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.