flying machines-第12节

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the　bore；　stroke　and　speed　being　the　same；　will　give

double　the　power　that　can　be　obtained　from　four；　but

this　does　not　always　hold　good。　Just　why　this　exception

should　occur　is　not　explainable　by　any　accepted　rule。



Horse　Power　and　Speed。



Speed　is　an　important　requisite　in　a　flying…machine

motor；　as　the　velocity　of　the　aeroplane　is　a　vital　factor

in　flotation。　At　first　thought；　the　propeller　and　similar

adjuncts　being　equal；　the　inexperienced　mind　would

naturally　argue　that　a　50…horsepower　engine　should

produce　just　double　the　speed　of　one　of　25…horsepower。

That　this　is　a　fallacy　is　shown　by　actual　performances。

The　Wrights；　using　a　25…horsepower　motor；　have　made

44　miles　an　hour；　while　Bleriot；　with　a　50…horsepower

motor；　has　a　record　of　a　short…distance　flight　at　the　rate

of　52　miles　an　hour。　The　fact　is　that；　so　far　as　speed

is　concerned；　much　depends　upon　the　velocity　of　the

wind；　the　size　and　shape　of　the　aeroplane　itself；　and　the

size；　shape　and　gearing　of　the　propeller。　The　stronger

the　wind　is　blowing　the　easier　it　will　be　for　the　aeroplane

to　ascend；　but　at　the　same　time　the　more　difficult

it　will　be　to　make　headway　against　the　wind　in　a　horizontal

direction。　With　a　strong　head　wind；　and　proper

engine　force；　your　machine　will　progress　to　a　certain

extent；　but　it　will　be　at　an　angle。　If　the　aviator　desired

to　keep　on　going　upward　this　would　be　all　right；　but

there　is　a　limit　to　the　altitude　which　it　is　desirable　to

reachfrom　100　to　500　feet　for　expertsand　after　that

it　becomes　a　question　of　going　straight　ahead。



Great　Waste　of　Power。



One　thing　is　certaineven　in　the　most　efficient　of

modern　aerial　motors　there　is　a　great　loss　of　power　between

the　two　points　of　production　and　effect。　The

Wright　outfit；　which　is　admittedly　one　of　the　most　effective

in　use；　takes　one　horsepower　of　force　for　the　raising

and　propulsion　of　each　50　pounds　of　weight。　This；

for　a　25…horsepower　engine；　would　give　a　maximum　lifting

capacity　of　1250　pounds。　It　is　doubtful　if　any　of　the

higher　rated　motors　have　greater　efficiency。　As　an　8…

cylinder　motor　requires　more　fuel　to　operate　than　a　4…

cylinder；　it　naturally　follows　that　it　is　more　expensive

to　run　than　the　smaller　motor；　and　a　normal　increase　in

capacity；　taking　actual　performances　as　a　criterion；　is

lacking。　In　other　words；　what　is　the　sense　of　using　an

8…cylinder　motor　when　one　of　4　cylinders　is　sufficient？



What　the　Propeller　Does。



Much　of　the　efficiency　of　the　motor　is　due　to　the　form

and　gearing　of　the　propeller。　Here　again；　as　in　other

vital　parts　of　flying…machine　mechanism；　we　have　a　wide

divergence　of　opinion　as　to　the　best　form。　A　fish　makes

progress　through　the　water　by　using　its　fins　and　tail；

a　bird　makes　its　way　through　the　air　in　a　similar　manner

by　the　use　of　its　wings　and　tail。　In　both　instances　the

motive　power　comes　from　the　body　of　the　fish　or　bird。



In　place　of　fins　or　wings　the　flying　machine　is　equipped

with　a　propeller；　the　action　of　which　is　furnished　by　the

engine。　Fins　and　wings　have　been　tried；　but　they　don't

work。



While　operating　on　the　same　general　principle；　aerial

propellers　are　much　larger　than　those　used　on　boats。

This　is　because　the　boat　propeller　has　a　denser；　more

substantial　medium　to　work　in　（water）；　and　consequently

can　get　a　better　〃hold；〃　and　produce　more　propulsive

force　than　one　of　the　same　size　revolving　in　the　air。

This　necessitates　the　aerial　propellers　being　much　larger

than　those　employed　for　marine　purposes。　Up　to　this

point　all　aviators　agree；　but　as　to　the　best　form　most　of

them　differ。



Kinds　of　Propellers　Used。



One　of　the　most　simple　is　that　used　by　Curtiss。　It

consists　of　two　pear…shaped　blades　of　laminated　wood；

each　blade　being　5　inches　wide　at　its　extreme　point；

tapering　slightly　to　the　shaft　connection。　These　blades

are　joined　at　the　engine　shaft；　in　a　direct　line。　The　propeller

has　a　pitch　of　5　feet；　and　weighs；　complete；　less

than　10　pounds。　The　length　from　end　to　end　of　the　two

blades　is　6　1/2　feet。



Wright　uses　two　wooden　propellers；　in　the　rear　of　his

biplane；　revolving　in　opposite　directions。　Each　propeller

is　two…bladed。



Bleriot　also　uses　a　two…blade　wooden　propeller；　but

it　is　placed　in　front　of　his　machine。　The　blades　are　each

about　3　1/2　feet　long　and　have　an　acute　〃twist。〃



Santos…Dumont　uses　a　two…blade　wooden　propeller；

strikingly　similar　to　the　Bleriot。



On　the　Antoinette　monoplane；　with　which　good　records

have　been　made；　the　propeller　consists　of　two　spoon…

shaped　pieces　of　metal；　joined　at　the　engine　shaft　in

front；　and　with　the　concave　surfaces　facing　the　machine。



The　propeller　on　the　Voisin　biplane　is　also　of　metal；

consisting　of　two　aluminum　blades　connected　by　a　forged

steel　arm。



Maximum　thrust；　or　stressexercise　of　the　greatest

air…displacing　forceis　the　object　sought。　This；　according

to　experts；　is　best　obtained　with　a　large　propeller

diameter　and　reasonably　low　speed。　The　diameter　is　the

distance　from　end　to　end　of　the　blades；　which　on　the

largest　propellers　ranges　from　6　to　8　feet。　The　larger

the　blade　surface　the　greater　will　be　the　volume　of　air

displaced；　and；　following　this；　the　greater　will　be　the

impulse　which　forces　the　aeroplane　ahead。　In　all　centrifugal

motion　there　is　more　or　less　tendency　to　disintegration

in　the　form　of　〃flying　off〃　from　the　center；　and

the　larger　the　revolving　object　is　the　stronger　is　this

tendency。　This　is　illustrated　in　the　many　instances　in

which　big　grindstones　and　fly…wheels　have　burst　from

being　revolved　too　fast。　To　have　a　propeller　break

apart　in　the　air　would　jeopardize　the　life　of　the　aviator；

and　to　guard　against　this　it　has　been　found　best　to　make

its　revolving　action　comparatively　slow。　Besides　this

the　slow　motion　（it　is　only　comparatively　slow）　gives

the　atmosphere　a　chance　to　refill　the　area　disturbed　by

one　propeller　blade；　and　thus　have　a　new　surface　for

the　next　blade　to　act　upon。



Placing　of　the　Motor。



As　on　other　points；　aviators　differ　widely　in　their

ideas　as　to　the　proper　position　for　the　motor。　Wright

locates　his　on　the　lower　plane；　midway　between　the　front

and　rear　edges；　but　considerably　to　one　side　of　the　exact

center。　He　then　counter…balances　the　engine　weight　by

placing　his　seat　far　enough　away　in　the　opposite　direction

to　preserve　the　center　of　gravity。　This　leaves　a

space　in　the　center　between　the　motor　and　the　operator

in　which　a　passenger　may　be　carried　without　disturbing

the　equilibrium。



Bleriot；　on　the　contrary；　has　his　motor　directly　in

front　and　preserves　the　center　of　gravity　by　taking　his

seat　well　back；　this；　with　the　weight　of　the　aeroplane；

acting　as　a　counter…balance。



On　the　Curtiss　machine　the　motor　is　in　the　rear；　the

forward　seat　of　the　operator；　and　weight　of　the　horizontal

rudder　and　damping　plane　in　front　equalizing　the

engine　weight。



No　Perfect　Motor　as　Yet。



Engine　makers　in　the　United　States；　England；　France

and　Germany　are　all　seeking　to　produce　an　ideal　motor

for　aviation　purposes。　Many　of　the　productions　are

highly　creditable；　but　it　may　be　truthfully　said　that

none　of　them　quite　fill　the　bill　as　regards　a　combination

of　the　minimum　of　weight　with　the　maximum　of

reliable　maintained　power。　They　are　all；　in　some　respects；

improvements　upon　those　previously　in　use；　but

the　great　end　sought　for　has　not　been　fully　attained。



One　of　the　motors　thus　produced　was　made　by　the

French　firm　of　Darracq　at　the　suggestion　of　Santos　Dumont；　and　on

lines　laid　down　by　him。　Santos　Dumont

wanted　a　2…cylinder　horizontal　motor　capable　of　developing

30　horsepower；　and　not　exceeding　4　1/2　pounds　per

horsepower　in　weight。



There　can　be　no　question　as　to　the　ability　and　skill

of　the　Darracq　people；　or　of　their　desire　to　produce　a

motor　that　would　bring　new　credit　and　prominence　to

the　firm。　Neither　could　anything　radically　wrong　be

detected　in　the　plans。　But　the　motor；　in　at　least　one

important　requirement；　fell　short　of　expectations。



It　could　not　be　depended　upon　to　deliver　an　energy

of　30　horsepower　continuously　for　any　length　of　time。

Its　maximum　power　could　be　secured　only　in　〃spurts。〃



This　tends　to　show　how　hard　it　is　to　produce　an　ideal

motor　for　aviation　purposes。　Santos　Dumont；　of　undoubted

skill　and　experience　as　an　aviator；　outlined　definitely

what　he　wanted；　one　of　the　greatest　designers

in　the　business　drew　the　plans；　and　the　famous　house　of

Darracq　bent　its　best　energies　to　the　production。　But

the　desired　end　was　not　fully　attained。



Features　of　Darracq　Motor。



Horizontal　motors　were　practically　abandoned　some

time　ago　in　favor　of　the　vertical　type；　but　Santos　Dumont

had　a　logical　reason　for　reverting　to　them。　He

wanted　to　secure　a　lower　center　of　gravity　than　would

be　possible　with　a　vertical　engine。　Theoretically　his

idea　was　correct　as　the　ho