PuttingontheCloth.
　　Wearenowreadytoputontheclothcoveringwhichholdstheairandmakesthemachinebuoyant.Thekindofmaterialemployedisofsmallaccountsolongasitislight，strong，andwind—proof，ornearlyso.Someaviatorsusewhatiscalledrubberizedsilk，otherspreferballooncloth.Ordinarymuslinofgoodquality，treatedwithacoatoflightvarnishafteritisinplace，willanswerallthepurposesoftheamateur.
　　Cuttheclothintostripsalittleover4feetinlength.
　　Asyouhave20feetinwidthtocover，andtheclothisoneyardwide，youwillneedsevenstripsforeachplane，soastoallowforlaps，etc.Thiswillgiveyoufourteenstrips.Gluetheendofeachstriparoundthefronthorizontalbeamsoftheplanes，anddraweachstripback，overtheribs，tackingtheedgestotheribsasyougoalong，withsmallcopperorbrasstacks.Indoingthiskeeptheclothsmoothandstretchedtight.Tacksshouldalsobeusedinadditiontotheglue，toholdtheclothtothehorizontalbeams.
　　Next，givetheclothacoatofvarnishontheclear，orupperside，andwhenthisisdryyourgliderwillbereadyforuse.
　　ReinforcingtheCloth.
　　Whilenotabsolutelynecessaryforamateurpurposes，reinforcementofthecloth，soastoavoidanytendencytosplitortearoutfromwind—pressure，isdesirable.Onewayofdoingthisistotacknarrowstripsofsomeheaviermaterial，likefelt，overtheclothwhereitlapsontheribs.Anotheristosewslipsorpocketsintheclothitselfandlettheribsrunthroughthem.Stillanothermethodistosew2—inchstrips（ofthesamematerialasthecover）onthecloth，placingthemaboutoneyardapart，buthavingthemcomeinthecenterofeachpieceofcovering，andnotonthelapswherethevariouspiecesarejoined.
　　UseofArmpieces.
　　Shouldarmpiecesbedesired，asidefromthoseaffordedbythecenterstruts，taketwopiecesofspruce，3feetlong，by1x13/4inches，andboltthemtothefrontandrearbeamsofthelowerplaneabout14inchesapart.
　　Thesewillbemorecomfortablethanusingthestruts，astheoperatorwillnothavetospreadhisarmssomuch.Inusingthestrutstheoperator，asarule，takesholdofthemwithhishands，whilewiththearmpieces，asthenameimplies，heplaceshisarmsoverthem，oneofthestripscomingundereacharmpit.
　　Frequentlysomebodyaskswhytheribsshouldbecurved.Theansweriseasy.Thecurvaturetendstodirecttheairdownwardtowardtherearand，astheairisthusforceddownward，thereismoreorlessofanimpactwhichassistsinpropellingtheaeroplaneupwards.
　　CHAPTERVI.
　　LEARNINGTOFLY.
　　Don’tbetooambitiousatthestart.Goslow，andavoidunnecessaryrisks.Atitsbestthereisanelementofdangerinaviationwhichcannotbeentirelyeliminated，butitmaybegreatlyreducedandminimizedbytheuseofcommonsense.
　　Theoretically，theproperwaytobeginaglideisfromthetopofanincline，facingagainstthewind，sothatthemachinewillsoaruntiltheattractionofgravitationdrawsitgraduallytotheground.Thisisthemannerinwhichexperiencedaviatorsoperate，butitmustbekeptinmindthatthesemenareexperts.Theyunderstandaircurrents，knowhowtocontroltheactionanddirectionoftheirmachinesbyshiftingthepositionoftheirbodies，andbysodoingavoidaccidentswhichwouldbeunavoidablebyanovice.
　　BeginonLevelGround.
　　Makeyourfirstflightsonlevelground，havingacoupleofmentoassistyouingettingtheapparatusunderheadway.Takeyourpositioninthecenterrectangle，backfarenoughtogivetheforwardedgesoftheglideraninclinationtotiltupwardveryslightly.Nowstartandrunforwardatamoderatelyrapidgait，onemanateachendofthegliderassistingyou.Astheglidercutsintotheairthewindwillcatchundertheupliftededgesofthecurvedplanes，andbuoyitupsothatitwillriseintheairandtakeyouwithit.Thisrisewillnotbegreat，justenoughtokeepyouwellclearoftheground.
　　Nowprojectyourlegsalittletothefrontsoastoshiftthecenterofgravityatrifleandbringtheedgesoftheglideronanexactlevelwiththeatmosphere.This，withthemomentumacquiredinthestart，willkeepthemachinemovingforwardforsomedistance.
　　EffectofBodyMovements.
　　Whentheweightofthebodyisslightlybackofthecenterofgravitytheedgesoftheadvancingplanesaretiltedslightlyupward.Thegliderinthispositionactsasascoop，takingintheairwhich，inturn，liftsitofftheground.Whenacertainaltitudeisreached——thisvarieswiththeforceofthewind——thetendencytoaforwardmovementislostandtheglidercomestotheground.
　　Itistoprolongtheforwardmovementasmuchaspossiblethattheoperatorshiftsthecenterofgravityslightly，bringingtheapparatusonanevenkeelasitwerebyloweringtheadvancingedges.Thisdone，solongasthereismomentumenoughtokeeptheglidermoving，itwillremainafloat.
　　Ifyoushiftyourbodywellforwarditwillbringthefrontedgesofthegliderdown，andelevatetherearones.
　　Inthiswaytheairwillbe"spilled"outattherear，and，havinglosttheairsupportorbuoyancy，theglidercomesdowntotheground.Afewflightswillmakeanyordinarymanproficientinthecontrolofhisapparatusbyhisbodymovements，notonlyasconcernstheelevatinganddepressingoftheadvancingedges，butalsoactualsteering.Youwillquicklylearn，forinstance，that，astheshiftingofthebodilyweightbackwardsandforwardsaffectstheupwardanddownwardtrendoftheplanes，soamovementsideways——totheleftortheright——affectsthedirectioninwhichtheglidertravels.
　　AscendsatanAngle.
　　Inascending，thegliderandflyingmachine，likethebird，makesanangular，notaverticalflight.Justwhatthisangleofascensionmaybeisdifficulttodetermine.
　　Itisprobableandinfactaltogetherlikely，thatitvarieswiththeforceofthewind，weightoftherisingbody，powerofpropulsion，etc.This，inthelanguageofphysicists，istheangleofinclination，and，asageneralthing，undernormalconditions（stillair）shouldbeputdownasaboutoneinten，or53/4degrees.Thiswouldbeanidealcondition，butithasnot，asvetbeenreached.Theforceofthewindaffectstheangleconsiderably，asdoesalsotheweightandvelocityoftheapparatus.Ingeneralpracticetheanglevariesfrom23to45degrees.Atmorethan45degreesthesupportingeffortisovercomebytheresistancetoforwardmotion.
　　Increasingthespeedorpropulsiveforce，tendstolessentheangleatwhichthemachinemaybesuccessfullyoperatedbecauseitreducesthewindpressure.
　　Mostofthemodernflyingmachinesareoperatedatanangleof23degrees，orless.
　　MaintaininganEquilibrium.
　　Stableequilibriumisoneofthemainessentialstosuccessfulflight，andthiscannotbepreservedinanuncertain，gustywind，especiallybyanamateur.Thenoviceshouldnotattemptaglideunlesstheconditionsarejustright.Theseconditionsare：Aclear，levelspace，withoutobstructions，suchastrees，etc.，andasteadywindofnotexceedingtwelvemilesanhour.Alwaysflyagainstthewind.
　　Whenareasonableamountofproficiencyinthehandlingofthemachineonlevelgroundhasbeenacquiredthefieldofpracticemaybechangedtosomegentleslope.Instartingfromaslopeitwillbefoundeasiertokeepthemachineafloat，buttheexperienceatfirstislikelytobeverydisconcertingtoamanoflessthanironnerve.Astheglidersailsawayfromthetopoftheslopethedistancebetweenhimandthegroundincreasesrapidlyuntiltheaviatorthinksheisupahundredmilesintheair.Ifhewillkeepcool，manipulatehisapparatussoastopreserveitsequilibrium，and"letnaturetakeitscourse，"hewillcomedowngraduallyandsafelytothegroundataconsiderabledistancefromthestartingplace.
　　Thisisoneadvantageofstartingfromanelevation——
　　yourmachinewillgofurther.
　　But，iftheaviatorbecomes"rattled";ifhelosescontrolofhismachine，seriousresults，includingabadfallwithriskofdeath，arealmostcertain.Andyetthispracticeisjustasnecessaryastheinitiallessonsonlevelground.Whenjudgmentisused，and"hastemadeslowly，"thereisverylittlerealdanger.WhileexperimentingwithgliderstheWrightsmadeflightsinnumerableunderallsortsofconditionsandneverhadanaccidentofanykind.
　　EffectsofWindCurrents.
　　Thelargerthemachinethemoredifficultitwillbetocontrolitsmovementsintheair，andyetenlargementisabsolutelynecessaryasweight，intheformofmotor，rudder，etc.，isadded.
　　Aircurrentsnearthesurfaceofthegroundaredivertedbyeveryobstructionunlessthewindisblowinghardenoughtoremovetheobstructionentirely.Take，forinstance，thecaseofatreeorshrub，inamoderatewindoffromtentotwelvemilesanhour.Asthewindstrikesthetreeitdivides，partgoingtoonesideandpartgoingtotheother，whilestillanotherpartisdirectedupwardandgoesoverthetopoftheobstruction.
　　Thismakesthehandlingofaglideronanobstructedfielddifficultanduncertain.Tohandleaglidersuccessfullytheplaceofoperationshouldbeclearandthewindmoderateandsteady.Ifitisgustypostponeyourflight.
　　Inthisconnectionitwillbewelltounderstandthevelocityofthewind，andwhatitmeansasshowninthefollowingtable：
　　MilesperhourFeetpersecondPressurepersq.foot1014.7.492
　　2536.73.075
　　5073.312.300
　　100146.649.200
　　Pressureofwindincreasesinproportiontothesquareofthevelocity.Thuswindat10milesanhourhasfourtimesthepressureofwindat5milesanhour.Thegreaterthispressurethelargeandheaviertheobjectwhichcanberaised.Anyboywhohashadexperienceinflyingkitescantestifytothis，Highwinds，however，arealmostinvariablygustyanduncertainastodirection，andthismakesthemdangerousforaviators.Itisalsoaself—evidentfactthat，beyondacertainstage，theharderthewindblowsthemoredifficultitistomakeheadwayagainstit.
　　LaunchingDeviceforGliders.
　　Onpage195willbefoundadiagramofthevariouspartsofalauncherforgliders，designedandpatentedbyMr.OctaveChanute.IndescribingthisinventioninAeronautics，Mr.Chanutesays：
　　"Inpracticing，thetrack，preferablyportable，isgenerallylaidinthedirectionoftheexistingwindandthecar，preferablyalightplatform—car，isplacedonthetrack.Thetruckcarryingthewinding—drumanditsmotorisplacedtowindwardasuitabledistance——sayfromtwohundredtoonethousandfeet——andisfirmlyblockedoranchoredinlinewiththeportabletrack，whichispreferably80or100feetinlength.Theflyingorglidingmachinetobelaunchedwithitsoperatorisplacedontheplatform—carattheleewardendoftheportabletrack.
　　Theline，whichispreferablyaflexiblecombinationwire—and—cordcable，isstretchedbetweenthewinding—
　　drumonthetrackanddetachablysecuredtotheflyingorglidingmachine，preferablybymeansofatrip—hoop，orelseheldinthehandoftheoperator，sothattheoperatormayreadilydetachthesamefromtheflying—
　　machinewhenthedesiredheightisattained.
　　HowGliderIsStarted.
　　"Thenuponasignalgivenbytheoperatortheengineeratthemotorputsitintooperation，graduallyincreasingthespeeduntilthelineiswounduponthedrumatamaximumspeedof，say，thirtymilesanhour.Theoperatoroftheflying—machine，whetherhestandsuprightandcarriesitonhisshoulders，orwhetherhesitsorliesdownproneuponit，adjuststheaeroplaneorcarryingsurfacessothatthewindshallstrikethemonthetopandpressdownwardinsteadofupwarduntiltheplatform—carunderactionofthewinding—drumandlineattainstherequiredspeed.
　　"Whentheoperatorjudgesthathisspeedissufficient，andthisdependsuponthevelocityofthewindaswellasthatofthecarmovingagainstthewind，hequicklycausesthefrontoftheflying—machinetotipupward，sothattherelativewindstrikingontheundersideoftheplanesorcarryingsurfacesshalllifttheflyingmachineintotheair.Itthenascendslikeakitetosuchheightasmaybedesiredbytheoperator，whothentripsthehookandreleasesthelinefromthemachine.
　　WhattheOperatorDoes.
　　"Theoperatorbeingnowfreeintheairhasacertaininitialvelocityimpartedbythewinding—drumandlineandalsoapotentialenergycorrespondingtohisheightabovetheground.Iftheflyingorglidingmachineisprovidedwithamotor，hecanutilizethatinhisfurtherflight，andifitisasimpleglidingmachinewithoutmotorhecanmakeadescendingflightthroughtheairtosuchdistanceascorrespondstothevelocityacquiredandtheheightgained，steeringmeanwhilebythedevicesprovidedforthatpurpose.
　　"Thesimplestoperationormaneuveristocontinuetheflightstraightaheadagainstthewind;butitispossibletovarythiscoursetotherightorleft，oreventoreturnindownwardflightwiththewindtothevicinityofthestarting—point.Uponnearingthegroundtheoperatortipsupwardhiscarrying—surfacesandstopshisheadwayuponthecushionofincreasedairresistancesocaused.Theoperatorisinnowaypermanentlyfastenedtohismachine，andthemachineandtheoperatorsimplyrestuponthelightplatform—car，sothattheoperatorisfreetorisewiththemachinefromthecarwhenevertherequiredinitialvelocityisattained.
　　MotorFortheLauncher.
　　"Themotormaybeofanysuitablekindorconstruction，butispreferablyanelectricorgasolenemotor.
　　Thewinding—drumisfurnishedwithanysuitableorcustomaryreversing—guidetocausethelinetowindsmoothlyandevenlyuponthedrum.Thelineispreferablyacablecomposedofflexiblewireandhavingacottonorothercordcoretoincreaseitsflexibility.Thelineextendsfromthedrumtotheflyingorglidingmachine.
　　Itsfreeendmay，ifdesired，begraspedandheldbytheoperatoruntiltheflying—machineascendstothedesiredheight，whenbysimplylettinggoofthelinetheoperatormaycontinuehisflightfree.Theline，however，ispreferablyconnectedtotheflyingorglidingmachinedirectlybyatrip—hookhavingahandleortripleverwithinreachoftheoperator，sothatwhenheascendstotherequiredheighthemayreadilydetachthelinefromtheflyingorglidingmachine."
　　CHAPTERVII.
　　PUTTINGONTHERUDDER.
　　Glidersasarulehaveonlyonerudder，andthisisintherear.Ittendstokeeptheapparatuswithitsheadtothewind.Unliketherudderonaboatitisfixedandimmovable.Therealmotor—propelledflyingmachine，generallyhasbothfrontandrearruddersmanipulatedbywirecablesatthewilloftheoperator.
　　Allowingthattheamateurhasbecomereasonablyexpertinthemanipulationofthegliderheshould，beforeconstructinganactualflyingmachine，equiphisgliderwitharudder.
　　CrossPiecesforRudderBeam.
　　Todothisheshouldbeginbyputtinginacrosspiece，2feetlongby1/4x3/4inchesbetweenthecenterstruts，inthelowerplane.Thismaybefastenedtothestrutswithboltsorbraces.Theformermethodispreferable.
　　Onthiscrosspiece，andontherearframeoftheplaneitself，therudderbeamisclampedandbolted.Thisrudderbeamis8feet11incheslong.HavingputtheseinplaceduplicatetheminexactlythesamemanneranddimensionsfromtheupperframeThecrosspiecesonwhichtheendsoftherudderbeamsareclampedshouldbeplacedaboutonefootinadvanceoftherearframebeam.
　　TheRudderItself.
　　Thenextstepistoconstructtherudderitself.Thisconsistsoftwosections，onehorizontal，theothervertical.
　　Thelatterkeepstheaeroplaneheadedintothewind，whiletheformerkeepsitsteady——preservestheequilibrium.
　　Therudderbeamsformthetopandbottomframesoftheverticalrudder.Totheseareboltedandclampedtwouprightpieces，3feet，10inchesinlength，and3/4
　　inchincrosssection.Theselatterpiecesareplacedabouttwofeetapart.Thiscompletestheframeworkoftheverticalrudder.Seenextpage（59）.
　　Forthehorizontalrudderyouwillrequiretwostrips6feetlong，andfour2feetlong.Findtheexactcenteroftheuprightpiecesontheverticalrudder，andatthisspotfastenwithboltsthelongpiecesofthehorizontal，placingthemontheoutsideoftheverticalstrips.Nextjointheendsofthehorizontalstripswiththe2—footpieces，usingsmallscrewsandcornerbraces.Thisdoneyouwillhavetwoofthe2—footpiecesleft.Thesegointhecenterofthehorizontalframe，"straddling"theverticalstrips，asshownintheillustration.
　　Theframeworkistobecoveredwithclothinthesamemannerastheplanes.Forthisabouttenyardswillbeneeded.
　　StrengtheningtheRudder.
　　Toensurerigiditytheruddermustbestayedwithguywires.ForthispurposetheNo.12pianowireisthebest.Beginbyrunningtwoofthesewiresfromthetopeye—boltsofstanchions3and4，page37，torudderbeamwhereitjoinstherudderplanes，fasteningthematthebottom.Thenruntwowiresfromthetopoftherudderbeamatthesamepoint，tothebottomeye—boltsofthesamestanchions.Thiswillgiveyoufourdiagonalwiresreachingfromtherudderbeamtothetopandbottomplanesoftheglider.Now，fromtheouterendsoftherudderframerunfoursimilardiagonalwirestotheendoftherudderbeamwhereitrestsonthecrosspiece.Youwillthenhaveeighttrusswiresstrengtheningtheconnectionoftheruddertothemainbodyoftheglider.
　　Theframeworkoftherudderplanesisthentobebracedinthesameway，whichwilltakeeightmorewires，fourforeachrudderplane.Allthewiresaretobeconnectedatoneendwithturn—bucklessothetensionmayberegulatedasdesired.
　　Informingtherudderframeitwillbewelltomortisethecorners，tackthemtogetherwithsmallnails，andthenputinacornerbraceintheinsideofeachjoint.
　　Indoingthisbearinmindthatthematerialtobethusfastenedislight，andconsequentlythelightestofnails，screws，boltsandcornerpieces，etc.，isnecessary.
　　CHAPTERVIII.
　　THEREALFLYINGMACHINE.
　　Wewillnowassumethatyouhavebecomeproficientenoughtowarrantanattemptattheconstructionofarealflyingmachine——onethatwillnotonlyremainsuspendedintheairatthewilloftheoperator，butmakerespectableprogressinwhateverdirectionhemaydesiretogo.
　　Theglider，itmustberemembered，isnotsteerable，excepttoalimitedextent，andmovesonlyinonedirection——againstthewind.Besidesthisitspowerofflotation——suspensionintheair——iscircumscribed.
　　LargerSurfaceAreaRequired.
　　Therealflyingmachineisthegliderenlarged，andequippedwithmotorandpropeller.Thefirstthingtodoistodecideuponthesizerequired.Whileagliderof20footspreadislargeenoughtosustainamanitcouldnotunderanypossibleconditions，bemadetorisewiththeweightofthemotor，propellerandsimilarequipmentadded.Astheloadisincreasedsomustthesurfaceareaoftheplanesbeincreased.Justwhatthisincreaseinsurfaceareashouldbeisproblematicalasexperiencedaviatorsdisagree，butasageneralpropositionitmaybeplacedatfromthreetofourtimestheareaofa20—footglider.[3]
　　[3]SeeChapterXXV.
　　SomePracticalExamples.
　　TheWrightsusedabiplane41feetinspread，and61/2
　　ft.deep.This，forthetwoplanes，givesatotalsurfaceareaof538squarefeet，inclusiveofauxiliaryplanes.
　　Thissustainstheengineequipment，operator，etc.，atotalweightofficiallyannouncedat1，070pounds.Itshowsaliftingcapacityofabouttwopoundstothesquarefootofplanesurface，asagainstaliftingcapacityofabout1/2poundpersquarefootofplanesurfaceforthe20—footglider.ThissameWrightmachineisalsoreportedtohavemadeasuccessfulflight，carryingatotalloadof1，100pounds，whichwouldbeovertwopoundsforeachsquarefootofsurfacearea，which，withauxiliaryplanes，is538squarefeet.
　　Toattainthesameresultsinamonoplane，thesinglesurfacewouldhavetobe60feetinspreadand9feetdeep.But，whilethisisthemathematicalrule，Bleriothasdemonstratedthatitdoesnotalwaysholdgood.
　　Onhisrecord—breakingtripacrosstheEnglishchannel，July25th，1909，theFrenchmanwascarriedinamonoplane241/2feetinspread，andwithatotalsustainingsurfaceof1501/2squarefeet.Thetotalweightoftheoutfit，includingmachine，operatorandfuelsufficientforathree—hourrun，wasonly660pounds.Withanengineof（nominally）25horsepowerthedistanceof21mileswascoveredin37minutes.
　　WhichistheBest？
　　Righthereanestablishedmathematicalquantityisinvolved.Asmallplanesurfaceofferslessresistancetotheairthanalargeoneandconsequentlycanattainahigherrateofspeed.Asexplainedfurtheroninthischapterspeedisanimportantfactorinthematterofweight—sustainingcapacity.Amachinethattravelsone—
　　thirdfasterthananothercangetalongwithone—halfthesurfaceareaofthelatterwithoutaffectingtheload.Seetheclosingparagraphofthischapteronthispoint.Intheorytheconstructionisalsothesimplest，butthisisnotalwaysfoundtobesoinpractice.Thedesigningandcarryingintoexecutionofplansforanextensivearealikethatofamonoplaneinvolvesgreatskillandclevernessingettingaframeworkthatwillbestrongenoughtofurnishtherequisitesupportwithoutanundueexcessofweight.Thispropositionisgreatlysimplifiedinthebiplaneand，whilethespeedattainedbythelattermaynotbequitesogreatasthatofthemonoplane，ithasmuchlargerweight—carryingcapacity.
　　ProperSizesForFrame.
　　Allowingthatthebiplaneformisselectedtheconstructionmaybepracticallyidenticalwiththatofthe20—footgliderdescribedinChapterV.，exceptastosizeandeliminationofthearmpieces.Insizethesurfaceplanesshouldbeabouttwiceaslargeasthoseofthe20—footglider，viz：40feetspreadinsteadof20，and6feetdeepinsteadof3.Thehorizontalbeams，struts，stanchions，ribs，etc.，shouldalsobeincreasedinsizeproportionately.
　　Whilecareintheselectionofclear，straight—grainedtimberisimportantintheglider，itisstillmoreimportantintheconstructionofamotor—equippedflyingmachineasthestrainonthevariouspartswillbemuchgreater.
　　HowtoSpliceTimbers.
　　Itispracticallycertainthatyouwillhavetoresorttosplicingthehorizontalbeamsasitwillbedifficult，ifnotimpossible，tofind40—footpiecesoftimbertotallyfreefromknotsandwormholes，andofstraightgrain.
　　Ifsplicingisnecessaryselecttwogood20—footpieces，3incheswideand11/2inchesthick，andone10—footlong，ofthesamethicknessandwidth.Planeoffthebottomsidesofthe10—footstrip，beginningabouttwofeetbackfromeachend，andtaperthemsothestripwillbeabout3/4inchthickattheextremeends.Laythetwo20—footbeamsendtoend，andunderthejointthusmadeplacethe10—footstrip，withtheplaned—offendsdownward.
　　Thejointofthe20—footpiecesshouldbedirectlyinthecenterofthe10—footpiece.Boretenholes（witha1/4—
　　inchaugur）equi—distantapartthroughthe20—footstripsandthe10—footstripunderthem.Throughtheseholesrun1/4—inchstoveboltswithround，beveledheads.
　　Inplacingtheseboltsusewasherstopandbottom，onebetweentheheadandthetopbeam，andtheotherbetweenthebottombeamandthescrewnutwhichholdsthebolt.Screwthenutsdownhardsoastobringthetwobeamstightlytogether，andyouwillhavearigid40—footbeam.
　　SplicingwithMetalSleeves.
　　Anevenbetterwayofmakingaspliceisbytonguingandgroovingtheendsoftheframepiecesandenclosingtheminametalsleeve，butitrequiresmoremechanicalskillthanthemethodfirstnamed.Theoperationoftonguingandgroovingisespeciallydelicateandcallsforextremenicetyoftouchinthehandlingoftools，butifthisdexterityispossessedthejobwillbemuchmoresatisfactorythanonedonewithathirdtimber.
　　Astheframepiecesaregenerallyabout11/2inchindiameter，thetongueandthegrooveintowhichthetonguefitsmustbecorrespondinglysmall.Beginbysawingintoonesideofoneoftheframepiecesabout4
　　inchesbackfromtheend.Makethecutabout1/2inchdeep.Thenturnthepieceoverandduplicatethecut.
　　Nextsawdownfromtheendtothesecuts.Whenthesawed—outpartsareremovedyouwillhavea"tongue"
　　intheendoftheframetimber4incheslongand1/2inchthick.Thenextmoveistosawouta5/8—inchgrooveintheendoftheframepiecewhichistobejoined.Youwillhavetouseasmallchiseltoremovethe5/8—inchbit.
　　Thiswillleaveagrooveintowhichthetonguewillfiteasily.
　　JoiningtheTwoPieces.
　　Takeathinmetalsleeve——thisismerelyahollowtubeofaluminumorbrassopenateachend——8incheslong，andslipitovereitherthetonguedorgroovedendofoneoftheframetimbers.Itiswelltohavethesleevefitsnugly，andthismaynecessitateasand—paperingoftheframepiecessothesleevewillslipon.
　　Pushthesleevewellbackoutoftheway.Coverthetonguethoroughlywithglue，andalsoputsomeontheinsideofthegroove.Useplentyofglue.Nowpressthetongueintothegroove，andkeeptheendsfirmlytogetheruntiltheglueisthoroughlydried.Ruboffthejointlightlywithsand—papertoremoveanyofthegluewhichmayhaveoozedout，andslipthesleeveintoplaceoverthejoint.Tackthesleeveinpositionwithsmallcoppertacks，andyouwillhaveanidealsplice.
　　Thesameoperationistoberepeatedoneachofthefourframepieces.Two20—footpiecesjoinedinthiswaywillgiveasubstantialframe，butwhensuitabletimberofthiskindcannotbehad，threepieces，each6
　　feet11incheslong，maybeused.Thiswouldgive20
　　feet9inches，ofwhich8incheswillbetakenupinthetwojoints，leavingtheframe20feet1inchlong.
　　InstallationofMotor.
　　Nextcomestheinstallationofthemotor.Thekindsandefficiencyofthevarioustypesaredescribedinthefollowingchapter（IX）.Allweareinterestedinatthispointisthemannerofinstallation.Thisvariesaccordingtothepersonalideasoftheaviator.Thusonemanputshismotorinthefrontofhismachine，anotherplacesitinthecenter，andstillanotherfindstherearoftheframethebest.Allgetgoodresults，thecomparativeadvantagesofwhichitisdifficulttoestimate.Whereoneman，asalreadyexplained，fliesfasterthananother，theonebeatenfromthespeedstandpointhasanadvantageinthematterofcarryingweight，etc.
　　Theideasofvariouswell—knownaviatorsastothecorrectplacingofmotorsmaybehadfromthefollowing：
　　Wrights——Inrearofmachineandtooneside.
　　Curtiss——Welltorear，aboutmidwaybetweenupperandlowerplanes.
　　Raich——Inrear，abovethecenter.
　　Brauner—Smith——Inexactcenterofmachine.
　　VanAnden——Incenter.
　　Herring—Burgess——Directlybehindoperator.
　　Voisin——Inrear，andonlowerplane.
　　Bleriot——Infront.
　　R.E.P.——Infront.
　　TheOneChiefObject.
　　Anevendistributionoftheloadsoastoassistinmaintainingtheequilibriumofthemachine，shouldbetheonechiefobjectindecidinguponthelocationofthemotor.Itmatterslittlewhatparticularspotisselectedsolongastheweightdoesnottendtooverbalancethemachine，orto"throwitoffanevenkeel."Itisjustlikeloadingavessel，anoperationinwhichtheexpertseekstosodistributetheweightofthecargoastokeepthevesselinaperfectlyuprightposition，andpreventa"list"orleaningtooneside.Themoreevenlythecargoisdistributedthemoreperfectwillbetheequilibriumofthevesselandthebetteritcanbehandled.Sometimes，whennotproperlystowed，thecargoshifts，andthisatonceaffectsthepositionofthecraft.Whenaship"lists"tostarboardorportapreponderatingweightofthecargohasshiftedsideways;ifboworsternisundulydepresseditisasureindicationthatthecargohasshiftedaccordingly.Ineithereventthehandlingofthecraftbecomesnotonlydifficult，butextremelyhazardous.
　　Exactlythesameconditionsprevailinthehandlingofaflyingmachine.
　　ShapeofMachineaFactor.
　　Inplacingthemotoryoumustbegovernedlargelybytheshapeandconstructionoftheflyingmachineframe.
　　Ifthebulkoftheweightofthemachineandauxiliariesistowardtherear，thenthenaturallocationforthemotorwillbewelltothefrontsoastocounterbalancetheexcessinrearweight.Inthesamewayifthepreponderanceoftheweightisforward，thenthemotorshouldbeplacedbackofthecenter.
　　Asthepropellerbladeisreallyanintegralpartofthemotor，thelatterbeinguselesswithoutit，itsplacingnaturallydependsuponthelocationselectedforthemotor.
　　RuddersandAuxiliaryPlanes.
　　Hereagainthereisgreatdiversityofopinionamongaviatorsastosize，locationandform.Thestrikingdifferenceofideasinthisrespectiswellillustratedinthechoicemadebyprominentmakersasfollows：
　　Voisin——horizontalrudder，withtwowing—likeplanes，infront;box—likelongitudinalstabilityplaneinrear，insideofwhichisaverticalrudder.
　　Wright——largebiplanehorizontalrudderinfrontatconsiderabledistance——about10feet——fromthemainplanes;verticalbiplanerudderinrear;endsofupperandlowermainplanesmadeflexiblesotheymaybemoved.
　　Curtiss——horizontalbiplanerudder，withverticaldampingplanebetweentherudderplanesabout10feetinfrontofmainplanes;verticalrudderinrear;stabilizingplanesateachendofuppermainplane.
　　Bleriot——V—shapedstabilizingfin，projectingfromrearofplane，withbroadendoutward;tothebroadendofthisfinishingedaverticalrudder;horizontalbiplanerudder，alsoinrear，underthefin.
　　Theseinstancesshowforcefullythewidediversityofopinionexistingamongexperiencedaviatorsastothebestmannerofplacingtheruddersandstabilizing，orauxiliaryplanes，andmakemanifesthowhopelesswouldbethetaskofattemptingtoselectanyoneformandadviseitsexclusiveuse.
　　RudderandAuxiliaryConstruction.
　　Thematerialusedintheconstructionoftheruddersandauxiliaryplanesisthesameasthatusedinthemainplanes——sprucefortheframeworkandsomekindofrubberizedorvarnishedclothforthecovering.Theframesarejoinedandwiredinexactlythesamemannerastheframesofthemainplanes，thepurposebeingtosecurethesamestrengthandrigidity.Dimensionsofthevariouspartsdependupontheplanadoptedandthesizeofthemainplane.
　　Nodetailsastoexactdimensionsoftheseruddersandauxiliaryplanesareobtainable.Thevariousbuilders，whilewillingenoughtosupplydataastothegeneralmeasurements，weight，power，etc.，oftheirmachines，appeartohaveoverlookedthedetailsoftheauxiliaryparts，thinking，perhaps，thatthesewereofnoparticularimporttothegeneralpublic.IntheWrightmachine，therearhorizontalandfrontverticalruddersmaybesetdownasbeingaboutone—quarter（probablyalittleless）
　　thesizeofthemainsupportingplanes.
　　ArrangementofAlightingGear.
　　Mostmodernmachinesareequippedwithanalightinggear，whichnotonlyservestoprotectthemachineandaviatorfromshockorinjuryintouchingtheground，butalsoaidsingettingunderheadway.Alltheleadingmakes，withtheexceptionoftheWright，arefurnishedwithaframecarryingfromtwotofivepneumaticrubber—
　　tiredbicyclewheels.IntheCurtissandVoisinmachinesonewheelisplacedinfrontandtwointherear.IntheBleriotandotherprominentmachinesthereverseistherule——twowheelsinfrontandoneintherear.Farmanmakesuseoffivewheels，oneinthe，extremerear，andfour，arrangedinpairs，alittletothefrontofthecenterofthemainlowerplane.
　　InplaceofwheelstheWrightmachineisequippedwithaskid—likedeviceconsistingoftwolongbeamsattachedtothelowerplanebystanchionsandcurvingupfarinfront，soastoactassupportstothehorizontalrudder.
　　WhyWoodIsFavored.
　　Afrequentlyaskedquestionis："Whyisnotaluminum，orsomesimilarmetal，substitutedforwood."
　　Wood，particularlyspruce，ispreferredbecause，weightconsidered，itismuchstrongerthanaluminum，andthisisthelightestofallmetals.Inthisconnectionthefollowingtablewillbeofinterest：
　　CompressiveWeightTensileStrengthStrengthpercubicfootpersq.inchpersq.inchMaterialinlbs.inlbs.inlbs.
　　Spruce258，0005，000
　　Aluminum16216，000
　　Brass（sheet）51023，00012，000
　　Steel（tool）490100，00040，000
　　Copper（sheet）54830，00040，000
　　Asextremelightness，combinedwithstrength，especiallytensilestrength，isthegreatessentialinflying—
　　machineconstruction，itcanbereadilyseenthattheuseofmetal，evenaluminum，fortheframework，isprohibitedbyitsweight.Whilealuminumhasdoublethestrengthofsprucewooditisvastlyheavier，andthustheadvantageithasinstrengthisoverbalancedmanytimesbyitsweight.Thespecificgravityofaluminumis2.50;thatofspruceisonly0.403.
　　ThingstoBeConsidered.
　　Inlayingoutplansforaflyingmachinetherearefiveimportantpointswhichshouldbesettleduponbeforetheactualworkofconstructionisstarted.Theseare：
　　First——Approximateweightofthemachinewhenfinishedandequipped.
　　Second——Areaofthesupportingsurfacerequired.
　　Third——Amountofpowerthatwillbenecessarytosecurethedesiredspeedandliftingcapacity.
　　Fourth——Exactdimensionsofthemainframeworkandoftheauxiliaryparts.
　　Fifth——Size，speedandcharacterofthepropeller.
　　Indecidingupontheseitwillbewelltotakeintoconsiderationtheexperienceofexpertaviatorsregardingthesefeaturesasgivenelsewhere.（SeeChapterX.）
　　EstimatingtheWeightsInvolved.
　　Infixingupontheprobableapproximateweightinadvanceofconstructionmuch，ofcourse，mustbeassumed.
　　Thismeansthatitwillbeamatterofadvanceestimating.Ifatwo—passengermachineistobebuiltwewillstartbyassumingthemaximumcombinedweightofthetwopeopletobe350pounds.Mostoftheprofessionalaviatorsarelighterthanthis.TakingthemediumbetweentheweightsoftheCurtissandWrightmachineswehaveanetaverageof850poundsfortheframework，motor，propeller，etc.This，withthetwopassengers，amountsto1，190pounds.Asthemachinesquotedareinsuccessfuloperationitwillbereasonabletoassumethatthiswillbeasafebasistooperateon.
　　WhattheNoviceMustAvoid.
　　Thisdoesnotmean，however，thatitwillbesafetofollowtheseweightsexactlyinconstruction，butthattheywillservemerelyasabasistostartfrom.Becauseanexpertcanturnoutamachine，thoroughlyequipped，of850poundsweight，itdoesnotfollowthatanovicecandothesamething.Theexpert’sworkistheresultofyearsofexperience，andhehaslearnedhowtoconstructframesandmotorplantsoftheutmostlightnessandstrength.
　　ItwillbesaferforthenovicetoassumethathecannotduplicatetheworkofsuchmenasWrightandCurtisswithoutaddingmateriallytothegrossweightoftheframeworkandequipmentminuspassengers.
　　HowtoDistributetheWeight.
　　Letustake1，030poundsasthenetweightofthemachineasagainstthesameaverageintheWrightandCurtissmachines.Nowcomesthequestionofdistributingthisweightbetweentheframework，motor，andotherequipment.Asageneralpropositiontheframeworkshouldweighabouttwiceasmuchasthecompletepowerplant（thisisforamateurwork）.
　　Theword"framework"indicatesnotonlythewoodenframesofthemainplanes，auxiliaryplanes，rudders，etc.，buttheclothcoveringsaswell——everythinginfactexcepttheengineandpropeller.
　　Onthebasisnamedtheframeworkwouldweigh686
　　pounds，andthepowerplant344.Thesefiguresareliberal，andtheresultsdesiredmaybeobtainedwellwithinthemasthenovicewilllearnashemakesprogressinthework.
　　FiguringonSurfaceArea.
　　ItwasProf.Langleywhofirstbroughtintoprominenceinconnectionwithflyingmachineconstructionthemathematicalprinciplethatthelargertheobjectthesmallermaybetherelativeareaofsupport.AsexplainedinChapterXIII，therearemechanicallimitsastosizewhichitisnotpracticaltoexceed，butthemainprincipleremainsineffect.
　　Taketwoaeroplanesofmarkeddifferenceinareaofsurface.Thelargerwill，asarule，sustainagreaterweightinrelativeproportiontoitsareathanthesmallerone，anddotheworkwithlessrelativehorsepower.Asageneralthingwell—constructedmachineswillaverageasupportingcapacityofonepoundforeveryone—halfsquarefootofsurfacearea.Acceptingthisasaworkingrulewefindthattosustainaweightof1，200pounds——machineandtwopassengers——weshouldhave600
　　squarefeetofsurface.
　　DistributingtheSurfaceArea.
　　ThelargestsurfacesnowinusearethoseoftheWright，VoisinandAntoinettemachines——538squarefeetineach.Theactualsustainingpowerofthesemachines，sofarasknown，hasneverbeentestedtothelimit;itisprobablethatthemaximumisconsiderablyinexcessofwhattheyhavebeencalledupontoshow.
　　Inactualpracticetheaverageisalittleoveronepoundforeachone—halfsquarefootofsurfacearea.
　　Allowingthat600squarefeetofsurfacewillbeused，thenextquestionishowtodistributeittothebestadvantage.Thisisanotherimportantmatterinwhichindividualpreferencemustrule.Wehaveseenhowtheprofessionalsdisagreeonthispoint，someusingauxiliaryplanesoflargesize，andothersdependinguponsmallerauxiliarieswithanincreaseinnumbersoastosecureonadifferentplanvirtuallythesameamountofsurface.
　　Indecidinguponthisfeaturethebestthingtodoistofollowtheplansofsomesuccessfulaviator，increasingtheareaoftheauxiliariesinproportiontotheincreaseintheareaofthemainplanes.Thus，ifyouuse600
　　squarefeetofsurfacewherethemanwhoseplansyouarefollowinguses500，itissimplyamatterofmakingyourplanesone—fifthlargerallaround.
　　TheCostofProduction.
　　Costofproductionwillbeofinteresttotheamateurwhoessaystoconstructaflyingmachine.Assumingthatthesizedecideduponisdoublethatofthegliderthematerialfortheframework，timber，cloth，wire，etc.，willcostalittlemorethandouble.Thisisbecauseitmustbeheavierinproportiontotheincreasedsizeoftheframework，andheavymaterialbringsalargerpricethanthelightergoods.Ifweallow$20asthecostoftheglidermaterialitwillbesafetoputdownthecostofthatrequiredforarealflyingmachineframeworkat$60，providedtheownerbuildsithimself.
　　Asregardsthecostofmotorandsimilarequipmentitcanonlybesaidthatthisdependsupontheselectionmade.Therearesomereliableaviationmotorswhichmaybehadaslowas$500，andthereareotherswhichcostasmuchas$2，000.
　　ServicesofExpertNecessary.
　　Nomatterwhatkindofamotormaybeselectedtheservicesofanexpertwillbenecessaryinitsproperinstallationunlesstheamateurhasconsiderablegeniusinthislinehimself.Asageneralthing$25shouldbealiberalallowanceforthiswork.Nomatterhowcarefullytheenginemaybeplacedandconnecteditwillbelargelyamatterofluckifitisinstalledinexactlythepropermanneratthefirstattempt.Thechancesarethatseveralalterations，promptedbytheresultsoftrials，willhavetobemade.Ifthisisthecasetheexpert’sbillmayreadilyrunupto$50.Iftheamateuriscompetenttodothispartoftheworktheentireitemof$50may，ofcourse，becutout.
　　Asageneralpropositionafairlysatisfactoryflyingmachine，onethatwillactuallyflyandcarrytheoperatorwithit，maybeconstructedfor$750，butitwilllackthebetterqualitieswhichmarkthehigherpricedmachines.Thiscomputationismadeonthebasisof$60formaterial，$50forservicesofexpert，$600
　　formotor，etc.，andanallowanceof$40forextras.
　　Nomanwhohastheflyingmachinegerminhissystemwillbelongsatisfiedwithhisfirstmoderatepricemachine，nomatterhowwellitmaywork.It’stheoldstoryoftheautomobile"bug"
　　overagain.Themanwhostartsinwithamodest$1，000automobileinvariablyprogressesbyeasystagestothe$4，000or$5，000
　　class.Thenaturaltendencyistowantthebiggestandbestattainablewithinthefinancialreachoftheowner.
　　It’sexactlythesamewaywiththeflyingmachineconvert.Themoreproficienthebecomesinthemanipulationofhiscar，thestrongerbecomesthedesiretoflyfurtherandstayintheairlongerthantherestofhisbrethren.Thisnecessitateslarger，morepowerful，andmoreexpensivemachinesastheworkofthegermprogresses.
　　SpeedAffectsWeightCapacity.
　　Don’toverlookthefactthatthegreaterspeedyoucanattainthesmallerwillbethesurfaceareayoucangetalongwith.Ifamachinewith500squarefeetofsustainingsurface，travelingataspeedof40milesanhour，willcarryaweightof1，200pounds，wecancutthesustainingsurfaceinhalfandgetalongwith250
　　squarefeet，providedaspeedof60milesanhourcanbeobtained.At100milesanhouronly80squarefeetofsurfaceareawouldberequired.Inbothinstancestheweightsustainingcapacitywillremainthesameaswiththe500squarefeetofsurfacearea——1，200pounds.
　　Oneofthesedayssomemathematicalgeniuswillfigureoutthisproblemwithexactitudeandwewillhaveadependabletablegivingthemaximumcarryingcapacityofvarioussurfaceareasatvariousstatedspeeds，basedonthedimensionsoftheadvancingedges.Atpresentitislargelyamatterofguessworksofarasmakingaccuratecomputationgoes.Muchdependsupontheshapeofthemachine，andtheamountofsurfaceofferingresistancetothewind，etc.
　　CHAPTERIX.
　　SELECTIONOFTHEMOTOR.
　　Motorsforflyingmachinesmustbelightinweight，ofgreatstrength，productiveofextremespeed，andpositivelydependableinaction.Itmatterslittleastotheparticularform，orwhetherairorwatercooled，solongasthefourfeaturesnamedaresecured.Thereareatleastadozensuchmotorsorenginesnowinuse.Allareofthegasolenetype，andallpossessingreaterorlesserdegreethedesiredqualities.
　　Someofthesemotorsare：
　　Renault——8—cylinder，air—cooled;50horsepower;
　　weight374pounds.
　　Fiat——8—cylinder，air—cooled;50horsepower;weight150pounds.
　　Farcot——8—cylinder，air—cooled;from30to100horsepower，accordingtoboreofcylinders;weightofsmallest，84pounds.
　　R.E.P.——10—cylinder，air—cooled;150horsepower;
　　weight215pounds.
　　Gnome——7and14cylinders，revolvingtype，air—cooled;
　　50and100horsepower;weight150and300pounds.
　　Darracq——2to14cylinders，watercooled;30to200
　　horsepower;weightofsmallest100pounds.
　　Wright——4—cylinder，water—cooled;25horsepower;
　　weight200pounds.
　　Antoinette——8and16—cylinder，water—cooled;50and100
　　horsepower;weight250and500pounds.
　　E.N.V.——8—cylinder，water—cooled;from30to80
　　horsepower，accordingtoboreofcylinder;weight150
　　to400pounds.
　　Curtiss——8—cylinder，water—cooled;60horsepower;
　　weight300pounds.
　　AverageWeightPerHorsePower.
　　ItwillbenoticedthattheGnomemotorisunusuallylight，beingaboutthreepoundstothehorsepowerproduced，asopposedtoanaverageof41/2poundsperhorsepowerinothermakes.Thisresultissecuredbytheeliminationofthefly—wheel，theengineitselfrevolving，thusobtainingthesameeffectthatwouldbeproducedbyafly—wheel.TheFarcotisevenlighter，beingconsiderablylessthanthreepoundsperhorsepower，whichisthenearestapproachtothelong—soughtengineequipmentthatwillmakepossibleacompleteflyingmachinethetotalweightofwhichwillnotexceedonepoundpersquarefootofarea.
　　HowLightnessIsSecured.
　　ThusfarforeignmanufacturersareaheadofAmericansintheproductionoflight—weightaerialmotors，asisevidencedbytheGnomeandFarcotengines，bothofwhichareofFrenchmake.Extremelightnessismadepossiblebytheuseoffine，speciallypreparedsteelforthecylinders，thuspermittingthemtobemuchthinnerthanifordinaryformsofsteelwereused.Anotherbigsavinginweightismadebysubstitutingwhatareknownas"autolubricating"alloysforbearings.Thesealloysaremadeofacombinationofaluminumandmagnesium.
　　Stillfurthergainsaremadeintheuseofalloysteeltubinginsteadofsolidrods，andalsobytheparingawayofmaterialwhereveritcanbedonewithoutsacrificingstrength.Thisplan，withtheexclusiveuseofthebestgradesofsteel，regardlessofcost，makespossibleamarkedreductioninweight.
　　MultiplicityofCylinders.