A review of the progress made towards achieving the Subsonic Fixed Wing project's noise goal for the next generation single aisle aircraft is presented. The review includes the technology path selected for achieving the goal as well as highlights from several in-house and partnership test programs that have contributed to this effort. In addition, a detailed, self-consistent, analysis of the aircraft system noise for a conceptual next generation single aisle aircraft is also presented. The results indicate that with the current suite of noise reduction technologies incorporated into the conceptual aircraft a cumulative noise reduction margin of 26 EPNdB could be expected. This falls 6 dB short of the N+1 goal, which is 32 EPNdB below Stage 4 noise standard. Potential additional noise reduction technologies to help achieve the goal are briefly discussed

Envia, Edmane

NASA Technical Reports Server

PROGRESS TOWARD N+1 NOISE GOAL  Abstract  A review of the progress made towards achieving the Subsonic Fixed Wing project’s noise goal for the next generation single aisle aircraft is presented. The review includes the technology path selected for achieving the goal as well as highlights from several in-house and partnership test programs that have contributed to this effort. In addition, a detailed, self-consistent, analysis of the aircraft system noise for a conceptual next generation single aisle aircraft is also presented. The results indicate that with the current suite of noise reduction technologies incorporated into the conceptual aircraft a cumulative noise reduction margin of 26 EPNdB could be expected. This falls 6 dB short of the N+1 goal, which is 32 EPNdB below Stage 4 noise standard. Potential additional noise reduction technologies to help achieve the goal are briefly discussed.     
https://ntrs.nasa.gov/search.jsp?R=20130013119 2019-08-31T00:55:43+00:00Z
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 1
Progress Toward N+1 Noise Goal
Ed Envia
API for Acoustics
Contributors: Jeff Berton, James Bridges, Casey Burley,
Mike Jones, Mehdi Khorrami, and John Rawls
Fundamental Aeronautics Program
12-Month Program Review
Washington, DC
November 5-6, 2008
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 2
CORNERS OF THE
TRADE SPACE
N+1 (2015 EIS)
Generation
Conventional 
Tube and Wing
(relative to B737/CFM56)
N+2 (2020 IOC)                                       
Generation               
Unconventional                        
Hybrid Wing Body              
(relative to B777/GE90)
N+3 (2030-2035 EIS)
Generation
Advanced Aircraft Concepts
(relative to user defined reference)          
Noise - 32 dB (cum below Stage 4)
- 42 dB
 (cum below Stage 4)
55 LDN (dB) 
at average airport boundary
LTO NOx Emissions
(below CAEP 6) -60% -75% better than -75%
Performance:
Aircraft Fuel Burn -33%**                             -40%**                           better than -70%
Performance:
 Field Length -33% -50%                   exploit metro-plex* concepts
** An additional reduction of 10 percent may be possible through improved operational capability
* Concepts that enable optimal use of runways at multiple airports within the metropolitan areas
 --- EIS = Entry Into Service; IOC = Initial Operating Capability
N+1
N+2
N+3
Approach
- Enable Major Changes in Engine Cycle/Airframe Configurations 
- Reduce Uncertainty in Multi-Disciplinary Design and Analysis Tools and Processes 
- Develop/Test/ Analyze Advanced Multi-Discipline Based Concepts and Technologies
- Conduct Discipline-based Foundational Research
System Level Metrics
…. technology for dramatically improving noise, emissions, & performance
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 3
Representation of SFW Noise Reduction Goals
• Relative ground contour areas for 
notional Stage 4 and SFW N+1, N+2, 
and N+3 aircraft
— Independent of aircraft type/weight 
— Independent of baseline noise level
• Noise reduction assumed to be evenly 
distributed between the three 
certification points
• Simplified model: Effects of source 
directivity, wind, etc. not included
Change in noise “footprint” area for a single event landing and takeoff
Current Rule: Stage 4
Baseline Area
N: Stage 4 – 11 dB CUM
Area = 52% of Baseline
N+3: 55 LDN
Area = 1.5% of Baseline
N+1: Stage 4 – 32 dB CUM
Area = 15% of Baseline
N+2: Stage 4 – 42 dB CUM
Area = 8.3% of Baseline
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 4
Technical Challenges
• Enabling Materials
— Development of low-noise aircraft components and systems often requires the use of 
novel materials or structures. The Materials and Structures (M&S) discipline is focused on 
addressing this technical challenge based on the requirements defined by the Acoustics 
discipline. 
• Engine/Airframe Integration
— A noise optimized N+1 aircraft will pose more challenging nacelle/airframe integration 
issues than a current generation aircraft. Through partnerships with industry, SFW project is 
addressing this technical challenge.
• Noise Reduction Technologies
— Dramatic changes in engine cycle alone will not be sufficient to achieve the N+1 noise 
goal. It is necessary to augment the benefits of low-noise engine cycles with aggressive 
propulsion and airframe noise reduction technologies. Acoustics discipline is primarily 
focused on addressing this particular technical challenge.
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 5
Assessing Technologies for Meeting N+1 Noise Goal
• Objective
— Define a technology path for meeting the N+1 noise goal using a notional next generation 
single aisle aircraft
• Strategy
— Seek a noise-optimized solution that leverages the cycle noise benefits of an ultra high 
bypass (UHB) turbofan engine together with rig and wind tunnel/static engine/flight validated 
noise reduction technologies for engine and airframe components
• Methodology
— Use analytical design tools, wind tunnel component noise data (where available), and 
measured benefits of various noise reduction technologies to develop a bottoms-up, self 
consistent system analysis of the noise levels of the notional aircraft
— Continue development of propulsion and airframe technologies needed to achieve the 
N+1 noise goal at high technology readiness level
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 6
Notional Aircraft
• The starting point is a baseline Boeing 737-800 with winglets developed in 
FLOPS (Flight Optimization System)
— Publicly available geometry, weight, and performance data
— NPSS (Numerical Propulsion System Simulation) model of CFM56-7B type engine
— Proprietary low speed and cruise aerodynamic data
• Minor calibrations performed to match published OEW (Operating Empty 
Weight) and range capability
• Some 787 technology enhancements (mostly composite materials) were 
applied to the baseline 737-800 model
— 15% reduction in wing, fuselage and empennage weight
— 1% reduction in drag for trailing edge variable camber and drag clean up
• Wing sweep increased to achieve a cruise Mach number of 0.8
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 7
• The System Analysis, Design and Optimization group at NASA analyzed 48 
engine designs within the design space covering a range of fan and overall 
pressure ratios, fan drive architectures and bypass nozzle geometry among 
other parameters
• Incorporated feedback obtained from P&W on approach and assumptions
— Adjusted engine component efficiency assumptions
— Ensured consistency between geared and direct drive engine cycles
— Considered higher overall pressure ratios
• Assessed sensitivity of efficiency, emissions, and noise tradeoffs to engine 
architecture and mission requirements
• Selected a geared-driven, noise-optimized,
UHB cycle with FPR = 1.4 & OPR = 42
Notional Engine
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 8
• Aircraft Noise Prediction Program (ANOPP)
• Source noise modeling
• Trajectory simulation
• Spectra propagation (spreading, atmospheric and 
lateral attenuation, ground effects, reflections)
• Frequency integration
• Tonal content and amplitude penalties
• Ground observer noise-time history
Noise certification points:
• Lateral (Sideline)
• Flyover (Cutback)
• Approach
2000 m
(6562 ft)
Flyover (Cutback)
Reference
Lateral (Sideline)
Reference
Approach
Reference
6500 m
(21 325 ft)
450 m
(1476 ft)
Time integration to
Effective Perceived Noise Level
Ob
se
rv
er
 P
NL
T 
(P
Nd
B)
Observer Time (s)
75
80
85
90
95
100
-10 -5 0 5 10
Lateral Location
Noise Metrics & Modeling Tools
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 9
Component Noise Calculations
• For fan and liner components used scale model fan stage wind tunnel noise 
data to estimate full-scale noise contributions
• For other propulsion components1 as well as airframe components2 used 
ANOPP to estimate full-scale noise contributions
Emission Yaw Angle:  43 deg
60
70
80
90
100
110
120
130
140
150
10 100 1000 10000 100000
1/3 Octave Band Center Frequency (Hz)
1/
3 
O
BS
PL
 (d
B)
Original Data
Corrected for Source Strength
Corrected for Non-Fan Sources
Corrected to Full-Scale
Corrected to Flight Conditions 85
95
105
115
125
135
145
0 50 100 150 200
Directivity Angle (deg.)
Lo
ss
le
ss
 O
AS
PL
, d
B
Data
ANOPP (ST2JET)
Jet noise predicted using ANOPPFan noise model data scaled up to engine size
1 Jet and core (combustor and turbine)
2 Landing gear, flap, slat, wing, horizontal tail, and vertical tail
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 10
Propulsion Noise Reduction Technology Benefits
• Over-The-Rotor Noise Benefit: 3 dB (TRL3, TRL 6*)
• TRL 5 (UHB) Test Completed (October 22) • Soft Vane Noise Benefit: 1.5 dB (TRL 3)
• TRL 5 (UHB) Test Completed (October 22)
Over-The-Rotor
Foam Metal Fan Case
2 Candidate Foam Metal Materials
Hollow Vane Interior Divided into Multiple Chambers
Each Tuned to a Different Frequency
Soft Vane Stator
* Williams International FJ44-3A (Low BPR) Engine Test
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 11
Airframe Noise Reduction Technologies
• Incremental airframe noise reduction technologies
— Higher TRL
— Includes gears fairings, slat cove filler, and flap porous tips
• Aggressive airframe noise reduction technologies
— Lower TRL
— Includes gear spoilers and fairings, aggressive slat cove 
filler, flap continuous mold-line link, and trailing edge treatments 
(e.g., serrated edges, brushes, etc)
Continuous
Mold-Line Link (CML)
Slat-Cove Filler
Pneumatic Concept
(Bench-Top Model)
Slat
Filler
Main Wing
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 12
Airframe Noise Reduction Technology Benefits
• Approach condition with ground effects included
Approach 
(Direct Method EPNL)
60
65
70
75
80
85
90
Gear Slat Flap Trailing Edge Airframe System
E
P
N
L
Baseline Incremental Aggressive
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 13
Sources Certification Point Noise Levels (EPNdB)
Sideline Cutback Approach
Fan* 77.5 76.7 85.8
Jet 72.0 66.5 61.1
Core 75.2 74.8 76.4
Engine (Fan + Jet + Core) 81.6 80.1 86.8
Airframe** 71.8 75.9 79.7
Aircraft 82.2 81.8 88.1
* Liner suppression and fan noise reduction technologies benefits included at all three certification points
** Aggressive airframe noise reduction benefits included for the approach condition only
Estimated Noise Levels for Notional Aircraft
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 14
-1.3
-7.4
-2.4
-11.1-11.1
-6.2
-9.0
-26.3
-40
-35
-30
-25
-20
-15
-10
-5
0
Sideline Margin Cutback Margin Approach Margin Cumulative Margin
EP
Nd
B
Current Generation Notional NGSA N+1 Goal
(All numbers relative to Stage 4 noise limit1)
Estimated Noise Margins for Notional Aircraft
2
1 Stage 4 “certification point limits” calculated by subtracting 3.33 EPNdB from the corresponding Stage 3 noise limits
2 Current generation is represented by a certified A318-111 with CFM56-5B8/P engines
N+1 (32.0)
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 15
Observations & Comments
• An in-depth, bottoms-up, self-consistent systems analysis study 
of an engine and airplane system using accepted NASA tools 
and methods was conducted
• The result is a “low-noise” corner of the trade space
• Status: Current prediction is -26 EPNdB cum below Stage 4 
noise limit
• Perspectives
— This is 6 cum EPNdB short of the N+1 goal
— P&W’s estimate for a B737 replacement with GTF engines is reported to be 20 
EPNdB cum relative to Stage 4 without benefits of noise reduction technologies 
included
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 16
Assessment Results / Implications
• Why the shortfall from the N+1 goal?
— The original -32 EPNdB goal analysis had incorporated benefits of continuous 
descent approach (credited at 2 EPNdB), which is inappropriate
— Unexpectedly small noise reduction margin at cutback. Alternative lapse, 
trajectory and throttle modeling could result in further 1-2 EPNdB reduction
— Tools, methods and assumptions have an error margin of 1 EPNdB
• This result indicates that a greater reliance on noise reduction 
technologies may be needed to achieve the N+1 goal
• Possible path to -32 dB goal could include more aggressive 
technologies, e.g.
— Core (and airframe?) noise reduction technologies
— Advanced liners (zero-splice, etc.)
— Low-count stator technology
— Architecture changes
— …
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 17
Propulsion Technology Development Effort
Partnership with Pratt & Whitney
• Fan Cycle and Fan Noise Reduction Technology Tests
— Scale model UHB cycle noise benefits test completed in November 2006.  Cycle 
benefits demonstrated.
— Fan noise reduction technology validation test completed in October 2008. 
Results being analyzed.
— Aerodynamic integration study test completed in May 2008. Nacelle-wing 
integration investigated.
Fan Noise Reduction Technology Test-bed 
in 9’x15’ Acoustic Wind Tunnel (‘08)
P&W GTF Model Scale Fan in 
9’x15’ Acoustic Wind Tunnel (‘06)
Powered Half-Span Model in 11’ 
Transonic Wind Tunnel (‘08)
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 18
Propulsion Technology Development Effort
Partnership with Pratt & Whitney
P&W GTF Demonstrator Engine 
Ground Test (‘08)
• Static Engine and Flight Demonstrator Tests
— Full scale geared turbofan (GTF) test completed in April 2008. Fan noise scaling 
laws validated.
— Flight demonstration of GTF engine on P&W 747 test-bed completed in July 
2008. Flight test on Airbus A340 currently underway.
GTF Demonstrator Engine Installed on 
P&W 747 Test-bed Aircraft (‘08)
Fundamental Aeronautics Program
Subsonic Fixed Wing Project 19
Airframe Noise Investigation Effort
Partnership with Gulfstream
Nose Gear Model Tests (‘07, ‘08)
Flight Test of G550 Aircraft (‘06)
• Airframe Noise Source Investigation and Mitigation Study
— First flight test of G550 aircraft completed in October 2006. Benchmark airframe 
noise data acquired.
— Wind tunnel aero and acoustic tests of the scale model nose gear completed in 
2007 & 2008. Sub-scale / full-scale data comparisons carried out.
— Half-span model of airframe to be tested in wind tunnel in 2009 (aero) and 2010 
(acoustic) followed by a second flight test in 2011.
BART Aerodynamic Test
UFL WT Acoustic Test
Half-Span G550 Sub-Scale Model Tests 
in 14’x 22’ Acoustic Wind Tunnel (‘09, ‘10) 


Progress Toward N+1 Noise Goal

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