KATnet II Bremen Presentation

BOEING is a trademark of Boeing Management Company.Copyright © 2009 Boeing. All rights reserved.

The Next Decade in Commercial Aircraft Aerodynamics –

A Boeing Perspective

Mark GoldhammerPaul VijgenBoeing Commercial AirplanesSeattle, Washington, U.S.A.

KATnet II Conference on Key Aerodynamic TechnologiesBremen, Germany12 -

14 May 2009

ROI 2009-0501-1167

Copyright © 2009 Boeing. All rights reserved. KATnet II Bremen 2009 | 2

The next decade in commercial airplane aerodynamics – a Boeing perspective

Outline

Historical look at aerodynamic configuration design at Boeing

Driving factors for the future

Aerodynamic levers for the next decadeAerodynamic product technologiesAerodynamic tools, processes and capabilitiesAirplane configurations

Concluding remarks



The beginnings of the commercial jet age at Boeing

Boeing Stratocruiser (circa 1947)Straight wingPiston-powered propellersFowler flaps

Boeing 367-80 (circa 1954)Prototype for KC-135, B707 family Boeing’s first low-swept-wing transportConfiguration basis for the future:

Wing-mounted pod engines Double-slotted Fowler flaps with LE Krueger flaps

(B707)



B737

B747

Configuration evolution of the Boeing family

Swept-wing, pod-mounted engines (2 or 4)Continually increasing aerodynamic technologies:

CFD advancesAirfoil/wing technology advancesLE/TE high lift device advancesLessons learned from earlier productsHigher Reynolds number wind tunnel testingImproved structural conceptsMore integrated wing/engine/pylon configurationsRelaxed stabilityLoad alleviationMultidisciplinary optimization

B757

Wing-mounted pod engines became the configuration of choice

B787

B777

B767



Other configurations

Wing-mounted pod engines were not always selectedAft-mount allows lower-to-the-ground configurationPerhaps more efficient with then-current technologyOdd number of engines (3)Cabin noise and vibration challenges

DC-10

DC-9

B727



Driving factors for future improvement

Boeing commitment:Each new commercial airplane generation delivers at least 15% improvement in CO2

emissions and fuel efficiency

Relat

ive fu

el us

e

Early jet airplanes

New Generation jet airplanes

Noise dB

MORE FUEL

LESSFUEL

HIGHERdB

LOWERdB

70%

fuel improvement and reduced CO2

90%

reduction in noise footprint

EVENLOWEREVEN

LESS

Nose footprint based on 85 dBa.1950s 1990s 2010s



Further drag reduction is required for future efficiency improvement

Systems

Materials

Aerodynamics

Engines

*Improvements are relative to 767-300ER

Core aircraft technologiesRelative contributors to

787 efficiency improvement*

For current aircraft configurations, remaining areas for significant fuel-burn improvement in next 10-20 years are:

Propulsion/propulsion integration Aerodynamic drag reductionMulti-disciplinary optimization

Alternate aircraft configurations may allow further integrated improvements from core technologies



Aerodynamic levers

(3) Airplane Configurations

Aerodynamic product technologies

Aerodynamic tools, processes, and capabilities

Airplane configurations



Aerodynamic levers








Laminar flow

Advanced variable camber concepts

Relaxed stabilityMulti-disciplinary optimization

Turbulent skin friction reduction

Active flow control

Advanced transonic wing concepts

Advanced trailing edge device concepts

Advanced leading edge device concepts

Integration of advanced engine concepts



Aerodynamic drag breakdown and reduction potential

Viscous and lift-induced drag are dominant drag components for subsonic aircraft in cruise

Advances in materials, structures and aerodynamics enable significant lift-induced drag reduction

Maximize effective span extension using compositesIncorporate advanced wing-tip devices

Viscous drag is remaining area with largest potential for further drag reduction

Drag breakdown (typical)

Induced and trim drag

Viscous drag

Wave drag

Excrescence drag



Laminar flow drag reduction benefits and issues

Natural Laminar Flow (NLF) and Hybrid Laminar Flow Control (HLFC) demonstrated in aerodynamic flight tests

Transition flow physics generally understoodScale and sweep affect laminar-flow application (NLF vs. HLFC)Continuous progress in analysis and design methods

Laminar flow reduces fuel burn, emissions and noise Benefit depends on scale of applicationImproved fuel burn allows smaller, lighter, quieter aircraftEstimated net potential fuel burn benefit for subsonic transports ~ 5 – 12 %

Laminar flow application issuesManufacturing, certification, and operational requirements and impactsDrag benefit needs to be traded against increased weight, maintenance, cost, reliability, etc.



Some laminar flow activities1990 1995 2000 2005

757 HLFCflight test

Wing HLFCWT test

HLFCVLA studies

Wing HLFCWT test

787NLF

Nacelle

F-16XL SLFCflight test

SLFC Studies

Product Development trade studyWind-Tunnel (WT) or flight test

Steps WT Tests

757 NLFFlight test

1985



757 HLFC flight test program Leading edge suction panel

HLFCleading edge

suction panel

Hot-film sensors

Pressure belt

Infra-red cameras

Krueger/insect shield

Laminar-flow instrumentation

Equivalent to 6% airplane drag reduction on 757-

size airplane

Laminar flow achieved up to shock location

HLFCleading edgesuction panel



Nacelles shaped for natural laminar flow (NLF) Committed to 787 in 2005

Nacelle contours optimized with laminar transition location as additional design parameterStructural design and manufacturing methods tailored for NLF benefit



Airline operations

Applied aerodynamics

Fluid dynamics

Design integration and manufacturing

Flow physicsTransition prediction HLFC suction flow physics

Wind tunnel testing/scalingOff-design performanceHigh lift performance

CertificationOperational/environmental effectsGround handlingMaintenance

Simplified HLFC systemsHigh lift systemsIce protection systemsManufacturing techniques

Increasing technology readiness

Laminar flow integration and implementation challenges

Potentially large aerodynamic benefit needs to be integrated into practical design that meets requirements over lifeof aircraftSignificant integration and operational challenges need to be addressed Risk in net economic benefit of laminar flow remains



Turbulent flow drag reduction benefits and issues

Riblet technology has been demonstrated to passively reduce local turbulent skin friction ~6 %

Tunnel and flight tests with riblet films conductedApplication constraints (shape, spacing, streamlining) are understood

Riblet application issues are not aerodynamic:Limited riblet shape and adhesive robustness over operational life (hydraulic liquids, hail, dirt and impact)Appearance relative to standard paint and liveryTime required to install, maintain, remove and re-apply

`



Boeing drooped-spoiler flap Committed to 787 in 2005

787Single/single slotted

767Double/single slotted withFowler motion

Simple-hinged flap with drooping spoilersFewer parts (reduced maintenance)Lower weightSmaller fairingsFacilitates small flap adjustments in flight

6-bar linkage



Inboard flapFlaperon

Outboard flapAileron

Boeing trailing edge variable camber Committed to 787 in 2005

Trailing edge variable camber allowsLoad optimizationCruise drag optimization

In cruise, trailing edge elements are adjusted at regular intervals to minimize dragSimplified actuation systemSmall angle variationsUp and down movements



High lift configurationwith AFC actuators

AFCAFC

Example: Application concept study with AFC augmented wing high lift system

(Reference NASA CR-1999-209338)

Active Flow Control (AFC)

Evaluating Active-Flow Control (AFC) actuator and integration concepts for simplified (lighter) systems with similar performance as traditional mechanical high-lift elements Robust, reliable and low-maintenance AFC actuation to be developed and demonstrated for commercial transportKey issues that affect application success for commercial aircraft are:

Actuator capability, robustness and noiseSystem power, complexity and costFailure modes and redundancy considerations



Aerodynamic levers







Aerodynamic tools, processes and capabilities

Computational fluid dynamics

Wind tunnel testing

Flight testing

Future aerodynamics engineers

Wind tunnel

Flight testing

CFD

Aerodynamic design

and analysis



Computational Fluid Dynamics (CFD)

Faster, more capable, and less costly computing hardwareFaster and better algorithms

Higher fidelity flow physics modeledExpanding simulations towards edges of flight envelopeIntegration with structural and systems modeling (MDO)Integration with wind tunnel and flight testing



CFD multipoint design/optimization

Transonic CFD for full configurationAdaptive grid technology for the design optimizationStructural model including aeroelasticsInclude weight effects in optimization Include manufacturing and structural constrainsFlight conditions from operating envelope

Drag accuracy is key to optimization

Tail-off

Lines Pre-test CFDSymbols Test data

Spar constraints

Spar constraints at side of body

Nacelle minimum keel height

Curvature constraints

Sample manufacturing and structural constraints

Tail-on and trimmed

Predictions of both drag

level and increment



CFD near edges of the flight envelope

Expanding calibrated CFD envelope to conditions with massively separated flows

Stability and controlBuffetWing deformations under extremer loadings

CFD challenges–

Large regions of separated flow–

Turbulence models–

RANS and URANS/DES–

Wind-tunnel test data needed for calibration–

Close to Mach one–

Model aeroelastics–

Wall effects

Separated flow

RANS four-engine transport

Cp comparison at approximately 2.5g at Mach dive



CFD near edges of the flight envelope

Asymmetric flight conditions for stability and control control-surface effectiveness

Full configurations in cruise and at low speedsComplex geometries (high-lift flaps, vortex generators)Shock boundary-layer interactionWing shape under loading

Lateral/Directional T&I and Wall Interference

Rudder effectiveness Yaw at high Mach number



CFD high lift aerodynamics

Pressure coefficients

Raw lofts

Positioned geometry Surface grid

Volume grid

Surface streamlines

Automated Navier-Stokes 3D process flow with one day turn around



Determine jet/flap interaction/loads

Design for desired thermal environment of aft fairing

Initial design temperature

Improved design temperature

Optimize installed performance

Minimize cabin (shock-cell) noise

CFD propulsion aerodynamics

CFD has eliminated most powered wind tunnel model testing on conventional configurations



The future for wind tunnels

Wind tunnels will continue to play a significant role in commercial airplane aerodynamic development:

Design verificationDatabase collectionCFD validationNew technologiesNew configuration concepts

Reduction in testing time enabled by availability of mature and “calibrated” CFD

Boeing’s primary wind tunnel evaluation criteria:

767(1980)

777(1990)

787

(2005)

Occ

upan

cy h

ours

-25 %

-30 %

Technical viability – can do the required testing

Accuracy and Validation – results that can be trusted

Availability – ready and available when needed

Productivity – complete required testing in a timely manner

Reliability – keeps working without interruption

Security – privacy and confidentiality assured

Cost efficiency – good value for the money

Tunnel testing time



Types of wind tunnel testing

Configuration development testingIncremental and absolute aerodynamic coefficient dataCruise, high-lift, and flight envelope limit dataAirframe noisePropulsion installationTare and interference testingFlow control conceptsAlternate configurations will require significant additional testing

Database development testingAirplane performanceStability and control including simulator databaseAerodynamic loads throughout envelope

Specialized testingFull scale Reynolds numberThrust reversersGround effectIce accretion/ice effects



Primary wind tunnels used by Boeing Commercial Airplanes (2000 and on)

Mountain View, CA

Farnborough, UK

Cologne, Germany

Hampton, VA

Gifu, JapanSeattle, WA

Philadelphia, PA

Le Fauga, France

Minneapolis, MN

http://anplab.ca.boeing.com/webroot/lg_photos/9x9003.jpg

http://anplab.ca.boeing.com/webroot/lg_photos/outside024.jpg



Flight testing aerodynamic technologies

Flight testing for certificationFlight testing for development/evaluation of aerodynamic technologies

Certain technologies are difficult to simulate on scaled models in tunnelConcept to be flight tested must integrate with test vehicleFlight testing to provide operational experience

Natural laminar flow Quiet-Technology Demonstrator (QTD2)



COLLEGE

Future aerodynamics engineers

Industry/ academia collaboration

Nurture students through funded research, internships, scholarships, etc.

Encourage programs that teach teamwork, multi-disciplinary studies

Continuing education and on-the-job training

Retain knowledge from retiring senior engineers

Encourage youth into science, technology, engineering, math (STEM) careers



Aerodynamic levers







Aerodynamic opportunities and challenges on alternate configurations

Geometries tailored to enhance laminar flow control

Advanced multi-

disciplinary optimization

Skin friction control

Aerodynamic surfaces designed for active flow control

Induced drag reduction with novel non-planar wing configurations

Boundary-layer ingestion for increased propulsion efficiency

Incorporation of novel propulsion systems (e.g., open fan)

Advanced integration of aerodynamics, structures and systems

Control configured empennage

Configuration optimized for noise



Alternate configuration concepts New challenges for aerodynamic design

Aerodynamic tools and processes that have been refined for tube-and-wing configurations must be updated/calibrated for non-classical aircraft configurations



Commercial airplane aerodynamics: What is next?

Readiness ofadvanced aerodynamic

technologies

Future configurations

Further significant reduction in fuel burn, noise, and emissions

Regulatory requirements

Market requirements



Summary

Aerodynamics will be key contributor to the future of aircraft designSafetyEfficiencyEnvironmental compatibility

The next decade of challenges will be multidisciplinaryNew aerodynamic technologies are on the horizonIntegration with structures, propulsion, and systems, enabled by further computational advancesManufacturability and maintainability to introduce flow control methods

Aerodynamic technologies, together with tools, processes, and people, will be keys to future advances

KATnet II Bremen Presentation

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