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MODULE 11.10FUEL SYSTEMS

CONTENTS

10 SYSTEM LAY-OUT.........................................................................10-1

10.1 Rigid tanks.................................................................................10-1Rigid Metal Tanks........................................................................10-2

10. F!"#i$!" F%"! Tanks....................................................................10-&10.2.1 Tank Coverings..............................................................10-310.2.2 Self-Sealing Coverings..................................................10-410.2.3 Attachments and ittings...............................................10-4

10.& 'nt"g(a! F%"! Tanks....................................................................10-)10.3.1 Tank !"m#ering.............................................................10-$10.3.2 %ater &raining...............................................................10-'10.3.3 %ater Scavenge S(stem...............................................10-10

10.* s%++!, S,st"s.........................................................................10-11

10.) Engin" F%"! F""d.......................................................................10-1110.$.1 &esign Re)"irements of an Aircraft "el eed S(stem..10-1110.$.2 *ngine "el eed +M"lti Tank and ,ooster "ms/.......10-1210.$.3 *ngine "el eed +Collector Tanks/...............................10-1210.$.4 *ngine "el eed +"el Cells/.......................................10-13

10.6 %"! ""d /+n"nts...............................................................10-1*10..1 "el "ms +,ooster "ms/........................................10-1410..2 et "ms......................................................................10-110..3 Se)"ence alves...........................................................10-110..4 Transfer alves..............................................................10-1.. alve.....................................................................................10-1'Cross eed alve........................................................................10-1'

10. A2U F%"! F""d...........................................................................10-0

10.3 D%+ing4 5"nting and D(aining...............................................10-

10. D%+ing 7J"ttisn8....................................................................10-

10.10 T9" 5"nt S%$-S,st"................................................................10-)10.10.1 5eneral..........................................................................10-2$10.10.2 enting &"e to 6eat.......................................................10-2$10.10.3 7nress"rised S(stem enting......................................10-2$

10.10.4 ress"rised "el Tanks..................................................10-2$10.10.$ loat alves...................................................................10-210.10. ent ie &rains............................................................10-2'

10.11 C(ss-F""d and T(ans"(..........................................................10-&110.11.1 A"to 8 transfer...............................................................10-3110.11.2 Man"al 8 transfer...........................................................10-32

10.1 'ND'CAT'ONS AND :ARN'NGS................................................10-&&

10.1& F%"! L";"! S"nsing....................................................................10-&610.13.1 6igh evel Sensing........................................................10-310.13.2 9verflo: Sensing...........................................................10-3;10.13.3 o: evel Sensing.........................................................10-3;

10.13.4 Cali#ration Sensing +"el Trim onl(/..............................10-3;10.13.$ 7nder "ll evel Sensing...............................................10-3;

10.1* F%"!

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10.1) 2(in/i+!" Ca+a/itan/" Ga%ging............................................10-&3

10.16 F%"!

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10 SYSTEM LAY-OUT

The "rose of the f"el s(stem is to store and deliver f"el to the engines and thea". An aircraft m"st #e a#le to carr( s"fficient f"el to ena#le the engines tooerate over long eriods. to meet this re)"irement there m"st #e some :a( of storing this f"el safel( and s"l(ing it to the engines in a s"ita#le condition andat a controlled rate. A t(ical f"el s(stem therefore :ill consist of a n"m#er of tanks> f"el lines>connections and fittings> :hich are comati#le :ith all t(es of f"el meetingengine and a" secifications.9ften> the f"el s(stem is s"#divided into storage> ref"elling> distri#"tion> transfer>venting and indicating s"#s(stems.The follo:ing e=amle of a s(stem la(o"t is for a t(ical large commercial t:inaircraft. The n"m#er of tanks and s(stem comle=it( :ill var( from aircraft toaircraft. Clearl( a fo"r-engine aircraft :ill have more comonents than a t:in.The fig"re sho:s a t(ical f"el cell la(o"t

T,+i/a! F%"! C"!! La,%tFig%(" 1

!9T*? or additional range> some oerators :ill install centre tanks> these areoffered as otional on most single isle and :ide #odied aircraft."el Tanks

"el tanks normall( fall into three categories of constr"ction?• Rigid

• le=i#le

•

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These are normall( made from metal or lastic material> the( are fitted internall(:here sace ermits. le=i#le f"el tanks have an advantage over rigid tanks>

#eca"se the( can #e shaed and fitted into odd shaed saces :here rigid tankscannot #e fitted. fle=i#le tanks are lighter and easier to handle andstore than rigid tanks. f"el tanks sho"ld #e shaed so that almost allthe f"el is availa#le to the engine. A:k:ard ockets :hich revent f"el fromleaving the tank are "ndesira#le and are avoided if ossi#le.

10.1.1 Rigid Metal Tanks

T,+i/a! Rigid 'nt"(na! F%"! TankFig%("

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"el tanks are made in shaes and si@es to fit the saces availa#le in eachartic"lar airframe and therefore the si@e and shae of the f"el tanks :ill not #e

the same for all aircraft. Metal f"el tanks are constr"cted from al"mini"m allo(>stainless steel or tinned steel and the( are riveted> :elded> or soldered together.The tank is a light str"ct"re :hich is strengthened #( the "se of internal stiffeners>angle ieces and #( incororating #affles to give strength and :hich arenecessar(> in large tanks> to red"ce the effects of f"el s"rge ca"sed :hen theaircraft manoe"vres. Sec"re attachment of a rigid tank :ithin the airframe ma(#e achieved #( #"ilt-in added cradles and added metal stras. The cradle isshaed to match the conto"rs of the tank and the stras sec"re the tank to itscradle. *ach tank :ill have the #rackets> stra g"ides and fittings to match theaircraft str"ct"re into :hich the tank is to #e fitted. a greater f"el caacit(is made availa#le to a artic"lar aircraft :hen fle=i#le tanks are "sed. Someaircraft f"el s(stems are designed to incl"de rigid> fle=i#le and e=ternal f"el tanksso that the greatest ossi#le f"el load is carried.The comartment for a fle=i#le f"el tank is made as smooth as ossi#le on theinside and roecting oints are covered to revent chafing the tank material.,efore a tank can #e fitted> the comartment m"st #e roerl( cleaned o"t and alls:arf and loose items removed. After a fle=i#le tank has #een inserted into the tank comartment> the tank iscaref"ll( "nfolded and the vario"s e=ternal fittings are aligned. 7s"all( the :alls

of the more fle=i#le tanks are attached to the comartment :alls #( a t(e of ress-st"d fitting. %hen filled :ith f"el> the tank e=ands to contact the :alls of the tank comartment so that the :eight of the f"el is carried #( the aircraftstr"ct"re and not #( the tank. ,eca"se the load is not carried #( the tank> fle=ingof the aircraft str"ct"re does not imose harmf"l loads "on the tank material.le=i#le f"el tanks are resilient> like an inner t"#e and #eca"se the( are resilient>the tanks can :ithstand a considera#le amo"nt of distortion or shock loading.

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10.2.1.1 R9T*CT A rotective covering ma( #e fi=ed to the o"tside of a fle=i#le f"el tank. The

covering is not secial to t(e and similar covering materials are "sed to rotectdifferent t(es of tank. The rotective covering "s"all( consists of several la(ersof fa#ric> or fa#ric and r"##er> :hich are cemented to the material of the tank :ithadhesives. %hen a tank is fitted :ith a rotective cover it> in general> #ecomesstiff eno"gh to s"ort its o:n :eight and retain its shae. 6o:ever> :hen thevario"s metal fittings are added> the tank :ill sag and it needs s"ort :henfitted.Some tanks> :hich do not have rotective covers> are reinforced #( n(lon fa#ricor net. This t(e of reinforcement does not stiffen the tank> :hich remains ver(fle=i#le and lim. This t(e of tank cannot s"ort its o:n :eight and is the t(e:hich is sometimes called a B#ag tank.


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10.2.2 Self-Sealing Coverings

These coverings have #een develoed to red"ce the magnit"de of a f"el leak if>for an( reason> the f"el tank is ierced or r"t"red. The self-sealing covering is"s"all( made from la(ers of cell"lar r"##er :ith an overall rotective cover of glass fa#ric or n(lon fa#ric on the o"tside. This t(e of r"##er is a material that isimmediatel( affected #( contact :ith f"el. the cell"lar r"##er s:ells on contact :ith the f"el and forces its :a( into the "nct"re to #lock thehole and red"ce or sto the leak. 7nfort"natel(> minor leaks ma( remain"ndiscovered for some time "ntil the self-sealing cover #egins to s:ell and #"lgeon the o"tside.

10.2.3 Attachments and ittings

To comlete a fle=i#le f"el tank> rovision m"st #e made for attaching f"el s(stemcomonents and for oining each tank into the f"el s(stem. The f"el tank isconstr"cted :ith mo"lded connectors and aert"res of an aroriate si@e andosition #"t #eca"se of the fle=i#le nat"re of the material> each aert"re needs to#e reinforced #efore a s(stem comonent can #e fitted. *ach aert"re isstrengthened and stiffened #( fitting a metal attachment ring. The attachmentrings are sometimes called Bst"d rings or B#olt rings.

Atta/9"nt Rings and M%!d"d Cnn"/tinsFig%(" &

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10.& 'nt"g(a! F%"! Tanks

rimar( :ing str"ct"re is "sed for aircraft integral tanks. The( are normall(located #et:een the front and rear :ing sars and #et:een the "er and lo:er :ing skin. Solid Btank end ri#s close the ends of each tank> :hile all the other ri#sact as f"el #affles to minimise f"el slosh. 9ften a centre tank traverses thef"selage #et:een the t:o inner :ing root ri#s. All f"el tanks are f"el tight. Close metal-to-metal fit of all arts forms the #asicseal> :ith sealing como"nds and sealing fasteners on all oints to comlete thefl"id tight seal. The centre tank :ill have a secondar( e=ternal #arrier coating torevent f"el vao"r entering the ress"rised section of the f"selage.Some of the :ing ri#s contain a series of free-s:inging> f"el-act"ated #afflecheck valves> to revent f"el flo: a:a( from the electric #oost "ms. Access

anels> "s"all( on the "nderside of the :ing> rovide access to each tank. Theo"ter ortion of the :ing rovides f"el overflo: #( means of a s"rge tank> :hichalso affords venting into the s(stem.The f"el tanks hold all the necessar( e)"iment for ref"ellingD de-f"elling andengine f"el feed. *)"iment "sed for f"el )"antit( indicating is also contained:ithin the f"el tank str"ct"re.

10.3.1 Tank !"m#ering

The maorit( of aircraft carr( f"el onl( in :ing and centre tanks. 6o:ever> a fe:Be=tended range aircraft :ill have an additional integral tank in the verticalsta#iliser. Aircraft man"fact"rers n"m#er f"el tanks> in :hich case the hilosoh(

:ill #e from left to right> nose to tail. 5enerall(> f"el tanks are n"m#ered as sho:nin ig 4.

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'nt"g(a! F%"! TanksFig%(" *

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Tank A//"ss 2an"!sFig%(" )

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Ba!" C9"/k 5a!;"sFig%(" 6

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,efore assem#l(> all the str"ct"ral arts that #ecome integral f"el tanks arecleaned to a artic"lar secificationE the clean arts are immediatel( coated :itha secial sealant and assem#led :et. the oint can #e covered #( a #arrier coating of a )"icker dr(ing s"#stance. The#arrier-coating material is not the same as the sealant "sed for ointing and it :illnot revent or c"re leaks. The #arrier-coat #ecomes tack-free in a relativel( shorttime and it is alied over artiall( c"red sealants to red"ce the ossi#ilit( of contamination from s:arf> :hen :ork m"st contin"e in the area of an "nc"red oint. To e=tend the leak-free life of the integral f"el tank> take great care :henhandling or :orking on the skin area :hich covers the integral f"el tank.

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'nt"g(a! Tank S"a!ingFig%("

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5enerall( seaking> large commercial aircraft have three tanks in each :ing>inner f"el tank> o"ter f"el tank and a s"rge tank. 9n some aircraft the f"el tanksare referred to as f"el cells. A centre tank is sometimes availa#le as a standardotion.Each f"el tank has additional sace for 2F e=ansion of the f"el :itho"t sillageinto the s"rge tank. Remova#le access anels are rovided in the lo:er :ings"rface. The centre tank> if fitted> is accessi#le thro"gh manholes in the rear sar.

10.3.2 %ater &raining

%ater drain valves are rovided at lo: oints of each tank. All valves ma( #eoened :ith standard tools and the o"ter seal of the valve is relacea#le :itho"temt(ing the tanks.

:at"( D(ain 5a!;"Fig%(" 3


'nt"g(a! Tank S"a!ingFig%(" *

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F%"! Tank D(ain 2intsFig%("

10.3.3 %ater Scavenge S(stem

A t(ical s(stem has a :ater scavenge s(stem fitted in the otional centre tank.T:o et "ms "sing taings on the tank "ms for motive o:er> collect :ater

from lo: oints and discharge it to:ards the f"el "m inlet. Remova#le accessanels are rovided in the lo:er :ing s"rface. The otional centre tank isaccessi#le thro"gh t:o manholes in the rear sar.

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:at"( S/a;"ng" S,st"Fig%(" 10

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10.* s%++!, S,st"s

10.) Engin" F%"! F""d

10.$.1 &esign Re)"irements of an Aircraft "el eed S(stem

9n an aircraft> a f"el s(stem sho"ld #e designed to coml( :ith man(re)"irements as laid do:n in oint Air:orthiness Re)"irements. An e=amle of these re)"irements is as follo:s?

1. *ach f"el s(stem sho"ld #e constr"cted and arranged to ens"re a flo: of f"elat a rate and ress"re to ens"re roer f"nctioning of the engine for eachlikel( oerating condition.

2. The f"el s(stem m"st allo: the s"l( of f"el to each engine thro"gh a

s(stem indeendent of the s(stem s"l(ing f"el to an( other engine.3. The s(stem design sho"ld #e s"ch that it is not ossi#le for an( "m to dra:

f"el from t:o or more tank sim"ltaneo"sl( "nless means are rovided torevent the introd"ction of air into the s(stem.

4. the f"el tank ventsand transfer s(stem m"st #e designed so that no str"ct"ral fail"re can occ"r #eca"se of over-filling.

$. ventilated and drained to the o"tside> 9R consist of a ie :itho"t fittings andro"ted or rotected against accidental damage.

. The s(stem shall incororate means to revent the collection of :ater and dirtor the deosition of ice or other s"#stances from satisfactor( f"nctioning of the s(stem.

'. ines> :hich can #e isolated from the s(stem #( means of valves or f"elcocks> shall incororate rovision for the relief of e=cess ress"re d"e to

e=ansion of the f"el.10. *ach f"el tank filler connection m"st #e marked :ith t(e of f"el and #e

rovided :ith a #onding oint and drain discharging e=cess f"el.

11. There m"st #e a f"el strainer at each f"el tank o"tlet or for the #ooster "m+s/.

12. *ach f"el line m"st #e designed> installed and s"orted to revent e=cessivevi#ration and allo: a reasona#le degree of deformation and stretching :itho"tleakage.


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10.$.2 *ngine "el eed +M"lti Tank and ,ooster "ms/

M"lti tank f"el s(stems can "se a lo:-ress"re f"el #ooster "m in each tank as

sho:n.

L/atin 2%+ Canist"( Ass"$!i"sFig%(" 11

The "ms are located in collector tanks :hich are e)"ied :ith check valves:hich rovide a one :a( f"el flo:.10.$.3 *ngine "el eed +Collector Tanks/

Rather than "se #ooster "ms in each tank> some aircraft f"el s(stems "segro"s of tanks that feed collector tanks as sho:n in the diagram.

Engin" F%"! F""d C!!"/t( Tanks

Fig%(" 1

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10.$.4 *ngine "el eed +"el Cells/

Another m"lti tank s(stem is the "se of fire cells. eachengine is s"lied from one "m in the otional centre tank or #oth "ms in thetank of its o:n :ing. An( one "m can s"l( the ma=im"m demand of oneengine. A cross-feed ie> controlled #( a do"#le motor act"ated sherical l"gvalve> allo:s #oth engines to #e fed from one side or all the f"el to #e "sed #(one engine. The valve is mo"nted on the rear sar in the centre section.

T:o l"g-in a.c. driven #ooster "ms s"lied from different #"s#ars are fitted ineach tank. *ach "m has a s"ction inlet. 9n each side> the t:o "ms in the:ing tank and one "m in the centre tank +:hen fitted/ deliver f"el via a #"ilt innon-ret"rn valve into a single ie. The "ms in the :ing tanks are fitted :ith

ress"re relief se)"ence valves that ens"re that :hen all "ms are r"nning> thecentre tank "ms :ill deliver f"el referentiall(. !o se)"ence valves arerovided on a t:o tank version aircraft.

the t:o act"ators are s"lied fromdifferent #"s#ars and the ca#les are ro"ted searatel(.Controls and indications for "ms and crossfeed valves of the feed s(stem arelocated on the overhead anel. all :ing "ms :ill remainon thro"gho"t the flight. s:itching of "ms is a"tomatic.

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Engin" F%"! F""dFig%(" 1&

10.6 %"! ""d /+n"nts10..1 "el "ms +,ooster "ms/

"ms emlo(ed in aircraft f"el s(stems differ in si@e> shae> o"t"t> etc.6o:ever regardless of t(e and an( secial feat"res the( ma( have> the( alloerate on the same rincile and consist of ver( similar comonents.*ach tank is normall( rovided :ith t:o f"el "ms. The( are all identical andinterchangea#le. These "ms are installed in the canister assem#lies to ena#lerelacement :itho"t de-f"elling the tank.The f"el "ms are centrif"gal "ms driven #( 11$ volts> three hase motors.The o"t"t of each "m is a#o"t 2$0-300 litres er min"te. Ma=im"m f"elress"re at @ero flo: is a#o"t 3 .s.i.*ach "m incl"des a non-ret"rn and a #(-ass valve.The #(-ass valve is to red"ce the ress"re dro allo:ing an engine to #eoerated on s"ction feed " to a#o"t 000 feet.

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The( are rotected #( a thermal f"se> :hich is activated at aro=imatel( 1;$

degrees centigrade.

Fig 1*

Some "ms have secial feat"res that are dictated #( the aircraft role and an(design re)"irements namel(?a. ress"re relief valve.#. !on-ret"rn valve.c. AC &C motor.d. Thermal tri devices.

e. Cannister sh"t off valve to facilitate "m relacement :ith f"el in the tanks.


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Cannist"( Ass"$!,Fig%(" 1)

10..2 et "ms

These are another method of transferring f"el aro"nd an aircraft f"el s(stem.

The( "se f"el #led from the #ooster "m :hich is contin"all( fed thro"gh thecentral no@@le into a vent"ri. The deression created in the vent"ri dra:s f"elfrom the s"rro"nding tank> in thro"gh the filter then " thro"gh the vent"ri t"#eand either into the ne=t f"el tank or straight to the collector #o=.

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JET 2UM2

F'GURE 16

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Fig%(" 1

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10..3 Se)"ence alves

Se)"ence valves are fitted to give an a"tomatic transfer from one tank to another>the follo:ing e=amle is for an aircraft :ith "ms in the centre tank> inner tankand o"ter tank.The valve limits the f"el ress"re of the o"ter tank "ms from 3 si to 1;.$ si.This is to give riorit( to the inner tank f"el "ms for str"ct"ral reasons.%hen the inner tanks are emt(> the engines :ill #e a"tomaticall( s"lied fromthe o"ter tanks So the o"ter f"el "ms r"n contin"o"sl(.

S"=%"n/" 5a!;"sFig%(" 13

10..4 Transfer alves

The e=amle at fig"re 13 sho:s the f"el tank slit into t:o cells at ri# 1$. Toena#le transfer to take lace> t:o transfer valves are fitted in this instance at ri#1$. 9eration of these valves is act"ated #( a signal from lo: level sensorssho:n "st in#oard of ri# 2.

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10..$ .. alve

alve

Fig%(" 1

The .. sh"t off valve ena#les isolation of the f"el s(stem in the event of fire andengine maintenance> i.e. engine removal. ocated at the to of the (lon on theo"tside of the front :ing sar it :ill #e controlled normall( #e oeration of the firehandles and activated #( either a air of electric motors or mechanicall( assho:n a#ove.10.. Cross eed alve

Cross-feed alve

Fig%(" 0


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The cross feed valve ena#les f"el to #e fed to an( engine from an( tank.

!ormall( of a sherical t(e constr"ction :ith t:o 2 &C electric motorsmo"nted on a differential gear#o=. 9ne motor onl( :ill drive the valve at an(time> the other motor is a #ack ". The cross feed valve :o"ld normall( #e fittedon the rear sar as sho:n in the fig"re.10. A2U F%"! F""dThe feed to the A7 is taken from the left engine feed #"t ma( #e taken from theright engine feed :hen the cross feed valve is oen.The tank #ooster "ms can s"l( f"el to the A7 at the re)"ired ress"re. or starting the A7 :itho"t electrical o:er availa#le for the tank "ms> a searate"m is rovided that can #e oerated from the aircraft #atteries and is mo"ntedin the feed line on the rear sar of the centre section.

The s"l( of f"el to the A7 can #e sh"t off #( a valve mo"nted on the rear sar of the centre section. the t:o act"ators are s"lied fromdifferent #"s#ars and the ca#les are located in searated ro"tes.The feed ie emerges from the to of the tank and asses thro"gh theress"rised f"selage in a drained and vented shro"d that e=tends to the A7 fire:all.

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A2U F%"! ""dFig%(" 1


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10.3 D%+ing4 5"nting and D(aining

10. D%+ing 7J"ttisn8"el ettison s(stems are fitted to a n"m#er of large commercial aircraft to allo:the ettisoning of f"el in an emergenc( th"s red"cing :eight so as to reventstr"ct"ral damage :hen landing."el ettison s(stems are often fitted after the installation of a centre tank>#eca"se of the e=tra f"el :eight.The s(stem ill"strated is from a :ide-#odied t:in fitted :ith m"lti tanks and#ooster "ms. The ettison ie is #ranched off the feed ie #et:een the inner tank f"el "m and the inner tank sh"t off valve. A check valve is installed to searate the o"ter tanks d"ring ettisoning. Thef"nction of this check valve is to revent the d"ming of the o"ter tanks f"el. The

ettison ie r"ns inside the :ing tanks thro"gh the ri#s into the o"ter tanks>:here the ettison valves are installed. These valves are fitted to the #ottom of the tank.

J"ttisn S,st"Fig%("

,eca"se of electrical emergenc( sit"ations> the valve :ill #e driven #( t:o 2&C electric motors. The motors are mo"nted from the o"tside and are attachedto the #ottom of the tank thro"gh a gear#o= and in man( instances areinterchangea#le :ith the cross feed valves.

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Sh"t 9ff alveFig%(" &

The o"tlet of the ettison ie is normall( at the end of the fla track fairing andfitted :ith an anti corona device to avoid vaorisation of the f"el. A normaltransfer rate :ill #e in the region of 30-3$0 litres er min"te.

F%"! J"ttisnFig%(" *


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The ettison oeration is controlled from a ettison anel located either on a flight

engineers station or from an overhead anel on a t:o cre: config"ration.!ormall( the anel is rotected #( a )"ick release cover. t:o s:itches are rovided to oerate the ettison valve.

i. A rimar( s:itch for motor n"m#er one.

ii. A g"arded secondar( s:itch for motor n"m#er t:o.

F%"! J"ttisn Cnt(!Fig%(" )

The osition of the right and left-hand ettison valve is monitored #( t:o magnetic

indicators> sho:ing green cross-line :hen the valve is closed and in-line :henthe valve is oen. As is common :ith this t(e of indicator> it :ill sho: am#er cross-line to indicate transit or malf"nction.

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10.10 T9" 5"nt S%$-S,st"

10.10.1 5eneral An air vent is fitted to the to of each tank to allo: free flo: of air in and o"t of thetank as the f"el level rises and falls. This is kno:n as in:ards and o"t:ardsventing and is re)"ired to revent over ress"risation of the tanks as the f"ellevel rises and deress"risation as it falls.10.10.2 enting &"e to 6eat

Another imortant asect of an aircraft vent s"#-s(stem is that it m"st #e a#le tocoe a"tomaticall( :ith an( e=ansion andDor contraction of the f"el. As the f"ele=ands> d"e to heat> the vent m"st allo: air and sometimes f"el> to escae toatmoshere via vent ies. Conversel( the s"#-s(stem m"st allo: air into thetanks d"ring contraction of the f"el :hen the o"tside air temerat"re +9AT/ is

decreasing.10.10.3 7nress"rised S(stem enting

This is a ver( simle method of venting tanks :hich re)"ires onl( that f"el tankvent orifices #e connected to a vent ie galler(> :hich leads to atmosheredirectl(. enting of this t(e is fo"nd mainl( in small aircraftE some helicotersand aircraft :ith lo: flight ceilings.The disadvantages of Goen orificeH or Goen ventedH tanks are that the( ares"#ect to f"el venting d"ring manoe"vres> the( limit the ma=im"m ceiling of theaircraft d"e to the fact that f"el #oils at the lo: am#ient atmosheric ress"refo"nd at altit"deE danger of cavitation in f"el s"l( lines if f"el sho"ld #oilEincreased rate of evaoration +R* as long as one or more f"el "ms arer"nning. 9n some aircraft f"el "ms are fitted to "m the f"el #ack to thetanks from the s"rge tank and :ill #e activated #( a float s:itch.*ach vent tank is vented to atmoshere via the !ACA valve.This valve ens"res tank ress"risation d"ring flight and allo:s the f"el to flo: o"t

in the event of a high level c"t-off fail"re d"ring ref"elling.


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9n some aircraft a frangea#le disc is fitted in the s"rge tank to revent str"ct"raldamage ca"sed #( over ress"re. A flame arrester is also fitted in the !ACA

intake in case of gro"nd fires.

5"nting S,st"

Fig%(" 6

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Fig%("

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10.10.$ loat alves

*ach :ing tank is rovided :ith an additional vent oening.

This oening is connected to the corresonding venting line and controlled #( avent float valve sit"ated at the highest oint of the tank.

5"nt F!at 5a!;"Fig%(" 3

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10.10. ent ie &rains

At the lo:est oints of each vent ie> a self-draining non-ret"rn valve is

connected. The t(e sho:n is made of s(nthetic r"##er.

5"nt D(ain 5a!;"

Fig%("


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The "se of the centre :ing #o= as a tank on some aircraft has made it necessar(

to rotect this area against leaking f"el. A vao"r seal is installed aro"nd thefor:ard and lo:er art of the tank. The sace #et:een the tank sink and thevao"r seal is ventilated :ith air coming from the air conditioning s(stem. The air is directed to the o"tside thro"gh several small o"tlets.

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10.11 C(ss-F""d and T(ans"(

Cross-feed alves ermit the transfer of f"el from an( tank to an( engine>:hereas Transfer alves ena#le f"el to #e transferred from tank to tank.

10.11.1 A"to 8 transfer

%hen an aircraft has a :ing :ith lateral dihedral the f"el "ms :ill normall( #ein#oard and the f"el flo: to:ards the :ing root. %hen the :ing contains morethan one tank> the o"t#oard tank :ill a"tomaticall( transfer into the in#oard tankand so #e the first to emt(. Since the in#oard tanks :ill #e feeding the engines>a transfer valve #et:een the in#oard and o"t#oard tanks :ill #e oeneda"tomaticall(> :henever a high level float s:itch in the in#oard tank detects it

#eing not f"ll.

C(ss F""d Cnt(! 2an"!Fig%(" &1


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Fig%(" &

10.11.2Man"al 8 transfer

!o in-flight transfer of f"el #et:een left and right mainlanes is ossi#le forreasons of trim. 6o:ever f"el can #e fed from an( tank to an( engine #( meansof #oost "m selection and the oening of a crossfeed valve from the flight

deck.

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10.1 'ND'CAT'ONS AND :ARN'NGS

rovision is made to disla( f"el tank )"antit(> #oost "m lo: ress"re>crossfeed valve and f"elDfire sh"t off valve osition> on the flight deck overheadanel. Tho"gh the la(o"t :ill var( from aircraft t(e to t(e> generall( it :ill #esimilar to the e=amles sho:n #elo:.


O;"(9"ad +an"! - 2%s9 s>it/9 t,+"Fig%(" &&

O;"(9"ad +an"! - Tgg!" s>it/9 t,+"Fig%(" &*

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Additionall(> a"ral and vis"al :arnings on the glare shield :ill res"lt if the f"el

s(stem develos a fa"lt.

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G!a(" S9i"!d and Fi(" :a(ning 2an"!Fig%("&)

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ECAM S,st" Dis+!a,Fig%(" &6


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10.1& F%"! L";"! S"nsing A modern aircraft :ill "se thermistors to send signals thro"gh amlifiers to

act"ate :arnings> se)"encing> etc. 9lder aircraft ma( "se float s:itches assho:n in the follo:ing diagram.

L> L";"! S"nsingFig%(" &

loat oerated s:itches are of a magnetic t(e> similar to the one sho:n a#oveand are designed to isolate the electrical mechanism from the f"el tank for safet(reasons. 7:ard movement of the float #rings the armat"re closer to the magnetand at a redetermined f"el level> it has s"fficient infl"ence to attract the magnet>:hich res"lts in oeration of the micro s:itch. As the f"el level and the float fall>the attraction of the armat"re is event"all( overcome #( the com#ined forces of

the co"nter:eight and the micro s:itch sring and the co"nter:eight falls>changing the micro s:itch circ"it.

%hether the( are float s:itches or thermistors> their f"nctions are as follo:s.

1 6igh level sensing.2 9verflo: sensing.3 o: level sensing.4 7nder f"ll level sensing.$ evel sensing for cali#ration +"el Trim onl(/.10.13.1 6igh evel Sensing

6igh level sensing is installed to revent an overfilling of the f"el tanks. %hen thef"el :ashes aro"nd the resective sensor> the?

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• associate ref"elDdef"el valve closes.

• #l"e 7 light on the f"elling anel comes on.

The high level signal from the inner and o"ter tanks co"ld #e "sed for com"tation "roses in the f"el )"antit( com"ter> :hen ref"elling in A7T9M9&*.10.13.2 9verflo: Sensing

the associated am#er 9 light comes on.The innerDcentre tank lo: level sensing have onl( in the A7T9 M9&* a f"nction+ref. f"el "m control/.10.13.4 Cali#ration Sensing +"el Trim onl(/

Cali#ration sensors are installed in centre tanks> inner tanks and trim tank. The(give a signal at a redetermined filling level in the trim tank for acc"rac( test of the f"el )"antit( indication d"ring ref"elling. or the trim tank the cali#rationsensor s:itching level is corrected #( the sta#iliser osition.10.13.$ 7nder "ll evel Sensing

%hen the f"el )"antit( dros in either o"ter tank #elo: a certain level> thema=im"m flight seed +M9/ #ecomes red"ced in order to rotect the :ingstr"ct"re. The sensor signals are sent to the A&C +Air &ata Com"ter/.

10.1* F%"!

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10.1) 2(in/i+!" Ca+a/itan/" Ga%ging A caacitor is an electrical device :hich stores electrical charge. The amo"nt of

charge it can hold deends "on three h(sical roerties of the caacitor itself>namel(?

a. The s"rface area of the lates.#. The si@e of the ga #et:een the lates.c. The ins"lating material +dielectric/ #et:een the lates. is either f"el or air or #oth. The amo"nt of charge held in the caacitor>:hen the tank is f"ll> :ill #e of a reset val"e. As the f"el level falls> the dielectric:ill grad"all( change to air and the amo"nt of charge stored :ill red"ce. Thischange in caacitance is sensed #( a signal conditioner and the change in f"ellevel is th"s sensed.10.16 F%"!

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The ro#es of each gro" are :ired in arallel and connected to a s"mming

adater> located on the :ing rear sar. The ro#e level signals are sent to thef"el )"antit( com"ter.

:ing Ca+a/itan/" 2($" 'nsta!!atinFig%(" &3

10.1.1 Caacitance

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The "rose of the inde= comensator is to sense the different t(es of f"els>additives> etc. and make correction signals for acc"rate f"el readings.

Ca+a/itan/" 'nd"# C+"nsat( - 'nsta!!atinFig%(" &

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2($" 'nsta!!atin ? T(i TankFig%(" *0


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10.1.2 Meas"rement

The signals from the caacitance ro#es in each tank are sent via adaters to thef"el )"antit( com"ter. The com"ter calc"lates the f"el )"antit(. To increasethe meas"ring acc"rac(> f"rther signals enter the com"tation?

• caacitance inde= comensator> #alances different f"el t(es.

• Condensicon sensor?

Senses :hile ref"elling the?&ensit(&ielectric constant of r"nning f"el.

• Attit"de Sensor?

Senses on gro"nd and in flight the attit"de of the aircraft to the?Roll a=is +longit"dinal/itch a=is +lateral/The attit"de signal com"tation deends on the A an innerand an o"ter tank.

!ote? The 9 lights in the indicator receive their signals from the o"ter tank9 sensing circ"it.

10.1 R"%"!!ing and D"-%"!!ing

10.13 R"%"!!ing As (o" :ill #e a:are> as an( li)"id flo:s thro"gh a ieline> it :ill rod"ce Static Electricity. an e=losion :o"ld res"lt> :ith ossi#le catastrohic res"lts.To therefore minimise the e=losion risks> the follo:ing g"idelines m"st #efollo:ed.Safet( reca"tions?

• Use correct grade of fuel (Av-gas, Av-tur, Av-tag).

• No smoking within 15m.

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• No metal studded or tipped footwear.

• orrect !onding of Aircraft and "owser.

• orrect positioning of "owser.

• No vehicles or #round $%uipment under the aircraft.

• &aintenance activit' kept to a minimum.

• No replenishment of *.

• No transmitting of +adar

• Aircraft "owser not to !e left unattended.

• heck and remed' fuel spillage or leakage.

• Appropriate ire Appliance readil' availa!le.

• he electrical state of the Aircraft must not change while connected

to the "owser.

Ref"elling a small aircraft is no more comle= than filling the famil( car. 9nelimitation is that on some aircraft it is not ossi#le to fl( the aircraft :ith all theseats occ"ied :ith f"ll #aggage allo:ance> when the tanks are full. This meansthat if the aircraft is to #e flo:n f"ll( loaded> it ma( #e necessar( to re-f"el to lessthan full, to kee the aircraft :ithin its :eight limits. As the aircraft #ecome more comle=> the ref"elling e=ercise has to #e carriedo"t :ith more care. there are several f"rther ro#lems to consider. !otonl( m"st the aircraft #e filled laterally in the correct order #"t> if the aircraft hasthe fin> taillane and rear f"selage tanks mentioned earlier> it m"st #e ref"elled inthe correct order longitudinally as :ell to ens"re the aircraft sta#ilit( ismaintained.


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Modern large aircraft "tilise ress"re ref"elling> :hich has relaced oen lineref"elling on most aircraft :ith high f"el caacities. The time taken to fill a ,oeing

;4; thro"gh a normal hose and no@@le s(stem :o"ld take ho"rs. %ith ress"reref"elling> a large diameter hose is rigidl( connected to a co"ling in the aircraftand f"el "nder ress"re of a#o"t 40 si is "med into the aircraft tanks. Toassist this oeration> most aircraft can have the total f"el load re-set at the ointof connection so that the aircraft stos the ref"elling at the correct time. Theill"strations sho: the location and la(o"t of a t(ical> ,oeing ;;;> ref"ellinganel.

B"ing R"%"!!ing 2an"!Fig%(" *1

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10.1.1 ress"re Ref"el 8 "nctional &escrition

"el flo:s from the ref"el adaters into the ref"elDettison manifold. %hen the

ref"el valves oen> f"el flo:s from the manifold into the f"el tanks. A flo: t"#e atthe end of each ref"el valve decreases the e=it force of the f"el. The flo: t"#ealso "ts the f"el in different arts of the tank.

R"%"! S,st" La,%tFig%(" *


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As each tank reaches f"ll> the high level sensor signals the ref"el valve to close

to sto f"el flo:. %hen all ref"el flo: ceases> f"el that is left in the ref"elDettisonmanifold goes thro"gh the manifold drain valves and into the main tanks. Themanifold has t:o vac""m relief valves. These valves ermit air into the manifold:hen the f"el leaves via the manifold drain valves.

Ref"el Manifold &rain alveig 43

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R"%"! Mani!d D(ain 5a!;"Fig%(" *&

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10.1 D"%"!!ing

&ef"elling a ress"re t(e f"el s(stem is almost the reverse of the ref"ellingroced"re. A de-f"el #o:ser :o"ld #e connected to the single f"el oint co"ling>and "sing a com#ination of #oth the #o:sers s"ction "m and the aircrafts o:nf"el s"l( #ooster "ms> selected tanks can have their contents ret"rned to the#o:ser.

D"%"! S,st" La,%tFig *)

10.0 Lngit%dina! Ba!an/" F%"! S,st"sThe :eight of the f"el is a large ercentage of an aircrafts total :eight> and the

#alance of the aircraft in flight changes as the f"el is "sed. These conditions addto the comle=it( of the design of an aircraft f"el s(stem.

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10.1 S%+"(sni/ F!ig9t F%"! T(ans"(

Lngit%dina! F%"! T(ans"( Fig%(" *6

th"s changingthe longit"dinal sta#ilit(. This :as comensated in aircraft like Concorde> #(moving the centre of gravit(> shifting f"el as necessar( #et:een the f"el tanks inthe rear f"selage and the :ings as sho:n in the revio"s diagram.

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