io-540 operations manual.pdf

L y c o m i n g F l y e r

Lycoming Flyer

O P E R A T I O N S


Mostpeopleseemtooperateonthephilosophythattheycanbestgettheirmoneysworthfromanymechanicaldevicebytreatingitwithgreatcare.Thisisprobablytrue,butinmanycases,itisnecessarytointerpretwhatgreatcarereallymeans.Thisispar-ticularlyapplicablewhenconsideringthebreak-inofamodern,reciprocatingaircraftengine.Aircraftownersfrequentlyaskabouttheproperproceduresforrun-inofaneworrebuiltenginesotheycancarefullycompletetherequiredsteps.Manyoftheserecommendedbreak-inproceduresalsoapplytoengineswhichhavebeenoverhauledorhadacylinderreplaced.Thefirstcarefulconsiderationforenginerun-inistheoiltobeused.ThelatestrevisionofLycomingServiceInstruction1014shouldbeconsultedforthisinformation.ThebasicrulewhichappliestomostnormallyaspiratedLycomingpistonenginesissimple:usestraightmineraloiloftheproperviscosityforthefirstfiftyhoursoruntiloilconsumptionstabilizes.Thenswitchtoashlessdispersant(AD)oil.Theexceptions to thebasic ruleaboveare theO-320-HandtheO/LO-360-Eseries.Theseenginesmaybeoperatedusingeitherstraightmineraloilorashlessdispersantoil;however,if theengineisdeliveredwithashlessdispersantoil installed,itmust remainonashlessdispersantoil.TheLycomingoiladditiveP/NLW-16702mustbeadded to theO-320-HandO/LO-360-Eenginesatairframeinstallation,andevery50hoursthereafterorateveryoilchange.AnFAA-approvedlubricatingoilthatcontains,intheproperamount,anoiladditiveequivalenttoLW-16702willmeettherequirementsfortheadditiveasstatedinLycomingServiceInstructionNo.1014M.AllLycomingturbochargedenginesmustbebrokeninwithash-lessdispersantoilonly.Whentakingdeliveryofanewaircraft, thereisanotherpointwhichmustbeemphasized.Someaircraftmanufacturersaddapprovedpreservativelubricatingoiltoprotectnewenginesfromrustandcorrosionatthetimetheaircraftleavesthefactory.Thispreservativeoilmustberemovedbytheendofthefirst25hoursofoperation.Eachneworrebuiltengineisgivenaproductiontestrunatthefactorybeforetheengineisdeliveredtoanaircraftmanufacturerorcustomer.Afterinstallationintheaircraft,theengineisrunagainduringthetestflights.Thesetestrunswillensurethattheengineisoperatingnormallyandwillprovideanopportunitytolocatesmalloilleaksorotherminordiscrepancies.Inaddition,thesetestrunsdotheinitialseatingofthepistonrings.Therestofthebreak-inistheresponsibilityofthepilotwhofliestheaircraftduringthenext50hours.Anew,rebuiltoroverhauledengineshouldreceive thesamestart,warm-upandpreflightchecksasanyotherengine.Therearesomeaircraftownersandpilotswhowouldprefertouselowpowersettingsforcruiseduringthebreak-inperiod.Thisisnotrecommended.Agoodbreak-inrequires that thepistonringsexpandsufficientlytoseatwiththecylinderwalls.Thisseatingoftheringwiththecylinderwallwillonlyoccurwhenpressures

insidethecylinderaregreatenoughtocauseexpansionofthepistonrings.Pressuresinthecylinderonlybecomegreatenoughforagoodbreak-inwhenpowersettingsabove65%areused.Fullpowerfortakeoffandclimbduringthebreak-inperiodisnotharmful;itisbeneficial,althoughenginetemperaturesshouldbemonitoredcloselytoensurethatoverheatingdoesnotoccur.Cruisepowersettingsabove65%,andpreferably in the70%to75%ofratedpowerrange,shouldbeusedtoachieveagoodenginebreak-in.Rememberthat if theneworrebuiltengineisnormallyaspi-rated(non-turbocharged),itwillbenecessarytocruiseatloweraltitudes toobtain the requiredcruisepower levels.Densityaltitudesinexcessof8000feet(5000feetisrecommended)willnotallowtheenginetodevelopsufficientcruisepowerforagoodbreak-in.Forthosewhostill thinkthatrunningtheenginehardduringbreak-infallsintothecategoryofcruelandunusualpunishment,thereisonemoreargumentforhighpowersettingsduringenginebreak-in.Theuseoflowpowersettingsdoesnotexpandthepistonringsenough,andafilmofoilisleftonthecylinderwalls.Thehightemperaturesinthecombustionchamberwilloxidizethisoilfilmsothatitcreatesaconditioncommonlyknownasglazingofthecylinderwalls.Whenthishappens,theringbreak-inprocessstops,andexcessiveoilconsumptionfrequentlyoccurs.Thebadnewsisthatextensiveglazingcanonlybecorrectedbyremovingthecylindersandrehoningthewalls.Thisisexpensive,anditisanexpensethatcanbeavoidedbyproperbreak-inprocedures.Tosummarize, thereare justafewitemstorememberaboutenginebreak-in:1.Ifapreservativeoilhasbeenaddedbytheaircraftmanufac-turer,drainitnolaterthanthefirst25hoursofoperation;2.Followtheenginemanufacturersrecommendationregardingtheoiltobeusedforbreak-inandtheperiodbetweenchanges;3.Runtheengineathighcruisepower levelsforbestpistonring/cylinderwallmating;4.Continuebreak-inoperationfor50hoursoruntiloilconsump-tionstabilizes.Thesesimpleproceduresshouldeliminate thepossibilityofcylinderwallglazingandshouldpreparetheengineforalongandsatisfactoryservicelife.

A direct reprint of Service Instruction 1094DRevisionDtoServiceInstructionNo.1094supersedesallprevious recommendations and should be used for engineleaningduringnormalflightoperations.All leaning recommen-dations are based on calibrated instrumentation.Lycomingstronglyrecommendsthatallengineinstrumentationbecalibratedannually.Allinstrumentationformanifoldpressure,engineRPM,oiltemperature,cylinderheadtemperature,exhaust


gas temperatureand turbine inlet temperature in theaircraftshouldbeincludedinthisannualcalibration.Regardlessof the fuelmeteringdevice, fuelmanagementofnormallyaspiratedenginesisprimarilydependantontheinstru-mentationavailable.Themethodisthesameforbothfixed-andcontrollable-pitchpropellers.LycomingrecommendationsforleaningturbochargedenginesinthisServiceInstructionrefertoLycoming-suppliedturbochargedengines.Foraftermarketturbochargerinstallations,contacttheSTCholderforproperleaninginstructions.CHT(cylinderheadtemperature)andTIT(turbineinlettempera-ture)probesarerequiredforleaningturbochargedengines.RefertothelatesteditionofServiceInstructionNo.1422forproperTITprobelocationsanddepth.

A. GENERAL RULES

1. Without exception, observe the red-line temperaturelimits during takeoff, climb and high-performance cruisepoweroperation.

a.CylinderheadtemperaturemaximumlimitlistedintheLycomingOperatorsManual.b.Oil temperature limitmaximumlimit listed in theLycomingOperatorsManual.c.TIT-maximumallowablelimitspecifiedintheLycomingOperatorsManual.

2.Whenevermixture is adjusted, richor lean, it shouldbedoneslowly.3. Always return mixture slowly to full before increasing power setting.4.Atall times,cautionmustbe takennot toshock-cool thecylinders.Themaximumrecommended temperaturechangeshouldnotexceed50Fperminute.

B. LEANING THE NORMALLY ASPIRATED ENGINES

1.Usefull-richmixtureduringtakeofforclimb.Carefulobser-vationofenginetemperatureinstrumentsshouldbepracticedtoensurethelimitsspecifiedinLycomingOperatorsManualareneverexceeded.Refer to theaircraftPOH(PilotsOperatingHandbook)orAFM(AircraftFlightManual)formorespecificinstructions.2.For5,000feetdensityaltitudeandabove,orhighambienttemperatures, roughnessor reductionofpowermayoccuratfullrichmixture.Themixturemaybeadjustedtoobtainsmoothengineoperation.Forfixed-pitchpropellers, leantomaximumRPM at full throttle prior to takeoffwhere airports are at5,000-feetdensityaltitudeorhigher.Limitoperationatfullthrottleonthegroundtoaminimum.Fordirect-driveandfornormallyaspiratedengineswithapropgovernor,butwithoutfuelfloworEGT,setthrottleatfullpowerandleanmixtureatmaximumRPMwithsmoothoperationoftheengineasadecidingfactor.3.Forcruisepowerswherebestpowermixture is allowed,slowly lean themixture fromfull rich tomaximumpower.Bestpowermixtureoperationprovidesthemostmilesperhourforagivenpowersetting.Forenginesequippedwithfixed-pitch

propellers,graduallyleanthemixtureuntileitherthetachometerortheairspeedindicatorreadingpeaks.Forenginesequippedwithcontrollablepitchpropellers,leanuntilaslightincreaseofairspeedisnoted.4.Foragivenpowersetting,besteconomymixtureprovidesthemostmilespergallon.Slowlyleanthemixtureuntilengineopera-tionbecomesroughoruntilenginepowerrapidlydiminishesasnotedbyanundesirabledecreaseinairspeed.Wheneithercondi-tionoccurs,enrichthemixturesufficientlytoobtainanevenlyfiringengineortoregainmostofthelostairspeedorengineRPM.Someenginepowerandairspeedmustbesacrificedtogainabesteconomymixturesetting.NOTE When leaned, engine roughness is caused by mis-firing due to a lean fuel/air mixture which will not support combustion. Roughness is eliminated by enriching slightly until the engine is smooth.5.Theexhaustgastemperature(EGT)offerslittleimprovementinleaningthefloat-typecarburetorovertheproceduresoutlinedabovebecauseofimperfectmixturedistribution.However,iftheEGTprobeisinstalled,leanthemixtureto100FontherichsideofpeakEGTforbestpoweroperation.Forbesteconomycruise,operateatpeakEGT.Ifroughnessisencountered,enrichthemixtureslightlyforsmoothengineoperation.6.WheninstallinganEGTprobe,theprobemustbeinstalledintheleanestcylinder.Contacttheairframeorkitmanufacturerforthecorrectlocation.Inexperimentalorcustomapplications,multipleprobeinstrumentationisrequired,andseveralpowersettingsshouldbechecked inorder todetermine the leanestcylinderforthespecificapplication.7.Duringnormaloperation,maintainthefollowingrecommendedtemperaturelimits:

a.CylinderheadtemperaturelimitlistedintheLycomingOperatorsManual.b. Oil temperature limit listed in the LycomingOperatorsManual.

8. For maximum service life, maintain the following rec-ommended limits for continuous cruise operation:

a. Engine power setting65% of rated or less.b. Cylinder head temperatures 400 F. or below.c. Oil temperature 165 F. 220 F.

C. LEANING THE TURBOCHARGED LYCOMING POWER PLANT

1.Thecylinderheadtemperature(CHT)andturbineinlettem-perature(TIT)gagesarerequiredinstrumentsforleaningwithturbochargingbyLycoming.EGTprobesonindividualcylindersshouldnotbeusedforleaning.2.Duringmanual leaning, themaximumallowableTITforaparticularenginemustnotbeexceeded.CheckthePOH/AFMortheLycomingOperatorsManualtodeterminethesetemperaturesandfuel-flowlimits.

8 L y c o m i n g F l y e r

3.Maintainingenginetemperaturelimitsmayrequireadjust-mentstofuelflow,cowlflapsorairspeedforcooling.4.Allnormaltakeoffs,withturbochargedpowerplants,mustbeatfull-richmixtureregardlessofairportelevation.5.Ifmanualleaningofthemixtureispermittedattakeoff,climbpowerorhigh-performancecruise, itwillbespecifiedin thePOH/AFMandwilllistrequiredrangesforfuelflow,powerset-tingsandtemperaturelimitations.6. Leaning to best economy mixture.

a.SetmanifoldpressureandRPMforthedesiredcruisepowersettingpertheaircraftPOH/AFM.b.Leanslowlyinsmallsteps,whilemonitoringinstrumen-tation,topeakTITormaximumallowableTIT,whicheveroccursfirst.

7. Leaning to best power mixture.Beforeleaningtobestpowermixture,itisnecessarytoestablishaTITreferencepoint.Thisisaccomplishedasfollows:

a.SetmanifoldpressureandRPMforthehighestcruisepowersettingwhereleaningtobesteconomyispermittedpertheaircraftPOH/AFM.b. Lean slowly in small steps until peak TIT or max-imum allowableTIT is reached.Record peakTIT as areferencepoint.c.Deduct125F.fromthisreference,andthusestablishtheTITtemperatureforbestpower-mixtureoperation.d.Returnthemixturetofull-rich,andadjustmanifoldpres-sureandRPMforthedesiredcruiseconditions.e. Lean mixture to the TIT temperature for bestpower/mixtureoperationestablishedinstepc.

8.Duringnormaloperation,maintainthefollowinglimits:a.Enginepowersettingrating listed in theLycomingOperatorsManual.b.CylinderheadtemperaturelimitlistedintheLycomingOperatorsManual.c.OiltemperaturelimitlistedintheLycomingOperatorsManual.d.TurbineinlettemperaturelimitlistedintheLycomingOperatorsManual.

9. For maximum service life, maintain the following recom-mended limits for continuous operation.

a.Enginepowersetting65%ofratedorless.b.Cylinderheadtemperatures400F.orbelow.c.Oiltemperature165F.220F.d.Turbineinlettemperaturemaintain100F.onrichsideofmaximumallowable.

D. LEANING THE SUPERCHARGED LYCOMING POWER PLANTS

1.All takeoffswith superchargedpower plantsmust be atfull-richmixtureregardlessoftheairportelevation.2.Ifmanualleaningofthemixtureispermittedatclimbpower,itwillbespecifiedinthePOH/AFMandwilllistrequiredrangesforfuelflow,powersettingsandtemperaturelimitations.3.Recommendedstandardcruisepowerfor thesuperchargedengineis65%.At65%powerorless,thistypeofenginemaybeleanedasdesiredaslongastheengineoperatessmoothly,andtemperaturesandpressuresarewithinmanufacturersprescribedlimits.4.Theexhaustgastemperature(EGT)gageisahelpfulinstru-mentforleaningthesuperchargedengineatcruisepowerwithamanualmixturecontrol.

L y c o m i n g F l y e r 9

This Article Now Incorporates Material From A Special On Fuel Management Which Has Been Eliminated

VariousLycomingFlyerarticleshaveemphasizedproperleaningatthemanufacturersrecommendedcruisepower.Beforedelvingintothesavingstobeobtainedbyleaning,itmaybeappropriatetoagainreviewthosefactorsthataffectleaningatcruise.First,wemustknowthatcruisepowerforLycomingnormallyaspiratedenginesisgenerallyconsideredtobe55%to75%ofthemaximumpowerforwhichtheengineisrated.Atthesepowerset-tings,theenginemay be leaned at any altitude.Therehasbeenconfusionaboutthereferencetonotleaningbelow5000-feetden-sityaltitude.Rememberthatthisreferenceonlyappliestothosepowersettingsabovethecruiserangethosenormallyusedfortakeoffandclimb.Oncecruisepowerhasbeenset,leaningtobesteconomyshouldbestandardprocedureasdamagetotheenginewillnotoccurfromleaningatcruisepowersettings.In thisarticle,wewillexpandourdiscussionof leaningandexplain(1)howitsavesdollars,and(2)howitaidssafeflight.Inapracticalapproachtooursubject,letslookcloselyatthechartprintedbelow:

Leaning the normally aspirated, direct-drive Lycoming engine at cruise vs. full rich at 4,000-feet density altitude, 75% power.

EngineModel AirplaneModel 300 HP Piper Cherokee 300 Full Best Economy Hours Hours Rich (PeakEGT) Rich Lean 19+gals. 15.6gals. 4.2hrs. 5.1hrs.

EngineModel AirplaneModel 250 HP Piper Aztec Full Best Economy Hours Hours Rich (PeakEGT) Rich Lean 16.2gals. 13.6gals. 4.3hrs. 5.1hrs.

EngineModel AirplaneModel 180 HP Cessna Cardinal Full Best Economy Hours Hours Rich (PeakEGT) Rich Lean 11.9gals .9.7gals. 4.1hrs. 5.1hrs.

Toputthecostofoperatingatafull-richmixturesettingduringcruiseflightintoperspective,letusassumethatthecostofavia-tiongasolineis$4.00pergallon.Ineachcase,itisonlyneces-sarytomultiplythedifferenceingallonsburnedatFullRichvs.BestEconomytimesthefuelprice.Thenumberobtainedwillbetheamountsavedeachhourofflightbyoperatingatbesteconomyduringcruise.Usingtheexamplesabove,thesearethesavingsforeachofthoseaircraftandengines:Aircraft Fuel-burn difference Fuel-cost savingsCherokee300 3.4gallonsX$4.00 =$13.60perhr.Aztec 5.2gallonsX$4.00 =$20.80perhr.Cardinal 2.2gallonsX$4.00 =$8.80perhr.Whileweareonadiscussionofunnecessarycostsofoperation,another important factor is thedamageoftendone toengineaccessoriesbyoperatingatfullrichatcruisepower.Enginesoperatingat full rich incruise tend toberough,resulting inshakingengineaccessoriesandenginemounts,therebyconsid-erablyreducingtheirlifeandoftenresultinginexpensiveearlyreplacement.Aproperlyleanedengineatcruisepowerisasmoothengineandwillsavemoney.InearlierissuesoftheFlyer,wehavebeentellingallconcernedaboutthebenefitstothesparkplugofproperleaningatcruisepower.That informationcanbe repeated in thisdiscussion,becauseithelpstoillustrateourpointonsavingdollars.Properleaningatcruisehelpspreventsparkplugfouling.Themainte-nancecosttoremoveandcleansparkplugscanbereducedbygoodleaningtechniques.Frequentcleaningofsparkplugsreducestheir lifeandrequiresearlyreplacement.Furthermore,badlyfouledsparkplugscouldalsobecomeasafety-of-flightproblem.Foraveryinterestingsafety-of-flightitem,letslookatthechartagain.Noticethedifferenceinhoursofflightatfullrichvs.leanatcruise.Intheillustrationofthe180HPengine,thereisonefulladditionalhourofflightwhenproperlyleaned.Theotherenginesprovidenearlyanadditionalhourofflighttimewhenleanedtobesteconomyduringcruise.Efficientfuelmanagementisaveryrealsafety-of-flightfact.Thesearesomeofthemoreimportantfactsthatillustratehowproperleaningatcruisepoweraidssafeflightandsavesdollars.

Somepilotshavedemonstratedalackofunderstandingwithregardtotheoperationofthedirect-drive,fixed-pitch,normallyaspiratedpowerplants.Whenapowerchartisprovided,itwillindicatethatastheairplaneisflownatdifferentaltitudesabovesealevel,itisneces-sarytouseahigherRPMforadequatecruiseperformancewithanincreaseinaltitude.AtypicalexamplemightbetheO-360,180HPLycomingpowerplant.Thepowerchartbytheairframemanufac-turerforthisfixed-landinggearaircraftlists75%powerat7,500feetat2675RPM(nomanifoldpressuregageintheirairplane).Thepilot


whodoesnotunderstandtheprinciplesofoperationinthethinairataltitudemayobservethatred-linetakeoffRPMis2700RPM,andisthenreluctanttoleaneitherforcruiseorclimbdespitethealtitudebecauseheispullingalmostthesameRPMasattakeoff.However,thepilotcanandshouldleantheengineatthesealti-tudesdespitethehighRPM,forthehorsepowerisdownto75%becauseofthethinnerair.Ontheotherhand,withanydirect-drivenormallyaspiratedLycomingengine, thepilotcanandshouldleanthemixtureatanyaltitudeaslongastheaircraftisincruiseconfigurationat75%powerorless.Lets lookat theairframemanufacturerspowerchartfor theO-360,180HPengine,andobserve thegradual increase inRPMrequiredwith the increase inaltitude,butmaintaining75%forcruiseateachaltitude.Whatthechartwillnotshowhereisthatforflightabove7500feet,itisnotpossibletoachieve75%powerwithanormallyaspiratedengine (meaningnotturbochargedorsupercharged).

POWER CHART

Percent Endurance on Altitude RPM of H. P. 59 gals. fuel 2500 255075% 4.8hours 3500 257575% 4.8hours 4500 260075% 4.8hours 5500 262575% 4.8hours 6500 265075% 4.8hours 7500 267575% 4.8hours

BecausethereareawidevarietyofLycomingenginesinopera-tion,theparagraphsbelowmaybehelpfulinunderstandingthedifferentmodesofoperationrequiredwhenoperatingeachtypeattakeoffandclimbpowersettings.ThePilotsOperatingHandbookfortheaircraftinwhichtheenginesareinstalledshouldbethefinalauthorityastohowtheengineshouldbeoperated.

DIRECT-DRIVE ENGINES

Most normally aspirated engines are rated at full powerfor takeoff and climb indefinitely, provided engine tem-peraturesandpressuresarewithin thegreenarcareaof theengine instruments.Extra fuel, sensible airspeed and cowlflaps, if available, are all helpful in keeping cylinder headtemperatureswithindesired limitsduring takeoffor climb.Climbrequirementsmayvary;forexample,onawarmdaywiththeairplaneclose togrossweight,andadirect-driveenginewithafixed-pitchprop, thepilotwillneedfull throttleall theway tocruisealtitude.Thesameairplaneonacolddayandlightly-loadedmaynotrequirefullpowerforclimb.Afterfull

throttleattakeoff,thepilotmaywanttoreducepower100or200RPMandstillnotseeperformancesuffer.Thosedirect-drivenormallyaspiratedengineswithapropgov-ernorarealsoratedindefinitelyatfullpower,andthemanualsallrecommendfullpowerfortakeoff,butspecifyasmallreductioninpower,generallyto85%powerclimb.StudythespecificairplanePilotsOperatingHandbookfordetailedpowersettings.

GEARED, TURBOCHARGED AND SUPERCHARGED ENGINES

Turningtothemorecomplexpowerplantssuchasthegeared,tur-bochargedandsuperchargedmodels,themanualsarequitespecificintheirdescriptionoftakeoffandclimbtechniques.Ourgearedandsuperchargedpowerplantshavealimitoffiveminutesattakeoffpower.However,itisadvisabletothrottlepowertotherecommendedclimbpowerasstipulatedinthemanualassoonastakeoffobstruc-tionshavebeenclearedandproperairspeedattained.TheturbochargedLycomings(includingtheTIGO-541-Eseries)donothaveafive-minutelimitattakeoffpower.However,themanualclearlystipulatesareductiontoaproperclimbpowerwhenclearofobstacles,whenclimbspeedhasbeenestablished,andwhencylinderhead,oilandturbineinlettemperaturesarewithinlimits.Duetothemorecompleteengineinstrumentationintheairplane,themanualsallowsomeleaningatclimb,butonlywiththeengineinstrumentsreadingwithinspecifiedlimitslistedintheairplanemanual.Themorecomplexpowerplants (geared, superchargedandturbocharged)demandsmooth,carefuloperationofthethrottleatall times,particularlyathighpower,butespeciallywhenenginesandoilarenotup tonormaloperating temperaturessuch as for the initial takeoff.Overboost or erratic engineoperationwill result fromabruptmovementsof the throttle.Allsuperchargedandturbochargedenginesmustusefull-richmixtureforalltakeoffsregardlessoffieldelevation.

Sincesomanyoperatorsofourenginesfrequentlyaskusabouttheuseofanexhaustgas temperaturewithourpowerplants,perhapsweshouldexaminethesystemandseehowitrelatestofuelmanagement.OneofthebetterpublicationsdescribingtheEGTthatwehaveseenwasputoutbyAlcorInc.,P.O.Box792222ofSanAntonio,Texas78279-2222.Thisexcellentbooklet is titled,EGTandCombustionAnalysisinaNutshell,andisavailablefreeonlineatwww.alcorinc.com.AnEGTsystemisnotacomplexorexpensiveitemtoinstall.Themoreeconomicalkitconsistsbasicallyofthegage,wiringand probe (see illustration).The system generates its ownelectricitytooperatetheinstrument.


INSTALLATION INFORMATION

Themechanicmustcarefullyfollowtheinstallationinstructionsconcerningplacingtheprobeintheexhauststack.Ifitiscloserthan1"tothecylinderhead,probelifewillbelimited,oriftoofardowntowardtheendoftheexhauststack,theresponseonthegagewillbeslow.Shouldtherebedoubtconcerninginwhichstackasingleprobeistobeinstalled,thatinformationmaybeavailablefromtheairframedealersservicedepartment.Theoperatormightdesirethemoreexpensiveinstallationofprobesinallcylinders,thereforetheaccompanyinggagewillgenerallyhaveaselectorswitchforindividualreadingsonallcylinderexhauststacks.Again,itismostimportantthattheinstallationinstructionsarecarefullyfollowedinordertogetreliablereadings.INTERPRETING THE SYSTEM

Mostof theEGTmanufacturershavestandardizedongageincrementmarkingsof25F(seeillustration).AfewEGTmanu-facturerswillgofurtherandshowthetemperaturerangeonthegageas1200Fto1700F.

Thesimplegageshownintheillustrationisquitesatisfactoryforthelesscomplexengines.AnadvantageoftheEGToverthecylinderheadtemperaturegageisoneofanalmostimmediateresponsetomanualmovementofthemixturecontrol,aslongasitisnotarapidmovementofthecontrol.RememberthatthepeakorpointofmaximumneedledeflectionoftheEGTgageisthebasicreferenceforfuelmanagement.IfanoperatorhasexperimentedwiththeEGTattheenginemanufacturersrecommendedcruisepower,heobservesthatgradualleaningdoesresultinpeakEGT.ThelocationofpeakEGTonthegagewillalsovarywithdif-ferentpowersettings,changesinaltitudeandchangeinambienttemperature.FrompeakEGT,eitherincreasingordecreasingthefuelflowcausesadecreaseinEGT.WhenricherthanpeakEGTcoolingoccursbecausethereisexcessfuel,andwhenleanerthanpeak,coolingoccursbecausethereisexcessair.PeakEGTwitha float-typecarburetedengine is frequentlyavaguepointbecauseof lessefficientdistribution(thanfuelinjection) to theindividualcylindersbythis typeofmeteringdevice.Asaresult,float-typecarburetedenginestendtooperate

smootherat+25to+50FontherichsideofpeakEGT.Whereas,thefuel-injectedenginesat250HPandhigherwillprovideamoreprecisepeak,andthereforetheEGTsystemislikewiseamoreprecisemethodoffuelmanagementwithfuelinjection.

DEFINITION OF PEAK EGT

AsimpledefinitionofpeakEGTisgivenusbyengineeringasthechemicallycorrectmixtureoffuelandairwhichgives100%utilizationofall thefuelandall theair.Remember,wesaidearlier thatatmixturesleanerthanpeakEGT,thereisexcessair,andatrichermixtures,excessfuel.OperationatpeakEGT,particularlyonlongflights,canbeanadvantagenotonlyforpurposesofincreasedrange,butthereislesslikelihoodofsparkplugfoulingaswell.Dontbesurprised toseevariations in temperaturebetweenindividualcylinderswherethereisaprobeforeverycylinder.It isfairlytypicaltoseeanaverage100Fvariationwithfuelinjection,andasmuchas200Fvariationwitha float-typecarburetor.Thelatter(carburetor)variationtendstobegreaterbecausefuel/airdistributionisnotasgoodaswithfuelinjec-tion.Incoldoutsideairtemperatureflightconditions,themix-turedistributionispoorerforbothfuel-injectedandcarburetedengines.However,withthefloat-typecarburetoroperatinginbelow-freezingambient temperatures, thefuel/airdistributionisdefinitelyworsened,resultinginnoticeablevariationsintem-peraturebetweenindividualexhauststacks.It isalsoimportanttounderstandthatleaningtoroughnessattheenginemanufacturersrecommendedcruisepowerisnotanindicationofdetonation,butindicatesnormalcharacteristicsofdistributiontotheindividualcylinders.Theroughnessindicatesthattheleanestcylinderhasbecomesolean,itisbeginningtomiss.Thisistypicalofanenginewithafloat-typecarburetor.Damage,toanenginefromleaningdoesnotoccuratthemanu-facturersrecommendedcruisepower,buttakesplaceathigherthancruisepower.Asfarasthepilot isconcerned,operatingontheleansideofpeakEGTcanonlybeaccomplishedwithfuel-injectedenginesofatleast250HPorhigherbecausethefuelflowsinthelowerhorsepowerenginesaresosmall.Itisntpossiblewithfloat-typecarburetorsbecauseofthefuel/airdistributionproblem.Inanycase,leaning past the peak is not recommended.

LIMITATIONS OF POWER AT PEAK EGT

Lycoming allows leaning to peakEGT at 75% power andbelow on our direct-drive normally aspirated engines.Welimit operation at peakEGT on our geared, superchargedpowerplantsat65%powerorbelow.WithLycomingturbochargedengines,wheretheEGTgageisusedtointerpretturbineinlettem-perature(TIT),themaximumallowableTITspecifiedinthePOHshouldnotbeexceededwhenattemptingtofindapeaktemperaturebymanualleaning.Whereacylinderheadtemperatureisalsoavail-able,theoperatorshouldalwayscross-checktheheadtemperatureasaroutineprocedurewhenleaning,andrememberthatwheneverCHTreachesthemaximumbeforereachingpeakEGT,thenCHTratherthanEGTshoulddictatethelimitofallowableleaning.


BEST ECONOMY MIXTURE

BesteconomymixtureasitrelatestotheEGTsystembeginsatpeak.ForallpracticalpurposeswithLycomingengines,peakEGTisrightattheedgeofbesteconomymixture,andisouronlypracticalpointofreferenceinthebesteconomymixturerange.Atthemanufacturersrecommendedcruisepower,peakEGTcausesaslightlossofhorsepowerusuallyreflectedintwoorthreemilesperhourofairspeed.IfthepilotattemptstogoleanerthanpeakEGT(withfuelinjectiononly),thepowerdecreasesrapidlyasfuelflowdecreases.

BEST POWER MIXTURE

Bestpowermixture,orsometimes termedmaximumpowerrange,asdepictedon theEGTgage, is in the rangeofplus100Fontherichsideofpeak.Bestpowermixturewillprovidefastest indicatedairspeedforacruisepowersetting,althoughitisgenerallynotconsideredapracticaleconomicmixtureforcruisepurposes.However,bestpowermixturegenerallyprovidesasafeamountoffuelforapowersettinghigherthantheenginemanufacturers recommendedcruise,except thatneededfortakeoffpower.Again,we repeat thatmaximum leaning (peakEGT)doesnotdamageanengineat theenginemanufacturers recom-mendedcruisepower.Damageiscausedbymaximumleaningathigherthanrecommendedcruisepowerwherethemanualsdonotspellitoutorallowit,andwhentheaircraftdoesnothaveacompletesetofreliableengineinstrumentstoprotectthepowerplants.Excessive leaningunder the latter highpowerconditionscancausedetonationand/orpreignitionandpossibleenginefailure.IfweweretosumupthemajoradvantagesofanEGTtotheoperator,theyareasfollows:1.Savesfuelaneconomyaid.2.Aidspropermixturecontrolmoreprecisefuelmanagement.3.Helpsincreaserange.4.Detectssometypesofenginetroubles.5.Aidspeakengineperformanceatcruise.6.Helpspreventsparkplugfouling.7.FitsanyGeneralAviationpistonaircraftengine.AlthoughuseoftheEGThastheadvantageslistedabove,fromapilotspointofview,therearealsosomepossibledisadvantages.Poormixturedistributiontothecylinders(particularlyincar-buretedengines)istheprimaryreasonforthesedisadvantages.TheEGTprobeistobeinstalledintheleanestcylinder,butthischangeswithaltitudeandpowersetting, thereforemaking itverydifficult,orperhapsimpossible,tochooseabestcylinderforprobeinstallation.WithoutanEGTinstallation,thepilotcaneasilyleanusingtheleanestcylinderofacarburetedenginebysimplyleaningtofindengineroughnessfromthefirst indica-tionofleanmisfire,andthenricheningthemixturetosmoothengineoperation.

Thepilotmustalsorealizethatevenwithafuel-injectedengine,therewillbevariationsinfuelflow.UtilizinganEGTwithprobesineachexhauststack(sometimescalledacombustionanalyzer)willshowthesevariations.Tryingtointerpretthevariationsintemperatureshownforeachcylinderhascausedsomepilotstosuspectproblemswiththeirenginewhenithasbeenoperatingnormally.Sometimestoomuchknowledgecanbeaproblem.Finally, theEGTsystemmustbe inperfectworkingorder togiveaccuratereadings.Theprobesintheexhaustsystemwilldeterioratewithageandcontinuoususe.Thisoftencausesthegagetoreada temperaturethat isnotaccurate,andthereforeapeakreadingthatisnotreachedsoonenough.Thisresultsinoverleaningtotheleansideofpeakwhereoperationisnotrecom-mended.Frequentmaintenancetoensurethattemperatureprobesareingoodconditionwillreducethepossibilityofinaccuracies,butthepilotcannotdeterminetheaccuracyofthisrathercriticalreadingduringoperation.Theexhaustgastemperaturesystem,whenwellmaintainedandthoroughlyunderstood,canbeanaidinproperleaningatcruisepowerwithfuel-injectedpowerplants.Itishopedthatthisinfor-mationwillhelptheoperatorsofLycomingenginesachievethebestpossibleengineefficiencythroughuseoftheEGTsystem.

Pilotsfrequentlyaskusforinformationandguidanceconcerninglandingsandtakeoffsfromhigh-elevationairports.Ourreferencepointinthisdiscussionwillbebasedondensityaltitude.Thediscussionalsorequires thatwetreatseparatelyoperationofnormallyaspirated,turbochargedandsuperchargedenginesathigh-elevationairports.

NORMALLY ASPIRATED

Thenormallyaspiratedengineperformsandreactstodensityaltitude.Asanexample, this typeofpowerplantat takeofffromanairportwithan indicatedaltitudeof3,000feet,butwithanambient temperatureat85F,wouldhaveadensityaltitudeofmorethan5,000feet.Theenginewouldlacksome20to25%ofitspowerandalsoprobablyrunroughbecauseofarichmixtureonthegroundatfullrich.Therefore,thetypicalnormallyaspirateddirect-driveenginerequiresthemixturebeleanedonthegroundforefficient takeoffperformancewhereairportsare5,000feet(densityaltitude)orhigher.Theover-richconditionissomethingthepilotcancompensateforbyleaning.However,thehigher-densityaltitudewithitsthinneraircannotbecompensatedforwithanormallyaspiratedengineunlessasuperchargerorturbochargerunitisaddedtothepowerplant.Thus,atdensityaltitudesof5,000-6,000feet,thepilotofanor-mallyaspiratedenginehasavailabletohimapproximately75%oftheenginepower,andmustplanhistakeoffaccordinglyaftersettingthemixture.


PROCEDURE FOR LEANING

1.Thefixed-pitchpropellerleantomaximumRPMatfullthrottleprior to takeoffwhereairportsare5,000feetdensityaltitudeorhigher.Limitoperationatfullthrottleonthegroundtoaminimumtime.2.Thedirect-drivenormallyaspiratedenginewithapropgov-ernorbutwithoutafuel-flowgage,setthrottleatfullpowerandleanmixtureatmaximumRPMwithsmoothoperationoftheengineasadecidingfactor.3.Withfuelinjection,ifthepowerplanthasamarkedfuel-flowgage, thensetmixtureinaccordancewithinstructionsonthefuel-flowgageand/or inaccordancewiththeairplanePilotsOperatingHandbook.4.PressurecarburetorAllLycomingenginesequippedwithBendixPScarburetorshaveanautomaticmixturecontrolwhichdoesnotrequireleaningfortakeoff.5.TurbochargedandsuperchargedenginesAlltakeoffsmustbeatfull-richmixture,becausetheengineisbroughtbacktosealevelhorsepowerwhichdoesnotpermitleaning.

DESCENT

Regardlessofthefieldelevationwherethepilotintendstoland,thedescentfromcruisealtitudetotrafficpatternaltitudeshouldbemadewiththeengineleanedforsmoothengineoperation.Lowelevationfields(below5,000feetdensityaltitude)willrequirethat themixturebemovedtofullrichin thebefore landingchecklist.Landingatairportsabove5,000feetdensityaltitude,themixturemustbeleanedtosmoothengineoperationduringtrafficpatternflightandlanding;otherwise,theenginemaystopontherunwaybecauseofexcessiverichness.

TO INCREASE POWERfirst,enrichmixture,increaseRPM,thenfollowwiththrottle.TO DECREASE POWERfirst,reducethrottle,reduceRPM,andthenadjustmixture.INCREASING POWERenrichmixturefirsttoensurepro-tectingtheengineagainstdamagefromhigherpowerwhenpreviouslyleanedoutforalowerpowersetting.Next, increaseRPMbecause insomemodels theengineandpropellerwouldhaveundesirablepressureandstresseswithahighmanifoldpressureandlowerRPM.Then,followwiththeappropriatemanifoldpressure,nowthatthemixtureandRPMhavebeencorrectlysettoaccommodatetheincreasedthrottle.DECREASING POWER Most models of our enginesrequirethebasicprocedurefordecreaseofpowerbyretardingthrottle, followedbyRPM.However,wedohaveanexcep-

tioninseveraloldermodelsofourgearednormallyaspiratedpowerplants,suchas theGO-480andGO-435series. In theclimbconfiguration,werecommendedfullthrottlethroughouttheclimbfor internal fuelcoolingwithRPMreductions ini-tiallyto3000RPMandthen2750RPMforprolongedclimb.

Turbochargedandsuperchargedenginesrequirecarefulapplica-tionofthebasicpowersequencesasoutlinedinthebeginning.ItisalsopossibletocreateanoverboostconditionontheseenginesbygoingtotakeoffmanifoldpressureatcruiseRPM,suchasmighttakeplaceinanunexpectedgo-around.Thestressesandpressuresonpropandenginewouldcreateathreattoboth.

Aletterreceivedhereat thefactoryaskedaquestionwehaveheardquiteoften:Is itafact,or is it fiction, thatengineswithconstantspeedprops should not use power settingswhere inches ofmer-curyexceedRPMinhundreds?Iamreferring,ofcourse, tonon-turbochargedenginesingeneral.Theanswer to thisquestion iseasily found incruisepowerchartsof theairframePilotsOperatingHandbook.WhateverthecombinationsofRPMandMPlistedinthechartstheyhave been flight tested and approved by the airframe andpowerplantengineers.Therefore,iftherearepowersettingssuchas2100RPMand24"MPinthepowerchart,theyareapprovedforuse.The confusion over so-called squared power settings(i.e.,2400x24"MP),appearstohavebeenacarry-overfromsomemodelsof theoldradialengineswhichwerevulnerabletoexcessivebearingwearwhereanMPhigherthansquaredwasused.MorepressureonthebearingswiththehigherthansquaredMPwasthecauseoftheirproblem.However,changesindesign,metalsandlubricantspermitchangesinoperationinthemoremodernflat-opposedpowerplants.LetslookatthepowerchartsinacoupleofthePilotsOperatingHandbooksoftwodifferentaircraftmanufacturers,butwherebothareusingthefour-cylinder200HPLycomingengine.CessnasModel177RG,usingtheLycomingIO-360-A1B6D,inthecruiserangeat6,000feet,listsacruisepower-settingrangeatthataltitudeofanywherefrom2100RPMto2500RPMwithvariationsallthewayfrom18"MPto24"MP.Theylistarecom-mendedpower-settingfor66%powerat2100RPMat24"MP.ThePiperArrow,poweredby theLycomingIO-360-Cseriesengine, lists thefollowingcruisepowersettingsat6,000feetin their chart at65%powerat full throttle (about23"MP)x2100RPM.


THE COMPLETE CHART FOR % POWER IS SHOWN AS FOLLOWS:

Altitude 2100 RPM 2400 RPM SL 25.9MP 22.9MP 1,000 25.6MP 22.7MP 2,000 25.4MP 22.5MP 3,000 25.1MP 22.2MP 4,000 24.8MP 22.0MP 5,000 F.T.MP 21.7MP 6,000 F.T.MP 21.5MP

Afterstudyingthepowerchart,thepilotwouldundoubtedlythenaskwhatcombinationofRPMandMPwouldbebesttouseatcruise.Werecommendthepilot trythevariouscombinationsofferedbythepowerchartoverafive-minuteperiodwhenflyinginsmoothair,andusethelistedRPMandMPcombinationwhichgavetheleastvibrationandthelowestnoiselevel.Inadditiontothequieterandsmootherconsideration,lowerRPMmeanslowerfrictionHP.Thisreducedlossofhorsepowerduetofrictionalsotranslatestoslightlyimprovedfueleconomy.ThePilotsOperatingHandbookisthebasicreferenceforthepilotasthissubjectillustrates.

Thehighpriceofaviationfueliscausingaircraftownersandpilotstoreviewtheiroperationsinsearchofwaystokeepoperatingcostsdown.ThoseoperatingaircraftwithcontrollablepropellershavebeenrequestinginformationoncruiseoperationinthelowRPMrange1800or1900RPMforexample.Thenumberofqueriesreceivedindicatesagreatdealofinterest,andthereforeitseemsappropriatetosharetheinformationonthissubjectwithallofourreaders.TheLycomingEngineOperatorsManual hasperformancecurves applicable to each engine series.The curve for theIO-540-Kseries,300-horsepowerengine isprintedhereasareferencefor thisarticle.Thecurvedoesprovidedataon themaximummanifoldpressure (MP),whichmaybeusedwithanyparticularRPMatsea levelandataltitude.The limitingmanifoldpressurelineclearlyrestrictshighmanifoldpressureswith low-RPMsettings.There isagoodreasonfor this;highmanifoldpressureandlowRPMissimilartoallowingyourauto-mobiletoluguphillinfourthgear.Thepingingyouhearinyourautomobiletellsyouthatdetonationisoccurring,andyoushouldshiftdowntoalowergear.Inanaircraft,detonationisnotlikelytobeheardasdamageoccursintheengine,anditisthentoolateforpreventivemeasures.Forthisreason,engineoperationshouldbewithin the limitationsestablished in thePilotsOperatingHandbook(POH).

Althoughtherearerestrictions,itisquiteapparentthatoperationispossibleinthe1800to1900RPMrange.LowerRPMwillresultinless-frictionhorsepowerwitharesultantfuelsavings,butmostofthefuel-flowreductionexperiencedwillbetheresultofamuchlowerpowersettingandthereforereducedperformance.ThisraisesaquestionabouttheamountofbenefitintermsofcostsavingsthatmightactuallybeachievedbyusingthelowerRPMsettingsforcruise.Oneofthefirstconsiderationsoflow-RPMcruiseisthatpowersettingsthislowshouldnotbeusedduringtheenginebreak-inperiod.Duringthebreak-inperiod,normalclimbpowerasspeci-fiedinthePilotsOperatingHandbookshouldbeused.Toseatthepistonringsinaneworoverhauledengine,cruisetheaircraftat65%to75%powerforthefirst50hours,oruntiloilconsump-tionhasstabilized.Lowpowerforbreak-inmayresultinglazedcylinderwallsandhighoilconsumptionthatcanonlybecuredbycylinderremovalandrehoning.Therearesomeotherconsiderationsoflow-powercruiseopera-tion.Lowmanifoldpressures,belowanarbitrarypointofperhaps18"forcontinuouscruise,maycauseexcessiveoilusageandoilbuildupinthevalveguideswhichcouldleadtostickingvalves.Particularlyduringcold-weatheroperation, low-poweropera-tionmayallowboththeoilandcylinderheadtemperaturestofallbelowthenormalrange.Thisisdetrimentaltogoodenginehealth.Oiltemperatureinparticularshouldbemaintainedbetween165Fand220Ftoachievemaximumservicelife.Atlowertemperatures,themoisturewhichgathersasaresultofcombustionwillnotvaporizeandbeexpelled.Thiscancausedilutionoftheoilwhichdetractsfromitslubricatingproperties.ThePilotsOperatingHandbookforeachaircraftprovidesavarietyofpowersettingsthatmostoftenshow2100or2200RPMastheminimumforcruise.ThetableshownhereisfortheIO-540-Kseriesenginewhichwasillustratedinthecurveshownearlier.Usingthatcurve,notethatcruiseflightat6,000feetusing1900RPMwouldbe limited toapproximately55%ofpowerwithmanifoldpressuresetat24".Asshowninthecurve,24"ofMPisverynearthelimitingmanifoldpressurelineandthereforeclosetothemaximumavailable.Quitefrequently,someonewillaskiftheenginewilllastlongerifitisrunataslowerRPMsetting.Theanswermustbequalified.OperationattherecommendedcruiseRPMsettingsshouldallowtheenginetoreachTBOifithasregularoilchanges,isoperatedwithinnormaltemperaturerangesandiswellcaredforbypilotsandmaintenancepersonnel.Longerenginelifemaybeexpectedfrommostengineswhentheoperatoriswillingtosacrificemax-imumperformanceforconservativecruiseoperationinthe60%to65%powerrange.Formanyengines,thesepowersettingsareachievedat2100or2200RPMratherthanthe1800or1900RPMmentionedearlierinthisdiscussion.Insummary,itispossibletorunanengineatcruiseusing1800or1900RPM.Acurve from theEngineOperatorsManualshouldbeconsultedtoensurethatmanifoldpressurelimitsarenotexceeded. In reality, the recommendationsof thePilotsOperatingHandbookprovidethebestguidanceforoperationofanaircraft/enginecombination,andthereforetherecommendationsandlimitationsofthePOHshouldbeobserved.


SEALEVELANDALTITUDEPERFORMANCECURVE-IO-540-K,-L,-M,-S


POWERTABLESETTINGLYCOMINGMODELIO-540-K,-L,-MSERIES,300HPENGINE


Thegasolineengineoperatesonafuel/airmixturethatisignitedbythesparkplugs.Enginesdonotrunwhenanyoftheseele-mentsaremissing.Pilotsknowpositivelythattheymustrefueltheaircraftonaregularbasisiftheywanttoflywithoutincident,butthepossibilityoflosingtheairpartofthefuel/airmixtureisnotalwaysconsideredandunderstoodaswellasitshouldbe.Perhapsthepersonalexperienceofseveral individuals,andsomefactsaboutinduction-systemicingcanbeusedtohelpFlyerreadersavoidanaccidentcausedbylackofairfortheirengines.Rememberthatanymaterialthatreducesorcutsofftheflowofairintheinductionsystemhasthepotentialtocausealossofpower.Amaterialfailureoftheairfilterisoneproblemwhichisreportedalltoooften.Thefilterisverynecessarytokeepdirtoutoftheengine;itmustbeinspectedfrequentlyandshouldbechangedonsomeregularschedule.Afilterwhichisseveralyearsoldandhasfilteredtheairduringhundredsofhoursofoperationmaybetired.Onepilotreportedthatonturn-upoftheenginebeforetakeoff,hecouldnotgetthestaticRPMthathisengineandfixed-pitchpropellershouldhaveproduced.Hewiselyelectedtoreturntothelineandhavetheengineinspected.Theairfilterhadpulledloosefromitssupportingframeandwaslodgedintheintakesystemwhereitwascuttingofftheairsupply.Ifthisincidenthadoccurredinflight,theenginewouldpossiblynothavebeenproducingenoughpower tomaintainaltitude.Dependingontheparticularairframe,therearesomeoptionswhichmightbeutilizedtoregainsomeofthelostpower.Analternateairsystemorcarburetorheatsystemisdesignedintotheinductionsystemprimarilytocombatinductionicing,butuseofthesesystemsmaypossiblyhelpwhenintakeairisblockedbyotherforeignmaterials.Insomecases,justleaningthemixturemayhelptoregainalittleofthelostpower.Severalyearsago,therewasareportedlossofenginepowerinheavyrain.Inthatcase,apaperairfilterwasbeingused.Whensaturatedwithwater, thepaperfilterelementbecameswollensothatairflowwasimpeded.Inthiscase,theuseofcarburetorheattobypassthefilterandreleaningtoachieveabetterfuel/airmixtureweresuccessfultacticsthatkepttheaircraftflyinguntilasafe,on-airportlandingcouldbemade.Weshouldkeepinmindthatitisnottheingestionofwaterthroughtheenginethatcausesaseriouslossofpower;itisthereducedairflow.Somepilotsbelieve thatfuel-injectedenginesare immunetoinductionicing.This isnotso.Althoughthepilotflyingwithafuel-injectedenginedoesnothavethesamethreatoficingattheventuriasthosewithacarburetor,rain,snow,slushandcoldtemperaturesmaycauseablockage(impact ice)toairflowinotherpartsoftheinductionsystem.Asanexample,thepilotofafuel-injectedsinglereportedflyingat11,000feetinlightdrizzle.Thetemperaturewasslightlyabove

freezingandwater readilyranoff thewindscreen.Althoughthiswouldseemtobeano-problemsituation,theenginestartedtolosepower.Afterconsiderationoftheavailableoptions,themanualalternateairsystemwasactivated.Theengineimmedi-atelyregainedpower,andflightwascontinuedtothehome-basedestination.Afterlanding,theaircraftwastakenintothehangerforexamination.Itwasfoundthattheairfilterwascoveredwithalayeroficethathadcutofftheairflow.Thisisnotanisolatedorunusualcase.Whenwaterisnearfreezing,movementofthewatermoleculesmaysometimescauseinstantaneousfreezing.Thisglazingoveroftheairfilterisaknownphenomenawhichpilotsshouldexpectandbereadytocopewith.Again,bypassingtheblockageofimpacticebyuseofalternateairprovedtobeasuccessfultacticforthispilot.Themostsubtleandinsidiousoftheairflowblockagepossibilitiesisprobablyrefrigeration ice,knownmorecommonlyascarbu-retorice,thatformsinthevicinityofthebutterflyorthrottleplate.Unfortunately, therearemanypilotswhoarenotfullyawareofwhatcarburetoricecandoorwhattodoaboutitwhenitdoesoccur.Anindicationofthisarestatementsmadebypilotsinvolvedinpower-lossaccidentswhohavesaidthattheytriedcarburetorheat,founditdidnotwork,andthenreturnedthecon-troltothecoldposition.Carburetorheatdoesnotprovideinstantreliefwhenappliedaftericehasformedinthecarburetor.Once

Rewritten and combined with article Induction Icing

CARBURETORICE


heatisapplied,itshouldbeleftonuntilenginepowerreturns.Leftuncorrected,iceaccumulationinthecarburetormaycausecompleteenginestoppage.Every pilotwho flies an aircraft powered by a carburetedengineshouldbethoroughlyeducatedaboutcarburetorice.Theyshouldknowthatundermoistconditions(arelativehumidityof50%to60%ismoistenough),carburetoricecanformwithanyoutsideairtemperaturefrom20to90F.Itismostlikelyinthe30to60Frange.Temperaturesinthecarburetorcandrop60to70F(refrigeratoreffect)asaresultoffuelvaporizationandthecarburetorventurieffect.Italsohappensthatcarburetoriceformsmorereadilywhentheengine isoperatedin the lowerpowerrange.Itwillformwhiletaxiing,andthismakesitveryimportanttocheckenginepowerbeforetakeoffandtoremovetheiceifnecessary.Careshouldbetakentoavoiddustyordirtyconditionswhenutilizingcarburetorheatontheground.Next,itisimperativethatthepilotrecognizecarburetoricewhenitformsduringflight.ThelossofpowerthatoccurswillcauseareductionofRPMwhenflyingwithafixed-pitchpropeller,andalossofmanifoldpressurewhenacontrollable-pitchpropellerisused.Ineithercase,alossofaltitudeorairspeedwilloccur.Thesesymptomsmaysometimesbeaccompaniedbyvibrationorengineroughness.Inanycase,it isagoodideatoconsidercarburetoriceasthecauseofanyunexplainedpowerlossduringcruiseflight.Onceapower loss isnoticedby thepilot, immediateactionshouldbetakentoeliminateicewhichhasalreadyformedinthecarburetor,and toprevent further ice formation.This isaccomplishedbyapplyingfullcarburetorheatwhichwillinitiallycauseafurtherlossofpower(perhapsasmuchas15%)andpos-sibly,engineroughness.Theadditionalpowerlossiscausedbytheheatedairthatisbeingdirectedintotheinductionsystem.Heatedairmakesthemixturericherandalsomeltstheicewhichthengoes through theengineaswater.The throttlemaybeadvancedandthemixturemaybeleanedtohelpgetsomeofthelostpowerback,butimmediatelyaftertheapplicationofcarbu-retorheat,thepilotmustbepatientandkeeptheairplaneflyinguntiltheicehascompletelymeltedandnormalpowerreturns.Howlongthiswilltakedependsontheseverityoftheicing,butthepilotshouldexpectadelayof30secondstoseveralminutes.Underthecircumstances, thisperiodoftimewillbestressfulandalwaysseemslongerthanitreallyis,buttheknowledgeablepilotwillnotretreatfromuseofcarburetorheat.Carburetorheatshouldremaininthehotpositionuntilpowerreturns.In conditions where carburetor ice is likely to form, thepilotmayuseheatduringcruisetopreventtheformationoficein thecarburetor. It isalsoappropriate tousefullcarburetorheat, ifneeded, topreventicingwhenoperatingat lowpowerfor instrumentapproaches,orforflight in thetrafficpattern.Unlesstheaircraftisequippedwithacarburetorairtemperature(CAT)gage,andveryfewgeneralaviationaircraftare,useoffullcarburetorheatisrecommended.Anunknownamountofpartialheatcanactuallycauseinductionice in thefloat-typecarburetor.Thismayoccurwhenmoistureincrystalformintheincomingairthatwouldordinarilypassthroughtheinduction

systemwithoutanyproblemismeltedbythepartialheat.Thismoisturethenfreezeswhenitcomesincontactwiththecoldmetalofthethrottleplate.Whenevercarburetorheatisusedinthelandingconfiguration,andago-aroundor touch-and-gotakesplace, therearesomeimportantstepsforthepilottoremember.Thethrottlemustbeadvanced,andthecarburetorheatleverplacedinthecoldposi-tion.Theorderinwhichthesestepsareaccomplishedisnottooimportant,butbothmustbedone.Leavingthecarburetorheatonduringago-aroundwillresultinalossofpowerthatcouldbecriticalatlowaltitudeandlowairspeed.DonotusecarburetorheatfortakeofforclimbwithaLycomingengineas it isnotnecessary,and itmaybringondetonationandpossibleenginedamage.Anexceptionto thisrulemightbejustifiedinextremelycold-weatherconditionssuchasthosefoundintheArctic,andtheseconditionsrequireaspecialknowl-edgetoaccommodateoperationundersuchextremeconditions.Areviewofthematerialdiscussedinthisarticleshouldhelppilotscopewithreductionofenginepowerwhenitiscausedbylossofintakeairforcombustion.Athoroughunderstandingoftheairintakesystemandtheknowledgetocompetentlydealwithinduc-tionicingareessentialtosafeflightingeneralaviationaircraft.Pilotsareencouragedtoenhancethesafetyoftheirflyingbyknowingwhattoexpectandwhatstepstotakewhentheairflowtotheengineiscutoffforanyreason.

Anote thatcamein themail fromaFlyer reader includedasuggestionthatwentsomethinglikethis,Howaboutanarticledealingmoreextensivelywith thecold-startproblem?Thissuggestionwasagoodoneasitprovidedanopportunitytoshareinformationaboutavarietyofcold-weatherconsiderationstohelpgettheenginestartedandtokeepitoperatingduringcold-weatherconditions.Althoughthesuggestionmadeinthefirstparagraphwasaimedathelpingwithcold-weatherstarting,thisarticlehasbeenexpandedtoincludetipsandinformationonpreflight,starting, in-flightsafetyandengineoperationalconsiderations.Keepinmindthatthismaterialdealswithnormalcold-weatheroperationexperi-encedattemperaturesto-25F,andnottheextremelylowtem-peraturesthatmaybefoundinArcticregions.Operationinthoseregionsmayrequiremorespecializedknowledge.Letsstartwiththegeneralhealthoftheengine.Whenattemptingastartunderadverseconditions,itisimperativethattheenginebe well maintained and in excellent operating condition.Sparkplugsandmagnetopointsshouldbeproperlygappedandready to functioneffectively. Inaddition to the ignitionsystem,theproperfunctioningofothersystemssuchasinduction,priming,exhaustandcarburetorheatcanhaveaneffectonthestartingandoperationoftheengine.

L y c o m i n g F l y e r 9

Regularmaintenanceshouldincludehavingtheheatingsystemcheckedfor leaks.Thiscold-weather tip isworthyofasepa-rate littlesentenceall itsownremember,youcantsmellcarbonmonoxide.Incoldweather,preheatisanotherfactorthatmustbeconsid-eredpriortostartingtheengine.TherearespecificguidelinesinLycomingserviceinstructionswhichestablishwhenpreheatshouldbeused,buthowmuch,or themethodofpreheat isgenerallylefttothegoodjudgmentofthepilotormaintenancepersondoingthepreheating.UseoftheheateddipstickisnotrecommendedbyLycoming,althoughmostothermethodsareconsideredtobesatisfactory.FormostLycomingmodels,preheatshouldbeappliedanytimetemperaturesareat10Forlower.Theexceptiontothisruleisthe76seriesmodelsthatincludetheO-320-H,andtheO/LO-360-E.Theseenginesshouldbepreheatedwhentemperaturesarebelow20F.Itisrecommendedthattheseguidelinesbefollowedevenwhenmulti-viscosityoil isbeingused.Inadditiontohardstarting,failuretopreheattheentireengineandoilsupplysystemasrecommendedmayresultinminoramountsofabnormalweartointernalengineparts,andeventuallytoreducedengineperformanceandshortenedTBOtime.Waterisoneofthemostlikelycontaminantsofaviationgaso-line.Theenginewillnotrunonwater,andalthoughwemaygetawaywithsmallamountsofmoistureinthefuelduringwarmweather,flightintofreezingtemperaturesmakesanyamountofmoistureinthefuelsystemverycritical.Evenatinybubbleofmoisturemayfreezeinthefuellineandtotallycutofftheflowoffuel.Twostepsshouldbetakentoavoidthisproblem.First,avoidwatercontaminationifpossible.Keepfuel tanksfull topreventcondensation,andbesurefuelcapsdonotallowleakageiftheaircraftisparkedoutsideinrainorsnow.Second,lookforcontaminationbeforeeveryflightbyreligiouslydrainingfueltanksandsumps.If flight isplannedforbadweather, thepreflight inspectionshouldincludeobservationofthereliefopeningintheenginebreathertubesothatanyfreezingofmoistureattheendofthebreatherwillnotresultinalossofengineoil.(SeeTheWhistleSlotinthisbook.)Onceonboard theaircraft,check thefuel-selectorvalveforfreedomofmovement.Itmaybefrozenfast(thishashappened),andyoudbetterfindoutwhilestillontheground.Mostofthetime,wethinkofstartinganyengineasaverysimpleprocess.Justengagethestarter,andlistenfortheenginetostartpurring.Unfortunately,whentheweather turnscold, it isnotalwaysthatsimple.Whendealingwithareciprocatingaircraftengine,itmaybeessentialtogetastartonthefirsttryinordertoavoidicingoverthesparkplugsandmakinganimmediatestartimpossible.Inordertoachieveastartonthefirsttry,thereareanumberoffactorstobeconsidered.Thosefactorswillbediscussedinthefollowingparagraphs.Althoughitmightbegoodproceduretouseanexternalpowersourceforstartingduringverycoldweather,mostofusexpectourbatterytodothejob.Weshouldrememberthatthebatteryishandicappedbycoldweather.Particularlywhenasingle-viscosityoilisbeingused,thecolderthetemperature,themorecranking

energyrequired.Combinethiswithreducedbatteryoutputatlowertemperatures,anditcanbeaserioushandicap.Whileonthesubjectofbatteries,rememberthatfreezingtem-peraturesprovideaperfectopportunitytodestroyanaircraftbat-tery.Thebatterywithafullchargesurvivesnicely,butonethatisdischargedwillfreeze.Oncethishappens,theproblemcanonlyberemediedbyreplacingthebattery,soitisveryworthwhiletotakepreventivemeasures.Shouldthebatteryberundownduringanattempttostart,donotleaveit;getitchargedimmediately.Andfinally,beabsolutelycertainthatthemasterswitchisalwaysOFFwhiletheaircraftisparkedbetweenflights.Iflefton,thebatterywilldischargeandfreeze.Theseratherminormistakescanbequiteexpensive.Oilisanotherfactortobeconsideredinthecold-weatherstartingprocess.Alloilsareaffectedbytemperatureandtendtothickenasthetemperaturedrops.Theenginemaybereluctanttoturnoverwhentheoilisstiff;asummerweightoilisnotsuitableincoldweather.Itisalsotheconditionwhichbringsouttheprimaryadvantageofmultiviscosityoilsandofpreheating.Becausemulti-viscosityoilsarethinner(lowerviscosity),theyallowtheenginetobeturnedovermoreeasily.Theeasierandquickeroilflowalsopromotesfasterlubricationofinternalenginepartswhentheenginedoesstart.Sincetheproperoilviscosityissoimportantinallaspectsofenginestartingandoperation,therecommendationsofoilgradevs.temperaturerangeshowninLycomingServiceInstructionNo.1014shouldbefollowed.Probably themost important factor instartinganengine isachievinga fuel/airmixture that issatisfactoryforcombus-tion.Sincetheengineusuallystartsveryeasily,manypilotsareunawareoforignorethechangeofstartingprocedureneededtosuccessfullystartundervaryingtemperatureconditions.Inwarmweather,theairislessdense,andthereforemustbemixedwithalesseramountoffuelthanincoldweather.Inadditiontothis,inwarmweather,thefuelwillvaporizereadilyandmakestartingeasier.Simplystated,astemperaturesgodownitbecomesmoreandmoreimportant thatwehaveaplanforprimingthatwillachievethecorrectfuel/airmixture.Whenpriming a carbureted engine, the pilots planmustconsiderthetemperature,thenumberofcylinderswhichhavepriminglinesinstalled,andthenumberofstrokesoftheprimerneededtoproducethecorrectfuel/airmixture.Theprimerlinesareorderedorinstalledbytheairframemanufacturerandnotallaircraftareconfiguredthesame.Someaircrafthaveactuallybeenproducedwithonlyonecylinderbeingprimed,andtheseenginesareextremelyhardtostartincoldweather.Thenumberofcylindersthatareprimedmustbeconsideredsincethetotalfueldeliveredbytheprimerwillbedividedandsenttothesecylinders.Astheairbecomescolderanddenser,theamountofprimeusedmustbeincreased,butthenumberofstrokestobeusedshouldbeplannedasaresultofsometrialanderrorexperimentationforeachaircraftapilotflies.Whenthecor-rectnumberofprimerstrokesforeachtemperaturerangehasbeenestablished,theenginewillusuallystartveryquickly.Wemayfindthatanenginestartseasilywhenonestrokeof theprimerisusedinthe60range,twostrokesinthe50range,threestrokesinthe40range,etc.Thisisanexampleofthe


trialanderrorwemightusetoestablishthenumberofprimerstrokes touseunder anyparticular temperature condition.Whilediscussingtheprimingofanengine,therehavebeensitu-ationswhereprimerlinesbecomeclogged.Thismakesenginestartingdifficultandnegatesanytrialanderrorexperimentationthatmayhavebeendone.Whenmaintenanceisdoneonanaircraftbeforethestartofwinter,itmaybewisetohavethoseprimerlinescheckedtoensurethatfuelwillflowthroughthem.Theamountoffuelneededtoachievethecorrectfuel/airmixtureforstartingafuel-injectedengineiscontrolledbytimingratherthannumberofprimerstrokes.Withtheelectricfuelpumpon,movingthemixturecontrol totherichpositionallowsfueltoflowtothecylinders.Forcold-weatherstarting,itmaybeneces-sarytokeepthemixturecontrolinrichsomewhatlongerthaninwarmweather.Thefuelpartofthefuel/airmixturemaybethepartwehavethemostcontroloverduringtheenginestart,butkeepinmindthattheamountofthrottleopeningdoeshaveaneffectontheair thatispumpedthroughtheengine.Justaswecompensateforcold/denseairbyaddingmorefuelforstart,itmayalsobeappropriatetoreducetheairpartofthemixturewhenthetem-peratureisverycold.Forexample,ifthethrottleisnormallysetopenone-halfinchforwarmweatherstarting,itmaybehelpfultoreducethistoone-quarterinchincoldweather.Again,itwillrequiresomeexperimentationtodeterminewhat isneededtoachievethecorrectfuel/airmixtureforanyparticularaircraftatanytemperaturerange.Whenanenginedoesnotstarteasily, itcanbefrustrating.Ofcourse, thiscanoccuratany timeof theyear,and it isverytemptingtojustkeepgrindingawaywiththestarterinanattempttogetitgoing.Shouldthishappentoyou,RELAX.Takecareof thatstarter,or itmayfail.Thegeneral rule forstarters isthat theyshouldonlybeoperatedforshortperiods,andthenallowed tocool. Ifenginestarthasnotoccurredafter three10-secondperiodsofoperationwithapausebetweeneach,afive-minutecoolingoffperiodisrequired.Withoutthistimelimitforoperationandanadequatecoolingoffperiod,thestarterwilloverheatandislikelytobedamagedortofailcompletely.Thepreviousparagraphshaveaddressedseveralissuesthatrelatetothecold-weatherpreflightandthecold-weatherstart.Thereareothercold-weather itemsthatshouldbeconsideredintheoperationoftheengine.Assumingtheenginehaskickedoff,checkforan indicationofoilpressure.Learn thecharacteristicsrelative toresponseofoilpressure indicationsofyouraircraft/enginecombina-tion.Onmost single-engine aircraft, an almost immediateresponseisnoted.Ontwin-engineaircraft,theresponsemaybemuch slower.On some twins, the oil pressuremay go up,andduringwarm-up,maydropagainforashortperiodoftime,thenagainrisetonormal.Allcasesmentionedmaybenormal,but the important thingis toknowwhat toexpectfromyouraircraft/enginecombination.Afterstart,donotidleenginebelow1000RPM.Itsnotgoodpracticetoidleenginesbelow1000RPMatanytime.Thisisparticularlytrueduringcoldweathertopreventleadfoulingofsparkplugs.(ExceptionPiperPressurizedNavajo)

Now,heresatipfornovicepilots.Whensettingupforcruiseconfiguration,beprecise,readyourinstrumentsandrememberwhatyouread.Example:Ifyoudecideon22"ofmanifoldpres-sure,setitrighton22.IftheRPMistobe2350,makeit2350.Selectanaltitude.Trimtheaircrafttoholdthatselectedaltitude.Noteairspeed.Now,ifanythingchanges,barringturbulentair,ithastobeachangeinpower.Perhapsitiscarburetororinduction-airicing.Supposeyoupickedupabitofcarburetorice,andtheenginesuffersaslightpowerloss.Therewillbeaslightdropinmanifoldpressure,alossinairspeed,andtheaircraftwillwanttolosealtitude,andifyouholdaltitude,youllfindbackpressureonthewheelisrequired.Therefore,eventhoughyoudidntdiscoverthepowerlossthroughinstrumentscanning,youllgetawarningthroughtheheavywheelorstick.Duringflightinverylowtemperatures,exerciseconstantspeedpropsaboutevery30minutestohelppreventcongealingofoilinthepropdome.Shouldoneengineofatwin,foranyreason,indicatethepropmustbefeathered,donttarrytoolongwithreducedpowerinverycoldweather.Atreducedpower,theoilmaycongealmakingfeatheringanimpossibility.Atipforeverypilot,dontrunonesetoffueltanksnearlydrybeforeswitchingtanks.Switchwithplentyoffuelremaininginthetanksfirstused.Thisismoneyinthebank,shouldyoufindtheselectorvalvefrozen.Althoughcarburetoriceisnotnecessarilyawintertimephenomena,acheckofcarburetorheatshouldbemadeduringtheenginerun-up.Generallyspeaking,wecansaythatcarburetorheatshouldneverbeusedfortakeoff,butthereisoneexception.ThisexceptionoccurswhenoperatingintemperaturessocoldthatapplicationofcarburetorheatproducesariseinRPM.Mostpilotswillneverfindthemselvesincircumstanceswhichrequireuseofcarburetorheatfortakeoffandclimb;thosewhoflycarburetedengineswillalmostcertainlyhaveoccasiontousecarburetorheatduringcruiseorletdown.Useofthefull-hotorfull-coldpositionisrecommended.Anintermediatesettingshouldonlybeselectediftheaircraftisequippedwithacarburetorairtemperature(CAT)gage.Engineoperatingtemperatureisanother itemthat isnotusu-allygivenenoughconsideration incoldweather.Weusuallyareverycautiousabouthighoiltemperaturewhichweknowisdetrimentaltogoodenginehealth,whilealowoiltemperatureiseasiertoaccept.ThedesiredoiltemperaturerangeforLycomingenginesisfrom165to220F.Iftheaircrafthasawinteriza-tionkit, it shouldbe installedwhenoperating inoutsideairtemperatures(OAT)thatarebelowthe40to45Frange.Ifnowinterizationkitissuppliedandtheengineisnotequippedwithathermostaticbypassvalve,itmaybenecessarytoimproviseameansofblockingoffaportionoftheairflowtotheoilcooler.Keepingtheoiltemperatureabovetheminimumrecommendedtemperature is a factor in engine longevity.Lowoperatingtemperaturesdonotvaporizethemoisturethatcollectsintheoilastheenginebreathesdampairfornormalcombustion.Whenminimumrecommendedoil temperaturesarenotmaintained,oilshouldbechangedmorefrequentlythanthenormallyrec-ommended50-hourchangecycle.Thisisnecessaryinordertoeliminatethemoisturethatcollectsandcontaminatestheoil.


And finally, power-off letdowns should be avoided. Thisis especially applicable to cold-weather operations whenshock-coolingofthecylinderheadsislikely.Itisrecommendedthatcylinderhead temperaturechangenotexceed50F.perminute.Planahead,reducepowergraduallyandmaintainsomepowerthroughoutthedescent.Alsokeepthefuel/airmixtureleanedoutduringthedescent.Ifanexhaustgastemperaturegageisinstalledwithanormallyaspiratedengine,keepitpeakedtoensurethegreatestpossibleengineheatfor thepowersettingselected;fora turbochargedinstallation, leantopeakduringdescentunlessotherwise specified in thePilotsOperatingHandbook,orunderconditionswherethelimitingturbineinlettemperaturewouldbeexceeded.Exposuretosnow,frostandcoldweatherwhileflyingrequirestheconsiderationofmanyfactors,bothairframeandenginerelated.Thisdiscussiondealswithissuesrelatingtotheengine.Whiletheremaybeotherissues,thoseitemswhichareaskedaboutmost frequentlyhavebeendiscussed.Safer flyingandlongerenginelifecouldresultfromcarefulconsiderationofthematerialaddressed.

ThefatalcrashofalighttwininwhichaflightinstructorandanapplicantforamultiengineratingwerekilledpromptedtheNTSBtoissueanurgentwarningtoallpilotssimulatinganengine-outconditiononmultiengineairplanes.TheBoards investigationrevealedthatsomeflightinstructorsdousethefuelselectororthemixturecontroltoshutdownanenginetotestamultiengineapplicant.Althoughthisisarecommendedprocedure,theurgentwarningwasaimedatflightinstructorswhowereusingthispro-cedureataltitudestoolowforcontinuedsafeflight.TheNTSBobservedthatuseofsuchproceduresattrafficpatternaltitudesmaynotpermit instructorsenoughtimetoovercomepossibleerrorsonthepartoftheapplicant.Therecommenda-tionbytheNTSBmeansthatallsimulatedengine-outoperationattheloweraltitudesshouldbeaccomplishedbyretardingthethrottle,andthisshouldbedoneslowlyandcarefullytoavoidenginedamageorfailure.Manyflightinstructorsdownthroughtheyearsusedthetech-niqueofabruptlycuttinganenginewithamultienginecan-didate to testhisemotional reactionand judgmentwith thisextremetechnique.Bigradialpistonengineswithshort,stubbycrankshafts could tolerate the abrupt technique.However,flat-opposedpistonengineswith their longcrankshaftsandattachedcounterweightscouldnotas readily take theabuseofsuddenlysnappingathrottleshut,particularlyat takeofforclimbpower.Useofthelattertechniquewouldtendtodetunecrankshaftcounterweightsandcouldpossiblyresult inanastyenginefailure.

Sinceitwascommontechniquebyflight instructorstotermi-natepowerabruptlytosimulateanenginepowerloss,wehadtoprotect theengine.Asaresult,wepublishedinourEngineOperatorsManualandinServiceBulletinNo.245,therecom-mendation that if thepowerwasabruptly terminated, itmustbeaccomplishedwiththemixturecontrol.Ofcourse,thiswasintended for the higher altitudeswhere a complete engineshut-downcouldbeconductedsafely.Thestudentwastoiden-tifythedeadenginebyretardingthatthrottletoabout12"MPtosimulatezerothrust,orsimilartohavingthepropfeathered.Atthatpoint,theinstructorcouldimmediatelyreturnthemixturetoanengine-operatingcondition,andpowerwouldbeavailableifneeded.Inourpublications,wethenexplainedthereasonforusingthemix-turetoabruptlyterminatepower.Byputtingthemixturecontrolinidlecutoffpositionwiththethrottleinanormalopenoroperatingposition,thepilotmerelycutoffthefuel,butallowedtheairtocon-tinuetofillthecylinderswithresultingnormalcompressionforcesthataresufficienttocushionthedecelerationoftheengineandpreventthedetuningofthecrankshaftcounterweights.However,anypracticeofsimulatedengine-outconditionatlowaltitudesshouldbebestaccomplishedbyaslowretardationofthethrottleinaccordancewiththeNTSBrecommendation.Thiscarefultechniquewillprotecttheengine,andatthesametime,provideforinstantpowerifitisneeded.

Although the smal ler four-cyl inder engines of thelow-compression,low-horsepowervarietydonotgenerallyuseacylinderhead temperaturegage, thehigherpowered,morecomplexpowerplantsrequireacylinderheadtemperaturegageinordertopreventunwittingabusebythepilot.If head temperatures are higher than normal during flight, it should not be ignored, because there is some reason for it. Itmaybecausedbyhotambienttemperatures,aleanfuelmeteringdeviceathigherthancruisepower,badbafflesorleakingcowling,ormalfunctioningof the ignitionsystem.Evenoldand tiredenginemountsthatallowtheenginetosagslightlymaycauseachangeintheairflowpatternandanabnormalincreaseinCHT.Itisalsopossiblethatamechanicalproblemmaybedevelopingintheengine.Whenhigherthannormalcylinderheadtemperaturesareshowingonthegage,thepilotshouldtakestepstobringthetemperaturesdowntothenormaloperatingrangeinordertokeeptheremainingflightsafe.Headtemperaturesmaybereducedby:1.Enrichingthemixture2.Adjustingcowlflaps3.Reducingpower4.Anycombinationoftheabove


Wesuggest that inorder tohelp themechanicdiagnose theproblem,thepilotorsomememberofthecrewshouldmakeawrittenrecordoftheengineinstrumentreadingsduringtheaboveflightconditionandpresentittothemaintenancepeople.Afirststepindiagnosingabnormalcylinderheadtemperatureswouldbeensuringthatthegagesareprovidingaccuratereadings.Iftheyare,themechaniccanthenproceedtocheckenginebafflesthatmayhavedeteriorated,properflowof thefuelmeteringdevice,andthenothermoretime-consumingchecksforignitionormechanicalmalfunction.

Thecylinderheadtemperaturegage(CHT)helpsthepilotpro-tecthisengineagainstthethreatofexcessiveheat.MostGeneralAviationaircraft taketheCHToff thehottestsinglecylinderofthefour-six-oreight-cylinderpowerplantsdeterminedbyextensiveflighttests.Optionalinstallationsofferreadingsfromallcylinders.InLycomingengines,allcylindersaredrilledtoaccommodateaCHTbayonet-typethermocouple.Someoperators in the fieldhavebeenusing a sparkpluggasket-type installation inorder toget cylinderhead tem-peraturereadings.LycomingEngineeringdoesnotcurrentlyapprove thismethodofdeterminingCHT.Notonly is themethod lessaccurate than the recommended thermocoupletype,butthetemperaturereadingsdiffernoticeablyfromtheapprovedinstallations.Minimumin-flightCHTshouldbe150F(65C),andmaximuminmostdirect-drivenormallyaspiratedLycomingengines is500F(260C).Someofourhigher-poweredmorecomplexengineshaveamaximumlimitof475F(245C).Althoughtheseareminimumandmaximumlimits,thepilotshouldoperatehisorherengineatmorereasonabletemperaturesinordertoachievetheexpectedoverhaullifeofthepowerplant.Inourmanyyearsofbuildingengines,theengineshavebenefitedduringcontinuousoperationbykeepingCHTbelow400Finordertoachievebestlifeandwearofthepowerplant.Ingeneral,itwouldbenormalduringall-yearoperations,inclimbandcruisetoseeheadtem-peraturesintherangeof350Fto435F.Ifanenginehasbayonetprobesinallcylinders,itisnotunusualtoseevariationsinCHTreadingsonfuel-injectedenginesof100Fbetweencylinders,andasmuchas150Fonengineswithfloat-typecarburetors.Withthelatter,animportantcauseofthevariationisthekindofdistributionoffuelandairtotheindividualcylinders.OtherinfluencesonCHTaresuchitemsascylinderbaffles,cowling,cowlingflaps,locationofengineaccessoriesand,ofcourse,manualcontroloffuelmixture.ItisveryimportantthattheCHTprobesbecheckedonaregularbasis.Whenthesebayonetprobesdeteriorate,theytendtogivereadingsthatarelessthantheactualtemperatureofthecylinderhead.Thiscanresultinoperationabovetherecommendedmax-imumtemperaturewithoutthepilotevenknowingit.

OperatorsfrequentlyaskaboutthedifferencebetweentheCHTandEGT(exhaustgastemperature)systems,andtheirmeaningtothepilotduringoperationoftheengineorengines.TheEGTprobeisinstalledinadifferentlocationfromtheCHT,oraboutfour inches fromthecylinderheaddown theexhaust stack.AlthoughtheEGThassometroubleshootingability, it ispri-marilyafuel-managementinstrument.Ontheotherhand,theCHTisanengineinstrumentdesignedtoprotectthepowerplantagainstitsenemy,excessiveheat.

Thepresent-daypistonengineinstrumentsusedinthetypicalgeneralaviationairplanearenotprecision laboratory instru-ments.Weexcludetheturbineandjet-poweredaircraftfromthisdiscussionandwillconsideronlypistonengines,recognizingthat themoreexpensivepressurizedtwin-enginemodelsmayalsobeexceptions.Nevertheless,thepurposeofthisbriefpresentationisapracticalapproachtointerpretingthereadingsofyourengineinstrumentsinaccomplishingasafeandefficientflight.If,forexample,youweretoobserveanirregularreadingofoneengineinstrument,itcallsforacross-checkonallotherinstruments,andnotrelyingononeinstrumentasabasisforadecisionaffectingflight.Sincetheengineisdependentonfuel,weconsiderthegasolinegageasarelatedengineinstrument.Ifpilotsaregoingtoattempttostretchtheirflightrangeclosetolimits,theyshouldbeawareoftheerrorsinthegagesvs.theactualusablefuel.Somemodernsingle-engineaircrafthavehadthegasgageshowseveralgallonsremaining,wheninreality, the tankwasempty.Othershaveindicatedaspecificnumberofgallonswhenfilled,butactuallythetankheldseveralgallonslessthanindicated.Therefore, inplanningforeachflight,rememberthatgeneralaviationengineinstrumentsarenotprecisionlaboratorytypes,socross-check,andgiveyourselfanextramarginforsafety.

Animportantpartoftheengine-startingprocedureistheprimingtechnique.Ofcourse,thePilotsOperatingHandbookwillspecifythestepsinstartingaspecificmodelengine.However,someofthepilothandbooksmaynotexplainwhycertainproceduresareusedinthestartingprocess.Primingcanbebestaccomplishedwithanengineprimingsystem,asopposedtouseofthethrottle.Theprimerpumpsextrafueldirectlyintothecylinderintakeportorinductionsystem.Somefloat-typeandpressurecarburetorsalsoprovideasupplementalsourceofpriming.Lycomingenginesofmorethan118HPhaveathrottlepumpwhichcanbeusedforprimingundermoderateambienttemperatureconditionswhileturningtheenginewiththestarter.


Pilotsshould,however,beadvisedthatexcessivethrottleprimingcancausefloodingofthecarburetorandairbox,andresult inafireintheinductionsystemorontheoutsidewherethefueldrainsoverboard.Iftheoperatorfloodstheenginebypumpingthethrottleandhasafire,itispossibletohandlesuchafireintheearlystagesbycontinuingtoturntheenginewiththestarter,therebysucking the fireback into theengine.Furthermore,ifthereisanyfireontheoutsideoftheengine,iftheenginestarts,thereisagoodchanceitwillblowouttheexternalfire.If there is floodingof theenginewithoutafire, theoperatorshouldopenthethrottlefullandclosethemixture;(seeOperatorsHandbookonmixture)turntheengineoverseveraltimeswiththestartertoclearit;thenbeginagainwithanormalstartroutine.MostLycoming fuel-injectedenginesaresimplyprimedbyturningthefuelboostpumpon,openingthemixturebrieflytofullrich,andcrackingthethrottle.Anypumpingofthethrottleisineffectiveuntiltheenginebeginstofire.FUEL CONTAMINATION Water (says the FAA) is the principal contamination of aviation fuel. For a safe flight, carefully drain fuel sumps at each preflight.

Asan enginemanufacturer,we are frequently asked abouttheproperuseof thefuelboostpumpwithourpowerplants.Althoughwecantpretend tobeanexperton thefuelboostpumpitself,wehavesomepositiverecommendationsconcerningitsusewithourengines.Whereaboostpumpisprovidedbytheairframemanufacturer,andtheairframePilotsOperatingHandbookhasalimitedtreatmentoftheuseofthefuelboostpump,perhaps thisdiscussioncanprovidethenecessaryfuelboostpumpinformationforthepilotinordertooperatehisorherengineassafelyaspossible.Itisnecessarytosupplytheenginewithasteady,uninterruptedflowoffuelforalloperatingconditions.Entrappedair,tempera-turechanges,pressuredrops,agitationinthefuellinesandotherfactorsaffectthereleaseofairandvaporfromthefuelsystem.Undersomecircumstanceswhereanengine-mountedfuelpumpisprovided,itmaynotbeabletopumpacontinuousfuelsupplyfreeofexcessivevapor.Aneffectivecontinuousfuelsupplyisprovidedbyuseofthefuelboostpump.Asageneralrecommendation,thefuelboostpumpshouldbeusedwithLycomingenginesinallconditionswherethereisanypossibilityofexcessivevaporformation,orwhenatemporarycessationoffuelflowwouldintroduceundesirablehazards.TheconditionsunderwhichLycomingrecommendsoperationofthefuelboostpumpareasfollows:1.Everytakeoff.2.ClimbaftertakeoffunlessPilotsOperatingHandbooksaysitisnotnecessary.

3.Whenswitchingfuelselectorsfromoneseparatefueltank toanother,thefuelboostpumpshouldbeoninthenew tankuntiltheoperatorisassuredtherewillbenointerruptionofthefuelflow.4.Everylandingapproach.5.Anytimethefuelpressureisfluctuating,andtheengineis affectedbythefluctuation.6.Hotweather,hotenginegroundoperationwherefuelvaporproblemscauseerraticengineoperation.7.SomeGeneralAviationaircraftrequiretheuseofthefuel boostpumpduringhigh-altitudeflight.Thiswillbespelled outinthePilotsOperatingHandbook.8.Iftheengine-mountedfuelpumpfails.Ifthefuelboostpumpisusedduringgroundoperation,dontfailtochecktheconditionoftheengine-mountedfuelpumpbeforetakeoffbyturningtheboostpumpoffbriefly,andthenbackonfortakeoff.Iftheengine-mountedpumphasfailed,itwouldbesafertoknowthatonthegroundratherthanintheairwhenthefuelboostpumpisturnedoff.Whenindoubt,dothesafestthingandusethefuelboostpumpwithLycomingengines.Dontbestingywiththeboostpump.Inmostcases,theylasttheoverhaullifeoftheengine,andarethenexchangedoroverhauledthemselves.ASAREMINDER,theairframePilotsOperatingHandbookistheauthorityifboostpumpinformationisspelledoutinit.

Suddencoolingisdetrimentaltothegoodhealthofthepistonaircraftengine.LycomingServiceInstruction1094Drecommendsamaximumtemperaturechangeof50Fperminutetoavoidshock-coolingofthecylinders.Operations that tend to induce rapid engine cooldown areoftenassociatedwithafastletdownandreturntothefieldafterdroppingparachutistsoraglidertow.ThereareoccasionswhenAirTrafficControlalsocallsforfastdescentsthatmayleadtosuddencooling.Theengineproblemsthatmaybeexpectedwhenpilotsconsis-tentlymakefastletdownswithlittleornopowerinclude:1.Excessivelywornringgroovesaccompaniedbybrokenrings.2.Crackedcylinderheads.3.Warpedexhaustvalves.4.Bentpushrods.5.Sparkplugfouling.Generallyspeaking,pilotsholdthekeytododgingtheseprob-lems.Theymust avoid fast letdownswith very lowpower(high-cruiseRPMandlowmanifoldpressure),alongwithrich


mixturesthatcontributetosuddencooling.Itisrecommendedthatpilotsmaintainatleast15"MPorhigher,andsettheRPMatthelowestcruiseposition.Thisshouldpreventringflutterandtheproblemsassociatedwithit.Letdownspeedshouldnotexceedhighcruisespeedorapproxi-mately1,000feetperminuteofdescent.Keepingdescentandairspeedwithin these limitswillhelp toprevent thesuddencooling thatmay result in cracked cylinder heads,warpedexhaustvalvesandbentpushrods.Themixturesettingalsohasaneffectonenginecooling.Toreducesparkplugfoulingandkeepthecylindercoolingwithintherecommended50per-minutelimit, themixtureshouldbeleftattheleansettingusedforcruiseandthenrichenedgradu-allyduringdescentfromaltitude.Theleanmixture,maintainingsomepowerandusingasensibleairspeedshouldachievethemostefficientenginetemperaturespossible.Theoperatingtechniquesrecommendedinthisarticleareworthconsiderationastheywillbeapositivesteptowardsavingdol-larsthatmightbespentonmaintenance.Whateverthecircum-stances,pilotsmustplantheirflightoperationssothatthepoten-tialdamagecausedbysuddenenginecoolingcanbeavoided.

Knowledgegainedfromtheexperienceofothersisusuallytheeasywaytolearn.Inthecaseofstickingvalvesthatmaydamageanengineorcauseittofail,itissurelybestiftheknowledgeisnotacquiredfirsthand.Theexperienceofothersisrelatedinthefollowingparagraphs.Oneof the regional servicemanagershereat theLycomingfactory indicated thathisexperienceover theyears includedworkingonengineswithstickingvalves.Hecommentedthattheenginewillalmostalwaysprovideawarningbyrunningveryroughatstart-up.As theenginewarmsup, itmay thensmoothoutafterafewsecondsandrunnormally,buttheini-tialroughnessisawarningthatpreventivemaintenanceactionisrequired.Justafewdaysafterthesecommentsweremade,aconversationwithanaircraftownerconfirmedthat theregionalmanagerscommentswererightontarget.Thisisthestorywhichtheaircraftownerrelated.Anaircrafthadbeenpurchasedrecently,andtheownerflewittoaltitudeinthevicinityofhishomeairporttosatisfyhimselfoftheaircraftcapabilitytoflyovermountainousterrainduringaplannedvacationtrip.Contentthattheaircraftandenginewerecapableofmeetinghisrequirements,thevacationtripwasundertaken.Allwentsmoothlyonthefirst300-milelegofthetripwhichendedwithaplannedovernightstop.When theenginewasstarted thenextday, itwasvery,veryrough,butsmoothedoutandrannormallyafterashorttime.Withtheenginerunningsmoothly,thevacationtripcontinuedtoits


destination.Theaircraftwasthentieddownandnotoperateduntilitwastimeforthereturntripaperiodofaboutoneweek.Astheenginewasstartedforthereturntrip,itagaingaveindica-tionsthatavalvewasmomentarilysticking...itranveryroughforseveralseconds,butthensmoothedout.Withtheenginerunningsmoothlyagain,thereturntripwasstarted.Afteronetotwohoursofflightataltitude,overmountainousterrain,theengineranveryroughagainforashortperiodoftime,andthensmoothedout.Thepilotdecidedtolandatthenearestairport.Examinationoftheenginerevealedaconsiderableamountofoilleakage.Thecauseavalvewhichhadstucksolidlyandcausedthepushrodtobend.Thisbendingrupturedthepushrodshroudtubeandallowedoiltoescape.Thisisaclassicexampleofthedamagethatstickingvalvescancause.The lesson tobe learned isquitesimple.Donotneglect thewarningsigns.Perhapstheexperiencerelatedherewillallowotherstorecognizearough-runningengineatstart-upasapos-sibleindicationofstickingvalves.Thenextstepistotakeimme-diateactiontopreventdamage.Although theremaybeanoccasionalexception, it isalmostalwaysanexhaustvalve thatsticks.Toprevent furthervalvestickingand toreduce thepossibilityofdamage,allexhaustvalveguidesshouldbecleanedofanycarbon,varnishorothercontaminationbuildup.This isaccomplishedbyreaming theguidestotheiroriginalsizeasspecifiedinLycomingPublicationSSP1776,TableofLimits.The latest revisionofLycomingServiceInstruction1425providesrecommendationstoreducethepossibilityofvalvesticking. Inparticular,Part IIIof theinstructiongivesaprocedureforreamingvalveguidesthatcanbeaccomplishedwithoutremovingtheenginefromtheaircraftorthecylindersfromtheengine.

Consideringthattheproperlytimedsequenceofvalveopeningandclosingisessentialtoefficientandreliableengineoperation.Anytimethosevalvesstickforanyreason,itisaseriousproblem.Therefore,thepurposeofthisarticleistoprovideourreaderswithsomeinsightintothisproblemalongwithmethodstohelpavoidit.Thespacebetweenthecontinuouslymovingvalvestemanditsstationaryvalveguideisextremelycritical.Notethattheamountofclearancecanbeaffectedbyhightemperatures,engineclean-linessandextendedperiodsofengine inactivity.Changes invalve-to-guideclearancecanoccurduringthecourseofengineoperation.Inotherwords,astickingorbrokenvalvemaynotbethefaultoftheengine.Itispossibletopromotevalvesticking,andthereareactionsthatcanbetakentoreduceoreliminatethepossibilityof thisphenomena.Theseactionswillaffectenginecooling,fuelmanagementandinternalenginecleanliness.Enginecleanlinessisaprimaryconsiderationthat isaffectedbymanymaintenanceandoperationalprocedures.Properfiltermaintenanceisonesuchitem.Theinductionairfilteristhefirst

lineofdefenseinkeepingdirtandabrasivesfromenteringtheengine.Topreventdirtfromenteringtheengine,thefiltermustformagoodsealwiththefilterholder,andtheinductionsystemshouldbefreeofairleaks.Theairfiltershouldbecleanedorchangedonaregularbasis.Inextremelydustyconditions,afilterchangecouldbenecessaryasfrequentlyaseveryfewhoursofoperation.Thesecond lineofdefenseagainstdirtandabrasives is thefull-flowoilfilterthatisstandardwithmostLycomingenginesnowbeingproduced.Olderenginesweremanufacturedwithapressurescreen,butmaybeconvertedtoafull-flowfilterformoreeffectivecleaningoftheoil.LycomingServicePublicationSSP-885-2providesinformationandinstructionsneededforthisconversion.Anothercontributortoavarietyofengineproblems,includingvalvesticking,isfrequentlongperiodsofinactivity.Anengineshouldbeflownregularlytostayintiptopcondition.Theoilinthesumpcollectsresiduefromcombustionsuchasmoisture,acidandleadsludge.Flyingtheaircraft tends toheat theoilenoughtovaporize themoistureandhelpeliminatesomeofthesecontaminants,butanengine that isnotflownwillcol-lectmoisture,acidsandgumswhichmaycontributetocorro-sionandtovalve-trainproblems.Inadditiontofrequentflight,thesecontaminantsarealsoeliminated from theenginebychanging theoil.LycomingServiceBulletinNo.480makesthese recommendations forenginesoperatingundernormal(non-dusty)conditions:

a.50-hourintervaloilchangeandfilterreplacementforallenginesusingafull-flowfiltrationsystem.b.25-hour intervaloilchangeandscreencleaningforallenginesemployingapressure-screensystem.c.Atotaloffourmonthsmaximumbetweenoilchangesforeitherofthesystemsdiscussedundera.andb.,eveniftheengineisnotflown.

Reportsfromaircraftownerscontinuetoindicatethattrouble-freeoperationthroughTBOismostoftenobtainedwithenginessubjected to frequentoilchange intervals.Absurdas itmayseem,anenginewhichdoesnotflyregularlyshouldhavetheoilchangedatmorefrequentflighttimeintervalsthanonethatdoesflyregularly.Preventingabuildupofcontaminants is justas importantaseliminatingthosethatdoform.Avoidinglongperiodsofgroundoperationisavitalstepsincemoisturecanenterthebreather,butwillnotvaporizewhentheoilisnotheatedtonormaloper-atingtemperatures.Groundrunningalsoinvolvesaslightlyrichmixturewhichcontributestotheformationofleadsludgeintheoil.Duringflight, thedepositof leadsludgeintheoilcanbeminimizedbyproperleaning.Althoughsomeexcessfuelisrequiredforenginecoolingduringhigh-poweroperation,properleaningatcruise-powersettingswillpromotecompleteburningofthefueland,therefore,aminimumofleadsludgedepositedintheoil.Thisisimportantsinceleadsludgeisnotfilteredout,butisremovedbychangingtheoil.Theairframemanufacturersrecommendationsandlimitationsforleaningshouldbeobserved,butitmaybebeneficialtobeaware


thatwhenpermittedbythePilotsOperatingHandbook,leaningtopeakEGTatcruise-powersettingswillproducecompleteburningofthefuel/airmixtureforbesteconomyandreductionofcombustion-relatedcontaminants.Having touchedonfuelmanagementandmaintenance itemsrequired tokeepanengineclean internally, the final factoraffectingpotentialvalvestickingisengineoperatingtempera-ture.Someoperatingproceduresalreadydiscussedalsohaveaneffectonenginetemperature.Prolongedenginegroundrun-upathigh-powersettings,forexample,cancauseengineoverheatingorhotspotssincecoolingairflowisnotalwaysadequatewhentheaircraftisstationary.Sinceproperengineoperatingtemperaturesfallwithinamin-imumandmaximumrange,itisimportanttoconsiderallaspects.Itmustbeemphasizedthatbaffles designed to direct cooling air over the cylinders must be maintained in good condition. Theyplayanextremelyimportantrole.Ifthesebafflesdeteriorateorareinstalledsothatcoolingairisnotadequatelycontainedanddirected,hotspotswhichpromotealeadorcarbonbuildupmayoccur.Duringhotweatherinparticular,thosebafflesorductsthatdirectcoolingairthroughtheoilcoolermustalsobemaintainedingoodcondition.Thepilot,aswellasmaintenancepersonnel,willplayanimpor-tantroleinensuringthatengineoperatingtemperaturesdonotpromotevalvesticking.Asmentionedearlier,groundrunningfarinexcessofthetimenecessaryforenginewarm-upshouldbeavoided.Alsotobeconsiderediscontinuousoperationatverylowaircraftspeedsthatmaynotgeneratethemostefficientflowofcoolingairovertheengine.Thislackofeffectivecoolingairmaycausesomeareasoftheenginetobeexcessivelyhot,andthereforehaveaneffectonanycontaminantsthatareintheoil.Theformationofdepositsispromoted,withtheexhaustvalveguidearea themost likely tobeaffected.Theresultof thesedepositsmaybeastuckorstickingvalve.Theotherendofthespectrumcontrollablebythepilotisexces-sivelyrapidcooldownofanengine thathasbeenrunningatnormaloperating temperatures.Lycomingenginesaremadewithvariousmetalsthatexpandandcontractatdifferentrateswhenexposedtoheatorcold.Itispoortechniquetochopthepowerfromcruiseorhigherpowersettingstoidleandthenstartarapidletdownwhichdevelopsexcessivecoolingairflowovertheengine.It isalwaysbesttoreducepowerinincrementssothatenginetemperaturechangeswilloccurgradually.Itisalsobeneficialtocontinuetheenginecoolingprocessafterlandingbyensuringthatseveralminutesofengineoperationat800to1200RPMareallowedbeforeshutdown.Atlargeairports,thisisusuallyaccomplishedby the timetaxi to theparkingareaiscompleted.Atairportswhereclearingtherunwayputs theaircraftintheparkingarea,ashortperiodofadditionaloperationinthe800to1200RPMrangepriortoengineshutdownwillallowtemperaturestostabilize.Alogicalquestionafterthislongseriesofthingstodoandthingsnot todomightbethis,Is thereanywaytotell ifavalveisstickingbeforeseriousdamageoccurs?Therearesometimeswarningsignsthatshouldbeinvestigated.Althoughtheremaybeothercauses,anintermittenthesitationormissintheengine

maybeanindicationthatcarbonorothersimilarcontaminantshavebuiltup inside thevalveguidecausing thevalvestemtodraginsteadofmovingfreely.Thesecontaminantsshouldberemovedbyreamingtheguideto thesizespecifiedin theLycomingTableofLimits(SSP1776).TheproceduretobeusedwhenreamingtoremovevalveguidedepositbuildupisfoundinLycomingServiceInstruction1425.KnownastheoldropetricktomanyA&Pmechanics,thisvalveguidereamingpro-cedurerestoresvalvestemtoguiderunningclearanceandcanbeaccomplishedwithoutremovingtheenginefromtheaircraft.Tosummarize,procedures toreducevalvestickingwillalsoreducetheprobabilityofadditionalenginedamagewhichmaycauselossofpowerandtheneedforcostlyrepairs.Theseproce-duresmaybereducedtorelativelysimpleterms:Themaintenanceandoperationalproceduresnecessarytoavoidstickingvalvesarethosethatkeeptheenginecleaninternallyandwhichcauseittorunwithinproperoperatingtemperatureranges.TheitemsdiscussedaboveshouldserveasaguideforA&Pmechanicsandforpilots.

Thesearesomeof themorecommonquestionsaskedatourservicehanger:QUESTION: Doyour new, rebuilt or overhauled enginesrequireabreak-inperiodthatconsistsofcruiseatlow-powersettings?ANSWER: Definitelynot.Flythemasyouwouldahigh-timeengine. In fact, so-calledslow flyingmayhaveharmfuleffects.Theringsmaynotseatproperlyresultinginhigherthannormaloilconsumption.QUESTION: Atwhatrateofoilconsumptiondoescontinuedoperationoftheenginebecomeahazard?ANSWER: Generally speaking,when theoil consumptionreachesonequartperhour,correctiveactionshouldbetaken.However,maximumpermissibleforeachparticularengineislistedintheengineoperatorsmanual.QUESTION: Whatarethedangersofoperatinganenginewithhighoilconsumption?ANSWER: Whenexcessiveamountsofoilgetpasttherings,thereisdangeroftheringstickingorbreakingwithadramaticrise inoil consumption.Thenoil soakedcarbon formsatafastrate.Atthesametime,thepresenceofoilinthecombus-tionchamberhastheeffectofloweringtheoctaneratingofthefuel.Operatingtemperaturesgoup.Wehavenowsetupconditionsinvitingdetonationand/orpreignition.QUESTION: IfIcantgetaviationfuel,mayIuseautomotivefuelifoctaneratingisequalorhigher?ANSWER: No.Asanenginemanufacturer,even theuseofautomotivefuelwhereanSTChasbeenissuedisconsideredriskyandisnotrecommended.Thereare4or5goodreasons


andallareimportant.Theycanbesummedupinthreewordspotentialenginefailure.QUESTION: What is themostcommoncauseofprematureenginewear?ANSWER: Dirt in the air entering the engine through thecarburetororinjectorduetoworn-outairfilter,torninductionhosesorbrokenairboxes,andthenbeingcarriedthroughtheenginebytheoil.QUESTION: Does thespacerbetween thepropellerand theengineserveanypurposeotherthanstreamliningthenacelle?ANSWER: Yes.Inmanycases,movingthepropellerforward,which increases theclearancebetweenpropellerandcowl,increasespropellerefficiencyandreducesnacellevibration.QUESTION: In some cases,wenote aminor discrepancybetweentheengineoperatorsmanualandtheairplanePilotsOperatingHandbook.Whichoneshouldbefollowed?ANSWER: TheairframePilotsOperatingHandbook.Forvariousreasons,aftertheengineisinstalledintheairframe,operationaltechniquesmaybealteredorcertainrestrictionsmaybeplacedontheengine.AsimpleexamplewouldbeaplacardrestrictingcontinuousoperationinacertainRPMrange.QUESTION: I fly an aircraft equippedwith a fixed-pitchpropeller.Duringcruise,ImtoldtokeepincreasingtheRPMasmycruisingaltitudeisincreased.SinceIflyprettyhigh,inordertohold65%power,IfindtheRPMismostlyat2550to2600.WontthishighRPMreducetheenginelife?ANSWER: No.ThehigherRPMwontharm theengineorreduceservicelife.Remember,youareincreasingtheRPMonly tohold the samepoweryouhadata loweraltitudeatsay,2350RPM.QUESTION: Is there really any difference betweengoodautomotiveoilandaviationoil?ANSWER: Yes, indeed there is!Donteveruseautomotiveoil inyouraircraft engine.Theseoils arenowblended forusewithunleadedfuels,and theadditives inautooilcauseproblemsinanaircraftengine thatoperatesatmuchhighertemperatures than theautomobileengine.Wehaveencoun-teredengineswithholesburnedinpistonsduetotheuseofautomotiveoilsthathaveanashdepositcausingpreignition.Itseemsawfullyhardtoconvincepeoplewhohavehadgreatsuccesswiththeoilusedintheircarthatitmaynotbeusedintheiraircraftengine.NOTE Since we have had several questions on fuels and oils, it might be well to mention that we cant think of a quicker way to void your engine warranty than by using anything other than the recommended and FAA-approved aviation fuels and oils.QUESTION: What are some commoncauses of excessiveoil consumptionother than theburningofoil due tohighenginetime?ANSWER: Buildingupofcrankcasepressureduetoblow-bycausedbyringwearmayresult inoilbeingblownoutof thebreather.Thesamethingcanresultfrombrokenpistonrings.Oil

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