WelcometotheAugust2023issueofRCM&E.
Ihavejustreturnedfrommyusualweekend morning f lyingsessionandtheconditionscouldn’t havebeenmoreperfect.Thesunwasshiningandthewind,whilst abitbreezy,wasmoreorlessstraightdownthestrip.
And,boy,whatastrip!Thechapsattheclubhaddonetheir usualsterlingwork(manythankstoFrankandhiscrew)andthe grasswas,Ithink,thebestIhaveeverseenit.It’sthenearesttoa bowlinggreenthatI’veever f lownfromatthatparticularsiteand eventheusualsheepdepositsanddivotsfromtheirhooveshad allbutdisappeared.Inshort,itwasalovelydayformodel f lying.
Therewasonlyonedampeneronproceedingsasforquite sometimeIwascompletelyonmyown!(Wheredoallthe aeromodellersgoonthebest f lyingdays?)Thatwasuntil, thankfully,oneoftheregularsturnedupforachatandashort f ly. Theweirdthingisthatunusuallyinthisdayandagethisclub normallyhasaverygoodattendanceatweekendsandso althoughitisquiteajourneyforme,andmuchfarthertotravelto thansomeofmyotherlocalclubs,Iliketovisitonaregularbasis ratherthan f lyonmyownelsewhere.
Havingsaidthis,thefollowingmorning,forwhichtheforecast wasnotthatgood,turnedouttobeanotherfineonesothelocals turnedoutinforce.SeemsthatIjustgotmytimingwrong!
Returningtomytrainofthoughtabove-‘inthisdayandage’ -whatIwasreallybuildinguptocommentonishowwhatI wouldcallthe‘usualclub f lyingdays’seemtohaveshif tedaway fromtheweekendsandnowtakeplaceduringtheweek.Iguess thisisanothersignofourageingaeromodellingpopulationand pointstothefactthatmanymodelpilotsarenowretiredor semi-retiredandsocan f lyonanydayoftheweekthatsuits them.Combinethiswithahostofdif ferentmeansof communicationssuchasclubFacebookandWhatsAppgroups, ratherthanjustrelyingontheoldtraditional‘Seeyounext Sundaymorning!’wayofdoingthingsmeansthatit’smucheasier toannouncea f lyingsessionwhentheweatherlooksgoodandbe sureofbeingjoinedbyafewclubmatesatthepatch.
It’sabitgallingthoughforthosemodellersstillatworkand trappedinanof fice,factoryorotherworkplacewhiletheirchums areoutenjoyinga f lightorthreewiththeirmodels.Nevermind ladsandlasses,hopefullywewillallgettheresomeday–unless somebrightsparkdecidestoputupthepensionageonceagain!
Ican’tcomplainthoughasI’mdoingajobIlove,andIdogetto nipoutmid-weekoccasionallyforabitoftest f lyingand photography.Yes,Iknow,it’sahardlife…
It’stimenowtotakeabrieflookatwhatwehavelinedupfor youintheAugustissueofRCM&E,startingwithourregular columns.
InhislatestBenchBlog,TimHooperdevoteshiscolumnto turningupanR/Ccarbforashelfbornedieselusinghisnew machinetools.InOneMan&HisShed,DaveGoodenoughdoes withoutamillingmachinebutstillmanagestorepairaglow motor.Thenit’sovertoChrisWilliamsformoreScaleGliding,this timefromtheWhiteSheetclub’sspringmeeting.Lateron,Keith Jackson’sAerobaticScenecolumnlooksatsomenewmodels beingpreparedfortheforthcomingF3AWorldChampsin AustraliabeforeGrahamAshbyandKicktheTyresinwhichhe broachesthethornysubjectofaccident-pronepilotsthenlightens themoodwithafewinspirationalmodels.
Forthismonth’scentre-foldPro-Planit’sbacktoChrisWilliams whointroducesthesecondpartofhisarticledescribingthebuild and f lyingofaclassiconesixthscalevintageglider,theSlingsby T.30Prefect.ThiscompletesthePrefectplanandarticlewhich startedintheJuneissue.
OurfeaturearticlesstartwithCreatingYourOwnModelin whichMartinHardyof ferswordsofencouragementtoany experiencedmodellerswishingtostepupanddesigntheirown largescalemodel.Next,ShaunGarrityvisitstheRAFMuseum MidlandsatCosfordfortheLMAStaticShowtoseeafine collectionoflargemodelsondisplayamongstthefull-size exhibits.Finally,wejoinDannyFentonashecontinueshisreport fromtheScaleIndoorNationals;thismonthDannyconcentrates onthefree f lightevents.
OntestthismonthDavidAshbystrapsintotest f lythenewT-7 RedHawkEDFjetfromXFly-Model.Finishingof f,yourstruly looksatanotherofthelasercutaccessoriesof feredbyFlightplan Models.ThistimethespotlightfallsontheirCofGBalance.
Ihopeyouenjoyreadingitall.
HappyFlying!
Photo: Chris Williams
This month Mar tin Hardy begins a t wo-par t ar ticle on Creating Your O wn Model Par t 1 cover s aircr af t selec tion, making a pr ac tic al f lying model, sources of information, determining the best size and what you may need by way of a plan Par t 2 (September issue) provides, a s an example, an over view of the build of a 7 ’ 6” span elec tric powered Mk 2 Avro Shackleton
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XFly-Model have relea sed a larger retr ac t equipped ver sion of their popular T-7 David A shby str aps in for a f light test
The Editor look s at another of the la ser cut accessories of fered by Flightplan Models. This time the spotlight f alls on their C of G Balance
22 CREATING YOUR OWN MODEL
Maybe you’ve reached the point of wanting to design your own large sc ale model If so, Mar tin Hardy of fer s some word s of encour agement
42 SUBSCRIBE … and receive Luf t waf fe Fighter s & Supermarine Secret Projec t s FREE!
64 LMA STATIC SHOW
Shaun Garrit y visit s the R AF Mu seum Midland s at Cosford to see a fine collec tion of large models on display among st the f ull size exhibit s
80 THE ROAD TO BULGARIA
Alex Ma x field prepares to compete a s par t of the GB F5J Team at the 2023 World Championships
86 SCALE INDOOR NATIONALS
Danny Fenton’s second repor t from Walsall concentr ates on the free f light sc ale event s
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16 BENCH BLOG
Tim Hooper machines up a replacement R/C c arburet tor for a longshelved diesel engine
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Dave Goodenough continues his ref urb of a barg ain SC glow engine
36 SCALE GLIDING
Chris Williams and chums def y the relentless depressing spring weather to enjoy a fine d ay of sc ale soaring from White Sheet Hill
72 AEROBATIC SCENE
This month Keith Jack son look s at new F3A models being aired prior to the World Champs being held later this year in Au str alia
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Chris Williams introduces par t t wo of his ar ticle describing the build and f lying of a cla ssic 1:6 sc ale vint age glider
Thisyear’sBMFASchoolandUniversityPayload ChallengewasheldattheBMFANational Centreonthe14thand15thofJune.Itwas attendedbythirteenuniversitiesandonehigh schoolfromacrosstheworld.Thecompetitive spiritandthebuzzwaspalpablethroughout thesiteanditwasgoodtoseesomanyyoung peoplecollaboratingandworkingtogetheron theirmodelsanddesigns.
Thestandardofcompetitionwashighand withahighrateofsuccess.Mostofthemodels wereconstructedtoaverygoodstandard andhadbeenextensivelytestedbeforethe competition.
Therewerethreecategoriesinthisevent:
Distance -withtwoteamsfromISchool Chenmai(China)andAGHUniversityKrakow (Poland).Althoughtherewereonlytwoteams enteredforthischallengethecompetitionwas closelyfoughtandAGHUniversityKrakowwon byonepoint.ItwasinterestingtonotethatI SchoolChenmaicloselymatchedthestandards oftheuniversityundergraduatesandforfuture yearsawinwouldnotbeimpossibleifthe judgingpointersarounddrawingstandards weretakennoteof.
Quantity -withfiveteams,includingfourfrom universitiesinChina(ISchoolChenmai,Hebei UniversityofScienceandTechnology,University ofHongKongandBeihangUniversity).The fifthteamcamefromLoughboroughintheEast Midlands.
Thespeedandprecisionofsomeofthe teamsloadingandunloadingthepayloadwas fascinatingtowatchassometeamswerelike F1mechanicsintheirspeedandaccuracy.This eventwasexcitingtowatchandthelevelof innovationandimaginationwashigh.
Weight -18teamswereregisteredbut,inthe event,onlyseventeencompeted.Again,there wasaninternationalentrycomprisingofthree teamsfromChina,twoteamsfromKrakow,one teamfromMunichandeleventeamsfromUK Universities.
Thiswasanexcitingandverycompetitive eventandmostteamsmanagedtogetatleast oneroundunderwaywiththeirdesigns.The gustingwindsmadeforsomeverynervewracking flightsbutthankfullytherewerefew modelcasualtiesthatcouldnotberepaired.
Inconclusionthisyear’sPayloadcompetition wasagreatsuccessandwasenjoyedbyall.There weresomeexcellentmodeldesignswhich flew beautifullyandsuccessfullymetthebrief.The onlythingtodonowistolookforwardtonext yearwithanevengreaterentry–wehope!
HelenJones,BMFAOutreachDirectorInthelastissuewegaveyouaglimpse ofMárioVilaça’slatestseaplaneproject, aMartinJRMMars,courtesyofour IberiancorrespondentArnaldoCorreia.
Arnaldohasrecentlybeenin contactagainandsays, ‘Justashort onetoletyouknowMáriohasfinished hisMartinMars.Whatwouldbeamajor projectformeis‘justaquickie’forMário, tounwindafterthatgorgeousFaireyIIID (seeSantaCruzaricles,Dec22&Jan23 RCM&E).Heislookingforwardtoflying itatameetinginJulyalthoughtherehas alreadybeenasuccessfulfirsttestflight.I’ll keepyouposted.’
Thankyou,Arnaldo.Here’sthevídeo oftheMars’test flight.She flieseverybit asgoodasshelooks: https://youtu.be/12qV8wJtcM0
Sadnewshasreachedusofafatalaccidentat amodel flyingsiteinSpainatthebeginning ofJunewhenamodellerretrievinghisaircraft fromtherunwaywashitbyanothermodel whichwaseitheronalowpassorlanding. Itwouldseemthattheaccidentoccurred becausethepilotofthesecondaircraftwas unawarethathisfellowpilothadenteredthe runwaytocollecthismodel.
Inlightofthistragiceventweaskedthe BMFAforcommentandweweretoldthat swiftactionwasbeingtakentoupdatethe relevantsectionoftheMembersHandbook,
specificallysection:13.3RadioControlFlying Safety
Paragraph13.3(n)willnowread:
(n)NEVERassumethatthelandingarea isclearevenifyouhavecalledlanding.In emergencysituationscallforhelpfromyour fellow flyersandalwaysbepreparedtolandin asafeplaceoffthelandingareaifnecessary. Pilotsretrievingmodelsfromtheactive runwaymustcallouttheirintentions‘loudand clear’andGETCONFIRMATIONfromanypilots still flyingthatitissafeforthemtodoso.In ALLcases,thesafetyofpeopleisparamount.
AlisdairClarkwasquicktorespondtoourrecent requestforpicturesofradiocontrolledCierva autogyros:
‘InoticedintheJuneissuetheanniversaryofthe firstsuccessful flightofanautogyrodesignedby JuandelaCiervaandyourinterestinanyscaleR/C versionsoftheseunusualaircraft. PleasefindtwophotosattachedofaC.30.Thisis fromtheLAhelikit,witha690mmrotordiameter,
exposedscaleradialengine,threechannels(rotorx2 andESC)and400g flyingweight.
Itisanicemodelbutisquitedelicate.Aswith allautogyrosit’simportanttospintherotorsupto flyingspeedbeforelaunch.
Thedistinctivewhooshand flightcharacteristics addtothefascinationoftheseaircraft,which
contributedsomuchtothelatersuccessofthe helicopter.’
Thanksforsendingpicturesofyourmodel, Alisdair.
LAheli’sautogyrokitscanbeviewedinthe Autogyrosectionat:https://www.laheli.com
Yes,Ihadtolookitup.ButnowIknowthat Boeing-Saab’sT-7RedHawkisanadvanced jettrainerselectedtoreplacetheNorthrop T-38Talon.Itbearsmorethanapassing resemblancetotheF-18andthefifth-generation fighterstowhichpilotswilladvance.Or,assome havecolloquiallycommented,it’saabitlikewhat you’dgetbymatinganF-16withanF-18.
AnewishbrandXFlymaybebutthereleases todatehaveimpressedreviewers.Thisistheir secondT-7Aanditjoinsthesmallerfixed-gear 64mmfanversion.Thedesignsuitsanelectric ductedfan(EDF)model,particularlythanksto awidefuselagethat’llhappilyacceptlarger6S LiPobatteries.
Tenservos-amixof9gand13gunits-are scatteredacrosstheairframe.ThereareLED wingtipandlandinglightstoobutit’sthe electricretractableundercarriagethatreally
impresses.Iftherewasaleaguetableforreadyto-flyelectricretractsthenthebeautifulitems fixedtoFMS’F-7FTigercatwouldbenearthetop, alongsidethoseyou’llfindhere.They’rescale, all-metal,verystrong,beautifullymadeand accompaniedbysequencedbaydoors.Icould watch‘emgoupanddownallday.
Ifyou’ve flownafewfoamiejets,particularly thosewithretracts,thenyou’llappreciatesome ofthesmalldetailsthatcontributetoamodel’s success.Reassuringlythereareplentyhere. Forstarterstherearethestronghornswith ball-socketlinks,whiletheall-movingstabiliser armsandmounts,potentiallyanareawhere problemsmayoccur,areverysturdy.Thewings useaquickconnectortoengagetheaileronand lightingelectricssoremovalfortransportation andstorageisquickandpainless.Thesamegoes forthefins.
It’sacontemporarydesign.Amongstothers, there’sabitofF-16andF-18inthere.
Name: T-7ARedHawk
Modeltype: Ready-to-fly80mmEDFjet
Manufacturedby: XFlyModel
Abespokefoamtrayprotectstheairframe sectionsverynicelybutdon’tconfusethe temporarywingjoiner(that’sdesignedto supportthefuselageintransit)withthelonger examplealsoincluded.Thelatteristheone you’llneedfor flying.
Initialinspectionrevealedaloosewooden coverovertheESCbutaccessedfromthe fuselageundersideitwasnothingthata littleUHUPorgluecouldn’tfix.Thataside, everythingwasnicelyfinishedandsuperbly protectedbythepackaging.
Guidedbyaverythoroughmanual,a 2mmhexwrenchisallthat’srequiredtoput everythingtogether.Amusingly,thefins seemlittlebiggerthanthewings,butIguess that’scontemporarymilitaryjetdesignfor you.Everythingslipstogetherreassuringly wellthough.Ifyourcarissmall,orstorage spacetight,thenthemodelcouldbequickly andeasilydisassembledthankstothe integratedwingrootconnectors.Don’tbin theprotectivepackagingtrayasitcouldbe usedtostorethesectionsbetweenflying sessions.
UKdistributor: CMLDistribution www.cmldistribution.co.uk
RRP: £549.99
Wingspan: 975mm(38.4”)
Fuselagelength: 1360mm(53.5”)
All-upweight: 3150g(111oz)
Wingarea: 21.5dm2(333sq.in.)
Wingloading: 146g/dm2(47oz/sq.ft.)
Powersystem: 3280size2200kVinrunner, 80mm12-bladefan,100A ESC
Connectortype: XT90
Req’dto fly: Receiver,6S40005000mAhLiPo
Anall-movingstabiliserneedsstrongmechanics andthat’scertainlythecasehere.
13gand9gdigitalmetalgearservosdothepushing andshoving.
Wingservoarmprotection.Anothernicetouch.
“AnewishbrandXFlymaybebut thereleasestodatehaveimpressed reviewers”
Apparently,BoeingandSaabintendtoofferan attackfighterversionoftheT-7induecourseso XFlyhaveincludedplentyofunderwingpylons andordnance.Theyslotintoplaceeasily enoughalthoughIsuspectthatfewwillfitsuch adraggypayload.Thelow-slungdroptankwill impedetakeofflongongrassystripstoo. Besides,Ithinkthemodellooksfarbetter flyingclean.
It’simportanttocalibratetheESCbefore flying.Themanualexplainshowthat’sdone whilealsoprovidinggeneralprogramming instructions,whichishandyshouldtheESC finditselfinanothermodeldowntheline.
Therewareno flaps,although flapperon (bothaileronsdown)deflectionmeasurements areprovided,alongwiththenecessary compensatorydownelevator.Theaileronservo Y-leadmustberemovedinordertodothat ofcourse.
Retracted,theundercarriageshiftsnotably forward,soIbalancedmymodelwiththe undercarriagedown.AlthoughtheCofG movedforwardsafewmmwhenthegearwas upit’snotenoughtoworryabout.
UnderwingstoresareprovidedalthoughI suspectfewpilotswillfitthem.Notethe absenceof flaps.
Theretractsarebeautifullydone.Notethe powerfullandinglights.
Likewise,thenoselegisasubstantivebitofkit.
Afull-lengthcanopyandcockpitmouldingcoversthebatteryandradiobay. Batterybayiscommodiousandeasilyacceptsthe6S4000-5000LiPos suggested. AmixingboardandmyRxsitjustbehindthenose cone.“XFlyhave includedplentyof underwingpylons andordnance”
TryasImight,I’vebeenunableto flythismodel onbetterdaysthisspring.Theweatherhasjust beensowindy.Insomewaysthat’sgoodasa decentheadwinddoeshelpanEDFjetget awayduringtake-off,especiallyonewithahigh wingloading.ThisT7-Aneedsagoodlongtake offrun,whichissomethingtobearinmindif yourtake-offsurfaceisgrassyandonthe shorterside.
Idon’tdropthewingtrailingedge(T.E.) fortake-off,butsheunstickswithapush ofelevatorandclimbsawaycomfortably. Onoccasions,whentheendoftherunway approachedandI’vehadnooptionbutto bitethebulletandpullelevator,itsliftedand rockedthewing,butneverstalledorfallen outofthesky.Witha12-bladefanspinning awaythesoundisgreatandthemodel behavespredictably.
Thelowratessuggestedshouldbefinefor most flyersandwhilethemanualmakesno mentionofexponentialit’sbestto flytheT-7 firstandseewhatyouthinkbeforediallingthat in.Justalittle,15%acrossaileronsandelevator, suitsme.Itrollsquicklyatlowratesbutnot uncomfortablyso.
EDFjetslikethisarebest flownsmoothly; carvebiglinesandyou’redoingtherightthing. Lowpasseslookandsoundimpressiveand loopscanbe flownfromlevel flight.
Ideploy flaperonsforlanding,with‘servo slow’enabledattheTx,somakingsurethe transitionissmooth.Thecompensatorydown elevatormixmentionedinthemanualdoes preventthenosefromrisingasaresult.She’s verywellbehavedwiththeT.E.loweredand theeffectcertainlyhelpstoscruboffspeedon
Pushthethrottleandit’llmovealongat anappreciablerateofknots.
approach,evenonawindyday.Iguessthe undercarriageandwidegearbayaredoing theirbittoslowthemodelbyaddingdrag too,butitmeansIhaven’treallynoticedthe absenceof flaps.
I’dreallylovetoreportthatthismodel rewardswithanimpressiveendurancebut my6S5000mAhpacks(700g)deliverno morethanfourminutesofeconomical flying.I setthetimerforthreeminutes,soensuringI havesomereserveforago-aroundifnecessary. Plentyofgoodthingsaregoingonhere though;it’swellmadewithafinefinish,has astrongretractableundercarriageandit flies wellwithnovicesthat’llcatchoutexperienced EDFpilots.Ifyour flyingfieldissmallor roughthenit’sprobablynotforyou,although thesamecanbesaidformanycomparable machines.
Below:ThisisXFly’ssecondT-7Aanditjoins thesmallerfixed-gear64mmfanversion.
Landing flapperonsandaslightnoseupattitude helpscrubsomespeedforlanding.
Itendnottodropthetrailingedgefortake-off.
“ …it’swellmade withafinefinish, hasastrong undercarriageand flieswellwithno vices”
Thismonth’svictimisthisPAW .2.49diesel,seenheresportingits shinynewcarburettor.
TimHoopermachinesupareplacementR/C carburettorforalong-shelveddieselengine words&photos»TimHooper
Asthecustodianofasmallcollectionof dieselengines,I’veoftenwishedthat moreofthemcouldbebroughtback intoactiveservicei.e.,doingwhattheyshould bedoing-poweringmodelaeroplanesaround theskies-asopposedtosittingonashelf.
So,whyaren’ttheybackinactiveservice? Well,unlikemyhardierfree flightbrethren, I’manR/Cmanandhavingaccesstoan inflightthrottlecontrolis,forme,anecessity. Unfortunately,mostofmylittlecollectionof vintagedieselspre-dateR/Cthrottlesandhave afixed-sizeinductionventuriwhichprecludes anyformofspeedcontrolintheair.
Aeromodellersofacertain,senior,agewill knowallthisalreadysoforgivethepreamble, okay?However,ifyou’reoffresher(electric) bloodthenamodelwithoutaspeedcontrol ismaybeascenarioyou’venotencountered before.
Ifyou’vebeenfollowingmyadventuresin metalmachiningoverthelastfewepisodes, youmightrecallthatoneofmyultimateaims istomanufactureaworkingtwo-strokeengine fromscratch.Andmyroutetowardsthatgoalis tostartbymakingreplacementpartsforsome oftheenginesIalreadyown.Alittlewhileago welookedatmakingareplacementaerofriendlycylinderheadfora.75ccDCMerlin, whichworkedoutwell.
Now,we’regettingabitmoreserious.Ihave twoPAW2.49diesels-onehasafactory-made R/Cthrottleandhasfounditsspiritualhome inthenoseofmyMurgvintagemodel,which it’sbeenhaulingaroundtheairforafewyears now.Theother,alas,hasnothrottleandsits forlornlyontheshelf.
Theplanisdeadsimple:copytheR/Ccarb fromthefunctionalengineandthenfitthe copiedcarbontotheshelfsitter.And,yes, beforeanybodysaysit,Iknowthatyoucanbuy anicenewcarbdirectfromPAW(stillaliveand wellinMacclesfield,bytheway)forapaltry £25orso,butthat’snotreallythepoint,isit?IfI wantedaneasylife,thenIcertainlywouldn’tbe anaeromodeller!
Themethodologywasgoingtobequite simple:striptheexistingcarb,makeanote ofallthesalientdimensionsandthenjust manufactureanewsetofcomponentsonthe latheandmillingmachine.Itshouldn’ttake morethananhourortwo,right?Well,no,asit turnedout…
Electingtostartwiththemainbodyofthecarb, Iusedthebandsawtohackanappropriate lumpofaluminiumfromalargerblock,after whichitwasmilledonallsixfacesdowntosize, usingadigitalverniergaugetocheck ondimensions.
Stillonthemill,Icross-drilleda10mmhole throughtheblocktoacceptthethrottlebarrel laterandthenturneditthrough90°soIcould drilla6mmholethroughitsentirelength.All oftheblock’soutsideedgesweredeburred withafinefileandanoldscalpelbladetook careoftheburrsaroundtheholes.
Thebarrelneedstobeaclose,smoothfitin
thebodyofthecarb.Ifit’sslackandleakingair, thenthecarbwon’tbeabletosuckfuelthrough fromthetank.Ipoppedalengthof12mmbrass rodintothelathe’schuckandturneddown theendby15mmsothatitwasjusttoolargeto enterthebarrel.Thefinalsizingwasdownto usingastripofabrasivepaper,alittleatatime, asthepiecespuninthechuck.Lightlyholding thetwoendsofthepaperstripbetweenthe fingerswastheorderoftheday,sokeepingmy clumsydigitsoutoftherangeofthechuck’s spinningjaws.
Afteraminuteorsothebrassrodwasa snug,rotatingfitinthebody,soIresisted anytemptationtopolishitanyfurtherand attackeditwithacentredrill,priortoboring theendwitha4mmdrilltoacceptthe spraybarlater.
Theentirebrassrodwasthenmountedup inthemill’svice,thecentrelinefoundand atransverse6mmholeboredthroughitto becomethethrottle’sventuri.Whenfittedinto thethrottlebodythisnewholelinedupnicely
Noneedtore-inventthewheel. IalreadyhadaPAWwithanR/Ccarb onwhichtobasemyrendition.
Asanasideit’sbeenabitofarevelationtolearn thatanordinarydrillbitisnotaprecisiontoolat all.Apparently,it’sraretofindonewherethe twocuttingedgesatitstipareperfectlyequal andcentred,whichmeansthatadrillusedalone willtendtowanderinacircleasitchewsitsway throughaworkpiece,thusproducingaslightly largerholethandesired.Thetrickistousea smallcentredrillfirsttoproduceatiny indentationandthenuseprogressivelylarger drillsuntilfinaldimensionisreached.
withtheholethroughthecarb’sbody.
Theendofthebrassrodwasgentlybevelled forneatness,andthenpartedoff.Theresulting barrelwas flippedendoverand,inthechuck, itwasfacedandbevelledsothatitsfinished lengthwasjustslightlygreater(by0.5mm) thanthewidthofthecarbbody.
“Theplanisdeadsimple:copythe R/Ccarbfromthefunctionalengine andthenfitthecopiedcarbontothe shelfsitter.”
Thenextpartofthislittleadventurewasto placethecarbbodyinthechuckandturndown theends-notaseasyasitwouldseem.That four-sidedblockisjustnotgoingtobeheld neatlyinthestandardthree-jawchuck.
LuckilytheChesterDB8lathecomeswith quiteafewextras,oneofwhichisachuckwith anextrafourthjaw.So,what’sthebigdealwith that,then?Well,onthethree-jawchuck,all threejawsoperatetogetherwhenthechuck keyisrotated,justthesameasthechuck onastandardelectricdrill.Notsowiththe four-jawunit,wherethejawsarecompletely independentofeachotherandneedtobe adjustedoneatatime.
Thispropertyofthefourjawisbotha blessingandatotalpaininthenetherregions. Yes,youcansecurefour-sided(orirregularly shaped)workpiecesveryaccurately,butthere’s quiteaprocessingettingthepiececentredto beexactlyconcentricwiththecentrelineofthe latheitself.
Therearequiteafewwaystocentreapart inthefour-jawchuckandaftermakinginitial adjustmentsbyspinningthechuckatalow speedandcheckingbyeye,Ichosetomount adialtestindicator(DTI)inthetoolholder. Then,usingtheadjustmentonthecrossslide,I positioneditsprobewithinthecentralboreof thecarbbody,justbearingononesideofthe bore.Rotatingthechuckbyhanditwasobvious bytheerraticmovementsofthedial’sneedle thatthecarbwasnowherenearaccurately centred.Theprocedureistoworkoutwhich waytoadjustthejawstocentrethepart,which wasnotatallintuitiveasfarasIwasconcerned. Thejawsmustbetreatedasoppositepairs. Whenthejawnearestyouisloosenedthenthe chuckmustberotatedby180°andtheopposite jawtightenedbyacorrespondingamountto movethepartoververyslightly.AndwhenI say‘slightly’we’retalkingabouthundredths ofamillimetrehere,soalighttouchis definitelyrequired.
Whenonepairofjawsisgettingcloseto centred,thenwe’llrotatethepiecebyonly90° toengagetheotherpairofjawsanddoitall again.Whenwe’reclose,we’llcheckthefirst pairagain,thenthesecondtofinishup.Phew! Ifallthissoundsverytedious,thenyou’dbe right.Centringthecarbbodyforthefirsttime tookmeabouttwentyminutesbuttheresult wasthat,asthechuckwasrotated,theDTI needleinthecentralborebarelyquivered.This meantthattheDTIcouldnowbeswappedfor acuttingtoolandthebottomofthecarbbody couldbeturneddowntomatchtheintakeport onthePAW’scrankcase.
Itwasn’tpossibletotrythecarbforfit onthecrankcaseinsitu,soIrecheckedmy measurementsyetagainbeforereleasingthe carbbodyfromthechuckbyslightlyloosening twoadjacentjawsandtryingitforreal.Luckily thebodyslidhomeintothecrankcasepretty perfectly,otherwiseI’dhavehadtocentreitup againformoremachiningtogetitright.
Timefortheotherendofthecarbbody, whichwasdestinedtoformtheairintake.
UsingPAW’sowncarbasaguideImilledthestartofthenewalibodyandbrassthrottlebarrel.
Usingadialtestindicator(DTI)withinthecarb’sboreensuresthatthefour-jawchuckiscentredcorrectly.
Theheartofthecarbisthesmooth,snugfitbetweenbodyandbarreltoallowleak-freeoperation.Precise measurementshelpgetitrightfirsttime.
AsthechuckjawswerestillwhereI’dleft them,itonlytookafewminutesto flipthe carbaroundandtrueitupagain.I’vewatched videoswhereexperiencedmachinistscan centreupafour-jawchuckfromscratchina coupleofminutes,sopracticeobviouslymakes perfect.Wecanonlyhopeso.
ThecarbonanoriginalPAWhasaparallel intaketubebut,feelingbrave,IthoughtI’d haveabashatmachiningatapered,trumpet shape,justforappearance’ssakereally.
Goingbacktobasicsforamoment:the lathe’sbigsaddle(carriage)movesalongthe lathebedandthesmallercrossslidemoves perpendicularlytothesaddleandmovesacross thebed.Ontopofthecrossslidesitsthemuch smallercompoundslide,whichcanbesetat awiderangeofangles-handyforproducing tapers,angledbevels,etc.
Isetthecompoundslideata10°angleand, usingaminiatureboringbar,Iwidenedthe carb’s6mmcentreboretogiveaninternalbell mouth.Changingthecuttingtoolagainletme cuttheoutsideofthebell,aswellbevellingthe topofthecarbbodytoo.Thiswasaparticularly rewardingoperationasitletmestampahintof individualityonamachinedpart.
Thenextcomponentstoconsiderwerethe needlevalveandspraybarassembly(NVA)and here’swherethingsgotabitfiddly.
Ifyou’renotICconversant,thenhere’show itworks.Fuelissuckedfromthetankbythe engine,whichactslikeasuctionpump.Asthe pistonmovesupanddownitcreatesapartial vacuuminthecrankcase,whichencourages theoutsideairtoenterthecarbandtheninto theengine.Onthewaythroughthecarbthe airpasseseithersideofthespraybarandis compressedbytherestriction.Thisrestriction causesthemovingairtospeedupabit, resultinginanareaofloweredpressure.This low-pressureactsonthefuelfilledholeinthe spraybar,thussuckingfuelintotheengine.
That’saverysimplifiedwayofexplaining whatgoesoninthecarb,andrepresents thelimitedrangeofmyownlevelofphysics
and fluiddynamics,sodon’tdelugemewith correctiveemails,okay?
Thespraybarisaturnedbarofbrass,bored throughfromeitherend.Onthefuelinlet sidethere’sa1mmhole,whilstontheother isa1.5mmhole.Wherethetwoholesmeeta tinyinternalshoulderisformed.There’san additional1mmholeboredthroughthesideof thespraybar,justadjacenttothisshoulder.
Thepointyneedlevalvefitsthroughthe larger1.5mmsideandseatsagainstthatlittle shoulder,thuscuttingoffanyfuel flow.Asthe needleisunscrewedtheinletholebecomes progressivelyopened,solettingthefuel through.Thereleasedfuelcannowexitthe spraybarthroughthatholeinitssideandbe sprayedintotheventuriandthenceintothe engine.That’sthetheory,asIunderstandit.
Inpracticea35mmlengthof8mmbrass barwaschuckedupandboredwithapuny 1mmdrill.Anotherpartofthelearningcurve withthismachiningmalarkeywastolearn thatthesmallerthedrillbit,thenthefasterit mustrotate.I’vealwaysrunsmalldrillsatslow speedstosavethemfrombreakageandthen wonderedwhytheyactuallydidbreaksooften!
Thetrickistorunsmalldrillsathighspeed (1500rpminthiscase)andtofeedtheminvery slowly,usingregulardripsofoiltoeasetheir passage.Thedrill’s flutessoonclogwithswarf thedeeperitgetssoitneedstoberetracted andcleanedrepeatedly.Thespraybarwasthen flippedaroundinthechuck,andtheother endwasdrilledwiththebigger1.5mmdrillto createthattinyinternalshoulder.
Theoutsideofthe8mmbrassbarreceived attentionnext.Thereasoningbehindsuch a‘large’diameterbaristobeabletoleavea portionneartooneendatfulldiameter,which willbuttupagainstthethrottlebarrel.
Thepartofthespraybarthatwilllivewithin thebarrelwasturneddownto4mmandthen
Inletandoutletstubsare machinedtosize.Ontherightis thefixedventurithatwasthe engine’soriginalfitment.
treatedtoamatching4mmexternalthread forpartofitslength,whichwillacceptthe needleshroud.
Thecentralpartofthespraybarwasturned downto3.5mmandthenthesideholewas drilledonthemill.Two flatsweremilledon the8mmportiontoallowtheuseofa6mm spanner.Confessionbeinggoodforthesoul,I mustadmittogettingthelocationoftheside holeallwrongandhavingtosolderitupand re-drillitintheproperplace.Butdon’ttell anybody,okay?
Backinthelatheagain,theotherendof thebarwasturneddowntocreateanipplefor thefueltubetoclingonto.Ialsoturnedupa brassdisc,withaninternalthreadandexternal flatstosuita10mmspanner.Thisdiscactsas anutthatwilltrapthethrottlebarrelonthe spraybarshaft.
Thesteelneedlecamenextanditstartedasa shortlengthof16SWGpianowire.I’dbeen ponderingthebestwaytotaperoneofitsends tocreatethepointybit.Thepointisdestinedto penetratethattinyshoulderwithinthe spraybar.Astheneedleisunscreweditretreats outofthecentralhole,progressivelyopening thefuelinletasitgoes.
Now,pianowireistough,springystuff,so Ifiguredthatthebestwaytotaperoneend wouldbetogrinditdownwhilstitrotatedat highspeed.Inaburstofclarity,Ifiguredout theeasiestwaytoachieveashallowtaperon suchaskinnylengthorwirewouldbetomount itinthechuckoftheDremel,spinituptotop speedandthenbringitintocontactwiththe sideoftherotatinggrindingwheelofmybench grinder.
Thismaysoundabitdodgy,butitworked sowellthatIgrounddownanothercouple ofneedlesforfutureusewhilstIwasatit.
“Thiswasaparticularlyrewarding operationasitletmestampahintof individualityonamachinedpart.”
WhilsttheneedlewasstillintheDremel’s chuckIpolisheditsmoothwitheverdecreasinggradesofwet‘n’drypaper.The completedneedlewassoftsolderedintothe brassthimbleshroud.
Theverylastpiecetomakewasthethrottle arm,whichservestorotatethebarrelwhen wiggledbytheappropriateservo.Thiswascut fromthinalisheetanddrilled.
Whenthecarbwasassembled,Ifoundthat therewasalittlebitoflateralplaybetween thebarrelandthecarbbody,asthebarrel protrudedoneitherside.
TocounterthissideplayImilledashallow (0.5mm)grooveintheendofthebarrel.Not onlydidthistakeuptheunwantedplaybutit alsogavethethrottlearmadefinitelocation sothatitcouldn’tturnwithoutturningthe barreltoo.
Attheendofallthisthenewcarbwas installedonthePAWengine,whichwasitself installedintheteststandtoawaitatrialrun.I didn’thavelongtowaitforasuitableday.
I’donlyrunthePAWoncebeforeandthat wasoverayearagowhenitfirstcamemy way.Sincethen,ithadsatontheshelf,dosed upwithautomatictransmission fluid(ATF), whichismyusualafter-runpreservative.I’d liketoreportthatitfiredupstraightaway, butittookseveralminutesto flushtheATF outandgetitsaturatedwithnewdieselfuel, whenitstartedtocheerfullypopaway.
Soyes,itstartedandranonthefewdrops offuelinthe‘tank’(anoldsyringe).Refuelled, itstartedreadilysoIjiggledthethrottle pushrodandwashappytoseeitrespond.
Outcamethephoneandthere’sashortvideo onYouTube:
https://youtu.be/v6r-d3e9zVE
So,that’sthat.Thenextstepistosortouta suitableairframetogivethePAWahomebut thatcanwaitawhile.
FINALTHOUGHTS
Well,it’snotoftenthatasingleproject
occupiesthewholeofaBenchBlogcolumnso apologiestoallwhowouldratherreadabout balsawork.Ihavetoconfessthatthelevelof detailandfocusneededtoproducethislittle carbhastakenanypreviousthoughtand planningrequiredtoawholenewlevel.Fora relativenewbielikemeit’sbeenafairly intenseexperience,butveryenjoyablefor allthat!
Partsofthenewcarballpresentandmoreorless correct.Thesawcutonthethimbleletmepressthe threadstogethertogiveafrictionfitonthe spraybar,tostopitvibratingloosewhentheengine isrunning.
Oldandnew.OriginalPAWcarbfeaturesathrottle stopscrewbutI’mhappytousetheTxtolimitthe travelasrequired,soIdidn’tbotherfittingone.
ThepianowireneedlevalvewasspunintheDremel, thengentlypressedagainstthesideoftherotating grindingwheel.
FlushedwithsuccessImadetwofurtherneedles whilstIwasonawinningstreak.Abrasivepaper gotthemtoanacceptablepolishedfinish.
Ievengottoplaywithmynewknurlingtoolonthe thimble!
Thesethingsdon’tjusthappenbythemselves.There’salotofworkingouttobedoneandthat’spartofthe joyofit.Here’sthesketchoftheneedleandspraybar.
Needlefullyinsertedinthespraybarandbeingsoft solderedintoitsbrassthimble.