are provided with some conclusions as to the ramifications of the data in terms of design criteria and configuration layout.

Evaluating and minimizing noise impact due to aircraft flyover

Abstract: Existing techniques were used to assess the noise impact on a community due to aircraft operation and to optimize the flight paths of an approaching aircraft with respect to the annoyance produced. Major achievements are: (1) the development of a population model suitable for determining the noise impact, (2) generation of a numerical computer code which uses this population model along with the steepest descent algorithm to optimize approach/landing trajectories, (3) implementation of this optimization code in several fictitious cases as well as for the community surrounding Patrick Henry International Airport, Virginia.

Airframe noise measurements on a small-scale model of a supersonic transport concept in an anechoic flow facility

Abstract: Airframe noise has been measured on a .015 scale model of an advanced supersonic transport concept (AST-100) in an anechoic flow facility. The model was equipped with leading- and trailing-edge flaps, nose and main landing gears, and engine nacelles. Each of these components was deployed, individually and collectively, to determine their contribution to the noise field. Results are presented which show that in the clean configuration the aircraft displays a symmetric dipole directivity, whereas in the more complex landing-approach configuration the directivity peaks in the forward quadrant. It was found that the landing-approach noise was due chiefly to the landing gear, the trailing edge flaps, and the aeroacoustic interaction between the two

Integrated Noise Model (INM). Version 2. User's Guide,

Abstract: : This document contains the instructions to execute the Integrated Noise Model (INM), Version 2. The INM is a collection of computer programs which can calculate the aircraft noise environment in the vicinity of an airport given certain information on airport location, layout, and the type and movement of its air traffic.