(i)
Advancepowerlever to position previously marked. Compare Ng with previouslyrecorded figure. If Ng has changed from previous value,ensureair bleed link (Figure 501) is locked hard againstpneumaticmaximum stop. Ng change up to 100 rpm is acceptable, but if change is greater than 100 rpm replacepropeller governor.
(j)
Shutdownengine, disconnect interconnectrod (Figure 501) at air bleed link. Secure link to minimumstop.
(k)
Restartengine. With propeller control lever set in fine pitch, advance power control lever to obtain constant speed. Check that Np governs at 95% + 1%of maximum speed set in step 6. Adjust pneumatic minimumeccentricadjuster(Figure 501) to meet this requirement.
(I)
Shutdown engine and reconnect air bleed link to interconnect rod.
(m)Restart engine and check reverse power setting.
Feathering GovernorMaximum Adjuster Speed Adjustment PneumaticMaximum Stop
Speed Adjustment (NotFor Field Adjustment)
Air Bleed Link
(ResetArm)
PneumaticMinimum EccentricAdjustment
PropellerGovernor
Figure 501
4. Removalof Overspeed Governor
(a)
Removeenginecowling.
(b)
Disconnectelectricalleads from overspeed governor.
(c)
Removenuts and washers securing overspeed governor to reduction gear box. Withdraw assemblyfrom mounting studs and discard mounting gasket.
(d)
Examine overspeed governor drivefor damage and wear; replaceif necessary.
5. Installationof Overspeed Governor
(a)
Install new mounting gasketover studs.
(b)
Installoverspeed governor on mounting pad. Ensure drive shaft is properly engaged,secure with washers and self-locking nuts, and torque to 125-170 inch-pounds.
(c)
Connectelectricalleads to overspeed governor.
(d)
Checkoverspeed governor operation and autofeather system, if installed.
(e)
Reinstallenginecowling.
EFFECTIVITY:
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PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL
A. Controlling (continued)
6. OverspeedGovernorOperationalChecks
Checkoverspeedgovernoroperationas follows:
(a)
Startengineand allowengineinstrumentsto stabilize.
(b)
Set powerleversfor 1600rpmpropellerspeed.
(c)
Set propellercontrolto full forward.
(d)
Pushup hydraulictoppinggovernorswitchesandobservedropin propellerrpm. Thedrop mustbe approximately75 rpm.
(e)
Releaseswitchesand proprpmmustincreaseto originalrpm.
7. AutofeatherSystem
Thissystemprovidesa quickmeansof automaticallyfeatheringa failed enginepropellerwhenthe systemis ON andthe followingfourconditionsexist:
(a)
Enginetorqueis below675 ± 65foot-pounds.
(b)
EngineP3pressureis below17± 1.0psi.
(c)
Thetorquedifferentialbetweenbothenginesisgreaterthan 500 foot-pounds.
(d)
Bothpowerleversare positionedabove80%N1.
NOTE: Whenan autofeatherconditionoccurs,powerleversno longerdeterminecondition, andpullingbackon leversdoesnotcauselossof autofeather.
Returnof anyof the otherthree conditionscancelsautofeatherand re-establishesleversasa
requirementfor autofeather.
NOTE: If an autofeatheredconditiontakesplace,all powerfrom armingcircuitto opposite engineis removed.Twoautofeatherconditionscannotoccursimultaneously.
8. AutofeatherSystemOperation
Thesystemiscontrolledby an ARM-OFFswitchand a separatetestswitchlocatedon the lower leftinstrumentpanel,alongwith its circuitbreakerlocatedon the non-essentialbusspanel. The systemis designedfor activationafterenginestartup,andremainsin operationuntilengine shutdown. Duringthis period,it will eitherbe in a self-checkor monitormode,a testmodeupon pilotcommand,or a controlmodewithself monitoringwhenpowerleversaresetabove80%N1.
Thepowerelementsof the systemareredundanttransistorswitchesanddrivingdumpsolenoid valveswhichcontrolgovernoroil pressureateachengine. Therearetwo circuits,onefor each engine,with exclusivelockoutin the eventof a dumpcommandin eithercontrolcircuit.Input informationto the circuitsconsistsoftorquemeterrampvoltages,P3 pressureswitches,(onefor eachengine)anda powerlever80%settingswitch.
Outputinformationconsistsof two systemarm lights,whichcomeon onlywhenthe 80%power leverswitchesareclosedandthe enginetorquehasexceeded675+ 65 foot-pounds.A single failurelightwill go on anytimea failureoccurs,regardlessoffailurelocation.
Inadditionto automaticoperation,the pilothasthe testfunctionavailablein the formof a test switch,whichallowstestingthe systemwhileenginesareat idle powersetting.
EFFECTIVITY:
PAGE
61-20-00
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PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCEMANUAL
A. Controlling (continued) 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：夏延飞机维护手册 Cheyenne IIIA PA-42-720 AMM 2(130)
