(UNISIM(BEHAS) - Introduction to Aerospace)-EAS105 -Lab6

8/7/2019 (UNISIM(BEHAS) - Introduction to Aerospace)-EAS105 -Lab6

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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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IntroductiontoAerospaceEngineeringLab6

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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

(UNISIM(BEHAS) - Introduction to Aerospace)-EAS105 -Lab6

Documents

Transcript of (UNISIM(BEHAS) - Introduction to Aerospace)-EAS105 -Lab6