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Methods of Controlling Distortion of Inlet Airflow During Static Acoustical Tests of Turbofan Engines and Fan Rigs

2020-03-13
WIP
AIR1935A
Generally it is desirable during static engine noise testing to simulate the noise-generating processes that occur during takeoff or landing. One factor that may have significant influence on fan noise from turbofan engines during static testing is the airflow distortion encountered by the low-pressure fan stage. This report presents technical details on devices that "condition" the airflow entering the engine to more nearly simulate flight operations without introducing a detrimental impact on sound propagating from the engine.
Standard

Ground-Plane Microphone Configuration for Propeller-Driven Light-Aircraft Noise Measurement

2020-03-13
WIP
ARP4055A
The scope of this ARP embraces the description of a configuration for a ground-plane microphone installation that may be used to determine sound pressure levels equivalent to those which would have been measured in an acoustic freefield at the microphone location. The one-third - octave-band center-frequency range over which equivalent freefield sound pressure levels may be obtained is from as low as 50 Hz to at least as high as 10,000 Hz. The specific application of the measurement technique described in this ARP is the determination of the equivalent freefield sound pressure levels of the noise produced by propeller-driven light aircraft, in flight, for sound incidence angles within 30 degrees of the normal to the ground. For larger angles to the normal, additional adjustments may be necessary which are outside the scope of this ARP.
Standard

Ground-Plane Microphone Configuration for Propeller-Driven Light-Aircraft Noise Measurement

1988-01-01
CURRENT
ARP4055
The scope of this ARP embraces the description of a configuration for a ground-plane microphone installation that may be used to determine sound pressure levels equivalent to those which would have been measured in an acoustic freefield at the microphone location. The one-third - octave-band center-frequency range over which equivalent freefield sound pressure levels may be obtained is from as low as 50 Hz to at least as high as 10,000 Hz. The specific application of the measurement technique described in this ARP is the determination of the equivalent freefield sound pressure levels of the noise produced by propeller-driven light aircraft, in flight, for sound incidence angles within 30 degrees of the normal to the ground. For larger angles to the normal, additional adjustments may be necessary which are outside the scope of this ARP.
Standard

TYPE MEASUREMENTS OF AIRCRAFT INTERIOR SOUND PRESSURE LEVELS IN CRUISE

1978-02-01
HISTORICAL
ARP1323
Recommendations of this Aerospace Recommended Practice (ARP) are not intended to satisfy the more detailed and stringent requirements of aircraft design development. Also, they may not be directly applicable to general or private aviation aircraft where special restraints on measurement locations and procedures may exist. However, many of the principles and standards discussed may apply to these aircraft. The recommended procedure for sound pressure level measurements in aircraft involves the recording of data on magnetic tape for subsequent processing and analysis after the flight. Sound level meter/octave-band analyzer measurements, because of inherent inaccuracies associated with manual data readings, are not as precise as those obtained from a tape-recorder/time integrating analyzer system and are, therefore, precluded from this recommended practice.
Standard

TYPE MEASUREMENTS OF AIRPLANE INTERIOR SOUND PRESSURE LEVELS DURING CRUISE

1990-08-01
HISTORICAL
ARP1323A
The primary measurement procedure recommended in this ARP includes the recording of sound pressure signals in the interior of an airplane during steady state cruise conditions with analysis after the flight into octave band (or one-third octave band) sound pressure levels.
Standard

MEASUREMENT OF FAR FIELD NOISE FROM GAS TURBINE ENGINES DURING STATIC OPERATION

1990-02-19
HISTORICAL
ARP1846
Recommendations presented in this document are intended primarily for the acquisition of far-field acoustical data. The test engine is to be appropriately configured and operated so that the acoustical signals generated are consistent with the specific objectives of the test. The principal output of the data reduction system is one-third octave band sound pressure levels. However, broader or narrower bandwidth analysis of the recorded data may also be accomplished when appropriate. Although not specifically intended to apply to special purpose engine noise testing (for example, tests involving unique instrumentation or procedures to identify specific noise sources), some of the practices described herein may be appropriate for such testing. Specification of reference conditions is outside the scope of this document although procedures to adjust data to a reference condition are described in 7.2.4.
Standard

Measurement of Far Field Noise from Gas Turbine Engines During Static Operation

2020-03-13
WIP
ARP1846B
Recommendations presented in this document are intended primarily for the acquisition of far-field noise data. The test engine is to be appropriately configured and operated so that the sound pressure levels obtained are consistent with the specific objectives of the test. The principal output of the data reduction system is one-third octave band sound pressure levels. However, when appropriate, data may be recorded for purposes of broader or narrower bandwidth analysis.
Standard

Measurement of Far Field Noise from Gas Turbine Engines During Static Operation

2008-03-05
CURRENT
ARP1846A
Recommendations presented in this document are intended primarily for the acquisition of far-field noise data. The test engine is to be appropriately configured and operated so that the sound pressure levels obtained are consistent with the specific objectives of the test. The principal output of the data reduction system is one-third octave band sound pressure levels. However, when appropriate, data may be recorded for purposes of broader or narrower bandwidth analysis.
Standard

Practical Methods to Obtain Free-Field Sound Pressure Levels From Acoustical Measurements Over Ground Surfaces

2020-03-13
WIP
AIR1672C
Acquisition of free-field data is of practical significance in the field of aeronautical acoustics. The need for free-field data includes (but is not restricted to) the following: comparison of acoustical data obtained from the same engine under various measurement conditions; comparison of the results obtained from models with those from an engine on a test stand; comparison of noise measurements made on the same engine under static and in-flight conditions; design of test facilities; standardization of techniques for 'in situ' acoustical measurements; spectral decomposition to isolate the contribution of different sources to the total noise; and prediction of aircraft noise on the basis of methods which, generally, provide free-field data. There is an increasing tendency to test full-scale engine components and scale models in anechoic test facilities that provide free-field conditions.
Standard

Method for Predicting Lateral Attenuation of Airplane Noise

2006-04-20
CURRENT
AIR5662
This document describes analytical methods for calculating the attenuation of the level of the sound propagating from an airplane to locations on the ground and to the side of the flight path of an airplane during ground roll, climbout after liftoff, and landing operations. Both level and non-level ground scenarios may be modeled using these methods, however application is only directly applicable to terrain without significant undulations, which may cause multiple reflections and/or multiple shielding effects. This attenuation is termed lateral attenuation and is in excess of the attenuation from wave divergence and atmospheric absorption.
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