Showing papers on "Aircraft noise published in 1980"

Subsonic aircraft: Evolution and the matching of size to performance

Abstract: Methods for estimating the approximate size, weight, and power of aircraft intended to meet specified performance requirements are presented for both jet-powered and propeller-driven aircraft. The methods are simple and require only the use of a pocket computer for rapid application to specific sizing problems. Application of the methods is illustrated by means of sizing studies of a series of jet-powered and propeller-driven aircraft with varying design constraints. Some aspects of the technical evolution of the airplane from 1918 to the present are also briefly discussed.

An improved prediction method for the noise generated in flight by circular jets

Abstract: A semi‐empirical model for predicting the noise generated by jets exhausting from circular nozzles is presented and compared with small‐scale static and simulated‐flight data. The present method is an updated version of that part of the original NASA Aircraft Noise Prediction Program (1974) relating to circular jet noise. The earlier method has been shown to agree reasonably well with experimental static and flight data for jet velocities up to ∼ 520 m/s. The poorer agreement at higher jet velocities appeared to be due primarily to the manner in which supersonic convection effects were formulated. The purely empirical supersonic convection formulation is replaced in the present method by one based on theoretical considerations. Other improvements of an empirical nature have been included based on model‐jet/free‐jet simulated‐flight tests. The effects of nozzle size, jet velocity, jet temperature, and flight are included.

Airframe Noise Component Interaction Studies

Abstract: Acoustic wind-tunnel tests were conducted to examine the noise-generating processes of an airframe during approach flight. The airframe model was a two-dimensional wing section, to which high-lift leading and trailing edge devices and landing gear were added. Far-field conventional microphones were utilized to determine component spectrum levels. An acoustic mirror directional microphone was utilized to examine differences in noise source distributions on airframe components extended separately and in combination. Measured spectra are compared with predictions inferred from aircraft flyover data. Aeroacoustic mechanisms for each airframe component are identified. Component interaction effects on total radiated noise generally were small (within about 2 dB). However, some interactions altered local flow velocities and turbulence levels, causing redistribution of local acoustic source strength. Possibilities for noise reduction exist if trailing edge flaps could be modified to decrease their noise radiation caused by incident turbulent flow.

Airframe Noise Reduction Studies and Clean-Airframe Noise Investigation

Abstract: Acoustic wind tunnel tests were conducted of a wing model with modified leading edge slat and trailing edge flap. The modifications were intended to reduce the surface pressure response to convected turbulence and thereby reduce the airframe noise without changing the lift at constant incidence. Tests were conducted at 70.7 and 100 m/sec airspeeds, with Reynolds numbers 1.5 x 10 to the 6th power and 2.1 x 10 to the 6th power. Considerable reduction of noise radiation from the side edges of a 40 deflection single slotted flap was achieved by modification to the side edge regions or the leading edge region of the flap panel. Total far field noise was reduced 2 to 3 dB over several octaves of frequency. When these panels were installed as the aft panel of a 40 deg deflection double slotted flap, 2 dB noise reduction was achieved.

The NASA high-speed turboprop program

Abstract: Technology readiness for Mach 0.7 to 0.8 turboprop powered aircraft with the potential for fuel savings and DOC reductions of up to 30 and 15 percent respectively relative to current in-service aircraft is addressed. The areas of propeller aeroacoustics, propeller structures, turboprop installed performance, aircraft cabin environment, and turboprop engine and aircraft studies are emphasized. Large scale propeller characteristics and high speed propeller flight research tests using a modified testbed aircraft are also considered.

Noise transmission into a light aircraft

Abstract: An analytical study on noise transmission into a cabin of a twin engine G/A aircraft is presented. The solution of the governing acoustic-structural equations of motion is developed utilizing modal expansions and a Galerkin type procedure. The exterior noise pressure inputs are taken from available experimental data. A direct comparison between theory and experiments on cabin noise levels is given. Interior noise reduction by stiffening, mass addition, and damping treatments is investigated. It is shown that a combination of added mass and damping could significantly reduce interior noise levels for this aircraft.

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.

Reliability of social survey data on noise effects

Abstract: The results of household interviews provide essential data for the formulation of noise control policies. However, only a few studies have investigated the reliability of such data, in terms of a test‐retest comparison. To help provide better evidence of reliability, 212 persons in the vicinity of Toronto International Airport were re‐interviewed in the summer of 1979, using essentially the same questionnaire they had answered in the summer of 1978. To test whether the reliability is affected by noise level, the sample was stratified by both aircraft and road traffic noise levels. Results show that, on an individual level, reliability of attitude scores is not particularly high (correlation coefficients of 0.50 ± 0.05 for several scales for both aircraft and road traffic noise), and that the reliability is affected by noise level. On the aggregate level (based on the percentage of the population reporting certain responses), much better reliability can be obtained. For attitude data, percent highly annoye...

Noise: hearing loss and psychological effects.

Abstract: There are many uncertainties about the effects of noise below the level that might harm hearing. The author suggests that there is good evidence that loud noises affect well being and health in the widest sense and reviews recent research on the subject. The level of annoyance experienced depends upon the nature of the source, the circumstances, the characteristics and attitude of the individual as well as the physical features of the noise. While annoyance increases with increasing noise there is a wide range of individual variation in response. There is evidence to show that introverts cannot tolerate noise as well as extroverts while anxious people tend to judge sounds to be louder than the non-anxious. Results show that although mentally disturbed and normal people are annoyed by aircraft noise, the former are more likely to be very annoyed. The effect of noise in work performance is not always adverse. Noise increases arousal and focuses attention on the dominant features of the task at the expense of the subsiding aspects. The ability to perform complex tasks and complex intellectual functions deteriorates in the presence of noise; accuracy and the response to the unexpected suffer. Changes in noise level appear to be particularly disturbing. (TRRL)

Effects of aircraft noise on an intelligibility task.

Abstract: The recorded sounds of three aircraft (T28 propeller airplane, Bell 204B helicopter, and Bell 206 helicopter) flying directly overhead at 300 ft and 900 ft (91.4 m and 274.3 m) were played While subjects engaged in an audiovisual task. The subjects viewed a series of 35-mm color slides of everyday scenes and heard them described by one-word labels. Each label was to be identified as "Right," "Wrong," or "Unheard." The results were in close agreement with previous field studies on the rated "annoyingness" of aircraft sounds and provided no support for the contention that impulsive helicopter noise ("blade-slap") is disruptive in ways not accoullfed for by simple measures of loudness level

Propeller signatures and their use

Abstract: The identification and use of the noise and vibration signatures of individual propellers, described herein, has provided a basis for rational advances in propeller-noise analysis and control. These signatures, or influence vectors, were used for 1) analytically determining optimum synchrophase angles and 2) diagnosing the specific paths—airborne and structure-borne—of the noise into the cabin. A number of significant conclusions are drawn from flight experiments in a Navy P-3C patrol aircraft. The results and techniques from this work are applicable to improving the passenger and crew comfort as well as equipment life in propeller-powered aircraft.

Prediction of the interior noise levels of high-speed propeller-driven aircraft

Abstract: The theoretical basis for an analytical model developed to predict the interior noise levels of high-speed propeller-driven airplanes is presented Particular emphasis is given to modeling the transmission of discrete tones through a fuselage element into a cavity, estimates for the mean and standard deviation of the acoustic power flow, the coupling between a non-homogeneous excitation and the fuselage vibration response, and the prediction of maximum interior noise levels The model allows for convenient examination of the various roles of the excitation and fuselage structural characteristics on the fuselage vibration response and the interior noise levels, as is required for the design of model or prototype noise control validation tests

Noise control prediction for high-speed, propeller-driven aircraft

Abstract: An analytical study is described which explores add-on treatments and advanced concepts for the reduction of noise levels in three high-speed aircraft driven by propellers. Noise reductions of 25 to 28 dB are required to achieve a goal of an A-weighted sound level not greater than 80 dB. It is found that only a double-wall system, with a limp inner wall or trim panel, can achieve the required noise reductions. Weight penalties are estimated for the double-wall treatments. These penalties are 0.75% to 1.51% of the aircraft takeoff weight for the particular baseline designs selected.

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.

Noise transmission and attenuation by stiffened panels

Abstract: An analytical study of noise transmission into semi-cylindrical and rectangular acoustic enclosures due to turbulent boundary layer pressure and propeller noise (prop-fan) is presented. The structural noise transmission models include a single panel, discretely stiffened elastic panel and stiffened viscoelastic sandwich panel. Response characteristics of the stiffened panels are evaluated using a transfer matrix procedure. The interior noise field is determined by a Galerkin-like method. The effect on interior noise due to aerodynamic surface flow, cavity back-up pressure, pressurization, mass, stiffness, and damping addition to the structure is investigated. It is shown that stiffened viscoelastic sandwich panels, while providing the same stiffening benefits as an equivalent elastic panel, could significantly reduce vibration levels and subsequently give similar benefits for interior noise control.

Assessing the Impact of Audible Noise From AC Transmission Lines: A Proposed Method

Abstract: A method is proposed for assessing the effects of audible noise caused by transmission line corona on residents living near the line. The method employs a procedure favored by the U.S. Environmental Protection Agency (EPA). It is based upon community noise impact studies of familiar sounds (i.e., traffic and aircraft noise), and is as yet unverified for corona noise.

Landing approach airframe noise measurements and analysis

Abstract: Flyover measurements of the airframe noise produced by the AeroCommander, JetStar, CV-990, and B-747 airplanes are presented for various landing approach configurations. Empirical and semiempirical techniques are presented to correlate the measured airframe noise with airplane design and aerodynamic parameters. Airframe noise for the jet-powered airplanes in the clean configuration (flaps and gear retracted) was found to be adequately represented by a function of airplane weight and the fifth power of airspeed. Results show the airframe noise for all four aircraft in the landing configuration (flaps extended and gear down) also varied with the fifth power of airspeed, but this noise level could not be represented by the addition of a constant to the equation for clean-configuration airframe noise.

An acoustic sensitivity study of general aviation propellers

Abstract: This paper describes the results of a study in which a systematic approach has been taken in studying the effect of selected propeller parameters on the character and magnitude of propeller noise. Four general aviation aircraft were chosen, i.e., a Cessna 172, Cessna 210, Cessna 441, and a 19 passenger commuter concept, to provide a range in flight velocity, engine horsepower, and gross weight. The propeller parameters selected for examination consisted of number of blades, rpm reduction, thickness/chord reduction, activity factor reduction, proplets, airfoil improvement, sweep, position of maximum blade loading, and diameter reduction.

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.

Prediction of noise constrained optimum takeoff procedures

Abstract: An optimization method is used to predict safe, maximum-performance takeoff procedures which satisfy noise constraints at multiple observer locations. The takeoff flight is represented by two-degree-of-freedom dynamical equations with aircraft angle-of-attack and engine power setting as control functions. The engine thrust, mass flow and noise source parameters are assumed to be given functions of the engine power setting and aircraft Mach number. Effective Perceived Noise Levels at the observers are treated as functionals of the control functions. The method is demonstrated by applying it to an Advanced Supersonic Transport aircraft design. The results indicate that automated takeoff procedures (continuously varying controls) can be used to significantly reduce community and certification noise without jeopardizing safety or degrading performance.

Simple method for prediction of aircraft noise contours

Abstract: A method for generating noise contours more rapidly and more simply than previously used programs is discussed. The method gives the area, the noise contour, and its extremities for an arbitrarily complex flight path for both takeoffs and landings with relative ease. The analysis reveals the fundamental nature of the contours and how the various factors that influence its size and shape enter into the analysis. It is noted that the effects of ground attenuation and shielding are omitted as they are important only on the initial portion of flight and are highly dependent upon aircraft configuration. However, the analysis shows that these effects could be included. It is emphasized the the single-event contour is an obvious choice for purposes of minimizing noise impact.

Aircraft noise prediction program validation

Abstract: A modular computer program (ANOPP) for predicting aircraft flyover and sideline noise was developed. A high quality flyover noise data base for aircraft that are representative of the U.S. commercial fleet was assembled. The accuracy of ANOPP with respect to the data base was determined. The data for source and propagation effects were analyzed and suggestions for improvements to the prediction methodology are given.

An overview of NASA's propeller and rotor noise research

Abstract: This paper presents a summary of NASA's propeller and rotor noise research. The objective of this research is to develop the technology and data base required to reduce propeller and rotor noise with minimum performance penalties. The status of current research will be described for both low- and high-speed propellers and for helicopter rotors. Recent results and future research thrusts are also discussed