Textron Cessna - Page 31

McCAULEYPROPELLERSYSTEMS
CONSTANTSPEEDCOMPOSITEOWNER/OPERATOR
INFORMATIONMANUAL
B.OnceRPMcontrolandpowersettingsareestablishedforaightattitude(cruise)andthentheattitude
isaltered(toclimb)withoutchangeofRPMandpowersettings,theengineRPMmaychangeslightly.
(1)PossibleCauses:
(a)Thiseffectiscommonlyknownas"creeping"oftheRPMsetting.Itisanaturalresultand
comesaboutinthefollowingmanner.WhenRPMandpowersettingsareestablished,the
governorcontrolvalvewillbeopenedanamounttoprovideapressurewhichbalances
thepropellerrotationalforcesandspringload,andanoilowwhichisdeterminedbythe
leakagethroughthepropellerpitchcontrolbearingatthatgivenpressure.Thiswillmaintain
thebladeanglesuchthatsetpowermaybeabsorbedatthedesiredRPM.
(b)Iftheattitudeoftheaircraftisalteredandtheairspeedchanges,thebladeanglewillchange
toabsorbthepoweratthisairspeed.Thischangeinbladeanglewillcausetheforces
tovaryandconsequentlywillchangethecontrolpressureandthepropellerpitchcontrol
bearingleakagerate.
(c)SincethegovernorhadbeenadjustedbytheRPMcontrolfortherstsetofconditions,
theeffectwillbetochangetheeffectiveequilibriumspeedofthepropellerwithnochange
ingovernorsetting.Theamountofchangevarieswithenginetransferbearingclearance.
(d)ThisRPMchangeisgenerallyanegligibleamountandisnotcauseforconcernsinceitis
anormalreactionofthecontrolsystem.
(e)Control-frictionlockintheaircraftisfaulty.
(2)CorrectiveAction:
(a)IfitisdesiredthattheoriginalRPMsettingbemaintainedinthenewightattitude,itmay
benecessarytoalterthepropellercontrolleverasrequiredaftertheaircraftistrimmedout.
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Refertotheaircraftmaintenancemanualformaintenanceinformationaffectingthe
propellercontrolfrictionlock.
4.ImproperPropellerStaticRPM
A.IncorrectpropellerRPMatagivenpowerandstaticRPMsetting.
(1)PossibleCause:
(a)IfmaximumstaticRPMisincorrect,theproblemcannormallybeattributedtoeither
incorrectlowbladeangleorinsufcientenginehorsepower.However,ifthemaximum
in-ightRPMisincorrect,thenanadjustmentofthegovernormaybenecessary.
NOTE:Onstaticruns,thepropellershouldpreventtheengineRPMfromgoingtored
line.Thisisdonetopreventoverspeedingandisadesigncharacteristicofthe
propeller.However,itshouldbewithin100RPMofredline.
(2)CorrectiveAction:
(a)OneareathatisoftenatfaultforindicatedRPMproblemsisthetachometer.Aviation
tachometerscanbeinaccurate,sobegintroubleshootingbyverifyingtheaccuracyofthe
tachometer.
(b)Verifythepropellerlowbladeanglesarecorrect.Thisismosteffectivelyaccomplishedat
aMcCauleyauthorizedpropellerrepairfacility.Thisisdonebymeasuringthebladeangle
atthereferencestation(generallythe30inch(762mm)station)andcomparingtheangles
tothoselistedineitherthetypecerticateoftheairframemanufacturerortheSTCunder
whichthepropellerwasinstalled.Iftheanglesarecorrect,thentheengineisnotproducing
theproperhorsepowerneededtomaketheratedstaticRPM.
(c)Begintroubleshootingtheengine.
5.ImproperPropellerMaximumRPMinFlight
A.IncorrectpropellerRPMwithmaximumRPMselectedinight.
(1)PossibleCause:
(a)Inaccuratetachometerreading.
(b)Linkageisoutofrig.
(c)Governorstopscrewrequiresadjustment.
(2)CorrectiveAction:
(a)Repairorreplacethetachometer.
(b)Governorstopscrewrequiresadjustment.
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©McCauleyPropellerSystemsJan9/2017