Strangeasitmayseem，multiplicityofcylindersdoesnotalwaysaddproportionateweight.Becausea4—
cylindermotorweighssay100pounds，itdoesnotnecessarilyfollowthatan8—cylinderequipmentwillweigh200pounds.Thereasonofthiswillbeplainwhenitisunderstoodthatmanyofthepartsessentialtoa4—
cylindermotorwillfilltherequirementsofan8—cylindermotorwithoutenlargementoraddition.
Neitherdoesmultiplyingthecylindersalwaysincreasethehorsepowerproportionately.Ifa4—cylindermotorisratedat25horsepoweritisnotsafetotakeitforgrantedthatdoublethenumberofcylinderswillgive50horsepower.Generallyspeaking，eightcylinders，thebore，strokeandspeedbeingthesame，willgivedoublethepowerthatcanbeobtainedfromfour，butthisdoesnotalwaysholdgood.Justwhythisexceptionshouldoccurisnotexplainablebyanyacceptedrule.
HorsePowerandSpeed.
Speedisanimportantrequisiteinaflying—machinemotor，asthevelocityoftheaeroplaneisavitalfactorinflotation.Atfirstthought，thepropellerandsimilaradjunctsbeingequal，theinexperiencedmindwouldnaturallyarguethata50—horsepowerengineshouldproducejustdoublethespeedofoneof25—horsepower.
Thatthisisafallacyisshownbyactualperformances.
TheWrights，usinga25—horsepowermotor，havemade44milesanhour，whileBleriot，witha50—horsepowermotor，hasarecordofashort—distanceflightattherateof52milesanhour.Thefactisthat，sofarasspeedisconcerned，muchdependsuponthevelocityofthewind，thesizeandshapeoftheaeroplaneitself，andthesize，shapeandgearingofthepropeller.Thestrongerthewindisblowingtheeasieritwillbefortheaeroplanetoascend，butatthesametimethemoredifficultitwillbetomakeheadwayagainstthewindinahorizontaldirection.Withastrongheadwind，andproperengineforce，yourmachinewillprogresstoacertainextent，butitwillbeatanangle.Iftheaviatordesiredtokeepongoingupwardthiswouldbeallright，butthereisalimittothealtitudewhichitisdesirabletoreach——from100to500feetforexperts——andafterthatitbecomesaquestionofgoingstraightahead.
GreatWasteofPower.
Onethingiscertain——eveninthemostefficientofmodernaerialmotorsthereisagreatlossofpowerbetweenthetwopointsofproductionandeffect.TheWrightoutfit，whichisadmittedlyoneofthemosteffectiveinuse，takesonehorsepowerofforcefortheraisingandpropulsionofeach50poundsofweight.This，fora25—horsepowerengine，wouldgiveamaximumliftingcapacityof1250pounds.Itisdoubtfulifanyofthehigherratedmotorshavegreaterefficiency.Asan8—
cylindermotorrequiresmorefueltooperatethana4—
cylinder，itnaturallyfollowsthatitismoreexpensivetorunthanthesmallermotor，andanormalincreaseincapacity，takingactualperformancesasacriterion，islacking.Inotherwords，whatisthesenseofusingan8—cylindermotorwhenoneof4cylindersissufficient？
WhatthePropellerDoes.
Muchoftheefficiencyofthemotorisduetotheformandgearingofthepropeller.Hereagain，asinothervitalpartsofflying—machinemechanism，wehaveawidedivergenceofopinionastothebestform.Afishmakesprogressthroughthewaterbyusingitsfinsandtail;
abirdmakesitswaythroughtheairinasimilarmannerbytheuseofitswingsandtail.Inbothinstancesthemotivepowercomesfromthebodyofthefishorbird.
Inplaceoffinsorwingstheflyingmachineisequippedwithapropeller，theactionofwhichisfurnishedbytheengine.Finsandwingshavebeentried，buttheydon’twork.
Whileoperatingonthesamegeneralprinciple，aerialpropellersaremuchlargerthanthoseusedonboats.
Thisisbecausetheboatpropellerhasadenser，moresubstantialmediumtoworkin（water），andconsequentlycangetabetter\"hold，\"andproducemorepropulsiveforcethanoneofthesamesizerevolvingintheair.
Thisnecessitatestheaerialpropellersbeingmuchlargerthanthoseemployedformarinepurposes.Uptothispointallaviatorsagree，butastothebestformmostofthemdiffer.
KindsofPropellersUsed.
OneofthemostsimpleisthatusedbyCurtiss.Itconsistsoftwopear—shapedbladesoflaminatedwood，eachbladebeing5incheswideatitsextremepoint，taperingslightlytotheshaftconnection.Thesebladesarejoinedattheengineshaft，inadirectline.Thepropellerhasapitchof5feet，andweighs，complete，lessthan10pounds.Thelengthfromendtoendofthetwobladesis61/2feet.
Wrightusestwowoodenpropellers，intherearofhisbiplane，revolvinginoppositedirections.Eachpropelleristwo—bladed.
Bleriotalsousesatwo—bladewoodenpropeller，butitisplacedinfrontofhismachine.Thebladesareeachabout31/2feetlongandhaveanacute\"twist.\"
Santos—Dumontusesatwo—bladewoodenpropeller，strikinglysimilartotheBleriot.
OntheAntoinettemonoplane，withwhichgoodrecordshavebeenmade，thepropellerconsistsoftwospoon—
shapedpiecesofmetal，joinedattheengineshaftinfront，andwiththeconcavesurfacesfacingthemachine.
ThepropellerontheVoisinbiplaneisalsoofmetal，consistingoftwoaluminumbladesconnectedbyaforgedsteelarm.
Maximumthrust，orstress——exerciseofthegreatestair—displacingforce——istheobjectsought.This，accordingtoexperts，isbestobtainedwithalargepropellerdiameterandreasonablylowspeed.Thediameteristhedistancefromendtoendoftheblades，whichonthelargestpropellersrangesfrom6to8feet.Thelargerthebladesurfacethegreaterwillbethevolumeofairdisplaced，and，followingthis，thegreaterwillbetheimpulsewhichforcestheaeroplaneahead.Inallcentrifugalmotionthereismoreorlesstendencytodisintegrationintheformof\"flyingoff\"fromthecenter，andthelargertherevolvingobjectisthestrongeristhistendency.Thisisillustratedinthemanyinstancesinwhichbiggrindstonesandfly—wheelshaveburstfrombeingrevolvedtoofast.Tohaveapropellerbreakapartintheairwouldjeopardizethelifeoftheaviator，andtoguardagainstthisithasbeenfoundbesttomakeitsrevolvingactioncomparativelyslow.Besidesthistheslowmotion（itisonlycomparativelyslow）givestheatmosphereachancetorefilltheareadisturbedbyonepropellerblade，andthushaveanewsurfaceforthenextbladetoactupon.
PlacingoftheMotor.
Asonotherpoints，aviatorsdifferwidelyintheirideasastotheproperpositionforthemotor.Wrightlocateshisonthelowerplane，midwaybetweenthefrontandrearedges，butconsiderablytoonesideoftheexactcenter.Hethencounter—balancestheengineweightbyplacinghisseatfarenoughawayintheoppositedirectiontopreservethecenterofgravity.Thisleavesaspaceinthecenterbetweenthemotorandtheoperatorinwhichapassengermaybecarriedwithoutdisturbingtheequilibrium.
Bleriot，onthecontrary，hashismotordirectlyinfrontandpreservesthecenterofgravitybytakinghisseatwellback，this，withtheweightoftheaeroplane，actingasacounter—balance.
OntheCurtissmachinethemotorisintherear，theforwardseatoftheoperator，andweightofthehorizontalrudderanddampingplaneinfrontequalizingtheengineweight.
NoPerfectMotorasYet.
EnginemakersintheUnitedStates，England，FranceandGermanyareallseekingtoproduceanidealmotorforaviationpurposes.Manyoftheproductionsarehighlycreditable，butitmaybetruthfullysaidthatnoneofthemquitefillthebillasregardsacombinationoftheminimumofweightwiththemaximumofreliablemaintainedpower.Theyareall，insomerespects，improvementsuponthosepreviouslyinuse，butthegreatendsoughtforhasnotbeenfullyattained.
OneofthemotorsthusproducedwasmadebytheFrenchfirmofDarracqatthesuggestionofSantosDumont，andonlineslaiddownbyhim.SantosDumontwanteda2—cylinderhorizontalmotorcapableofdeveloping30horsepower，andnotexceeding41/2poundsperhorsepowerinweight.
TherecanbenoquestionastotheabilityandskilloftheDarracqpeople，oroftheirdesiretoproduceamotorthatwouldbringnewcreditandprominencetothefirm.Neithercouldanythingradicallywrongbedetectedintheplans.Butthemotor，inatleastoneimportantrequirement，fellshortofexpectations.
Itcouldnotbedependedupontodeliveranenergyof30horsepowercontinuouslyforanylengthoftime.
Itsmaximumpowercouldbesecuredonlyin\"spurts.\"
Thistendstoshowhowharditistoproduceanidealmotorforaviationpurposes.SantosDumont，ofundoubtedskillandexperienceasanaviator，outlineddefinitelywhathewanted;oneofthegreatestdesignersinthebusinessdrewtheplans，andthefamoushouseofDarracqbentitsbestenergiestotheproduction.Butthedesiredendwasnotfullyattained.
FeaturesofDarracqMotor.
Horizontalmotorswerepracticallyabandonedsometimeagoinfavoroftheverticaltype，butSantosDumonthadalogicalreasonforrevertingtothem.Hewantedtosecurealowercenterofgravitythanwouldbepossiblewithaverticalengine.Theoreticallyhisideawascorrectasthehorizontalmotorliesflat，andthereforeofferslessresistancetothewind，butitdidnotworkoutasdesired.
AtthesametimeitmustbeadmittedthatthisDarracqmotorisamarvelofingenuityandexquisiteworkmanship.
Thetwocylinders，havingaboreof51—10
inchesandastrokeof47—10inches，aremachinedoutofasolidbarofsteeluntiltheirweightisonly84—5
poundscomplete.Theheadisseparate，carryingtheseatingsfortheinletandexhaustvalves，isscrewedontothecylinder，andthenweldedinposition.Acopperwater—jacketisfitted，anditisinthisconditionthattheweightof84—5poundsisobtained.
Onlongtrips，especiallyinregionswheregasoleneishardtoget，theweightofthefuelsupplyisanimportantfeatureinaviation.Asanaturalconsequenceflyingmachineoperatorsfavorthemotorofgreatesteconomyingasoleneconsumption，provideditgivesthenecessarypower.
AnAmericaninventor，Ramseybyname，isworkingonamotorwhichissaidtopossessgreatpossibilitiesinthisline.Itsdistinctivefeaturesincludeaconnectingrodmuchshorterthanusual，andacrankshaftlocatedthelengthofthecrankfromthecentralaxisofthecylinder.Thishastheeffectofincreasingthepistonstroke，andalsoofincreasingtheproportionofthecrankcircleduringwhicheffectivepressureisappliedtothecrank.
Makingtheconnectingrodshorterandleavingthecrankmechanismthesamewouldintroduceexcessivecylinderfriction.ThisRamseyovercomesbythelocationofhiscrankshaft.Theeffectofthelongpistonstrokethussecured，istoincreasetheexpansionofthegases，whichinturnincreasesthepoweroftheenginewithoutincreasingtheamountoffuelused.
PropellerThrustImportant.
Thereisonegreatprincipleinflyingmachinepropulsionwhichmustnotbeoverlooked.Nomatterhowpowerfultheenginemaybeunlessthepropellerthrustmorethanovercomesthewindpressuretherecanbenoprogressforward.Shouldtheforceofthispropellerthrustandthatofthewindpressurebeequaltheresultisobvious.Themachineisatastand—stillsofarasforwardprogressisconcernedandisdeprivedoftheessentialadvancingmovement.
Speednotonlyfurnishessustentationfortheairship，butaddstothestabilityofthemachine.Anaeroplanewhichmaybejerkyanduncertaininitsmovements，sofarasequilibriumisconcerned，whenmovingataslowgait，willreadilymaintainanevenkeelwhenthespeedisincreased.
DesignsforPropellerBlades.
Itistheobjectofallmenwhodesignpropellerstoobtainthemaximumofthrustwiththeminimumexpenditureofengineenergy.Withthispurposeinviewmanypeculiarformsofpropellerbladeshavebeenevolved.Intheoryitwouldseemthatthebesteffectscouldbesecuredwithbladessoshapedastopresentathin（orcutting）edgewhentheycomeoutofthewind，andthenattheclimaxofdisplacementaffordamaximumofsurfacesoastodisplaceasmuchairaspossible.
Whilethisistheformmostgenerallyfavoredthereareothersinsuccessfuloperation.
Thereisalsowidedifferenceinopinionastotheequipmentofthepropellershaftwithtwoormoreblades.Someaviatorsusetwoandsomefour.Allhavemoreorlesssuccess.Asamathematicalpropositionitwouldseemthatfourbladesshouldgivemorepropulsiveforcethantwo，buthereagaincomesinoneofthepuzzlesofaviation，asthisresultisnotalwaysobtained.
DifferenceinPropellerEfficiency.
Thatthereisagreatdifferenceinpropellerefficiencyismadereadilyapparentbythecomparisonofeffectsproducedintwoleadingmakesofmachines——theWrightandtheVoisin.
Intheformeraweightoffrom1，100to1，200poundsissustainedandadvanceprogressmadeattherateof40milesanhourandmore，withhalftheenginespeedofa25horse—powermotor.Thiswouldbeasustainingcapacityof48poundsperhorsepower.ButtheactualcapacityoftheWrightmachine，asalreadystated，is50
poundsperhorsepower.
TheVoisinmachine，withaviator，weighsabout1，370
pounds，andisoperatedwithaso—horsepowermotor.
AllowingitthesamespeedastheWrightwefindthat，withdoubletheengineenergy，theliftingcapacityisonly271/2poundsperhorsepower.Towhatshallwechargethisremarkabledifference？Thesurfaceoftheplanesisexactlythesameinbothmachinessothereisnoadvantageinthematterofsupportingarea.
ComparisonofTwoDesigns.
OntheWrightmachinetwowoodenpropellersoftwobladeseach（eachbladehavingadecided\"twist\"）
areused.Asone25horsepowermotordrivesbothpropellerstheengineenergyamountstojustone—halfofthisforeach，or121/2horsepower.Andthisenergyisutilizedatone—halfthenormalenginespeed.
OntheVoisinaradicallydifferentsystemisemployed.
Herewehaveonemetaltwo—bladedpropellerwithaveryslight\"twist\"tothebladesurfaces.Thefullenergyofa50—horsepowermotorisutilized.
ExpertsFailtoAgree.
Whyshouldtherebesuchamarkeddifferenceintheresultsobtained？Whoknows？SomeexpertsmaintainthatitisbecausetherearetwopropellersontheWrightmachineandonlyoneontheVoisin，andconsequentlydoublethepropulsivepowerisexerted.
Butthisisnotafairdeduction，unlessbothpropellersareofthesamesize.Propulsivepowerdependsupontheamountofairdisplaced，andtheenergyputintothethrustwhichdisplacestheair.
Otherexpertsarguethatthedifferenceinresultsmaybetracedtothedifferenceinbladedesign，especiallyinthematterof\"twist.\"
Thefactisthatpropellerresultsdependlargelyuponthenatureoftheaeroplanesonwhichtheyareused.
Apropeller，forinstance，whichgivesexcellentresultsononetypeofaeroplane，willnotworksatisfactorilyonanother.
Therearesomefeatures，however，whichmaybesafelyadoptedinpropellerselection.Theseare：Asextensiveadiameteraspossible;bladearea10to15percentoftheareaswept;pitchfour—fifthsofthediameter;
rotationslow.Themaximumofthrusteffortwillbethusobtained.
CHAPTERX.
PROPERDIMENSIONSOFMACHINES.
Inlayingoutplansforaflyingmachinethefirstthingtodecideuponisthesizeoftheplanesurfaces.Theproportionsofthesemustbebasedupontheloadtobecarried.Thisincludesthetotalweightofthemachineandequipment，andalsotheoperator.Thiswillbearatherdifficultproblemtofigureoutexactly，butpracticalapproximatefiguresmaybereached.
Itiseasytogetattheweightoftheoperator，motorandpropeller，butthematterofdetermining，beforetheyareconstructed，whattheplanes，rudders，auxiliaries，etc.，willweighwhencompletedisanintricateproposition.
Thebestwayistotakethedimensionsofsomesuccessfulmachineandusethem，makingsuchalterationsinaminorwayasyoumaydesire.
DimensionsofLeadingMachines.
Inthefollowingtableswillbefoundthedetailsastosurfacearea，weight，power，etc.，ofthenineprincipaltypesofflyingmachineswhicharenowprominentlybeforethepublic：
MONOPLANES.
SurfaceareaSpreadinDepthinMakePassengerssq.feetlinearfeetlinearfeetSantos—Dumont111016.026.0
Bleriot1150.624.622.0
R.E.P121534.128.9
Bleriot223632.923.0
Antoinette253841.237.9
No.ofWeightWithoutPropellerMakeCylindersHorsePowerOperatorDiameterSantos—Dumont2302505.0
Bleriot3256806.9
R.E.P7359006.6
Bleriot7501，2408.1
Antoinette8501，0407.2
BIPLANES.
SurfaceAreaSpreadinDepthinMakePassengerssq.feetlinearfeetlinearfeetCurtiss225829.0
28.7
Wright253841.0
30.7
Farman243032.9
39.6
Voisin253837.9
39.6
No.ofWeightWithoutPropellerMakeCylindersHorsePowerOperatorDiameterCurtiss8506006.0
Wright4251，1008.1
Farman7501，2008.9
Voisin8501，2006.6
Ingivingthedepthdimensionsthelengthoverall——
fromtheextremeedgeofthefrontauxiliaryplanetotheextremetipoftherearisstated.ThuswhilethedimensionsofthemainplanesoftheWrightmachineare41feetspreadby61/2feetindepth，thedepthoverallis30.7.
FiguringOuttheDetails.
Withthisdataasaguideitshouldbecomparativelyeasytodecideuponthedimensionsofthemachinerequired.
Inarrivingatthemaximumliftingcapacitytheweightoftheoperatormustbeadded.Assumingthistoaverage170poundsthemethodofprocedurewouldbeasfollows：
Addtheweightoftheoperatortotheweightofthecompletemachine.ThenewWrightmachinecompleteweighs900pounds.This，plus170，theweightoftheoperator，givesatotalof1，070pounds.Thereare538
squarefeetofsupportingsurface，orpracticallyonesquarefootofsurfaceareatoeachtwopoundsofload.
Therearesomemachines，notablytheBleriot，inwhichthesupportingpowerismuchgreater.Inthislatterinstancewefindasurfaceareaof1501/2squarefeetcarryingaloadof680plus170，oranaggregateof850
pounds.Thisistheequivalentoffivepoundstothesquarefoot.Thisratioisphenomenallylarge，andshouldnotbetakenasaguidebyamateurs.
TheMatterofPassengers.
Thesedeductionsarebasedoneachmachinecarryingonepassenger，whichisadmittedlythelimitatpresentofthemonoplaneslikethoseoperatedforrecord—makingpurposesbySantos—DumontandBleriot.Thebiplanes，however，haveatwo—passengercapacity，andthisaddsmateriallytotheproportionoftheirweight—sustainingpowerascomparedwiththesurfacearea.Inthefollowingstatementallthemachinesarefiguredontheone—passengerbasis.CurtissandWrighthavecarriedtwopassengersonnumerousoccasions，andanextra170
poundsshouldthereforebeaddedtothetotalweightcarried，whichwouldmateriallyincreasethecapacity.
Evenwiththetwo—passengerloadthelimitisbynomeansreached，butasexperimentshavegonenofurtheritisimpossibletomakemoreaccuratefigures.
AverageProportionsofLoad.
Itwillbeinteresting，beforeproceedingtolayoutthedimensiondetails，tomakeacomparisonoftheproportionofloadeffectwiththesupportingsurfacesofvariouswell—knownmachines.Herearethefigures：
Santos—Dumont——Atrifleunderfourpoundspersquarefoot.
Bleriot——Fivepounds.
R.E.P.——Fivepounds.
Antoinette——Abouttwoandone—quarterpounds.
Curtiss——Abouttwoandone—halfpounds.
Wright——Twoandone—quarterpounds.
Farman——Atrifleoverthreepounds.
Voisin——Alittleundertwoandone—halfpounds.
ImportanceofEnginePower.
Whilethesefiguresareauthentic，theyareinawaymisleading，astheimportantfactorofenginepowerisnottakenintoconsideration.Letusrecallthefactthatitistheenginepowerwhichkeepsthemachineinmotion，andthatitisonlywhileinmotionthatthemachinewillremainsuspendedintheair.Hence，toattributethesupportsolelytothesurfaceareaiserroneous.
True，thatonceunderheadwaytheplanescontributelargelytothesustainingeffect，andareabsolutelyessentialinaerialnavigation——themotorcouldnotrisewithoutthem——still，whenitcomestoaquestionofweight—
sustainingpower，wemustalsofigureontheenginecapacity.
IntheWrightmachine，inwhichthereisaliftingcapacityofapproximately21/4poundstothesquarefootofsurfacearea，anengineofonly25horsepowerisused.
IntheCurtiss，whichhasaliftingcapacityof21/2
poundspersquarefoot，theengineisof50horsepower.
Thisisanotherofthepeculiaritiesofaerialconstructionandnavigation.Herewehaveagainof1/4poundinweight—liftingcapacitywithanexpenditureofdoublethehorsepower.ItisthisfeaturewhichenablesCurtisstogetalongwithasmallersurfaceareaofsupportingplanesattheexpenseofabigincreaseinenginepower.
ProperWeightofMachine.
Asageneralpropositionthemostsatisfactorymachineforamateurpurposeswillbefoundtobeonewithatotalweight—sustainingpowerofabout1，200pounds.
Deducting170poundsastheweightoftheoperator，thiswillleave1，030poundsforthecompletemotor—
equippedmachine，anditshouldbeeasytoconstructonewithinthislimit.Thisimplies，ofcourse，thatduecarewillbetakentoeliminateallsuperfluousweightbyusingthelightestmaterialcompatiblewithstrengthandsafety.
Thisplanwilladmitof686poundsweightintheframework，coverings，etc.，and344forthemotor，propeller，etc.，whichwillbeample.Justhowtodistributetheweightoftheplanesisamatterwhichmustbelefttotheingenuityofthebuilder.
ComparisonofBirdPower.
Thereisaninterestingstudyintheaccompanyingillustration.Notethatthesurfaceareaofthealbatrossismuchsmallerthanthatofthevulture，althoughthewingspreadisaboutthesame.Despitethisthealbatrossaccomplishesfullyasmuchinthewayofflightandsoaringasthevulture.Why？Becausethealbabossisquickerandmorepowerfulinaction.Itistheapplicationofthissameprincipleinflyingmachineswhichenablesthoseofgreatspeedandpowertogetalongwithlesssupportingsurfacethanthoseofslowermovement.
MeasurementsofCurtissMachine.
SomeideaofframeworkproportionmaybehadfromthefollowingdescriptionoftheCurtissmachine.Themainplaneshaveaspread（width）of29feet，andare41/2feetdeep.Thefrontdoublesurfacehorizontalrudderis6x2feet，withanareaof24squarefeet.Totherearofthemainplanesisasinglesurfacehorizontalplane6x2feet，withanareaof12squarefeet.Inconnectionwiththisisaverticalrudder21/2feetsquare.
Twomovableailerons，orbalancingplanes，areplacedattheextremeendsoftheupperplanes.Theseare6x2
feet，andhaveacombinedareaof24squarefeet.Thereisalsoatriangularshapedverticalsteadyingsurfaceinconnectionwiththefrontrudder.
Thuswehaveatotalof195squarefeet，butastheofficialfiguresare258，andthesizeofthetriangular—
shapedsteadyingsurfaceisunknown，wemusttakeitforgrantedthatthismakesupthedifference.Inthematterofproportionthehorizontaldouble—planerudderisaboutone—tenththesizeofthemainplane，countingthesurfaceareaofonlyoneplane，theverticalrudderone—fortieth，andtheaileronsone—twentieth.
CHAPTERXI.
PLANEANDRUDDERCONTROL.
Havingconstructedandequippedyourmachine，thenextthingistodecideuponthemethodofcontrollingthevariousruddersandauxiliaryplanesbywhichthedirectionandequilibriumandascendinganddescendingofthemachinearegoverned.
Theoperatormustbeinpositiontoshiftinstantaneouslythepositionofruddersandplanes，andalsotocontroltheactionofthemotor.Thislatterissupposedtoworkautomaticallyandasageneralthingdoessowithentiresatisfaction，buttherearetimeswhenthesupplyofgasolenemustberegulated，andsimilarthingsdone.
Airshipnavigationcallsforquickaction，andforthisreasonthematterofcontrolisanimportantone——itismorethanimportant;itisvital.
SeveralMethodsofControl.
Someaviatorsuseasteeringwheelsomewhatafterthestyleofthatusedinautomobiles，andbythisnotonlymanipulatetherudderplanes，butalsotheflowofgasolene.Othersemployfootlevers，andstillothers，liketheWrights，dependuponhandlevers.
Curtisssteershisaeroplanebymeansofawheel，butsecuresthedesiredstabilizingeffectwithaningeniousjointedchair—back.Thisissoarrangedthatbyleaningtowardthehighpointofhiswingplanestheaeroplaneisrestoredtoanevenkeel.Thesteeringpostofthewheelismovablebackwardandforward，andbythismotionelevationisobtained.
TheWrightsforsometimeusedtwohandlevers，onetosteerbyandwarptheflexibletipsoftheplanes，theothertosecureelevation.Theyhavenowconsolidatedallthefunctionsinonelever.Bleriotalsousesthesinglelevercontrol.
Farmanemploysalevertoactuatetherudders，butmanipulatesthebalancingplanesbyfootlevers.
Santos—Dumontusestwohandleverswithwhichtosteerandelevate，butmanipulatestheplanesbymeansofanattachmenttothebackofhisoutercoat.
ConnectionWiththeLevers.
Nomatterwhichparticularmethodisemployed，theconnectionbetweentheleversandtheobjecttobemanipulatedisalmostinvariablybywire.Forinstance，fromthesteeringlevers（orlever）twowiresconnectwithoppositesidesoftherudder.Asaleverismovedsoastodrawintheright—handwiretherudderisdrawntotherightandviceversa.Theoperationisexactlythesameasinsteeringaboat.Itisthesamewayinchangingthepositionofthebalancingplanes.Amovementofthehandsorfeetandthemachinehaschangeditscourse，or，iftheequilibriumisthreatened，isbackonanevenkeel.
Simpleasthisseemsitcallsforacoolhead，quickeye，andsteadyhand.Theleasthesitationorafalsemovement，andbothaviatorandcraftareindanger.
WhichMethodisBest？
Itwouldbeaboldmanwhowouldattempttopickoutanyoneofthesemethodsofcontrolandsayitwasbetterthantheothers.Asinothersectionsofaeroplanemechanismeachmethodhasitsadvocateswhodwelllearnedlyuponitsadvantages，butthefactremainsthatallthevariousplansworkwellandgivesatisfaction.
Whatthenoviceisinterestedinknowingishowthecontroliseffected，andwhetherhehasbecomeproficientenoughinhismanipulationofittobeabsolutelydependableintimeofemergency.Noamateurshouldattemptaflightalone，untilhehasthoroughlymasteredthesteeringandplanecontrol.Iftheservicesandadviceofanexperiencedaviatorarenottobehadthenoviceshouldmounthismachineonsomesuitablesupportssoitwillbewellclearoftheground，and，gettingintotheoperator’sseat，proceedtomakehimselfwellacquaintedwiththeoperationofthesteeringwheelandlevers.
SomeThingstoBeLearned.
Hewillsoonlearnthatcertainmovementsofthesteeringgearproducecertaineffectsontherudders.If，forinstance，hismachineisequippedwithasteeringwheel，hewillfindthatturningthewheeltotherightturnstheaeroplaneinthesamedirection，becausethetillerisbroughtaroundtotheleft.Inthesamewayhewilllearnthatagivenmovementoftheleverthrowstheforwardedgeofthemainplaneupward，andthatthemachine，gettingtheimpetusofthewindundertheconcavesurfacesoftheplanes，willascend.Inthesamewayitwillquicklybecomeapparenttohimthatanoppositemovementoftheleverwillproduceanoppositeeffect——theforwardedgesoftheplaneswillbelowered，theairwillbe\"spilled\"outtotherear，andthemachinewilldescend.
Thetimeexpendedinthesepreliminarylessonswillbewellspent.Itwouldbeanactoffollytoattempttoactuallysailthecraftwithoutthem.
CHAPTERXII.
HOWTOUSETHEMACHINE.
Itisamistakenideathatflyingmachinesmustbeoperatedatextremealtitudes.True，undertheimpetusofhandsomeprizes，andtheincentivetoadvancescientificknowledge，professionalaviatorshaveascendedtoconsiderableheights，flightsatfrom500to1，500feetbeingnowcommonwithsuchexpertsasFarman，Bleriot，Latham，Paulhan，WrightandCurtiss.Thealtituderecordatthistimeisabout4，165feet，heldbyPaulhan.
Oneoftheinstructionsgivenbyexperiencedaviatorstopupils，andforwhichtheyinsistuponimplicitobeyance，is：
\"Ifyourmachinegetsmorethan30feethigh，orcomesclosertothegroundthan6feet，descendatonce.\"SuchmenasWrightandCurtisswillnottolerateaviolationofthisrule.Iftheirinstructionsarenotstrictlycompliedwiththeydeclinetogivetheoffenderfurtherlessons.
WhyThisRulePrevails.
Thereisgoodreasonforthisprecaution.Thehigherthealtitudethemorerarefied（thinner）becomestheair，andthelesssustainingpowerithas.Consequentlythemoredifficultitbecomestokeepinsuspensionagivenweight.Whensailingwithin30feetofthegroundsustentationiscomparativelyeasyand，shouldafalloccur，theresultsarenotlikelytobeserious.Ontheotherhand，sailingtoonearthegroundisalmostasobjectionableinmanywaysasgettinguptoohigh.Ifthecraftisnavigatedtooclosetothegroundtrees，shrubs，fencesandotherobstructionsareliabletobeencountered.
Thereisalsothehandicapofcontraryaircurrentsdivertedbytheobstructionsreferredto，andwhichwillbeexplainedmorefullyfurtheron.
HowtoMakeaStart.
Takingitforgrantedthatthebeginnerhasfamiliarizedhimselfwiththemanipulationofthemachine，andespeciallythecontrolmechanism，thenextthinginorderisanactualflight.Itisprobablethathismachinewillbeequippedwithawheeledalightinggear，astheskidsusedbytheWrightsnecessitatetheuseofaspecialstartingtrack.Inthisrespectthewheeledmachineismucheasiertohandlesofarasnovicesareconcernedasitmaybeeasilyrolledtothetrialgrounds.This，asinthecaseoftheinitialexperiments，shouldbeaclear，reasonablylevelplace，freefromtrees，fences，rocksandsimilarobstructionswithwhichtheremaybedangerofcolliding.
Thebeginnerwillneedtheassistanceofthreemen.
Oneoftheseshouldtakehispositionintherearofthemachine，andoneateachend.Onreachingthetrialgroundtheaviatortakeshisseatinthemachineand，whilethemenattheendsholditsteadytheoneintherearassistsinretainingituntiltheoperatorisready.Inthemeantimetheaviatorhasstartedhismotor.Liketheglidertheflyingmachine，inordertoaccomplishthedesiredresults，shouldbeheadedintothewind.
WhentheMachineRises.
Undertheimpulseofthepushingmovement，andassistedbythemotoraction，themachinewillgraduallyrisefromtheground——providedithasbeenproperlyproportionedandputtogether，andeverythingisinworkingorder.Thisisthetimewhentheaviatorrequiresacoolhead，Atamodestdistancefromthegroundusethecontrollevertobringthemachineonahorizontallevelandovercomethetendencytorise.Theexactmanipulationofthisleverdependsuponthemethodofcontroladopted，andwiththistheaviatorissupposedtohavethoroughlyfamiliarizedhimselfaspreviouslyadvisedinChapterXI.
Itisatthisjuncturethattheoperatormustactpromptly，butwiththeperfectcomposurebegottenofconfidence.Oneofthegreatdrawbacksinaviationbynovicesisthetendencytobecomerattled，andthisismuchmoreprevalentthanonemightsuppose，evenamongmenwho，underotherconditions，arecoolandconfidentintheiractions.
Thereissomethinginthesensationofbeingsuddenlyliftedfromtheground，andsuspendedintheairthatisdisconcertingatthestart，butthiswillsoonwearoffiftheexperimenterwillkeepcool.Afewsuccessfulflightsnomatterhowshorttheymaybe，willputalotofconfidenceintohim.
MakeYourFlightsShort.
Bemodestinyourinitialflights.Don’tattempttomatchtherecordsofexperiencedmenwhohavedevotedyearstomasteringthedetailsofaviation.Paulhan，Farman，Bleriot，Wright，Curtiss，andalltherestofthembegan，andpracticedforyears，inthemannerheredescribed，beingcontenttomakejustalittleadvancementateachattempt.Aflightof150feet，cleanlyandsafelymade，isbetterasabeginningthanoneof400
yardsfullofbunglingmishaps.
Andyettheselatterhavetheiruses，providedtheoperatorisofadiscerningmindandcantakeadvantageofthemasobjectlessons.But，itisnotwelltoinvitethem.Theywilloccurfrequentlyenoughunderthemostfavorableconditions，anditisbesttohavethemcomelaterwhenthefeelingoftrepidationanduncertaintyastowhattodohaswornoff.
Aboveall，don’tattempttoflytoohigh.Keepwithinareasonabledistancefromtheground——about25or30
feet.Thisadviceisnotgivensolelytolessentheriskofseriousaccidentincaseofcollapse，butmainlybecauseitwillassisttoinstillconfidenceintheoperator.
Itiscomparativelyeasytolearntoswiminshallowwater，buttheknowledgethatoneistemptingdeathindeepwaterbegetstimidity.
PreservingtheEquilibrium.
Afterlearninghowtostartandstop，toascendanddescend，thenextthingtomasteristheartofpreservingequilibrium，theknackofkeepingthemachineperfectlylevelintheair——onan\"evenkeel，\"asasailorwouldsay.Thissimileisparticularlyappropriateasallaviatorsareinrealitysailors，andmuchmoredaringonesthanthosewhocoursetheseas.Thelatterareincraftwhicharekeptafloatbythebuoyancyofthewater，whetherinmotionorotherwiseand，solongasnormalconditionsprevail，willnotsink.Aviatorssailtheairincraftinwhichconstantmotionmustbemaintainedinordertoensureflotation.
Themanwhohasriddenabicycleormotorcyclearoundcurvesatanythinglikehighspeed，willhaveaverygoodideaastotheprincipleofmaintainingequilibriuminanairship.Heknowsthatinroundingcurvesrapidlythereisamarkedtendencytochangethedirectionofthemotionwhichwillresultinanupsetunlessheovercomesitbyaninclinationofhisbodyinanoppositedirection.Thisiswhyweseeracersleanwelloverwhentakingthecurves.Itsimplymustbedonetopreservetheequilibriumandavoidaspill.
HowItWorksIntheAir.
Iftheequilibriumofanairshipisdisturbedtoanextentwhichcompletelyovercomesthecenterofgravityitfallsaccordingtothelocationofthedisplacement.
Ifthisdisplacement，forinstance，isateitherendtheapparatusfallsendways;ifitistothefrontorrear，thefallisinthecorrespondingdirection.
Owingtouncertainaircurrents——theairiscontinuallyshiftingandeddying，especiallywithinahundredfeetorsooftheearth——theequilibriumofanairshipisalmostconstantlybeingdisturbedtosomeextent.Evenifthisdisturbanceisnotseriousenoughtobringonafallitinterfereswiththeprogressofthemachine，andshouldbeovercomeatonce.Thisisoneofthethingsconnectedwithaerialnavigationwhichcallsforprompt，intelligentaction.
Frequently，whenthedisplacementisveryslight，itmaybeovercome，andthecraftimmediatelyrightedbyamereshiftingoftheoperator’sbody.Take，forillustration，acaseinwhichtheextremerightendofthemachinebecomesloweredatriflefromthenormallevel.
Itispossibletobringitbackintoproperpositionbyleaningovertotheleftfarenoughtoshifttheweighttothecounter—balancingpoint.Thesameholdsgoodastominorfrontorreardisplacements.
WhenPlanesMustBeUsed.
Thereareotherdisplacements，however，andthesearethemostfrequent，whichcanbeonlyovercomebymanipulationofthestabilizingplanes.Themethodofproceduredependsupontheformofmachineinuse.TheWrightmachine，aspreviouslyexplained，isequippedwithplaneendswhicharesocontrivedastoadmitoftheirbeingwarped（positionchanged）bymeansofthelevercontrol.Theseflexibletipplanesmovesimultaneously，butinoppositedirections.Asthoseononeendrise，thoseontheotherendfallbelowthelevelofthemainplane.Bythismeansairisdisplacedatonepoint，andanincreasedamountsecuredinanother.
Thismayseemlikeacomplicatedsystem，butitsworkingsaresimplewhenonceunderstood.Itisbythemanipulationorwarpingoftheseflexibletipsthattransversestabilityismaintained，andanytendencytodisplacementendwaysisovercome.Longitudinalstabilityisgovernedbymeansofthefrontrudder.
Stabilizingplanesofsomeformareafeature，andanecessaryfeature，onallflyingmachines，butthemethodsofapplicationandmanipulationvaryaccordingtotheindividualideasoftheinventors.Theyalltend，however，towardthesameend——thekeepingofthemachineperfectlylevelwhenbeingnavigatedintheair.
WhentoMakeaFlight.
Abeginnershouldneverattempttomakeaflightwhenastrongwindisblowing.Thefiercerthewind，themorelikelyitistobegustyanduncertain，andthemoredifficultitwillbetocontrolthemachine.Eventhemostexperiencedanddaringofaviatorsfindthereisalimittowindspeedagainstwhichtheydarenotcompete.Thisisnotbecausetheylackcourage，buthavethesensetorealizethatitwouldbesillyanduseless.
Thenovicewillfindacomparativelystillday，oronewhenthewindisblowingatnottoexceed15milesanhour，thebestforhisexperiments.Themachinewillbemoreeasilycontrolled，thetripwillbesafer，andalsocheaperastheconsumptionoffuelincreaseswiththespeedofthewindagainstwhichtheaeroplaneisforced.
CHAPTERXIII.
PECULIARITIESOFAIRSHIPPOWER.
Asageneralpropositionittakesmuchmorepowertopropelanairshipagivennumberofmilesinacertaintimethanitdoesanautomobilecarryingafarheavierload.Automobileswithagrossloadof4，000pounds，andequippedwithenginesof30horsepower，havetravelledconsiderabledistancesattherateof50milesanhour.Thisisanequivalentofabout134poundsperhorsepower.Foranaveragemodernflyingmachine，withatotalload，machineandpassengers，of1，200
pounds，andequippedwitha50—horsepowerengine，50
milesanhouristhemaximum.Herewehavetheequivalentofexactly24poundsperhorsepower.Whythisgreatdifference？
NolessanauthoritythanMr.OctaveChanuteanswersthequestioninaplain，easilyunderstoodmanner.Hesays：
\"Inthecaseofanautomobilethegroundfurnishesastablesupport;inthecaseofaflyingmachinetheenginemustfurnishthesupportandalsovelocitybywhichtheapparatusissustainedintheair.\"
PressureoftheWind.
Airpressureisabigfactorinthematterofaeroplanehorsepower.Allowingthatadeadcalmexists，abodymovingintheatmospherecreatesmoreorlessresistance.
Thefasteritmoves，thegreateristhisresistance.
Movingattherateof60milesanhourtheresistance，orwindpressure，isapproximately50poundstothesquarefootofsurfacepresented.Ifthemovingobjectisadvancingatarightangletothewindthefollowingtablewillgivethehorsepowereffectoftheresistancepersquarefootofsurfaceatvariousspeeds.
HorsePowerMilesperHourpersq.foot100.013
150044
200.105
250.205
300.354
400.84
501.64
602.83
806.72
10013.12
Whilethepressurepersquarefootat60milesanhour，isonly1.64horsepower，at100miles，lessthandoublethespeed，ithasincreasedto13.12horsepower，orexactlyeighttimesasmuch.Inotherwordsthepressureofthewindincreaseswiththesquareofthevelocity.
Windat10milesanhourhasfourtimesmorepressurethanwindat5milesanhour.
HowtoDetermineUponPower.
Thiselementofairresistancemustbetakenintoconsiderationindeterminingtheenginehorsepowerrequired.
Whenthemachineisunderheadwaysufficienttoraiseitfromtheground（about20milesanhour），eachsquarefootofsurfaceresistance，willrequirenearlynine—tenthsofahorsepowertoovercomethewindpressure，andpropelthemachinethroughtheair.Asshowninthetabletheratioofpowerrequiredincreasesrapidlyasthespeedincreasesuntilat60milesanhourapproximately3horsepowerisneeded.
InamachineliketheCurtisstheareaofwind—exposedsurfaceisabout15squarefeet.Onthebasisofthisresistancemovingthemachineat40milesanhourwouldrequire12horsepower.Thiscomputationcoversonlythemachine’spowertoovercomeresistance.Itdoesnotcoverthepowerexertedinpropellingthemachineforwardaftertheairpressureisovercome.TomeetthisimportantrequirementMr.Curtissfindsitnecessarytousea50—horsepowerengine.Ofthispower，ashasbeenalreadystated，12horsepowerisconsumedinmeetingthewindpressure，leaving38horsepowerforthepurposeofmakingprogress.
Theflyingmachinemustmovefasterthantheairtowhichitisopposed.Unlessitdoesthistherecanbenodirectprogress.Ifthetwoforcesareequalthereisnostraight—aheadadvancement.Take，forsakeofillustration，acaseinwhichanaeroplane，whichhasdevelopedaspeedof30milesanhour，meetsawindvelocityofequalforcemovinginanoppositedirection.Whatistheresult？Therecanbenoadvancebecauseitisacontestbetweentwoevenlymatchedforces.Theaeroplanestandsstill.Theonlywaytogetoutofthedifficultyisfortheoperatortowaitformorefavorableconditions，orbringhismachinetothegroundintheusualmannerbymanipulationofthecontrolsystem.
Takeanothercase.Anaeroplane，capableofmaking50milesanhourinacalm，ismetbyaheadwindof25
milesanhour.Howmuchprogressdoestheaeroplanemake？Obviouslyitis25milesanhourovertheground.
Putthepropositioninstillanotherway.Ifthewindisblowingharderthanitispossiblefortheenginepowertoovercome，themachinewillbeforcedbackward.
WindPressureaNecessity.
Whileallthisistrue，thefactremainsthatwindpressure，uptoacertainstage，isanabsolutenecessityinaerialnavigation.Theatmosphereitselfhasverylittlerealsupportingpower，especiallyifinactive.Ifabodyheavierthanairistoremainafloatitmustmoverapidlywhileinsuspension.
Oneofthebestillustrationsofthisistobefoundinskatingoverthinice.Everyschoolboyknowsthatifhemoveswithspeedhemayskateorglideinsafetyacrossathinsheetoficethatwouldnotbegintobearhisweightifhewerestandingstill.Exactlythesamepropositionobtainsinthecaseoftheflyingmachine.
Thenon—technicalreasonwhythesupportofthemachinebecomeseasierasthespeedincreasesisthatthesustainingpoweroftheatmosphereincreaseswiththeresistance，andthespeedwithwhichtheobjectismovingincreasesthisresistance.Withavelocityof12milesanhourtheweightofthemachineispracticallyreducedby230pounds.Thus，ifunderaconditionofabsolutecalmitwerepossibletosustainaweightof770pounds，thesameatmospherewouldsustainaweightof1，000
poundsmovingataspeedof12milesanhour.Thissustainingpowerincreasesrapidlyasthespeedincreases.