Calculated values of airframe noise levels corresponding to FAA noise certification conditions for six aircraft are presented. The aircraft are: DC-9-30; Boeing 727-200; A300-B2 Airbus; Lockheed L-1011; DC-10-10; and Boeing 747-200B. The prediction methodology employed is described and discussed

Raney, J. P.

English

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3 1176 00162 7778 NASA-TM-81849 19800025710
NASA Technical Memorandum 81849
PREDICTEDAIRFRAMENOISELEVELS
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SEPTEMBER1980 ,OOT16 i_0
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National Aeronautics and
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LangleyResearchCenter
Hampton, Virginia 23665
https://ntrs.nasa.gov/search.jsp?R=19800025710 2020-03-21T15:38:17+00:00Z

PREDICTEDAIRFRAMENOISE LEVELS
J. P. Raney
Langley Research Center
INTRODUCTION
Concern over predicted airframe noise levels as they appeared in a paper
by P. Block (ref. I) has been voiced by the major aircraft manufacturers in
the U. S. The controversy stems mainly from figure 13 in reference 1 where
predicted airframe noise levels for a number of aircraft types are shown
together with the FAR 36 stage 3 approach noise rule and some approach noise
certification data points. The predicted airframe noise levels in this figure
are significantly lower than the stage 3 approach noise rule. The concern
of the manufacturers related to technical matters is focused upon the possi-
bility that (I) regulatory agencies may use these predicted airframe noise
levels as a basis for setting approach noise rules in the future; and (2) the
airframe noise prediction method adopted in ANOPPmay underpredict airframe
noise by a significant margin.
The aircraft approach speed and flap setting used by Block to compute the
airframe noise were obtained from a summary published in Aviation Week and
Space Technology and these parameters were clearly identified in reference I.
However, these conditions were not the same as required for certification, but
rather the conditions for the expected normal operations of these aircraft.
Therefore, there is some inconsistency in the representation of this particular
figure in reference I. In order to rectify this inconsistency and to clarify
the concern existing in the industry, this document will describe the ANOPP
airframe noise prediction method and the computational results specifically
related to six aircraft which are part of the current commercial airline
fleet.
CERTIFICATIONCONDITION
The aircraft approach speeds and flap settings used by P. Block in
reference 1 are given in table I. These values were obtained from a summary
published in the March 12, 1979 issue of Aviation Week and Space Technology.
These landing speeds and flap settings do not correspond to the conditions
required for noise certification. The certification approach speeds are
generally higher than the approach speeds as shown in reference I.
The certification approach speeds and flap settings for the six aircraft
considered in this document, namely, DC-9-30, Boeing 727-200, A300-B2 Airbus,
DC-IO-IO, L-IOll, and Boeing 747-200B, have been obtained from FAA and the
values arealso shown in table I.
COMPUTATIONSOF AIRFRAMENOISE
In order to address the points of concern outlined in the Introduction,
airframe noise has been computed in several ways for the six aircraft under
consideration. First, the airframe noise computations have been repeated
for the conditions specified in ref. I. The ANOPPairframe noise prediction
method is the one developed and published by M. R. Fink in 1977 (ref. 2). In
this set of computations, the atmosphere is chosen as the ISA standard +I0 °
centigrade day at sea level, and ground reflection effects at the microphone
position have been included. The results are identical to those reported in
reference 1 as expected since the ANOPPairframe noise computation module
has not been modified since the computations were executed for reference I.
A second set of airframe noise levels are calculated by using the certifica-
tion approach conditions which are specified in table I. The results for
both sets of computations are tabulated in table II. Since the airframe noise
intensity depends on the fifth power of the aircraft speed, the higher approach
speed during certification resulted in an average increase in noise of 2.5
EPNdBfor these six aircraft. In particular, the predicted airframe noise of
DC-9-30, B-727, and A300-B2 Airbus for certification are significantly higher
than the corresponding levels given in reference 1 for nominal aircraft
operating conditions.
Since the publication of reference 2, additional information regarding
the physical behavior of airframe noise has become available. Based on this
new information, some changes to the airframe noise prediction method were
recommended by Fink. In his method the main contributions to airframe noise
are produced by the landing gear and the trailing edge flap. In the original
Fink prediction method, directivity patterns for these two components are
static dipoles. The gear noise dipole is normal to the flight path while the
trailing edge flap dipole is normal to the plane of the flap. The modifica-
tions recommended by Fink are as follows:
I. The directivity pattern of the gear noise component should be changed
to a convected monopole. The OASPLradiated at 90 degrees from the flight
path should remain the same as previously given in reference 2.
2. The directivity of the trailing edge flap noise component should be
changed to a convected dipole pattern. The OASPLradiated along the axis
of the dipole should remain unchanged. However, in the new directivity
pattern the dipole axis is in a direction normal to the flight path regardless
of the flap angle setting.
In both cases, the convection factor is suggested to be (l-MaCOSS)-3,
which is based upon empirical data correlation. These changes in directivity
result in a net increase in total radiated sound power.
Since these changes appear to be reasonable from an analytical standpoint,
a third set of airframe noise levels are computed according to these modifica-
tions recommended by Fink. The results are also tabulated in table II. In
this set of computations, the input is chosen to be the certification approach
conditions. It can be seen from table II that the modifications in directivity
result in an increase in noise level of approximately 1.5 EPNdBon average
for the six aircraft. Therefore, between the predicted airframe noise at
certification approach conditions using a modified Fink method and the pre-
dicted airframe noise as shown in reference I, a net increase in level of about
4 EPNdBis observed on the average. The computational results are also
summarized in figure I.
THE ISSUE OF SPECTRALMODIFICATION
In light of the concern over the possibility of underprediction of air-
frame noise by the Fink method as given in reference 2, the basis for arriving
at the recommendedspectrum for the trailing edge flap noise has also become
an issue. Reference 2 recommends separate spectra for flaps with two segments
and three segments. The three segment spectrum has a much higher composition
of high frequency noise. The original data base used by Fink contains seven
sets of data with three sets coming from measurements of VC-IO aircraft
(fig. 2). It is evident from figure 2 that the VC-IO flap noise spectra are
rich in high frequency components. In reference 2, Fink treated the VC-IO
as a three-segment flap system while it has actually a two-segment flap system.
As a consequence, the VC-IO data were correlated with the Boeing 747 data to
determine the three-segment flap spectrum. Because of this error, the correct
recommendation for the flap noise spectra is now at issue.
Fink has recently recommended that the three-segment flap noise spectrum
should be used for predicting the flap noise component for large airplanes
with either a two-segment flap system or a three-segment flap system. However,
this recommendation is not adopted for ANOPPcomputations because, this
particular change in procedure by itself increases the predicted EPNLby
approximately 5.5 EPNdB, and such levels for the L-IOll, and DC-IO would have
exceeded, by a significant margin, the airframe noise levels suggested by the
manufacturers in reference 3. Therefore, the merit of this particular change
in prediction procedure is questionable. In essence, the only data of
airframe noise for a wide body jet within the data base for the development of"
the spectral curve are provided by the recent measurement of airframe noise
of an L-IOll by Fethney and Jelly (ref. 4). The Fink recommendation is made,
therefore, with minimal support of data. While it is possible that the
current two-segment flap spectrum is deficient in high frequency levels, a new
recommended standard spectrum cannot be established without a careful reevalua-
tion of the evidence.
CONCLUSIONS
Based on computations of airframe noise levels for six important types of
commercial aircraft, the inconsistency in a key figure previously published by
Block in reference 1 has been rectified. After using the correct certifica-
tion approach conditions and incorporating some modifications to the Fink
3
method of airframe noise prediction, the predicted airframe noise levels
have shown a net increase of about 4 EPNdBas compared with the levels
given in reference I.
REFERENCES
I. Block, P. J. W.: Assessment of Airframe Noise. AIAA Paper 79-4148,
J. Aircraft, vol. 16, no. 12, Dec. 1979, pp. 834-841.
2. Fink, Martin R.: Airframe Noise Prediction Method. Federal Aviation
Administration Report FAA-RD-77-29, March 1977.
3. AIA Position Paper on Airframe Noise Levels and Research Programs.
Transmitted by letter from J. C. Snodgrass, Jr., Director, Aviation
Programs, Aerospace Industries Association of America, Inc. to Chief,
ASD, LRC, July 25, 1980.
4. Fethney, P. and Jelly A. H.: Airframe Self-Noise Studies on the
Lockheed LOIOII Tristar Aircraft. AIAA Paper 80-1061, June 1980.
TABLE I. AIRFRAMENOISE PREDICTIONSTUDY
Input Parameters
ORIGINAL
(J. Aircraft) CERTIFICATION
No. of
Flap TOGW Velocity Flaps Velocity Flaps
Aircraft Segments (Mega Newton) (m/sec) (deg) (m/sec) (deg)
DC-9-30 2 0.505 64.43 45 73.6 40
727-200 3 0.780 64.84 30 71.55 40
A300-B2 2 1.390 67.94 45 83.50 25
L-IOll 2 1,915 73.34 45 77.16 42
DC-IO-IO 2 1.825 70.64 45 77.16 50
747-200B 3 3.440 72,44 45 85.14 30
TABLE II. AIRFRAMENOISE PREDICTIONSTUDY
Approach EPNL
ORIGINAL CERTIFICATION
(J, Aircraft)
Current AFM Current AFM Modified AFM
Aircraft Module Module Module
DC-9-30 84.3 87.2 88.7
727-200 89.6 93.6 94.9
A300-B2 88.5 91.8 93.9
L-IOll 90.2 91.2 93,1
DC-IO-IO 90.3 92.8 94.8
747-200B 97.5 99.6 100.9
110 --
100 -- 3 FLAP
J
Level,
EPNdB Z FLAP
.. 90 - 7 DC-10
. _ _,o,,
, / - <> Reference1
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<_DC-9 • Cert.condition,originalANOPP
• Cert. condition,modifiedANOPP
80 .i I I I I i I I I
0.5 1.0 Z.0 3.0 4.0 5.0 I0.0 Z0.0
TOGW, 1%4newtons
Figure 1. Predicted airframe noise levels, approach.
1 10 - EMPIRICAL APPROXIMATION
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o .-. Triple slotted flaps
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- 0Q
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slotted flaps
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Strouhal number based on flap chord, fcF/U
Figure 2. Measured airframe noise data.
1. Report No. 2. GovernmentAccessionNo. 3. Recipient'sCatalogNo.NASATM-81849
4. Title and Subtitle 5. Report Date
Sep,tembe.r.1980
Predicted Airframe Noise Level s 6. PerformingOrganizationC de
7. Author(s) 8. Performing Orgamzation Report No.\
J. P. Raney
10. Work Unit No.
9. PerformingOrganizationNameandAddre= 505-32-03
11. Contract or Grant No.
NASALangley Research Center
Hampton, Virginia 23665 13. Type of Report and Period Covered
12. Sponsoring Agency Name and Address Technical Memorandum
National Aeronautics and Space Administration
14. Sponsoring Agency Code
Washington, D. C. 20546
15. Supplementary Notes
16. Abstract
Calculated values of airframe noise levels corresponding to FAA noise
certification conditions for six aircraft are presented: DC-9-30, Boeing
727-200, A300-B2 Airbus, Lockheed L-1011, DC-]0-10, and Boeing 747-200B.
The prediction methodology employed is described and discussed.
17. Key Words (Sugg_ted by Author(s)} 18. Distribution Statement
Airframe Noise Prediction
Aircraft Noise Unclassified - unlimited
ANOPP Subject Category 71
19. Security Classif.(of this report] 20. Security Classif.(of this page) 21. No. of Pages 22. Price*
Unclassified Unclassified 8 A02
* ForsalebytheNationalTechnicalInformationService,Springfield,Virginia22161





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