2010 L5 Introduction Rotor Craft

8/4/2019 2010 L5 Introduction Rotor Craft

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Unmanned Aircraft Design,Modeling and Control

VTOLAircraftLecture1:IntroductiontoRotorcraft

Dr.SamirBouabdallah

VTOL=VerticalTakeOffandLanding


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AircraftandSpacecraftSystemsDesign RotorcraftPart 2

Coursesectioncontents

Lecture1:Introductiontorotorcraft (today)

Lecture2:Dynamicmodelingofrotorcraft

Lecture3:Controlofrotorcraft

Lecture4:HelicopterElements:Rotorhead

Lecture5:OutlookonMAVResearch,UASCollisionAvoidance,Q&A


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Introduction

Unfortunately,theuseofhelicoptersisrestrictedtoapplicationswhereotherconceptsarenotsuitable!

Himaintenancecosts

Highpowerrequiredforflying

However,thehelicopterabilitytohover,allowsittolandalmosteverywhere

Idealforrescuemissions(inmountains,inoceans,...)

A helicopter is a collection of vibrations held together by differential equations John Watkinson

The helicopter is probably the most complex flying machine


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Ashorthistory

Chinesetops(2000yearsago...)

DaVincishelicalairscrew(1490)

FirstmannedhelicopterGyroplanNr.1byBreguet&Richet(1907)

Aflying...dreamer


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Typesofrotorcraft

Powerdrivenmainrotor+tailrotor

The

thrust

(T)

is

tothe

tip

path

plane

TheairflowsfromTOPtoBOTTOM

Tiltsitsmainrotortoflyforward

Helicopter

T

Undrivenmainrotor,tiltedaway

Forward

propeller

for

propulsion

TheairflowsfromBOTTOMtoTOP

Notailrotorrequired

Notcapableofhovering

exceptin:

Gyroplane(Autogyro)

wind

Powerdrivenmainrotor+tailrotor

Rearwardpropellerforpropulsion

Mainrotorremains//todir.offlight

TheairflowsfromTOPtoBOTTOM

Gyrodyne


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Rotorconfigurations

Contrarotating,noneedfortailrotor

Totaldiskarea< 2xdiskarea

TheCoGpositionisnotcritical

Muchlesssensitivetowinddirection

duringhovering

Tandemrotor(frontrear)


Higherefficiencyinforwardflight

Highstructuraldrag

Rarelyused

Tandemrotor(sidebyside)


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Rotorconfigurations

Intermeshedcontrarotatingrotors,(drivenbyonlyonegearbox)

Torquesdonotcancelperfectlyinthehorizontalplane

Theadvancingbladesareonthe

"inside(becauseofdragonthehull inFF)

Synchropter


Lossesduetoupperrotordownwash(somerecoveredfromtheswirlenergy)

Compactsize

Coaxial


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AirfoilTheoryin2D(seelecture#1)

Pressuredistributiononthesurfacecanbereduced to2forcesandonemoment:

Liftforce

Dragforce

Moment chordvSCM M 2

2

2

2vSCF DD

2

2vSCF LL

with

: Density of fluid (air)S : Wing area

v : Flight speed

CL : Lift coefficient

CD : Drag coefficient

CM : Moment coefficient


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Drag

Profiledrag isthedragincurredfromfrictionalresistanceofthebladespassingthroughtheair.

Induceddrag isthedragincurredasaresultofproductionoflift.Itistheportionofthetotalaerodynamicforce whichisorientedinthedirectionopposingthemovementoftheairfoil.(decreaseswithFwdspeed,thankstocleanair!)

Parasitedrag isthedragincurredfromthenonliftingportionsoftheaircraft(fuselage,etc.)


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Flightwitharigidrotorhead

Hover

Thrust(T)balancesexactlytheweight(W)

TheforcesonthebladesdoNOT varyastheyturn

T

W

Forwardflight Forward

speed

=

130mph Propellerspeed(linear)=420mph

Relativeairspeedunbalance

Maximum

speed

at

=90 (min.

at

=270)

Largeforceunbalance Largestress@rotorroot=largerollingmoment


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Forcesontherotorhead

gF

LiftF

gF

LiftF

gF

=0 >0

>0

Bladesareaffectedbycentrifugalforceduetorotationandliftingforce(leadstorotorconing)

Coningeffectslargemomentsatbladeroots


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Articulatedrotorhead

Reductionofstressatbladeroot

Rotorbladesarenotrigidlyattachedtohead,buthingesupported

Threejoints:Feathering,laggingandflapping

Flapping (up &down) Reduces stressdueto rolling moments

But,allows largeCoriolismoments inthe planeof rotation(dueto Centerof Mass displacement)

Flapping

Lagging

Feathering

Lagging (forward &backward) Releasesthe rotor from these Coriolismoments

Feathering

Enables

the

pitch

angle

to

be

changed


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Rotorcontrol:theswashplate

Swashplateconvertssteeringsignalinto

blade

pitch

change

(rotationaboutfeatheringaxis)

Collectivepitchforaltitudecontrol

Cyclicpitchforrollandpitchcontrol


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Gyroscopicprecession

Therotorofahelicopterisagyroscope

Anappliedforceismanifested90 laterinthedirectionofrotationfromwherethe

forcewasapplied.

Helicopterswithcontrarotatingrotors

minimize

the

gyroscopic

effect

(coaxial,synchropter,quadrotor,...)


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Stabilityaugmentation:theflybar

Gyroscopicbehavior

Actsonthefeatheringaxis

Slowstherateoftherotorchangeofattitude,

proportionallytotheflybarinertia

Theflybartiltisproportionaltotheroll (orpitch)rateofturn

the

angle

between

the

flybar

&

the

mast

is

a

measureofroll(orpitch)rate

E.g.TheBellbarsystem

Withsensorbasedcontrol,theflybarbecameobsoleteforfullscalehelicopters

Onsomemodelhelicopters(coaxial),theflybarisstillused(becauseofthehighdynamics)

IthasfullcontrolofpitchoftheupperrotorCourtesy of E-flight


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Thetailrotor

Thetailrotorprovidesatorquetobalancethemainrotorcountertorque

Variablebladepitchenablesyawcontrol

(BladepitchvariationbySwashplate mechanism)

(collectivepitchonly)

Fail Tail

Isthereapossibilitytogetridofthetailrotor?

TipJetHelicopters


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Tailrotoralternativeconcepts

Workslikeaductedfan

(tips

enclosed,

large

#

of

blades) Morequietandsafer

Tailboombehaveslikeawinginthemain

rotordownwash

(effectedbyairstreamfromCoanda*slots)

Highergroundclearance

Morequietandsafer

(*SeeCoandaeffect)

Fenestron NOTAR(NOTAilRotor)


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Groundeffect

Itisdueto: Theinterference ofthegroundwiththeairflowpatternoftherotorsystem

...Whichcausesreductionofthevelocityoftheinducedairflow

...Whichcauseslessinduceddragandamoreverticallift

FlyinginGEtendstoreducetherotortipvortex...Whichcauseshigherrotorbladeefficiency

upto~onerotordiameter.


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Kineticenergy

Groundspeed =Speedofapointonthehelicopter,seenfromtheground

Windspeed =Speedofaparticleofair(incaseofwind),seenfromtheground

Helicopterflyingat30ktINTO a30ktwind KE=m.V=m.(Airspeed Windspeed)

KineticEnergy:KE=0

Helicopterflyingat30ktWITH a30ktwind KE=m.V=m.(Airspeed+Windspeed)

KineticEnergy:KE>0

Airspeed = Groundspeed Windspeed

Ifcaseof180 turn LackofKE Altitudeloss

In

case

of

180 turn

Excess

of

KE

Altitude

gain


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HelicoptersattheUAVMAVsize

4rotorsincrossconfiguration

Directdrive(nogearbox)

Verygoodtorquecompensation

Hiagility

Quadrotor

Passivelystable

Compact

Suitableforminiaturization

Coaxial(swashplateless)

CGshift

Std.Helicopter

Veryagile

Complextocontrol


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References

BOOKS

J.Watkinson:TheArtoftheHelicopter

(mainsourceforthislecture,AvailableinNEBIS.CHinelect.format)

BramwellsHelicopterDynamics

R.W.Prouty:HelicopterPerformance,Stability,andControl

WEBSITES

http://www.cybercom.net/~copters/helo_aero.html(helicopter)

http://www.grc.nasa.gov/WWW/K12/airplane/short.html(general)


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AdditionalSlides


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HelicopterPrinciple


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AutogyroPrinciple


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NOTAR

2010 L5 Introduction Rotor Craft

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