Showing papers on "Aircraft noise published in 2016"

Intermittency ratio: A metric reflecting short-term temporal variations of transportation noise exposure.

Abstract: Most environmental epidemiology studies model health effects of noise by regressing on acoustic exposure metrics that are based on the concept of average energetic dose over longer time periods (i.e. the Leq and related measures). Regarding noise effects on health and wellbeing, average measures often cannot satisfactorily predict annoyance and somatic health effects of noise, particularly sleep disturbances. It has been hypothesized that effects of noise can be better explained when also considering the variation of the level over time and the frequency distribution of event-related acoustic measures, such as for example, the maximum sound pressure level. However, it is unclear how this is best parametrized in a metric that is not correlated with the Leq, but takes into account the frequency distribution of events and their emergence from background. In this paper, a calculation method is presented that produces a metric which reflects the intermittency of road, rail and aircraft noise exposure situations. The metric termed intermittency ratio (IR) expresses the proportion of the acoustical energy contribution in the total energetic dose that is created by individual noise events above a certain threshold. To calculate the metric, it is shown how to estimate the distribution of maximum pass-by levels from information on geometry (distance and angle), traffic flow (number and speed) and single-event pass-by levels per vehicle category. On the basis of noise maps that simultaneously visualize Leq, as well as IR, the differences of both metrics are discussed.

Living with aircraft noise: Airport proximity, aviation noise and subjective wellbeing in England

Abstract: Airport expansion is an issue of intense public debate due to the potential impacts on climate change and the quality of life of affected local communities. This paper is the first study to analyse the relationships between airports and multiple subjective wellbeing measures, by merging national-level population statistics with noise measurement maps for seventeen English airports. The presence of daytime aviation noise was found to consistently negatively impact on five subjective wellbeing measures. We found a marginal negative association with every additional decibel of aircraft noise. We found no significant association between wellbeing and living within night-time noise contours or living in close airport proximity. We conclude that living under air traffic flight paths has a negative effect on peoples’ overall and momentary wellbeing, equivalent to around half the effect of being a smoker for some wellbeing measures. The subjective wellbeing method findings support wider revealed preference literature showing lower market demand in areas affected by aviation noise.

Acoustic Characterization and Prediction of Representative, Small-Scale Rotary-Wing Unmanned Aircraft System Components

Abstract: In this study, hover performance and acoustic measurements are taken on two different isolated rotors representative of small-scale rotary-wing unmanned aircraft systems (UAS) for a range of rotation rates Each rotor system consists of two fixed-pitch blades powered by a brushless motor For nearly the same thrust condition, significant differences in overall sound pressure level (OASPL), up to 8 dB, and directivity were observed between the two rotor systems Differences are shown to be in part attributed to different rotor tip speeds, along with increased broadband and motor noise levels In addition to acoustic measurements, aeroacoustic predictions were implemented in order to better understand the noise content of the rotor systems Numerical aerodynamic predictions were computed using the unsteady Reynoldsaveraged Navier Stokes code OVERFLOW2 on one of the isolated rotors, while analytical predictions were computed using the Propeller Analysis System of the Aircraft NOise Prediction Program (ANOPP-PAS) on the two rotor configurations Preliminary semi-empirical frequency domain broadband noise predictions were also carried out based on airfoil self-noise theory in a rotational reference frame The prediction techniques further supported trends identified in the experimental data analysis The brushless motors were observed to be important noise contributors and warrant further investigation It is believed that UAS acoustic prediction capabilities must consider both rotor and motor components as part of a combined noise-generating system

Statistical modeling of the spatial variability of environmental noise levels in Montreal, Canada, using noise measurements and land use characteristics.

Abstract: The availability of noise maps to assess exposure to noise is often limited, especially in North American cities. We developed land use regression (LUR) models for LAeq24h, Lnight, and Lden to assess the long-term spatial variability of environmental noise levels in Montreal, Canada, considering various transportation noise sources (road, rail, and air). To explore the effects of sampling duration, we compared our LAeq24h levels that were computed over at least five complete contiguous days of measurements to shorter sampling periods (20 min and 24 h). LUR models were built with General Additive Models using continuous 2-min noise measurements from 204 sites. Model performance (adjusted R2) was 0.68, 0.59, and 0.69 for LAeq24h, Lnight, and Lden, respectively. Main predictors of measured noise levels were road-traffic and vegetation variables. Twenty-minute non-rush hour measurements corresponded well with LAeq24h levels computed over 5 days at road-traffic sites (bias: -0.7 dB(A)), but not at rail (-2.1 dB(A)) nor at air (-2.2 dB(A)) sites. Our study provides important insights into the spatial variation of environmental noise levels in a Canadian city. To assess long-term noise levels, sampling strategies should be stratified by noise sources and preferably should include 1 week of measurements at locations exposed to rail and aircraft noise.

Airport noise predicts song timing of European birds.

Abstract: Anthropogenic noise is of increasing concern to biologists and medical scientists. Its detrimental effects on human health have been well studied, with the high noise levels from air traffic being of particular concern. However, less is known about the effects of airport noise pollution on signal masking in wild animals. Here, we report a relationship between aircraft noise and two major features of the singing behavior of birds. We found that five of ten songbird species began singing significantly earlier in the morning in the vicinity of a major European airport than their conspecifics at a quieter control site. As birds at both sites started singing before the onset of air traffic in the morning, this suggests that the birds in the vicinity of the airport advanced their activity to gain more time for unimpaired singing before the massive plane noise set in. In addition, we found that during the day, chaffinches avoided singing during airplane takeoffs, but only when the noise exceeded a certain threshold, further suggesting that the massive noise caused by the airport can impair acoustic communication in birds. Overall, our study indicates that birds may be adjusting their mating signals and time budgets in response to aircraft noise.

Analysis of landing gear noise during approach

Abstract: Airframe noise is becoming increasingly important during approach, even reaching higher noise levels than the engines in some cases. More people are affected due to low flight altitudes and fixed traffic routing associated with typical approaches. Formost air- craft types, the landing gear system is a dominant airframe noise source. However, this element can only be modeled in an approximate manner in wind tunnel experiments. In this research, flyovers of landing aircraft were recorded using a 32 microphone array. Fun ctional beamforming was applied to analyze the noise emissions from the landing gear system. lt was confirmed that for some aircraft types, such as the Airbus A320 and the Fokker 70, the nose landing gear is a dominant noise source du ring approach. The correlation between the noise levels generated by the landing gear and the aircraft velocity was found to be significant, explai ning about 70% of the varia bility found in the noise levels, which is in good agreement with all known theory. Moreover, the experimental resu lts for the Airbus A320 measurements were compared with those obtained using the DLR system noise prediction tool PANAM. Whereas the total aircraft noise levels were in good agreement. the measurements indicate a higher contribution from the nose landing gear noise compared to the predictions.

Perceived Noise Analysis for Offset Jets Applied to Commercial Supersonic Aircraft

Abstract: A systems analysis was performed with experimental jet noise data, engine/aircraft performance codes and aircraft noise prediction codes to assess takeoff noise levels and mission range for conceptual supersonic commercial aircraft. A parametric study was done to identify viable engine cycles that meet NASA's N+2 goals for noise and performance. Model scale data from offset jets were used as input to the aircraft noise prediction code to determine the expected sound levels for the lateral certification point where jet noise dominates over all other noise sources. The noise predictions were used to determine the optimal orientation of the offset nozzles to minimize the noise at the lateral microphone location. An alternative takeoff procedure called "programmed lapse rate" was evaluated for noise reduction benefits. Results show there are two types of engines that provide acceptable mission range performance; one is a conventional mixed-flow turbofan and the other is a three-stream variable-cycle engine. Separate flow offset nozzles reduce the noise directed toward the thicker side of the outer flow stream, but have less benefit as the core nozzle pressure ratio is reduced. At the systems level for a three-engine N+2 aircraft with full throttle takeoff, there is a 1.4 EPNdB margin to Chapter 3 noise regulations predicted for the lateral certification point (assuming jet noise dominates). With a 10% reduction in thrust just after clearing the runway, the margin increases to 5.5 EPNdB. Margins to Chapter 4 and Chapter 14 levels will depend on the cumulative split between the three certification points, but it appears that low specific thrust engines with a 10% reduction in thrust (programmed lapse rate) can come close to meeting Chapter 14 noise levels. Further noise reduction is possible with engine oversizing and derated takeoff, but more detailed mission studies are needed to investigate the range impacts as well as the practical limits for safety and takeoff regulations.

Simulation-Based Airframe Noise Prediction of a Full-Scale, Full Aircraft

Abstract: A previously validated computational approach applied to an 18%-scale, semi-span Gulfstream aircraft model was extended to the full-scale, full-span aircraft in the present investigation. The full-scale flap and main landing gear geometries used in the simulations are nearly identical to those flown on the actual aircraft. The lattice Boltzmann solver PowerFLOW® was used to perform time-accurate predictions of the flow field associated with this aircraft. The simulations were performed at a Mach number of 0.2 with the flap deflected 39 deg. and main landing gear deployed (landing configuration). Special attention was paid to the accurate prediction of major sources of flap tip and main landing gear noise. Computed farfield noise spectra for three selected baseline configurations (flap deflected 39 deg. with and without main gear extended, and flap deflected 0 deg. with gear deployed) are presented. The flap brackets are shown to be important contributors to the farfield noise spectra in the mid- to high-frequency range. Simulated farfield noise spectra for the baseline configurations, obtained using a Ffowcs Williams and Hawkings acoustic analogy approach, were found to be in close agreement with acoustic measurements acquired during the 2006 NASA-Gulfstream joint flight test of the same aircraft.

Environmental Issues for Aircraft Operations at Airports

Abstract: Nowadays, besides safety issues, environmental protection is the main issue to be considered during the aircraft operations. Recorded total CO2 aviation emissions are approximately 2% of the Global Greenhouse Emissions with the approximated expected growth around 3-4% per year. Therefore, variety of standards and recommending practices have been developed to address aircraft noise and engine emissions embracing technological improvements, operating procedures, proper organization of air traffic, appropriate airport and land-use planning, and the use of market-based options. This paper is based on environmental pressures from long distance air transport with the focus on passenger transport. The paper deals with variety of parameters important for aircraft operations on ground. Those parameters could be grouped within safety, technical, infrastructural, weather, meteorological conditions, etc. It is not possible consider only one group of parameters since aircraft operations on ground present complex environment for the aircraft structure loads, weight limitation or cost efficiency flight performance. Nowadays, research of aircraft ground operations is much oriented to environmental protection and noise limitation issues which influent new technologies of aircraft building or equipment production or airport capacity and air side characteristics. The paper analyzes specific operation parameters related to aircraft capabilities and performance in order to understand the quality and cost efficiency while selecting certain aircraft from fleet to operate on origin/destination airport. Obtained results and final conclusions address future measures for minimizing the environmental pressures based on environmental trends in aviation to 2050 provided by ICAO and EASA.

Airframe Noise Prediction of a Full Aircraft in Model and Full Scale Using a Lattice Boltzmann Approach

Abstract: Unsteady flow computations are presented for a Gulfstream aircraft model in landing configuration, i.e., flap deflected 39deg and main landing gear deployed. The simulations employ the lattice Boltzmann solver PowerFLOW(Trademark) to simultaneously capture the flow physics and acoustics in the near field. Sound propagation to the far field is obtained using a Ffowcs Williams and Hawkings acoustic analogy approach. Two geometry representations of the same aircraft are analyzed: an 18% scale, high-fidelity, semi-span model at wind tunnel Reynolds number and a full-scale, full-span model at half-flight Reynolds number. Previously published and newly generated model-scale results are presented; all full-scale data are disclosed here for the first time. Reynolds number and geometrical fidelity effects are carefully examined to discern aerodynamic and aeroacoustic trends with a special focus on the scaling of surface pressure fluctuations and farfield noise. An additional study of the effects of geometrical detail on farfield noise is also documented. The present investigation reveals that, overall, the model-scale and full-scale aeroacoustic results compare rather well. Nevertheless, the study also highlights that finer geometrical details that are typically not captured at model scales can have a non-negligible contribution to the farfield noise signature.

System Noise Prediction of the DGEN 380 Turbofan Engine

Abstract: The DGEN 380 is a small, separate-flow, geared turbofan. Its manufacturer, Price Induction, is promoting it for a small twinjet application in the emerging personal light jet market. Smaller, and producing less thrust than other entries in the industry, Price Induction is seeking to apply the engine to a 4- to 5-place twinjet designed to compete in an area currently dominated by propeller-driven airplanes. NASA is considering purchasing a DGEN 380 turbofan to test new propulsion noise reduction technologies in a relevant engine environment. To explore this possibility, NASA and Price Induction have signed a Space Act Agreement and have agreed to cooperate on engine acoustic testing. Static acoustic measurements of the engine were made by NASA researchers during July, 2014 at the Glenn Research Center. In the event that a DGEN turbofan becomes a NASA noise technology research testbed, it is in the interest of NASA to develop procedures to evaluate engine system noise metrics. This report documents the procedures used to project the DGEN static noise measurements to flight conditions and the prediction of system noise of a notional airplane powered by twin DGEN engines.

Superconducting Electromagnetic Launch System for Civil Aircraft

Abstract: This paper considers the feasibility of different superconducting technologies for electromagnetic launch (EML) to assist civil aircraft takeoff. EML has the potential of reducing the required runway length by increasing aircraft acceleration. Expensive airport extensions to face constant air traffic growth could be avoided by allowing large aircraft to operate from short runways at small airports. The new system positively affects total aircraft noise and exhaust emissions near airports and improves overall aircraft efficiency through reducing engine design constraints. Superconducting linear synchronous motors (SCLSMs) can be exploited to deliver the required takeoff thrust with electromagnetic performance that cannot be easily achieved by conventional electrical machines. The sizing procedure of an SCLSM able to launch A320 in weight is presented. Electromagnetic and thermal aspects of the machine are taken into account, including the modeling of ac losses in superconductors and thermal insulation. The metallic high-temperature superconductor (HTS) magnesium diboride (MgB2) is used and operated at 20 K, the boiling temperature of liquid hydrogen. With modern manufacturing technology, multifilament MgB2 wires appear to be the most cost-effective solution for this application. Finally, the impact of the cryocooler efficiency on the machine performance is evaluated.

Functional Beamforming applied to full scale landing aircraft

Abstract: Aircraft noise is becoming an increasingly important problem for the aerospace industry and for the residents living in the vicinities of airports. For efforts aiming at reducing aircraft noise levels, it is important to know all the aircraft elements which generate noise and their relative contribution. Experimental measurements with aircraft under operational conditions provide essential information for this purpose. The use of microphone arrays and high resolution beamforming techniques are required to image the acoustic sources at the relatively large distance between the observer and the aircraft. Functional beamforming is a novel nonlinear technique which offers improved array spatial resolution and dynamic range. For an appropriately selected exponent value, most array sidelobes are substantially decreased. This method requires a similar computational time as the conventional beamforming algorithm. In this research, the performance of functional beamforming is investigated with full scale aircraft under operational conditions. The sound of 115 landing aircraft fly-overs was recorded in Amsterdam Airport Schiphol utilizing a 32 microphone array. It was found that functional beamforming provides a good performance, allowing for the identification of individual noise sources on the aircraft. The dynamic range obtained is approximately 30 times larger and its array spatial resolution is about 6 times better than the conventional beamformer.

Health Impairments, Annoyance and Learning Disorders Caused by Aircraft Noise Synopsis of the State of Current Noise Research

Abstract: The article reviews the results of scientific research on aircraft noise induced health impairments, annoyance as well as learning disorders and summarizes consequences for legislative and political decisions. The association of noise with an increased incidence of chronic arterial hypertension has been shown in large-scale epidemiological studies. Identified risks are up to 20% per 10 dB increase in day-evening-night level (above 50 dB(A)) and for nightly noise exposure within a range of 19-34% per 10 dB (above 30-35dB(A)). Identified risks regarding the use of antihypertensive drugs are partly higher. Also an increase in strokes is documented in recent epidemiological studies and understood as a consequence of hypertension. The same applies in the case of heart failure. Likewise an increase in myocardial infarctions has been confirmed in the recent studies with large populations included. Moreover, the annoyance due to aircraft noise has been significantly underestimated in the last 15 years. Compared to the EU-position paper of 2002 the sound level at a given extent of annoyance (25% HA) is at least 10 dB(A) lower. Impairments of cognitive performance in children attending schools exposed to high aircraft noise have been demonstrated in national and international studies up to the year 2014. As consequence of the present knowledge in noise effect research legal and political decisions must form the base to reduce aircraft noise exposure during the 24h-day to Lden = 50 and during the night to Ln = 45 dB(A).

Development and Calibration of a Field-Deployable Microphone Phased Array for Propulsion and Airframe Noise Flyover Measurements

Abstract: A new aeroacoustic measurement capability has been developed consisting of a large channelcount, field-deployable microphone phased array suitable for airframe noise flyover measurements for a range of aircraft types and scales. The array incorporates up to 185 hardened, weather-resistant sensors suitable for outdoor use. A custom 4-mA current loop receiver circuit with temperature compensation was developed to power the sensors over extended cable lengths with minimal degradation of the signal to noise ratio and frequency response. Extensive laboratory calibrations and environmental testing of the sensors were conducted to verify the design's performance specifications. A compact data system combining sensor power, signal conditioning, and digitization was assembled for use with the array. Complementing the data system is a robust analysis system capable of near real-time presentation of beamformed and deconvolved contour plots and integrated spectra obtained from array data acquired during flyover passes. Additional instrumentation systems needed to process the array data were also assembled. These include a commercial weather station and a video monitoring / recording system. A detailed mock-up of the instrumentation suite (phased array, weather station, and data processor) was performed in the NASA Langley Acoustic Development Laboratory to vet the system performance. The first deployment of the system occurred at Finnegan Airfield at Fort A.P. Hill where the array was utilized to measure the vehicle noise from a number of sUAS (small Unmanned Aerial System) aircraft. A unique in-situ calibration method for the array microphones using a hovering aerial sound source was attempted for the first time during the deployment.

Determination of aircraft noise variability using an acoustic camera

Abstract: Nowadays, aircraft noise is one of the major problems to be dealt with by the aerospace industry and especially suffered by the residents living in the vicinities of airports. The enforcement of noise control environmental laws around airports is hindered due to the large variability observed in the noise levels for flyovers of the same aircraft type. These variations are not properly considered by the current assessment tools, such as the Noise-Power-Distance tables. In this paper, a measurement campaign was performed in Amsterdam Schiphol Airport using a 32 microphone array, where 115 flyovers of landing aircraft were recorded in order to determine these variations for various aircraft types and investigate the causes. It was assumed that the main cause of this variability are the differences in the emitted aircraft noise, since previous experience confirmed that the effect of the variable atmosphere (for the distances considered) is negligible. A strong correlation was found between the noise levels and the fan rotational speed (determined from the spectrograms), with almost 40% of the observed total noise variation explained by the engine settings variation. The use of a microphone array allows for acoustic imaging, thus discerning the noise of the aircraft elements from those of other sound sources. It was shown that for many aircraft types the turbofan engines were the main noise sources. After applying functional beamforming to the acoustic data focusing on the engines location, this correlation is even higher, explaining over 62% of the noise level variability.

Toward Reduced Aircraft Community Noise Impact Via a Perception-Influenced Design Approach

Abstract: This is an exciting time for aircraft design. New configurations, including small multi-rotor uncrewed aerial systems, fixed- and tilt-wing distributed electric propulsion aircraft, high-speed rotorcraft, hybrid-electric commercial transports, and low-boom supersonic transports, are being made possible through a host of propulsion and airframe technology developments. The resulting noise signatures may be radically different, both spectrally and temporally, than those of the current fleet. Noise certification metrics currently used in aircraft design do not necessarily reflect these characteristics and therefore may not correlate well with human response. Further, as operations and missions become less airport-centric, e.g., those associated with on-demand mobility or package delivery, vehicles may operate in closer proximity to the population than ever before. Fortunately, a new set of tools are available for assessing human perception during the design process in order to affect the final design in a positive manner. The tool chain utilizes system noise prediction methods coupled with auralization and psychoacoustic testing, making possible the inclusion of human response to noise, along with performance criteria and certification requirements, into the aircraft design process. Several case studies are considered to illustrate how this approach could be used to influence the design of future aircraft.

Numerical assessment of the vibration control effects of porous liners on an over-the-wing propeller configuration

Abstract: An over-the-wing position of propellers comes with noise shielding and significantly reduced sound emission to the ground. A drawback of this configuration may be the additional impact due to the passing propeller blades on the airfoil’s surface inducing structure-borne sound in the wing. This structural sound propagates within the wing and the fuselage and can radiate further into the cabin as airborne sound. In order not to trade the advantage of reduced noise transmission to the ground with higher sound pressure levels within the cabin, a remedy is proposed, which consists in placing a poroelastic liner on the wing’s surface below the rotor where the blade tips move closely to the airfoil’s skin. In this work, a numerical approach to assess the effects of porous liners for an over-the-wing propeller configuration is presented. A simplified generic channelwing structure is exposed to pressure fluctuations on its surface which are caused by an over-the-wing propeller. Porous liners are applied to the wing’s surface where the blade tips pass in close proximity. Structural vibrations are determined using the finite element method in frequency domain. Surface data is obtained from CFD computations. The porous material is represented by Biot’s theory.

Potential for Landing Gear Noise Reduction on Advanced Aircraft Configurations

Abstract: The potential of significantly reducing aircraft landing gear noise is explored for aircraft configurations with engines installed above the wings or the fuselage. An innovative concept is studied that does not alter the main gear assembly itself but does shorten the main strut and integrates the gear in pods whose interior surfaces are treated with acoustic liner. The concept is meant to achieve maximum noise reduction so that main landing gears can be eliminated as a major source of airframe noise. By applying this concept to an aircraft configuration with 2025 entry-into-service technology levels, it is shown that compared to noise levels of current technology, the main gear noise can be reduced by 10 EPNL dB, bringing the main gear noise close to a floor established by other components such as the nose gear. The assessment of the noise reduction potential accounts for design features for the advanced aircraft configuration and includes the effects of local flow velocity in and around the pods, gear noise reflection from the airframe, and reflection and attenuation from acoustic liner treatment on pod surfaces and doors. A technical roadmap for maturing this concept is discussed, and the possible drag increase at cruise due to the addition of the pods is identified as a challenge, which needs to be quantified and minimized possibly with the combination of detailed design and application of drag reduction technologies.

ANOPP2 User's Manual: Version 1.2

Abstract: This manual documents the Aircraft NOise Prediction Program 2 (ANOPP2). ANOPP2 is a toolkit that includes a framework, noise prediction methods, and peripheral software to aid a user in predicting and understanding aircraft noise. This manual includes an explanation of the overall design and structure of ANOPP2, including a brief introduction to aircraft noise prediction and the ANOPP2 background, philosophy, and architecture. The concept of nested acoustic data surfaces and its application to a mixed-fidelity noise prediction are presented. The structure and usage of ANOPP2, which includes the communication between the user, the ANOPP2 framework, and noise prediction methods, are presented for two scenarios: wind-tunnel and flight. These scenarios serve to provide the user with guidance and documentation references for performing a noise prediction using ANOPP2.

Auralization of NASA N+2 Aircraft Concepts from System Noise Predictions

Abstract: Auralization of aircraft flyover noise provides an auditory experience that complements integrated metrics obtained from system noise predictions. Recent efforts have focused on auralization methods development, specifically the process by which source noise information obtained from semi-empirical models, computational aeroacoustic analyses, and wind tunnel and flight test data, are used for simulated flyover noise at a receiver on the ground. The primary focus of this work, however, is to develop full vehicle auralizations in order to explore the distinguishing features of NASA's N+2 aircraft vis-a-vis current fleet reference vehicles for single-aisle and large twin-aisle classes. Some features can be seen in metric time histories associated with aircraft noise certification, e.g., tone-corrected perceived noise level used in the calculation of effective perceived noise level. Other features can be observed in sound quality metrics, e.g., loudness, sharpness, roughness, fluctuation strength and tone-to-noise ratio. A psychoacoustic annoyance model is employed to establish the relationship between sound quality metrics and noise certification metrics. Finally, the auralizations will serve as the basis for a separate psychoacoustic study aimed at assessing how well aircraft noise certification metrics predict human annoyance for these advanced vehicle concepts.

Flyover Noise Measurements and Predictions of Commercial Airplanes

Abstract: A series of flyover noise measurements has been taken to gather data for noise prediction, analysis, and computer program validation. A selected database of measurements is presented for the Airbus A320-200, the Boeing B737-800, and the ATR72 (turboprop). The experimental setup, the microphone positions, the effect of background noise, and the atmospheric effects are presented. It is shown that landing measurements are generally coherent with one another, with consistent peaks in noise levels and uniform noise levels ±5 s from the overhead position. In contrast, at takeoff, there are considerable variations in peak noise level, which are attributed to different takeoff procedures and gross weights. Comparisons with noise predicted using ray tracing are shown. These comparisons indicate that it is possible to predict with some accuracy the noise peaks, the rise and fall of overall sound level, and the integral noise metrics (effective perceived noise level and LAmax).