flying machines-第12章

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without　adding　materially　to　the　gross　weight　of

the　framework　and　equipment　minus　passengers。



How　to　Distribute　the　Weight。



Let　us　take　1；030　pounds　as　the　net　weight　of　the　machine

as　against　the　same　average　in　the　Wright　and

Curtiss　machines。　Now　comes　the　question　of　distributing

this　weight　between　the　framework；　motor；　and

other　equipment。　As　a　general　proposition　the　framework

should　weigh　about　twice　as　much　as　the　complete

power　plant　（this　is　for　amateur　work）。



The　word　〃framework〃　indicates　not　only　the　wooden

frames　of　the　main　planes；　auxiliary　planes；　rudders；

etc。；　but　the　cloth　coverings　as　welleverything　in　fact

except　the　engine　and　propeller。



On　the　basis　named　the　framework　would　weigh　686

pounds；　and　the　power　plant　344。　These　figures　are

liberal；　and　the　results　desired　may　be　obtained　well

within　them　as　the　novice　will　learn　as　he　makes　progress

in　the　work。



Figuring　on　Surface　Area。



It　was　Prof。　Langley　who　first　brought　into　prominence

in　connection　with　flying　machine　construction　the

mathematical　principle　that　the　larger　the　object　the

smaller　may　be　the　relative　area　of　support。　As　explained

in　Chapter　XIII；　there　are　mechanical　limits　as

to　size　which　it　is　not　practical　to　exceed；　but　the　main

principle　remains　in　effect。



Take　two　aeroplanes　of　marked　difference　in　area　of

surface。　The　larger　will；　as　a　rule；　sustain　a　greater

weight　in　relative　proportion　to　its　area　than　the　smaller

one；　and　do　the　work　with　less　relative　horsepower。　As

a　general　thing　well…constructed　machines　will　average

a　supporting　capacity　of　one　pound　for　every　one…half

square　foot　of　surface　area。　Accepting　this　as　a　working

rule　we　find　that　to　sustain　a　weight　of　1；200　pounds

machine　and　two　passengerswe　should　have　600

square　feet　of　surface。



Distributing　the　Surface　Area。



The　largest　surfaces　now　in　use　are　those　of　the

Wright；　Voisin　and　Antoinette　machines538　square

feet　in　each。　The　actual　sustaining　power　of　these　machines；

so　far　as　known；　has　never　been　tested　to　the

limit；　it　is　probable　that　the　maximum　is　considerably

in　excess　of　what　they　have　been　called　upon　to　show。

In　actual　practice　the　average　is　a　little　over　one　pound

for　each　one…half　square　foot　of　surface　area。



Allowing　that　600　square　feet　of　surface　will　be　used；

the　next　question　is　how　to　distribute　it　to　the　best

advantage。　This　is　another　important　matter　in　which

individual　preference　must　rule。　We　have　seen　how

the　professionals　disagree　on　this　point；　some　using

auxiliary　planes　of　large　size；　and　others　depending　upon

smaller　auxiliaries　with　an　increase　in　number　so　as　to

secure　on　a　different　plan　virtually　the　same　amount　of

surface。



In　deciding　upon　this　feature　the　best　thing　to　do　is

to　follow　the　plans　of　some　successful　aviator；　increasing

the　area　of　the　auxiliaries　in　proportion　to　the　increase

in　the　area　of　the　main　planes。　Thus；　if　you　use　600

square　feet　of　surface　where　the　man　whose　plans　you

are　following　uses　500；　it　is　simply　a　matter　of　making

your　planes　one…fifth　larger　all　around。



The　Cost　of　Production。



Cost　of　production　will　be　of　interest　to　the　amateur

who　essays　to　construct　a　flying　machine。　Assuming

that　the　size　decided　upon　is　double　that　of　the　glider

the　material　for　the　framework；　timber；　cloth；　wire；　etc。；

will　cost　a　little　more　than　double。　This　is　because　it

must　be　heavier　in　proportion　to　the　increased　size　of

the　framework；　and　heavy　material　brings　a　larger　price

than　the　lighter　goods。　If　we　allow　20　as　the　cost　of

the　glider　material　it　will　be　safe　to　put　down　the　cost

of　that　required　for　a　real　flying　machine　framework

at　60；　provided　the　owner　builds　it　himself。



As　regards　the　cost　of　motor　and　similar　equipment

it　can　only　be　said　that　this　depends　upon　the　selection

made。　There　are　some　reliable　aviation　motors　which

may　be　had　as　low　as　500；　and　there　are　others　which

cost　as　much　as　2；000。



Services　of　Expert　Necessary。



No　matter　what　kind　of　a　motor　may　be　selected　the

services　of　an　expert　will　be　necessary　in　its　proper

installation　unless　the　amateur　has　considerable　genius

in　this　line　himself。　As　a　general　thing　25　should　be

a　liberal　allowance　for　this　work。　No　matter　how　carefully

the　engine　may　be　placed　and　connected　it　will　be

largely　a　matter　of　luck　if　it　is　installed　in　exactly　the

proper　manner　at　the　first　attempt。　The　chances　are

that　several　alterations；　prompted　by　the　results　of　trials；

will　have　to　be　made。　If　this　is　the　case　the　expert's　bill　may

readily　run　up　to　50。　If　the　amateur　is　competent　to　do　this

part　of　the　work　the　entire　item　of　50　may；　of　course；　be　cut

out。



As　a　general　proposition　a　fairly　satisfactory　flying　machine；

one　that　will　actually　fly　and　carry　the　operator　with　it；　may　be

constructed　for　750；　but　it　will　lack　the　better　qualities　which

mark　the　higher　priced　machines。　This　computation　is　made　on

the　basis　of　60　for　material；　50　for　services　of　expert；　600

for　motor；　etc。；　and　an　allowance　of　40　for　extras。



No　man　who　has　the　flying　machine　germ　in　his　system　will　be　long

satisfied　with　his　first　moderate　price　machine；　no　matter　how

well　it　may　work。　It's　the　old　story　of　the　automobile　〃bug〃

over　again。　The　man　who　starts　in　with　a　modest　1；000　automobile

invariably　progresses　by　easy　stages　to　the　4；000　or　5；000

class。　The　natural　tendency　is　to　want　the　biggest　and　best

attainable　within　the　financial　reach　of　the　owner。



It's　exactly　the　same　way　with　the　flying　machine

convert。　The　more　proficient　he　becomes　in　the　manipulation

of　his　car；　the　stronger　becomes　the　desire　to　fly

further　and　stay　in　the　air　longer　than　the　rest　of　his

brethren。　This　necessitates　larger；　more　powerful；　and

more　expensive　machines　as　the　work　of　the　germ　progresses。



Speed　Affects　Weight　Capacity。



Don't　overlook　the　fact　that　the　greater　speed　you

can　attain　the　smaller　will　be　the　surface　area　you　can

get　along　with。　If　a　machine　with　500　square　feet　of

sustaining　surface；　traveling　at　a　speed　of　40　miles　an

hour；　will　carry　a　weight　of　1；200　pounds；　we　can　cut

the　sustaining　surface　in　half　and　get　along　with　250

square　feet；　provided　a　speed　of　60　miles　an　hour　can

be　obtained。　At　100　miles　an　hour　only　80　square　feet

of　surface　area　would　be　required。　In　both　instances　the

weight　sustaining　capacity　will　remain　the　same　as　with

the　500　square　feet　of　surface　area1；200　pounds。



One　of　these　days　some　mathematical　genius　will

figure　out　this　problem　with　exactitude　and　we　will　have

a　dependable　table　giving　the　maximum　carrying　capacity

of　various　surface　areas　at　various　stated　speeds；

based　on　the　dimensions　of　the　advancing　edges。　At

present　it　is　largely　a　matter　of　guesswork　so　far　as

making　accurate　computation　goes。　Much　depends　upon

the　shape　of　the　machine；　and　the　amount　of　surface

offering　resistance　to　the　wind；　etc。







CHAPTER　IX。



SELECTION　OF　THE　MOTOR。



Motors　for　flying　machines　must　be　light　in　weight；

of　great　strength；　productive　of　extreme　speed；　and

positively　dependable　in　action。　It　matters　little

as　to　the　particular　form；　or　whether　air　or

water　cooled；　so　long　as　the　four　features　named　are

secured。　There　are　at　least　a　dozen　such　motors　or

engines　now　in　use。　All　are　of　the　gasolene　type；　and

all　possess　in　greater　or　lesser　degree　the　desired　qualities。

Some　of　these　motors　are：



Renault8…cylinder；　air…cooled；　50　horse　power；

weight　374　pounds。



Fiat8…cylinder；　air…cooled；　50　horse　power；　weight

150　pounds。



Farcot8…cylinder；　air…cooled；　from　30　to　100　horse

power；　according　to　bore　of　cylinders；　weight　of　smallest；

84　pounds。



R。　E。　P。10…cylinder；　air…cooled；　150　horse　power；

weight　215　pounds。



Gnome7　and　14　cylinders；　revolving　type；　air…cool