iata technology roadmap technical annex · iata technology roadmap technical annex ......

IATA Technology RoadmapTechnical Annex

Prepared in collaboration with theAerospace Systems Design Laboratory (ASDL),

Georgia Institute of Technology

Table of ContentsAnnex 1: Technical Descriptions of Evaluated Technologies

A.1.1 Airframe................................................................................................................................. 5A.1.1.1.Aerodynamic.Technologies....................................................................................................... 6

. A.1.1.1.1.Wingtip.Devices................................................................................................................ 6

. A.1.1.1.2.Drag.Reduction.Coatings............................................................................................... 7

. A.1.1.1.3.Transonic.Shock.Control................................................................................................. 8

. A.1.1.1.4.Natural.Laminar.Flow........................................................................................................ 8

. A.1.1.1.5.Hybrid.Laminar.Flow......................................................................................................... 9

. A.1.1.1.6.Variable.Camber..............................................................................................................10

A.1.1.2.Structural.Concepts.................................................................................................................12

. A.1.1.2.1.Active.Load.Alleviation...................................................................................................12

. A.1.1.2.2.Morphing.Airframe..........................................................................................................13

. A.1.1.2.3.Morphing.Materials.........................................................................................................14

A.1.1.3.New.Aviation.Materials............................................................................................................15

. A.1.1.3.1.Welding.and.Fastening..................................................................................................15

. A.1.1.3.2.Cabin.Interiors.................................................................................................................16

. A.1.1.3.3.Advanced.Alloys..............................................................................................................17

. A.1.1.3.4.Hybrid.Alloys....................................................................................................................18

. A.1.1.3.5.Advanced.Composites..................................................................................................18

A.1.1.4.Non-propulsion.Systems.........................................................................................................19

. A.1.1.5.1.Zonal.Dryer.......................................................................................................................19

. A.1.1.5.2.Landing.Gear.Drive........................................................................................................20

. A.1.1.5.3.Flight.Control.System....................................................................................................20

. A.1.1.5.4.More.Electric.Aircraft.Architecture..............................................................................21

. A.1.1.5.5.Auxiliary.Power.Units......................................................................................................22

. A.1.1.5.6.Fuel.Cells..........................................................................................................................23

A.1.1.4.Innovative.Aircraft.Configurations.........................................................................................26

. A.1.1.4.1.Hybrid-Wing-Body.........................................................................................................26

. A.1.1.4.2.Cruise-Efficient.Short.Take-off.and.Landing............................................................27

. A.1.1.4.3.Truss.and.Strut-braced.Wing......................................................................................28

Chapter.References................................................................................................................................29

A.1.2 Engine...................................................................................................................................36A.1.2.1.Engine.Turbo.Machinery.Systems.Components...............................................................36

. A.1.2.1.1.Fans....................................................................................................................................36

. A.1.2.1.2.Compressors...................................................................................................................37

. A.1.2.1.3.Turbines.............................................................................................................................37

. A.1.2.1.4.Advanced.Combustor....................................................................................................38

. A.1.2.1.5.Variable.Geometry.Chevron.........................................................................................38

. A.1.2.1.6.Advanced.Engine.Materials..........................................................................................39

A.1.2.2.Evolutionary.Engine.Core.Improvements............................................................................40

. A.1.2.2.1.New.Engine.Core.Concepts........................................................................................41

. A.1.2.2.2.Adaptive/active.Flow.Control.......................................................................................41

A.1.2.3.New.Architectures....................................................................................................................41

. A.1.2.3.1.Geared.Turbofan.............................................................................................................42

. A.1.2.3.2.Counter-rotating.Fan......................................................................................................44

. A.1.2.3.3.Open.Rotor.......................................................................................................................44

. A.1.2.3.4.Embedded.Distributed.Multi-fan.................................................................................45

A.1.2.4.Revolutionary.Engine.Cycles..................................................................................................46

. A.1.2.4.1.Adaptive.Cycles..............................................................................................................46

. A.1.2.4.2.Pulse.Detonation.............................................................................................................46

A.1.2.5.Nacelles.and.Installation..........................................................................................................47

. A.1.2.5.1.Variable.Fan.Nozzle........................................................................................................47

. A.1.2.5.2.Boundary.Layer.Ingesting.Inlet....................................................................................47


A.1.3 Alternative Fuels.........................................................................................................52A.1.3.1.Requirements.for.Drop-in.Fuels............................................................................................52

A.1.3.2.Liquid.Fuels................................................................................................................................53

. A.1.3.2.1.Fischer-Tropsch.Synthesis.Process...........................................................................54

. A.1.3.2.2.Hydroprocessed.Renewable.Jet.(HRJ)......................................................................55

. A.1.3.2.3.Transesterification...........................................................................................................56

. A.1.3.2.4.Furans................................................................................................................................56

. A.1.3.2.5.Alcohols.............................................................................................................................57

A.1.3.3.Gaseous.Fuels...........................................................................................................................58

. A.1.3.3.1.Compressed.Natural.Gas.............................................................................................58

. A.1.3.3.2.Liquid.Hydrogen..............................................................................................................58

. A.1.3.3.3.Liquid.Methane................................................................................................................58

. A.1.3.3.4.Liquefied.Petroleum.Gas...............................................................................................59

A.1.3.4.Thermodynamic.properties.of.fuels.......................................................................................59


A1.4 Air Traffic Management.........................................................................................63A.1.4.1.Globally.Harmonised.Implementation.of.the.Future.ATM.System.................................63

A.1.4.2.Enabling.Technologies.............................................................................................................64

. A.1.4.2.1.Communication...............................................................................................................64

. A.1.4.2.2.Navigation.........................................................................................................................65

. A.1.4.2.3.Surveillance......................................................................................................................65

. A.1.4.2.4.Hazard.and.Safety.Systems.........................................................................................66

. A.1.4.2.5.Airborne.ATM.–.Displays.and.Decision.Support.Tools..........................................66

A.1.4.3.Operational.Concepts.............................................................................................................67


Annex 2: Technology Evaluation Methodology and Assessment Matrices

A.2.1 Methodology..................................................................................................................72A.2.1.1.Introduction................................................................................................................................72

A.2.1.2.Background................................................................................................................................73

A.2.1.3.Strategic.Prioritisation.and.Planning.Applied.to.TERESA..............................................73

A.2.1.4.Breakout.Sessions....................................................................................................................75

A.2.2 Evaluation and Results........................................................................................76A.2.2.1.Evaluation.mapping..................................................................................................................76

A.2.2.2.Creation.of.Technology.Roadmap........................................................................................81


Glossary.............................................................................................................................................83Acronyms.........................................................................................................................................86Acknowledgements...............................................................................................................89

Annex 1Technical Descriptions of

Evaluated Technologies

5...TECHNOLOGy.ROADMAP.REPORT

A.1.1 AirframeThe. survey. of. airframe. technologies. focused. on. the. following. five. areas:. aerodynamics,. structural. concepts,. materials,.on-board.systems.that.are.not.part.of.the.propulsion.system.and.innovative.concepts.that.depart.from.the.standard.tube-and-wing.designs..Within.each.area,.the.surveyed.technologies.are.presented.roughly.in.the.order.of.technology.readiness.

The. amount. of. CO2. emitted. from. kerosene-burning. aircraft. engines. depends. solely. on. the. amount. of. fuel. consumed..If. alternative. fuels. are. considered,. the. specific.CO2. emission. per. kg. fuel. changes. but. fundamental. rules. of. aircraft. fuel.consumption.still.apply..

The.variables.influencing.fuel.consumption.can.easily.be.examined.using.the.Bréguet.range.equation..One.form.of.the.range.equation.for.the.special.case.of.constant.lift.coefficient.–.i.e..at.constant.cruise/climb.–.reads:

with.WTO.representing.aircraft.take-off.weight,.R.the.mission.range,.

V..the.cruise.speed,.TSFC..the.thrust.specific.fuel.consumption,.η.the.over-all.engine.efficiency.and.H.the.calorific.value.of.the.fuel..

The.first.equation.can.be.rewritten.to.give.fuel.consumption.in.kg.per.kg.payload

where.CD0.is.the.zero-lift.drag,.S.is.the.wing.area,.e.is.the.Oswald.factor,.b.is.the.wing.span,.CL.is.the.aircraft’s.lift.coefficient.and.ηth.and.ηprop.are.the.engine’s.thermal.and.propulsive.efficiencies..

Minimising.fuel.weight,.with.respect.to.CO2.emission.for.a.given.payload.and.range.can.thus.be.obtained.by:

• Aerodynamics:

. -.Maximise:.CL,.e.and b.

. -.Minimise:.CD0.and.S

• Structure:

. -.Minimise:.WE/WP

• Engine:.

. -.Maximise:.ηth.and.ηprop.

• Fuel:.

. -.Maximise:.H.

Most.of.the.following.technologies.can.be.identified.to.modify.one.or.more.of.the.above.listed.parameters.(excluding.wave.drag,.ATM-related.technology)

6..ANNEx.1

A.1.1.1 Aerodynamic TechnologiesBeyond. the.development.of. innovative.wing-body.alternatives,. there. lies.an.entire.set.of. technologies.applicable. to.both.conventional.and.new.aircraft.configurations..These.technologies.include.those.that.reduce.skin.friction.drag.by.maintaining.laminar.flow.over.a.greater.portion.of.the.aircraft.surface,.decrease.the.drag.associated.with.turbulent.flow,.and.increase.the.aerodynamic.efficiency.(lift-to-drag.ratio).of.the.wings.

A.1.1.1.1 Wingtip DevicesA. variety. of.wing-tip. devices. and.winglets. exist. on. today’s. aircraft. or. are. under. development,. such. as.wing-tip. fences,.blended.winglets.[2],.raked.wingtips.[3],.and.non-planar.wingtip.extensions.[4]..These.devices.work.to.reduce.the.wingtip.vortex.strength.and.thus.reduce.the.induced.drag.during.flight..The.primary.benefit.of.induced-drag.reduction.is.a.decrease.in.mission.fuel.burn..Historically,.conventional.winglets.have.provided.approximately.4%.drag.reduction..Depending.on.the.design,.advanced.wingtip.devices.can.provide.further.improvements.in.drag.reduction.and.fuel.burn.

Although.most.aerodynamicists.think.that.an.optimal.wing.design.would.make.winglets.obsolete,.non-aerodynamic.constraints.often.prevent.such.an.optimisation..For.example,.aircraft.types.are.divided.into.six.categories.according.to.their.wingspan..Aircraft.of.higher.categories.are.not.allowed.to.operate.at.airports.or.use.certain.gates.that.are.designed.for.lower.categories.only..Winglets.may. help. achieve. a. certain. aerodynamic. performance.without. exceeding. the.wingspan. limit. for. a. certain.category..Moreover,.winglets.are.easy.to.retrofit.to.improve.the.performance.of.flying.aircraft..

The.wingtip.fence,.shown.in.Figure.A.1.1-.1,.is.the.simplest.of.the.current-generation.devices..It.is.most.common.on.Airbus.designs.including.the.A320.series.and.the.A380..Reductions.in.induced.drag.are.provided.with.minimal.changes.in.wing.bending.moment.

Since.the.advent.of.the.standard.winglet,.similar.to.that.used.on.the.Boeing.747-400.series,.noteworthy.advancements.have.been.made.in.the.field.of.3-D.computational.fluid.dynamics..As.a.result,.modern.winglet.design.has.focused.on.reducing.the. interference. drag. and. improving. winglet. performance.. Aviation. Partners,. a. company. that. cooperates. with. airframe.manufacturers.to.produce.winglets.for.existing.aircraft,.indicates.that.the.blended.winglet.available.for.the.Boeing.737-800,.shown.in.Figure.A.1.1-.2,.provides.a.3.0%.to.3.5%.fuel.burn.improvement.on.a.980.nautical-mile.mission.[6]..The.technology.has.also.been.certified.for.retrofit.in.other.Boeing.models,.including.the.757-200,.737-300,.737-500,.and.737-900..A.more.advanced.blended.winglet.retrofit.package.has.recently.been.certified.by.Aviation.Partners.to.the.Boeing.Company.for.the.767-300ER.models..The.anticipated.fuel.burn.improvements.over.the.basic.767-300ER.range.upwards.of.5.0%.on.a.5000.nautical-mile.mission.[7],.in.addition.to.improvements.in.take-off.and.landing.performance..One.area.of.potential.detriment.is.that.a.wing.retrofitted.with.a.blended.winglet.may.require.additional.stiffening,.which.will.add.extra.weight.that.may.negate.some.of.the.projected.savings.in.fuel.economy.and.vehicle.performance.

Every.wing.can.be.improved.aerodynamically.by.adding.a.wing.tip.device..However,.the.wing.tip.device.generates.additional.forces.onto.the.wing.structure..The.size,.i.e..the.gain.of.the.wing.tip.device.is.thus.limited.by.the.structural.reserves.of.the.wing..The.efficiency.gain.by.adding.a.winglet.is.higher.for.“previous.generation”.initial.wing.designs..All.this.makes.numerical.indications.of.winglet.efficiencies.quite.difficult.to.compare.

Figure.A.1.1-.1:.Wingtip.fence.of.an.A319.[1] Figure.A.1.1-.2:.Blended.winglet.of.a.Boeing.737-800.[5]


Beyond.the.wingtip.fence.and.winglet.are.the.raked.wingtip.and.non-planar.wing.extensions..Both.devices.trade.a.wingspan.increase.for.an.even.greater.improvement.in.fuel.burn..Boeing.first.used.the.raked.wingtip.on.the.767-400ER,.and.it.has.subsequently.been.incorporated.into.the.777-200LR/300ER.aircraft..It.is.also.planned.for.inclusion.on.the.U.S..Navy’s.P-8.variant.of.the.Boeing.737..According.to.Boeing,.the.original.767-400.raked.wingtip.offered.approximately.5.5%.reduction.in.induced.drag.[8]..Boeing.is.using.a.more.advanced,.blended.version.of.the.raked.wingtip.on.the.787,.while.Airbus.is.planning.on.integrating.a.similar,.non-planar.wing.extension.into.the.design.of.the.A350..

In.addition.to.wingtip.devices,.there.are.designs.that.potentially.offer.further.reductions.in.fuel.burn..One.such.technology.is.the.spiroid.wingtip.[9]..The.spiroid.wingtip.promises.not.only.a.reduction.in.induced.drag,.up.to.10%.on.the.Gulfstream.II,.but.also.the.potential.to.reduce.wingtip.vortex.strength,.with.the.possibility.of.reducing.aircraft.spacing,.if.the.regulations.for.wake.vortex-related.separations.are.modified.accordingly..This.reduction.in.spacing.would.allow.for.greater.capacity.at.airports.and.the.potential.for.further.fuel.savings.at.the.fleet.level.[10]..ONERA.investigated.the.spiroid.wingtip.for.application.on.an.Airbus.A380.[11].and.obtained.a.3.3%.reduction.of.lift.induced.drag.with.the.spiroid.having.a.height.of.3.8%.of.the.half.wing.span.(1,52m)..Wingtip.devices.can.also.be.designed.to.be.adaptive,.e.g..by.incorporating.flaps..This.allows.for.active.control.of.the.wing.twist,.thereby.giving.the.chance.to.reduce.wing.structure.weight.

A.1.1.1.2 Drag Reduction CoatingsManufacturers.continually.investigate.new.surface.finishing.techniques.and.coatings.in.the.quest.to.reduce.skin.friction.drag..The.main.thrust.of.these.investigations.is.in.retrofittable.and.easily.maintainable.coatings.that.could.further.reduce.aircraft.skin.friction.drag..These.coatings.fall.into.two.main.categories:.those.that.maintain.laminar.flow.and.delay.the.transition.to.a.turbulent.boundary.layer.and.those.that.work.with.already.turbulent.boundary.layers.to.minimise.thickness.and.prevent.flow.separation..While.these.two.techniques.are,.locally,.mutually.exclusive,.they.can.be.used.in.different.areas.on.the.same.aircraft.to.maximise.the.drag.reduction.

Laminar Flow Drag Coatings

The.transition.from.laminar.to.turbulent.boundary.layers.occurs.due.to.the.build.up.of.small.flow.disturbances.that.create.adverse.pressure.gradients.in.the.boundary.layer..The.rate.at.which.this.occurs.is.a.function.of.the.overall.pressure.gradient.and.properties.of.the.actual.surface..Significant.work.has.been.undertaken.to.develop.appropriate.shapes.of.the.leading.edge.of.the.aircraft.wing,.nacelle,.fuselage.and.empennage.that.delay.the.onset.of.turbulence..However,.this.shaping.is.neither.applicable.to.existing.aircraft.as.retrofit,.nor.is.it.often.robust.to.operational.degradation..Consequently,.there.is.a.search.for.coatings.that.either.reduce.the.creation.of.or.dampen.the.small.flow.disturbances.at.the.origin.of.turbulence..The.reduction.in.creation.of.disturbances.can.be.achieved.through.the.use.of.films.that.smooth.out.the.skin.of.the.aircraft..Additionally,.coatings.have.the.potential.to.make.the.build.up.of.occlusions.less.likely.that.lead.to.degradation.of.laminar.flow,.e.g..dead.insects.on.the.aircraft.skin.

A. second.area.of. laminar. flow.coatings. is. known.as. “compliant”. coatings,.which.dampen. turbulent.disturbances.. These.work.by.allowing.hydroelastic.microdeformations.in.the.surface.of.the.aircraft.[12]..Initial.work.with.compliant.coatings.was.mainly.focused.on.marine.applications..However,.more.recent.work.has.focused.on.aircraft.applications..A.reduction.of.20%.in.wing.skin.friction.drag.might.be.possible.through.the.promotion.of.increased.laminar.flow.[12]..This.would.translate.into.approximately.5%.reduction.in.total.drag..Additional.applications.to.the.fuselage.could.produce.even.greater.benefits.

Turbulent Flow Drag Coatings

The.best-known.coatings.to.reduce.turbulent-flow.drag.are.aerodynamic.riblets..These.are.either.small.grooves.or.protrusions.aligned.with.the.local.air.flow.[12]..Initial.studies.indicated.that.the.effect.of.riblets.on.an.already.turbulent.boundary.layer.could.decrease.the.local.skin.friction.in.the.order.of.6%..Further.work.indicates.that,.with.optimal.sizing.and.spacing,.it.should.be.possible.to.achieve.local.skin.friction.drag.reductions.closer.to.10%.[13].

8..ANNEx.1

Since.riblets.work.by.affecting.the.characteristics.of.turbulent.boundary.layers..These.devices.can.be.used.in.conjunction.with.surfaces.that.are.too.large.to.maintain.a.laminar.boundary.layer.along.their.entire.length..NASA.estimates.that.natural.laminar.flow.regions.would.occupy.approximately.20%.of.wing.and.tail.surface.areas.of.an.advanced.aircraft.in.the.2020.timeframe..This.could.be.especially.useful.for.fuselages.and.inboard.sections.of.the.aircraft.wing.[14,15]..Small-scale.tests.of.an.A320.model.with.riblets.at.Mach.0.7.indicated.a.viscous.drag.saving.of.approximately.5%.[16]..For.these.tests.adhesive.films.with.a.riblet.structure.were.used..These.proved.to.be.vulnerable.due.to.surface.contamination.[16],.as.well.as.insufficient.ultraviolet.radiation.stability.of.adhesive.films..Increased.airframe.maintenance.is.necessary.to.minimise.the.degradation..

Another.reason.for.the.degradation.of.the.effectiveness.of.riblets.is.misalignment.with.the.local.airflow..Higher.design.accuracy.is.required.to.minimise. losses. in. flight.conditions.deviating.from.the.design.point..As.an.alternative,.structures.with.small.point-like.bumps.achieve.a.non-directional.drag.control.

A.1.1.1.3 Transonic Shock ControlA.weak.transonic.shock.is.usually.present.at.design.point.on.modern.transport.aircraft.wings.with.supercritical.airfoils.. In.off-design.condition.strong.shocks.form,.thereby,.defining.the.drag.rise.and.buffet.boundaries..Future.aircraft.with.airfoils.designed.to.maintain.laminar.flow.face.the.problem.of.a.rear.location.of.a.shock.wave.even.at.design.condition.due.to.the.necessary.favourable.pressure.gradient.on.the.suction.side..Thus,.mechanisms.for.reducing.shock.strength.in.order.to.limit.wave.drag.are.beneficial.both. for. laminar.and. turbulent.wings..The.most.promising.shock.control. technique. is.a.variable.contour.bump.placed.at.the.foot.of.the.shock.creating.a.λ-shock.structure.with.compression.waves.in.the.supersonic.region..This.device.was.intensively. investigated.in.the.1990s.in.the.project.ADIF.(Adaptive.Wing).by.DLR.and.EADS.[17]..More.recent.investigations.by.Birkemeyer.et.al..[18].and.Ogawa.&.Babinsky.[19].demonstrate.that.a.reduction.of.wave.drag.without.affecting.viscous.drag.is.attainable.on.swept.wings,.in.optimal.condition.amounting.to.a.reduction.of.50%.of.wave.drag.at.transonic.speed.

A.1.1.1.4 Natural Laminar FlowThe.principle.behind.natural.laminar-flow.designs.and.materials.is.to.optimise.the.shape.and.surface.of.an.aircraft,.so.that.the.transition.of.the.boundary.layer.from.a.laminar.state.to.a.turbulent.state.is.delayed..Such.a.delay.reduces.skin.friction.drag,.thereby.reducing.fuel.burn..The.point.of.transition.is.dependent.upon.the.altitude,.airspeed,.distance.and.pressure.gradient.along.the.specific.component,.and.the.surface.qualities.of.that.component..An.effective.transition.delay.can.be.obtained.with.a.smooth.and.slow.pressure.gradient.along.the.flow...On.a.swept.wing.there.is.always.a.flow.component.along.the.leading.edge,.which.may.encounter.instabilities..Therefore.laminarity.is.difficult.to.obtain.for.wings.with.a.sweep.angle.of.more.than.approximately.20°.

Figure.A.1.1-.4:.Sketch.of.contour.bump.on.suction.side.of.airfoil.[18]

Figure.A.1.1-.3:.Surface.riblet.example.[13]


Designing.wings,.nacelles,.and.even. fuselages.to.maintain. laminar. flow. is.not.new.. Indeed,. the.practice.has.been. in.use.since.the.Second.World.War..For.example,. the.NACA.6-series.of.airfoils,. including.the.one.used.on.the.P-51.Mustang,.incorporated.the.principles.of.natural. laminar. flow.design.[20]..Since.then,.numerous.aircraft. in.both.the.military.and.civil.sectors.have.been.manufactured.with. laminar. flow.wing.designs..This. includes.many.smaller.business. jets,. including. the.one.shown.in.[20]..Laminar.nacelle.design.has.been.demonstrated.in.the.European.HyLDA.project.(Hybrid.Laminar.Flow.Demonstration.on.Aircraft)..

Although.laminar.flow.designs.have.been.used.on.commercial.transports,.specifically.on.wing.and.stabiliser.leading.edges,.it.is.only.recently.that.more.extensive.use.of.the.technology.has.been.undertaken..Advances.in.composite.construction.and.material.joining.techniques,.for.instance,.have.culminated.in.the.design.of.a.natural.laminar-flow.nacelle.on.the.Boeing.787..Boeing.predicts.that.an.airline.that.can.maintain.the.natural.laminar.flow.properties.of.the.nacelle.can.expect.to.save.100,000.litres.of.fuel.per.787.aircraft.every.year.[21].

Beyond. the.787.generation.of. transports,.NASA.has.asserted. that. it. could.be.possible. to.maintain.natural. laminar. flow.over.20%.of. the.wing.and. tail,. as.well.as.30%.of. the.nacelles.on.a. transport.plane. fielded. in. the.2015. timeframe. [22]..This.contributes.to.a.possible.fuel.burn.reduction.of.25%.for.the.next.generation.single-aisle.aircraft..Research.under.the.European.Joint.Technology.Initiative.(JTI).Clean.Sky.aim.at.obtaining.natural.laminar.flow.on.the.outer.wing.of.an.A340.just.by.optimal.wing.shaping..

A.1.1.1.5 Hybrid Laminar FlowThe.purpose.behind.hybrid.laminar.flow.control.(HLFC).is.to.maintain.laminar.flow.over.a.large.portion.of.the.aircraft,.especially.the.wing,. by. directly.manipulating. the. boundary. layer.. This. is. typically. achieved. by. augmenting. the. natural. laminar. flow.construction.with.either.surface.suction.or.blowing.[20]..Research.on.laminar.flow.control.using.suction.started.during.the.Second.World.War.with.a.series.of.tests.on.a.B-18.aircraft.[20].. In.the.1950s,.both.the.U.K..and.the.U.S..experimented.further.with.jet-propelled.HLFC.aircraft.that.culminated.in.the.x-21.research.aircraft.[20]..None.of.these.designs,.however,.were.very.successful.due.to.problems.such.as.icing.and.surface.contamination.

In.the.early.and.mid.1980s,.NASA.experimented.with.an.HLFC.design.that.was.intended.to.combine.the.benefits.of.both.natural. laminar. flow.design.and.active. flow.control.without. the.associated.drawbacks. [20,23]..NASA,. the.U.S..Air.Force.(USAF),.and.Boeing.flight-tested.a.HLFC.wing.glove.on.a.company.owned.757-200.in.1990.[20]..The.primary.goal.of.this.test.was.to.demonstrate.the.readiness.of.HLFC.technology.and.reduce.the.level.of.risk.for.future.programmes..

The.flight-test.results.showed.that.if.the.entire.wing.span.of.the.Boeing.757.was.modified,.then.a.potential.10%.reduction.in.drag.could.be.realized.[24]..Additionally,.design.work.at.NASA.Langley.Research.Center. indicated.that.with.HLFC.on.both. the.wing. and. stabilizers,. a.15%. reduction. in. fuel. burn. over. conventional. designs. could.be. achieved.on. a. notional.300-passenger.transport.plane[20].

Airbus. indicates. that. its.version.of. the.HLFC,.along.with.advanced.surface.coatings. that.allow. further. reduction. in.drag,.could.be.ready.for.the.A30x.[25]..In.the.1990s,.an.A320.test.bed.reportedly.achieved.a.10%.net.decrease.in.fuel.burn.due.to.active.flow.control.on.the.wing,.tail,.and.nacelles.[26]..The.reduction.of.friction.drag.over.the.wing.by.45.to.50%.is.also.seen.to.be.attainable.with.a.partially.laminar.(boundary.layer).wing..Nevertheless,.the.difficulties.associated.with.maintaining.a.HLFC-enabled.wing.might.limit.its.application.to.lower.sweep.angles.and.thus.could.reduce.the.vehicle.cruise.speed.to.Mach.0.75.or.possibly.lower..

The.suction.or.blowing.system.represents.a.significant.weight.penalty,.which.must.be.more.than.balanced.by.the.benefits.of.laminarity..Moreover,.the.system.is.subject.to.high.reliability.requirements..If.the.operator.cannot.be.sure.of.achieving.laminar.conditions.during.all.the.flights,.he.would.need.to.carry.extra.fuel.in.case.of.laminarity.breakdown,.which.limits.fuel.savings.to.a.fraction.of.the.possible.maximum.....

Figure.A.1.1-.5:.General.aviation.jet.with.natural.laminar.flow.wing.[20]

10..ANNEx.1

A.1.1.1.6 Variable CamberThe.key.characteristic.of.the.variable.camber.concept.is.the.continuous.and.seamless.variation.of.section.airfoil.shape.in.chord-wise.and/or.span-wise.directions.to.adapt.it.to.the.conditions.of.different.flight.phases..Numerous.leading.edge.(LE).and.trailing.edge.(TE).devices.(e.g..slats.and.flaps).have.long.been.used.as.camber-variance.methods,.albeit.in.a.discrete.manner..The.primary.benefits.of.a.variable.camber,.which.is.continuously.tailored.for.each.flight.segment,.are.a.lift.to.drag.(L/D). ratio. near. to. optimum. over. a. relatively. broad. range. of. flight. speed,. improved. buffet. boundary,. and. reduced.wing.structural.weight..The.development.of.variable.camber.technology.has.a.range.of.potential.applications..At.its.most.basic.a.simple.variable.camber.system.can.be.created,.for.at.least.a.portion.of.the.wing,.by.enabling.small.deflections.in.trailing.surfaces.to.optimise.L/D.across.a.range.of.flight.conditions..This.could.be.coupled.with.the.sensor.and.actuator.set.that.enables.active.load.alleviation,.described.later.in.this.Appendix..Near-term.benefit.can.thus.be.achieved.with.the.existing.set.of.flight-control.surfaces.and.high-lift.devices,.just.by.retrofitting.advanced.software..On.future.new.aircraft.there.is.potential.for. the.specific.design.of.aircraft.control.surfaces.and.structures. to.enable.a.more.sophisticated.and.ubiquitous.variable.camber.installation..

The.technological.genesis.of.the.variable.camber.idea.can.be.traced.back.to.NASA.and.Boeing’s.Mission.Adaptive.Wing.(MAW).program.of. the.1970s. and.1980s.. The. focus. then.was.on. the.performance. enhancement. of. tactical. aircraft. by.maintaining.laminar.flow.across.a.range.of. lift.coefficients.using.automated,. in-flight.control..This.was.accomplished.by.a.variable.camber.mechanism.with.the.use.of.a.flexible.wing.upper.skin.and.a.sliding.joint.in.the.lower.skin.that.allowed.the.wing.to.deflect.the.leading.and.trailing.edges.as.needed..The.overall.benefit.of.MAW.was.significantly.improved.manoeuvrability,.increased.level.flight.speed/range,.and.reduced.wing.bending.moment.

Building.upon. innovations. in.structural.design.and.actuation.mechanisms. from. the.MAW.program,. the.Mission.Adaptive.Compliant.Wing.(MACW).program.was.created.in.order.to.minimise.the.force.required.to.morph.surfaces,.while.maintaining.the.stiffness.required.to.undertake.external,.aerodynamic.loading..Through.the.use.of.modern.materials.and.newly.developed.structural.design.methods,.the.weight.of.adaptive.flap.systems.has.been.significantly.reduced,.and.abrupt.surface.breaks.during. flap.deployment.were.eliminated..MACW.flaps.can. indeed.require. less. force.and.power. than.a.comparably.sized.conventional.flap..MACW.technology.also.allows.the.flap.to.be.positioned.with.a.linearly.varying.flap.deflection.along.the.wingspan..Progression.to.a.full.composite.MACW.flap.from.the.current.aluminium.construction.is.reportedly.underway.[27].

The.application.of.the.MACW.flap.to.a.commercial.transport.plane.has.been.studied.by.FlexSys.et.al.[27]..

The.result.is.quite.promising.with.considerably.increased.aerodynamic.efficiency.(L/D).reported.for.a.wide.range.of.the.flight.envelope..A.medium-range.transport.incorporating.the.MACW.flap.system.is.projected.to.save.around.400.litres.of.jet.fuel.on.a.typical.North.American.transcontinental.flight.(around.4,000.km),.assuming.compliant.flap.cruise.L/D.improved.3.3%..Depending.on.aircraft.utilisation,.fuel.savings.of.200.tonnes/year.for.a.B737.or.A320.sized.aircraft.are.anticipated..A.new.wing.design.that.capitalises.on.the.capabilities.of.MACW.could.save.as.much.as.15%.in.fuel.costs.plus.additional.gains.

Figure.A.1.1-.7:.Variable.camber.wing.concept.[27]Figure.A.1.1-.6:.European.Hybrid.Laminar.Flow.Control.Demonstrator.(Courtesy.of.DLR)


from.weight.savings.due.to.less.fuel,.smaller.wing-root-bending-moment,.and.lighter.and.more.efficient.flap.[28]..The.main.advantage.of.variable.camber.comes.from.the.fact.that.the.aircraft.flies.efficiently.(L/D.near.optimum).also.in.“off-design”.conditions,.i.e..when.air.traffic.control.sends.it.onto.non-optimal.flight.levels,.or.when.the.pilot.is.obliged.to.fly.at.higher.than.design.speed.to.recover.a.delay.

In.Europe,.both.the.Active.Aeroelastic.Aircraft.Structure.(3AS).and.the.Active.Adaptive.Wing.Camber.(AAWC).concepts.are.being.researched.along.with.a.rotating.ribs.mechanism,.which.can.generate.a.continuous.camber.variation.along.the.wingspan.by. the.movements.of.actuator. ribs.and.TE.slide.bearings. [29]..One.of. the.main.difficulties.associated.with. implementing.variable.camber.technology.on.commercial.transports.is.the.structural.complexity.due.to.compatibility.with.high.lift.structures,.such.as.flap.carriage.support.tracks.and.slat.track.systems..Consequently,.a.compact.actuation.mechanism,.which.can.fit.inside.the.flap.mould.lines,.and.a.modified.retracting/extending.mechanism.would.be.useful.

Adaptive.structures.can.be.found.on.the.Boeing.787:.when.the.flaps.are.deployed,.the.spoilers.can.be.moved.downwards.to.get.an.optimised.width.of.the.gap.between.wing.body.and.flap..A.similar.mechanism.is.found.on.the.A350..

In.conjunction.with.variable.camber.TE,.LE.devices.have.also.evolved.from.conventional.slats.to.seamless.variable.camber.mechanisms..FlexSys.has.developed.a.LE.morphing.structure.using.MACW.technology. [27],.which.greatly. reduces. the.mechanical.complexity.by.adopting.smart.structures.and.efficient.actuation.mechanisms.

To.exploit.fully.the.advantages.of.the.adaptive.variable.camber.mechanism.in.cruise,.it.is.necessary.to.provide.a.method.to.identify,.in.flight,.small.amounts.of.incremental.drag.(in.the.order.of.1%).for.effective.control.[32]..The.previous.MAW.system.used. either. pre-determined. deflection. schedules. or. a. real-time,. trial-and-error. approach. for. finding. the. optimal. camber.control.scheme..More.recent.flight-testing.of.MACW.demonstrated.technical.feasibility.of.real-time,.adaptive.maximisation.of.the.range.of.laminar.flow.(the.so-called.laminar.bucket).for.the.prototype.wing.section.in.high-altitude,.long-endurance.flight.environments..Although.it.has.been.demonstrated.that.maintaining.minimum.drag.over.wide.lift.ranges.can.result.in.significant.fuel.savings,.accurate.identification.of.current.drag.levels.and.potential.environmental.contamination.(e.g..insect.strikes,.icing).are.yet.to.be.addressed.before.a.judgment.on.the.technology’s.commercial.feasibility.can.be.made.[28].

Figure.A.1.1-.9:.Typical.Fowler. kinematic.system. (left,. retracted.position).and.modified.mechanism. for. variable.camber.trailing.edge.(right,.extended.position).[30]

Figure.A.1.1-.8:.Aerodynamic.efficiency.improvement.with.variable.geometry.trailing.edge.[27]

12..ANNEx.1

A.1.1.2 Structural Concepts

A.1.1.2.1 Active Load AlleviationAn.active.load.alleviation.system.reduces.or.distributes.the.aerodynamic.loads.on.the.aircraft.wing.by.an.active.reaction.of.its.control.surfaces.to.these.loads..For.a.newly.designed.wing,.this.allows.the.wing.structure.to.be.lighter.and.the.aerodynamics.of.the.wing.to.be.tailored.to.each.specific.flight.condition.[33].(see.also.variable.camber)..The.concept.is.not.particularly.new,.the.Lockheed.L-1011-500.used.accelerometers.located.on.the.wingtips,.combined.with.outboard.ailerons,.to.reduce.the.gust.loads.on.the.outboard.section.of.the.wing.[34]..This.allowed.Lockheed.to.increase.the.wing’s.span.and.aspect.ratio.without.having.to.increase.its.structural.weight..Since.then,.more.advanced.load.alleviation.systems.have.been.designed,.including.those.that.seek.to.reduce.the.bending.moment.on.the.wings.during.manoeuvres..These.systems.can.be.found.on.the.A340-500/600,.Boeing.777F,.and.Boeing.787.[35,36,37],.which.allow.for.a.comparatively.lighter.wing..Airbus.claims.a.7%.reduction.in.induced.drag.is.possible.through.a.combination.of.shape.optimisation,.adaptive.wing.devices,.wing-tip.devices,.and.load.control.technologies..Research.on.active.load.control.is.also.part.of.the.Joint.Technology.Initiative.Clean.Sky.in.Europe..

While.load.alleviation.has.served.to.reduce.the.weight.of.current.generation.aircraft.structures,.there.is.still.potential.to.extract.further.benefits.from.the.concept..NASA.has.proposed.coupling.a.forward.looking.LIDAR.system,.with.both.elevators.and.wing.flaps,.to.reduce.the.gust.loads.for.the.entire.aircraft.by.as.much.as.90%.[34]..This.reduces.the.movement.of.the.entire.aircraft’s.centre.of.gravity,.thereby.not.only.reducing.loads.on.the.wings.and.stabilizers,.but.also.on.the.fuselage..Additionally,.the.reduction.in.gust.movements.would.significantly.increase.passenger.comfort.under.turbulent.weather.conditions.

A.more.advanced.version.of.the.same.concept.is.the.active.aeroelastic.wing..It.combines.load.alleviation.with.active.variable.camber.and.significantly.reduced.structural.stiffness.to.bend.itself.into.the.most.appropriate.shape.for.a.given.flight.condition.[38]..To.date,.the.technology.has.been.demonstrated.on.a.modified.F/A-18.aircraft,.and.it.has.the.potential.to.reduce.wing.weight.further.and.tailor.aerodynamic.efficiency..By.actively.controlling.wing.twist.and.shape,.it.is.possible.to.reduce.the.need.for.large.control.surfaces,.further.reducing.the.structural.weight.of.the.aircraft.[39]..This.would.effectively.revive.the.Wright.brothers’.“wing.warping”.concept.

Figure.A.1.1-.10:.Leading.edge.variable.camber.mechanisms.[31]


A.1.1.2.2 Morphing AirframeIn.the.longer-term.future,.it.is.conceivable.that.an.aircraft.would.reconfigure.its.aerodynamic.surfaces.“on.the.fly”.to.achieve.maximum.performance. during. each. element. of. the. flight. profile. [40].. Key. enablers. for. this. significant. gain. in. adaptation.capabilities,.in.conjunction.with.flight.controls.and.mission.objectives.that.exploit.the.ability.to.drastically.morph,.are:

Materials.capable.of.supporting.flight.loads.and.undergoing.high.strain.without.creep.•.

Compact.actuators.consuming.exceptionally.low.power,.yet.are.able.to.generate.substantial.forces.and.displacements.•.[41]..The.use.of.piezoceramic.actuators.as.well.as.adaptronics.technology.is.under.consideration.

The.aerospace.industry. is.currently. investigating.the.practicality.of.morphing.structures.that.combine.smart.materials.and.compact. actuators.. For. instance,. the.USAF/NASA/Boeing.Active. Aeroelastic.Wing. (AAW). programme’s. objective. is. to.control.the.twist.of.a.flexible.wing.in.to.induce.roll.movements,.thereby.obviating.conventional.roll-control.surfaces.that.are.mechanically.complex.[40]..

The.Morphing.Aircraft.Structures. (MAS).programme.of. the.US.Defense.Advanced.Research.Projects.Agency. (DARPA).involves.the.development.of.multiple.vehicular.platforms.by.Lockheed,.Raytheon.Missile.Systems,.and.NextGen.Aeronautics..The.program’s.primary.emphasis. is.on.realizing. the. technological. feasibility.of. large-scale,. in-flight.morphing..Lockheed’s.Z-wing.concept.has.a.seamless.folding.structure.to.provide.conformal.coverage.over.the.wing-fold.area.at.each.fold..The.seamless. skins. are.made.out. of. elastomers.produced. through. the. vacuum.assist. resin. transfer.mold. (VARTM).process..The.wing.folds.itself.through.hierarchically.mechanized.servo-drive.systems,.locked.by.fold.brake.systems.once.folding.is.achieved.

NextGen.Aeronautics,.Inc..has.also.developed.an.in-flight.morphing.concept.[42]..It.possesses.mechanized.four-bar.linkages,.whose.motion.is.governed.by.computer-controlled.linear.actuators..In.addition,.flexible.elastomeric.skins.with.out-of-plane.stiffeners.accommodate.the.wing’s.motion,.while.transferring.the.air.loads.to.the.wing.sub-structures.[43]..

Both.Lockheed.and.NextGen.Aeronautics.have.reported.no.significant.aeroelastic.instabilities.from.wind.tunnel.tests..The.demonstration.work.has.now.moved.to.the.flight-testing.phase.[41,42]..

Some.military.aircraft,.such.as.Tornado,.use.another.type.of.morphing,.known.as.swing-wings..These.change.their.sweep.angle.according.to. the. flight.phase..However,. the.weight.and.complexity.of. the.related.mechanics.prevent.a.commercial.business.case.and.environmental.benefit..The.same.argument.is.valid.for.most.other.morphing.concepts..

Figure.A.1.1-.11:.N-MAS.wind.tunnel.model.(left),.morphing.structure.layout.(center),.and.elastomeric.skin.with.ribbons.(right).[43]

14..ANNEx.1

A.1.1.2.3 Morphing MaterialsThe.use.of.adaptive.materials.has.emerged.as.a.technological.enabler.for.morphing.aircraft.structures..Also.known.as.smart.materials,.they.have.the.remarkable.ability.to.support.both.shape.changing,.such.as.large.variations.in.wing.area,.seamless.camber-changing,.etc..and.load-carrying.functions..Such.materials.may.even.be.self-actuated.by.external.stimuli,.such.as.light,.heat,.and.electromagnetic.fields..Self-actuating.materials.include.heat-activated.shape.memory.alloys.(SMAs),.such.as.NiTiNol;.ceramics,.such.as.lead.zirconate.titanate;.light-activated,.lightweight,.flexible.shape.memory.polymers;.electrically.activated.piezoelectrics;.and.magnetorheological.fluids.[44]..Each.displays.a.wide.spectrum.of.mechanical.response..As.an.example,.piezoelectric.materials.exhibit.high.force.but.low.stroke,.whereas.the.SMAs.are.dynamically.limited.in.their.actuation.bandwidth.[45]..Therefore,.a.comprehensive.understanding.of.the.mechanical.responses.(e.g.,.hysteresis,.fatigue,.long-term.behaviour,.damage.behaviours,.etc.).of.these.materials.becomes.particularly. important.when.evaluating.them.for.potential.aviation.applications.

The.challenges.associated.with.developing.stiff.morphing.structures.are.increasing.the.interest.in.flexible.matrix.composites.(FMCs)..By. arranging. the. fibres. and.matrices.correctly,. a. FMC.material. that. is. flexible. in. certain.directions,.while.being.strong.and.stiff.in.other.directions,.can.be.fabricated..Figure.A.1.1-.12.shows.how.a.shape-changing.actuator.can.be.made.out.of.a.FMC.tube..The.flexible.fibres.within.the.tube.walls.allow.pressure.forces.to.cause.it.to.contract.or.elongate.in.the.axial.direction.. Integrating.many.such.cells.(tubes).into.one.continuous.structure.creates.an.adaptive.structure.with.multi-directional.actuation.capability.[46].

Another.application.of.FMCs.is.in.the.make-up.of.pneumatic.artificial.muscles.(PAMs).to.construct.the.so-called.morphing.skin.[47]..The.idea.here.is.that.the.characteristics.of.FMCs.could.be.exploited.to.manufacture.a.skin.suitable.for.an.aircraft.wing,.which.must.not.only.support.the.broad-scale.structural.deformation.of.a.non-porous.surface,.but.also.simultaneously.maintain.resistance.to.aerodynamic.loading..Somewhat.similar.to.natural.muscles,.PAMs.are.unidirectional.actuators.that.are.capable.of.producing.significant.force.levels.only.when.contracted..This.implies.that.two.PAMs.can.be.arranged.in.opposing.directions.to.produce.bi-directional.rotational.motion.about.a.hinge.

While.many.of. the.proposed.morphing.concepts. rely. on. the.utilization.of. hinges,. screws,. and/or. hydraulic. actuators. for.movement,. others. that. depend.on. a. continuous. supply. of. power. have.been. suggested..Piezoceramic.or. shape-memory.alloy.actuators,.for.instance,.can.deform.a.structure.from.its.natural.equilibrium.configuration.to.another.configuration.in.an.elastic.manner..Moreover,.asymmetric.composite. laminates.do.not.require.the.continuous.application.of.moments.to.hold.the.structure.in.shape..This.is.because.moments.are.only.required.to.initiate.the.changing.of.the.configuration;.a.particular.lamination.scheme.results.in.multiple.shapes.with.different.twisting,.as.well.as.bending.curvatures..To.this.end,.Macro-Fibre.Composite.(MFC).actuators,.which.are.orthotropic.piezoceramic.actuators,.are.being.researched.[48]..The.main.advantage.here.is.that.the.supply.of.power.becomes.only.necessary.when.shape.changing.of.the.laminate.is.desired,.and.not.to.hold.it.in.a.particular.shape..Thermal.induction.of.morphing.the.same.types.of.laminates.is.also.being.investigated.for.bi-stable.blended.winglets.and.the.variable.camber.TE.[49].

Figure.A.1.1-.12:.FMC.actuator.converting.internal.pressure.to.axial.contraction.or.extension.(left).and.multi-cellular.FMC..morphing.structure.(right).[46]

Figure. A.1.1-. 13:. Wing-span. extension. using. FMC. morphing. skin. and. PAM-actuated.sub-structures.[47]


Tendon-actuated.compliant.cellular.trusses.are.being.developed.as.a.large-scale.morphing.structure.at.Penn.State.University.[50]..Here,. compliant. cellular. trusses.with. tendons. are. used. as. active. elements. capable. of. achieving. continuous. stable.deformations.over.a.large.range.of.aircraft.shapes..Actuation.is.achieved.by.pulling.on.one.set.of.cables.while.controlling.the.release.of.another,.so.that.the.stability.of.the.structure.is.maintained.in.any.intermediate.position.[51]..

The. Cornerstone. Research. Group,. Inc.. has. commercialized. various. heat. adaptive. materials;. additionally,. NanoSonic. is.developing.an.adaptive.material.called.Metal.Rubber,.which.can.be.elastically.stretched.(up.to.double.its.original.size).while.maintaining.high.specific. strength,. temperature. resistance,. and.electrical. conductivity. akin. to. that.of. a. solid.metal..More.specifically,.Metal.Rubber. is.a.nanotechnology.product.that. is.fabricated.molecule.by.molecule.from.the.source.materials.of.positively.charged.metallic.ions.and.the.elastic.polymers.[51]..This.exotic.new.technology,.shown.in.Figure.A.1.1-.14,.is.currently.being.tested.for.artificial.muscles.and.aircraft.morphing.structures,.among.other.potential.applications.

A.1.1.3 New Aviation MaterialsEvery.additional.kilogramme.of.structural.weight.on.an.aircraft. requires.additional. lift. to.counteract. it,.additional. thrust. to.overcome.the. incremental. increase. in.drag,.and.additional. fuel. to.provide.the.same.range.of. flight..A.new.aircraft.design.that.needs.to.generate.more.lift.and.to.carry.more.fuel.is.likely.to.result.in.a.higher.wing.loading.or.a.larger.wing.area..This.would.either.increase.speeds.and/or.lead.to.higher.wing.weights..For.most.conventionally.designed.aircraft,.this.translates.to.a.gross.weight.increase.ranging.from.2.to.10.kilogrammes.for.every.extra.kilogramme.of.additional.empty.weight.[52],.this.“snowball.effect”.being.especially.strong.for.long-range.aircraft..

Weight.reduction.is.thus.key.to.enhancing.the.fuel.burn,.emissions,.and.consequent.cost.characteristics.of.future.commercial.aircraft..The.most.important.way.to.achieve.it.is.the.development.and.use.of.lighter.and.stronger.materials..In.the.sections.that.follow,.some.of.the.more.important.materials.that.have.been.introduced.into.recently.developed.commercial.airframes.are.discussed,.as.well.as.those.that.are.expected.to.find.significant.aviation.applications.in.the.next.decade..Similarly,.advanced.manufacturing.techniques.for.structural.components.such.as.laser-beam.welding.help.reduce.the.material.needed.to.achieve.the.required.strength,.and.thus.reduce.structural.weight.

A.1.1.3.1 Welding and FasteningStructural. weight. reduction. can. be. achieved. not. only. by. the. use. of. more. lightweight. materials,. but. also. by. advanced.manufacturing. and. fastening. techniques.. New.welding. techniques,. such. as. electron. beam.welding. (EBW),. laser. beam.welding.(LBW),.and.friction.stir.welding.(FSW),.developed.by.launch.vehicle.manufacturers.and.adapted.by.the.automotive.industry,. are.expanding. to.commercial. aviation. to. replace.conventional.arc.welding.and. riveting.practices..Reductions. in.structural.weight,.as.well.as.a.decrease.in.friction.drag.by.preservation.of.the.laminar.boundary.layer.near.the.leading.edges,.where.the.boundary.layer.is.of.similar.thickness.as.rivet.protrusions,.are.the.primary.benefits.that.are.anticipated.from.these.welding.technologies.

Figure. A.1.1-. 15:. Schematic. of. friction. stir.welding.process

Figure.A.1.1-.14:.NanoSonic’s.Metal.Rubber.[51]

16..ANNEx.1

These.techniques.not.only.widen.the.applicability.of.welding.to.previously.non-weldable.metals.such.as.2000.series.aluminium.alloys,.but.also.provide.high.quality.joining.of.aluminium.or.titanium.alloys,.characterized.by.small.heat.affected.zone.(HAZ)..Lower.post-weld.distortion.(Figure.A.1.1-.15).is.also.made.possible.by.the.utilization.of.intensive.heat.sources,.such.as.laser.and.frictional.heat..However,.expensive.high-energy.sources.and.computerized.processing.equipment.are.required.

In.addition.to.product.quality.improvement,.the.new.welding.processes.have.also.shown.some.potential.for.reducing.the.cost.and.weight.of.commercial.aircraft..A.typical.EBW.process.provides.15.to.20%.higher.weld-strength.with.a.much.narrower.HAZ,.compared.to.conventional.arc.welding,.resulting.in.lighter.weight.products.[53]..LBW.will.soon.replace.riveting.in.the.joining.of.stringers.to.the.skin.plate.in.the.Airbus.318.and.380.aircraft.[54]..In.the.specific.case.of.the.design.switch.for.a.wing.access.panel.of.the.Airbus.A318.and.A320.from.riveted.aluminium.to.titanium.processed.by.Superplastic.Forming.(SPF).and.Diffusion.Welding.(DFW).achieved.weight.savings.in.excess.of.40%.[55].

The.overall.benefits.of.advanced.welding.and.fastening.techniques.are.a.reduction.in.part.count.and.weight..An.additional.benefit.arises.from.the.improved.fit.and.form.of.the.joints..This.reduces.steps.and.gaps.with.a.contribution.to.the.transition.of.the.boundary.layer.from.laminar.to.turbulent.flow..This.is.especially.true.for.the.leading.edges.of.the.nacelles,.wing,.and.empennage.

A.1.1.3.2 Cabin Interiors The.reduction.of.cabin.and.interior.weight.provides.a.significant.benefit.for.both.existing.and.future.aircraft.designs...Since.airplane. interiors.are. replaced.and.upgraded.many. times.over. the. life.of.a.given.airplane,. there. is.an.opportunity. to. take.advantage.of.advances.in.materials.technology...Reducing.the.weight.of.interior.fittings,.including.sidewalls,.panels,.seats,.etc..provides.either.a.potential.to.increase.the.payload.carried.over.a.given.range.or.reduce.the.fuel.burn.required.to.carry.a.given.payload.

Traditionally,.ceiling.and.sidewall.panels.have.been.made.of.fibreglass..By.utilizing.currently.available.carbon.fibre.panels,.hundreds.of.kilos.of.weight.can.be.removed.from.the.interior...Some.possible.benefits.from.addition.of.lightweight.materials.include.a.possible.reduction.of.40%.in.the.weight.of.leather.seat.covers.[56],.and.a.sidewall.weight.savings.that.could.be.achieved.by. switching. to. stronger. and.more.ductile. polyetherimide.based.plastics. [57].. .Composite. components. in. the.seats.not.only.meet.the.shock.load.requirements.but.also.reduce.weight..By.using.systems.integration.techniques,.cabin.entertainment.systems.can.be.better.integrated.into.the.design,.which.can.also.result.in.a.further.weight.reduction.

New. plastic. fasteners. have. now. been. developed. that.weigh. less. than. the. previous.metal. fasteners.. . Also,. new. joining.techniques.using.a.tab.and.slot.design.to.reduce.weight.for.the.interior.panels.by.eliminating.many.of.the.heavy.metal.posts.that.were.previously.used.to.attach.the.panels..These.advances.can.be.retrofitted.into.the.existing.fleet.of.airplanes.when.interior.upgrades.are.made.

Another.promising.material.is.High.Strength.Glass.Microspheres..These.are.made.of.hollow.borosilicate.glass.and.are.used.to.reduce.the.weight.of.plastics.and.rubber.compounds..These.microspheres.are.between.15.and.30.microns,.have.a.very.high.crush.strength,.and.have.a.specific.gravity.ranging.from..38.to..60,.making.them.ideal.for.injection.moulding,.compression.moulding,.and.extrusion.profile.processes.

The.primary.technical.benefits.of.incorporating.glass.microspheres.into.optimized.plastic.resins.and.rubber.compounds.are:.mass.reduction;.reduced.resin.consumption;.higher.filler.loading.for.improved.mould.flow;.improved.dimensional.stability.of.a.part;.reduced.warpage.and.differential.shrinkage.

Most.aircraft.interior.plastics.are.made.from.heavily.loaded.phenolic.resins,.which.have.a.specific.gravity.around.1.18-g/cm³..Typical. interior.components.made.from.this.type.of.resin.material.are.ceiling.panels,.sidewalls,.floorboards,.stowage.bins,.lavatories,.galleys.and.bulkhead.separator.panels..

By.incorporating.a.loading.level.of.11.5%.of.glass.microspheres.into.each.one.of.these.components,.the.overall.weight.of.the.above.parts.could.be.reduced.10%..For.perspective,.a.Boeing.777.has.11,000.pounds.(5,000.kg).of.phenolic.resins.in.its.interior..By.incorporating.glass.microspheres.into.these.parts,.a.weight.reduction.of.1,100.pounds.can.be.achieved..Adding.microspheres.to.rubber.compounds.in.an.interior.would.further.reduce.weight.

The.high.strength.glass.microspheres.are.commercially.available..Glass.microspheres.have.been.used.in.a.variety.of.industries.for.over.20.years,.including.oil.and.gas,.recreation,.construction.materials.and.paints.and.coatings.

Figure.A.1.1-.16:.Cross-section.comparison.of.electronic.beam. welding. (left). with. conventional. gas. tungsten. arc.welding.(right).[52]


A.1.1.3.3 Advanced AlloysMost.damage.and.strength-critical.structural.components.of.current.aircraft.are.made.out.of.aluminium..[58]..For.decades,.aluminium.alloys.have.demonstrated.a.steady.rate.of.improvement.in.strength,.corrosion.resistance,.durability,.and.damage.tolerance.

Aluminium-Lithium Alloys

Compared.to.conventional.aluminium.alloys,.Aluminium-Lithium.(Al-Li).alloys.have.two.distinguishing.material.properties;.that.is,.lower.density.and.higher.modulus.(higher.bending.strength)..This.is.made.possible.by.the.presence.of.lithium..Each.weight.percentage.of.lithium.lowers.the.alloy.density.by.approximately.3%.and.increases.the.modulus.by.approximately.6%.[59]..As.a.group,.these.alloys.also.possess.attractive.fatigue.properties.and.are.thus.suitable.for.superplastic.forming,.welding,.milling,.bonding,.anodizing,.cladding,.and.painting..The.alloys.often.display.considerable.anisotropy,.especially.in.the.short.transverse.direction,.and.are.currently.more.expensive.and.difficult.to.process.than.conventional.aluminium.alloys.

Al-Li. alloys. have. yet. to. replace. conventional. aluminium. alloys. in.many. aerospace. applications. because. of. their. fracture.behaviour.[60]..Low.fracture.toughness.was.an.area.of.concern.with.the.first.commercial.alloy.2020.(Al-Li-x)..Consequently,.newer.Al-Li.alloys.have.been.developed.to.improve.fracture.toughness.with.sophisticated.processing.procedures...At.present,.they.have.toughness.levels.that.are.comparable.to.the.conventional.aluminium.alloys.while.offering.lower.densities.and.higher.moduli.

Applications.of.these.newer.classes.of.Al-Li.alloys.in.aircraft.building.include.the.leading.edges.and.outer.lower.skins.of.the.Airbus.A330.and.A340,.some.components.of.the.C-17.military.transport.and.the.stringers.of.the.F-16..In.spacecraft.building,.the.alloy.selected.for.the.super-light-weight.external.fuel.tank.of.the.space.shuttle,.offers.a.50%.strength.increase,.a.5%.elastic.modulus.increase,.and.a.5%.density.reduction.compared.to.the.conventional.alloy.that.it.will.replace..

Third-generation.Al-Li.alloys.have.recently.become.available.with.more.attractive.material.properties,.such.as.high.corrosion.resistance,.excellent.damage.tolerance,.and.are.interchangeable.with.advanced.hybrid.materials.

Advanced Titanium Alloys

Titanium.(Ti).alloys.are.expanding.their.market.share.in.the.aviation.sector,.primarily.due.to.their.high.strength-to-weight.ratio,.good.damage-tolerance,.and.excellent.corrosion.resistance..However,.the.conventional.usage.of.Ti-based.alloys.has.been.strongly.limited.by.their.price..

Ti.alloys.could.be.an.alternative.to.high.strength.steel,.even.though.the.structural.efficiency.of.steel.is.considerably.higher.at.the.highest.strength.level..The.main.issue.is.the.susceptible.embrittlement.caused.by.the.hydrogen.content.of.steel..The.landing.gear.of.most.commercial.aircraft.has.been.conventionally.fabricated.in.high.strength.steel,.and.its.service.history.has.shown.numerous.hydrogen.embrittlement.failures.despite.stringent.maintenance.procedures..Primarily.due.to.this.reason,.the.Boeing.777.adopts.a.high.strength.Ti.alloy.for.its.landing.gear.

As.the.usage.of.composite.materials.has.increased,.so.has.the.need.to.use.Ti.alloys.for.fittings.and.attachments.to.mitigate.galvanic.corrosion..The.superior.corrosion-resistance.traits.of.Ti.alloys.also.make.them.attractive.for.embedded.components.that.cannot.be.inspected.frequently,.resulting.in.the.reduction.of.maintenance.costs.

Space.limitation.is.another.motivator.behind.the.preference.of.Ti.alloys.to.aluminium.alloys..The.higher.strength.of.Ti.alloys.allows.the.same.load.to.be.carried.by.a.physically.smaller.structural.member.(there.are,.however,.no.benefits. in.terms.of.component.weight)..Therefore,.the.Boeing.747’s.landing.gear.beam.was.designed.with.Ti.alloys;.it.would.not.have.otherwise.fitted.within.the.available.space.of.the.lower.fuselage.

Ti.alloy.usage.by.weight.in.aircraft.is.increasing.relative.to.Al-based.alloys.and.steel.with.each.new.product.generation;.i.e.,.from.2.6%.in.the.Boeing.747-100.to.8.3%.of.the.Boeing.777..The.ensuing.cost.penalty.must.still.be.traded.off.with.the.aspired.levels.of.weight.reduction,.maintenance.cost.decrease,.and.reliability.improvements.

Aluminium-Magnesium-Scandium Alloys

Aluminium-Magnesium-Scandium.(Al-Mg-Sc).alloys.are.the.newest.type.of.aluminium-based.alloys.under.development,.which.have.excellent.corrosion.resistance.without.being.clad.or.painted..These.new.alloys.are.in.the.near-commercial.development.phase.for.welding.and.low-cost.creep.forming.materials,.despite.the.high.cost.of.scandium.[61].

18..ANNEx.1

A.1.1.3.4 Hybrid AlloysAn.advanced.hybrid.alloy.is.defined.as.the.hybrid.of.metal.products.(e.g.,.sheet,.plate,.extrusion).and.high.performance.fibres.

Laminated. hybrids. of. aluminium. sheet. with.Glare. (glass-fibre-reinforced),. or. ARALL. (aramid-fibre-reinforced),. represent.the. first-generation.metal-composite. hybrid.materials. developed. in. the.1980s.. These. hybrid. alloys. possess. high. fatigue.resistance.compared.to.conventional.aluminium.alloys..Fatigue. is.a.phenomenon.that.arises.after. long-term.exposures.to.cycling.loading,.which,. in.turn,.eventually.results. in.fracture..The.potential. for.savings.in.aircraft.weight. is.thus.significant,.typically.7.to.10.times.of.monolithic.aluminium.sheets,.although.at.the.expense.of.very.high.material.costs.[63].

The.upper.fuselage.panels.of.the.Airbus.A380.are.fabricated.with.Glare,.which.accounts.for.3%.of.the.total.airframe.weight.(Figure.A.1.1-.18)..The.cargo.door.of.the.C-17.is.fabricated.from.ARALL..Both.offer.extra.functionality,.such.as.load.monitoring.and.damage.detection.that.can.result.in.maintenance.cost.reduction..Nevertheless,.technical.problems.have.been.reported.when.attempting.to.fabricate.thick.forms.of.these.laminates.for.fatigue.sensitive.components,.such.as.the.lower.wing.skins,.due.to.the.complicated.manufacturing.process.that.involves.thin.sheet.milling,.pre-treatment,.storage,.and.multiple.lay-ups.

The.CentrAl.concept.(Figure.A.1.1.-.17).features.a.central.layer.of.fibre.metal.laminate.(FML).that.is.sandwiched.between.one.or.more.thick.layers.of.high-quality.aluminium.or.advanced.aluminium.alloys..This.creates.a.robust.construction.material.that.is.not.only.exceptionally.strong,.but.also.insensitive.to.fatigue..The.new.CentrAl.constructions.are.stronger.than.the.carbon.fibre.reinforced.plastic.(CFRP).constructions.that.have.seen.usage.on.the.wings.of.the.Boeing.787..By.using.CentrAl.as.a.primary.construction.for.a.similar-sized.wing,.up.to.20%.saving.in.weight.is.theoretically.possible.[61].

This.patented.new.concept.is.the.product.of.collaboration.between.GTM.Advanced.Structures,.Alcoa,.and.the.Faculty.of.Aerospace.Engineering.of.Delft.University.of.Technology..The.USAF,.Alcoa.and.GTM.are.reportedly.talking.about.creating.“carefree.structures”.with.the.CentrAl.concept..An.aircraft.built.out.of.these.structures.is.expected.to.be.less.sensitive.to.damage.from.fatigue.or.external.impacts..Carefree.aircraft.constructions.will.also.be.characterized.by.significantly.reduced.maintenance.costs.[65].

Alcoa.plans.to.develop.enhanced.applications.of.advanced.hybrid.materials.for.wings.and.fuselages..Such.aerostructures.have.the.potential. to.offer.more.than.10%.reduction. in.the.empty.weight.of.commercial-class.air.transports..The.intrinsic.advantage.here.is.the.advances.in.both.aluminium.alloy.products.and.high.performing.fibres.could.produce.new.laminate.compositions.tailored.to.the.specific.requirements.of.each.part.[61].

A.1.1.3.5 Advanced CompositesA.composite.material.consists.of. two.or.more.distinct.materials. in. the. form.of. fibre.and.matrix..Fibres.are. the.dispersed.reinforcement.that.bears.the.majority.of.stress,.and.the.matrix.is.the.continuous.material.surrounding.these.fibres..Depending.on.what.the.matrix.material. is,.man-made.composites.are.classified. into.polymer.matrix.composites.(PMCs),.metal.matrix.composites.(MMCs),.and.ceramic.matrix.composites.(CMCs)..Such.synthetic.composites.are.made.from.adding.reinforcement.fibres. into. polymer,.metal,. or. ceramic.matrices.. PMC,. sometimes. referred. to. as. fibre. reinforced. polymer. (FRP),. can. be.further.categorized.in.accordance.to.its.method.of.fibre.reinforcement:.carbon-fibre.reinforced.polymer.(CFRP),.glass-fibre.reinforced.polymer.(GFRP),.and.aramid-fibre.(Kevlar).reinforced.polymer.(AFRP).

Figure.A.1.1-.17:.Cross.section.of.various.laminar.structures.of.CentrAl.[62]

Figure.A.1.1-.18:.Glare.construction.for.upper.fuselage.skin.of.modern.commercial.jet.[64]

Single side reinforcement

8.mm.aluminium

Glare..1-5/4-0.4

Glare..1-5/4-0.4

4.mm.aluminium 4.mm.aluminium

adhesive.FM.94.Kadhesive.FM.94.K

Center reinforcement


Numerous.secondary.structures.and.empennage.components.have.been.made.out.of.composites.over.the.last.30.years..It.has.been.difficult,.however,.to.ascertain.whether.or.not.an.adequate.level.of.risk.reduction.has.been.achieved.economically.to.fabricate.larger.primary.structures,.such.as.wings.or.fuselages,.in.composites..Because.both.the.wing.and.the.fuselage.typically.account.for.approximately.two-thirds.of.an.airframe’s.weight,.the.associated.20%.savings.in.vehicle.weight.should.result. in. greater. operating. economies. [66]..Most. recently,. the.Boeing. 787. has. been. rolled. out. as. the. first. commercial,.mid-size.aircraft.with.composite.primary.structures. (Figure.A.1.1-.20)..The.Airbus.A350. is.also.known. to.be.more. than.50%-composite.in.its.make-up..Depending.on.the.commercial.success.of.these.latest.models,.the.inherently.higher.technical.and.monetary. risks.associated.with.developing.and.certifying.an.all-composite.wing.or. fuselage.could.be. justified..More.revolutionary.airframe.concepts.like.the.blended.wing.body.would.require.an.all-composite.airframe.due.to.the.unusually.large.secondary.bending.forces.during.cabin.pressurization,.which.would.render.conventional.aluminium.skin.and.stringer.designs.unusable.[66].

A.1.1.4 Non-propulsion SystemsA.number.of.new.technologies.have.been.developed.in.the.area.of.aircraft.onboard.systems,.which.aim.to.reduce.mainly.the.aircraft’s.energy.consumption.or.support.weight.reduction..Several.of.them.are.detailed.in.the.following.sections..Further,.several.of.these.technologies.are.specifically.designed.to.be.retrofitable.onto.the.existing.fleet.of.commercial.aircraft.while.providing.the.majority.of.their.benefits.

A.1.1.5.1 Zonal DryerThe.purpose.of.the.zonal.dryer.is.to.provide.a.capability.to.remove.moisture.from.the.cabin.crown.and.sidewall.insulation..This.is.achieved.by.pumping.dry.air.through.the.crown.and.sidewall.space..Additionally,.some.of.the.moist.return.is.heated.and.passed.through.the.cabin,.raising.the.cabin.humidity.and.passenger.comfort.[69]..The.result.is.that.the.aircraft.operating.weight.can.be.reduced.by.up.to.½.ton.[69]..

Figure.A.1.1-.19:.Percentage.of.composite.components.in.commercial.aircraft.[67]

Figure.A.1.1-.20:.Materials.breakdown.for.modern.commercial.transports:.Boeing.787.(above).[67],.Airbus.A350.(below).[68]

Carbon.laminate

Carbon.sandwich

Fiberglass

Aluminium

Aluminium/steel/titanium

20..ANNEx.1

One.zonal.dryer.concept,.the.Zonal.Drying™.System.has.been.chosen.by.Boeing.for.inclusion.as.standard.equipment.on.the.B787..The.technology.is.also.available.for.retrofit.or.as.a.build.to.order.option.on.the.B737NG.and.other.aircraft.models.[70]..The.additional.of.a.zonal.dryer.adds.between.18.and.80.kg.(CRJ.and.747).to.the.weight.of.the.aircraft,.and.has.the.potential.to.reduce.the.amount.of.trapped.moisture.by.approximately.10.times.that.amount.[69,.70,.71]..Air.New.Zealand,.which.has.committed.to.install.the.system.on.its.fleet,.anticipates.a.saving.of.approximately.500,000.gallons.of.fuel.a.year.across.its.fleet.of.42.aircraft.[71].

A.1.1.5.2 Landing Gear DriveElectric.landing-gear.drive.is.a.potential.system.add-on,.either.for.retrofit.or.new.aircraft.development,.which.is.designed.to.provide.taxi.capability.without.the.use.of.the.primary.aircraft.power.plant..Most.of.the.concepts.are.devised.around.the.addition.of.a.motor.or.series.of.motors.to.either.the.nose.or.main.landing.gear..One.such.implementation.is.the.WheelTug®.system,.which.uses.a.series.of.hub.mounted.motors.on.the.nose.landing.gear.of.existing.aircraft.[72]..This.configuration.is.shown.in.Figure.A.1.1-.22..WheelTug.has.several.partners.including.Delta.Air.Lines,.and.hopes.to.certify.its.drive.sometime.in.2009.[73]..Additional.landing.gear.drive.programs.have.been.examined.by.both.major.airframe.OEMs.with.Airbus.investigating.the.viability.of.an.electric.drive.system.for.the.A320.in.2008.[74]..

WheelTug.estimates.that.its.system.could.save.a.significant.amount.of.fuel.during.the.taxi.portion.of.the.ground.operation..It.estimates.that.for.a.Boeing.737-800.the.saving.could.be.between.13.and.21.pounds.of.fuel.per.minute.as.only.the.APU.is. required. for. the. operation. of. the.WheelTug. system. [72].. Actual. fuel. burn. savings.will. depend. on. aircraft. and. engine.combinations,.plus.specific.operating.procedures.and.duty.cycles.that.vary.between.airlines..

A.1.1.5.3 Flight Control SystemFly-by-WireState-of-the-art.digital.technology.enables.complex.fly-by-wire.(FBW).systems.that.combine.flight.management,.navigation,.guidance,.control,.sub-system.health.monitoring,.and.maintenance.indications..Furthermore,.special.features,.such.as.collision.detection.or.remote.controlling.in.the.event.of.a.terrorist.take-over.can.be.designed.to.assist.pilots.in.the.event.of.such.near.catastrophic.events..Since.the.aviation.sector.has.now.fully.embraced.FBW,.most.of.the.challenges.originate.from.the.high.development.costs..The.verification.and.validation.of.the.flight.control.system.(FCS).software,.for.instance,.is.an.expensive.undertaking.

The.trend.toward.increasingly.demanding.design.goals.(e.g.,.range,.payload,.reliability,.safety,.noise,.emissions).of.commercial.air-vehicles.would.require.a.FCS.that.is.fully.integrated.with.every.digitally.manageable.aspect.of.the.control.system..Although.such.intelligent.and.adaptive.flight.control.techniques.are.currently.pursued.only.by.military.aviation,.their.eventual.crossover.to.civil.aviation.is.expected.to.yield.the.same.types.of.anticipated.benefits.[44].

Figure.A.1.1-.22:.WheelTug®.motor.configuration.[72]Figure.A.1.1-.21:.Zonal.Drying™.system.blower.[69]


Fly-by-LightFly-by-light.(FBL).control.systems.are.different.from.their.FBW.counterparts.in.that.they.use.fibre-optic.links.instead.of.wires.to.transmit.data.from.the.flight.control.computers.to.the.actuator.controller..Fibre-optic.systems.are.capable.of.transmitting.multiple.channels.of.bidirectional.information.with.lighter.hardware,.are.intrinsically.immune.to.electromagnetic.interference,.and.possess. a. broader. transmission. spectrum.. The. FBL. system. transmits. a. redundant. signal,.which. requires. a. second.wire.bindle. in. a. traditional. FBW.system. [75]..Despite. the. fact. that. fibre-optics. technology.has.extensive. applications. in.communications,.it.has.not.yet.seen.significant.applications.in.civil.aviation.due.to.integration,.validation,.reliability,.and.cost.factors..Several.of.the.latest.fighter.aircraft,.including.the.Eurofighter.Typhoon,.uses.a.fibre-optic.control.link,.and.Gulfstream.recently. flight-tested.a.FBL-version.of. the.G650. [75].. The.German.DLR.operates. the. first. and.only. fly-by-light. research.helicopter.

Wireless Flight ControlIn.1997,.ground-based.feasibility.tests.for.a.novel.wireless.flight.control.system.(WFCS).were.performed.at.NASA’s.Dryden.Flight.Research.Center.[76]..This.test.demonstrated.that.it.was.feasible.successfully.to.control.the.aileron.on.the.F-18.Iron.Bird. (a. retired.F-18.airframe). via.wireless.means.. The. implementation.of. carrier. suppression.and.code.diversity.multiple.access.(CDMA).techniques.were.also.planned..Nevertheless,.a.WFCS.in.operation.would.be.susceptible.to.active.accidental.radio-frequency.interference..The.aim.of.the.ground-based.tests.was.to.accumulate.enough.insights.and.data.to.develop.a.closed-loop.WFCS.that.could.be.utilized.as.either.a.redundant,.back-up.of.the.primary.wired.system.to.provide.enhanced.safety.and. reliability.or.a. replacement.of. the.wired.system. in.order. to.decrease. the.size,.weight,.and.cost.of. the.control.sub-systems.[77].

Active StabilityFor.a.conventional.aircraft.in.trimmed.flight,.the.horizontal.tail.produces.a.down-force..Thus,.flying.with.an.aft.centre.of.gravity.(CG).can.help.to.minimize.trim.drag..This.can.be.achieved.for.example.by.moving.heavy.equipment.to.the.back.of.the.aircraft,.managing.the.passenger.seating.configuration.or.by.developing.fuel.burn.sequences.between.fuel.tanks.[78,.79]..Controlling.the.position.of.CG.in.flight.is.possible.by.pumping.fuel.into.special.trim.tanks.in.the.aft.of.the.aircraft..This.is.done.for.example.on.the.Airbus.A330.and.A340.aircraft..Table.A.1.1.-.1.shows.the.increase/decrease.in.specific.range.(SR).for.a.flight.with.more.rearward/forward.centre.of.gravity.than.with.the.reference.CG..The.data.is.given.for.optimum.altitude.

Table.A.1.1.-.1:.Change.in.Specific.Range.(SR).with.Shifting.Centre.of.Gravity.(CG).[80]

Aircraft Type Reference CG Aft CG Fwd CG SR for Aft CG SR for Fwd CG

A300-600 27% 35% 20% +1.7% -0.9%

A310 27% 35% 20% +1.8% -1.8%

A330 28% 37% 20% +0.5% -1.3%

A340 28% 37% 20% +0.6% -0.9%

Instead.of.shifting.payload.or.fuel.a.future.approach.to.reduce.CO2.emissions.could.be.the.operation.with.reduced.stability.or.even.unstable.as.done.in.military.aviation..However.this.implies.a.substantial.effort.both.in.developing.new.flight.control.architectures.and.corresponding.aircraft.layout.and.adapting.certification.regulations.

A.1.1.5.4 More Electric Aircraft ArchitectureThe.growing.worldwide.demand.for. increased.efficiency,.safety.and.comfort. in.air. transport. in.the.past. few.decades.has.steadily.driven.the.requirements.toward.higher.payload.capacities.and.non-propulsive.power.loads..Confronted.with.such.an. ever-increasing. need. for. non-propulsive. loads,. the. conventional. aircraft. equipment. system. (AES). is. approaching. its.performance. limits. in. terms.of. the. individual.component-level.efficiencies.and,.more. importantly,. in. its. layout. for.airframe/engine.integration..Future.commercial.fleets.will.have.more.demanding.technical.loads.(fuel.and.hydraulic.pumps,.avionics,.flight.control.actuators,.environmental.control.system,.etc.)..The.boom.in.consumer.electronics,.coupled.with.increased.flight.durations,.has.also.resulted.in.an.increase.in.commercial.loads.(i.e..in-flight.comfort.and.entertainment.systems).[81]..For.example,.the.electric.power.demand.on.the.Boeing.787.is.nearly.1.MW,.which.is.twice.as.much.as.that.of.the.Boeing.777.[82]..Therefore,.there.is.pressure.for.the.airlines.to.be.able.to.cope.more.efficiently.with.the.increased.number,.capacity,.and.complexity.of.energy-consuming.systems.on.board.an.aircraft;.improve.the.comfort,.health,.and.safety.of.the.passengers;.and.mitigate.the.global.impact.of.aviation.on.the.environment..The.key.challenge.is.to.be.able.to.provide.all.of.this.at.a.lower.cost.than.before..The.European.Union.has.initiated.the.Power.Optimized.Aircraft.(POA).programme.[76]..The.main.objective.of.POA.is.to.identify,.optimize,.and.validate.the.next.generation.aircraft.equipment.systems.for.the.reduction.in.the.consumption.of.non-propulsive.loads.[83]..

22..ANNEx.1

‘Integration’.means.the.physical,.functional,.and.requirements.integration.of.key.propulsion.and.power.system.components,.an.act.that.combines.them.into.fewer,.multifunctional.units.tied.together.to.the.more.electric.aircraft.(MEA).architecture.[44]..Key.components.and.functions.include.engine.starting,.electrical.power.generation,.power.conditioning.and.routing,.air.cycle.environment.control,.avionics,. fuel/oil.cooling,.ventilation,. flight.control.actuation,.and.overall. vehicle.&.propulsion.system.thermal.management.-.especially.waste.heat.recovery.and/or.rejection.

The.traditional.evolution.cycle.of.an.aircraft.equipment.system.has.been.one.of.incremental.improvements,.with.little.regards.for. the.effect.a.particular.component.or.sub-system.improvement.may.have.on.the.entire.aircraft..Such.practices.are.the.legacy.of.supply.chain.driven.infrastructure,.in.which.suppliers.individually.design,.develop,.and.validate.the.products.based.on.component-level.specifications..Therefore,.a.new.modelling.and.simulation.capability. is.necessary.so. that.a.variety.of.analysis. tools. can.be.used.within. a. top-level. design. framework. to. justify. the. system-level. benefits. of. a.given. integrated.component..It.would.be.worth.conducting.a.study.to.evaluate.how.much.functionality.is.gained.at.what.levels.of.weight.and/or.cost.penalties..Both.industry.and.academia.are.actively.pursuing.research.into.state-of-the-art.multidisciplinary.modelling.and.simulation.methodologies.[84]..More.comprehensive.approaches.will.eventually.necessitate.a.hardware-in-the-loop.rig,.including.one.for.the.propulsion.system,.for.tests.and.validation.purposes.[44].

The.growth.of.new.MEA.loads.is.being.driven.by.advances.in.the.capabilities.of.electric.actuators.and.controls,.and.it. is.being.enabled.by.the.development.of.advanced.aircraft.power.generators..Due.to.the.extent.that.systems.integration.has.been. emphasized. in. EOASys,. airframe.manufacturers,. such. as.Boeing. and.Airbus,. are. likely. to. play. a.major. role. in. the.development.of.future.energy.optimized.aircraft..The.MEA.concept.has.been.implemented.for.the.first.time.in.the.Boeing.787.with.the.elimination.of.the.engine-fed.bleed.air.system..In.the.“No-Bleed”.architecture,.the.pneumatic.aircraft.systems,.namely.engine. starting,.wing.de-icing,. landing.gear.deployment. system,. secondary. flight. control. actuators,. cabin.pressurization,.environmental.control,.and.braking.systems.will.be.replaced.by.electrically.powered.machines.for.the.first.time.in.civil.aviation..Research.is.ongoing.to.obtain.the.weight.savings.benefits.of.a.full.more.electric.architecture.implementation.[85].

A.1.1.5.5 Auxiliary Power UnitsMore Efficient Gas Turbine APUWith.the.advent.of.the.power/energy.optimized.and.more.electric.aircraft.paradigm,.there.is.also.the.opportunity.to.move.away.from.turbine-based.APUs..This.may.be.in.the.form.of.re-designing.future.APUs.without.the.compromises.necessary.to.extract.both.pneumatic.and.electrical/mechanical.power..It.is.also.entirely.possible.that.a.shift.away.from.turbine.based.APUs.will.occur..For.instance,.a.transition.to.fuel.cells,.with.which.Airbus.recently.completed.flight.trials.[86],.makes.sense.when.considering.the.intertwined.goals.of.fuel.burn.reduction.and.environmental.performance..More.exotic,.hybrid.power.systems.that.include.solar.and.wind.power.may.become.viable.one.day.for.smaller.air-vehicles..As.newer.power.technologies.mature,.it.may.become.worthwhile.for.the.APU.to.power.all.non-propulsive.loads.throughout.the.entire.flight,.further.off-loading.the.burden.on.the.primary.propulsion.system.and.thus.leading.to.additional.reduction.in.fuel.burn.and.emissions.

Fuel Cell Type Operating Temp. (ºC) Premier Applications

Alkaline

Proton ExchangeMembrane

Direct Methanol

Phosphoric Acid

Molten Carbonate

SpaceMilitary

Transportation

90 - 100

30 - 100

150 - 220

Portable20 - 90

Stationary

Stationary600 - 700

Solid Oxide StationaryTransportation

500 - 1100

Fuel Cell Type Operating Temp. (ºC) Premier Applications

Alkaline

Proton ExchangeMembrane

Direct Methanol

Phosphoric Acid

Molten Carbonate

SpaceMilitary

Transportation

90 - 100

30 - 100

150 - 220

Portable20 - 90

Stationary

Stationary600 - 700

Solid Oxide StationaryTransportation

500 - 1100

Figure.A.1.1-.23:.Classification.of.fuel.cell.technologies


A.1.1.5.6 Fuel CellsA.fuel.cell.is.a.variant.of.galvanic.cells,.which.directly.convert.chemical.energy.into.electricity.via.an.electrochemical.reaction.[87]..The.typical.base.reactants.are.hydrogen.(reductant).as.the.fuel,.which.is.either.carried.on.board.in.pure.form.(liquid.or.pressurised).or.taken.from.hydrogen-containing.fuels.such.as.hydrocarbons.or.methanol,.and.oxygen.(oxidant).from.the.air,.and.the.sole.product.from.this.redox.reaction.is.pure.water..Components.that.are.required.to.integrate.individual.cells.into.a.fuel.cell.system.or.a.stack.include:.flow.fields.for.the.reactant.streams,.current.collectors,.at.least.one.electrolyte.and.two.electrodes.to.support.the.redox.half-cell.reactions,.and.bipolar.plates.or.interconnects..Fuel.cells.are.classified.according.to.their.electrolyte.types..Some.of.the.more.common.types.of.fuel.cells.are.listed.in.Figure.A.1.1.-.23,.along.with.their.range.of.operating.conditions.and.premier.applications.

The.rate.at.which.fuel.cell.technology.has.advanced.during.its.relatively.short.history.has.been.remarkable..In.the.1990s,.a.seven-fold.increase.in.specific.power.(power-to-weight.ratio).was.reported.in.five.years.[88],.a.feat.that.required.almost.50.years.for.the.developers.of.jet.engines.to.achieve.[89]..Such.a.high.rate.of.demonstrated.growth.forms.an.encouraging.basis.for.considering.the.aeronautical.applications.of.the.technology,.as.it.implies.that.certain.types.of.fuel.cells.may.be.applicable.for.aviation..This.foresight.is.depicted.in.Figure.A.1.1-.24,.which.is.a.version.of.the.chart.found.in.Ref..90..Both.cleanness.and.high.conversion.efficiency.are.the.two.intrinsic.technological.characteristics.that.are.anticipated.to.bring.about.“greener.skies,”.[91].as.well.as.the.expansion.of.aviation.mission.space.and.vehicle.systems.space.

Figure.A.1.1-.24:.Envisioned.aviation.applications..of.fuel.cell.technology

24..ANNEx.1

Proton Exchange Membrane Fuel CellsProton.exchange.membrane.or.polymer.electrolyte.membrane. fuel.cells.are.considered. to.be. the. leading. technology. for.future.vehicular.applications.[92]..The.name.is.derived.from.the.fact.that.its.polymer.electrolyte.conducts.hydrogen.cations,.or.protons,.from.the.cathode.(positive.electrode).to.the.anode.(negative.electrode)..

At.present,.proton.exchange.membrane.fuel.cells.(PEMFCs).are.arguably.the.most.technologically.mature.among.all.fuel.cells,.but.this.has.not.always.been.the.case..Ballard.Power.Systems.[93].is.principally.responsible.for.resurrecting.the.technology.in.the.1980s..Prior.to.1984,.PEMFCs.had.lost.out.in.favour.of.Alkali.Fuel.Cells.(AFC).for.the.Apollo.missions,.despite.the.fact. that. it.was. the. first.operational. fuel.cell. technology. to.be.used.on.board.a.manned.spacecraft. -. the.Gemini.3. [94]..Substantial.investment.in.the.technology.over.the.past.decade.has.allowed.many.improvements.to.be.made.in.enhancing.the.performance.(Figure.A.1.1-.25).and.cost.characteristics.of.PEMFCs.

A.comprehensive.survey.of.high-profile.demonstration.programmes.in.the.U.S..[95],.Europe.[96,97],.and.Japan.[98].reveals.that.all.prototype.automobiles.and.buses.employed.proton.exchange.membrane.fuel.cells.(PEMFCs).as.their.power.plants..The.popularity.of.PEMFCs.is.generally.credited.to.the.following.attributes,.which.make.the.technology.especially.suitable.for.vehicular.applications:.compactness,.i.e.,.high.specific.power.and.volumetric.density.(power-to-volume.ratio);.fast.start-up.time;.high.durability;.and.low.temperature.operation..

The. same. attributes. have. also. motivated. various. organizations. within. the. aviation. sector. to. pursue. proof-of-concept.programmes.for.PEMFC.powered.aircraft..The.first.manned.fuel.cell.powered.flight.occurred.on.February.26th,.2008.[99]..Therefore,. the.current.status. regarding.PEMFC.powered. flight.can.be.assigned.a.TRL.of.3,.as. the. flight. tests.are.being.conducted.on.limited.bases.to.assess.the.applicability.and.feasibility.of.the.technology..During.2007.and.2008.Airbus.and.DLR.tested.a.20kW.PEMFC.system.installed.in.the.cargo.bay.of.DLR’s.A320.research.aircraft..Starting.in.2008.flight.tests.demonstrated.compatibility.with. the.aircraft.electrical.system,.and.the.ability.of. the. fuel.cell. to.operate.under.normal.and.adverse.flight.conditions.[100].

Nevertheless,.the.same.challenges.responsible.for.the.downfall.of.the.technology.in.the.late.1960s.still.persist.today..Water.management,.which.has.a.direct.influence.on.cell.performance.and.efficiency,.is.important;.the.need.for.platinum.as.a.catalyst.is.still.a.cost-driver,.and.hydrogen.of.very.high.purity.is.required.to.prevent.poisoning.by.carbon.monoxide.of.the.membrane..Furthermore,. driving.down. the.weight. and. volume.of. the. ancillary. equipment. (balance.of. plant,. power.management. and.distribution.system,.etc.).associated.with.making.a.fuel.cell.stack.operational.is.a.top.priority.to.ensure.the.long-term.feasibility.of.the.technology.in.the.aerospace.domain.

Figure.A.1.1-.25:.Past.and.projected.evolution.of.proton-exchange.membrane.fuel.cell.technology


Solid Oxide Fuel CellsA.solid.oxide.fuel.cell.(SOFC).is.a.high-temperature,.anionic.fuel.cell,.whose.electrolyte.conducts.anions.(oxygen.ions).from.the.cathode.to.the.anode..Although.SOFCs.operate.in.temperature.regions.that.approach.1100.oC,.the.electrolyte.made.out.of.oxide. ion-conducting.ceramic.materials.remains. in.solid.state.[101]..The.resulting.mechanical.simplicity.allows.the.shaping.of.SOFCs.into.different.geometric.configurations,.such.as.tubes,.planes,.and.monoliths..Recent.advances.in.lower,.intermediate.temperature.SOFCs.[102],.as.well.as.planar.SOFC.stack.designs,.have.made.it.possible.for.the.applications.of.SOFC.systems.to.be.realized.on.a.much.smaller.scale.than.previously.thought.practical;.for.instance,.as.an.auxiliary.power.source.on.ground.vehicles.[103].

There.are.a.number.of.compelling.reasons.to.examine.the.aeronautical.potential.of.SOFCs..Above.all,.the.higher.operating.temperature.ranges.of.SOFCs.enable.them.to.have.much.higher.electrochemical.efficiencies.than.PEMFCs..High-temperature.operation.also.allows.a.meaningful.synergy.with.bottoming.cycles,.such.as.those.of.gas.turbine.(GT).engines,.in.improving.the.overall.system.efficiency..Furthermore,.SOFCs.are.inherently.fuel-flexible,.unlike.the.PEMFCs.that.require.pure.hydrogen,.as.these.solid-state.cells.are.quite.tolerant.of.CO.and.CO2..Therefore,.an.aeronautical.SOFC.system.could.utilize.ordinary.hydrocarbon.fuels.that.are.commonly.in.use.today,.such.as.Jet.A,.without.the.logistical,.infrastructural,.or.storage.concerns.that.are.associated.with.using.hydrogen.as.a.new.aviation.fuel..This.is.an.additional.advantage.from.a.vehicle-level.perspective,.as.hydrogen,.even.in.its.liquid.state,.is.not.as.volumetrically.energy-dense.as.most.liquid.hydrocarbon.fuels.

The.hybrid.nature.of.the.system.is.shown.by.the.bottoming.cycle.with.the.gas.turbine..The.hot.exit.stream.out.of.the.SOFC.stack.is.further.combusted.to.serve.three.purposes:.to.match.the.air.temperature.to.that.of.the.stack.temperature.prior.to.the.oxidant.stream’s.insertion.into.the.cathode;.to.generate.the.steam.required.for.the.reformer.from.liquid.water;.and.finally.to.drive.the.radial.turbine,.which,.in.turn,.drives.the.centrifugal.compressor.for.air.delivery.and.stack.pressurization.

For.the.shown.architecture,.researchers.at.NASA.Glenn.Research.Center.(GRC).have.developed.a.variety.of.performance.analysis.and.sizing.models..Freeh.et.al.[104].developed.a.parametric,.bulk.SOFC.voltage.model.from.first.electrochemical.principles..Tornabene.et.al.. [105].developed.parametric.weight.and.volume.models.for.all.of.the.sub-system.components.such. as. interconnecting. piping. and. tubing,. hot. box. assemblies,. and. a. starter/generator.. Together,. these. models. were.subsequently.applied.to.the.design.of.a.large,.commercial.transport.class.SOFC/GT.hybrid.auxiliary.power.unit.(APU)..Both.packaging.[106].and.off-design.analysis.[107].results.have.been.reported..Most.recently,.a.modified.version.of.the.simulation.environment.was.used.to.assess. the.applicability.of. the.same.hybrid.architecture. for.high-altitude. [108].and. low-altitude.[109].UAV.applications..The.latter.study.also.included.models.based.on.Ref..110.for.state-of-the-art.performance,.as.well.as.data.from.Ref..111.and.112.to.simulate.catalytic.partial.oxidation.and.direct.internal.reformation,.respectively.

Additionally,.Boeing.performed.a.2005.study.that.assumes.that.the.technology.will.reach.a.TRL.of.6.by.2010.[113]..Another.Boeing.study,.shown.in.Figure.A.1.1-.26.estimates.that.significant.savings.in.fuel.burn.could.be.achieved.if.the.conventional.turbine-powered.APU.on.a.300.passenger-class.transport.were.to.be.replaced.by.an.SOFC/GT.hybrid.APU.[114]..However,.no.active.commercialisation.activities.have.been.undertaken. for. an.aeronautical.SOFC.system,.whereas. the.commercial.viability.of.SOFC.technology.in.other.sectors.is.being.developed.by.organisations.such.as.the.Solid.State.Energy.Conversion.Alliance. (SECA)..See. the.homepage.of.SECA. for. information.on. the. latest.developments. in. the. technology’s.stationary,.military,.and.vehicular.applications.[115].

Many. technical.challenges.still. remain.before.SOFCs.can.become. feasible. for. transport.applications..These. include. low.specific.power;.less.robustness.to.frequent.start.and.stop.cycles,.which.is.critical.for.vehicular.operations;.additional.ancillary.equipment.needed.to.manage.the.complex.fluidic.and.thermodynamic.interactions.between.the.sub-system.components;.the.need.for.hot.boxes,.namely.extra.layers.of.insulation.to.protect.the.environment.around.the.high.temperature.components;.material.concerns.such.as.susceptibility.to.fatigue,.thermal.expansion,.etc.

Figure.A.1.1-.26:.Estimated.fuel.savings.from.solid.oxide.fuel.cell./.gas.turbine.hybrid.auxiliary.power.unit.[114]

26..ANNEx.1

Solid Acid Fuel CellsThe.solid.acid.fuel.cell.(SAFC).is.a.relatively.recent.development.in.modern.fuel.cells.that.might.challenge.the.dominance.of.PEMFCs.in.the.automotive.sector..Pioneered.by.a.research.group.from.the.California.Institute.of.Technology.[116],.SAFC.technology.is.now.exclusively.marketed.by.Superprotonic.[117].

As.the.name.implies,.the.SAFC.uses.solid.acid-based.materials.as.its.electrolyte..Superprotonic’s.SAFCs.specifically.exploit.the.reorienting.properties.of.caesium.hydrogen.sulphate.at.elevated.temperatures.to.conduct.protons..Such.a.mechanism.of.proton.transfer.from.one.sulphate.tetrahedron.to.another.[118],.reportedly.results.in.conductivity.ranges.comparable.to.those.of.state-of-the-art.polymer.electrolytes.used.in.leading.PEMFCs.

Compared.to.either.PEMFCs.or.SOFCs,.SAFCs.offer.several.technological.advantages.when.applied.for.aeronautical.purposes..First,.a.nominal.operating.pressure.of.1.atmosphere. (ambient.pressure.at.ground. level).would.still. require.pressurization.during.flight,.but.the.resulting.parasitic.losses.at.high.altitudes.would.be.more.manageable..Its.band.of.operating.temperature.(between.100.and.300.oC).is.significantly.narrower.than.that.of.SOFCs.to.eliminate.the.need.for.hot.boxes..Such.intermediate.temperature.conditions,.combined.with.SAFC’s.unique.method.of.proton.conduction,.are.touted.as.enabling.simpler.BOP.design.related.to.the.water.and.thermal.management.aspects.of.PEMFC-based.systems..All.of.the.aforementioned.factors.are.claimed.to.result.in.savings.in.hardware.weight.and.volume,.as.well.as.enhancing.the.economical.advantages.of.an.SAFC-based.system.to.the.point.of.being.competitive.with.internal.combustion.engines.

A.1.1.4 Innovative Aircraft ConfigurationsThe.current.design.paradigm.for.subsonic.commercial.transports,.a.cylindrical.fuselage.with.swept.wings.and.podded.engine.nacelles,.stems.from.developments.made.during.and.shortly.after.the.Second.World.War..The.early.stages.of.this.design.paradigm.are.evident.in.Boeing’s.medium.and.heavy.strategic.bombers,.the.B47,.and.B52..While.the.arrival.of.the.British.DeHavilland.Comet.series.initiated.the.era.of.commercial.jet.travel,.it.was.not.until.the.arrival.of.the.Boeing.707.,.Douglas.DC-8,.and.their.competitors.that.signalled.the.adoption.of.the.modern.paradigm..Since.then,.there.have.been.two.fundamental.design.paradigms.regarding.commercial.transports:.those.that.use.engines.mounted.under.the.wing;.and.those.continuing.the.legacy.of.the.Sud.Aviation.Caravelle,.with.the.aft.fuselage-mounted.engines.

These. basic. configurations. have. served. the. aviation. industry.well,. achieving. significant. improvements. in. the. overall. fuel.efficiency. and.operating. costs. through. successive. generations..However,. there. are. several. potential. new.concepts. that.may.offer.another,.potentially.faster.path.to. improved.fuel.efficiency..Three.of.these.wing-body.concepts.are. listed.in.this.section..Two.of.those.ideas.offer.the.possibility.of.significantly.reduced.aerodynamic.drag.(Hybrid/Blended.Wing.Body.and.Truss-Based.Wing),.whereas.the.third.(Cruise.Efficient.Short.Take-Off.and.Landing).option.offers.the.potential.to.change.substantially.the.operating.paradigm,.in.addition.to.providing.direct.fuel.burn.improvements.

A.1.1.4.1 Hybrid-Wing-BodyThe.hybrid.or.blended.wing.body.(BWB).concept.originated.at.McDonnell.Douglas. in.the. late.1990s.in.response.to.the.question.posed.by.NASA’s.Dennis.Bushnell,.“renaissance.for.the.long-haul.transport?”.[119].Initial.iterations.of.McDonnell.Douglas’.and.the.Boeing.Company’s.BWB.designs.indicated.a.25%.reduction.in.per-seat.fuel.burn.over.an.800.passenger-conventional,.tube-and-wing.configuration.[120,.121].

Figure.A.1.1-.27:.NASA.blended.wing.body.rendering.[122]


Subsequent.studies.have. focused.on.aircraft.concepts. ranging. from.200.to.600.passengers..The.most. recently.studied.concept,.which.is.funded.under.NASA’s.N+2.Subsonic.Fixed.Wing.program,.is.a.300-passenger.replacement.for.the.Boeing.777..NASA.design.efforts. indicate.that. the.BWB.configuration.alone.produces.a.10%.fuel.burn.saving.comparable.to.a.B777-200ER.with.GE90.engines.on.a.7,000.nautical.mile.mission.carrying.a.full.passenger.load..The.aerodynamic.benefits.are.larger.for.very.big.BWB.aircraft..However,.an.800+.seat.BWB.has.a.wingspan.of.90.to.100.metres..This.is.incompatible.with.today’s.airport.compatibility.rules,.which.limit.aircraft.size.to.80.metres.length.by.80.metres.span..The.BWB.shape.that.is.totally.different.from.today’s.aircraft.also.generates.a.number.of.other.airport.operations.issues.that.need.to.be.solved..Another.main.unsolved.issue.is.pressurisation.of.a.big.lens-shaped.cabin.

A.significant.amount.of.research.has.been.performed.in.this.area.by.Boeing..The.Silent.Aircraft.Initiative.is.a.venture.between.the.University.of.Cambridge.and.the.Massachusetts.Institute.of.Technology,.and.within.the.European.research.projects.VELA.and.NACRE.

The.current.generation.of.the.Silent.Aircraft.Initiative,.the.SAx-40,.has.focused.on.developing.an.aircraft.configuration.that.would.provide.a.20%.reduction.in.fuel.burn).over.current.generation.commercial.transports,.and.limit.the.perceptual.noise,.commonly.taken.to.include.a.Day-Night.Noise.Level.greater.than.55dB,.to.within.the.perimeter.of.a.typical.international.airport.[123]..

While.the.BWB.appears.attractive.on.paper,.the.technology.is.relatively.immature..Thus.far,.only.subscale.demonstrators,.including.the.Boeing.x-48,.have.been.flight-tested.[124]..Significant.design,.maintenance,.and.airport.compatibility.issues.must.be.addressed,.all.of.which.may.delay.the.commercialization.of.the.BWB.to.beyond.the.2020.timeframe..Nevertheless,.the.U.S..military.has.expressed.interest.in.the.concept.as.either.a.transport.aircraft.or.an.aerial.refuelling.tanker.[125].and.NASA.and.other.organizations.are.continuing.the.technology.risk.reduction.programme.

A.1.1.4.2 Cruise-Efficient Short Take-off and LandingThe.Cruise-Efficient.Short.Take-off.and.Landing.(CESTOL).concept.was.devised.to.provide.a.capability.to.perform.missions.of.around.1000.NM,.similar.to.the.majority.of.flights.performed.today.by.the.Boeing.737.and.Airbus.A320.families.of.aircraft,.while.operating.from.smaller.regional.and.“metroplex”.(city).airports..These.have.stringent.demands.for.low.noise.and.short.and/or.steep.climb.and.descent.requirements.[126].

The.CESTOL.is.a.response.to.NASA’s.Horizon.Missions.Methodology.(HMM).[127]..Under.the.HMM,.it.is.envisaged.that.there.will.be.a.shift.in.airline.network.structures.toward.a.more.distributed.framework.[128]..This.would.decrease.the.average.number.of.passengers.carried.on.an.individual.flight..Moreover,.these.passengers.would.desire.to.operate.out.of.local.airports.closer.to.home,.which.are.often.not.equipped.with.runways.or.facilities.capable.of.handling.larger.aircraft..A.CESTOL.aircraft,.on.the.other.hand,.could.operate.on.runways.as.short.as.500.metres.and.cruise.at.Mach.numbers.near.those.of.current.generation.civil.transports.[129]..

An.advantage.of.the.CESTOL.concept,.even.when.operating.in.larger.airports,.is.that.the.aircraft.would.be.able.to.operate.in.and.out.of.runways.that,.at.present,.can.only.be.used.by.small.regional.jets.and.turboprops..This.would.relieve.many.existing.airports.from.congestion,.and.thus.reduce.the.fuel.burn.associated.with.taxiing.and.holding..This.is.only.an.operational.fuel.saving,.since.a.CESTOL.aircraft’s.fuel.burn.per.passenger-km.might.be.rather.higher.than.for.current.ones..

Figure.A.1.1-.28:.Notional.cruise-efficient.short.take-off.and.landing.concept

28..ANNEx.1

A.1.1.4.3 Truss and Strut-braced WingBeginning.with.the.inception.of.the.Boeing.707,.nearly.all.modern.subsonic.transport.aircraft.bear.a.close.resemblance.to.one.another.in.their.external.configurations..Along.with.continued.investigations.on.several.revolutionary.configurations,.such.as.the.Blended.Wing.Body.and.the.Joined.Wing.[130],.the.Truss-Braced.Wing.(TBW).[131].concept.has.been.recognized.as.another.alternative.subsonic.configuration.that.could.considerably.enhance.the.aerodynamic.efficiency.of.a.conventional.take-off.and.landing.aircraft.

The.motivation.toward.the.TBW.configuration.is.grounded.on.the.well-known.relationship.between.induced.drag.and.wing.aspect. ratio.. Extensive. increases. in. the. aspect. ratio. or.wingspan.would. yield. a. considerable. reduction. in. drag,. thereby.enhancing.the.lift-to-drag.ratio.during.cruise..Nevertheless,.this.idea.is.not.likely.to.be.realized.with.conventional.cantilever.wings.due.to.weight.penalties..Wing.weight.increases.with.increasing.wing.aspect.ratio,.thus.negating.any.gains.associated.with. improved. aerodynamic. efficiency,. such. as. savings. in. fuel. weight,. from. an. aircraft. perspective.. However,. the. TBW.concept.would.allow.a.substantial. increase. in.wingspan.with. few.significant.weight.penalties,.or. in.some.cases,.savings.in.wing.weight.are.likely.[132]..Such.aerodynamic.enhancement.at.little.structural.cost.would.further.serve.to.reduce.wing.area.and.aircraft.weight.according.to.a.general.aircraft.sizing.routine..Additionally,.the.resultant.downsizing.of.the.propulsion.system.would,. in. turn,.allow.a.synergistic.reduction. in.noise.emissions. levels..A.recent.study.[133].on.Strut-Brace.Wing.configurations,.which.can.be.considered.as.a.subset.of.the.TBW,.indicates.that.an.optimized.single-strut.configuration.can.allow.a.nearly.20%.reduction.in.take-off.gross.weight.and.a.29%.reduction.in.fuel.burn.when.compared.to.a.technologically.similar.cantilever-wing.configuration.[134,135]..Such.remarkable.improvements.in.cruise.performance.would.logically.enable.nominal.reductions.in.pollutant.engine.emissions..These.benefits,.which.originate.solely.from.aerodynamic.enhancements,.would.be.further.augmented.if.appropriate.supporting.technologies.were.to.be.synergistically.integrated.into.a.working.TBW.concept..

A.TBW.configuration.designed.for.civil.transport.is.most.likely.to.have.a.very.long.wingspan,.possibly.larger.than.the.gate-box.limit.of.80.metres..This.is.why.a.folding.wing.concept,.similar.to.that.applied.to.the.Boeing.777.as.an.optional.feature,.is.considered.to.be.one.of.the.core.enablers.for.the.TBW.aircraft..Such.extremely.high.aspect.ratio.wings,.however,.are.a.cause.of.significant.unknowns.with.respect.to.the.ability.to.manufacture.and.maintain.TBWs..Further,.the.additional.weight.of.the.wing.folding.mechanism.will.reduce.and.possibility.eliminate.the.fuel.burn.benefit..There.is.ongoing.research.at.NASA.that.focuses.on.risk.reduction.related.to.the.TBW.concept.

Figure.A.1.1-.29:.Notional.truss-braced.wing.concept.[134]


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A.1.2 EngineSince.the.late.1950s,.commercial.aircraft.have.been.primarily.propelled.and.powered.by.gas.turbine.engines,.which.take.the.form.of.turbojet,.turbofan,.and.turboprop.power.plants..These.designs.have.served.aviation.well.by.achieving.significant.increases.in.efficiency.and.capability. in.the.ensuing.decades..Mechanical,.hydraulic,.electrical,.and.pneumatic.power.has.been. supplied. to. the. aircraft’s. sub-systems. either. from. the. primary. power. plant. or. from. an. engine-attached.APU.. Very.significant.improvements.in.fuel.efficiency.and.noise.and.emissions.reduction.have.been.achieved.from.the.early.jet.age.to.the.present.time.

While.the.performance.of.current.high-bypass.turbofan.engines.can.still.be.slightly.improved.at.component.level,.a.big.step.in.fuel.efficiency.is.expected.by.new.engine.architectures,.such.as.the.geared.turbofan,.the.counter-rotating.fan.and.the.open.rotor.engine.(see.Figure.A.1.2.-.1)..The.expected.improvements.in.fuel.burn.and.emissions.reduction.for.the.new.generation.of.single-aisle.aircraft.largely.rely.on.these.new.concepts..In.the.longer.term,.some.more.revolutionary.concepts.have.been.proposed.

A.1.2.1 Engine Turbo Machinery Systems ComponentsThis.section.describes.how.engine.systems.(fan,.compressor,.turbine,.combustor.and.chevron).are.expected.to.evolve.to.meet.future.aviation.requirements..It.is.expected.that.these.systems.will.adopt.newly.developed.structural.concepts.made.with.lighter.alloys.and/or.composite.materials..Furthermore,.Section.A.1.2.1.6.will.discuss.how.advanced.material.technologies.will.be.used.in.conjunction.to.the.turbo.machinery.systems..

A.1.2.1.1 FansRequirements.for. increased.thrust.and.propulsive.efficiencies.are.resulting. in.the.growing.diameter.of.ducted.fan.blades..Future.fan.sections.will.likely.require.fan.blade.materials.that.are.not.only.light,.but.also.rugged.enough.to.survive.damage.by.foreign.objects.and.erosive.elements..The.enduring.challenge.is.to.design.blades.that.deliver.improved.performance.and.are.capable.of.withstanding.the.loading.associated.with.bird.impacts.[2]..Assuming.that.a.fan.accounts.between.20.to.30%.of.the.engine.weight.[3],.composite.or.hollow.titanium.blades.are.often.mentioned.as.the.next.evolutionary.step.in.fan-blade.technology.to.reduce.weight.and.increase.structural.strength.with.low.aspect.ratio.airfoil.[4]..P&W.is.currently.investigating.the.feasibility.of.adding.composite.fan.casing.and/or.blades.to.the.Mitsubishi.Regional.Jet.version.of.the.Geared.Turbofan.[5].

Figure.A.1.2.-.1:.Considerable.gas.turbine.efficiency.improvements.are.still.possible.[1]

37..ANNEx.1

A.1.2.1.2 CompressorsEngine.performance.is.a.strong.function.of.(high-pressure).compressor.exit.temperature..Higher.allowable.temperatures.at.that.location.result.in.higher.cycle.pressure.ratios,.as.well.as.improvements.in.core.thermal.efficiency..As.with.the.fan,.titanium.has.become.a.major.enabler.of.compressor.technology..Lightweight.and.more.temperature.resistant.materials.hold.the.key.to.increasing.compressor.exit.temperatures..In.this.regard,.metal.matrix.composites.(MMCs).are.a.promising.solution,.as.shown.in.Figure.A.1.2.-.2..

MMCs.with. fibres. oriented. in. the. direction. of. the. circumference. can. also. provide. enhanced. specific. strength,.which. is.desirable.given.the.severe.centrifugal.loads.and.radial.thermal.gradient.on.the.compressor.elements..

Blisk and BlingConventional.blade/disc.systems.for.engine.compressors.are.subject.to.fretting,.and.thus.require.maintenance.at.predetermined.intervals..Part.of.the.motivation.for.introducing.the.full.bladed.disc.(blisk).rotor,.shown.in.Figure.A.1.2.-.3:.Compressor.weight.reduction.via.advanced.structural.concepts.[6],. is. to.ensure.a.full.on-condition.maintenance.operation..A.more.ambitious.design.is.the.integral.bladed.metal.matrix.rings.(blings),.which.offer.more.benefits.in.terms.of.component.weight.savings..(e.g..15%.more.compare.to.blisk.for.the.first.two.stages.[7]).and.design.flexibility.(e.g..positioning.of.the.bearings,.etc.).due.to.the.enlargement.of.the.rotor.drums.[8].

A.1.2.1.3 TurbinesTo.date,. advanced.cooling. technologies. have.been. largely. responsible. for. the. steady. increase. in. allowable. turbine. inlet.temperature. (Figure.A.1.2. -.4).. In.order. to.meet. the. turbine.entrance. temperature. target. value.of.1800.K,.however,. the.application.of.ceramic.matrix.composite.(CMC).materials.to.the.turbine.stages.is.expected..Critical.turbine.elements,.such.as.airfoils,.discs,.cases,.etc.,.made.out.of.CMCs.are.anticipated.to.further.improve.thermal.efficiency.(Figure.A.1.2.-.5).

Figure.A.1.2.-.2:.Metal.matrix.composite.for.advanced.compressor.elements

Figure.A.1.2.-.3:.Compressor.weight.reduction.via.advanced.structural.concepts.[6]

Figure.A.1.2.-.4:.Factors.influencing.thermal.efficiency.[9]


A.1.2.1.4 Advanced CombustorThere.have.been.considerable.advances.in.aircraft.engine.combustors.over.recent.decades..The.primary.benefit.of.these.combustor. improvements. has. been. the. reduction. in. emissions,. specifically. NOx. emissions.. This. compensates. the.main.disadvantage. of. high. combustion. temperatures. made. possible. by. new. materials,. which. improve. engine. efficiency. but.increase.NOx.formation..Such.reduction.in.globally.harmful.emissions.is.the.primary.focus.of.modern.combustor.development.programmes..The.target.for.any.advanced.combustor.is.to.achieve.emissions.goals.without.any.loss.in.combustion.efficiency.and.pressure. [11]..This. is.a.stringent. requirement,.given. that.modern.combustor.designs.are.already.extremely.efficient,.exhibiting.>99.9%.efficiency.and.very.low.drop.in.pressure.[11]..Another.challenge.is.to.achieve.all.of.the.above.without.limiting.the.operating.conditions.of.current-generation.combustors...Despite.the.odds,.all.major.aircraft.engine.manufacturers.are.developing.a.range.of.advanced.combustors.that.would.be.fielded.during.the.2015-2020.timeframe..These.include.the.second.and.third.generation.of.the.GE.Twin.Annular.Premixing.Swirler.(TAPS).combustor.[12],.the.P&W.Talon.x.combustor.[11],.and.a.similar.Rolls.Royce.design.

Beyond. 2020,. lean. staged. and.Rich.Quench. Lean. (RQL). combustors. offer. the. possibility. for. further. reduction. in.NOx.emissions. (70%.below.CAEP2. [13]),. without. compromising. fuel. efficiency. [11].. These. combustors. are. currently. in. the.technology.readiness. level. (TRL).5-6.range,.but.are. likely. to.require.another.5.to.10.years.before.commercialisation..yet.another.approach,.which.is.being.investigated.by.Airbus,.is.the.hydrogen.rich.combustion.concept.[14],.whereby.hydrogen.is.extracted.from.kerosene.and.injected.into.the.combustion.chamber..The.resulting.higher.heat.generation.would.reduce.the.emissions.of.solid.particulates,.mostly.soot.

A.1.2.1.5 Variable Geometry ChevronBoeing.has.experimented.with.NiTiNol.Shape.Memory.Alloy.(SMA).for.the.company’s.own.morphing.structure:.the.variable.geometry.chevron.(VGC)..One.source.of.engine.noise.is.the.turbulent.mixing.of.the.hot.jet.exhaust,.fan.stream,.and.ambient.air..Chevrons.immersed.into.the.flow.at.the.nacelle.trailing.edge.have.shown.to.lower.jet-induced.noise.appreciably.(up.to.2.dB.in.the.low.frequency.jet.mixing.noise.for.static.chevron.[15]).at.take-off.and.reduce.shock-cell.noise.(3.to.5.dB.[16]).during.cruise..Nonetheless,.the.practical.use.of.these.devices.dictates.a.compromise.between.noise.reduction.and.engine.performance.because.the.immersion.of.chevrons.actually.increases.drag..The.VGC.employs.morphing,.as.illustrated.in.Figure.A.1.2.-.6,.to.obviate.the.need.to.compromise.–.the.chevron.shapes.can.vary.from.a.configuration.optimised.for.take-off,.and.another.optimised.for.cruise.[17]..The.technology.was.successfully. flight-tested.on.a.Boeing.777-300ER.with.GE-115B.engines,.thereby.demonstrating.the.positive.impact.of.morphing.structures,.even.small.ones.

Figure.A.1.2.-.5:.Ceramic.matrix.composite.reduces.weight.and.improves.performance.of.engine.components.[10]

Figure.A.1.2.-.6:.Variable.geometry.chevron.[17]

39..ANNEx.1

A.1.2.1.6 Advanced Engine MaterialsFor.aircraft.propulsion.systems,.the.research.in.advanced.engine.materials.has.two.main.purposes:.(1).provide.higher.combustor.temperature.for.a.more.efficient.combustion.(also.resulting.in.an.unwanted.increase.in.NOx.formation),.and.(2).improve.the.component’s.specific.strength.to.reduce.operating.costs.by.increasing.the.component’s.life.and.reduce.maintainability..To.achieve.these.goals,. thermal.barrier.coating,.advanced.alloys.and.composite.materials.are.being.researched.and.present.some.advanced.materials.that.may.be.incorporated.onto.the.next.generation.of.engines..This.section.will.describe.some.of.these.technologies..

Thermal Barrier Coating

The.process.of.Thermal.Barrier.Coating.(TBC).is.used.to. increase.the.operating.temperature.of.the.engine.components,.specifically. the.gas. inlet. temperature..This. improves.combustion.efficiency,.which.also.adversely. increases. the. formation.of.NOx..The.TBC.technology. is.capable.of.providing.metal. temperature.reductions.of.approximately.140°C,.even.though.potential.benefits.are.estimated.to.be.in.excess.of.170°C.[18]..The.application.of.TBC,.in.conjunction.with.active.cooling,.has.enabled.operations.at.combustion.gas.temperatures.in.excess.of.250°C.above.the.melting.temperature.of.super.alloys.(e.g..in.the.early-stage.turbine.blades.and.vanes).

Thermally.shielding.a.piece.of.component.also.extends.its.service.life,.which.is.the.primary.contribution.of.TBC.to.current-generation.aircraft.engines..Before.the.technology.can.be.demonstrated.to.be.sufficiently.reliable,.the.following.issues.must.be.resolved:.1).TBC.does.not.provide.self-renewing.protection;.2).extension.of.service.life.due.to.TBC.is.subject.to.scatter;.3).effective.means.of.monitoring.TBC.life.has.been.elusive;.and.4).existing.life.prediction.methods.are.not.yet.accurate.[19]..

New Titanium Alloys for Engine Components

Ti.alloys.and.Ni-based.super.alloys.constitute.the.largest.weight.fraction.of.modern.gas.turbine.engines..A.relatively.new.alloy,.IMI834,.has.the.potential.for.replacing.Ni-based.super.alloys.because.of.its.capability.to.withstand.higher.temperatures:.70°C.hotter.than.conventional.Ti.alloys..Should.this.advanced.alloy.replace.all.Ni-based.super.alloys.found.within.the.engine,.then.that.alone.can.lead.to.savings.in.system.weight.

In.addition. to.conventional.Ti.alloys,.efforts.have.been.devoted. to.developing.Ti-based. intermetallic.compounds. for.high.temperature.applications..While. such.compounds. (Ti3Al,. Ti2AlNb,. and.TiAl). are. indeed.promising. for. higher. temperature.environments,.there.are.still.issues.associated.with.low.ductility,.environmental.sensitivity,.and.high.cost.[20]..In.the.case.of.replacing.Ni-based.super.alloys.and/or.steel.with.TiAl,.approximately.40%.reduction.in.compressor.and.turbine.blade.weight.is.expected.[21]..

Figure.A.1.2.-.7.Material.strength.and.temperature.capability.(left).and.candidates.for.engine.components.(right).[21]


Advanced Nickel-based Super Alloys

Nickel-based.super.alloys.are.used.for.engine.components.for.which.strength.in.high.temperature.environments,.toughness,.and.resistance.to.degradation.in.corrosive.or.oxidising.environments.is.required.[22]..In.general,.these.materials.constitute.40-50%.of.the.total.weight.of.an.aircraft.engine.and.are.used.most.extensively.where.elevated.temperatures.are.maintained.during.operation. (e.g.,.combustor,. turbine,.etc.). [23]..Ni-based.super.alloys. that.can.withstand.higher. temperatures.have.been.in.constant.demand,.and.now.state-of-the-art.single.crystal.(SC).super.alloys.can.endure.temperature.levels.upward.of.1100°C..

If.the.maximum.allowable.temperature.is.improved.by.50.°C.(from.1100.to.1150°C),.then.the.cooling.flow.inside.the.turbine.blades.can.be.sufficiently.reduced.to.have.an.impact.on.fuel.burn.by.reducing.the.energy.needed.for.the.cooling.system..The.50.°C.improvement.is.equivalent.to.prolonging.the.creep.rupture.life.by.600%.

Powder Metallurgy

Compared.to.ingot.metallurgy.processes,.aluminum.powder.and.rapid.solidification.techniques.promise.alloys.of.improved.strength,. toughness,. and. corrosion. resistance. [3].. Powder.metallurgy. also. has. the. potential. to. produce.Al-based. alloys.capable.of.withstanding.up. to.480°C,.which.could.make. them.more.competitive.with. the.more.high-end.materials. (e.g.,.titanium).in.both.airframe.and.engine.applications.

A.1.2.2 Evolutionary Engine Core ImprovementsIn.2008,.GE.announced.the.“eCore”. initiative. that.embodies.the.response.of.CFM.International. (a. joint.venture.between.GE.Aviation.and.Snecma).to.Pratt.&.Whitney’s.Geared.Turbofan.[25]..The.program.will.leverage.both.the.LEAP56.program.and.GEnx.technology.to.achieve.15-20%.reduction.in.fuel.burn.compared.with.current.engines,.50-60%.reduction.in.NOx.emissions.relative.to.CAEP/6,.and.noise.signatures.15dB.cumulative.below.Stage.4.by.2015..This.architecture.is.characterised.by.ultra-high.core.ratios.of.15:1.to.20:1,.an.eight-stage.high-pressure.compressor,.ceramic-matrix.composite.high-pressure.turbine.(HPT).blades,.resin-transfer.moulding.fan.blades,.and.a.15%.higher.loaded.single-HPT.stage..First.rounds.of.testing.are.scheduled.for.the.middle.of.2009,.with.full.tests.planned.for.2012..The.company.aims.to.achieve.certification.in.2016..By.2020.a.full.open-rotor.engine,.fitted.with.an.eCore,.could.be.available.

For.military. aviation,. the.Highly.Efficient.Embedded.Turbine.Engine. (HEETE).program.aims. to.push. this. trend. further.by.realising.ultra-high.bypass.ratios.with.a.new.compressor.technology..GE,.one.of.the.project’s.participants,.is.aiming.for.an.overall.pressure.ratio.of.70:1.[26]..For.comparison,.the.pressure.ratio.for.a.GE90.engine.is.43:1.

Besides.striving.to.increase.further.the.compression.ratio.of.the.engine.core,.alternative.approaches.have.been.researched.to.improve.the.fuel.efficiency.and.environmental.performance.of.future.engines..Four.examples.of.progress.in.this.area.have.been.reported.out.of.the.new.aero.engine.core.technology.(Newac).initiative.[27],.summarised.in.Table.A.1.2.-.1.

Technology Name Description Potential Benefits

Intercooled.Recuperative.Aero.Engine

•.Uses.heat.exchanger.modules..in.the.main.exhaust.to.extract.thermal.energy.and.transfer.it.back.into.the.combustion.chamber

•.Fuel.savings.up.to.17%

Active.Core.Engine •.Adapts.the.core.to.each.phase.of.the.mission•.Thermal.and.mechanical.active.turbine.tip.clearance

•.Active.surge.control.with.air.injection.in.the.compression.stages

•.Efficiency.improvement

Flow-Controlled.engine.core •.Tip.flow.control/injection•.Stator,.blade.and.hub.aspiration•.Flow.stability.control•.Management.of.rubbing

•.Increase.efficiency.2.5.%.•.Improve.performance.retention.by.30%•.Improve.stall.margin.by.16%

Intercooled.engine •.Air.exiting.the.LP.compressor.is.cooled.before.entering.the.HP.compressor.by.using.bypass.air.scooped.into.a.set.of.heat.exchangers

•.Reduce.Nox.emission•.Reduce.core.size

Table.A.1.2.-.1:.Recent.progress.in.engine.core.research

41..ANNEx.1

A.1.2.2.1 New Engine Core ConceptsThe. new. engine. core. concepts. are. designed. to. improve. fuel. efficiency. while. reducing. undesirable. emissions...The.core.of.the.engine.includes.the.compressor,.combustor.and.high-pressure.turbine;.consequently.the.new.engine.core.is.not.a.unique.technology.but.a.combination.of.technologies..

New.cores.are.expected.to.include.advanced.materials,.new.thermal.management.systems,.new.aerodynamic.design.airfoils,.and.next.generation.combustor.such.as.the.Twin-Annular.Premixed.Swirler.(TAPS).as. illustrated.in.Figure.A.1.2.-.8..This.combustor.technology.is.expected.to.reduce.the.combustion.temperature.through.a.more.homogeneous.and.leaner.mix.of.fuel.and.air..Reducing.the.combustion.temperature.will.also.significantly.reduce.NOx.emissions.[28].

A.1.2.2.2 Adaptive/active Flow ControlAdaptive./.active.flow.control.technologies.use.control.devices.to.improve.the.efficiency.of.aerodynamic.surfaces.under.a.wide.range.of.conditions.[30]...For.an.engine.these.technologies.are.applied.to.internal.flow.surfaces.and.are.expected.to.improve.operability.and. lower.engine.noise..Consequently. the.benefits.are.assessed. in. terms.of. improved.fuel.efficiency,.lower.emissions.and.lower.operating.costs.[30]..

Studies.have.evaluated.the.impact.of.active.flow.systems.on.the.inlet,.compressor..and.combustor..The.active.inlet.control.is.designed.to.be.used.on.high-speed.civil.transport.aircraft.to.maintain.the.leading.shock.and.the.engine.inlet.[30]..The.active.stall.control.is.designed.to.improve.engine.efficiency,.since.the.best.operating.point.of.a.turbine.engine.compressor.is.close.to.the.compressor.stall.line.[30]..Finally.active.combustion.control.is.intended.to.allow.a.complete.combustion.of.fuel,.which.would.result.in.fewer.polluting.emissions..

A.1.2.3 New ArchitecturesSince.the.advent.of.the.Boeing.747,.Lockheed.L1011,.and.McDonnell.Douglas.DC-10,.the.trend.in.jet.aircraft.has.been.to.incorporate.high-bypass.ratio.turbofans..These.engines.power.a.single.stage.fan,.a.low-pressure.compressor,.and.a.high-pressure.compressor.from.two.or.three.directly.linked.turbines..Such.architectures.have.been.very.successful.in.providing.high. reliability,. low.noise,.and. low. fuel.burn..Through. incremental.advances,. the.environmental. impact.of.aircraft.engines.has.been.steadily.reduced..The.increase.in.engine.bypass.ratios,.from.1.(turbojet.such.as.in.the.Comet,.1957).via.4.or.5:1.(Boeing.747-100,.1977).to.8.to.9.5:1.(Boeing.777,.1995).in.the.latest.engines,.resulted.in.a.70%.reduction.in.fuel.burn.and.75%.reduction.in.noise.(20.dB)..However,.the.current.architectures.are.relatively.mature,.so.it.may.be.necessary.to.explore.alternative.architectures.to.achieve.the.aggressive.fuel-efficiency.goals.that.the.future.market.will.require.

Several. promising. alternative. architectures. have. already. been. proposed.. Some. of. these. architectures. either. have. been.demonstrated. in. the. past. or. are. currently. undergoing. active. industrial. development.. Others. are. the. object. of. ongoing.research.

Figure.A.1.2.-.8:.Twin-annular.premixed.swirler.combustor.[29]


A.1.2.3.1 Geared Turbofan.Previously.known.as.the.Advanced.Technology.Fan.Integrator.(ATFI).demonstrator.engine.[31],.the.Geared.Turbofan.is.a.next-generation,.high.bypass-ratio.turbofan.engine.currently.under.development.by.Pratt.&.Whitney.(P&W)..The.unique.feature.of.the.concept.is.the.integration.of.an.epicyclical.gearing.system.into.the.shaft.connecting.the.fan.and.the.low-pressure.(LP).compressor.and.turbine.stages,.as.shown.in.Figure.A.1.2.-.9.[32]..This.is.the.key.technology.that.enables.the.fan.and.the.LP.stages.to.share.a.common.shaft,.yet.rotate.at.their.respective.optimal.speeds..

Decoupling.the.fan.from.the.LP.stages.through.gearing.brings.about.a.number.of.performance,.weight,.and.cost.benefits..The.reduction.in.fuel.burn.is.the.most.obvious.expectation,.as.both.the.fan.and.LP.turbo.machinery.can.operate,.independent.of.each.other’s.rotation,.at.maximum.efficiency..Moreover,.the.planetary.gearbox.installed.behind.the.fan.contains.reduction.gears,.meaning.that.the.fan.rotates.slower.than.the.LP-stage.components..Lower.rotational.speeds.can.lead.not.only.to.a.quieter.engine.with.a.fan.of.the.same.size,.but.also.a.larger.fan.diameter.for.the.same.blade.tip.speed..The.primary.benefit.of.being.able.to.increase.fan.diameter.with.few.noise.penalties.is.the.reduction.in.fuel.burn.due.to.higher.bypass.ratio,.but.there.are.also.ramifications.in.terms.of.weight.and.cost..The.GTF.has.18.fan.blades,.which.is.about.half.the.number.of.blades.on.a.similar.sized,.previous-generation.turbofan.engine..Each.single.blade.can.also.be.made.lighter.due.to.the.slow.rotational.speed.of.the.fan..Therefore,.the.combination.of.fewer.parts.and.lighter.weight.per.part.will.contribute.towards.reduced.engine.weight,.fuel.burn.(-12%).and.operating.costs..[34].

Gearing.is.also.beneficial.for.the.LP.compressor.and.turbine.for.the.same.reasons,.although.the.benefits,.in.this.case,.are.derived.from.faster.rotational.speeds..An.LP.turbine.rotating.at.higher.speeds.is.able.to.drive.the.compressor.and.fan.with.fewer.stages..Similarly,.a.faster.rotating.compressor.can.be.constructed.with.fewer.stages.for.the.same.mass.flow.rating..Both.factors.lead.to.an.overall.reduction.in.the.number.and.weight.of.LP-stage.components..

At.the.propulsion-system.level,.P&W.is.targeting.the.GTF.to.offer.significant.savings.in.fuel.burn.while.still.allowing.a.10.dB.(50%).reduction.in.noise.emissions..This.is.illustrated.in.Figure.A.1.2.-.10,.in.which.the.dotted.green.line.(“Paradigm.Shift”).represents.the.projected.performance.of.the.GTF.[35].

Figure.A.1.2.-.9:.Geared.turbofan.architecture.[33]

Figure.A.1.2.-.10:.Projected.benefits.of.geared.turbofan-powered.aircraft.[Modified.from.35]

43..ANNEx.1

Mitsubishi.Heavy.Industry.Ltd..selected.the.GTF.for.its.saving.potential.as.the.exclusive.power.plant.for.its.new.Mitsubishi.Regional.Jet.(MRJ).[36]..This.will.be.available.in.two.versions..The.shorter,.70-seat.variant.will.be.outfitted.with.a.15,000-lbf-thurst.GTF,.while.the.longer,.90-seat.MRJ.will.be.powered.by.a.17,000-lbf-thrust-class.version.of.the.GTF..The.MRJ’s.scheduled.in-service.date.of.2013.coincides.with.P&W’s.planned.development.timeline.of.the.GTF..

The. sole-source. agreement.with.Mitsubishi. for. the.GTF. proves. the. benefits. of. the. concept;. nevertheless. a. commercial.success.similar.to.that.of.the.JT8D.in.the.single-aisle,.short-haul.market.is.expected..It.is.projected.that.the.next-generation.narrow-body.replacements.from.Boeing.and.Airbus.will.account.for.a.significant.portion.of.the.civil. transport.sector.[37]..P&W.believes.that.annual.savings.of.up.to.US$1.5.million..(Fy2007).per.narrow-body.aircraft.using.2.engines.are.attainable.compared.to.today’s.engine.architectures.[38]..If.a.GTF.installed.on.a.single-aisle.aircraft.demonstrates.the.projected.15.dB.reductions.from.current.Stage.4.regulations,.then.GTF-powered.aircraft.could.be.allowed.to.fly.over.congested.urban.areas..For.example,.an.eastbound.aircraft.taking.off.from.Lon.Angeles.Airport.at.night.could.take.off.due.east,.rather.than.climbing.due.west.to.achieve.a.reduced.noise.signature.over.the.city.of.Los.Angeles..Such.optimal.flight-path.tracking.is.estimated.to.save,.on.average,.12.minutes.of.flight.time,.further.serving.to.reduce.fuel.burn.and.GHG.emissions.[39].

Bombardier.has.selected.the.GTF.as.the.exclusive.propulsion.system.for.its.proposed.CSeries,.scheduled.to.enter.service.in.2013.[40]..Both.the.100-seat.C110.and.the.130-seat.C130.represent.Bombardier’s.entry.into.the.narrow-body.aircraft.market..P&W.has.an.upgrade.plan.to.further.improve.the.GTF’s.fuel.burn.(5-7%).by.2020..Table.A.1.2.-.2.lists.a.summary.of.GTF.performance.targets.or.specifications.known.to.date.

Status Two.exclusive.agreements.

Ground.trials.on.a.30,000.lbf-thrust-class.version.is.ongoing

Key.Performance.Targets

Fuel.burn 12%.reduction.vs..state-of-the-art.turbofans

Noise 15dB.below.Stage.IV

Emissions 70%.below.CAEP/2.limit

Costs 40%.reduction.in.maintenance

Published.Technical.Data

Thrust.range.per.engine •.15,000.lbf.(MRJ.–.70.PAx)•.17,000.lbf.(MRJ.–.90.PAx)•.23,000.lbf.(CSeries.–.110.&.130.PAx)•.40,000.lbf.(Maximum)

Bypass.ratio 11:1.(for.CSeries)

Fan.diameter •.56.inches.for.MRJ.•.70.inches.for.CSeries.•.77.inches.for.30,000.lbf-class

Fan.RPM One.third.of.LP.stages

HP.architecture Eight-stage.compressor

Two-stage.turbine

LP.architecture •.Three-stage.compressor•.Two-.or.three-stage.turbine

Rotational.speed.of.LP.stages 9,000.RPM

Table.A.1.2.-.2:.Summary.of.published.GTF.data


A.1.2.3.2 Counter-rotating FanCurrent.turbofan.engines.use.a.single-stage.fan.driven.by.a.multi-stage.low-pressure.turbine..Because.there.is.only.one.fan.stage.connected.to.a.single.shaft,.all.of.the.turbine.stages.must.rotate.in.the.same.direction..Therefore,.in.order.to.remove.the.swirl.imparted.on.the.flow.inside.the.turbine,.a.row.of.fixed.stator.vanes.must.be.added.after.each.rotating.turbine.stage..Additionally,.behind.the.fan,.a.set.of.fixed.vanes.must.be.incorporated.to.straighten.the.flow..Each.of.the.fixed.set.of.vanes,.however,.induces.drag,.leading.to.a.loss.in.efficiency..The.weight.penalties.from.these.fixed.stages.should.be.addressed,.as.they.increase.overall.fuel.burn..

In.response.to.such.deficiencies.caused.by.uni-directional.rotation.inside.the.engine,.Snecma,.General.Electric,.and.other.engine.manufactures.are.exploring.the.counter-.or.contra-rotating.turbofan.concepts.(Figure.A.1.2.-.11).[41,.42]..The.idea.here.is.a.natural.follow-on.to.the.modern.practice.of.rotating.different.compressors,.shafts,.and.turbines.in.opposite.directions..Both.the.Rolls.Royce.Trent.900.and.1000.engines,.as.well.as.General.Electric’s.GEnx.engine,.employ.counter-rotating.shafts.[43,.44]..According.to.Snecma,.such.architecture.enables.the.bypass.ratio.to.be.increased.significantly,.allowing.the.concept.to.meet,.in.combination.with.material.and.installation.improvements,.the.goal.set.for.the.European.Union’s.VITAL.project.of.an.18%.reduction.in.fuel.burn.over.current-generation.engines.[45,.46,.47].

A.1.2.3.3 Open RotorAlso.known.as.unducted. fan. (UDF),.ultra-high.bypass. (UHB).or.open. rotor.engine,. the.prop. fan.was.an.unconventional.architecture.that.was.trialled.in.the.late.1980s..The.jet.exhaust.drives.two.counter-rotating.turbines.that.are.directly.coupled.to.the.fan.blades..These.large.span.fan.blades,.made.of.composite.materials,.have.variable.pitch.to.provide.the.proper.blade.angle.of.attack.to.meet.varying.aircraft.speed.and.power.requirements..As.indicated.by.the.names.“unducted.fan”.or.“open-rotor.engine”,. fan.blades.are.placed.outside.the.nacelle..A.pusher.configuration.was.favoured. in.the.U.S.,.as.seen. in.the.designs.in.Figure.A.1.2.-.12..The.P&W/Allison.578-Dx.was.also.a.pusher,.whereas.a.tractor.configuration.was.adopted.in.the.former.Soviet.Union,.e.g..the.Progress.D-27.[48]..A.favoured.installation.concept.is.two.open.rotors.mounted.side-by-side.on.top.of.the.aft.end.of.the.fuselage.[49]..Regardless.of.the.configuration,.the.resulting.unconventional.design.is.the.product.of.wanting.to.combine.the.high-thrust.and.speed.capacity.of.a.turbofan.with.the.high.fuel.efficiency.of.a.turboprop..

A.prop.fan.is.intended.to.be.highly.fuel.efficient,.having.grown.out.of.the.NASA-led.advanced.turboprop.(ATP).initiative.of.the.late.70s..The.ATP.was.one.of.the.products.of.the.1973.oil.crisis,.and.NASA.established.an.ambitious.goal.of.reducing.fuel.consumption.by.up.to.50%.for.narrow.body.aircraft.[51]..The.end.result.was.impressive.even.by.today’s.standards..In.1987,.an.MD-80.powered.by.the.GE36.UDF.demonstrated.a.30%.improvement.in.fuel.consumption,.full.Stage.III.noise.compliance,.and.acceptable.levels.of.cabin.noise.and.vibration.[52]..Although.the.578-Dx.measured.similar.performance.gains,.McDonnell.Douglas’.selection.of.the.IAE.V2500.for.the.MD-90.ended.the.commercial.viability.of.prop.fans.in.the.West.

Recently.revived.interest.in.prop.fans.is.due.to.the.same.motivating.factors.behind.the.revival.of.the.GTF.–.growing.environmental.concerns,.skyrocketing.fuel.prices,.and.expected.efficiency.gains.for.next-generation.narrow-body.aircraft..Officials.at.Rolls.Royce.believe.that.“10-15%.fuel.consumption.benefits.over.advanced.turbofan.technologies.and.30%.over.current.turbofan.designs”.will.be.[49].attainable.and.a.50%.improvement.is.“not.out.of.the.question.for.the.total.system.”.[53].However,.many.technical.and.timeline.hurdles.remain.before.a.go/no.go.decision.can.be.reached.for.the.open-rotor.concept.in.time.for.either.Boeing’s.(737.by.2015).or.Airbus’.(A320.by.2017).single-aisle.replacements.[54]..

One.challenge.is.noise..Because.the.fan.blades.are.unducted,.it.is.yet.to.be.demonstrated.whether.a.reduction.of.at.least.10.dB. in.perceived.external. noise.can.be.obtained. in. an.open-rotor. [55]..While.officials. at.Rolls.Royce.and.Airbus.are.optimistic.that.a.considerably.silent.pusher.version,.at.a.TRL.of.7.or.8,.will.be.demonstrated.by.2011,.their.counterparts.at.CFM.International.have.been.lowering.expectations.by.stating.that.the.company.is.pursuing.“open.rotor.designs.that.would.produce.roughly.the.same.sort.of.noise.signatures.as.current.aircraft.”.[51].

Figure.A.1.2.-.11:.Contra-rotating.fan.stages.[46] Figure.A.1.2.-.12:.CFM.International.open.rotor.concepts.[50]

45..ANNEx.1

The.exterior-mounted.fan.blades.also.make.prop.fans.inherently.larger.in.diameter.compared.to.the.conventional.ducted-fan.designs,. including. the.GTF..A.GTF. rated.at.25,000. lbf.would.be.no.more. than.96. inches.wide,.whereas.an.open-rotor.design.of.the.same.thrust.class.can.be.as.big.as.168.to.204.inches.in.diameter.[38]..Consequently,.prop.fans.are.likely.to.be.heavier,.pose.more.challenging.airframe-engine.integration.issues.(essentially.leaving.the.empennage.as.the.only.installable.location),.and.certification.hurdles.(possibly.facing.blade.containment.regulations,.vibration,.and.maintenance.issues).than.other.advanced.engine.architectures..There.is.also.lower.reliability,.as.admitted.by.CFM,.due.to.the.presence.of.a.variable-pitch.mechanism..

All.of.these.reasons.are.expected.to.delay.the.in-service.date.of.the.next-generation.UDF.until.“very.late.in.the.second.decade.at.the.earliest.[51],”.although.some.rig.tests.are.currently.occurring..Rolls.Royce.began.wind.tunnel.testing.on.its.1/6.scale.open.rotor.demonstrator.in.July.2008.[53],.and.CFM.has.also.conducted.its.own.sub-scale.rig.trial.in.late.2008.as.part.of.the.company’s.LEAP56.program.[56].

A.1.2.3.4 Embedded Distributed Multi-fanThe.goal.of.the.distributed.propulsion.concept.(Figure.A.1.2.-.13).is.to.maximise.the.propulsive.efficiency.of.both.the.engine.and.the.overall.vehicle..The.intention.is.to.provide.improvements.in.both.noise.and.fuel.burn.performance..The.typical.turbofan.engine.has.a.single.axial.flowpath.but.multi-fan.engine.concepts.have.multiple.flowpaths..Such.a.departure.from.conventional.design.allows.the.bypass.ratio.to.be.increased.semi-independent.of.the.external.diameter.of.the.engine.

The.basic.premise.of.the.multi-fan.concept.is.to.provide.additional.fans.driven.by.a.single.gas-turbine.[57]..This.linkage.can.be.mechanical.[57],.electrical,.hydraulic,.or.pneumatic.[58]..In.some.designs,.there.is.a.provision.to.“de-clutch”.the.extra.fans.from.the.gas.turbine.when.they.are.no.longer.needed.[57]..By.providing.multiple.flow-paths,.the.same.fan.area.and.mass.flow.can.be.achieved.with.significantly.smaller-diameter.fans,.which.lead.to.either.decreased.fan.tip.speed.and/or.increased.blade.passing.frequency.[59]..Both.phenomena.decrease.the.noise.generated.by.the.fan..Because.of.the.gearing.between.the.core.and.each.fan,.benefits.similar.to.those.demonstrated.by.the.GTF.could.become.attainable..The.gearing,.with.other.efficiency.improvements,.may.yield.a.decrease.in.cruise.fuel-burn.between.5.and.10%.[70]..

The.distributed,.multi-fan.idea.has.been.described.in.multiple.U.S..patents.[58,.60]..It.was.also.chosen.as.the.basis.for.the.SAx-40’s.propulsion.system.[60]..Nevertheless,.no.prototypes.have.been.constructed..Several.airframe/engine.integration.issues.that.need.addressing.include.the.weight.of.the.transmission.system,.as.well.as.the.possibility.of.additional.drag.[60]..The.concept.is.inherently.synergistic.with.other.engine-related.advances,.such.as.the.buried.engines.with.boundary.layer.ingestion.(BLI).

Figure.A.1.2.-.13:.Distributed.multi-fan.concept.[60]


A.1.2.4 Revolutionary Engine Cycles

A.1.2.4.1 Adaptive CyclesThe.Spanish.technology.company.FIPSA.under.the.name.“FREENOx”.has.proposed.an.engine.architecture.that.assembles.several.new.elements.that.help.to.reduce.NOx.emissions.and.fuel.consumption.[61],.see.Figure.A.1.2.-.14..The.“FREENOx”.jet.engine.uses.two.new.technologies.to.achieve.a.particularly.high.thrust-to-weight.ratio:.

An.“Endothermic.Reaction.System”.produces.activated.oxygen,. thus. improving.fuel.combustion.during.the.different. flight.stages. (start,. take.off,. cruise.and. landing)..The.system.carries.out. the. functions.and.optimal.mixtures. (activated.oxygen,.compressed.air.and.fuel).depending.on.the.current.flight.stage,.considering.the.outside.temperature,.pressure,.altitude,.and.so.on..This.feature.and.the.design.of.the.combustion.chambers,.the.fuel.injection.system.and.the.cooling.system.are.intended.to.reduce.NOx.emissions.

The.air.pressure.to.operate.the.Endothermic.Reaction.System.is.generated.by.a.‘central.compression.unit’.in.the.fuselage.before.being.distributed. to.each.engine,. in.order. to.save.overall.weight..Additionally,.during.cruise. it. is.expected. to.add.propulsion.to.the.aircraft,.when.the.system.reduces.power.to.the.engines,.thus.reducing.fuel.consumption.and.CO2.emissions..The.developers.predict.a.total.mission.fuel.burn.reduction.of.30%.compared.to.current.engines.as.well.as.a.considerable.noise.reduction..First.design.presentations.have.been.made.at.a.number.of.engine.manufacturers.

A.1.2.4.2 Pulse DetonationThe.pulse.detonation.engines.are.small.disposable.engines.that.offer.few.moving.parts,.high.efficiency,.high.thrust,.low.weight.and.cost,.and.are.scalable.[62]..This.technology.is.based.on.the.principle.of.supersonic.detonation.of.fuel..As.illustrated.in.Figure.A.1.2.-.15,.the.cycle.starts.by.filling.a.tube.with.a.mix.of.fuel.and.air,.then.the.mixture.is.detonated.releasing.the.exhaust.[62]..The.pulse.detonation.engines.have.a.broad.range.of.operability,.since.they.have.the.potential. to.operate.at.speeds.ranging.from.static.to.hypersonic.with.competitive.efficiency.with.respect.to.conventional.gas.turbine.engine.[62]..The.main.advantages.of.the.concept.are.a.small.number.of.moving.parts,.implying.reduced.operating.costs..

Figure.A.1.2.-.16.illustrates.the.Borealis.(a.modification.of.the.Long-EZ.by.Scaled.Composites),.the.first.pulse.detonation.aircraft.that.first.flew.in.January..2008.[63]..During.that.flight,.the.pulse.detonation.engine.operated.under.its.own.power.for.10.seconds.at.an.altitude.of.100.feet..Throughout.this.short.period,.the.engine.was.generating.up.to.200.lb.of.thrust.using.four.tubes.producing.pulse.detonations.at.80.Hz.[63]...

.Figure.A.1.2.-.16:.Modified.Scaled.Composites.Long-EZ.aircraft.with.a.pulse.detonation.engine.[63]

Figure.A.1.2.-.15:.Pulse.detonation.engine.cycle..(modified.from.[62])

Figure.A.1.2.–.14:.“FREENOx”.concept.(left:.engine,.right:.endothermic.reaction.system.with.central.compression.unit).[61]

47..ANNEx.1

A.1.2.5 Nacelles and Installation

A.1.2.5.1 Variable Fan NozzleThe.benefit.of.the.variable.area.nozzle.is.its.ability.to.tune.the.fans.to.lower.pressure.ratios.[64,.65]..Historically,.the.variable.area.nozzle.was.considered.to.be.too.heavy.and.complicated.for.installing.on.modern.turbofans,.but.modern.shape-memory.alloys.[64].are.expected.to.provide.a.solution..If. implemented,.the.technology.allows.for.a.reduction.of.fan.pressure.ratio,.a.decrease.in.the.exhaust.velocity.at.low.speeds,.and.an.increase.in.pressure.ratio.and.exhaust.velocity.at.cruise.[65]..The.overall.implication.is.an.increase.in.the.propulsive.efficiency.of.the.engine.over.a.variety.of.flight.conditions,.which.would.–.in.turn.–.serve.to.decrease.both.engine.noise.(objective.of.2dB.reduction).while.maintaining.cruise.efficiency..The.idea.has.been.described.in.both.U.S..patents.and.a.NASA.report.[64,.66].

A.1.2.5.2 Boundary Layer Ingesting InletRecent. trends. in. the. development. of. engine. nacelles. and. engine/nacelle. integration. have. focused. on. reducing. the.interference. losses,. fuel. burn. (~3.8.%. based. on. Silent. Aircraft. [60]). and.minimising. noise.. However,. there. are. several.potential.developments.in.nacelle.design.that.promise.not.only.to.reduce.noise,.but.also.to.mitigate.engine.installation.losses..These.technologies.include.the.buried,.boundary.layer.ingesting.installation.concepts.shown.in.Figure.A.1.2.-.17.and.the.variable.area.fan.nozzle.

Motivated.by.the.drive.to.create.a.silent.aircraft,.designers.have.been.investigating.burying.and/or.shielding.the.propulsion.system.from.the.external.flows..This.typically.involves.placing.the.engine.inside.the.fuselage.or.the.wing,.or.putting.a.portion.of.the.vehicle’s.structure.between.the.engine.and.an.observer..The.issue.here.is.that.the.body.of.the.vehicle.disrupts.the.flow..In.the.past,.either.an.engine’s.inlet.was.located.outside.of.the.boundary.layer,.or.the.disturbed.air.was.diverted,.as.it.contributed.to.losses.in.efficiency..The.boundary-layer.ingesting.inlet,.on.the.other.hand,.is.devised.to.re-energise.the.wake.of.the.aircraft.[59].by.ingesting.the.incoming.boundary.layer..The.downside.of.this.concept.is.that.the.distortion.of.the.airflow.occurs.at.the.engine.fan.face,.which.has.the.potential.to.decrease.fan.efficiency.and.increase.the.stress.on.the.fan.blades.[60,.68]..It.is.therefore.doubtful.if.this.design.principle.can.be.made.beneficial.for.modern.engines.

Figure.A.1.2.-.17:.Boundary.layer.ingesting.inlets.[60]


Chapter References

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49..ANNEx.1

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25.. Norris,.G.,.“Core.Values,”.Aviation.Week.&.Space.Technology,.vol..169,.iss..2,.pp..54-55,.July.2008.

26.. Phillips,.E..H.,.“INDUSTRy.OUTLOOK,”.Aviation.Week.&.Space.Technology,.vol..168.iss..22,.p..14,.June.2008.

27.. Norris,.G.,.“HEART.of.MATTER,”.Aviation.Week.&.Space.Technology,.vol..168,.iss..19,.pp..46-51,.May.2008.

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29.. Carlson,.D.,.“Flying.with.Next.Generation.Engine.Technology”,.GE.Advanced.Engine.Systems.presentation,.http://www.kuwaitairtransport.com/ge2.pdf,.[Online.accessed.March.2009]

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32.. Kjelgaard,.C.,.“Japanese.Airliner.to.Introduce.PW’s.New.Engine.Technology.”.http://www.aviation.com/technology/071009-pw-geared-turbofan-powering-mrj.html,.October.2007..[Online;.accessed.16-April-2008].

33.. Epstein,.A.,.“Reducing.Environmental.Impact.With.New.Technology.–.The.PW.Geared.TurbofanTM..Engine”,.ACI.Environmental.Affairs.Conference,.Denver,.May.2008,.http://www.aci-na.org/static/entransit/Epstein.pdf..[Online;.accessed.25-February-2009].

34.. Pratt.&.Whitney,.“PurePower.1000G”,.http://www.pw.utc.com/,.[Online;.accessed.25-February-2009].

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37.. Norris,.G.,.“GEARING.UP.AGAIN,”.Flight.International,.vol..169,.iss..5026,.pp..30-31,.March.2006.

38.. Norris,.G.,.“Gearing.Up;.Crucial.engine.selection.for.Mitsubishi.Regional.Jet.paves.way.for.P&W.geared.turbofan.launch,.but.hurdles.remain,”.Aviation.Week.&.Space.Technology,.vol..167,.iss..15,.pp..44-45,.October.2007.

39.. Epstein,.A.H.,.“Hearing.on.Aviation.and.Environment:.Noise,”.Subcommittee.on.Aviation.Committee.on.Transportation.and.Infrastructure,.U.S..House.of.Representatives,.October.24,.2007.

40.. Wall,.R.,.“Powering.Up;.Pratt.secures.second.GTF.customer.with.Bombardier.CSeries.commitment,”.Aviation.Week.&.Space.Technology,.vol..167,.iss..20,.pp..35-36,.November.2007.

41.. Baudier,.D..and.Piquet,.F.,.“Snecam,.a.VITAL.Player,”.Snecma.Magazine,.No..7,.November.2004,.pp..28-33.

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43.. Rolls-Royce,.“Trent.900.”.http://www.rolls-royce.com/civil_aerospace/products/airlines/trent900/technology_flash.jsp,.2007..[Online;.accessed.20-April-2008].

44.. GE.Aviation,.“New.Revolutionary.Turbine.”.http://www.geae.com/engines/commercial/genx/turbine.html,.2008..[Online;.accessed.20-April-2008].

45.. European.Commission,.“EnVIronmenTALly.Friendly.Aero.Engine.”.http://www.ist-world.org/ProjectDetails.aspx?ProjectId=f51347678532456aac8a17e9bcb7429b,.Sixth.Framework.Programme,.January,.2005.–.December,.2008..[Online;.accessed.20-April-2008].

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A.1.3 Alternative Fuels This.annex.looks.at.potential.fuels,.other.than.the.current.jet.fuels,.that.could.one.day.be.used.in.gas.turbine.aircraft.engines..If.renewable.energy.sources.are.to.become.widespread,.improvements.will.be.required.in.feedstock.extraction.and.improvements.in.technology..As.a.result,.technical.information.about.drop-in.fuels,.i.e..fuels.which.do.not.require.changes.in.aircraft/engine.architectures.and.can.be.mixed.with.current.kerosene.(Jet.A.or.Jet.A1),.and.non.drop-in.fuels,.which.would.require.deviations.from.existing.aviation.infrastructure,.are.contained.herein...In.a.short.term.only.drop-in.fuels.are.acceptable.for.commercial.airline.operations,.whereas.other.fuels.should.not.be.excluded.in.a.long-term.perspective.

A.1.3.1 Requirements for drop-in fuelsCertification.of.drop-in.fuels.can.either.be.for.the.pure.substance.or.for.a.blend.limited.to.a.percentage.conventional.fuel/new.fuel.for.which.fuel.quality.can.be.guaranteed..Candidate.drop-in.fuels.must.have.certain.properties.that.will.enable.their.use.in.current.aircraft..The.main.properties.are.the.flow.ability.at.low.temperatures,.defined.as.freezing.point.(currently.min.-40.ºC.for.Jet.A.and.-47.ºC.for.Jet.A1),.energy.content.(min..42.8.MJ/kg).and.specific.gravity.(775.–.840.kg/m3).

The.main.certification.standards.are.ASTM.International.(formerly.American.Standards.for.Testing.and.Materials),.D1655.and.the.United.Kingdom.Ministry.of.Defence.Standard.91-91..Both.certification.agencies.have.comparable.approval.protocols,.consisting.of.the.test.program,.OEM.internal.review.and.the.specification.change,.see.Figure.A.1.3.-.1..

Figure.A.1.3.-.1:.Overview.fuel.and.additive.approval.process

The. aviation. industry. is. developing. a. new. specification. ballot.Dxxxx. –Specification. for.Aviation. Turbine. Fuels. containing.Synthesized.Hydrocarbons...The.intention.is.to.control.the.production.process.with.Dxxxx.and.to.then.recertify.the.finished.fuel.to.D1655..The.current.Dxxxx.specification.focuses.only.on.Fischer-Tropsch.derived.fuels.

53..ANNEx.1

A.1.3.2 Liquid FuelsPotential. drop-in. fuels. include.both. fuels.with. a.comparable.chemical. structure. to.conventional. jet. fuel. types.as.well. as.different. types. of. chemical. substances.. But. the.molecular. structure. of. each. jet. fuel. is. never. exactly. the. same.. The. key.advantage.of.drop-in.fuels.is.that.they.induce.minimal.changes,.if.any,.to.existing.aircraft.designs.or.fuel.handling.procedures..Fuels.must.meet.mandatory. airworthiness. and. certification. demands;. preserve. and. improve. safety. levels;. and.meet. gas.turbine.and.aircraft.requirements.[1]..The.technical.feasibility.of.a.transester.biojet.fuel.in.a.20%.biojet./.80%.Jet.A-1.has.been.demonstrated.in.the.Virgin.Atlantic.flight.performed.on.23.February.2008.from.London.to.Amsterdam.in.usual.flight.operation.[2]..Other.flight.demonstrations.with.Hydroprocessed.Renewable.Jet.(HRJ).fuel.were.conducted.in.commercial.aircraft.and.one.demonstration.flight.on.a.gas-to-liquids.fuel..The.following.demonstration.flights.were.performed:

•. Airbus.flew.a.A380.in.early.2008.with.one.engine.powered.by.FT.Gas.to.Liquid.fuel.

•. Virgin.Atlantic.flew.a.Boeing.747-400.on.23.February.2008.with.one.engine.operating.on.a.20%.biofuel.mix..of.babassu.oil.and.coconut.oil.

•. Air.New.Zealand.flew.a.Boeing.747-400.with.one.engine.on.50%.jatropha.derived.biofuel.and.50%.kerosene.on.30.December.2008.

•. Continental.Airlines.flew.a.Boeing.737-800.with.one.engine.using.50%.jet.fuel.and.50%.algae.and.jatropha.mix.on.7.January.2009.

•. Japan.Airlines.trialled.a.50%.biofuel.(camelina,.jatropha.and.algae).and.50%.kerosene.mix.on.a.Boeing.747-300.with.P&W.engines.on.30.January.2009.

Fuels. can.be.produced.using.many.different. production.paths,. but.most. production.processes. largely. fall. under. one.of.three. categories:. Thermochemical,. Biochemical,. and. Hybrid. (combination. of. thermochemical. and. biochemical).. The.thermochemical.process.utilises.heat.and.catalysts. to.convert.a.carbohydrate. (or.other.carbon-containing.materials). into.synthetic.gas.(syngas).or.other.products..In.general,.the.process.is.very.inefficient.in.converting.the.raw.material.into.useful.products..The.biochemical.process.uses.enzymes.and/or.organisms.for.converting.the.biomass.into.fuel,.with.the.main.end.product.being.an.alcohol..The.hybrid.system.uses.the.best.of.both.processes,.resulting.in.an.optimised.end.product.as.well.as.an.optimised.lifecycle.energy.efficiency.

.

Figure.A.1.3.-.2:.Strategies.for.biofuel.production.[2]


Depending.on. the. feedstock. for. each. fuel. type,. a.diverse.group.of.manufacturing.processes.have.been.established,. as.graphically.summarised.in.Figure.A.1.3.-.2..Fossil.feedstock.such.as.coal,.natural.gas,.and.petroleum.coke.are.primarily.used.to.produce.synthetic.fuels.through.the.Fischer-Tropsch.synthesis.process..Biomass.feedstock.can.be.available.from.diverse.sources,.including.corn,.sugar.cane,.soy.beans,.switch.grass,.the.weeds.jatropha.and.camelina,.oil.from.the.Brazilian.babassu.palm.and.algae..These.species.can.be.converted.to.biodiesel,.hydrogenated.vegetable.oils.or.alcohols,.such.as.ethanol.and.butanol.through.transesterification.or.fermentation.

Only.two.processes.are.capable.of.producing.alternative.aviation.fuels.that.are.“drop-in”,.i.e..compatible.with.existing.fuel.infrastructure.and.providing.the.performance.specifications.required.of.civilian.or.military.aviation.fuels..The.first.is.biomass.gasification.followed.by.Fischer-Tropsch.synthesis.and.the.second.is.Hydroprocessed.Renewable.Jet.(HRJ).produced.from.plant.or.animal.lipids.via.hydrochemical.deoxygenation.and.selective.cracking/isomerisation...Fermentative.routes.to.ethanol.or. butanol. do. not. provide. an. aviation. grade. fuel. without. subsequent. chemical. oligerisation. (limited. polymerisation). and.deoxygenation.

Each.production.path.can.also.be.characterised.by.its.means.of.feedstock.harvesting,.heat.inputs.for.chemical.reactions,.and.unique.set.of.co-products..Such.factors.are.useful.in.comparing.the.economic,.environmental.(e.g..net.greenhouse.gas.emissions),.and/or.political.(e.g..competition.with.food.production).viability.of.one.production.path.to.another.

A.1.3.2.1 Fischer-Tropsch Synthesis ProcessThe.Fischer-Tropsch.(F-T).process.was.developed.in.1920.by.two.German.scientists.to.produce.synthetic.fuels.from.coal..Since.then,.it.has.matured.to.a.means.of.transforming.under-utilised.hydrocarbon.resources.into.alternative.synthetic.fuels.and.chemicals.[3]..Figure.A.1.3.-.3.shows.the.key.steps.of.a.general.F-T.process.

The.hydrocarbons. in. the. feedstock.are. first.broken.down. to.carbon.monoxide.and.hydrogen,.a.mixture.commonly.called.“syngas.”.Following.this.gasification.process,.the.syngas.is.converted.to.diesel.fuel.and.naphtha.(basic.gasoline).through.the.formation.of.polymer.chains..This.conversion.takes.place.in.the.presence.of.a.catalyst,.usually.iron.or.cobalt.and.a.variety.of.co-products.(various.chemicals).are.also.produced,.which.are.essential.to.the.economics.of.the.process..The.simplified.form.of.the.overall.reaction.from.syngas.to.the.end.product.can.be.given.as:

Figure.A.1.3.-.3:.Flow.diagram.of.the.general.Fischer-Tropsch.process.[4]

55..ANNEx.1

There.are.various.types.of.reactors.for.implementing.the.F-T.process..The.circulating.fluidised.bed.and.the.fixed.fluidised.bed.reactors.are.used.in.the.production.of.low.molecular.weight.hydrocarbons.and.gasoline..The.multi-tubular.fixed.bed.and.the.slurry.reactors.work.better.for.producing.high-value.linear.waxes.and.diesel..Sasol,.Exxon.and.Statoil.use.the.slurry.reactor.technology.with.a.cobalt-based.catalyst..Rentech.also.uses.the.slurry.reactor,.although.with.an.iron-based.catalyst,.whereas.Shell.and.BP.have.adopted.the.fixed-bed.reactor..Each.company,.whose.F-T.plants.are.shown.in.Figure.A.1.3..-.4.,.has.its.own.proprietary.process.for.efficient.coal-to-liquid.(CTL).and/or.gas-to-liquid.(GTL).conversion.[5].

The.SASOL.plant.in.South.Africa.produces.already.certified.Jet.A-1.fuel..The.general.term.that.is.applied.for.the.FT.derived.fuel.is.Synthetic.Paraffinic.Kerosene.(SPK)..

A.1.3.2.2 Hydroprocessed Renewable Jet (HRJ)Fat.hydrogenation.was.first.discovered.and.patented.by.Wilhelm.Normann..The.process.uses.a.metal.catalyst.to.make.the.fatty.acid.react.with.hydrogen.so.that.saturated.molecules.can.be.formed.[6]..The.hydrogenation.process.is.well.known.in.oil.refining.[7].to.improve.product.quality.[8]..

Hydrogenating.oils.and.fats.result.in.clean.paraffins.that.have.a.similar.molecular.structure.to.F-T.derived.fuels..For.this.reason.hydrogenated.oils.and.fats.are.expected.to.be.the.easiest.alternative.fuel,.other.than.F-T.fuels,.to.be.certified.for.aviation.[9]..The.inclusion.of.plant.seed.oil.in.crude.oil.refineries.is.already.being.considered.for.the.production.of.jet.fuels..

The.US.Government.has.sponsored.a.major.study.to.demonstrate.the.production.of.JP-8.(Jet.A-1).from.vegetable.and.animal.oils.and.fats..This.study.demonstrated.the.economical.production.of.JP-8.on.specification.using.hydrodeoxygenation.and.selective.cracking/isomerisation..Subsequently,.the.Boeing.Company.and.partners.such.as.UOP.LLC.produced.a.significant.quantity.of.HRJ. fuel,.which.was.used. for. three. flight.demonstrations. (see.above. flights.by.Air.New.Zealand,.Continental.and.JAL).using.1:1.blends.of.HRJ.and.conventional.Jet.A-1.fuels..These.fuels.were.produced.from.a.variety.of.non-edible.vegetable.oils.including.jatropha,.camelina.and.algal.oils..This.process.is.under.commercialisation.by.UOP.LLC.and.is.shown.in.Figure.A.1.3.-.5.

Hydroprocessed.Renewable.Jet.is.the.most.attractive.alternative.aviation.fuel.as.it.is.a.drop.in.fuel.with.the.most.favourable.economics.for.production.from.non-edible.biological.oils.

Oil DeoxygenationSelective Cracking/

Isomerization

Synthetic paraffinic Kerosene

(SPK)

Aromatics (<25%)

Renewable JP-8

(Jet A-1)

Figure.A.1.3.-.4:.Feedstock.and.production.capacities.of.Fischer-Tropsch.plants.[3]

Figure.A.1.3.-.5:.Hydroprocessed.renewable.jet.fuel.process


A.1.3.2.3 TransesterificationThe.transesterification.process.is.the.reaction.of.a.triglyceride.(fat/oil).with.an.alcohol.to.form.esters.and.glycerol.(clear.gel.often.used.for.pharmaceutical.purposes)..During.the.esterification.process,.the.triglyceride.is.reacted.with.alcohol.(mostly.methanol.or.ethanol).in.the.presence.of.a.catalyst..The.alcohol.reacts.with.the.fatty.acids.to.form.the.mono-alkyl.ester.and.crude.glycerol.

Most.fuels.produced.through.transesterification.are.more.akin.to.diesel.than.jet.fuels,.due.to.the.carbon.chain.length.of.the.basic.material..Therefore,. “biodiesel”. is. the. layman’s. term. for. transesterified.oils.and. fats..The.primary. factors. that.affect.the.quality.of.biodiesel.are.reaction.temperature,.mixing.ratio.of.oil.(and/or.fat).and.alcohol,.catalyst.types,.and.the.purity.of.reactants..

Figure.A.1.3.-.6.shows.the.basic.chemistry.of.transesterification,.as.well.as.the.more.detailed.procedural.steps..The.main.advantage. of. biodiesel. is. the. relatively. cheap. production. process. compared. to. the. hydrogenation. of. fats/oils,. which. is.presented.next.

Alkyl. ester,. or. a.mixture. of. alkyl. esters,. obtained. from. saturated. fatty. acids.with. carbon. chain. length. from.8. to. 10. and.monohydric.alcohols.having.a.carbon.chain.length.of.3.–4.is.patented.as.jet.fuel.[11]..The.first.time.transesterified.fuel.was.used.in.aviation.was.for.a.Pratt.&.Whitney.PT.6.engine.[12]..Test.flights.with.a.King.Air.65-A90.aircraft.were.conducted.up.to.7.62.km.(25,000.ft).in.steps.of.1.52.km.(5,000.ft)..The.operational.challenge.of.ester-based.fuels.for.aviation.is.their.relatively.low.energy.content,.±38.MJ/kg,.compared.to.the.minimum.standard,.42.8.MJ/kg.[13]..Work.is.being.done.to.address.the.stability.and.freezing.points.of.the.fuel.

Applying.biodiesel.in.aircraft.would.require.changes.to.the.aircraft.to.ensure.safe.operation..The.freezing.point.of.biodiesel.is.between.-40.oC.and.5.oC..This.would.require.heating.the.fuel.tanks.and.fuel.system.to.prevent.the.fuel.freezing.and.blocking.the.fuel.flow..The.lower.energy.density.(38.MJ/kg).reduces.the.flight.range..This.will.mainly.affect.the.long.range.flights.in.which.the. fuel.weight. is.more. important..The.short-range. flights. limited.by. the.maximum.zero. fuel.weight.can.carry.more.weight.without.having.a.big.impact.on.the.payload..The.result.of.a.higher.fuel.weight.is.higher.fuel.consumption..

For.these.reasons.(energy.density,.freeze.point,.thermal.stability).and.the.fact.that.transesterified.fuels.are.incompatible.with.existing.petroleum.aviation.fuels,.they.cannot.be.considered.as.drop-in.replacements.for.petroleum.based.aviation.fuels.

Figure.A.1.3.-.6:.Basic.chemistry.of.transesterification.and.detailed.process.[10]

A.1.3.2.4 FuransThe.furan.family.of.fuels.is.produced.out.of.carbohydrates..This.biomass.has.low.energy.content.due.to.the.large.amounts.of.oxygen.atoms. in. its.molecular.structure..A.compound.of. furan-based. fuels. that.has.a.high.energy.density.per.volume.is.the.2,5-dimethylfuran.(DMF)..It.is.produced.via.a.hybrid.production.route.shown.in.Figure.A.1.3.-.2),.in.which.starch.is.reformed. (with. enzymes). into. fructose..Extracting. hydroxyl. groups. from.basic. cyclo-ether. into. the. intermediate.molecule.5-hydroxymethylfurfural.(HMF).is.next,.followed.by.a.catalytic.reaction.with.hydrogen.to.extract.the.last.hydroxyl.group.and.formed.aldehyde..

Due.to.the.relatively.low.energy.content,.38.MJ/kg,.and.high.specific.weight,.890.kg/m3,.2,5-DMF.is.not.a.good.drop-in.product.for.a.full.range.blending..Although.the.freezing.point.is.lower.than.current.average.jet.fuel,.there.are.some.concerns.about.the.toxicity,.material.compatibility,.mixability,.additive.compatibility,.sooting.tendency.and.flash.point.[9].

There.is.no.operational.experience.with.furan-based.fuels.in.aviation.or.in.large-scale.production..

57..ANNEx.1

A.1.3.2.5 AlcoholsIn.chemical.terms,.alcohols.are.defined.as.a.series.of.oxygenated.hydrocarbons.that.are.often.created.via.the.fermentation.of.biomass.sugars.and.starches..Alcohols.are. lower-density. fuels.when.compared.with. the.current-generation.Jet-A. (1),.because.alcohol.fuels.are.oxygenated.hydrocarbons..Additionally,.alcohol.is.soluble.in.both.water.and.oil..

Alcohols. are. characterised. by. the. hydroxyl-group. (-OH). in. it,.which.makes. smaller. carbon. chain. alcohols. attract.water..This.can.lead.to.combustion.problems.in.aircraft.engines.and.has.therefore.to.be.excluded.from.consideration.as.a.jet.fuel..Alcohols.with.higher.carbon.chains.are.preferred.as.transportation.fuels;.simply.put,.the.smaller.the.carbon.chain,.the.lower.the.heat.content.[15]..Alcohols.can.be.produced.via.fermentative.and.non-fermentative.pathways..The.fermentative.pathway.is.well.known,.having.been.used.for.hundreds.of.years.to.produce.consumer.ethanol..The.non-fermentative.pathways.utilise.processes.that.extract.the.oxygen.atoms.from.the.basic.material.

Some.potential.alcohol.fuels.include:

•. Ethanol

The.production.of.ethanol.is.well.known.and.widely.applied..The.key.steps.of.the.feedstock-to-ethanol.conversion.process.are.shown.in.Figure.A.1.3.-.7..The.technical.and.practical.implementation.of.using.ethanol.in.commercial.aircraft.has.several.drawbacks..Due.to.the.low.energy.content,.28.9.MJ/kg,.an.aircraft.would.have.to.carry.about.60%.more.fuel.to.meet.the.same.mission..The.amount.of.extra.fuel.would.reduce.fuel.efficiency.between.15%.on.a.500.nautical.mile.mission.and.26%.on.a.3000.nautical.mile.mission,.compared.to.a.Jet-A.fuelled.plane.[16]..

Ethanol.is.applied.as.a.replacement.for.avgas,.aviation.gasoline,.in.Lycoming.IO.-360,.IO.-540.and.Cessna.152.aircraft.[17,.18]..In.Brazil.about.100.–.200.small.aircraft.are.converted.to.operate.on.ethanol..The.higher.octane.level.of.ethanol.allows.the.compression.ratio.of.the.engine.to.be.increased.for.higher.performance.and.fuel.efficiency.

•. Butanol

Butanol.is.the.only.high.carbon.chain.alcohol.that.is.produced.in.large.enough.quantities.to.be.a.transportation.fuel.substitute.[19,.20]..The.energy.content.of.butanol,.at.33.MJ/kg,.is.higher.than.that.of.ethanol,.but.is.still.less.than.the.minimum.required.heat.content.of.current.Jet.A-1.fuel,.42.8.MJ/kg.[13]..There.is.currently.no.operational.experience.with.butanol.in.aviation..

Figure.A.1.3.-.7:.Ethanol.production.steps.by.feedstock.and.conversion.technique


Alcohols.with.longer.carbon.chains.than.butanol.have.more.favourable.heat.content.(e.g..pentanol,.34.7.MJ/kg).but.they.have.neither.been.produced.through.fermentative.pathways.nor.considered.as.aviation.fuel.substitutes.[22,.23,.24,.25,.26,.27]..Therefore,.the.production.of.higher.chain.alcohols.by.non-fermentative.pathways.appears.to.be.more.promising.

Alcohols.alone.are.thus.not.suitable.as.a.commercial.aviation. fuel..However,.some.applications.are. found. in.general.and.agricultural.aviation,.e.g..in.Brazil,.where.the.use.of.bio.alcohols.as.a.transport.fuel.is.very.popular..In.these.cases.of.short-haul.flights.the.problem.of.low.energy.density,.i.e..high.fuel.weight,.is.less.severe..

Alcohols.may.also.be.used.as.feedstocks.for.other.chemical.conversion.processes..The.fermentation.process.needs.to.be.coupled.with.catalytic.polymerisation.technology. from.the.refining. industry. to.convert.ethanol.and/or.butanol. to. jet. range.hydrocarbons.

A.1.3.3 Gaseous FuelsGaseous.fuels.would.require.new.aircraft.design.including.significant.changes.in.aircraft.structure.and.fuel.systems..The.main.focus.of.commercial.and.military.aviation.industry.stakeholders.is.today.on.drop-in.fuels.[1,.9,.28]..This.paragraph.focuses.on.the.application.of.gaseous.fuels.for.aircraft,.which.today.still.represent.considerable.challenges.in.terms.of.aircraft.design.as.well.as.infrastructure.and.logistics..Their.widespread.use.is.therefore.not.envisaged.before.several.decades.from.now.

A.1.3.3.1 Compressed Natural GasNatural.gas.primarily. consists.of.methane.and.possesses.a.high.energy.density.of.50.MJ/kg..Compressing. it. to.around.200-220.bar.increases.the.volumetric.density.of.the.fuel,.although.the.trade-off.here.is.the.relatively.heavy.weight.of.high-pressure.tanks..Compressed.natural.gas.(CNG).is.used.in.public.transit.systems.(buses,.trucks,.taxies,.etc.).due.to.its.lower.price.(except.in.the.U.S.).and.local.environmental.benefits.[29,.30]...Use.of.CNG.as.an.aviation.fuel.is.not.applicable.in.the.foreseeable.future,.as.it.would.require.extensive.alterations.to.the.fuel.infrastructure.and.aircraft.equipment.

A.1.3.3.2 Liquid HydrogenHydrogen’s.energy.density.is.very.high.per.unit.mass.but.poor.per.unit.volume,.even.in.its.liquid.state..If.available.in.large.quantities,.however,.it.is.compatible.with.fuel.cells..Onboard.hydrogen,.stored.at.or.near.cryogenic.temperatures.(-253.oC),.can.also.enable.the.synergistic.integration.of.highly.efficient.and.power-dense.superconducting.electrical.components.into.an.aircraft.

If.hydrogen.were. to.be.used.as.a.combustible. fuel,.several.challenges. related. to.storage,.combustor.design. (high. flame.speed.of.hydrogen.[31]),.generation,.and.handling.would.have.to.be.overcome..Nevertheless,.there.are.precedents,.in.which.liquid.hydrogen.powered.aircraft.have.been.successfully.flown..A.Tu-155,.with.a.re-designed.and.hydrogen-fuelled.NK-86.starboard.engine,.completed.a.demonstration.flight.in.1988.[32]..A.Grumman.“Cheeta,”.powered.by.a.150.hp.Lycoming.E2G.engine.was.also.successfully.flown.on.hydrogen.in.1988.[33]..

In.the.case.of.the.Tu-155,.all.hydrogen.related.components.were.placed.inside.a.pressurised.container.for.safety.reasons..Although.the.lower.volume-density.of.liquid.hydrogen.forced.the.airframe.to.grow.larger.and.thus.have.significantly.degraded.aerodynamic.properties.(10%.or.more.reduced.lift-to-drag.ratio),.gains.were.quantified.in.the.following.areas:.a.66.to.75%.saving.in.fuel.load;.a.25.to.50%.reduction.in.gross.take-off.weight;.a.10.to.13%.increase.in.specific.thrust;.and.a.5.to.6%.reduction.in.engine.dimensions.[32]...However,.use.of.liquid.hydrogen.as.an.aviation.fuel.is.not.applicable.in.the.foreseeable.future,.as.it.would.require.extensive.alterations.to.the.fuel.infrastructure.and.aircraft.equipment..Moreover,.aircraft.that.are.able.to.fly.on.hydrogen.need.to.be.equipped.with.appropriate.systems.to.guaranty.safety..

A.1.3.3.3 Liquid MethaneBeyond.CNG.and.compressed.methane,.it.is.possible.to.further.compress.and.cool.methane.to.a.liquid.state.(-161.oC)..Similar.to.the.case.of.liquid.hydrogen,.it.is.necessary.to.maintain.the.near.cryogenic.temperature,.but.applying.methane,.instead.of.kerosene,.can.result.in.30.to.40%.reduction.in.pollutant.emissions.and.a.near.100%.reduction.in.particle.emissions..

The.energy.content.of.methane.(50.MJ/kg).is.16%.higher.than.conventional.jet.fuel.and.therefore.the.fuel.weight.will.be.lower.than.the.conventional.fuel.weight.of.Jet.A-1..The.density.of. liquid.methane.is.lower.than.Jet.A-1.resulting.in.a.higher.fuel.volume...Furthermore,.the.use.of.liquid.methane.would.involve.complicated.cryogenic.systems.and.high-pressure.fuel.tanks.that.would.have.significant.weight.penalties.for.aircraft.hardware.

59..ANNEx.1

A.1.3.3.4 Liquefied Petroleum GasLiquefied.Petroleum.Gas.(LPG).is.similar.to.liquid.methane,.except.that.its.constituent.components.are.mostly.butane.and.propane..Its.specific.power.and.energy.density.are.comparable.to.those.of.Jet.A(1)..Additionally,.the.fuel.poses.less.of.a.storage.challenge.than.LNG.or.LH2,.thanks.to.the.low.pressure.(±.8.bar).whereby.it.liquefies.at.room.temperature..The.main.challenge.with.LPG.is.meeting.future.demand..It.is.projected.that.75.million.tonnes.would.have.to.be.supplied.by.2010,.and.85.million.tonnes.would.be.needed.by.2015.[35]..However,.the.use.of.liquid.hydrogen.as.an.aviation.fuel.is.not.applicable.in.the.foreseeable.future.as.it.would.require.extensive.alterations.to.the.fuel.infrastructure.and.aircraft.equipment.

A.1.3.4 Thermodynamic properties of fuelsTable. A.1.3. -. 1. is. an. overview. of. the. thermodynamic. properties. of. selected. alternative. fuels.. Should. these. fuels. fail. to.meet.existing.specifications.as.jet.fuels.in.the.future,.the.aviation.industry.can.pursue.alternate.options,.such.as.recertifying.conventional.engines,.modifying.processes.to.yield.higher.energy-dense.fuel,.developing.acceptable.additives.to.adjust.for.densities,.and.applying.new.fuel.certification.

Table.A.1.3.-.1:.Thermodynamic.properties.of.alternative.aviation.fuels

Fuel Heat of Combustion (MJ/kg)

Flash Point (oC) Freeze Point (oC)

Jet A-1 42.8, minimum 38, minimum -47, maximum

Single Paraffinic Kerosene 43.8.–.44.2 45 -51

Hydroprocessed Renewable Jet (HRJ)

44.0.–.44.2 41.–.46.5 -54.5..to.–.63.5

Transester fuel ±38 ±135 -47.to.5

CNG 50 N.A -182.2

Liquid Hydrogen 120.(when.evaporated) -253.(Boiling.point) -259.2

Liquid Methane 50 -162.(Boiling.point) -182.5

Liquefied Petroleum Gas ±46 -.42.to.-.0.5.(Boiling.point.range).

<.-138.4

Furans ±38 ±-62

Butanol 33 37 -90

Ethanol 28.9 13 -114


Chapter References

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24.. Dickinson,.J.R..et.al.,.“A.13C.nuclear.magnetic.resonance.investigation.of.the.metabolism.of.leucine.to.isoamyl.alcohol.in.Saccharomyces.cerevisiae,”.J..Biol..Chem.,.vol..272,.pp..26871–26878,.1997.

25.. Dickinson,.J.R.,.Harrison,.S.J.,.and.Hewlins,.M.J.,.“An.investigation.of.the.metabolism.of.valine.to.isobutyl.alcohol.in.Saccharomyces.cerevisiae,”.J..Biol..Chem.,.vol..273,.pp..25751–25756,.1998.

26.. Dickinson,.J.R.,.Harrison,.S.J.,.Dickinson,.J.A.,.and.Hewlins,.M.J.,.“An.investigation.of.the.metabolism.of.isoleucine.to.active.Amyl.alcohol.in.Saccharomyces.cerevisiae,”.J..Biol..Chem.,.vol..275,.pp..10937–10942,.2000.

61..ANNEx.1

27.. Dickinson,.J.R..et.al..“The.catabolism.of.amino.acids.to.long.chain.and.complex.alcohols.in.Saccharomyces.cerevisiae,”.J..Biol..Chem.,.vol..278,.pp..8028–8034,.2003.

28.. Haacker,.J.,.“Four.Pillar.Strategy”.in.Global.Media.Day,.December.12,.2007.

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30.. Centre.Area.Transportation.Authority,.“CATA’s.Compressed.Natural.Gas.(CNG).Program:.1993.–.2006,”.http://www.catabus.com/accngprog.htm,.May,.2005.[Online;.accessed.12-September-2008]

31.. Briones,.A.M.,.Aggarwal,.S.K.,.and.Katta,.V.R.,.“Effects.of.H2.enrichment.on.the.propagation.characteristics.of.CH4-air.triple.flames,”.April.7,.2008.

32.. Fulton,.K.,.“Cryogenic-Fueled.Turbofans:.Kuznetsov.Bureau’s.pioneer.work.on.LH2.and.LNG.duel-fuel.engines,”.Aircraft.Engineering.and.Aerospace.Technology,.vol..65,.Iss..11,.pp..8-11,.1993.

33.. “Hydorgen.Fueled.Aircraft”,.Aircraft.Engineering.and.Aerospace.Technology,.vol..60,.Iss..8,.pp..26-27,.1988.

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35.. Poten.&.Partners,.“A.Global.LPG.Outlook..Poten.Keynote.Address.to.the.International.LP.Gas.Seminar,.Tokyo”,.http://www.poten.com/Document.aspx?id=3250&filename=Global%20LPG%20Outlook%20(Mar%202008).pdf,.February.28,.2008.[Online;.accessed.12-September-2008]..


A.1.4 Air Traffic ManagementWhereas.airframe.and.engine.technology.help.reduce.the.fuel.consumption.and.CO2.emissions.for.a.given.flight.length.and.profile,.improvements.in.air.traffic.management.aim.to.reduce.the.flight.length.itself.and.to.use.more.fuel-saving.climb.and.descent.profiles..For.these.improvements.to.be.effective,.both.the.aircraft.avionics.systems.and.the.air.navigation.service.providers’.ground.and.satellite-based.systems.must.be.equipped.with.the.appropriate.technologies..

A.1.4.1 Globally Harmonised Implementation of the Future ATM SystemCivil.aviation.is.expected.to.grow.over.the.next.decades..To.remain.competitive.with.other.national.transportation.systems,.civil.aviation.will.have.to.ensure.efficient,.safe.and.environmentally.sustainable.travel..[1]..This.challenge.requires.the.evolution.of.the.air.traffic.management.system.to.allow.optimum.use.of.enhanced.capabilities.through.technological.advancements...

Air.traffic.management.provides.the.means.for.airspace.efficiency.improvements.that.directly.relate.to.reduced.fuel.use.that.yield.reduced.emissions.for.aircraft...

The.International.Civil.Aviation.Organization.(ICAO).set.out.a.structure.to.support.the.future.of.a.global.air.navigation.system...Table.A.1.4.–.1.depicts.this.

Table.A.1.4.-.1:.ICAO.documentation.Structure.in.Support.of.a.Global.Air.Navigation.System.[1]

Air.Traffic.Management.(ATM).is.being.redefined.by.two.major.programmes,.The.next.Generation.Air.Transportation.System.(NextGen).[2,.3].in.the.U.S..and.the.Single.European.Sky.ATM.Research.(SESAR).in.Europe.[4]..Both.of.these.programmes.aim. to. increase. airspace.capacity.while. at. the. same. time. improving. efficiency,. safety. and. security..A. comparative. study.between. the.programmes.establishes.some.difference. in. their.Concept.of.Operations. (CONOPS). [5]..SESAR. is.opting.for.a.complete.“gate-to-gate”.process.while.NextGen.includes. intermodal.security.considerations.hence.a.“curb-to-curb”.approach.. Another. distinction. recognised. by.NextGen. is. the. impact. of.weather. on. the.U.S.. national. airspace. [5].. Both.NextGen.and.SESAR.are.expected.to.build.on.a.suite.of.enabling.technologies.to.bring.the.new.U.S..National.Airspace.vision.and.the.Single.European.Sky.from.vision.to.reality..

Description Objective Role

ATM Operational Concept The.ATM.Operational.Concept.(ATMOC).presents.the.ICAO.vision.of.an.integrated,.harmonised.and.globally.interoperable.air.navigation.system..The.planning.horizon.is.up.to.and.beyond.2025.

To.achieve.an.interoperable.global.air.navigation.system,.for.all.users.during.all.phases.of.flight,.that.meets.agreed.levels.of.safety,.provides.for.optimum.economic.operations,.is.environmentally.sustainable.and.meets.national.security.requirements

Vision

Global Air Navigation Plan Strategic.document.that.describes.the.methodology.for.global.air.navigation.harmonisation.

Establishes.the.focus.for.near.and.medium.term.activities.

Strategy

Global Plan Initiatives A.set.of.implementation.methodologies.derived.from.today’s.operational.environment.and.available.guidance.materials.

Measurable.progress.towards.the.implementation.of.the.ATMOC.

Tactics

Regional Plans Regional.work.programmes.including.the.planning.and.monitoring.of.the.detailed.activities.and.their.timelines,.which,.inter.alia,.lead.to.the.realisation.of.a.global.air.navigation.system.as.envisaged.in.the.operational.concept.

Contains.the.performance.directives.and.associated.requirements.for.facilities.and.services,.established.through.regional.air.navigation.agreements,.in.support.of.the.global.air.navigation.infrastructure.

Action

64..ANNEx.1

A.1.4.2 Enabling Technologies Enabling. technologies. are. required. to. provide. the. capabilities. envisaged. by. SESAR. and. NextGen.. Depending. on. the.technologies’.maturity,. they.will. have.different.development. roadmaps. from.concept. to. service. application.. Technologies.planned.for.a.later.time.frame.will.require.further.research,.development,.regulation,.certification.and.implementation..Once.this.cycle.is.complete,.the.technology.will.be.considered.safe.and.mature.enough.for.commercial.application..

Technologies’. enablers. related. to. operational. improvements. can. be. found. for. SESAR. at. “The European Air Traffic Management Master Plan Portal”.[6],.and.for.NextGen.at.“Next Generation Air Transportation System – Joint Planning and Development Office”.[7]..These.two.interactive.websites.include.large.databases.of.information.regarding.technology.benefits,.objectives,.needs,.roadmaps,.and.relationships.with.the.concept.of.operations..

From.these.two.sources.of.information,.one.common.objective.stands.out.–.to.improve.ways.of.sharing.and.communicating.information.between.all.the.air.transportation.system.stakeholders..Consequently,.the.next.sections.will.focus.on.the.aircraft.centric.avionics.technologies.required.to.enable.the.following.capabilities.of.the.future.air.transportation.system.[8]:.

• Safety enhancements;

• Published routes and procedures;

• Negotiated trajectories;

• Delegated separation;

• Low visibility approach/departure and taxi;

• ATM efficiencies.

Aircraft. systems. are. in. transition. from. traditional. federated. solutions. that. enable. access. to. airspace. to. a. more. robust,.performance-based.approach.that.is.not.equipment.specific,.but.outlines.the.performance.necessary.to.operate.in.the.future.airspace...This.allows.aircraft.to.operate.in.the.most.effective.and.efficient.way.

The.aircraft.based.avionic. technologies.have.been.grouped. into. five.categories:.communication,.navigation,.surveillance,.hazard.and.safety.systems,.and.airborne.automation.(displays.and.decision.support.tools)..These.sections.provide.examples.of.avionic.technologies.but.do.not.provide.an.exhaustive.list.of.all.ATM.technologies.available...Furthermore,.Section.A.1.4.3.will.discuss.the.environmental.impacts.of.using.avionics.technologies.within.specific.operational.concepts..

A.1.4.2.1 Communication The.need.for.improved.information.sharing.between.aircraft.and.ground.automation.systems.to.support.enhanced.airspace.operations.will.be.met.through.collaborative.decision.making.capabilities.that.engages.all.stakeholders.in.the.system...This.information.sharing.need.is.driving.the.shift.from.traditional.analogue.voice.communications.to.enhanced.digital.data.links...These.exchanges.will.include.airline.operations.centres,.air.traffic.service.providers,.and.the.flight.deck...Both.NextGen.and.SESAR.recognise.the.need.for.this.information.exchange.through.expanded.communications.capabilities.often.referred.to.as..network-enabled.communication.exchanges..Table.A.1.4.-.2.lists.an.example.set.of.communication.technologies.

Based.on.these.key.technology.enablers,.different.hardware.and.software.configurations.are.under.investigation.[9]..Data.communication.is.expected.to.enhance.security.as.well.as.effectiveness..

ATN Aeronautical Telecommunications NetworkCommunications.Protocol.for.Communications.Management

FANS-1/A FANS-1/A Communications ProtocolOceanic.Data.Link.Communications.using.SATCOM

ACARS Aircraft Communications and Reporting SystemVHF/HF/SATCOM

Table.A.1.4.-.2:.Communications.Enabling.Technologies.[8,.9]


A.1.4.2.2 Navigation Navigation. is. evolving. from.ground. based. navigation. aids. to. satellite. based. positioning. systems. coupled.with. on-board.navigation. solutions.. Additionally,. navigation. requirements. are. evolving. from. specific. navigation. sensor. equipment. to.performance-based.navigation.[10,.11].specifications.(defined.in.terms.of.accuracy,.integrity,.availability,.functionality,.and.containment).needed.for.operation.in.the.context.of.a.particular.airspace.concept.(e.g..Flow.Managed.Airspace,.Terminal.Airspace,.Autonomous.Airspace)..Table.A.1.4.-.3.lists.an.example.set.of.navigation.technology.enablers..

These.technologies.support.more.precise.operations.that.enhance.repeatability.and.allow.improved.path.and.performance.management...By.coupling.the.path.and.performance.to.the.automation.systems,.improvements.in.routing.efficiency,.flexibility,.and.predictability.ensure.optimised.fuel.utilisation.and.reduced.emissions.

A.1.4.2.3 SurveillanceATM.surveillance.is.transitioning.from.ground.based.radar.technologies.to.cooperative.surveillance.technologies,.such.as,.Automatic.Dependent.Surveillance.Broadcast. (ADS-B)..ADS-B.allows. improved.monitoring.by.providing.precise.aircraft.position. information. to. the. separation.management. systems.. . The. technology. uses. precision. positions. derived. from. the.signals. from.GNSS.that.are. then.broadcast.using.on-board. transponders. to.provide.pilots.and.controllers.with.accurate.information.regarding.aircraft.separation.in.flight.and.on.the.ground.[13]..Table.A.1.4.-.4.lists.an.example.set.of.surveillance.technology.enablers.

ADS-B.is.enabled.with.both.the.cooperative.broadcast.of.position,.address,.etc..called.ADS-B.Out.as.well.as.the.ability.to.receive.and.display.other.traffic.in.the.air.and.on.the.ground.using.ADS-B.In...ADS-B.In.will.greatly.improve.the.situational.awareness.on.the.flight.deck...But.beyond.the.visual.representation.of.adjacent.traffic,.the.on-board.automation.can.process.the.information.and.issue.aural.and.visual.alerts.to.the.pilot.should.a.conflict.occur...

ADS-B OUT Automatic.Dependent.Surveillance.Broadcast..[14,.15]

FIS-B Flight.Information.Service-Broadcast.[22]

ADS-B IN Automatic.Dependent.Surveillance.Broadcast..[14,.15]

TIS-B Traffic.Information.Service.–.Broadcast

ADS-C Automatic.Dependent.Surveillance.Contract.[16]

Table.A.1.4.-.3:.Navigation.Enabling.Technologies.[8]

Table.A.1.4.-.4:.Surveillance.Enabling.Technologies

GNSS Global Navigation Satellite System

e.g..GPS,.Galileo,.GLONASS,.etc.

SBAS Satellite Based Augmentation System

e.g..WAAS

GBAS Ground Based Augmentation System

e.g..LAAS

GLS GPS.Landing.Systems.[12]

FMS Flight.Management.Systems

66..ANNEx.1

A.1.4.2.4 Hazard and Safety SystemsCollision.avoidance,.terrain.and.obstacle.awareness,.weather.–.both.tactical.and.strategic,.all.support.the.hazard.and.safety.systems.of.the.aircraft...By.integrating.each.of.the.“threats”.offered.by.these.sensors,.an.improved.path.can.be.developed.and.optimised...Further,.the.independence.of.these.systems.from.other.traditional.sensors.ensures.that.safety.can.be.maintained.in.the.event.of.the.loss.of.any.single.sensor.

Each.of.these.sensors.provides.a.constraint.to.the.flight.path.that.is.considered.and.optimised.in.near.real.time.and.exchanged.with.ground.automation.to.integrate.all.information.into.the.necessary.decision.support.tools.

A.1.4.2.5 Airborne ATM – Displays and Decision Support ToolsFuture.airspace.will.rely.on.a.distributed.decision.making.system.comprised.of.airborne.and.ground.decision.support.tools...Today’s.visual.flight.rule.infrastructure.will.be.duplicated.in.all.weather.operations.using.Equivalent.Visual.Operations.based.on.enhanced.display.capabilities...Table.A.1.4.-.5.lists.an.example.set.of.display.and.decision.support.technology.enablers..

These.technologies.are.expected.to.enhance.the.flight.crew.awareness.by.providing.them.with.relative.spacing.with.other.aircraft,. information.such.as. track.and.ground.speed,.and.clear.synthetic. images. in. low.visibility.situation.. is.showing.an.example.of.synthetic.vision.systems..

The. integration.of.on-board.databases.and.displays.will. further. improve. integrated.operations.. .Moving.map.displays. for.surface.operations,.en-route.charts.and.maps,.and.the.trend.toward.the.“paperless.cockpit”.will. remove.weight. from.the.aircraft.which.provides.a.residual.fuel.saving.while.improving.overall.operations...Enhanced.planning.and.performance.tools.will. be. integrated. in. secondary. planning. tools. like. Electronic. Flight.Bags,.which.may. also. enable. enhanced. operational.capabilities.on.aircraft.

Figure.A.1.4.-.1:.Synthetic.vision.[20]

CDTI Cockpit.Display.of.Traffic.Information..[18] HGS Head-up.Guidance.Systems

EFVS Enhanced.Flight.Vision.Systems.[19] Traffic Computer

Integration.of.Traffic.Information.and.Conflict.Management.System

SVS Synthetic.Vision.Systems.[20] Performance Computer

Path.Performance.Calculation.(part.of.the.FMS)

Table.A.1.4.-.5:.Displays.and.Decision.Support.Tool.Enabling.Technologies.[8]


A.1.4.3 Operational Concepts The.objective.of.the.TERESA.programme.is.to.assess.the.environmental.impacts.of.technologies.on.the.reduction.of.fuel.burn.and.emissions..For.most.of.the.airframe.and.engine.technologies,.it.is.possible.to.identify.a.direct.link.between.the.application.of.the.technologies.and.their.environmental.impact..However.for.the.avionic.ATM.technologies,.their.environmental.benefits.are.blended.within.the.operation.of.the.aircraft,.which.is.dependant.on.the.procedures.and.regulations.in.place.within.the.respective.national.airspace..Consequently,.the.avionics.technology.environmental.impacts.need.to.be.assessed.within.a.set.of.operational.concepts..Table.A.1.4.-.6.lists.four.operational.concepts.planned.for.NextGen.and.SESAR.that.require.the.implementation.of.ATM.avionics.technologies.

Table.A.1.4.-.6:.Operational.Concepts.Overview

Using.a.single-aisle.aircraft.(B-737.or.A-320).as.baseline,.one.can.estimate.the.combined.impacts.of.the.operational.concepts.described.above.with.the.avionics.technologies..Table.A.1.4.-.6.shows.fuel.burn.reduction.between.the.operational.concepts.(including.the.avionics.technologies).and.with.four.areas.of.operations..It.assesses.the.impact.on.fuel.burn.as.low,.medium.or.high..The.impacts.are.based.on.a.notional.single-aisle.aircraft.mission.of.5,000.km.range.using.approximately.18,000.kg.of.fuel...Consequently,.a.low.impact.mission.can.be.assumed.to.reduce.the.fuel.burn.by.less.than.1%.(<180kg),.medium.impact.between.1%.to.3%.(180.to.540.kg).and.a.high.impact.by.more.than.3%.(>.540.kg)..

Table.A.1.4.-.7:.Qualitative.Assessment.of.Fuel.Burn.Reduction.due.to.ATM.Technologies..

Concept Ground Terminal Area En-Route Oceanic

Performance.Based.Operations

Low High Medium Medium

Trajectory.Based.Operations

Low High High High

Delegated.separation Medium Low High

Low-visibility.operations Medium Medium

Reduced.separation Medium Low Low

Concept Description Enabling technologies Examples

Trajectory based and operations

Aircrafts.will.fly.pre-negotiated.trajectories.and.the.air.traffic.control.will.shift.from.fixed.to.dynamic.clearances.based.on.performance-.based.airspace.principles.[21].

•.Communications.

•.Navigation.

•.Surveillance

Optimised.Profile.Climbs.and.Descents.(e.g..Continuous.Descent.Arrivals),.4D.Trajectories,.Required.Time.of.Arrival.

Delegated separation Capability.of.the.aircraft/flight.crew.to.accept.the.delegated.separation.responsibility.from.ATC.[22].

•.ADS-B.(IN/OUT) Merging.and.Spacing,.Closely.Spaced.Parallel.Runway,.and.Terminal.area.operations

Low-visibility operations Some.operators.are.required.to.access.airport.in.all.visibility.conditions.

•.Enhanced.Flight.Vision..System.

•.Synthetic.Vision.Systems.

All.Weather.Operations.in..all.phases.of.flight

Reduced separation Reducing.the.distance.between.aircrafts.to.increase.the.airspace.efficiency.and.terminal.areas.capacity.

•.ADS-B.(IN/OUT)

•.RNP/RNAV

•.Improved.GNSS.Sensors

Sequencing.and.merging,.Crossing.and.passing,.Independent.Parallel.or.Converging.Approach

68..ANNEx.1

Performance.based.operations.ensure.that.the.right.information.is.available.at.the.right.time.to.optimise.decisions...Figure.A.1.4.–.2.illustrates.the.planning.horizons.of.performance-based.airspace...From.the.early.planning.horizon.to.the.actual.flight.execution,.information.exchange.is.critical.to.optimised.system.performance.

.Figure.A.1.4.-.2:.Performance.Based.operations.–.Planning/Execution.Time.Horizon.[10]

Energy.managed.operations.are.a.significant.part.of.the.performance.system...This.includes.surface.operations.where.minimum.runway.occupancy. times,.direct. taxi-to-gate.path.optimisation. through.data. link.delivery.of. taxi.clearances,.and.brake-to-vacate.principles.are.applied.to.minimise.the.time.the.aircraft.is.powered.and.operating...Terminal.area.operations.will.utilise.Optimized.Profile.Climb.and.Descent.procedures.to.minimise.fuel.consumption.during.these.critical.phases.of.flight.

Trajectory.Based.Operations.are.focused.on.overall.business.efficiencies,.which.further.minimise.fuel.consumption...Scheduled.operations.are.structured.to.ensure.minimal.disruptions.to.the.planned.flow.by.exchanging.information.throughout.the.flight.with.a.focus.on.performing.to.precise.times.of.arrival.at.key.“waypoints”.such.as.top.of.climb.and.top.of.descent...System.constraints.are.exchanged.and.are. integrated. into. the.path.and.performance.profiles.of. the.aircraft. to.ensure.optimised.energy.management.

Part.of.that.system.optimisation.will.be.to.delegate.certain.operations.to.the.aircraft.to.perform.key.in-flight.procedures.like.merging.and.spacing.and.sequencing.of.aircraft.to.optimise.system.flows...This.is.enabled.by.improved.information.sharing.between.the.aircraft.and.ground.planning.systems.of.the.future.

To.improve.system.efficiencies.further,.the.impact.of.weather.and.other.unplanned.events.will.be.minimised.through.improved.prediction.tools.and.high.integrated.system.components...Low.visibility.operational.capabilities.on.the.aircraft.will.provide.equivalent.visual.operations.during.degraded.visual.operations...The.use.of.enhanced.and.synthetic.vision.systems.will.enable.operations.in.impaired.conditions.


Improved.surveillance.and.optimised.path.management.tools.on.the.aircraft.will.allow.an.overall.reduction.in.separation.and.new.procedures.can.be.developed. to. improve. system.performance. in. high.density. operations.. The. improved. situational.awareness.of.on-board.and.ground.tools.will.enhance.the.performance.of.the.system.through.all.phases.of.flight.

The.implementation.of.the.operational.concept.taking.full.advantages.of.the.enabling.avionics.technologies.will.require.time..The.Federal.Aviation.Administration.in.the.US.(FAA).is.targeting.mid-term.(2018).operations,.such.as.Required.Navigation.Performance. (RNP),. leveraging. existing. infrastructure. and. current. aircraft. capabilities. [25].. In. this. case,. aircraft. avionics.technologies.would.further.evolve.to.include.data.communication,.GLS,.ADS-B.IN/OUT,.and.CDTI..It.is.expected.that.these.new.capabilities.will.have.a.significant.impact.on.airspace.efficiency..The.full.efficiency.potential.of.the.ATM.system.will.require.longer.term.improvements.in.trajectory.management,.flow.contingency.management.and.capacity.management.

As.a.consequence,.the.fuel.burn.reduction.achievable.with.the.new.operational.concepts.will.increase.step.by.step.in.the.next.years,.in.line.with.growing.implementation.of.both.ground./.satellite-based.systems.and.new.avionics.onboard.aircraft..Current.estimates.vary.between.a.4%.improvement.in.worldwide.average.between.2005.and.2020.and.a.goal.of.10.to.12%.improvement.in.the.SESAR.programme..There.is.a.significantly.higher.improvement.potential.in.already.congested.airspaces.and.airports.like.Europe.or.the.United.States,.compared.to.a.worldwide.average,.where.many.routes.through.uncongested.airspace.are.already.near.to.optimal.

70..ANNEx.1

Chapter References

1.. International.Civil.Aviation.Organization,.“Global.Air.Navigation.Plan”,.Doc.9750.AN/963,.Third.Edition,.2007..

2.. Federal.Aviation.Administration,.“FAA’s.NextGen.Implementation.Plan.–.Overview.2008”,.online:.http://www.faa.gov.[last.accessed.January.27th,.2009].

3.. International.Air.Transport.Association,.“NextGen.Federal.Aviation.Administration’s.Next.Generation.ATM”,.online:.http://www.iata.org.[last.accessed.January.27th,.2009].

4.. Eurocontrol,.“SESAR”,.online:.http://www.eurocontrol.int/sesar/public/subsite_homepage/homepage.html.[last.accessed.January.27th,.2009].

5.. Joint.Planning.and.Development.Office,.“A.Comparative.Assessment.of.the.NextGen.and.SESAR.Operational.Concepts”,.Paper.No:08-001,.Washington,.DC,.May,.2008..

6.. Eurocontrol,.“The.European.Air.Traffic.Management.Master.Plan.Portal”,.online:.https://www.atmmasterplan.eu,.[last.accessed.January.29th,.2009]...

7.. Joint.Planning.and.Development.Office,.“Next.Generation.Air.Transportation.System.–.Joint.Planning.and.Development.Office”,.online.http://jpe.jpdo.gov/ee/,.[last.accessed.January.29th,.2009]...

8.. Joint.Planning.and.Development.Office,.“NextGen.Avionics.Roadmap”,.Version.1.0,.October.2008..

9.. Federal.Aviation.Administration,,.“Data.Communication.Programs.–.Avionic.discussion”,.faaco.faa.gov/attachments/Avionics_Summary_for_12_23_08_release.doc.[last.accessed.February.25th,.2009]

10.. Joint.Planning.and.Development.Office,.“Concept.of.Operations.for.the.Next.Generation.Air.Transportation.System”,.Version.2.0..June.2007.

11.. Butler,.V..Increasing.Airport.Capacity.Without.Increasing.Airport.Size..Reason.Foundation,.2008

12.. Rockwell.Collins,.“GPS.navigation.and.precision.landing.system”,.http://www.rockwellcollins.com/content/pdf/pdf_10575.pdf.,.[last.accessed.February.25th,.2009].

13.. Federal.Aviation.Administration,.“Fact.Sheet.–.Automatic.Dependent.Surveillance-Broadcast.(ADS-B)”,.online:..http://www.faa.gov.[last.accessed.January.27th,.2009].

14.. Federal.Aviation.Administration,.“Automatic.Dependent.Surveillance.Broadcast.(ADS-B)”,.online:.http://www.faa.gov/airports_airtraffic/technology/ads-b/,.[last.accessed.January.28th,.2009].

15.. Civil.Aviation.Safety.Authority,.““Automatic.Dependent.Surveillance-.Broadcast.(ADS-B)”,.Australian.Government,.online:.http://www.casa.gov.au/pilots/download/ads-b.pdf,.[last.accessed.January.28th,.2009].

16.. Federal.Aviation.Administration,.“Aeronautical.Information.Manual.–.Official.Guide.to.Basic.Flight.Information.and.ATC.Procedures”,.07/31/08,.http://www.faa.gov/airports_airtraffic/air_traffic/publications/atpubs/aim/,.[last.accessed.February.25th,.2009]..

17.. Eurocontrol,.“ADS-C:.Automatic.Dependent.Surveillance-Contract”,.http://elearning.eurocontrol.int/ATMTraining/PreCourse/SUR/ADS/Taste%20the%20Course/32501.10.32657.77.16014/Default.html,.[last.accessed.February.25th,.2009].

18.. NASA.AMES,.“Advanced.Cockpit.Situation.Display”,.Flight.Deck.Display.Research.Laboratory,.http://human-factors.arc.nasa.gov/ihh/cdti/cdti.html.[last.accessed.February.25th,.2009]..

19.. Rockwell.Collins,.“Enhanced.Vision.System.to.be.offered.on.Falcon.EASy.aircraft”,.October.2004,.http://www.rockwellcollins.com/news/prn_page5706.html,.[last.accessed.February.25th,.2009].

20.. NASA,.“No.More.Flying.Blind”,.October.5ht,.2004,.http://www.nasa.gov/vision/earth/improvingflight/svs_reno.html,.[last.accessed.February.25th,.2009].

21.. Federal.Aviation.Administration,.“Initiate.Trajectory.Based.Operations”,.online:.http://www.faa.gov.[last.accessed.January.28th,.2009].

22.. Federal.Aviation.Administration,.“Aircraft.and.Operator.Requirements.–.Solution.Set.Smart.Sheet”,.online:...http://www.faa.gov.[last.accessed.January.28th,.2009].

23.. ARINC,.“Meteorological.Data.Collection.and.Reporting.Systems”,.http://www.arinc.com/products/weather/mdcrs.html,.[last.accessed.February.25th,.2009].

24.. Eurocontrol,.“Flexible.Use.of.Airspace.(FUA)”,.online:.http://www.eurocontrol.int/airspace/public/standard_page/148_FUA.html,.[last.accessed.January.27th,.2008].

25.. Federal.Aviation.Administration,.“NextGen.Targeted.Mid-Term.Avionics”,.Updated.February.5th,.2009;.online:..http://www.faa.gov.[last.accessed.February.26th,.2009].


Annex 2 Technology Evaluation

Methodology and Assessment Matrices

Prepared for and elaborated with the results of theTechnology Assessment Workshop-Georgia Institute of Technology, Atlanta, GA 30 September – 1 October 2008


A.2.1 Methodology A.2.1.1 IntroductionA.two-day.workshop.was.held.at.the.Aerospace.Systems.Design.Laboratory.(ASDL).of.the.Georgia.Institute.of.Technology.on.30.September.and.1.October.2008. in. the. framework.of. the.TERESA.project.. Its.main.objective.was.to.prioritise. the.identified.technologies.with.respect.to.IATA’s.goals.of.reducing.fuel.burn.and.greenhouse.gases.(GHGs),.identified.in.Table.2-3.of.the.IATA.Technology.Roadmap.report..This.Table.is.reproduced.as.Table.A.2.1.-.1.below.

.

Goals Aircraft.Attributes Implementation.Criteria

Improve.fuel.efficiency Reduce.airframe.weight Increase.aerodynamic.efficiency

Ability.to.retrofit

Reduce.green.house.gases Reduce.engine.weight Increase.fuel.energy.density Retrofit.costs

Improve.local.air.quality Reduce.specific.fuel.consumption

Increase.non-propulsive.energy.efficiency

R&D.investment.required

Reduce.community.noise Reduce.airframe.noise Increase.air.traffic.management.system.flexibility

Annual.operating.costs

Increase.capacity./.reduce.delays

Reduce.engine.noise Increase.asset.utilisation On-aircraft.investment.costs

Increase.operational.efficiency

Reduce.non-CO2.emissions Maintain.infrastructure.compatibility

Time.for.implementation

Reduce.maintenance.costs Technology.Readiness.Level

Reduce.personnel.costs

Reduce.delays

Table.A.2.1.-.1:.Goals,.implementation.criteria.and.aircraft.attributes.considered.at.workshop

As. illustrated. in.Figure.A.2.1. -.1,. the. impact.of. the. technologies. implemented.by. the.OEMs.and.at. the.operational. level.influences.the.airlines.(i.e..better.fuel.efficiency,.weight.reduction,.lower.carbon.emissions).and.ultimately.induces.a.beneficial.impact.on.the.environment.

Figure.A.2.1.-.1:.Impact.of.technology.on.OEMs,.airlines,.and.the.environment

73..ANNEx.2

Each.technical.group.was.given.tasks:.first,.to.categorise.each.technology.in.terms.of.retrofitability,.rough.order.of.magnitude.of.costs.and.technology.maturity;.and.secondly,.qualitatively.assess.the.impact.of.the.technologies.on.a.pre-defined.list.of.aircraft.attributes.(Table.2-3.of.Roadmap.Report)..The.contribution.of.the.aircraft-level.attributes.to.the.top-level.goals.was.then.agreed.by.all.participants..Subsequently,.the.consensus.that.was.reached.in.each.step.of.the.workshop.was.compiled.in.an.ASDL-developed.technology.ranking.and.prioritisation.tool..What.follows.is.a.more.detailed.description.of.methodological.and.procedural.aspects.of.the.workshop.itself.

A.2.1.2 BackgroundTraditional.methods.of.investment.in.technology.development.programs.have.been.described.as.lacking.rigor.and.ad.hoc..Szakony.states,.“Many.Research.and.Development.(R&D).selection.techniques.have.been.developed.in.the.last.30-40.years,.but.few.have.been.used.by.R&D.companies.in.industry..In.fact,.the.methods.used.aren’t.much.more.advanced.than.two.or.three.decades.ago,.even.though.the.state.of.the.art.has.advanced.rapidly”.[1]..Reinforcing.this.statement,.Cetron.observes.five.traditional.approaches.of.allocating.R&D.resources.for.technology.development.[2]:

Squeaking.Wheel:.cut.resources.from.every.area,.then.wait.and.see.which.area.complains.the.most..Based.on.the.•.loudest.and.the.most.insistent,.allocate.the.restored.budget.until.ceiling.is.hit.

Level.Funding:.budget.perturbations.minimised.and.status.quo.maintained;.if.this.approach.continues.within.a.rapidly.•.changing.technology.field,.the.company,.group,.or.agency.will.end.up.in.serious.trouble.

Glorious.Past:.“once.successful,.always.successful;”.assign.resources.only.on.past.record.of.achievement.•.

White.Charger:.best.speaker.or.last.person.to.brief.the.boss.wins.the.money.or.whichever.department.has.the.best.•.presentation.

Committee:.a.committee.tells.the.decision-maker.how.to.allocate.resources.•.

Based. on. the. above-mentioned. observations,.Cetron. emphasises. that. the. scientific. and. objective. foundations. of. these.approaches.are.lacking.and.naïve,.but.such.approaches.are.in.widespread.use..Therefore,.the.resultant.business.case.lacks.substance,.which.strongly. suggests. the.need. for. a.means.by.which.more. informed.and.substantiated.decisions.can.be.made.

A.2.1.3 Strategic Prioritisation and Planning Applied to TERESAThe.Strategic.Prioritisation.and.Planning.(SP2).process.is.an.approach.developed.at.ASDL.with.the.intention.to.specifically.address. the. shortcomings. of. the. traditional. resource. allocation. approaches.. This. process. provides. a. means. by. which.technology.strategic.plans.may.be.more.rigorously.justified.by.addressing.the.following.questions:

What.are.the.strategic.goals?•.

How.much.performance.capability.is.needed.to.meet.the.goals?•.

How.difficult.is.it.to.achieve?•.

When.is.the.entry.into.service.date?•.

How.risky.is.the.endeavour?•.

How.is.expert.opinion.incorporated?•.


The.SP2.process.can.be.considered.an.evolution.of.Quality.Engineering.Methods,.including.Quality.Function.Deployment.(QFD).and.Design. for.Six.Sigma. (DFSS),.but.with.various.dynamic.aspects. that.allow. the. formulation.of.a.portable.and.powerful.decision.making.environment..It.has.been.extensively.utilised.in.a.Congressional.study.for.an.integrated.five-year.research.and.technology.plan.for.U.S..aeronautics.[3].. It.was.also.applied.to.the.NASA.Exploration.Systems.Architecture.Study,.as.well.as.the.NASA.Vehicle.Systems.Program.and.the.Office.of.Naval.Research.Science.and.Technology.

The.SP2.process.is.composed.of.eight.steps.starting.with.the.scope.definition.and.ending.with.the.creation.of.an.interactive.decision-making.support.tool,.as.illustrated.in.Figure.A.2.1.-.2..This.tool.should.be.regarded.as.a.living.document,.allowing.the.decision.makers.to.analyse.different.technology.portfolios.under.multiple.scenarios.

Figure.A.2.1.-.2:.SP2.Implementation.for.TERESA.project

The. “Group. Telecons”. prior. to. the.workshop,. shown. in. Figure. A.2.1. -. 2,. were. used. to. gather. the. required. technology.information,. which.was. then. used. to. create. an. initial. structure. between. the. organisational. goals,. aircraft. attributes. and.technology.characteristics.depicted.in.Figure.A.2.1.-.3..During.this.phase,.it.was.important.to.define.the.terminology.used.in.the.mapping.structure..These.definitions.are.critical.to.build.the.common.nomenclature.used.during.the.ensuing.workshop.

Figure.A.2.1.-.3:.Mapping.decomposition.and.synthesis

The.information.necessary.to.establish.a.balanced.portfolio.should.also.be.identified,.which.may.include.schedule,.budgets,.sources.of.funding,.risk,.and.specific.timeframes..Such.information.will.vary.based.on.the.problem.at.hand.and.the.organisation..

75..ANNEx.2

In.many.instances,.the.goals.will.vary.based.on.a.near-,.mid-,.or.long-term.perspective..For.each.timeframe,.a.set.of.scenarios.may.be.defined.to.capture.the.variation.of.importance.of.the.organisational.goals.The.mappings.presented. in.Figure.A.2.1.-.3.are.slightly.different. from.the.relationships.established. in. the.QFD.process..Unlike.a.traditional.QFD,.which.only.considers.the.strengths.of.the.identified.relationships,.the.SP2.process.also.considers.the.direction.of.each.relationship..A.scale.that.can.be.customised,.usually.consisting.of.seven.levels,.is.used.to.define.the.qualitative.relationships..The.qualitative.descriptions.for.the.seven.levels.and.the.translation.to.a.quantitative.scale.are.then.defined..In.general,.a.non-linear.utility.function.is.used.for.this.relationship.to.discriminate.the.medium.to.strong.impacts.from.the.weak.relationships..As.the.planning.matrix.is.populated,.the.rationale.as.to.the.relationships.should.be.documented.such.that.an.audit.trail.of.information.is.generated..Once.the.planning.matrix.is.complete,.the.relative.contribution.of.each.attribute.to.all.of.the.customer.requirements.can.be.determined.via.matrix.manipulation.

A.2.1.4 Breakout SessionsThe.mappings. between. the. Industry.Goals,. Aircraft. Attributes. and. Technologies.were. populated. during. the. technology.assessment.workshop. in. the. form.of. two.matrices..These.matrices.are. illustrated. in.Figure.A.2.1.-.4,.and.they.represent.the.mapping.between.the.industry.goals.and.aircraft.attributes,.and.that.between.the.aircraft.attributes.and.the.technology.characteristics..Consequently,.five.breakout.sessions.took.place:.four.technically-oriented.sessions.and.one.industry-oriented.session.that.required.every.participant’s.input..In.these.breakout.sessions,.a.qualitative.relationship.between.each.element.was.mapped.via.a.structured.matrix,.and.the.results.of. this.mapping.exercise.were.subsequently.compiled. into.and.then.analysed.within.a.technology.prioritisation.and.ranking.tool.

The.technical.breakout.sessions.called.for.the.participants.to.be.grouped.by.the.industry.that.they.represent.to.review.the.technologies.and.populate.the.mapping.between.the.technology.characteristics.(e.g..weight.variation).and.aircraft.attributes.(e.g..performance)..The.participants.from.the.various.research.centres.were.given.the.choice.to.attend.the.sessions.that.best.matched.their.expertise.

The. industry. breakout. session. assessed. the. mapping. between. the. aircraft. attributes. and. the. air. transport. goals.. This.session.was.conducted.with.all.workshop.participants.to.evaluate.the.potential.of.the.current.and.future.aircraft.to.meet.the.environmental.challenges.of.tomorrow.

The.results.of.the.breakout.sessions.were.compiled.and.synthesised.at.the.end.of.the.first.day.of.the.workshop..The.synthesis.approach.and.results.were.presented.at.the.beginning.of.the.second.day..Subsequently,.the.decision.making.tool.was.used.to.evaluate.how.the.technology.development.programmes.could.be. leveraged.to.address.the.environmental.air. transport.challenges..

Figure.A.2.1.-.4:.Format.of.breakout.sessions


A.2.2 Evaluation and ResultsA.2.2.1 Evaluation MappingThis.section.presents.the.actual.mapping.performed.by.the.TERESA.partners.during.the.workshop.of.30.September.and.1.October.2008..The.mapping.between.the.environmental.air.transport.goals.and.the.aircraft.attributes.is.presented.in.Table.A.2.2.-.1:..This.mapping.was.performed.by.all.workshop.attendees.gathering.again. in. the.same.room.after. the.breakout.sessions..Attendees.agreed.the.final.selection.of.the.mapping..The.strength.of.the.mapping.(high,.medium.and.low).represents.the. level. of. correlation.between. the.goals. and.attributes. regardless.of. the.direction. (good.or.bad).. The.direction.of. the.relationships.will.be.assessed.in.the.subsequent.mappings..

Table.A.2.2.-.1:.Mapping.between.air.transport.goals.(top).and.aircraft.attributes.(left)

The.subsequent.figures.represent.the.airframe.and.engine.technology.mappings..These.mappings.were.established.during.the.breakout.session.phase.of.the.workshop,.implying.that.only.the.technical.experts.in.the.respective.fields.participated.in.the.evaluation..For.each.of.the.subsystems,.two.types.of.mapping.were.performed:.filters.used.for.technology.categorisation.and.down-selection,.and.mapping.between.the.technologies.and.aircraft.attributes..Seven.filters.were.used;.they.are.listed.with.their.respective.options.in.Table.A.2.2.-.2...These.filters.represent.an.order of magnitude.and.not.a.unique.number;.for.instance.selecting.annual.operating.costs.of.“1%”.means.that.the.operating.costs.for.that.specific.technology.are.estimated.to.be.between.1.%.and.10%...

77..ANNEx.2

Table.A.2.2.-.3.lists.the.mapping.used.to.evaluate.the.relationships.between.the.technologies.and.the.aircraft.attributes..This.mapping.is.directional.since.it.includes.a.“benefit”.and.“degradation”.aspect..Consequently,.the.direction.of.improvement.of.the.technologies.is.taken.into.account.when.the.overall.impact.of.the.technologies.is.combined.with.the.air.transport.goals..

FILTERS Available.for.Retrofit.to.Existing.Fleet

Estimated.R&D.investment.required.to.develop.the.technology.(by.OEM)

Annual.Operating.costs.(by.airline)

On-aircraft.investment.costs

Retrofit.costs.per.aircraft.(average.estimate)

Timeline.to.be.available.for.commercial.aviation

Current.development.status.(TRL.#)

OPTIONS Applicable.to.new.design.after.2020

Greater.than.1B

Greater.than.10%

Greater.than10M

Greater.than10M

2050.or.later 1.to.9.

Applicable.to.new.design.before.2020.

100M 1% 1M 1M 2040.or.later

Applicable.for.current.production.Aircraft.

10M 0.1% 100K 100K 2030.or.later

Applicable.to.retrofit.on.current.Aircraft

1M 0 10k 10k 2020.or.later

Less.than.1M -0.1% Less.than.10k Less.than.10k 2010.or.later

-1% Currently.available

Less.than.-10%

Table.A.2.2.-.2:.Technology.filter.mapping

Impact.Metric Acronym Numerical.Value

Strong.Benefit SB 9

Moderate.Benefit MB 5

Weak.Benefit WB 1

No.Impact NI 0

Weak.Degradation WD -1

Moderate.Degradation MD -5

Strong.Degradation SD -9

Table.A.2.2.-.3:.Weighting.matrix.for.impact.degrees.of.technologies.on.aircraft.attributes


Table.A.2.2.-.4:.Filter.settings.for.airframe.technologies

Table.A.2.2.-.5:.Mapping.between.airframe.technologies.and.aircraft.attributes

79..ANNEx.2

Table.A.2.2.-.6:.Filter.settings.for.engine.technologies

Table.A.2.2.-.7:.Mapping.between.engine.technologies.and.aircraft.attributes

The.evaluation.of.the.technology.ranking.requires.the.evaluation.of.the.air.transport.goals’.importance,.as.illustrated.in.Table.A.2.2.-.8:...With.this.information,.it.is.now.possible.to.establish.direct.relationships.between.the.air.transport.goals.and.the.technologies,.which.would.lead.to.the.ranking.of.technologies.illustrated.in.Figure.A.2.2.-.11..Since.qualitative.relationships.were.used,.the.score.associated.with.each.technology.is.a.normalised.score,.1.meaning.that.the.technology.is.essential.to.achieve.the.goals.and.0.meaning.that.either.more.information.is.required.to.define.the.technology.or.that.the.technology.is.not.needed.to.achieve.the.air.transport.goals...

Table.A.2.2.-.8:.Air.transportation.goals.-.weight.attribution


Figure.A.2.2.-.1:.Sorting.of.technologies.based.on.air.transport.goals.weighting.

81..ANNEx.2

A.2.2.2 Creation of Technology RoadmapThe.SP2.methodology.as.applied.to.the.TERESA.project.has.provided.a.structured,.traceable,.and.transparent.process.for.technology.prioritisation.and.planning..The.process.can.be.tailored.to.any.desired. level.of.detail. to.enhance.the.decision.making.process.for.investment.strategies.as.more.information.becomes.available..The.SP2.methodology.is.a.living.process.that.should.guide.strategic.planning.and.be.continuously.updated.as.a.programme.evolves.

Figure.A.2.2.-.2.is.a.graphical.summary.of.how.the.TERESA.process.has.evolved.thus.far..The.end.product.of.the.workshop.(“Execute.Calculator”).has.enabled.IATA.to.perform.specific.scenario.analysis.through.a.dynamic.and.interactive.environment..It.has.thus.served.as.the. foundation. for. the.creation.of.a.strategic. technology.R&T.roadmap.for. IATA..Note.that. the. final.technology.roadmap.obtained.from.the.TERESA.workshop.is.described.in.detail.in.the.IATA.Technology.Roadmap.report..

Figure.A.2.2.-.2:.From.project.vision.to.roadmap


Chapter References

1.. Szakony,.R.,.“So.Many.Projects,.So.Little.Time:.Improving.the.Selection.of.R&D.Projects,”.Technology.Management:.Case.Studies.of.Innovation,.Edited.by.R..Szakony,.Auerbach,.Boston,.1992.

2.. Cetron,.M.J.,.“Technology.Forecasting.for.the.Military.Manager,”.An.Introduction.to.Technological.Forecasting,.Edited.by.J.P..Martino,.Gordon.&.Breach:.London,.1972.

3.. National.Institute.of.Aerospace,.“Responding.to.the.Call:.Aviation.Plan.for.American.Leadership.”.http://www.nianet.org/pubs/AviationPlan.php,.2005..[Online;.accessed.17-September-2008].

83..ANNEx.2

Active.Load.Alleviation =..a.means.of.using.aerodynamic.surfaces.to.minimise.structural.loads,.useful.for.countering....gusts,.allowing.wing.weight.reduction,.or.increasing.wing.span.without.increasing.wing.structure

Adaptive.cycle.engine =..engine.that.can.adapt.its.operating.condition.during.flight.to.the.given.mission,.thereby.optimising.component.and.cycle.behaviour

Aeronautical.Telecommunications.Network

=..global.aviation.standard.allowing.dynamic.ground-to-ground.and.air-to-ground.telecommunication.services

Aircraft.Communications.and.Reporting.System

=..air-to-ground.data.link.for.transmission.of.small.messages.between.aircraft.and.ground.station.e.g..pre-departure.clearance...

Area.Navigation.(RNAV) =..a.navigation.process.allowing.aircraft.to.choose.any.course.within.the.coverage.of.station-reference.navigation.systems.or.limits.of.self-contain.aids.

Automatic.Dependent.Surveillance.Broadcast.(ADS-B)

=..a.cooperative.surveillance.protocol.to.provide.accurate.information.and.frequent.updates.to.flight.crew.and.controllers

Auxiliary.power.unit =..device,.usually.a.gas.turbine,.to.provide.energy.for.functions.other.than.propulsion,.such.as.main.engine.start,.electricity.and.pressurised.air.generation

Bleed.air =..compressed.hot.air.taken.from.the.engine.for.pressurising.the.cabin,.de-icing.etc.

Blended.winglet =..vertical.winglet.with.a.rounded.transition.to.the.wing.for.further.induced-drag.reduction

Bling =..engine.compressor.component.made.using.metal.matrix.rings.including.an.enlarged.drum.rotor.disc.and.blades.

Blisk =..single.engine.compressor.component.combining.rotor.disc.and.blades

Boundary.layer =..part.of.the.flow.close.to.the.aircraft.surface,.subject.to.viscous.forces

Boundary.layer.ingesting.inlet =..suction.of.boundary.layer.over.aircraft.surface.to.prevent.flow.separation

Cabin.crown.area =..area.between.the.cabin.ceiling.panels.and.the.upper.part.of.the.fuselage.structure

CentrAl =..laminated.hybrid.material.sandwiching.Glare-type.fibre-metal-laminate.between.thick.layers.of.advanced.aluminium.alloys.

Continuous.Climb.Departure =..climb.procedure.eliminating.level.segments.as.much.as.possible.to.get.aircraft.to.cruise.altitude.as.quickly.as.possible

Continuous.Descent.Arrival.(CDA) =..approach.procedure.allowing.the.aircraft.flying.its.individual.optimal.vertical.profile.down.to.runway.threshold.with.engines.at.or.near.idle,.minimising.fuel.burn

Counter-rotating.fan =..multi-stage.fan.system.in.which.the.fan.stages.rotate.in.opposite.directions

Creep.rupture =..rupture.under.a.continuously.applied.stress.at.a.point.below.the.normal.tensile.strength

Crossing.and.passing =..procedures.allowing.an.aircraft.to.cross.or.pass.a.target.aircraft,.including.lateral,.as.well.as.vertical.crossing.and.passing.manoeuvres

Diffusion.welding =..solid.state.welding.process.by.which.two.dissimilar.metals.can.be.bond.together

Distributed.multi-fan =..multiple.propulsive.fans,.embedded.in.airframe,.sharing.a.common.turbofan.core

Drop-in.fuel =..fuel.with.similar.properties.as.crude.derived.jet.fuel,.mixable.in.all.proportions.with.current.jet.fuel,.needing.no.engine.modifications

Electron-beam.welding =..a.fusion.welding.process.in.which.a.beam.of.high-velocity.electrons.is.applied.to.the.materials.being.joined

Enhanced.Flight.Vision.Systems =..display.system.providing.real-world.visual.image.enhanced.by.externally.mounted.Systems

Flight.Information.Service-Broadcast =..a.service.providing.information.products.(e.g..national.weather.&.temporary.flight.restrictions).to.be.delivered.to.the.aircraft.in.flight

Flight.Management.Systems =..an.avionics.system.controlling.the.navigation.of.the.aircraft.based.on.a.flight.plan.

Fly-by-light =..fibre-optic.links.transmit.data.from.flight.control.computer.to.actuators

Friction.stir.welding =..solid-state.welding.process.using.friction.to.locally.heat.metal.(which.is.not.melted.during.the.process),.primarily.used.on.aluminium

Fuel.cell =..electrochemical.conversion.device.producing.electricity.from.a.fuel.(often.hydrogen).and.an.oxidant.(normally.oxygen.from.air).

Furans =..heteroaromatic.compounds,.the.aromatic.ring.containing.an.oxygen.atom.

Geared.turbofan =..ultra.high.engine.bypass.ratio.is.enabled.by.a.gear-driven,.low-speed.fan

Glossary


Glare =..fibre-metal-laminate.hybrid.material.combining.aluminium.sheets.with.reinforcement.of.glass.fibres

Ground.Based.Augmentation.System =..a.system.that.supports.augmentation.(improvement.of.navigation.system.attributes).through.the.use.of.terrestrial.radio.messages

Head-up.Guidance.Systems =..transparent.display.presenting.navigation.information.to.the.pilot.in.his.forward.field.of.view

Hybrid.Laminar.Flow.Control. =..a.means.of.maintain.laminarity.through.both.natural.laminar.flow.design.and.the.addition.of.active.boundary.layer.management.techniques.including.boundary.layer.sucking.or.blowing.

Hybrid.wing.body =..airframe.design.incorporating.features.from.both.a.tube-and-wing.and.a.flying.wing.design,.intended.for.increased.fuel.economy.and.environmental.friendliness

Hydrogenated.oil/fat =..oil/fat.treated.by.hydrogen.to.purify.the.carbon.chain.from.non-hydrogen.and.non-carbon.atoms

Independent.parallel.or.converging.approach

=..approach.scheme.allowing.closely.spaced.parallel.runways.to.be.used.independently

Induced.drag =..drag.force.that.occurs.due.to.wings.or.a.lifting.body.redirecting.air.to.cause.lift

Laminar.flow =..“smooth”,.streamlined.flow.where.the.air.flows.in.parallel.layers,.opposite.of.turbulent.flow

Laser.beam.welding =..manufacturing.method.using.extremely.concentrated.laser.heat.source.for.superior.weld.quality.with.smaller.distortion

Local.Area.Augmentation.System =..real-time.differential.correction.system.used.to.correct.GPS.signals.allowing.operation.such.as.all-weather.aircraft.landing

More.electric.aircraft =..aircraft.system.architecture.replacing.traditional.pneumatic.and.hydraulic.powered.aircraft.equipment.architecture.systems.with.electrical.subsystems.

Morphing.Airframe. =..a.concept.where.the.shape.and/or.size.of.the.wing.are.changed.to.tailor.the.design.to.specific.flight.conditions

Morphing.material =..a.broad.range.of.substances.that.can.shorten,.elongate,.flex,.and.otherwise.respond.mechanically.to.electricity,.heat,.light,.or.magnetic.fields.

Natural.laminar.flow =..laminar.flow.covering.areas.of.lifting.surfaces.and.engine.inlets.that.are.maximised.by.appropriate.component.design.but.without.use.of.active.flow.control

Non.drop-in.fuel =..fuel.that.requires.changes.in.existing.aircraft.fuel.systems.and.supporting.infrastructure

Non-Brayton.cycle.engine =..gas.turbine.whose.thermodynamic.cycle.deviates.from.the.conventional.“Brayton.cycle”,.can.involve.constant.volume.combustors,.have.higher.theoretical.thermal.efficiencies,.etc.

Open.rotor/unducted.fan =..engine.architecture.in.which.jet.exhaust.drives.two.counter-rotating.turbines.that.are.directly.coupled.to.the.fan.blades.that.are.placed.outside.the.nacelle

Performance.Based.Navigation.(PBN)

=..technology.to.reduce.emissions.and.to.raise.air.traffic.flow.efficiency,.providing.means.for.flexible.air.traffic.routes.and.terminal.procedures

Proton.exchange.membrane.fuel.cell =..low-temperature.fuel.cell.with.polymer.electrolyte.membrane.

Pulse.detonation.engine =..constant.volume.combustion-based.engine,.compression.being.achieved.through.trapped.supersonic.shock.waves,.with.combustion.velocities.greater.than.the.speed.of.sound

Raked.wingtip =..swept-back.wing.extension.device.reducing.induced.drag.by.increased.aspect.ratio

Regenerative/recuperative.engine =..engine.with.compressor.inter-cooling.and.recuperation.of.the.core.exhaust.heat.to.pre-heat.combustor.entrance.air

Required.Navigation.Performance.(RNP)

=..a.statement.of.the.navigation.performance.necessary.for.operation.of.aircraft.within.a.defined.airspace,.the.achieved.performance.being.monitored.with.alert.in.case.of.failure

Riblets =..skin.friction.reduction.technology.for.turbulent.boundary.layer.using.an.array.of.small.grooves.or.protrusions.on.aerodynamic.surfaces

Satellite.Based.Augmentation.System

=..a.navigation.system.supporting.wide-area.or.regional.augmentation.through.the.use.additional.satellite-broadcast.messages

Sequencing.and.merging =..enables.the.merging.and.spacing.from.designated.aircraft.as.stipulated.in.new.controller.instructions

Shape-memory.alloy =..alloy.that.“remembers”.its.shape,.and.can.be.returned.to.that.shape.after.being.deformed,.by.applying.heat.to.the.alloy

Skin.friction.drag =..drag.arising.from.the.friction.of.the.aircraft.skin.against.the.air,.directly.related.to.the.area.of.the.aircraft.surface.in.contact.with.the.fluid.(wetted.surface).

Solid.acid.fuel.cell =..intermediate-temperature.fuel.cell.technology.with.solid.acid-based.membranes

Solid.oxide.fuel.cell =..high-temperature.fuel.cell.type.with.solid-state,.ion-conducting.ceramic.membrane

Spiroid.wingtip =..spiral-shaped.wingtip.device.that.looks.attached.to.the.wing’s.upper.surface

Steep.approach =..approaching.the.runway.at.a.steeper.glide.slope.than.the.standard.3°.

Superplastic.forming =..a.process.for.forming.sheet.metal.in.its.superplastic.state.in.which.solid.material.is.deformed.well.beyond.its.usual.breaking.point

85..ANNEx.2

Synthetic.Vision.System =..a.display.system.providing.an.artificial.vision.of.the.outside.world.using.terrain.databases.to.create.a.realistic.and.intuitive.view.of.the.environment

Traffic.Information.Service.–.Broadcast

=..broadcasts.surveillance.system.providing.position.reports.for.ADS-B.equipped.aircraft.

Trajectory.based.operations =..operational.concept.based.on.aircraft.flying.negotiated.trajectories,.and.air.traffic.control.moving.to.management.by.trajectory

Transesterification.fuel =..fuel.produced.by.reacting.a.triglyceride.(natural.oil.or.fat).with.an.alcohol.to.form.esters

Transonic.speed =..range.of.flight.speeds.for.which.a.part.of.the.airflow.around.the.aircraft.is.supersonic,.and.the.remaining.part.is.not

Transonic.shock =..shock.wave.occurring.in.the.supersonic.flow.around.a.transonic.wing,.which.can.cause.boundary.layer.separation,.stall.or.buffet.resonance.

Truss-braced./.strut-braced.wing =..wing.design.where.struts.or.trusses.are.placed.under.the.wing.to.significantly.increase.its.aspect.ratio.with.minimal.increase.in.structural.weight

Turbulent.flow =..a.fluid.regime.characterised.by.chaotic.rapid.variation.of.pressure.and.velocity.in.space.and.time,.opposite.of.laminar.flow

Twin.Annular.Premixing.Swirler =..combustor.design.comprising.two.high-energy.swirlers.adjacent.to.the.fuel.nozzles,.creating.a.fairly.homogeneous.and.lean.mix.of.fuel.and.air,.allowing.lower.combustion.temperatures

Variable.area.fan.nozzle =..nozzle.capable.of.tuning.fan.pressure.ratios.based.on.propulsive.needs

Variable.Camber =..a.series.of.technologies.that.allow.the.shape.of.the.wing.airfoil.to.be.adjusted.to.tailor.aerodynamic.properties.to.specific.flight.regimes

Variable.cycle.engine =..engine.that.operates.two.or.more.thermodynamic.cycles.depending.on.flight.regime

Variable.geometry.chevron =..triangular.tips.(chevrons).at.nacelle.trailing.edge.suppressing.both.turbulent.jet-mixing.noise.at.take-off.and.shock-cell.noise.at.cruise.by.heat-activated.morphing

Viscous.drag =..see.skin.friction.drag

Wave.drag =..drag.caused.by.the.formation.of.shock.waves.around.the.aircraft,.which.radiate.away.a.considerable.amount.of.energy

Weather.data.acquisition.and.distribution

=..weather.data.processing.for.optimised.hazard.avoidance.through.a.combination.of.datalink.technologies.and.trajectory.management.applications

Wide.Area.Augmentation.System =..an.air.navigation.system.using.the.global.positioning.system.to.improve.accuracy,.integrity.and.availability,.which.enables.aircraft.to.perform.precision.operations.

Winglet =..wing-tip.device.consisting.of.a.near-vertical.extension.of.the.wing.tips

Wing-tip.device =..a.device.placed.upon.the.tip.of.a.wing.to.improve.the.aerodynamic.efficiency.of.a.wing.by.reducing.induced.drag

Wingtip.fence =..winglet.variant.with.surfaces.extending.both.upward.and.downward.from.the.wingtip

Zonal.dryer =..device.removing.the.humidity.out.of.the.cabin.air.to.avoid.condensation.and.thus.weight-adding,.in.the.insulation.blankets


3AS =.Active.Aeroelastic.Aircraft.Structure

AAW =.Active.Aeroelastic.Wing

AAWC =.Active.Adaptive.Wing.Camber

ACARE =.Advisory.Council.on.Aeronautics.Research.in.Europe.

ACARS =.Aircraft.Communications.and.Reporting.System

ADIF =.Adaptive.Wing.(German.project)

ADS-B =.Automatic.Dependent.Surveillance.–.Broadcast.

ADS-C =.Automatic.Dependent.Surveillance..-.Contract

AES =.Aircraft.Equipment.System

ANSP =.Air.Navigation.Service.Provider

APU =.Auxiliary.Power.Unit

ARALL =.Aramide.Reinforced.Aluminum.Laminate

ARFP =.Aramid.Reinforced.Plastic

ASDL =.Aerospace.Systems.Design.Laboratory.at.Georgia.Tech

ASMGC-S =.Advanced.Surface.Management.Guidance.and.Control.System.

ATC =.Air.Traffic.Control

ATFI. =.Advanced.Technology.Fan.Integrator.

ATM =.Air.Traffic.Management

ATMOC.=.ATM.Operational.Concept.

ATN =.Aeronautical.Telecommunications.Network

ATP. =.Advanced.Turboprop.

ATS =.Air.Traffic.Service

BLI. =.Boundary.Layer.Ingestion

BtL =.Biomass.to.Liquid

C&P =.Crossing.and.Passing

CAAFI =.Commercial.Aviation.Alternative.Fuels.Initiative.

CAEP =.Committee.on.Aviation.Environmental.Protection.

CCD =.Continuous.Climb.Departure

CDA =.Continuous.Descent.Arrival

CDM =.Collaborative.Decision.Making

CDMA =.Code.Diversity.Multiple.Access

CDTI =.Cockpit.Display.of.Traffic.Information

CESTOL =.Cruise.Efficient.Short.Take-off.and.Landing

CMC.=.Ceramic.Matrix.Composite.

CNS =.Communication,.Navigation.and.Surveillance

CO2 =.Carbon.dioxide

CONOPS.=.Concept.of.Operations.

CRFP =.Carbon.Reinforced.Plastic

CtL =.Coal.to.Liquid

DFW =.Diffusion.Welding

DLR =.German.Aerospace.Center

DME =.Distance.Measuring.Equipment.

EBW =.Electron.Beam.Welding

EEFAE =.Environmental.Efficient.Friendly.Aircraft.Engine

Acronyms


EFVS =.Enhanced.Flight.Vision.Systems

EGNOS =.European.GNSS.Navigation.Operating.System

FAME =.Fatty.Acid.Methyl.Esters

FANS =.Future.Air.Navigation.System

FIS-B =.Flight.Information.Service-Broadcast

FMS =.Flight.Management.System

FMC =.Flexible.Matrix.Composites

FML =.Fibre.Metal.Laminate

FMS =.Flight.Management.Systems

FSW =.Friction.Stir.Welding

GBAS =.Ground.Based.Augmentation.System

GE =.General.Electric.

GLS =.GNSS.Landing.System

GNSS =.Global.Navigation.Satellite.System

GRFP =.Glass.Fibre.Reinforced.Polymer

GT =.Gas.Turbine

GtL =.Gas.to.Liquid.

GTAW =.Gas.tungsten.arc.welding

GTF. =.Geared.Turbofan

HAZ =.Heat.Effected.Zone

HEETE =.Highly.Efficient.Embedded.Turbine.Engine

HF =.High.Frequency

HFDL =.High.Frequency.Data.Link

HGS =.Head-up.Guidance.Systems

HLFC =.Hybrid.Laminar.Flow.Control:.combines.both.active.and.natural.laminar.flow.concepts

HP =.High.Pressure

HPT =.High.Pressure.Turbine

HyLDA =.Hybrid.Laminar.Flow.Demonstration.on.Aircraft

IAE. =.International.Aero.Engines

ICAO =.International.Civil.Aviation.Organization

ILS =.Instrument.Landing.System

IRS =.Inertial.Reference.System

JPDO =.Joint.Planning.and.Development.Office

JTI =.European.Joint.Technology.Initiative

LORAN =.Long-range.Navigation

LTO =.Landing.and.Takeoff.cycle

LAAS =.Local.Area.Augmentation.System.

LBW =.Laser.Beam.Welding

LED =.Light-Emitting.Diode.

LP =.Low.Pressure..

MACW =.Mission.Adaptive.Compliant.Wing

MAS =.Morphing.Aircraft.Structures

MAW =.Mission.Adaptive.Wing.(Programme)

MEA =.More.Electric.Aircraft.

MFC =.Micro.Fiber.Composite

MLAT =.Multilateration

MMC.=.Metal.Matrix.Composites.

MRJ. =.Mitsubishi.Regional.Jet


NAS =.National.Airspace.System

NASA =.National.Aeronautics.and.Space.Administration

Newac =.New.Aero.Engine.Core.Concepts

NextGen =.Next.Generation.Air.Transportation.System

NOx. =.Nitrogen.oxides

NSR =.New.Short.Range

OEM.=.Original.Equipment.Manufacturer

ONERA =.Organisation.Nationale.d’Études.et.de.Recherche.Aérospatiale.(French.aerospace.research.lab)

PAM =.Pneumatic.Artificial.Muscles

PBN.=.Performance.Based.Navigation

PEMFC =.Proton.Exchange.Membrane.Fuel.Cell

PMC =.Polymer.Matrix.Composites

POA =.Power.Optimized.Aircraft

RTA =.Required.Time.of.Arrival

R&D =.Research.and.Development.

R&T =.Research.and.Technology

RNAV =.Area.Navigation.

RNP =.Required.Navigation.Performance.

RQL.=.Rich.Quench.Lean.

RR =.Rotating.Rib,.a.variable.camber.enabling.technology

RVSM =.Reduced.Vertical.Separation.Minima

S&M =.Sequencing.&.Merging.

SAFC =.Solid.Acid.Fuel.Cell

SBAS.=.Space.Based.Augmentation.System

SC =.Single.Crystal.

SECA =.Solid.state.Energy.Conversion.Alliance

SESAR =.Single.European.Sky.ATM.Research

SFC =.Specific.Fuel.Consumption.

SMA =.Shape.Memory.Alloy.

SOFC =.Solid.Oxide.Fuel.Cell

SPF =.Super.Plastic.Forming

SR =.Specific.Range

SVS =.Synthetic.Vision.Systems

SWIM =.System-Wide.Information.Management

TAPS.=.Twin.Annular.Premixing.Swirler.

TBC.=.Thermal.Barrier.Coating.

TBW =.Truss.Based.Wing

TCAS.=.Traffic.Collision.Avoidance.System

TIS-B =.Traffic.Information.Service.–.Broadcast

TRL =.Technology.Readiness.Level

UDF =.Unducted.Fan.

UHB =.Ultra-High.Bypass.

VARTM =.Vacuum.Assisted.Resin.Transfer.Mold

VGC.=.Variable.Geometry.Chevron.

VHF. =.Very.High.Frequency

WAAS =.Wide.Area.Augmentation.System

WFCS =.Wireless.Flight.Control.System


The.following.individuals.have.participated.in.writing.this.Technical.Annex:

IATA:

John.Banbury.

David.Behrens

Quentin.Browell

Norma.Campos.

Carlos.Cirilo.

Chris.Markou

Thomas.Roetger

Vincent.Toepoel

Georgia Institute of Technology:

Taeyun.P..Choi

Stéphane.Dufresne

Peter.Hollingsworth

DLR:

Eike.Stumpf

We.thank.all.contributors.for.their.engaged.work.

Acknowledgements

www.iata.org