Showing papers on "Aircraft noise published in 1982"

Aircraft noise prediction program theoretical manual, part 2

Abstract: Detailed prediction methods for specific aircraft noise sources are given. These sources are airframe noise, combustion noise, fan noise, single and dual stream jet noise, and turbine noise. Modifications to the NASA methods which comply with the International Civil Aviation Organization standard method for aircraft noise prediction are given.

Community annoyance from aircraft and ground vehicle noise

Abstract: Data from published noise‐annoyance surveys are related to a common measure of noise exposure Ldn. The results provide means for predicting the annoyance (experienced by percentages of people of normal and of supersensitivity) attributable to noise from aircraft and from street and road traffic. Correlations of 0.90 to 0.95 are found between Ldn and percentages of people annoyed by aircraft noise when low, moderate, and higher levels of annoyance are measured for both a broad range (35 dB) and a restricted range (20 dB) of Ldn. Noise from urban street and road traffic is shown to cause less annoyance than the noise from aircrafts when both have the same Ldn as typically measured or estimated for outdoors. The difference, equivalent to a difference of about 10 dB in Ldn, is attributed to acoustical factors that diminish in‐and‐around‐the‐home noise dosages from ground vehicular traffic compared to dosages from aircraft operations. Generalized functions showing degrees of annoyance and percentages of U.S. u...

Flight effects of fan noise

Abstract: Simulation of inflight fan noise and flight effects was discussed. The status of the overall program on the flight effects of fan noise was reviewed, and flight to static noise comparisons with the JT15D engine were displayed.

Propeller tip vortex - A possible contributor to aircraft cabin noise

Abstract: Wind tunnel model tests support the hypothesis that a propeller tip vortex may subject a downstream wing surface to greater excitation than would be experienced by the aircraft fuselage side wall exposed to propeller-generated noise, ultimately transmitting this structural response to incident dynamic pressure to the cabin interior. Even if structure-borne excitations are less efficient than airborne excitations in the creation of cabin noise, the higher level of the former could still govern cabin noise levels.

A preliminary comparison between the SR‐3 propeller noise in flight and in a wind tunnel

Abstract: The noise generated by supersonic-tip-speed propellers is addressed. Models of such propellers were tested for acoustics in the Lewis 8-by-6-foot wind tunnel. One of these propeller models, SR-3, was tested in flight on the Jetstar airplane and noise data were obtained. Preliminary comparisons of the maximum blade passing tone variation with helical tip Mach number taken in flight with those taken in the tunnel showed good agreement when corrected to the same test conditions. This indicated that the wind tunnel is a viable location for measuring the noise of these propeller models. Comparisons of the directivities at 0.6 and 0.7 axial Mach number showed reasonable agreement. At 0.75 and 0.8 axial Mach number the tunnel directivity data fell off more towards the front than did the airplane data. A possible explanation for this is boundary layer refraction which could be different in the wind tunnel from that in flight. This may imply that some corrections should be applied to both the airplane and wind tunnel data at the forward angles. At and aft of the peak noise angle the boundary layer refraction does not appear to be significant and no correction appears necessary.

Comments on K. D. Kryter’s paper, ’’Community annoyance from aircraft and ground vehicle noise’’

Abstract: This paper presents a critique of K. D. Kryter’s paper, ’’Community Annoyance from Aircraft and Ground Vehicle Noise’’ [J. Acoust. Soc. Am. 72, xxx–xxx (1982)] in which he purports to show that an earlier paper of Schultz, ’’Synthesis of social surveys on noise annoyance’’ [J. Acoust. Soc. Am. 64, 377–405 (1978)], significantly underestimates the annoyance associated with aircraft noise, and underestimates that due to surface traffic noise. While the earlier Schultz paper may not be entirely correct, a careful study of Kryter’s new analysis suggests that his conclusions are considerably more dubious than he regards those of Schultz.

A note on the general scaling of helicopter blade-vortex interaction noise

Abstract: : A model-rotor acoustic experiment in a three meter open section anechoic wind tunnel (CEPRA-19) is described. The important scaling parameters are reviewed and some on-line acoustic data are presented for conditions known to produce blade-vortex interaction noise on a single rotor helicopter. Time averages of the model-scale acoustic pulses are compared with similar full-scale data taken in-flight under the same non-dimensionalized conditions. Good general agreement between model and full-scale pulse shapes and amplitudes of blade- vortex interaction noise is shown for one advance ratio over a range of inflow conditions for the rotor. Directivity sweeps for a condition known to generate blade-vortex interactions are presented. Some model rotor testing limitations of the CEPRA-19 facility in its present configuration are indicated.

Aircraft noise prediction program theoretical manual, part 1

Abstract: Aircraft noise prediction theoretical methods are given. The prediction of data which affect noise generation and propagation is addressed. These data include the aircraft flight dynamics, the source noise parameters, and the propagation effects.

Should helicopter noise be measured differently from other aircraft noise? A review of the psychoacoustic literature

Abstract: A review of 34 studies indicates that several factors or variables might be important in providing a psychoacoustic foundation for measurements of the noise from helicopters These factors are phase relations, tail rotor noise, repetition rate, crest level, and generic differences between conventional aircraft and helicopters Particular attention was given to the impulsive noise known as blade slap Analysis of the evidence for and against each factor reveals that, for the present state of scientific knowledge, none of these factors should be regarded as the basis for a significant noise measurement correction due to impulsive blade slap The current method of measuring effective perceived noise level for conventional aircraft appears to be adequate for measuring helicopter noise as well

Direct measurement of transmission loss of aircraft structures using the acoustic intensity approach

Abstract: A measurement technique is developed in order to obtain the sound transmission loss of an aircraft fuselage which obviates the need for the two-room transmission suite. The sound transmission paths were determined in tests on a light aircraft fuselage using a two-microphone acoustic intensity method for measuring the acoustic intensity transmitted to the interior when the fuselage was exposed to an external random incidence sound-field. The intensity transmitted through different sections of the fuselage can be estimated accurately using this new technique. Results of these tests show that the plexiglass window is the major transmission path in the high frequency range. In addition, the transmission losses through a single and a double layer window were predicted theoretically by using the Statistical Energy Analysis Model. Very good agreement is found between the predictions and the measurements.

We have just begun to create efficient transport aircraft

Abstract: Factors affecting the cost-effectiveness and economics of the air transportation industry are reviewed. The delivery of more fuel-efficient aircraft and eventual total replacement in the 1990's by fleets of advanced aircraft are seen to offset rising fuel costs. Better airport operations are perceived to eliminate fuel-costly delays due to overcrowded runways, lack of available carriers, and maintenance of aircraft in holding patterns. Noise reduction research will lower the lawsuit costs from noise pollution, and the introduction of advanced turbofans for long, short, and medium range flights, advanced commuter planes, and advanced SSTs offering projected 50% increases in current aircraft efficiencies are seen to be limited only by the airlines' ability to provide purchase financing, rather than by a lack of available new technology.

Reduction of high-speed impulsive noise by blade planform modification of a model helicopter rotor

Abstract: The reduction of high speed impulsive noise for the UH-1H helicopter was investigated by using an advanced main rotor system. The advanced rotor system had a tapered blade planform compared with the rectangular planform of the standard rotor system. Models of both the advanced main rotor system and the UH-1H standard main rotor system were tested at 1/4 scale in the 4 by 7 Meter Tunnel. In plane acoustic measurements of the high speed impulsive noise demonstrated that the advanced rotor system on the UH-1H helicopter reduced the high speed impulsive noise by up to 20 dB, with a reduction in overall sound pressure level of up to 5 dB.

Cabin Noise Control for Twin Engine General Aviation Aircraft

Abstract: An analytical model based on modal analysis was developed to predict the noise transmission into a twin-engine light aircraft. The model was applied to optimize the interior noise to an A-weighted level of 85 dBA. To achieve the required noise attenuation, add-on treatments in the form of honeycomb panels, damping tapes, acoustic blankets, septum barriers and limp trim panels were added to the existing structure. The added weight of the noise control treatment is about 1.1 percent of the total gross take-off weight of the aircraft.

An investigation of rotor harmonic noise by the use of small scale wind tunnel models

Abstract: Noise measurements of small scale helicopter rotor models were compared with noise measurements of full scale helicopters to determine what information about the full scale helicopters could be derived from noise measurements of small scale helicopter models. Comparisons were made of the discrete frequency (rotational) noise for 4 pairs of tests. Areas covered were tip speed effects, isolated rotor, tandem rotor, and main rotor/tail rotor interaction. Results show good comparison of noise trends with configuration and test condition changes, and good comparison of absolute noise measurements with the corrections used except for the isolated rotor case. Noise measurements of the isolated rotor show a great deal of scatter reflecting the fact that the rotor in hover is basically unstable.

Methodology for Multiaircraft Minimum Noise Impact Landing Trajectories

Abstract: The problem of optimizing landing trajectories with respect to noise impact index is addressed. In contrast with previous work, multilandings are considered. In order to make the problem tractable the trajectories are specified in functional form with certain parameters left free for selection by the optimization methods. Constraint of aircraft dynamic behavior, trajectory separation, pilot workload, passenger comfort, and maximum noise intensity all enter into the determination of what is an allowable trajectory. A version of the quasi-Newton iterative procedure is used to determine the optimum parameter values. The results show improvement in noise impact to the airport considered and the potential for even greater improvement at many airports.

Annoyance caused by propeller airplane flyover noise

Abstract: Two laboratory experiments were conducted to examine the annoyance response of people to the noise of propeller airplane flyovers and to assess potential method of quantifying that annoyance. In each experiment, 64 subjects judged the annoyance of recordings of propeller and jet airplane operations presented at D‐weighted sound pressure levels of 70, 80, and 90 dB in a testing room which simulates the outdoor acoustic environment. The first experiment examined 11 propeller airplanes with maximum takeoff weights greater than or equal to 5700 kg. The second experiment examined 14 propeller airplanes weighing 5700 kg or less. Five jet airplanes were included in each experiment. Perceived noise level predicted annoyance better than A‐, D‐, or E‐weighted sound pressure level. Corrections for tones greater than or equal to 500 Hz generally improved prediction ability for the heavier propeller airplanes. Tone corrections generally degraded prediction ability for the light propeller airplanes. Duration corrections improved prediction ability for the heavier propeller airplanes and degraded prediction ability for the light propeller airplanes. The effect on prediction ability of critical band corrections to perceived noise level varied.

Evaluation of noise control technology and alternative noise certification procedures for propeller-driven small airplanes

Abstract: : This report considers the effectiveness of current noise regulations in Appendix F of FAR Part 36, examines the potential effectiveness of future technology to achieve further noise reduction, and evaluates a number of new concepts for noise certification procedures for propeller-driven small aircraft. The latter were based, in part, on results of a flight test program carried out with Cessna Aircraft Company, to evaluate the utility of takeoff noise tests and the possible use of sound exposure level as a suitable metric for noise certification of the subject aircraft. The study indicates that existing regulations have been effective in stimulating development of quieter propellers for the existing fleet of propeller-driven small aircraft. However, it does not appear economically feasible to achieve more noise reduction in most of this fleet using existing technology with the possible exceptions of some of the two-engine aircraft. However, application of future noise reduction technology, primarily for quieter propellers, should allow a reduction in current noise limits by about 6 dB and should reduce levels of the noisiest aircraft in the current fleet by as much as 10 dB. A takeoff test is appropriate for all propeller aircraft except those equipped with cruise-optimized fixed-pitch propellers. For this test, the current level flyover test appears to represent the noisiest operating condition.

Rough analysis of installation effects on turboprop noise

Abstract: A rough analysis of noise from a propeller operated at angle of attack, and in the nonuniform flow due to a line vortex approximating a wing flow field suggests installation can significantly affect turboprop noise levels. On one side of the propeller, where the blades approach the horizontal plane from above, decreases of noise occur; while on the other side noise increases. The noise reduction is due to negative interference of steady and unsteady sources. An angle of attack, or distance between propeller and vortex, exists for which noise is a minimum. The relative contributions of thickness and loading noise are discussed, and results are presented both as plots of directivity and as plots of maximum noise level.

Design and test of aircraft engine isolators for reduced interior noise

Abstract: Improved engine vibration isolation was proposed to be the most weight and cost efficient retrofit structure-borne noise control measure for single engine general aviation aircraft. A study was carried out the objectives: (1) to develop an engine isolator design specification for reduced interior noise transmission, (2) select/design candidate isolators to meet a 15 dB noise reduction design goal, and (3) carry out a proof of concept evaluation test. Analytical model of the engine, vibration isolators and engine mount structure were coupled to an empirical model of the fuselage for noise transmission evaluation. The model was used to develop engine isolator dynamic properties design specification for reduced noise transmission. Candidate isolators ere chosen from available product literature and retrofit to a test aircraft. A laboratory based test procedure was then developed to simulate engine induced noise transmission in the aircraft for a proof of concept evaluation test. Three candidate isolator configurations were evaluated for reduced structure-borne noise transmission relative to the original equipment isolators.

Measurement of speech levels in the presence of time varying background noise

Abstract: Short-term speech level measurements which could be used to note changes in vocal effort in a time varying noise environment were studied. Knowing the changes in speech level would in turn allow prediction of intelligibility in the presence of aircraft flyover noise. Tests indicated that it is possible to use two second samples of speech to estimate long term root mean square speech levels. Other tests were also performed in which people read out loud during aircraft flyover noise. Results of these tests indicate that people do indeed raise their voice during flyovers at a rate of about 3-1/2 dB for each 10 dB increase in background level. This finding is in agreement with other tests of speech levels in the presence of steady state background noise.

Helicopter Noise Exposure Curves for Use in Environmental Impact Assessment.

Abstract: : This report establishes the current (1982) FAA helicopter noise data base for use in environmental impact assessment. The report sets out assumptions, methodologies, and techniques used in arriving at noise-exposure-versus-distance relationships. Noise data are provided for 15 helicopters, including five flight regimes each: takeoff, approach, level flyover, hover in-ground-effect (HIGE) and hover out-of-ground effect (HOGE). When possible, level flyover data are presented for a variety of airspeeds. Sound exposure level (SEL) is provided for all operational modes except hover. In the case of hover operations (both HOGE and HIGE), the maximum A-Weighted Sound Level (LAM) is identified as a function of distance. The report also includes a discussion of helicopter performance characteristics required for full computer modeling of helicopter/heliport noise exposure. (Author)

Prediction of jet exhaust noise on airframe surfaces during low-speed flight

Abstract: The behavior of pressure fluctuations measured on the airframe of a prototype high-lift jet transport (YC-14) is presented. Efforts to characterize the data in terms of a modest number of parameters and the resulting prediction procedures are described. Comparisons with near field engine exhaust noise of a conventional jet transport (Boeing 747) are presented. The results suggest that at low speeds the same exhaust noise source is important for both aircraft types. The results also suggest a consistent frequency sensitivity, as well as level sensitivity to airplane velocity. The frequency result appears to be new data.

Recommendations for field measurements of aircraft noise

Abstract: Specific recommendations for environmental test criteria, data acquisition procedures, and instrument performance requirements for measurement of noise levels produced by aircraft in flight are provided Recommendations are also given for measurement of associated airplane and engine parameters and atmospheric conditions Recommendations are based on capabilities which were available commercially in 1981; they are applicable to field tests of aircraft flying subsonically past microphones located near the surface of the ground either directly under or to the side of a flight path Aircraft types covered by the recommendations include fixed-wing airplanes powered by turbojet or turbofan engines or by propellers The recommended field-measurement procedures are consistent with assumed requirements for data processing and analysis

Annoyance due to street traffic and aircraft noise

Abstract: Annoyance is an important criterion to assess the health-impairing effects of noise. Affected are especially communications, due to speech interference, as well as relaxation and sleep. The extent of annoyance increases with rising noise load in the street traffic as well as in the air traffic. Air-traffic noise in residential areas should lie below NNI-values of 35; values of above 45 NNI result in a heavy noise load and require sound-protection measures. Street-traffic noise in residential areas should not surpass an Leq value of 60 dB(A) in daytime and 50 dB(A) at night; Leq values of more than 65 dB(A) are qualified as considerable annoyance and are thus critical. In recreation areas the threshold limits should be 5 dB(A) below these values, whereas for shops and offices at main thoroughfares values higher by 5 dB(A) can be tolerated. The noise load should first of all be diminished by stricter regulations for vehicles as well as by measures regarding traffic organization. Furthermore, noise-conscious driving is recommended. Very great traffic noise also requires sound protection measures. Language: de