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Waterrocketuseswaterasapropellant.
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Itisbasedonthe
NEWTONS THIRD LAW OF MOTION.
For a simple model, water rocket
consists
of
a
bottle
having
water
above
which there is pressurized air. On
launching, air pushes the water outside
providing the rocket an upward thrust.
PRINCIPLE
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Awaterrockethastwomainparts.
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BODY
1.Bodyofawaterrocket canbeassimpleas
asingle2lsoftdrinkbottleandalsoascomplex
asabodyofamultistagerocket.
2.Toachievegreatervolumeandaerodynamic
stability,twoormorebottlescanbe
splicedi.e.joinedtogetherasshowninthe
figurebelow.
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FINSWhydorocketshavefins?
1.Thepurposeofputtingfinsonarocketisto
providestability
during
flight,
that
is,
to
allow
therockettomaintainitsorientationand
intendedflightpath.
2.Finsaresymmetricallyplacedaroundthe
body(threeorfour),withenoughareaso
thatwhentherockettipsoffofitspatha
littlebit,thefinsprovideaerodynamicforce
toputitstraightagain.
3. Morethanfourfinsadddragandweight.
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Drag
> >
NOSE CONE1.Theconeisshapedtooffer
minimumaerodynamicresistance.
2.Itconsists
of
simply
top
portion
ofacolddrinkbottle.
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NOZZLE1. Nozzleservesthepurposeof
controllingthethrustprovidedbywater.
2.Smallerdiameternozzlescanbeusedtoprolongthetime
offlightbyreducedexhaust
rate.3.Inourcase,wewillhavea
fixedsize.Themouthofthebottlewillactasanozzle.
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LAUNCHERItactsasameanstopressurizetherocketwithair
andas
abase
to
provide
support
to
the
rocket
before
launch.
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MAKING OF A LAUNCHER
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CABLE TIES1. Theyhelptoholddownthe
rocketwhilefillingtheair.
2. Thecollarisapipethatcanslide
overtheinnerpipe.Whenpushed
up,itwillclosethecableties.(They
arein
open
position
in
the
above
pic).Whenclosed,theywillhold
thebottleandwillnotallowitto
movewhile
pressurizing.
The
collar
ispulleddowntoreleasethebottle
whendesiredpressureisreached.
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RELEASE MECHANISM
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PARACHUTETherocketusesaparachutetoincreasedragtoslowits
descent.
Ithelpsinthesmoothlandingoftherocketafterthefuelis
over.
Theparachuteisgenerallykeptinsidethenoseconebefore
launch.
Afterattaining
the
apogee
the
nose
cone
separates
from
the
rocketreleasingtheparachute.
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WORKING
Awater
rocket
works
using
the
sameprinciplesasotherrockets.
Therearethreemainforcesin
action:thrust(Fapp),drag(Ffr)and
weight(w=mg).
The
water,
which
is
forcedoutbythedifference
betweeninternalandatmospheric
pressure,is
areaction
mass
that
providesthethrust.
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Whenawaterrocketislaunched,the
differencebetweeninternaland
atmosphericpressures
forces
the
rocketoffthepressureseal,followed
bytheexpulsionofwaterandairout
ofthe
nozzle
until
the
internal
and
atmosphericpressuresareequalized.
Thisactioncreatesadownward
force,by
applying
Newtons
Third
LawofMotion.
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Pumpingair
into
the
bottleincreasesitspressure
Eventuallythe
nozzle
is
pushedoutallowingthewatertoescape
Theair
pushes
the
water
downwhichmeansthe
waterpushesitback.Thisforceisthentransferredtotherocket.
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Arocket'sstabilityiscriticalfor
achievinghigh
altitude
flights
an
unstablerocketwillgoupabout50
feet(max.)andthenflutterback
downtotheground.
STABILITY
Theruleisknownasthe
alphabeticalstabilityruleand
statesthat
G
comes
before
P(in
thealphabet).Fromthetopofthe
rocket,theCGcomesbeforethe
CP.
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Wecall
the
average
location
of
the
pressurevariationthecenterofpressureinthesamewaythatwe
callthe
average
location
of
theweightofanobjectthecenter
ofgravity.Theaerodynamicforces
liftanddrag actthroughthe
centerof
pressure
in
flight.
CentreOfPressure
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Thisis
because
the
aerodynamic
forcescenteredatthecenterofpressureareinthe
directionoftherelativewind(theoppositedirection
oftherocket).Iftherocketismovingup,the
aerodynamicforces
are
pushing
down
onit.Ifthecenterofpressureislocatedaftofthe
centerofgravity,theaerodynamicforceswillworkto
pull
the
bottom
of
the
rocket
backinlinewiththerelativewind,pointingtherocket
backinthedirectionoftherelativewind.Thismakesa
stablerocket.Ifthecenterofpressurewereforward
ofthe
center
of
gravity,
the
opposite
would
happen.
Theaerodynamicforceswouldpullthenoseinthe
oppositedirectionthatitshouldmove,causingthe
rockettospinoutofcontrolanunstablerocket.
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FLYING HIGHER
Usehigherpressuresbutinsafelimits(100psi)Keepweighttoaminimum.Increaserocketvolume.Streamlinethebodyoftherockettoreducedrag.Usetherightamountofwater(30to40%)Streamlinetheleadingandtrailingedgesofyourfins.
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WATER ROCKET WITH
BOOSTERS1.Oneofthepossiblemodificationsinthesimplewaterrocketis
makingwater
rocket
with
boosters.
2.Inourcase,inadditiontomainstage,wehavethree
dropawayboostersattachedwithittoincreasethe
launchvelocity
in
order
to
achieve
agreater
altitude.
3.Whenthewaterintheboostersrunsout,they
automaticallygetdetachedfromthemainbody,allowing
ittogomuchhighereasily.
4.We
are
going
to
attach
the
boosters
at
an
angle
of
120
degreestooneanothertomaketherocketstableduring
theflight.
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The 2004 w or ld record a l t i t ude for a w a te r bot t le rock e t
i s more than 300 met e rs .
The max imum a i r speed fo r a w a te r rocke t has been
c loc ked a t up t o 200 km /h
SOME PICS OF OUR BOOSTER WATER
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Pictureodf
main
stage
SOME PICS OF OUR BOOSTER WATER
ROCKET
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Photoof
components
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Contacts:-
Jeetesh Agrawal : 9795669413
Kratika Agrawal : 9616354932
Tushar Sikroria : 9450683065
http://students.iitk.ac.in/aeromodelling
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