Ma te ria ls S c ie nc e &Te c hno lo gy
Aircraft Noise: Source Model
R. Bütikofer
Laboratory of Acoustics
Empa, Switzerland

Aircraft Noise: Source Model
1. General remarks
2. Structure of the source model
3. Measurement methods
Empa, R. Bütikofer, October 2006 2

Acoustic engine of IMAGINE
S o urc e
Pro pag atio n No is e
o utput
re c e ptio n
Lde n
S ound powe r le ve l Dis ta nce , a ir a bs orption, ground Long te rm
dire ctivity, e ffe ct, curve d pa ths , s cre e ning a ve ra ge
ope ra tion
condition
ite ration
Empa, R. Bütikofer, October 2006 3

IMAGINE WP 4
Deliverable D10:
Default source description and
methods to assess source data for aircraft
WP 4 delivers a data structure, examples and a
description on how to do it, not a complete data
base.
Empa, R. Bütikofer, October 2006 4

Practitioner Modeller End-user
- Consultant - Scientist - Policymaker
- Adviser - Programmer - Administrator
- Analyst - Auditor - Planner
- Technician - Public
INPUTS MODEL OUTPUT
Scenario Database Contour
- Airport - Acoustic - Area
- Aircraft - Performance - Population
- Traffic - Other
- Routeings - Impact
- Weights
- Procedures Volume 2
- Population
- Geophysical
- Meteorology Volume 1
From DOC.29 (2005) Vol. 1 Applications guide www.ecac-ceac.org
Empa, R. Bütikofer, October 2006 5

Literature:
Special edition of Acta Acustica spring 2007
Empa, R. Bütikofer, October 2006 6

The 4 components of a calculation
Input Output
Data from the Scenario Aircraft sound Noise
real world calculation program contour
(Leq, Lden)
Aircraft per- Aircraft
formance data acoustic data
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Structure of the Source Model
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Characteristics of the source emission
Free field conditions (no ground influence)
Spectral data (1/3 octaves): 50 Hz … 10 kHz
Describes lateral and longitudinal directivity
Doppler effect is not removed
Empa, R. Bütikofer, October 2006 9

Geometry
flight path
height
r
ground track
sideline
distance
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Descriptor
Sound power, including direction dependent level adjustment: Lw,dir
Sound pressure level at receiver:
Lp (f, , ,r) = Lw (f) + Dc(f, , ) - C - A(f,r)
Lp (f, , ,r) = Lw,dir (f, , ) - 11 - A(f,r)
Sound pressure level at 1 m in free field (A 0):
Lp (f, , ,1m) = Lw,dir (f, , ) - 11
Empa, R. Bütikofer, October 2006 11

Parameters
aircraft type / engine
operation
flaps / slats / gear
thrust source module Lw,dir - Spectrum
speed
longitudinal angle
lateral angle
Empa, R. Bütikofer, October 2006 12

Lateral symmetry of sound emission
For fixed wing jet aircraft (but NOT for propeller or helicopters!):
= + 180°/ - 180°
Vertical symmetry
(upper / lower hemisphere)
= 90° = - 90°
Lateral symmetry
(left / right)
= 0° =±
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Sphere in Cartesian coordinates (I)
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Sphere in Cartesian coordinates (II)
Example:
xx: fields use the interpolated (or constant) value of neighbouring cells
Empa, R. Bütikofer, October 2006 15

Data base structure
Tables for specific aircraft and operation
conditions may be arranged in a data base
Not all combinations of operation conditions will
have data typical configurations with data,
rest with default values
Not all aircraft will have data grouping of
acoustically similar aircraft and substitution of
acoustically less important aircraft
Empa, R. Bütikofer, October 2006 16

Measurement methods
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Measurement methods
Reverse engineering from NPD data
„In-flight“ measurements under
operational conditions
Arranged „In-flight“ measurements
Processed data from manufacturers
Empa, R. Bütikofer, October 2006 18

„In-flight“ measurements under operational
conditions (I)
Set – up
Several microphones perpendicular to the axis
of the runway
at 3 to 5 km after brake release (departure)
at 1 to 3 km prior to touch down (landing)
Measurement of the normal airport traffic during
several days
Empa, R. Bütikofer, October 2006 19

„In-flight“ measurements under operational
conditions (II)
Requirements
Precision tracking of aircraft (tracking radar or
optical)
Time synchronisation of position and of the
acoustic recordings
Exact aircraft identification (type, engine, carrier,
ATOW)
Information from carriers on flight procedures
Empa, R. Bütikofer, October 2006 20

„In-flight“ measurements under operational
conditions (III)
Advantages
Measurement of „real-life“ situation
Average over many samples of the same aircraft
type
No additional costs for aircraft operation
Variety of different aircraft measured in the same
measurement period
Empa, R. Bütikofer, October 2006 21

„In-flight“ measurements under operational
conditions (VI)
Disadvantages
Thrust is unknown (unless FDR recordings are
available)
Limited to specific parameter combinations
(speed, flaps, gear, thrust)
Measurements only close to the airport
(sufficient signal to noise ratio)
Empa, R. Bütikofer, October 2006 22

Arranged „In-flight“ measurements (I)
Set – up
Microphone array perpendicular to axis of flight
May be single sided array for fixed wing aircraft
U – shaped with cranes
One aircraft with test pilot operates at various
levels and speeds
Positional information (GPS + time) on board
Empa, R. Bütikofer, October 2006 24

Arranged „In-flight“ measurements (II)
Requirements
Airfield reserved for measurements
Aircraft available for test flights
Advantages
Well controlled measurements
Various lateral angles by varying the flight level
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Arranged „In-flight“ measurements (III)
Disadvantages
Expensive
Only one sample measured. No information on
variations of sound power for a number of
aircraft in normal operation.
Example
WP 4 Flight tests (Nico van Oosten)
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Example: Empa Measurement of Helicopters 1998
1
11
Array of 20 microphones
12 2
50m
13 3
16 18 20 22 6
14 4
15 17 19 21 23 7 5 5m
150 m
Flig
h t pa
ths
2 cranes left and right

Example: Wallops study of NASA (DC9, B767)
Report NASA/TM-2003-212433
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dB Tower
Project
(USAF,
Wyle,
NLR)
400 m high
300 m from
runway
Empa, R. Bütikofer, October 2006 30

Processing of measurements (I)
1/3 octave band processing, retaining exact time
For many discrete aircraft positions: combine
geometry ( , , ,r) with measured spectrum.
„Depropagate“ the spectra for Lw,dir ( , ):
Calculate propagation for the specific geometry, using
temperature and humidity of the measurement day.
Subtract propagation from measurement
Empa, R. Bütikofer, October 2006 31

Processing of measurements (II)
For each 1/3 octave: Average and interpolate
Lw,dir ( , ) in the spherical coordinates and
Generate look-up tables Lw,dir (f, , )
Validate results by reproducing measured data
Empa, R. Bütikofer, October 2006 32

Thank you for your attention
Why did you became a What did
noise control expert? you say?
Empa, R. Bütikofer, October 2006 33