CabinEnvironmentalControl
Systems
Chapter16
Atmosphere
Atmosphere
Gases
•  Humansrequireoxygentosurvive
•  Astheal=tuderises,theoxygenpressurelowers
•  Above7,000feet,theoxygenpressureistoolow
tofullysaturatethebloodwithoxygen
•  Hypoxia–oxygendepriva=on(notenough)
•  Solu=ons:
Increasethepercentageofoxygen
!  Pressurizethecabin
!
•  Carbondioxide–CO2
Partofyourexhale
!  Thebodyneedssomebuttoomuchwillkill
!
Gases
•  CarbonMonoxide–CO
Colorless,odorlessgas
!  Poison
!  Bodythinksitisoxygen
!  Byproductofcombus=on
!  Carbonmonoxidedetectorscanbeused
!
•  Forms:
!
Oxygen
Gaseous
•  Mostcommon
!
Liquid(LOX)
•  Notseenincommercialavia=on
•  Forms:
!
Oxygen
Chemical/Solid
•  Sodiumchlorateproducesoxygenwhenburned
•  Volumestoragecapacityaboutthree=mesthatof
compressedoxygen
•  Oncelit,can’tstop
•  Systemgeneratorsareinertbelow400°Fevenunder
severeimpact
•  Usedasbackupsupplyonairliners
•  “Oxygencandle”
•  OnboardOxygenGenera=ngSystem(OBOGS)
!
Separatesoxygenfromatmosphere
GaseousOxygenSystems
•  Cylinders:
!
Green
•  Steel,aluminumoraluminumwrappedinKevlar
•  Usuallyratedfor1,800to1,850psi
•  Cer=fiedbyDepartmentofTransporta=on(DOT)
•  Stampedwith:
!
!
!
!
!
Dateofmanufacture
DOTcer=ficatenumber
Serialnumber
Dateoflasttest
Locatedneartheneckofthecylinder
•  Labeledwith“AVIATOR'SBREATHINGOXYGEN”
GaseousOxygenCylinder
GaseousOxygenCylinderRa=ngs
FAA says 10,000
GaseousOxygenSystems
•  Cylinders:
!
Tes=ng
•  Hydrosta=ctes=ng
!
!
Placedinawatertank,filledwithwater,andpressurizedto5/3of
itsra=ng
Noleaksordeforma=on
•  Mustbedoneonaregularbasis,usually3or5years
!
Limitedlife
•  Agerlimit,cylinderisscrapped
!
Shouldnotbeemp=edbelow50psi
•  Allowsmoisturetogetin–maincauseofcontamina=on
•  Ifbelow50psi,openandletstandfor2hours,thenpurge
withoxygenbeforerefilling
GaseousOxygenSystems
•  Cylinders:
!
Filledwith“avia=onbreathingoxygen”
•  Nowaterinit
!
Watercanfreezeatal=tude
•  Differentthanmedicaloxygen–haswater
•  Cleanerthanweldingoxygen
!
Theamountofoxygeninthecylinderisdetermined
byapressuregauge
GaseousOxygenRegulators
•  Types:
Con=nuousflow
!  Demandflow
!
•  Con=nuousflow
!
Oxygenisalwaysflowing
•  Lessefficientuseofoxygen
Usesloosefilngmaskorcannula
!  Mayusearebreatherbagtomixpureoxygenwith
exhaledair
!  Flowcontrolledbycalibrated(fixed)orifice,control
valveorcabinpressuresensi=vedevice
!
Con=nuousFlowBreathDevices
GaseousOxygenRegulators
•  FlowDemand
!
Deliversoxygenastheuserinhalesor“ondemand”
•  Moreefficientuseofoxygen
Tightmask
!  Diluter-demandtypemixesoxygenwithcabinair
!
•  Airflowmeteringaneroidassemblyadjustsoxygenflowas
cabinpressurechanges
!
Pressure-demandoxygenforceoxygenintolungsfor
beoerbloodsatura=on
GaseousOxygenSystem
•  Pressurereducer–reducestankpressurebefore
sendingtopressureregulator
!
Helpslimitpressureinoxygenlines
•  Pressureregulator–adjustsfinaloxygen
pressuretodetermineflow
•  Pressurereliefvalve–releasesoxygenif
pressureinsystemistoohigh
•  Greenblowoutdisk–Thediskbreakswhen
systempressureisexceeded
!
Systemmustbeserviced
GaseousOxygenSystem
GaseousOxygenSystem
GaseousOxygenSystem
GaseousOxygenSystemService
•  Pureoxygenwillcauseitemstospontaneously
ignite-keepawayfromgreasesandoils
•  UseTeflontapeasthefilngsealant
•  Openvalvesslowly
•  Checkservicedatesoncylinders
•  Checkgreenblowoutdisk
•  Useanbubblingleakchecksolu=ondesignedfor
oxygen
!
Don’tusesoapywater
•  Drainoxygeninanareathatwilldissipatethe
oxygen
FillOxygenSystem
FillOxygenSystem
•  Checkcylinderdatesandthatpressureisabove
50psi
•  Groundrefillcarttoaircrag
•  Purgeoxygenlinesandconnect
•  Startfillwiththerefillcylinderthatisthelowest
pressurethatiss=llhigherpressurethanthe
aircragsystem
!
Mayhavetoswitchcylinders
•  Filltotemperatureadjustedpressure
•  Disconnectfilllineandthenground
FillOxygenSystem
HighAl=tudeCondi=ons
PressureDifference
•
•
•
•
•
•
FuselageForces
At40,000g,thereisan8.2psidifference
Thestandardaluminumsheetsweuseare8’X4’
8’X4’=32g2
1g2=144in2(12X12)
32g2X144in2/g2=4,608in2
4,608in2X8.2psi=37,785.6lbs
18.9tonsexertedonasinglesheet
!  14.5MiniCoopers
!
•  Goals
!
Pressuriza=onBasics
Keepcabinatthepressureequaltothatat8,000g
•  10.72psi
•  Rangeisusually6,000to8,000g
!
CirculatefreshairtogetridofCO2
•  Startbypumpinginairatpressureshigherthan
neededtopressurizecabin
•  Anaircragpressuriza=oncycleisnormally
consideredtobeonecompleteseriesofevents
oropera=onsthatrecurregularly.
Pressuriza=onBasics
•  Letexcessairescape
Providesaircircula=on
!  Bycontrollingtheamountofairescape,thecabin
pressureiscontrolled
!
•  Moreescapingair,lowercabinpressure
•  Lessescapingair,highercabinpressure
Pressuriza=onTerms
•  CabinPressure–theairpressureinsidethe
cabin
Measuredinal=tudeonastandardday
!  Usuallyaround8,000g
!
•  10.92psi
•  CabinDifferen=alPressure–thedifference
betweentheairpressureinsidethecabinand
outsidethecabin
•  CabinRateofClimb–therateofchangeofair
pressureinsidethecabin
!
Expressedinfeetperminute(fpm)
PressureSource–PistonEngine
PressureSource–PistonEngine
PressureSource–TurbineEngine
PressureSource–TurbineEngine
Pressuriza=onControlSystem
Pressuriza=onPanel
Pressuriza=onModes
•  Isobaric–thecabinal=tudepressureisheldata
singlepressure
e.g.8,000g
!  Normalmodeofopera=on
!
•  Constantdifferen=al–aconstantpressure
differenceismaintainedbetweentheair
pressureinsidethecabinandoutsidethecabin
•  Whenanaircragfliestoohighandpressure
differenceistoogreat,thesystemwillswitch
fromisobarictoconstantdifferen=almode
!
Preventsthestructurefromoverstressing
Pressuriza=onComponents
•  Ouslowvalves–opensandclosestocontrolthe
amountofairexi=ngthecabin
•  Cabinpressureregulator–controlsthecabin
pressure
!
Regulatestheopera=onsoftheouslowvalveto
establishthecabinpressure
•  Pressurereleasevalve–preventsthecabinfrom
overpressurizing
!
Hasapresetdifferen=alpressurevalue.Ifthevalue
isexceeded,cabinairisreleased
Pressuriza=onComponents
•  Cabinal=tudelimiters–keepthecabinpressure
fromgoingtoolow
!
Closestheouslowvalves
•  Nega=vepressurereliefvalve–ensuresthat
outsideairpressureisnothigherthanthecabin
pressure
!
Preventsthecabinpressurefrombecominghigher
thanairplaneal=tude
•  Pressuriza=ondumpvalve–usedtoquickly
depressurizetheaircrag
!
Ogenconnectedtothelandinggearsquatswitch
Pressuriza=onComponents
•  Deliveryairductcheckvalveclosestoprevent
pressuriza=onlossifpressurizedairsourcefails
•  Sources
AircragHea=ng
Bleedair
!  Electricheat
!  Exhaustshroud
!  Combus=onheater
!
ExhaustShroudHeater
Ashroudaroundpartoftheexhaustsystemservesasa
sourceofheatforsomeofthesmalleraircragcabins.
ExhaustShroudHeater
ExhaustShroudHeater
ExhaustShroudHeater
•  Drawsheatfromthepistonengineexhaust
•  Theheatcyclingoftheenginecausescracksin
theexhaustsystemwhichcanleadtoCO
contamina=on
•  Pressurechecksystemtoinsurenoleaks
!
Applyairpressureandsprayonsoapysolu=on
•  CheckwithCOdetector
Combus=onHeater
Combus=onHeater
•  GeneratesheatbyburningAVGAS
!
Fueltakenfromsametankssupplyingengine(s)
•  Freshoutsideairistakenin,mixedwithfuel,
burntandexhaustissentoverboard
•  Outsideairispassedovercombus=onchamber,
warmedandsentintothecabin
CalledVen=la=onair
!  Doesn’tmixwithairusedforcombus=on
!
•  Thermostatcontrolstemperaturebystar=ngand
stoppingtheburningprocesscalledcycling
!
Shutsoffelectricigni=onandfuel
Combus=onHeater
•  Overhea=ngswitchshutsdowncombus=onto
preventoverhea=ngunit
•  Combus=onairreliefvalveoradifferen=al
pressureregulatorpreventtoomuchairfrom
enteringtheheatersasairpressureincrease
•  Maintenanceincludesinspec=onssimilarto
exhaustshroudheatersplusmaintaining
combus=onsystem
•  UsuallyhasTBO
•  Types
!
AirCondi=oningSystems
Aircycle
•  Usedwithturbineengines
!
Vaporcycle
•  Usedwithpistonandsmallturbineengines
•  Typeofsystemusedincars
AirCycleAirCondi=oning
Expansion
Turbine
AirCycleAirCondi=oning
•  Goal–Coolthepressurizedbleedair
•  Outsideair(ramair)isusedtocoolbleedair
•  Anexpansionturbinefurthercoolsbleedairby
extrac=ngenergy
!
Thebleedairpressuredropswhichcausesthe
temperaturetodrop
•  Amixingvalvecombinesthehot,warmandcold
bleedairinthecorrectra=otoachievethe
desiredcabintemperature
VaporCycleAirCondi=oning
•  Heatpump–movesheatfromcabinandgetrid
ofitbydumpingintotheoutsideatmosphere
!
•
•
•
•
Coldisnotcreated,heatismovedorpumped
Video1
Video2
Video3
Video4
VaporCycleAirCondi=oning
VaporCycleAirCondi=oning
•  Refrigerant
Thefluidusedtotransferheat
!  CalledFreon
!  R12–Oldandnotproducedsince1996
!
•  Producesphosgenegaswhenburned
•  Mixeswithwatervaporstoformhydrochloricacidwhichis
highlycorrosive
R134a–newertype
!  Don’tmixtypes
!
VaporCycleAirCondi=oning
•  Refrigerant
!
Allrefrigerantmustberecycle
•  Vacuumpumpsareusedtosuckoutalltherefrigerant
!
Thevacuum’slowpressurecausewatertoboilandexitthe
system
•  Removerefrigerantslowlysocompressoroilisnotsucked
out
!
Refrigerantleaks
•  DyescanbeaddedtorefrigeranttomakeitglowunderUV
light(blacklight)
•  Electricdetectorscanbeuse
•  Presenceofcompressoroilisanindica=onofaleak
VaporCycleAirCondi=oning
•  ReceiverDryer
Storesextrarefrigerant
!  Dryer–trapswaterinadesiccant
!  Hasasightglasstodeterminerefrigerantlevel
!
•  Shouldbeallliquid
•  Bubblesindicatelowrefrigerant
!
Give=metoreachastablecondi=onbeforedeclaringlow
VaporCycleAirCondi=oning
•  ExpansionValve
Barrierbetweenthe“high”and“low”sideofthe
system
!  Inputsidehashothighpressureliquid
!  Outputsidehascoollowpressureliquid
!  Anadjustableorifice(valve)
!
•  Changessizetogetthecorrectflowofrefrigerant
•  Shouldleaveoutputsideasaliquid
•  Adjustsopeningbymeasuringthetemperatureand/or
pressureofrefrigerantintheoutletoftheevaporator
!
!
Refrigerantstatechangeshouldhappenattheevaporator
Mostlikelycomponent,insystem,tobeblockedby
dirtandcausesystemnottocharge
ExpansionValve
VaporCycleAirCondi=oning
•  Evaporator
Heatexchanger–coilwithfins
!  Loca=on
!
•  Insidecabin
!
!
!
Fanblowscabinairoverevaporator
Airiscooled/evaporatorcoiliswarmed
Evaporatorcoilabsorbsheatfromcabin
•  Lowpressuresideofthesystem
•  Coldsideofthesystem
Refrigerantentersaslowpressureliquid
!  Refrigerantexitsaslowpressurevapor
!
•  Refrigerantchangesstateinevaporator
!
Liquidtovapor–absorbsheat
VaporCycleAirCondi=oning
•  Evaporator
!
Waterfromcabinaircondensesoncoldevaporator
coils
•  Drainageforwatermustbeprovided
!
Goodplaceformoldtogrow,keepclean
•  Ifinadequate(notenough)airovercoil,waterwillfreeze
andturnintoice
VaporCycleAirCondi=oning
•  Compressor
Barrierbetweenthe“high”and“low”sideofthe
system
!  Compressesvapor
!
•  Vaporenterscoolandlowpressure
•  Vaporexitshotandhighpressure
!
Drivenby:
•  Beltandpulleyoffofengine
!
Useselectricclutch
•  Electricmotor
•  Hydraulicmotor
•  Usuallyapistonpump
VaporCycleAirCondi=oning
•  Compressor
!
Usesspeciallubricant
•  Checkoilwhenservicingrefrigerant
•  Systemleakscanbedetectedbypresenceoflubricant
!
Caremustbetakenwhenfillingsystem
•  Ifliquidrefrigerantgetsintolowpressureside,the
compressorpumpswilltrytocompressliquidandbreak
VaporCycleAirCondi=oning
•  Condenser
Heatexchanger–coilwithfins
!  Loca=on
!
•  Outsidecabin
!
!
!
Fanblowsoutsideairovercondenser
Outsideairiswarmed/condensercoiliscooled
Outsideairabsorbsheatfromcondensercoil
•  Highpressuresideofthesystem
•  Hotsideofthesystem
Refrigerantentersashighpressurevapor
!  Refrigerantexitsashighpressureliquid
!
•  Refrigerantchangesstateincondenser
!
Vaportoliquid–releasesheat
VaporCycleAirCondi=oning
•  Sub-cooler
Heatexchanger–coilwithfins
!  Coolsrefrigerantagerleavingreceiverdryer
!  Preventsprematurevaporiza=on
!
•  Helpsinsurerefrigerantchangesstateinevaporator
•  Servicingvideo