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MohdAshrafMohdIsmail
LaboratoryExperiment6
Name : Mohammed Ashraf Bin Mohammed Ismail
Student No: N0806406
Contact No: 98225529
Date Submitted:
Lab. : Anti Skid Braking Systems
Course Instructor: Mr Roger Chua
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Table of Contents
ABSTRACT .................................................................................................................. 3
INTRODUCTION.........................................................................................................4
OBJECTIVES................................................................................................................5
EXPIREMENT PROCEDURE.....................................................................................6
EXPIREMENT RESULT..............................................................................................7
TEST 1...................................................................................................................7
DISCUSSION OF RESULT........................................................................................10
CONCLUSION............................................................................................................11
REFERENCE .............................................................................................................. 12
APPENDIX..................................................................................................................13
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Abstract
This experiment provides an overview of the aircraft anti-skid system, which is design
to provide training on functional aircraft anti-skid braking system. The major features
of the system are its multiple disc braking system and associated anti-skid controls.
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Introduction
An aircraft anti-skid system is to prevent the wheel from locking while applying
brakes. This system will allow the wheel continue to roll forward and create a lateral
control as directed by the pilot during take off or landing.
The primary function of antiskid control is to reduce the force applied to the brakeswhen a skid condition is detected. The antiskid system detects an incipient skid of the
aircraft tires on the runway during braking. The goal of the antiskid system is to
control braking such that braking efficiency is maximized, tire damage is minimized,
and loss of aircraft control is prevented.
As the pilot applies pressure to the brake pedals, in the absence of an incipient skid,
the antiskid system does not interfere. When an incipient skid is detected, the antiskid
system overrides the pilot commanded pressure and reduces brake pressure by
dumping hydraulic pressure through an antiskid control valve, allowing the wheel to
spin up. When tire slip is reduced, the controller allows brake pressure to be
reapplied.
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Objectives
Toprovidetrainingonafunctionalaircraftanti-skidbrakingsystem.
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Experimental Procedure
Anti-SkidSystemTrainerOperation.
1.Preflight[aircraftstationary]
1.1Makesureallpowerswitches(master,drivewheel,hydraulicpump,and24VDC
powersupply)areturnedoffbeforepluggingtheunitin.
1.2Releasepressurebetweenfrictiondrivewheelandthetyrewiththetension
adjuster.Thefrictiondrivewheelshouldnotbeengagedwiththetyrewhen
startingthedrivewheelmotor.
1.3Placegearswitchindownposition.
1.4Placeanti-skidswitchinAnti-Skidmodeposition.
1.5Placesquatswitchinongroundposition.[ SquatSwitchOpen]
1.6Switchonthemainpowersupply(AC230V)onthewall.
1.7Turnonthe24VDCpowersupplylocatedonrearoftrainer.1.8Turnmasterswitchon.
1.9Busslightandgeardownlightshouldbeilluminated.
2.BeforeTakeoff[Startmoving][SquatSwitchisstillopen]
2.1Simulateenginestartbyturningonhydraulicpump.Whenthehydraulicsystem
is
functioningnormallyandbrakepressureisavailable,thesystempressureshouldbe
indicating500to1000psi,brakepressure0psi.
2.2Applybrake.Brakepressureshouldregisteronthebrakepressuregauge.
2.3Withbrakedepressed,setanti-skidswitchtoNormal/Test/Reset.Brake
pressureshouldregisteronthebrakepressuregauge.[ TestMode]2.4Ifthesystemisoperatingproperly,thiswillcausetheanti-skidsolenoidvalveto
directnormalpressuretothebrake.
2.5Thesystemwarninglightshouldremainilluminatedandnormalbrakepressure
shouldbeshownonthepressuregauge.
2.6Returnanti-skidswitchtoanti-skidmodeposition.[Thesystemwarninglight
shouldgooff.]
3.Takeoff
3.1Turnonthedrivewheelswitchtoturnonthedrivemotorandengagedrive
wheel.Themainlandinggearwheelassemblyspinsuptosimulatetakeoff.The
rotationofthewheelatfullsystemrpmrepresentsanactualgroundspeedofapproximately40mph.
3.2Placesquatswitchuptotheairborne(inflight)position[ SquatSwitchClosed].
Depressthebrakepedalandobserveanychangesonbrakepressure.[Theanti-skid
controlvalveopensandreleasesallbrakepressure.]
3.3Disengagethefrictiondrivewheel.[Atthispoint,youmayturnoffthedrive
wheelswitch.]Thissimulatestheaircrafttakeoff.Afterthewheelleavestheground
itsrotationreducesuntilthewheelstopsturning.
3.4Movethelandinggearselectortothegearupposition.
4.Cruise
4.1Applybrakes.Normalbrakeactionwilloccur.Thebrakepressureshouldregisteronthebrakepressuregauge.
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5.BeforeLanding[SquatSwitchisstillclosed]
5.1Movelandinggearselectortothegeardownposition.
5.2ThissystemfeaturesTouchdownProtectionwhichpreventstheapplicationof
pressuretothebrakesuntilthewheelshavespunup.Thispreventsinadvertent
(unknowingly)brakeapplicationattouchdown.5.3Toillustratethisfeature,pressthebrakepedals.Nopressureshouldregisteron
thebrakepressuregauge.
5.4Withthebrakepedalsdepressed,selecttheNormal/Test/Resetpositiononthe
anti-skidsystemswitch.Brakepressureshouldregisteronthebrakepressure
gauge.
5.5Inthispositiontheswitchsendsasignalthroughthewheelspeedsensors,
simulatingawheelspeedofgreaterthan20mph.
5.6Ifthesystemisoperatingproperly,thiswillcausethecontrolvalvetodirect
normalpressuretothebrake.
5.7Thewarninglightshouldremainonaslongasthetestswitchisinthe
Normal/test/resetposition.Normalbrakepressureshouldbeshownonthepressuregauge.
5.8Whentheanti-skidsystemswitchisreturnedtoAnti-Skidmodebrakepressure
willdroptozero,indicatingthattheanti-skidsystemisreleasingpressureoffthe
brakes.Theantiskidwarninglightshouldgoout,indicatingthatthesystemisinthe
anti-skidoperationmode.
6.Landing
6.1Tosimulatelanding,turnthedrivemotoronandengagethedrivemotoronand
engagethedrivewheel,causingtheaircraftwheelandtyreassemblytorotate.
6.2Movethesquatswitchtotheongroundposition.[ SquatSwitchOpen]
6.3Applymaximumpressuretothebrakepedal.Notethatitisimpossibletostoptherotationofthewheeltoinduceaskid.
6.4Thebrakepressurerisesuntilthewheelstartstoslow.Thesystemsensesthe
slowingofthewheelandopensthebrakevalveand,releasingthebrakepressure.
6.5Thewheelthenacceleratesto94%ofthesimulatedaircraftspeed.Thebrake
valveclosesandthecyclestartsagain.[Note:Ifthewarninglightcomeson,
increasesdrivewheeltension.]
6.6Thiscontinuesuntilthespeedoftheaircraftislessthan20mph.Atthispointthe
brakevalvecloses.Skiddingisnolongerasignificantoperationfactor.
6.7Atthispointtheanti-skidsystemisautomaticallydeactivatedtogivethepilot
fullcontrolofthebrakesformaneuveringandparking.
Note:Assoonastheairplanetouchesdown,thesquatswitchopensandthewheelstartstospinup.Bythetimeitreachesaspeedofabout20mph,thevoltagebeing
sentbythewheelspeedsensorishighenoughtocausethelockedwheeldetectorto
removethetouchdowncontrolsignalfromtheamplifier,andthecontrolvalvewill
allowfullpressuretobeappliedtothebrakes.
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Discussion of Result
ReportsI.Observations
1.Whatarethethreefluidlinesthatconnecttothepowerbrakevalve?
ThethreefluidlinesareSystemPressureLine,BrakeLineandReturnLine.
2.
Whenyouaretestingthebrake[BeforeTakeoff,step2.2andstep2.3],discuss
wheretheoutputflowfromthepumpgoesto,withreferencetothemovementofthespoolofthepowerbrakevalve,whenthebrakepedalis
(i) Depressedandheldsteady-When the brake pedal is depressed, theplunger spring moves the spool to the left, shutting off the passage to the
return line and connecting the pressure port to the brake line. If the brakepedal is pressed continuous steady, the combined force from the return
spring and fluid pressure on the spool moves the spool to the right justenough to shut off the passage to the pressure line. Thus it maintains a
constant pressure to set the brakes
(ii) Released-Whenthe brake pedal is released, the spool moves to the right,opening the passage between the brake and return line, thus releasing the
brakes.
3.Instep3.2,didyouobserveanypressurereadinginthebrakepressuregauge
whenyoudepressedthebrakepedal?Givereason.
In the airborne mode, the squat switch closes there deactivating the anti-skid. There is
no pressure reading in the brake pressure gauge when you depressed the brake pedal.
4.Duringstep5[BeforeLanding],whichmodeistheanti-skidswitchset?ItissettoTouchdownProtectionMode.
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5.(i)Whenyouareperformingstep5.3,whatdidyouobserve?
There is no pressure indication on the brake pressure gauge
ii)Whatdoyouthinkthepossiblecausesare?
When the aircraft is in the air mode, the brakes are deactivated to preventsinadvertently setting of brakes on at touchdown. The lock-wheel detector circuit to
send a signal through the amplifier to the antiskid control valve to port the hydraulic
pressure to the return manifold until the wheels have spun up minimum speed of
20mph.
(iii)Whatsystemfeatureisillustratedinthisoperation?
ItissettoTouchdownProtectionMode.
6.Insteps6.1to6.5,whatfunctiondoestheanti-skidcontrolsystemperform?
ItperformstheNormalSkidControlandtheLockedWheelSkidControl.
II.Writedowntheanswerstothefollowingquestions:
1.WritedownthenamesofthethreebasiccomponentsofanAnti-SkidControl
System.
a) Wheel-SpeedSensor(WheelDrivenGenerator)b) ControlBoxc) Anti-SkidSolenoidValve
2.Drawablockdiagramfortheabovethreecomponentsonly,showingthedirection
ofsignalflowsintherightorder.
3.NameFOURfunctionsperformedbyanti-skidcontrolsystemonanaircraft.
a) LockedWheelSkidControlb) TouchdownProtectionc) NormalSkidcontrold) Fail-SafeProtection.
4.Whatisasquatswitch?Brieflyexplainitsfunction/s.
Squat switch is an electrical device which senses the weight on wheel ( hence, it is
sometimes known as WOW switch ) to find out whether the aircraft is on the groundor in flight.
ControlBox
Wheel-Speed
Sensor
Anti-Skid
SolenoidValve
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III.Fromtheinternetoranyotherappropriatesource,findoutaboutthenew
developmentinaircraftantiskidbrakingtechnology.The latest development on the anti-skid is to use a Pulse Width Modulated (PWM)
anti-skid control valve.
The conventional approach to aircraft antiskid control is to use a servo valve to
control brake pressure. The latest development in Anti skid uses a Pulse WidthModulated (PWM) antiskid valve. The resulting system gives state of the art
performance at less weight and cost. Internally developed control algorithms drive
the PWM valve, perform the antiskid function, and incorporate features for safety,
performance, and maintainability.
Pulse-width modulation (PWM) of a signal or power source involves the modulation
of its duty cycle, to either convey information over a communications channel orcontrol the amount of power sent to a load.
An example of PWM: the supply voltage
(blue) modulated as a series of pulsesresults in a sine-like flux density
waveform (red) in a magnetic circuit ofelectromagnetic actuator. The
smoothness of the resultant waveformcan be controlled by the width and
number of modulated impulses (per
given cycle)
The advantage of using the Pulse Width Modulation are:
Shorter stop distance by optimizing tire slip force during braking and cornering
Excellent reliability through reduced mechanical complexity in the control valve
Fault Detection with modes for power up and operation as well as data storage Fail Safe Design through redundancies and if-then fault response
Compact size controller, antiskid valve and wheel speed transducer
Light Weight overall system through reduced power and complexity
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Reference
1. Anti Skid Goodrich 5th
October 2008.
2. Micheael J. Kroes, Willism A. Watkins, Frank Delp. Aircraft Maintenance &Repair. Sixth Edition. Macmillan/McGrraw-HillSchool Publishing Company,
1993.
3. Brake antiskid Control System control. General Atomics. 5th October 2008.
4.
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Appendix