Download - B2-13h Instruments Gyroscopic SR
-
7/25/2019 B2-13h Instruments Gyroscopic SR
1/104
StudentResource
SubjectB2-13h
InstrumentsGyroscopic
Copyright 2008 Aviation Australia
Allrightsreserved.Nopartofthisdocumentmaybereproduced,transferred,sold,orotherwisedisposedof,withoutthewrittenpermissionofAviationAustralia.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
2/104
Thispageintentionallyleftblank
-
7/25/2019 B2-13h Instruments Gyroscopic SR
3/104
Part 66 Su j
b ec tAA Form TO-19
IssueBJanuary2008 Revision3 B2-13h-i
B2-13h Instruments Gyroscopic
CONTENTS
Topic
Definitions ii
Studyresources iii
Introduction v
Gyroscopes 13.8.2.1
ArtificialHorizons 13.8.2.2.1
SlipIndicators 13.8.2.2.2
DirectionalGyros 13.8.2.2.3
-
7/25/2019 B2-13h Instruments Gyroscopic SR
4/104
Part 66 Su
bjectAA Form TO-19
IssueBJanuary2008 Revision3 B2-13h-ii
B2-13h Instruments Gyroscopic
Tosetforthinwords;declare.
DEFINITIONS
Define
Todescribethenatureorbasicqualitiesof.
Tostatetheprecisemeaningof(awordorsenseofaword).
State
Specifyinwordsorwriting.
Identify
Toestablishtheidentityof.
List
Itemise.
Describe
Representinwordsenablinghearerorreadertoformanideaofanobjectorprocess.
Totellthefacts,details,orparticularsofsomethingverballyorinwriting.
Explain
Makeknownindetail.
Offerreasonforcauseandeffect.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
5/104
Part 66 Su
bjectAA Form TO-19
IssueBJanuary2008 Revision3 B2-13h-iii
B2-13h Instruments Gyroscopic
STUDY RESOURCES
E.H.J.Pallett,AircraftInstruments&IntegratedSystems,Chapter4
JeppesenAircraftInstrumentsandAvionicspp2941
AvionicsFundamentals,IAPInc.Chapter5
B2-13hStudentHandout
-
7/25/2019 B2-13h Instruments Gyroscopic SR
6/104
Part 66 Su
bjectAA Form TO-19
IssueBJanuary2008 Revision3 B2-13h-iv
B2-13h Instruments Gyroscopic
This page intentionally left blank
-
7/25/2019 B2-13h Instruments Gyroscopic SR
7/104
Part 66 Su
bjectAA Form TO-19
IssueBJanuary2008 Revision3 B2-13h-v
B2-13h Instruments Gyroscopic
INTRODUCTION
ThepurposeofthissubjectistoallowyoutogainknowledgeofAircraftSystems,Instruments
Gyroscopic.Oncompletionofthefollowingtopicsyouwillbeableto:
Topic 13 8 2 1 Gyroscopic Terminology and Characteristics
DefineGyroscopicrelatedterms.
Explainthefollowing:
Earthrateandcalculateitforvariouspositionsontheearthinrespecttoapparentprecession
Rigidityandlistthefactorswhichaffectit
2and3gimballedgyroscopelayouts Gimballockcondition;
methodsofavoidingand
rectifyingagyrointhiscondition
Realdriftandapparentdriftandlistthefactorswhichaffectthem
Free,tied,earthandrategyros.
Describegyroscopicprecessionanddeterminethedirectionofprecessionresultingfromanappliedforce.
Identifythefollowinggyroscopicinstrumentsystems,statetheirpurposeandexplaintheiroperation:
ArtificialHorizons
SlipIndicators
DirectionalGyros
Describeprecautionsinvolvedwithgyroscopicinstruments/components.
13 8 2 2 1 Gyroscopic Instrument Systems: Artificial Horizons
Identifythefollowinggyroscopicinstrumentsystem,statetheirpurposeandexplaintheiroperation:
ArtificialHorizons;
13 8 2 2 2 Gyroscopic Instrument Systems: Slip Indicators
Identifythefollowinggyroscopicinstrumentsystem,statetheirpurposeandexplaintheiroperation:
SlipIndicators(Turn&BankIndicators)and
13 8 2 2 3 Gyroscopic Instrument Systems: Directional Gyros
Identifythefollowinggyroscopicinstrumentsystem,statetheirpurposeandexplaintheiroperation:
DirectionalGyros.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
8/104
Part 66 SubjectAA Form TO-19
B2-13h-vi
B2-13h Instruments Gyroscopic
IssueBJanuary2008 Revision3
Thispageintentionallyleftblank
-
7/25/2019 B2-13h Instruments Gyroscopic SR
9/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page1of56
B2-13h Instruments Gyroscopic
TOPIC 13.8.2.1: GYROSCOPES
Newtons 1st Law of Motion
Inertia
Anobjectinmotionwillremaininmotionandanobjectatrestwillremainatrestunlessactedonbyanunbalanced force.Thismeansthatif therewerenofriction,egspace,youcouldthrow/pushsomethinganditwillcontinueatthatsamespeedforevermore.Inrealityintheatmosphereoftheearthwehaveplenty offrictionfromairandgravitywhichprovides theadditionalforcetoopposetheinitialmotionimpartedbyyou.Buttheconceptisthatamovingmasswillcontinuetomoveinthesamedirectionunlesssomeotherforceactsuponit.
Whenarotorismadetospinathighspeedthedevicebecomesagyroscopepossessingtwoimportantfundamentalproperties:
Gyroscopic Rigidity or Gyroscopic Inertia:
causedbytheinertiaofthemass,keepingtheaxisrigidorpointinginthesamedirection.
Gyroscopic Precession:
describestheapplicationofaforcetothegyroandtheeffectoftheangulardisplacement.
Boththesepropertiesdependontheprincipleofconservationofangularmomentum,whichmeansthattheangularmomentumofabodyaboutagivenpointremainsconstantunlesssomeforceisappliedtochangeit.Angularmomentumistheproductofthemomentofinertia(I)andangularvelocity(w) ofa bodyreferredtoagivenpointthecentreofgravityin thecaseofagyroscope.
Theseratherintriguingpropertiescanbeexhibitedbyanysysteminwhicharotatingmassis
involved.Althoughitwasleftformantodevelopgyroscopesandassociateddevices,itistruetosaythatgyroscopicpropertiesareasoldastheearthitself:ittoorotatesathighspeedand
-
7/25/2019 B2-13h Instruments Gyroscopic SR
10/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page2of56
B2-13h Instruments Gyroscopic
Sopossessesrigidity,andalthoughithasnogimbalsystemorframeonwhichexternalforcescanact,itcan,anddoes,precess.Thereare,however,manymechanicalexamplesarounduseverydayandoneofthem,thebicycle,affordsaverysimplemeansofdemonstration.Ifweliftthefrontwheelofftheground,spinitathighspeed,andthenturnthe
handlebars,wefeelrigidityresistingusandwefeelprecessiontryingtotwistthehandlebarsoutofourgrasp.Theflywheelofamotor-carengineisanotherexample.Itsspinaxisisinthedirectionofmotionofthecar,butwhenturningacorneritsrigidityresiststheturningforcessetup,andasthisresistancealwaysresultsinprecession,thereisatendencyforthefrontofthecartomoveupordowndependingonthedirectionoftheturn.Otherfamiliarexamplesareaircraftpropellers,compressorandturbineassembliesofjetengines;gyroscopicpropertiesareexhibitedbyallofthem.
Elements of the Gyroscope
Therotorisaperfectlybalancedmass,mountedonacentralshaft.
Gyro Rotor Construction
Thegyrowheelorrotorunitmustbeperfectlysymmetricalandcircularaboutthespinaxis.Anyothershapewouldcausean imbalanceduringrotation.Togainhighermomentumandthereforestability,theweightisnormallyconcentratedontherim.Toomuchweightcausesexcessivebearingfrictionandconsequentlydrift,soa compromisemustbemadebetweenmomentumandfriction.Becauseinertiadependsuponthesquareoftheradius,therotorsaremadeaslargeaspossiblewiththegreatestmassconcentratedattherim.
Gyroscopic Balance
Thegyroscopemustbeperfectlybalancedtoreducethevibrationfeltduringthehighspeedsatwhichtheyarerotated.Thereforetheyarebothstatically anddynamically balanced.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
11/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page3of56
B2-13h Instruments Gyroscopic
Static Balance: tobestaticallybalanced,thecentreofgravitymustbeactinguponthespinaxis.
Dynamic Balance: to be dynamically balanced, the plane of spin must be acting at rightanglestotheaxisofspin.
Constructionoftherotorwilldirectlyaffecttherigidityofthegyro.Theheaviertherotorisandthecloser totheoutsiderim that theweightcanbedistributedwillcontributetothegyrosrigidity.
Weaddaframewithbearingsandwehavecreatedthefirstaxisofspin.Thisframewillsoonbecomeourinnergimbalbutuntoitispivoteditselfweonlyhaveasingleaxisofspin.
Gyroscopic Rigidity or Gyroscopic Inertia:causedbytheinertiaofthemass,keepingtheaxisrigidorpointinginthesamedirection.
Gyroscopic Precession:describestheapplicationofaforcetothegyroandtheeffectoftheangulardisplacement.
Boththesepropertiesdependontheprincipleofconservationofangularmomentum,whichmeansthattheangularmomentumofabodyaboutagivenpointremainsconstantunlesssomeforceisappliedtochangeit.Angularmomentumistheproductofthemomentofinertia(I)andangularvelocity(w) ofa bodyreferredtoagivenpointthecentreofgravityin thecaseofagyroscope.
Theseratherintriguingpropertiescanbeexhibitedbyanysysteminwhicharotatingmassisinvolved.Althoughitwasleftformantodevelopgyroscopesandassociateddevices,itistruetosaythatgyroscopicpropertiesareasoldastheearthitself:Ittoorotatesathighspeedandsopossessesrigidity,andalthoughithasnogimbalsystemorframeonwhichexternalforcescanact,itcan,anddoes,precess.Thereare,however,manymechanicalexamplesarounduseverydayandoneofthem,thebicycle,affordsaverysimplemeansofdemonstration.Ifweliftthefrontwheelofftheground,spinitathighspeed,andthenturnthehandlebars,wefeelrigidityresistingusandwefeelprecessiontryingtotwistthehandlebarsoutofourgrasp.The flywheel ofamotor-car engine isanother example. Its spinaxis is inthe direction ofmotionofthecar,butwhenturningacorneritsrigidityresiststheturningforcessetup,andasthisresistancealwaysresultsinprecession,thereisatendencyforthefrontofthecartomoveupordowndependingonthedirectionoftheturn.Otherfamiliarexamplesareaircraftpropellers, compressor and turbine assemblies of jet engines; gyroscopic properties areexhibitedbyallofthem.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
12/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page4of56
B2-13h Instruments Gyroscopic
Asamechanicaldeviceagyroscopemaybedefinedasasystemcontainingaheavymetal
wheel,orrotor,universallymountedsothatithasthreedegreesoffreedom:
Spinningfreedomaboutanaxisperpendicularthroughitscentre(axisofspinXX 1){thismeansthelinefromXtoX1}
Tiltingfreedomaboutahorizontalaxisatrightanglestothespinaxis(axisoftiltYY1)
Veeringfreedomaboutaverticalaxisperpendiculartoboththespinandtiltaxes(axisofveerZZ1).
Axes of Freedom
Engineershaveusedmanyandvariouswaysofdescribingthemountingandaxisreferencesofthegyroscope.Athree frame gyro wassaidtohave three degrees of freedom whichwere
namely: spinningfreedom,whichenabledagyroscopesrotortospin.
tilting freedom, where the gyro case or inner gimbal was free to rotate about thehorizontalplane,atrightanglestothespinaxis.
veeringfreedom,wheretheoutergimbalwasfreetorotateabouttheverticalplane,whichisperpendiculartoboththespinandtiltaxes.
Theoutergimbalissupportedintheframeorcaseofthegyrosystem.Themoderntechnicalterminologyusedtoexpressthedegreesoffreedomofgyroscopestendstowardsacceptingas fact, that a gyromust spin toshow the gyroscopic properties.Therefore, a two framegyroscope has only one degree of freedom, while the three frame gyroscope has two
degrees of freedom.The three degrees of freedom are obtained by mounting the rotor in two concentricallypivoted rings, called inner and outer gimbal rings. The whole assembly is known as the
-
7/25/2019 B2-13h Instruments Gyroscopic SR
13/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page5of56
B2-13h Instruments Gyroscopic
gimbalsystemofafreeorspacegyroscope.Thegimbalsystemismountedinaframe,sothatinitsnormaloperatingposition,alltheaxesaremutuallyatrightanglestooneanotherandintersectatthecentreofgravityoftherotor.
Thegyromustbe universallymountedor ingimbalssoastomaintainthetwodegreesoffreedomrequired,thatisverticalandhorizontal(inthisexplanationthespinaxisof freedomisignoredalthoughthetextreferstotwodegreesoffreedom,itmeansfullfreedomofspin,tilt&veer).Theconstructionofthegyrodeterminestheshapeandformofthegimbalswhichinturndependsonhowthegyrowillbeusedandinwhichplaneitwillberequiredtosensemovement.
Gimbalspermitthegyroframe(oranaircraft)tomovearoundthegyrowhileitmaintainsitsoriginalattitudeanddirectionofspinaxis.
Planeofspindoesnotrequireagimbalasthisplaneissimplythefreedomoftherotortospinonitsaxis.Agyrocannotdetectmovementaboutitsplaneofspin,egaDGcannotdetectpitchandanAHcannotdetectyaw.
Eachothergyroaxisrequiresagimbaltoprovideitwithfreedom.
Only1gimbalonlypermitsfreedominonly1axis(inadditiontoplaneofrotationexplainedabove).Asecondgimbalisrequiredtoprovidefreedominbothaxissoftiltandveer.
Wecanlimitthegimbals toouradvantage inmeasuring things,ega rategyroonlyhas1
gimbal,butthatwillbecoveredindepthlater.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
14/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page6of56
B2-13h Instruments Gyroscopic
Gyroscopic Inertia or Rigidity
Thepropertyofrigidityofthegyroscopeisitsabilitytoresistanyforcewhichtendstochange
theplaneof rotationof its rotor. Thismeansthat ifa forceis applied totry andmove thegyroscope to another position the rotors axis of spin will try and remain in the constantdirection inspace. This property is the result of its high angular velocity, and the kineticenergypossessedintherotor.Thegyroscopicinertiaorrigiditycanbeincreasedby:
increasingthemassoftherotor
increasingtherotorspeed
concentratingmoremassneartherimoftherotor.Thisiscalledincreasingtheradiusofgyration.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
15/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page7of56
B2-13h Instruments Gyroscopic
Precession.Theangularchangeindirectionoftheplaneofrotationundertheinfluenceofanappliedforce.Thechangeindirectiontakesplace,notinlinewiththeappliedforce,butalwaysatapoint90awayinthedirectionofrotation.
Therateofprecessionalsodependsonthreefactors:
Strengthanddirectionoftheappliedforce
Momentofinertiaoftherotor(rigidityofrotor-weight)
Angularvelocityoftherotor(Rigidityofrotorspeed)
Thegreatertheforce,thegreateris therateofprecession,whilethegreaterthemomentofinertiaand the greater the angular velocity, the smaller is the rateofprecession. (greater
rigiditysmallerrateofprecessionforequalamountofappliedforce)
Precessionofarotorwillcontinue,whiletheforceisapplied,untiltheplaneofrotationisinlinewiththeplaneoftheappliedforceanduntilthedirectionsofrotationandappliedforcearecoincident.Atthispoint,sincetheappliedforcewillnolongertendtodisturbtheplaneofrotation,therewillbenofurtherresistancetotheforceandprecessionwillcease.gyrowilleventually gimbal lock or topple if unrestrained a rate gyro functions on the basis ofprecession, but the gyro rotor is restrained by springs so does not gimbal lock rotorcontinuestoprecessagainstspringpressurewhilstturningforceisdetectedbygyrorotormoreonrategyroslater.
Theaxisaboutwhichatorqueisappliedistermedtheinputaxis,andtheoneaboutwhichprecessiontakesplaceintermedtheoutputaxis.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
16/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page8of56
B2-13h Instruments Gyroscopic
Theproperty ofprecessiononlybecomesapparentwhenanexternal forceis appliedto aspinningmass.Thiswillcausetheplaneofrotationtochangedirection.Thechangetakesplace,notatthedirectionoftheappliedforce,butatapoint90awayinthedirectionofgyrorotation.Therateofprecessionalsodependsuponthreefactors:
Strengthanddirectionoftheappliedforce
Rigidityoftherotor;(massoftherotor,whereitisconcentratedandspeed)
Thegreatertheforce,thegreateristherateofprecession,whilethegreatertherigidityoftherotor,thesmalleristherateofprecession.
Sinceprecessionistheangularchangeinpositionoftheplaneofrotation(spin)thatoccurswhen the applied force exceeds the rotational force, the direction of the precessionalmovementisdependentuponthedirectionoftheappliedforceandthedirectionofthegyrorotation.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
17/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page9of56
B2-13h Instruments Gyroscopic
Unavoidable precession is caused by aircraftmaneuvering and by the internal friction ofattitudeanddirectionalgyros.Thiscausesslow"drifting"andthuserroneousreadings.Whendeflectiveforcesaretoostrongorareappliedveryrapidly,mostoldergyrorotorstoppleover,rather thanmerely precess.This is called "tumbling" or "spilling" the gyro and should be
avoidedbecauseitdamagesbearingsandrenderstheinstrumentuselessuntilthegyroiserectedagain.Someof theoldergyroshavecagingdevicesto hold thegimbals inplace.Eventhoughcagingcausesgreaterthannormalwear,oldergyrosshouldbecagedduringaerobaticmaneuverstoavoiddamagetotheinstrument.Thegyromaybeerectedorresetbyacagingknob.Manygyroinstrumentsmanufacturedtodayhavehigherattitudelimitationsthantheoldertypes.Theseinstrumentsdonot"tumble"whenthegyrolimitsareexceeded,but,however,donot reflectpitchattitudebeyond85degreesnoseupornosedown fromlevelflight.Beyondtheselimitsthenewergyrosgiveincorrectreadings.Thesegyroshaveaself-erectingmechanismthateliminatestheneedforcaging.
Gimbal lock is normally prevented by limiting the movement of the inner gimbal withmechanical stops as shown on the slide. A mechanical stop applied to prevent gimballocking. This physically prevents the inner gimbal and the outer gimbal from becomingaligned.Ifthegimbalsdoreachthesestops,theforcesactingonthegimbalsystemcause
thesystemtoprecessrandomlyandtopple.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
18/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page10of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
19/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page11of56
B2-13h Instruments Gyroscopic
Free or Space Gyros
Anunrestricted,un-referenceddisplacementgyro is calleda spacegyro.Thesearegyrosthathavecompletefreedomaboutthreeaxiswhichareallactingatrightanglestoeachother
(spin,tilt,andveer).Thisenablesthegyrotomaintainitspositionrelativetosomepointinspace for an indefinite time assuming that thereare no bearing imperfectionsorexternalforcessuchasmagneticfieldsorgravity.
Typical gyro training aids and gyro toys are space gyros. They are not referenced toanything,notevengravity.Ifyouweretositandwatchaperfectlybalancedandfrictionlessspacegyro,itwillappeartorotateordriftawayfromtheperpendicular,butinrealitytherotoris remaining rigidly fixed inspace, and as the earthrotates, the framerotatesaround therotor,appearingtothevieweronearthasthoughthegyroisrotating.
Obviouslyanun-referencedspacegyroisofnouseinanaircraft.Forastartiftheaircraftweresittingstillonthegroundthegyrowouldbedriftingoffatarateof15perhourduetotheearthsrotation.Agyroinanaircraftmustbereferencedtothehorizon,ortheearth.Soa
spacegyromustbecontrolledtoremainrigid,butwithrespecttothecentreoftheearth,thisisusuallyachievedbyusinggravityasareferencetomaintainthegyroerect&referencedtothecentreoftheearth.
Free or Space Gyros
Thesearegyrosthathave completefreedomabout threeaxiswhichareall actingatrightangles to each other (spin, tilt, and veer). This enables the gyro to maintain its positionrelative tosome point in space for an indefinite time assuming that thereare nobearingimperfectionsorexternalforcessuchasmagneticfieldsorgravity.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
20/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page12of56
B2-13h Instruments Gyroscopic
Tied Gyros
Aspacegyrowouldbeofnousewhateverinestablishingtheneededverticalandhorizontalreferences required for safe instrument flight.Weneed to havegyros that have freedom
about threeaxis at rightangles toeachother, but whichare controlledbysomeexternalforce,sotheyassumeanattitudeinrespecttosomegivenpoint.Bytyingthegyrospinaxistosomefixedpoint,wecreatewhatiscalledatiedgyro.Thedirectionalgyroindicatorusesatiedgyroscope.Thegyrospinaxisbeingtiedhorizontalinrespecttotheindicatorcaseandassuch isparallel to the aircraft lateral and longitudinal axes.This type ofapplication iscalledacasetiedgyro.
Earth Gyros
Thesearetiedgyroswhosespinaxisismaintainedinaverticalpositionwithrespecttotheearthssurfacebyagravitationaldevice.Thesetypesofgyroscopesarecalledverticalgyrosandisthebasicelementofthegyrohorizonorartificialhorizonindicator.
Rate Gyros
Thesearetiedgyros,whicharetiedtoaparticularreferencepointbysprings,creatingagyrowhichhasonlyonedegreeoffreedom.Itisconstructedsoastoindicaterateofmovementaboutaplaneatrightanglestoboththeplaneofrotationandtheplaneoffreedomwhichinthiscaseisthetiltingplane.Thegyroscopeisspring-restrictedaboutthetiltaxissothatwhentheunitisturnedabouttheverticalaxis,theamountofdisplacementduetoprecessionisameasureoftherateofturn.
References Established by Gyroscopes
Theapplicationofthegyroscopeintoaircraftsystemsistoprovidetwoessentialreferencedatums:
vertical flight reference
Againstwhichaircraft attitude changesarenotedandused to indicateboth pitchand rollfunctionsoftheaircraft.
directional flight reference
Againstwhich aircraft heading changesare noted and used to indicatemovement of theaircraftabouttheverticalaxis.
These referencesareestablishedbygyroscopeshaving their spin axisarrangedverticallyand horizontally. The vertical gyro is the sense element of all attitude gyros, whilst thehorizontal gyro is the sense element of the directional gyro providing aircraft headinginformation.
Fromtheabovedescription,itcanbeseenthatthethreegyrocontrolledflightinstrumentsusedbythepilotarealltiedgyros.Ineachcasehowever,adifferentmethodisusedtotiethegyroinstrumenttoitsappropriatereferencepoint.
Earth Gyro
Before a free gyroscope can be ofpractical use asanattitude reference inaircraft flightinstrumentsandotherassociatednavigationalequipment,driftandtransportwandermustbecontrolledsothatthegyroscopesplaneofspinismaintainedrelativetotheearth;inotherwords,itrequiresconversiontowhatistermedanearthgyroscope.
ASpaceGyroreferencedtoearthis thentermedanEarthgyro.AnySpacegyroreferenced
toaparameterisreferredtoasatiedgyro,soanEarthGyro(tiedtocentreoftheearth)isaformofTiedgyro.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
21/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page13of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
22/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page14of56
B2-13h Instruments Gyroscopic
Rate Gyros
The difference between a displacement gyro, and that provided by a rate gyro: where adisplacementgyroutilisesagyrospropertyof rigidity inspace andmeasuredisplacement
around it, a rategyrorelies ona gyrobeingsubjected toprecessiveforcesagainstspringpressuretodeterminerateofmovement.Thehighertherateofmovementthegreatertheinertial force applied to the gyro resulting in precession. The higher the rate of turn, thegreatertheprecessiveforce,thegreaterthemovementagainstspringpressure.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
23/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page15of56
B2-13h Instruments Gyroscopic
Displacement Gyros
Aircraftinflightarestillverymuchapartoftheearth,i.e.allreferencesmustbewithrespect
totheearthssurface.Thefreeorspacegyroscopewehavebeenreferringtoinpresentinggyrotheorywouldservenousefulpurposeinanaircraftandwouldhavetobecorrectedfordriftwithrespecttotheearthsrotation,calledapparentdrift,andforwanderasaresultoftransportingthegyroscopefromonepointontheearthtoanother,calledtransportwander.
Itwillalsobenotedthatthepitch,roll,anddirectionalattitudesoftheaircraftaredeterminedbyitsdisplacementwithrespecttoeachappropriategyroscope.Forthisreason,therefore,the gyroscopesare referred toasdisplacement typegyroscopes. Eachonehas the threedegrees of freedom, and consequently three mutual axes, but for the purpose ofattitudesensing,thespinaxisofthegyroisdiscountedsincenousefulattitudereferenceisprovidedwhendisplacementstakeplaceaboutthespinaxisalone(displacementaroundaxisofspin
isnotdetected).Thus,inthepracticalcase,vertical-axisandhorizontal-axisgyroscopesarefurtherclassifiedastwo-axisdisplacementgyroscopes.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
24/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page16of56
B2-13h Instruments Gyroscopic
Gyroscope Applications in Aircraft
Foruseinaircraft,gyroscopesmustestablishtwoessentialreferencedatums:
Referenceagainstwhichpitchandrollattitudechangesmaybedetected
Directionalreferenceagainstwhichchangesabouttheverticalaxismaybedetected
Thesereferencesareestablishedbygyroscopeshavingtheirspinaxesarrangedverticallyandhorizontallyrespectively.Bothtypesofgyroscopeutilisethefundamentalpropertiesinthefollowingmanner:
Rigidityestablishesastabilisedreferenceunaffectedbymovementofthesupportingbody
Precessioncontrolstheeffectsofapparentandrealdriftthusmaintainingstabilisedreferencedatums(erectionsystemstoreferencetoearth).
Foruseinaircraft,gyroscopesmustestablishtwoessentialreferencedatums:areferenceagainstwhichpitchandrollattitudechangesmaybedetected,andadirectionalreferenceagainst which changes about the vertical axis may be detected. These references areestablished by gyroscopes having their spin axes arranged vertically and horizontallyrespectively.
Both typesofgyroscopeutilizethe fundamentalpropertiesin thefollowingmanner:Rigidityestablishes a stabilized reference unaffected by movement of the supporting body, andprecessioncontrolstheeffectsofapparentandrealdriftthusmaintainingstabilisedreference
datums.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
25/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page17of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
26/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page18of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
27/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page19of56
B2-13h Instruments Gyroscopic
Tocompensateaspacegyrotoeliminateearthrate,attheequatorwecouldprecessitat15perhour,sothatitwillcompletelyrotateevery24hours(sameastheearthsrotation)thusappearing to remain erect with respect to earth. If the gyro is not at the equator, theprecessionvaluecanstillbeeasilycalculatedbecauseapparentdriftequals15sin(where
equalsangleoflatitude).Canbeachievedbyelectricaltorquingsignals,orbyunbalancinggimbalstocausegyrotodriftatdesiredrate.
Controlofdriftwhich,relatesonlytohorizontal-axisgyroscopesandcanbeachievedeitherby:
calculatingcorrectionsusingtheearth-rate formulagivenin theprecedingtableandapplyingthemasappropriate;e.g.tothereadingsofadirectionindicator:
applyingfixedtorqueswhichunbalancethegyroscopeandcauseittoprecessatarateequalandoppositetotheearthratewe,
applying torqueshaving a similar effect to that stated inabove, but which can bevariedaccordingtothelatitude.
Agyrocorrectedforearthrateorapparentdriftwillmaintainsitsattitudewithreferencetotheearth,itwillcontinuetopointtothecentreoftheearthevenastheearthrotates.
This is the name given to the apparent drift which becomes evident in the directionalgyroscopeduetotheearthsrotation.Itisacombinationofbothapparenttiltandapparentveer.Apparentprecessionoccursatarateof15degreesperhourxsineofthelatitudeinwhich the gyro is operating. Apparent drift compensation is carried out by causing thegyroscopetobeprecessedintheoppositedirectiontotheearthsrotation.Thisisachievedbyplacingweightsinthespinaxisofthegyrorotortounbalancetheunitsothattheweightforcecauses the gyro toprecess.The rate ofprecession isdeterminedby the latitude inwhichthegyroisbeingoperated.
Real drift results from imperfections in themanufactureof the gyroscope suchasbearingfriction,gimbalimbalances.Imperfectionscancauseunwantedprecessionwhichcanonlybeminimisedbyapplyingprecisionengineeringtechniques.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
28/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page20of56
B2-13h Instruments Gyroscopic
Transport Rate
Assumenowthatthegyroscopeistransportedfromonepointontheplanettoanother,withitsspinaxisalignedwiththelocalverticalcomponentofgravity.Itwillhaveappearedtoanobserverontheearththatthespinaxisofthegyroscopehastiltedthisistransportwander
The control of transport wander is normally achievedbyusing gravity-sensing devices toautomatically detect tilting of the gyro scopes spin axis, and to apply the appropriatecorrectivetorques.Examplesofthesedevicesarelaterdescribed.
Transport Rate
IfagyroweretransportedfromtheNorthPoletotheequatoritwillappearasthoughithastilted90.Infactyouhavemovedandnotthegyro.Inthediagrams,theoneontheleftshowsan uncorrected gyro which would display transport rate, the one on the right shows acorrectedgyro.
Transportrateiscorrectedbyreferencingthegyrotothecentreoftheearth,orgravity.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
29/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page21of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
30/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page22of56
B2-13h Instruments Gyroscopic
Gimbal errors
:occurinalldirectionalgyroswhich,asyouwillrecall,haveahorizontalspinaxis.Thegimbalerrorsarecausedduringaircraftmaneuvers.Theyarecausedby lossofgimbal relationshipundercertainconditions, in thatthegyro spin axis andgimbalsarenolongerat90degreestoeachother.Gimbalerrorsarenotcausedbyexternalforces,butby
the output from sensing synchros, as a result of the outer gimbal moving as the aircraftrotates about the spin axis. This output causes heading errors on inter-connectedinstrumentsduringmaneuvershowever,theseerrorsareeliminatedwhentheaircraftreturnstostraightandlevelflight.Iftheaircraftgyroframeisrotatedabouttherotorspinaxis,theoutergimbalmustmovetomaintainthedirectionoftherotorspinaxis.Thismovementoftheoutergimbalwillbedetectedbytheoutergimbalheadingsynchro.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
31/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page23of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
32/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page24of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
33/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page25of56
B2-13h Instruments Gyroscopic
Handling
-
7/25/2019 B2-13h Instruments Gyroscopic SR
34/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page26of56
B2-13h Instruments Gyroscopic
Ring Laser Gyro
Lasergyrosarenowwidelyused inaircraftnavigationapplications.Theyprovideaccurate,independent navigational data with high accuracy and reliability. They are still a dead
reckoningsystem,andrequirenoexternalinputstofunction.ThistypeofInertialReferenceUnitisreferredtoasastrapdownsystembecauseitdoesnotrequire a gyro stabilised platform as described in a conventional INU. Pitch and rollmovementswhichwouldnormally introduceerrorsinanaccelerometer,areprovidedtothecomputer and the accelerometer outputs are modified electronically to compensate forattitudechanges.
Thisformof InertialReferenceUnitnormallyprovidesprimaryAttitudeinformation,andcanalsomeasurealtitude(inertially),rateofascentanddescentandgroundspeed.OutputsfromanIRUaretypicallydistributedoveradigitaldatabustoflightcontrolcomputers,navigationcomputers,multi-functiondisplays,etc.
Fundamentals of Laser Operation
LASER isanacronymforLightAmplificationbyStimulatedEmissionofRadiation.Sinceitsdiscoveryin1960,LASERtechnologyhasexpandedrapidlywithapplicationinmanyfieldsotherthanaviationincludingmedical,agricultureandengineering.ThefirststepinproducingLaseristheionisationofagaswhichmaybehelium,argon,krypton,neonorxenon.Eachgasproducesadifferentcolour(andwavelength)oflight.Amixtureofheliumandneonisused in ring laser gyros. This gas mixture is held at low pressure inside a sealed tubeexposedtoananodeandcathodeplate.Whenahighvoltageisappliedacrosstheseplatesthe gases ionise, producing a glow discharge similar to fluorescent tubes. In lasergyroscopestheappliedvoltageisaround3000volts.
Whatisthedifferencebetweenlaserlightandsayordinarywhitelight?Firstly,whitelightisamixtureofmanywavelengths;laserlightisasinglewavelengthwhichisdependantonthe
typeofgas used.Secondly, ordinary light isscattered inall directionsbut laser light isaparallelbeam.Forexample,recentexperimentsusingapencilsizedlaserlightaimedatthemoon founditspread toadistanceofonly twomilesover the distanceof250,000miles.Laseristermedcoherent light whichmeansitisofaspecificwavelength.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
35/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page27of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
36/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page28of56
B2-13h Instruments Gyroscopic
Construction of the Ring Laser Gyroscope
Ringlasergyrosarenotgyroscopesinthesensethatweknowthem.Theyaresimplytwobeamsoflaserlightrotating inoppositedirectionsengineeredtodetectmotionandbehave
likeagyro.Laserringgyrosareconstructedsothattwolaserbeamsarereflectedaroundatrianglecausingthelighttotravelinanenclosedloop.Thelighttravelsinbothdirectionsatthesametime,sowehaveaclockwisebeamandacounter-clockwisebeam.
So how can this be used to detect motion? Picture a merry-go-round platform which isstationary, with two people walking around it from the same starting point. One walksclockwiseandtheotheranticlockwise,andbothcanwalkentirelyaroundthemerry-go-roundbacktotheirstartingpointbywalking100steps.However,iftheplatformisrotatedslowlyclockwise,thepersonwalkingwiththeplatformwouldneedtotakeshorterstepstocompletethe journey in the same number of steps. Conversely, the person walking against thedirectionofrotationwouldneedtotakelongerstepstocompletethejourneyin100steps(likewalkingonanescalatormorestepstoachievethesamedistance).
ThiscanalsobeexplainedusingtheDopplerprinciple.Asimilarphenomenontakesplaceinourlasergyro.Ifthegyroisturnedclockwise(CW),theCWbeamcompletes the journeyina shorter time.Inordertocompletethe journeyinthesamenumber ofcycles thebeamwavelengthmustbe compressed, that is, the frequencymust be increased. Conversely, the counter-clockwise (CCW) beam wavelength mustincrease(frequencydecreased).
-
7/25/2019 B2-13h Instruments Gyroscopic SR
37/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page29of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
38/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page30of56
B2-13h Instruments Gyroscopic
Fibre Optic Gyro
FibreOpticGyros(FOGs)arealaterexpansionoftheRLGprinciple.SimilartoRLGs,they
operate on exactly the same principle of sending two light beams, in different directionsaroundafibreopticpath.AnymovementoftheFibreOpticcoilineitherdirectionwillresultinthepathoflighttravellingfurtherinonebeamwhiletheotherlightpathtravelslessdistance.Bringingthetwolightbeamsouttosomeformofdetector,whichlooksatthephaseofthelight, will then give an output signal which will relate directly to the amount of rotationencounteredbythecoil.ThisisagainusingtheSagnaceffectasdotheRLGs.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
39/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page31of56
B2-13h Instruments Gyroscopic
The reason FOGs are finding greater use than RLGs is that they can be made in muchsmallerandcompactinstallations.Alsothepaththatthebeamsarerequiredtotravelaround,can bemademuch longer thanasimilarRLG lightpath,and this increaseinpath lengthmeans that more accurate and smaller changes of rotation can bemeasured. Typically,
FOGscan have fibreoptic coilswhich canmeasureanywhere from100metres toover5kilometresinlength.Thelongerthepath,meansbasicallythemoreaccuratetheFOGcanbe, which in turn means that the Inertial Measurement Unit will provide far greaternavigationalaccuracy.
Most modern day FOGs, because of their much smaller physical size than RLGs, areincorporatedwithGPS receivers andAir Dataunits.What thisdoes is togive the aircraftdesigneracompact,fullyselfcontained,navigationunitcapableofveryhighaccuracies.
Becauseoftheiroperationandthevirtualabsenceornearlyallmovingparts,themeantimebetween failure (MTBF) for these types of units is nowmeasured in the order of yearsbetween failures. Typical MTBFs are measured in excess of 50,000 hours of continuousoperation, which in laymens terms means nearly over 6 years of continuous operation
betweenreportedfaults.
TheaccuracyoftheseunitsisalsohigherthantypicalRLGunits.Accuraciesintheorderof15metresorless,anywhereintheworld,issomethingthatAirlinesareveryhappytoaccept.
Atypicalunit fromNorthropGrummanasshownaboveiscurrentlyfittedtotheAirbusA380.Itweighs less than8 kilograms,and draws less than 36 watts ofpower from the aircraftelectricalsystem.ThisunitcombinesthefunctionsofGPS,InertialReferenceandAirDatamodulesintoonepackage.Whatthisdoesisgiveasmalllightweightpackagewhichdrawsverylittlepower,yetprovidesextremelyaccuratenavigationalaccuracy.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
40/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page32of56
B2-13h Instruments Gyroscopic
Gyroscope Erection Systems
Therearetwomaintypeofairdrivengyroerectionsystems:
wedgeplate
pendulousvane.
Bothtypesrelyonthegyroscopicprecessiontomovethespinningrotorbacktoabalancedorerectposition.
Wedge Plate
Thewedgeplatesystemsimplydeflectstheairfromtherotorsystemacrossawedgeshapedplate.Thisdeflectedairwhenexhaustedevenlyorbalancedacrosstheplatehasnoeffectontheoutergimbal.Whenanunbalanceddeflectionoccursduetothemovementoftherotorfrom the vertical, the air isdistributedmoreonone sideof the plate than the other. Thisdifferential air flow causes a precessioneffect on the outer gimbal and therefore tries toreturnthespinningrotortotheverticalposition.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
41/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page33of56
B2-13h Instruments Gyroscopic
A negative pressure is created so that the cabin air enters the filtered inlet and passesthroughthechannelstothejets.Theairfromthejetshitstherotorbuckets,evenlydrivingtherotor at approximately 15,000 rev./min. After spinning the rotor, the air passes through apendulousvaneunitattachedtotheundersideoftherotorcasingandisfinallydrawntothe
vacuumsource.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
42/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page34of56
B2-13h Instruments Gyroscopic
Pendulous Vane
Thependulousvaneunitoperatesonanairdrivengyrospinningaroundaverticalaxis,suchasanartificialhorizon.Thistypeoferectionsystemportstheexhaustedairthroughfourports
locatedatrightangles toeachother. Thependulousvanesin thenormal positionportairequallyacrossalloutletsandthereforenoprecessioneffectisgenerated.Inanunbalancedsituation,thegyrorotoristiltedandthegravitationaleffectautomaticallyadjuststhepositionof the pendulous vanes and therefore directs the air differentially. This differential forcecausestherotortoprecessbacktothenormalposition.
Erection Systems for Electrically Driven Gyros
Mechanical
For electrically driven gyros, a mechanical form of erection is to manually cage thegyroscope.Thisactionmechanicallyforcesthegyrogimbalstoapositionatrightanglesto
eachother, that is,pitch, rollandyaw.Caremustbe takenwhencaginganinstrumentasdamagecanresulttogimbalsandbearingsifcagingisundertakenincorrectly.
Ball Type Erection System
Therearetwomaintypesofballstylelevellingorerectionsystemsusedonartificialhorizonsorattitudegyros:
ballcagetype
rollingballtype.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
43/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page35of56
B2-13h Instruments Gyroscopic
Ball Cage Type
Theballcagetypeusesanumberofsteelballsusuallybetween5and8suspendedbelowthe gyroand free to roll across a radiused discwith hooks locatedaround the perimeter.Thesehookscapturetheballsastheirmassmovesandapplyaprecessionforcetoerectthegyro.Intheverticalplane,themassofballsiscentredandthereforenoprecessionforceisapplied.Theprecessionalforceappliedwillerectthegyro.
Rolling Ball Type
Therollingballtypesystemwhenusedasalevellingdeviceincorporatesaslotteddiscwithaballfreetotravelinsidetheslot.Theslotisdriveninatauniformspeedapproximately30rpm.Whentheassemblyistiltedtheballexertsaneffectonthedisc.Whentilted,theballrollstothelowerendandwaitsuntilthebottomoftheslotcatchesup.Goinguphilltheballispushedbythedisc.Thismeansthattheaverageweightonthedownhillsideislessthantheuphill and therefore produces a torque effect which is related to tilt angle. This torqueprecessesthegyroassemblyinthedesireddirectiontomovethegyrobacktothevertical
position.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
44/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page36of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
45/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page37of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
46/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page38of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
47/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page39of56
B2-13h Instruments Gyroscopic
Erection Systems for Electrically Driven Gyros
Torque Motors and Sensors
The application of torquemotors is themost commonlyused formofgyro correctionandpossiblytheeasiesttouse.Thetorquemotorissimilartoasmallelectricmotorexceptthatthe output shaft applies a twistingmotion or forcewhich is called torque, to the erection
gimbal systemwhenenergised. The power issupplied through levelling switchesand thetorquemotorsaresituatedbetweenthegimbalandthenextsupportingframe.
Becauseoftheforceofprecession,agyrospinningabouttheverticalaxisrequiresthepitchtorquemotortobepositionedbetweentheinnerandoutergimbalandtherolltorquemotorpositionedbetweentheoutergimbalandframe.
Mercury Switches
Alevellingswitchmountedparalleltotheaircraftslongitudinalandlateralaxis(pitchandroll)detect any deviation from leveland therefore control current flow to the torquemotors byapplying a torque opposite to the force creating it. The levelling switches can be eitherstraightorcurved,thecurvedvarietyrequiringagreaterforcetooperate.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
48/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page40of56
B2-13h Instruments Gyroscopic
Torque Motors
The erectiontorquemotors are squirrel cagemotors witha laminated iron rotor,mountedconcentricallyaboutthestator.Theironcorestatorhastwowindings,areferencewinding
andacontrolwinding.Thereferencewindingisprovidedwithaconstantfieldandinnormaloperation, that is, nodisplacement, it has current flowing via a capacitor and is thereforephaseshiftedby90 degrees. The controlwinding is intwo partsand isable toprovideareversiblefield.ThiscircuitissuppliedfromthesameACsource,asitisdirectlyconnectedtothesupply there isnophaseshift, leading thereferencewinding.Thecombinedmagneticfield interactswith the field inthe stator and the result controlsthe direction of the torquemotorandprovidescorrectionaltorqueto thegyroassembly.Inthenormalpositionthereisnocurrentflowinginthetorquemotorcircuitsduetothelevellingswitchbeinginthelevelposition.
DC Coils and Permanent Magnets
Both systems use the resultant flux lines to impart a magnetic field which will tend to
magnetically displace the gyro and therefore impart a precessional force. A permanentmagnet isusedwhereaconstantcorrectionforceis required toact,as isthecaseforthecorrectionofapparentdrift.Thesuccessofthistypeofpermanentfieldwilldependontheoperating environment of the aircraft, and the drift rate of the location. DC coilsoffer theabilityofbeingabletobeswitchedonoroffthroughtheuseofcutoutswitches,limitswitches,mercuryswitchesorsimplyasameansoffasterectionofthegyro.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
49/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page41of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
50/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page42of56
B2-13h Instruments Gyroscopic
Erectionsystemsarenecessaryforerectingandmaintainingthegyrospinaxisinaverticalorhorizontalpositionrelativetotheearthssurface.Foranattitudeindicatortobeaccuratethegyrosspinaxismustbekeptvertical,thisisachievedbytheerectiondevicesdetectinganderectingthegyrotothelocalvertical.Duetotheconstructionoferectiondevices,theywillbe
displacedwhenevertheaircraftchangesairspeedoraltersdirection.Unless provision ismade to counter act the acceleration and turning forces, the erectiondeviceswillprecessthegyroaxistoafalseverticalandindoingsowillpresentanincorrect
-
7/25/2019 B2-13h Instruments Gyroscopic SR
51/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page43of56
B2-13h Instruments Gyroscopic
indicationoftheaircraftsattitude.Theimportanceoferectionsystemsandtheircorrectionmethodsmustbeclearlyunderstood.
Erection Errors
The erectionerrors caused byacceleration deceleration and turning forces actingon theconducting medium in the electrical leveling switches, or pendulous vanes used in themechanicalerectionsystemscanbecompensatedforbyusingthecharacteristicsofrigidityandprecessiontocorrecttheerrors.
Erection Error Correction
Tocorrectfortheerectionerrorsencounteredduringaccelerationordecelerationandturningforces,acorrecting torque isappliedto theoutergimbal.Thisresults inprecessionoftheinnergimbaltocounteractthefalseverticalerror.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
52/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page44of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
53/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page45of56
B2-13h Instruments Gyroscopic
Caging
Thegyrocanbecagedmanuallybyaleverandcammechanismtoproviderapiderection.When the instrument is not getting sufficient power for normal operation, an "OFF" flagappearsintheupperrightfaceoftheinstrument.
Theinstrumentpermits360ofrotationaboutthepitchandbankaxeswithouttumblingthegyro.Theexpandedmotionofthehorizonbarprovidessensitivepitchindicationsnearthelevelflightposition.
Whentheaircraftexceedsthemaximumof27inpitchupordown,thehorizonbarisheldinextremepositionandthespherebecomesthenewreference.Acontinuedincreaseofclimbordiveangleapproachingtheverticalattitudeisindicatedbygraduationsonthesphere.
When the aircraftnears vertical, the sphere begins torotate 180.Assoonasthe aircraftdeparts from the vertical, the instrument again indicates the attitude of the aircraft. Thismomentary rotation of the sphere is known as controlled precession and should not beconfusedwithgyrotumbling.Theattitudeoftheaircraftabouttherollaxisisshownbythe
-
7/25/2019 B2-13h Instruments Gyroscopic SR
54/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page46of56
B2-13h Instruments Gyroscopic
anglebetweenthehorizonbarandtheminiatureaircraft,andalsobythebankindexrelativetothedegreemarkingonthebezelmask(faceplate).
Errors
Followingrecoveryfromunusualattitudes,displacementofthehorizonbarinexcessof5inpitchand/orbankmayresult.Oncetheinstrumentsensesgravitationalforces,theerectionmechanismwillimmediatelybegintocorrecttheprecessionerrorsatarateof3to6persecond. Inanormal turn,centrifugal forceacting on the erectionmechanismwill producenormalprecessionerrorsinpitchand/orbankupto5onreturntostraight-and-levelflight.Accelerationordecelerationwillalsoresultinprecessionerrorsinproportiontothedurationandmagnitudeofthespeedchange.Followingacceleration,theaircraftpitchattitudewillbelowerthantheinstrumentindication;followingdeceleration,theaircraftattitudewillbehigherthanthepitchindicationuntiltheerectionmechanismrealignsthegyro.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
55/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page47of56
B2-13h Instruments Gyroscopic
Aircraft Gyro Vacuum Systems
Aircraftgyroinstrumentscanbepoweredbyvacuum(air)orelectricity.ElectricgyroscanrunoffACorDCpower,dependinguponwhattheyweredesignedfor.
Airdrivengyroscanrunonpositivepressure,orvacuumpressure.Airpressureisprovidedbyanenginedrivenvacuumpump,andthevacuum(morepredominantly)isthenplumbedthroughthegyroinstrumentstorunupthegyrorotors.Invacuumgyrosystemsthefiltersarevery important items as any contamination entering the gyro will dramatically shorten itsserviceablelife.Filtersmustberegularlyserviced
Aircraftuseaventurisystemwhentheydonothavethefacilityforanenginedrivenvacuumpumptopowertheirairdrivengyros.Theventuritubeisanopenendedmetaltubetaperingtowardsthecentreorthroat.It isfittedtothefuselageormainplanewiththeinletendinlinewiththedirectionofflight,andusuallylocatedinthepropwasharea.
Inflight,theairisforcedintotheinletendofthetubeandacceleratesthroughthenarrowingsectionorthroatofthetubetoahighervelocity.Thisincreaseinvelocityproducesalowerpressureatthethroatwhichisconnectedthroughtubingtoasuctionreliefvalveandthentothecaseofthegyroinstruments.Thecaseofthegyroisalsoconnectedthroughafilterbacktoatmosphere.As the pressure in the throat of the venturi is lower thanatmosphere, theatmospherecausesaflowofairorsuctionthroughtheinstrumentstotheventurithroatandback toatmosphere as the air leaves the venturi.Venturi tubesasa vacuum source arenormally confined to early light aircraftand some of the later types of simple home builtaircraft.Theventuriisextremelyinefficientandlimitedinitscapacitytodriveinstruments.
Venturitubesareratedbytheamountofvacuumtheywillproduceat120Mphor104Kts.Thetwo-inch/50mmventuriisusedtoproducetwoinchesofmercurysuctiontodriveoneturn and bank indicator, while the larger four-inch tubesare used for the directional andattitudegyros.Onedesignofthelargertubesiscalledthesuper-venturioreight-inchventuri.Thisventurihasanauxiliaryventuriinitsthroatandiscapableofmoresuctionforthesame
speed.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
56/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page48of56
B2-13h Instruments Gyroscopic
Problems
Themostcommonproblemwithaventuriisfrom:
beingstruck
thetubeassemblybeingdamaged
beingblockedbyaforeignobject.
Alwaysmake sure that the tubeand fittingsare clean, free fromobstructionsandhaveagoodphysicalappearance.
Withtheintroductionofnewaircraft,theaircraftsystemsandinstrumentationbecamemorecomplex.Higherspeedsandincreasedaltituderequiredamoresophisticatedvacuumsupplysource.Themajorproblemwiththeventurisystemistheformationoficeinthethroatandotherdamagebeingsustainedbythetubeassemblystickingoutintheairflow.Thevacuumpoweredgyroscopicflightinstrumentsfittedtothemanytypesofaircraftvaryinthedemandplaced on the vacuum system. The two main types of positive displacement, vane type
vacuumpumpswhicharedrivenfromtheengineaccessorydrivesare:
wettype
drytype
andareclassifiedaccordingtotheirconstruction.
Wet Pumps
Theearliervacuumpumpswerenearlyallofthesteelvanetypewhichwerelubricatedfromtheenginelowpressureoilsystem.Thisoilhasaone-waypassagethroughthepumpandislostwiththedischargeairoverboard,viatheventtube.Insomedesignsthisoilisreturnedto
theenginecrankcasebyseparatingtheoilfromthedischargeairinanoilseparatorbeforetheairisallowedtoentertheatmospherewhichpreventstheoilcausingstreaksalongthesideofthefuselage.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
57/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page49of56
B2-13h Instruments Gyroscopic
Themodern pumpsare dry; that is, theyhave theirwearingpartsmadeofTeflon and orcarbon.Thepumprotorsaremadeofafibrematerialandtherotorbladesareofcarbon.Thepump housing is high grade cast iron finely machined and in some cases the surface isTefloncoated.Thesepumpscannormallybedriveninonlyonedirectionwhichisindicated
byanarrowonthehousingTopreventmechanicaldamagetotheengineaccessorydrivesystem,thepumpshaveaweak-linksheardrivedesignedtofailshouldthepumpsufferaninternalfault.
Problems with Vacuum Pumps
Look for a show of oil or evidence of vibration. The vacuum pump should be smooth inoperationandanerraticoutputischaracterisedbyadifficulttoadjustsuctionreliefvalve.Thevacuumpumpshearlinkmustbecheckedforsignsofstressandthepumpmustappeartobeingoodorder.
Anaircraftvacuumsourcecanbeeitherfromavacuumpumpwhichisenginedrivenorfrom
aventuriwhichislocatedinthepropwash,externaltotheaircraft.Thevacuumsupplyinbothcasesisasourceoflowpressure.
Anaircraftvacuumsourcecanbeeitherfromavacuumpumpwhichisenginedrivenorfromaventuriwhichislocatedinthepropwash,externaltotheaircraft.Thevacuumsupplyinbothcasesisasourceoflowpressure.
Pressurisedairportedovercupsingyrorotor,orvacuumairsuckedacrosscups.Spinsgyrorotor up to speed and is also used for gyro erection system reference gyro to earth toeliminate transport rate.Onlyever lowpressureair used.Only likely tobe incorporated inlightaircraft.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
58/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page50of56
B2-13h Instruments Gyroscopic
Athighaltitudesvacuum-drivengyroscopicinstrumentssufferfromtheeffectsofadecreaseinvacuum due to the loweratmosphericpressure; the resulting reduction in rotor speedsaffecting gyroscopic stability. Other disadvantages of vacuumoperation areweight due topipelines, special arrangements to control the vacuum in pressurized cabin aircraft, and,
sinceairmustpassthroughbearings,thepossibilityofcontaminationbycorrosionanddirtparticles
Vacuum-Driven Gyro Horizon
The rotor ispivoted inball bearingswithina case forming the inner ring,which in turn ispivotedinarectangular-shapedouterring.
Intherearendcoveroftheinstrumentcase,aconnectionisprovidedforthecouplingofthevacuumsupply.Withthevacuumsystem inoperation, thesurroundingatmosphereentersthe filteredinletandpasses throughthechannelsto the jets.Theair issuingfromthe jetsimpinges on the rotor buckets, thus imparting even driving forces to spin the rotor atapproximately 15,000 RPM. After spinning the rotor, the air passes through a pendulous
vaneunitattachedtotheundersideoftherotorcasing,andisfinallydrawnoffbythevacuumsource.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
59/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page51of56
B2-13h Instruments Gyroscopic
Disadvantages of air driven gyro systems
Dirtanddustareamajorproblemwithairdriveninstrumentsandthereforeinstrumentfiltersandsystemfiltersmustbechecked,cleanedorchangedatregularintervals.
Whencigarettesmokingwasallowedonaircraft,theresiduefromthesmokewasamajorproblemforgyroscopicairdriveninstruments.
Enginedrivenvacuumpumpsmustberegularlycheckedforcorrectoperation.
Incorporationofmechanicalpumpsaddsanadditionalpieceofequipmentrequiringservicing,inadditiontotheaircraftsalternator/generator.
Toovercomethedisadvantagesoftheairdrivengyroscopicinstrumentsinhighperformanceaircraft,gyroscopicinstrumentsweredesignedforoperationonelectricalpowerderivedfromthe aircraft power supplies. This power is generally 115V 400Hz three phase alternatingcurrentassuppliedfromtheaircraftalternatorsorinvertersor28Vdirectcurrent,thelatterbeing requiredfor the operation ofsome turnand bank indicators.The alternatingcurrent
applicationhasbeenusedforthelatertypesofturnandbank,gyrohorizonindicatorsandtheremotely located attitudeand directional gyros associatedwith flight control systems andremote-indicatingcompasssystems.
Electricalgyrosonlyneedasmallamountofpowerfromtheexistingaircraftpowersupplyhenceanadditionalenginedrivencomponent(thevacuumpump)isnolongernecessary.
ACelectricallypoweredgyroscanrunmuchfasterthanairdrivengyrossoprovideamorerigidgyroscopicreference.
Electricallydrivengyrosincorporatemoresolidstatecomponentsandthereforerequirelessmaintenanceeffortcomparedtopneumaticallydrivengyros.
Aparticularlimitationofairdrivengyrosovermostelectricallydrivengyrosis that thegyro
should never beremoved fromtheaircraftuntilat least30minuteshavepassed from thetime the vacuum source was disconnected, or rotor has ceased spinning, as the inertiacontainedwithintherotor,andtherelativeabsenceoffrictionwithinthebearings,mayallowtherotortospinforuptothislengthoftime.Electricallydrivengyrosoftenincorporateaformofelectrical ordynamicbrakingwhichwill slow the gyro rotorvery quicklyoncepower isremoved.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
60/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page52of56
B2-13h Instruments Gyroscopic
Thedirectcurrentelectricalgyrousesamethodofconstructionwheretherotorisactuallythearmaturewindingandthestatoristhepermanentmagnet.Thisprincipleofconstructionallowsthegreatermasscontainingthearmaturewindingtospinastherotorgivinggreaterrigidity.
Thisdirectcurrentapplicationutilisesthegyrorotorwhichcontainsthearmaturewindingofasmall permanentmagnet motor. This is supplied with 28 voltsDC via two spring loadedbrushescontactingacommutator,whichismountedontherotorarmatureshaft.Thestatorisatwo-polepermanentmagnetandformspartofthegimbalframe.Inthisapplication(TurnandSlipindicator)therotorspeediskeptatapproximately4,200RPM.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
61/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page53of56
B2-13h Instruments Gyroscopic
AC Drive Methods and Motor Types
AC gyros are usually poweredby a three phase115 volt 400Hz squirrel cage inductionmotor, consistingofa rotor andastator.Anormal inductionmotorhas the rotorrevolvinginsidethestator.Inthisinstancethemotorhasbeenredesignedsothattherotorrotateson
theoutsideofthestator,thisincreasesthemassoftherotorinordertoprovidetherequiredinertia.
The115voltsACissuppliedtothestatoranda rotatingmagneticfieldisestablishedinthestator.Thisrotatingfieldcutsthebarsinthesquirrelcagerotorandinducesacurrent,theeffectofwhichproducesamagneticfieldaroundthebarswhichcombinewiththe statorsfieldcausingtherotortospinatapproximately22,500RPM.
AC Drive Methods and Motor Types
AC gyros are usually poweredby a three phase115 volt 400Hz squirrel cage inductionmotor, consistingofa rotor andastator.Anormal inductionmotorhas the rotorrevolvinginsidethestator.Inthisinstancethemotorhasbeenredesignedsothattherotorrotatesontheoutsideofthestator,thisincreasesthemassoftherotorinordertoprovidetherequiredinertia.
The115voltsACissuppliedtothestatoranda rotatingmagneticfieldisestablishedinthestator.Thisrotatingfieldcutsthebarsinthesquirrelcagerotorandinducesacurrent,theeffectofwhichproducesamagneticfieldaroundthebarswhichcombinewiththe statorsfieldcausingtherotortospinatapproximately22,500RPM.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
62/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page54of56
B2-13h Instruments Gyroscopic
Electric Gyro Horizon
Madeupofthesamebasicelementsasthevacuum-driventype,withtheexceptionthattheverticalgyroscope isa3-phasesquirrel-cage inductionmotor (consistingofa rotoranda
stator).One of the essential requirements of any gyroscope is to have the mass of the rotorconcentrated as near to the periphery as possible, thus ensuring maximum inertia. Thispresents nodifficulty where solidmetal rotors are concerned, but when adopting electricmotors asgyroscopes some rearrangement of theirbasicdesign isnecessary inorder toachieve the desiredeffect. An induction motor normally has its rotor revolving inside thestator,buttomakeonesmallenoughtobeaccommodatedwithinthespaceavailablewouldmeantoosmallarotormassandinertia.However,bydesigningtherotoranditsbearingssothatitrotatesontheoutsideofthestator,thenforthesamerequiredsizeofmotorthemassoftherotorisconcentratedfurtherfromthecentre,sothattheradiusofgyrationandinertiaareincreased.Thisisthemethodadoptednotonlyingyrohorizonsbutinallinstrumentsandsystemsemployingelectricgyroscopes.
Themotorassemblyiscarriedinahousingwhichformstheinnergimbalringsupportedinbearingsintheoutergimbalring,whichisinturnsupportedonabearingpivotinthefrontcoverglassandintherearcasting.
The115V400Hz3-phasesupplyisfedtothegyrostatorviasliprings,brushesandfingercontactassemblies.Theinstrumentemploysatorque-motorerectionsystem,theoperationofwhichisdescribedinPallettAircraftInstrumentsonpage136,butwillnotbecoveredhere.
Whenpowerisswitchedonarotatingmagneticfieldissetupinthegyrostatorwhichcutsthebarsformingthesquirrel-cageintherotor,andinducesacurrentinthem.Theeffectofthis current is toproducemagnetic fields around the barswhich interactwith the statorsrotatingfieldcausingtherotortoturnataspeedofapproximately20,00023,000rev./min.
FailureofthepowersupplyisindicatedbyaflagmarkedOFFandactuatedbyasolenoid.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
63/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.1GyroscopesIssueB:January2008 Revision2 Page55of56
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
64/104
Part 66 SubjectAA Form TO-19
B2-13.8.2.1GyroscopesIssue on Page56of56
B2-13h Instruments Gyroscopic
B:January2008 Revisi 2
Thispageintentionallyleftblank
-
7/25/2019 B2-13h Instruments Gyroscopic SR
65/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page1of16
B2-13h Instruments Gyroscopic
TOPIC 13.8.2.2.1: ARTIFICAL HORIZONS
Inordertomeasureamovement,youneedareference,andinthisinstancethegyrobecomesthereferenceorstablepoint.Theamountofmovementordeflectionsmadebytheaircraftaroundthisstablepointaremeasuredanddisplayedonthecockpitinstruments.
GyroSpinaxisisvertical,soplaneofspinishorizontal.Thispermitsrigidityinlateralandlongitudinalaxisandthedisplacementofthegimbalsfromthestablereferenceiswhatprovidestherollandpitchreadout.
Thegyroisatiedgyroreferencedtotheearthsgravitytomaintaintheverticalspinaxisshouldimperfectionsorerrorscausethegyrotodrift.Theerectionsystemwillre-alignthegyrowithrespecttogravity.
Mostgyrohorizonshaveapulltocageknobtore-alignthegyroinstraightandlevelflightifitisnotedtobedriftingoff,orifittumblesorsuffersgimballock.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
66/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page2of16
B2-13h Instruments Gyroscopic
This form of gyro horizon has a fixed back plate or sky plate and the aircraft symbol isattachedtothegimbalsandmoveswithrespecttothebackplatetoindicatepitchandyawattitudes.Thiswasanoldmethodofdisplayingthisinformationandprobablynotveryoftenseeninmoderntimes.
Thepitchrestrictionat85istoavoidgimballock.Thisisnotaconcernintherollaxis.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
67/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page3of16
B2-13h Instruments Gyroscopic
Thispictureisamoreexactillustrationofthewaythegyrohorizonactuallyprovidesadisplayofpitchandroll.Thedialisfixedandonceuponatimewouldonlyhavehadahorizonlinedrawnacrossthemiddle.Inmorerecenttimegyrohorizonshavebeencolouredwithalight
colourabove,typicallyblue,torepresenttheskyandadarkercolourbelowtorepresenttheground.
Whenthehorizonpointer isupand intheblueitmeans theaircraftis climbing,andwhendown in thegreen it is diving. Thehorizonbar is restricted in pitchmovement up to 85otherwisegimballockwilloccur,whereastherollingactionisunrestricted.
Thedisplaycanthereforeindicateunrestrictedfullbarrellrollsbutifaloopwereperformedthe indicatorwouldshowaclimbup to85 (when the aircraftnose isalmost vertical, notwhenitsatthetopoftheloop)theassemblywouldthenroll180.Thehorizonpointerwouldindicatestraightandlevelinvertedflightcorrespondingwiththeaircraftbeingupsidedownatthetopoftheloop.Astheaircraftcomesdowntocompletetheloopthehorizonbaragainshowstheaircraftheadingforthegrounduntilit ispointingalmoststraightat theearth(85
nosedown)whenitwillagainspin180.Thismeanstheaircraftsymbolwillcontinuepointingattheearth(indicatingadive).Astheaircraftrecoverstostraightandlevelflightagainatthebottomoftheloopthewholeassemblywillbebackinitsoriginalattitudewiththehorizonbaragainshowingstraightandlevelflight.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
68/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page4of16
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
69/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page5of16
B2-13h Instruments Gyroscopic
With thevacuumsystem inoperation,anegativepressure iscreatedso that thecabinairentersthefilteredinletandpassesthroughthechannelstothejetswhicharedirectedontothebucketscarvedintothegyrosrotor.Theairfromthejetshitstherotorbuckets,evenlydriving the rotoratapproximately15,000 rev./min. Afterspinning the rotor, the air passes
throughapendulousvaneunit attachedtothe underside of the rotorcasing and isfinallydrawntothevacuumsource.Theairisexhaustedthroughthependulousvaneunit,whichappliesacorrectionalorprecessionforcetkeepthegyroperpendiculartotheearthssurface.
Thisisachievedthroughthemagicofprecessionandasthegyrotiltsofftheverticalanairportisuncoveredpermittingagreaterflowofairfromthatportasitexitsfromthegyrosrotor.Theadditionalairflowexertsaforceonthegyrowhichisfelt90inthedirectionofrotationandwillcausethegyrotoprecessbacktothevertical.
Operation
Theoperationoftheinstrumentisbasicallycontrolledbytheprincipleofgyroscopicinertiaorrigidity. Thegyrospinaxis ismaintained ina verticalposition relativetotheearth.Astheaircraft rollsand pitches in flight, the indication isgivenona two colour dial, the top halfrepresentingtheskyandthebottomhalfwhichisdarker,representstheground.
Thehorizontalgyrospinsabouttheverticalaxisandthereforeitcansenserotationabouttherollandpitchattitudeoftheaircraft.
Disadvantages of air driven gyro systems
Dirtanddustareamajorproblemwithairdriveninstrumentsandthereforeinstrumentfiltersandsystemfiltersmustbechecked,cleanedorchangedatregularintervals.
Whencigarettesmokingwasallowedonaircraft,theresiduefromthesmokewasamajorproblemforgyroscopicairdriveninstruments.
Enginedrivenvacuumpumpsmustberegularlycheckedforcorrectoperation.
Incorporationofmechanicalpumpsaddsanadditionalpieceofequipmentrequiringservicing,inadditiontotheaircraftsalternator/generator.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
70/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page6of16
B2-13h Instruments Gyroscopic
Toovercomethedisadvantagesoftheairdrivengyroscopicinstrumentsinhighperformanceaircraft,gyroscopicinstrumentsweredesignedforoperationonelectricalpowerderivedfromthe aircraft power supplies. This power is generally 115V 400Hz three phase alternatingcurrentassuppliedfromtheaircraftalternatorsorinvertersor28Vdirectcurrent,thelatter
beingrequiredfor the operation ofsome turnand bank indicators.The alternatingcurrentapplicationhasbeenusedforthelatertypesofturnandbank,gyrohorizonindicatorsandtheremotely located attitudeand directional gyros associatedwith flight control systems andremote-indicatingcompasssystems.
Electricalgyrosonlyneedasmallamountofpowerfromtheexistingaircraftpowersupplyhenceanadditionalenginedrivencomponent(thevacuumpump)isnolongernecessary.
ACelectricallypoweredgyroscanrunmuchfasterthanairdrivengyrossoprovideamorerigidgyroscopicreference.
Electricallydrivengyrosincorporatemoresolidstatecomponentsandthereforerequirelessmaintenanceeffortcomparedtopneumaticallydrivengyros.
Aparticularlimitationofairdrivengyrosovermostelectricallydrivengyrosis that thegyroshould never beremoved fromtheaircraftuntilat least30minuteshavepassed fromthetime the vacuum source was disconnected, or rotor has ceased spinning, as the inertiacontainedwithintherotor,andtherelativeabsenceoffrictionwithinthebearings,mayallowtherotortospinforuptothislengthoftime.Electricallydrivengyrosoftenincorporateaformofelectrical ordynamic brakingwhichwill slow the gyro rotorvery quicklyoncepower isremoved.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
71/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page7of16
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
72/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page8of16
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
73/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page9of16
B2-13h Instruments Gyroscopic
The need for integrating the functions and indications of certain flight and navigationinstrumentsresultedinthemainfromtheincreasingnumberofspecialisedradioaidslinkingaircraftwithgroundstations.Theseweredevelopedtomeetthedemandsofsafeen-route
navigationandtocopewithincreasingtrafficcongestionintheairspacearoundtheworldsmajorairports.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
74/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page10of16
B2-13h Instruments Gyroscopic
The required information isprocessed by black boxes which can bestowed inelectricalcompartments and radio racks, but in order that the necessary precision flying may beexecuted,informationmuststillbepresentedtothepilot.Thisrequiresmoreinstrumentsandmoreinstrumentscouldmeanmorepanelspace.Themethodofeasingtheproblemwasto
combinerelatedinstrumentsinthesamecaseandtocompoundtheirindicationssothatalargeproportionofintermediatementalprocessingonthepartofthepilotcouldbebypassedandtheindicationsmoreeasilyassimilated.
Duringthatphaseofaflightinvolvingtheapproachtoanairportrunway,itisessentialforapilottoknow,amongotherthings,thatheismaintainingthecorrectapproachattitude.Suchinformationcan beobtained from the gyrohorizon and fromaspecial ILS indicatorwhichrespondstoverticalandhorizontalbeamsignalsradiatedbythetransmittersofanInstrumentLandingSystemlocatedattheairport.ItwasthereforealogicalstepinthedevelopmentofintegrationtechniquesinwhataretermedFlightDirectorSystems,toincludetheinformationfromboththegyrohorizonandILSindicator.
Themethodsadoptedfortheintegrationofsuchinformation,andthemannerinwhichitis
presentedvarybetweensystems.Acompletesystemnormallycomprisestwoindicators:
-flightdirector,attitudeflightdirectororanapproachhorizon
-coursedeviationindicator(CDI)orahorizontalsituationindicator(HSI).
Theflightdirectorindicatorhastheappearanceofaconventionalgyrohorizon,butunlikethisinstrument thepitchandroll indicatingelementsareelectricallycontrolled froma remotelylocatedverticalgyrounit.
TheapproachattitudeofanaircraftwithrespecttoitsILSsignalsisindicatedbyindependentpointersmonitoredbytherelevantILSreceiverchannels.Displacementoftheaircrafttothe
leftorrightofthelocaliserbeamisindicatedbydeflectionsofthelocaliserpointer.Glideslopepointerfunctionsinsimilarfashion.
AttitudeDirectorsarebasicallyArtificialHorizonswithcommandsteeringbarsincorporated.Theinstrumentprovidesthepilotwithanindicationofpitchandroll,butalsohascommandbarswhichcanbeusedtoguidethepilotontoaselectedcourse,ortoaselectedaltitude.Thecommandbarsappearandthepilotfliestheaircrafttoaligntheaircraftsymbolwiththe
commandbars.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
75/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page11of16
B2-13h Instruments Gyroscopic
Flight Director Indicator FDI)
Thisinstrumentmaybeknownasanattitudedirectorindicator(ADI)oranattitudereferenceindicator(ARI).Theyallhaveslightlydifferentdisplays,buttheyalloperateinthesameway.Thebasic functionof theFDI is tosupply the pilotwith theaircraftsattitudeandsteeringinformation. This represents a view from behind the aircraft looking forward. Steeringcommandandaircraftattitudearedisplayedaroundafixedaircraftsymbol.
Attitude Sphere
Thesphereisfreetomove360inrollanddependingontype,90or360inpitch.Gimballocklimitationminimisedoreliminated
Bank Pointer
Thisdisplays thebankangleof theaircraft,andisreadagainstascaleon thecaseof theinstrument.
Command Bars
Therearetwocommandbars,oneforpitch,andoneforroll.Theyarecalledcommandbarsbecausetheycommandthepilottoflytheaircraftsymboltowardsthecommandbars.The
commands are supplied from the flight director computer, which can receive referencesignalsfromarangeofnavigationaidreceiversorINS
Glideslope Pointer
This is locatedonthe left sideof the FDI and isusedwhen the aircrafthascapturedtherunwayglideslopebeams,whenlanding.Theaircraftsverticalpositionwithinthebeamsisshownbythepointer.Whenthepointerisonthecentreline,theaircraftisinthecentreoftheglideslope.Whenthepointerisonthedotclosesttothecentreline,thepitchcommandbarcomesintoview,andthepilotfliestowardsit.Figure3.13showstheglideslopepointer.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
76/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page12of16
B2-13h Instruments Gyroscopic
Localiser Deviation Indicator
Localiser pointershows theaircrafts positionin relationto the localiser beams.When thepointerisinthecentreofthescaletheaircraftispositionedinthecentreofthebeams.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
77/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page13of16
B2-13h Instruments Gyroscopic
Theflightdirectorindicatorhastheappearanceofaconventionalgyrohorizon,butunlikethisinstrument thepitchandroll indicatingelementsareelectricallycontrolled froma remotelylocatedverticalgyrounit.
Electricalinterconnectionoftheflightdirectorindicatorcomponentsprimarilyconcernedwithpitch and roll attitude information is shown on the slide. Whenever a change of aircraftattitudeoccurs,signalsflowfrompitchandrollsynchrostothecorrespondingsynchroswithintheindicator.Errorsignalsarethereforeinducedintherotorsandafteramplificationarefedto the servomotors, whichrotate toposition the pitchbar andhorizondisc (or Sphere, or
cylinder)toindicatethechangingattitudeoftheaircraft.Atthesametime,theservomotorsdrivethesynchrorotorstothenullposition.
ThesecondcircuitshowstheinterconnectionoftheglideslopeandlocaliserpointerwiththeILS.DuringanILSapproachthereceiveronboardtheaircraftdetectsthesignalsbeamedfromgroundtransmitters inverticalandhorizontalplanes. If theaircraft isabove theglidepath,signalsarefedtothemetercontrollingtheglideslopepointercausingittobedeflecteddownwardsagainstthescale,thusdirectingthepilottobringtheaircraftdownontotheglidepath.Anupwarddeflectionofthepointerindicatesflightbelowtheglidepathandthereforedirectsthattheaircraftbebroughtuptotheglidepath.Thepointerisalsoreferencedagainstthe pitchbar to indicateany pitchcorrection required tocapture and hold the glidepath.Whenthishasbeenaccomplished,theglideslopepointerandpitchbararematchedatthehorizontalcentreposition.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
78/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page14of16
B2-13h Instruments Gyroscopic
If,duringtheapproach,theaircraftistotheleftofthelocaliserbeamandrunwaycentre-line,thelocaliserpointerisdeflectedtotherightdirectingthattheaircraftbebankedtotheright.Flighttotherightofthelocalizerbeamcausespointerdeflectiontotheleft,directingthattheaircraftbebankedtotheleft.Wheneitherofthesedirectionshasbeensatisfied,thepointeris
positionedverticallythroughthecentrepositionofthehorizondisc.
Flight director indicator houses a number of servo/synchro devices. Aircraft pitch & rollinformation from twin gyro platform positions horizon disc & pitch bar. Additionalservo/synchrodevicestodrivecommandbarsdrivenbysignalsfromflightdirectorcomputer.Typical remote indicator housing servo/synchro systems to repeat informationsensed/processedbyaremoteequipmentrackmountedblackbox.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
79/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssueB:January2008 Revision2 Page15of16
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
80/104
Part 66 SubjectAA Form TO-19
B2-13.8.2.2.1ArtificialHorizonsIssue on Page16of16
B2-13h Instruments Gyroscopic
B:January2008 Revisi 2
Thispageintentionallyleftblank
-
7/25/2019 B2-13h Instruments Gyroscopic SR
81/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.2SlipIndicatorsIssueB:January2008 Revision2 Page1of14
B2-13h Instruments Gyroscopic
TOPIC 13.8.2.2.2: TURN AND SLIP INDICTORS
Turn Indicators
Theturnandbankindicatororturnandslipindicatorasitismostoftencalled,isoneofthefirst instruments developed for instrument flying. The instrument actually combinesa turnindicatorandaslipindicatorintheoneinstrument.Inearlydaysofflyingtheturn-and-bank,whenusedinconjunctionwiththeaircraftcompassmadeavaluablecontributiontotheartofIFRflying.Itwasthusconsideredtheprimaryblindflyinginstrument.Withdevelopmentsinaircraft instrument technology the turn-and-bank has been replaced as the primary IFRinstrumentbytheAH,althoughinsomelightaircrafttheturn-and-bankisstillconsideredaprimary flight instrument. In larger aircraft the turn-and-bank has become a secondaryinstrumentorisnotused.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
82/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.2SlipIndicatorsIssueB:January2008 Revision2 Page2of14
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
83/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.2SlipIndicatorsIssueB:January2008 Revision2 Page3of14
B2-13h Instruments Gyroscopic
Principle of Operation
The rategyros spinaxis ishorizontaland correspondswith the aircrafts lateral axis, thatmeanstheplaneofspinisthroughthelongitudinalaxisoftheaircraft.Therategyroonlyhas
onegimbalmountedwithinthe frameorcaseofthe instrumentsoit isonlypermittedonedegreeoffreedomwhichis intilt.Thepivotpoint for thegimbal isforeandaftofthegyrorotorsoitispivotedinthelongitudinalaxisoftheaircraft.
Thegyrosensesmovementabouttheyawingaxisoftheaircraft.ItiseffectivelymountedlikeaDG, butdoesnot havethe freedomofaDG.When theaircraftyaws the gyrowants toremaininitscurrentattitudeandalignment,butcannotbecausethereisnogimbaltopermitveer.Becausethegyrocannotremainpointinginthesamedirectiontheturningmotionoftheaircrafthasthesameeffectasifsomeoneappliedaprecessiveforcetothefrontandrearofthegyrorotor,tryingtochangeitsheading.Thisforceisfelt90indirectionofrotation,sowill precess the gyro so itwill tilt over. If the gyrowasnot restrainedbysprings itwouldcontinuetoprecessinthetiltaxiswhileevertheyawingmotionwasfelt.Becausethegyroisheldinplacebysprings,whileevertheyawingmotion(orrateofturn)remainsconstantthe
gyro precession force will remain constant against spring pressure providing a constantindicationoftherateofturn.Iftherateofturnisincreasedtheprecessionforceincreasestiltingthegyrofurtheragainstspringpressure.Whentheturningmotionendstheprecessionforceisremovedsothegyrowillreturntotheoriginalattitude,iespinningintheverticalplanecorrespondingwiththeaircraftslongitudinalaxis.
Rotoraxisparalleltoaircraftslateralaxis
Yawingmotionsensed&duetoprecessionrotortriestolieoveragainstspringpressure
Lieoverangleproportionaltorateofturn&isopposed/restrictedbycalibratedspringtension
2Minuteand4MinuteTurns
Gyrodoesntbeginto layoveruntilaftertheturnhasbegun,iewhentheheadingbeginstochange.ThisstatementwillbereferredbacktowhencoveringTurnCoordinators.
Spinaxisparalleltoaircraftlateralaxis
-
7/25/2019 B2-13h Instruments Gyroscopic SR
84/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.2SlipIndicatorsIssueB:January2008 Revision2 Page4of14
B2-13h Instruments Gyroscopic
Yawingmotionsensedrotortriestolieoveragainstspringpressureduetoprecession
Lieoverangleproportionaltorateofturn
Gyrolaysoverwhenheadingchanges
Rateofprecession(lieoverangle)dependson:
Rateatwhichheadingischanging
Rigidityofrotor(rotorspeed)
Rateofprecessiondependantuponspeedofgyrorotor(gyrorigidity)
RateofTurnindicatorrotorspeedcritical:
toofast&instrumentunderreads
tooslow&instrumentoverreads
Rateofturnindicatorsincorporaterotorspeedgovernortoensureaccuracyofindications
-
7/25/2019 B2-13h Instruments Gyroscopic SR
85/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.2SlipIndicatorsIssueB:January2008 Revision2 Page5of14
B2-13h Instruments Gyroscopic
-
7/25/2019 B2-13h Instruments Gyroscopic SR
86/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.2SlipIndicatorsIssueB:January2008 Revision2 Page6of14
B2-13h Instruments Gyroscopic
The Mechanism of a Typical Direct-Current Operated Turn-and-Bank Indicator
Directcurrentisfedtothebrushesandcommutatorviaaradiointerferencesuppressorandflexiblespringswhichpermitmovementoftheinnerring.
The rotor speed is controlled by two identical symmetrically opposed centrifugal cut-outs.Each cut-out consists of a pair of platinum-tipped governor contacts, one fixed and one
movable,whicharenormallyheldclosedbyagovernoradjustingspring.Eachcut-outhasaresistor across its contacts, which are in series with half of the rotor winding. When themaximum rotor speed is attained, centrifugal forceacting on the contacts overcomes thespringrestraintcausingthecontactstoopen.Thearmaturecurrentthereforepassesthroughtheresistors,thusbeingreducedandreducingtherotorspeed.Bothcut-outsoperateatthesamecriticalspeed.
Angularmovementof thegimbalringistransmittedto thepointerthroughageartrain,anddampingisaccomplishedbyaneddy-currentdragsystemmountedattherearofthegyroassembly.Thesystemconsistsofadragcup,whichisrotatedbythegimbalring,betweenafieldmagnetandafieldring.
Apower-failurewarningflagisactuatedbyastirruparmpivotedonthegimbalring.Whenthe
rotor is stationary, the stirrup arm is drawn forward by the attraction between a magnetmounted on it and an extension (flux diverter) of the permanent-magnet stator. In thisconditiontheflag,whichisspring-loadedintheretractedposition,isdepressedbythestirruparm so that the OFF reading appears through an aperture in the dial. As rotor speedincreases, eddy currents are induced in the rotor rim by the stirrup magnet, and at apredeterminedspeed,reactionbetweenthemagnetandinducedcurrentcausesthestirruparmtoliftandtheOFFreadingtodisappearfromview.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
87/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.2SlipIndicatorsIssueB:January2008 Revision2 Page7of14
B2-13h Instruments Gyroscopic
Major Parts
Rotorspeedandrigidityiscrucialforthisinstrumenttoindicateaccurately.Ifspeeddropsoff,egsclogged filter inanair driven system, the gyrowill slowdownandwill thenprecess
furtherwithlessforceapplied(rememberfactorsthatcontributedtoamountofprecession,gyrorigidityandlevelofforceappliedtothegyro).Soaslowergyrowilloverread.Speedcontrolisreliableinelectricalinstrumentsbutinairdrivensystemsthepilotmustensurethevacuumgaugeisreadingcorrectly.Agaugereadinganincreasedvacuum(meaningnearly0psi)would indicate that the system filtersweredirtybecause the pump isevacuating thesystemduetothefactthataircannotcomeinthroughthefiltertoreplacetheairthepumpissuckingout.Thisindicationofagreatervacuum(almost0psia)meansthegyrorotorsofallthe air driven instrumentswouldbe running slower,and hence the turnand slip indicatorreadoutwouldbeinaccurate.LossofrigidityintheDGandAHwouldbecomeapparentduetothemdriftingoffmoreoften,buttheirreadoutswouldstillbereasonablereliable,whereastheturnandbankreadoutwouldbecompromised.Rotorspeediscrucialinaturnandbank.
Noerectionmethodisincorporatedinaturnandbankbecauseitisphysicallypreventedfrom
drifting off. It does have an earth rate correction in that the gimbals would be weightedappropriatetocounteracttheearthsrotation,butthisformofcorrectionisengineeredintotheturnandbankatthetimeofmanufacture.
Limitations of the Turn and Slip Indicator
TurnandSlip indicatorwill not respond toan aircraftbank, itwill only indicatea turn ifayawingmotionissensed.
-
7/25/2019 B2-13h Instruments Gyroscopic SR
88/104
Part 66 Subject
AA Form TO-19
B2-13.8.2.2.2SlipIndicatorsIssueB:January2008 Revision2 Page8of14