aeroplanes- 第15部分

1；　and　four　intermediate　vertical　lines　are　then

drawn；　as　2；　3；　4；　5；　thus　providing　five　divisions；

each　eight　feet　wide。　In　the　first　division　the

planes　A；　B；　are　placed；　and　the　tail；　or　elevator

C；　is　one…half　the　width　of　the　last　division。



_Fig。　58。　Plan　of　Monoplane。_



The　frame　is　3　1/2　feet　wide　at　its　forward　end；

and　tapers　down　to　a　point　at　its　rear　end；　where

the　vertical　control　plane　D　is　hinged；　and　the

cross　struts　E；　E；　are　placed　at　the　division　lines

3；　4；　5。



The　angles　of　the　planes；　with　relation　to　the

frame；　are　usually　greater　than　in　the　biplane；

for　the　reason　that　the　long　tail　plane　requires

a　greater　angle　to　be　given　to　the　planes　when

arising；　or；　instead　of　this；　the　planes　A；　B；　are

mounted　high　enough　to　permit　of　sufficient　angle

for　initiating　flight　without　injuring　the　tail　D。



Some　monoplanes　are　built　so　they　have　a　support

on　wheels　placed　fore　and　aft。　In　others

the　tail　is　supported　by　curved　skids；　as　shown

at　A；　Fig。　59；　in　which　case　the　forward

supporting　wheels　are　located　directly　beneath　the　planes。

As　the　planes　are　at　about　eighteen　degrees

angle；　relative　to　the　frame；　and　the　tail　plane

B　is　at　a　slight　negative　angle　of　incidence；　as

shown　at　the　time　when　the　engine　is　started；　the

air　rushing　back　from　the　propeller；　elevates　the

tail；　and　as　the　machine　moves　forwardly　over

the　ground；　the　tail　raises　still　higher；　so　as　to

give　a　less　angle　of　incidence　to　the　planes　while

skimming　along　the　surface　of　the　ground。



_Fig。　59。　Side　Elevation；　Monoplane。_



In　order　to　mount；　the　tail　is　suddenly　turned

to　assume　a　sharp　negative　angle；　thus　swinging

the　tail　downwardly；　and　this　increases　the　angle

of　planes　to　such　an　extent　that　the　machine　leaves

the　ground；　after　which　the　tail　is　brought　to　the

proper　angle　to　assure　horizontal　flight。



The　drawing　shows　a　skid　at　the　forward　end；

attached　to　the　frame　which　carries　the　wheels。

The　wheels　are　mounted　beneath　springs　so　that

when　the　machine　alights　the　springs　yield　sufficiently

to　permit　the　skids　to　strike　the　ground；

and　they；　therefore；　act　as　brakes；　to　prevent　the

machine　from　traveling　too　far。







CHAPTER　X



POWER　AND　ITS　APPLICATION





THIS　is　a　phase　of　the　flying　machine　which　has

the　greatest　interest　to　the　boy。　He　instinctively

sees　the　direction　in　which　the　machine　has　its

life；its　moving　principle。　Planes　have　their

fascination；　and　propellers　their　mysterious　elements；

but　power　is　the　great　and　absorbing　question

with　him。



We　shall　try　to　make　its　application　plain　in

the　following　pages。　We　have　nothing　to　do　here

with　the　construction　and　operation　of　the　motor

itself；　as；　to　do　that　justice；　would　require　pages。



FEATURES　IN　POWER　APPLICATION。It　will　be

more　directly　to　the　point　to　consider　the　following

features　of　the　power　and　its　application：



1。　The　amount　of　power　necessary。



2。　How　to　calculate　the　power　applied。



3。　Its　mounting。





WHAT　AMOUNT　OF　POWER　IS　NECESSARY。In　the

consideration　of　any　power　plant　certain　calculations

must　be　made　to　determine　what　is　required。

A　horse　power　means　the　lifting　of　a　certain

weight；　a　definite　distance；　within　a　specified

time。



If　the　weight　of　the　vehicle；　with　its　load；　are

known；　and　its　resistance；　or　the　character　of　the

roadway　is　understood；　it　is　a　comparatively　easy

matter　to　calculate　just　how　much　power　must　be

exerted　to　overcome　that　resistance；　and　move　the

vehicle　a　certain　speed。



In　a　flying　machine　the　same　thing　is　true；　but

while　these　problems　may　be　known　in　a　general

way；　the　aviator　has　several　unknown　elements

ever　present；　which　make　estimates　difficult　to

solve。



THE　PULL　OF　THE　PROPELLER。Two　such　factors

are　ever　present。　The　first　is　the　propeller

pull。　The　energy　of　a　motor；　when　put　into　a

propeller；　gives　a　pull　of　less　than　eight　pounds

for　every　horse　power　exerted。



FOOT　POUNDS。The　work　produced　by　a　motor

is　calculated　in　Foot　Pounds。　If　550　pounds

should　be　lifted；　or　pulled；　one　foot　in　one　second

of　time；　it　would　be　equal　to　one　horse　power。



But　here　we　have　a　case　where　one　horse　power

pulls　only　eight　pounds；　a　distance　of　one　foot

within　one　second　of　time；　and　we　have　utilized

less　than　one　sixty…fifth　of　the　actual　energy　produced。



SMALL　AMOUNT　OF　POWER　AVAILABLE。This　is

due　to　two　things：　First；　the　exceeding　lightness

of　the　air；　and　its　great　elasticity；　and；　second；

the　difficulty　of　making　a　surface　which；　when　it

strikes　the　air；　will　get　a　sufficient　grip　to　effect

a　proper　pull。



Now　it　must　be　obvious；　that　where　only　such

a　small　amount　of　energy　can　be　made　available；

in　a　medium　as　elusive　as　air；　the　least　change；　or

form；　of　the　propeller；　must　have　an　important

bearing　in　the　general　results。



HIGH　PROPELLER　SPEED　IMPORTANT。Furthermore；

all　things　considered；　high　speed　is　important

in　the　rotation　of　the　propeller；　up　to　a　certain

point；　beyond　which　the　pull　decreases　in

proportion　to　the　speed。　High　speed　makes　a

vacuum　behind　the　blade　and　thus　decreases　the

effective　pull　of　the　succeeding　blade。



WIDTH　AND　PITCH　OF　BLADES。If　the　blade　is

too　wide　the　speed　of　the　engine　is　cut　down　to　a

point　where　it　cannot　exert　the　proper　energy；　if

the　pitch　is　very　small　then　it　must　turn　further　to

get　the　same　thrust；　so　that　the　relation　of　diameter；

pitch　and　speed；　are　three　problems　far　from

being　solved。



It　may　be　a　question　whether　the　propeller　form；

as　we　now　know　it；　is　anything　like　the　true　or

ultimate　shape；　which　will　some　day　be　discovered。



EFFECT　OF　INCREASING　PROPELLER　PULL。If　the

present　pull　could　be　doubled　what　a　wonderful

revolution　would　take　place　in　aerial　navigation；

and　if　it　were　possible　to　get　only　a　quarter　of

the　effective　pull　of　an　engine；　the　results　would

be　so　stupendous　that　the　present　method　of　flying

would　seem　like　child's　play　in　comparison。



It　is　in　this　very　matter；the　application　of

the　power；　that　the　bird；　and　other　flying　creatures

so　far　excel　what　man　has　done。　Calculations

made　with　birds　as　samples；　show　that　many

of　them　are　able　to　fly　with　such　a　small　amount

of　power　that；　if　the　same　energy　should　be　applied

to　a　flying　machine；　it　would　scarcely　drive

it　along　the　ground。



DISPOSITION　OF　THE　PLANES。The　second　factor

is　the　disposition　or　arrangement　of　the　planes

with　relation　to　the　weight。　Let　us　illustrate　this

with　a　concrete　example：



We　have　an　aeroplane　with　a　sustaining　surface

of　300　square　feet　which　weighs　900　pounds；

or　30　pounds　per　square　foot　of　surface。



DIFFERENT　SPEEDS　WITH　SAME　POWER。Now；　we

may　be　able　to　do　two　things　with　an　airship　under

those　conditions。　It　may　be　propelled　through

the　air　thirty　miles　an　hour；　or　sixty　miles；　with

the　expenditure　of　the　same　power。



An　automobile；　if　propelled　at　sixty；　instead　of

thirty　miles　an　hour；　would　require　an　additional

power　in　doing　so；　but　an　airship　acts　differently；

within　certain　limitations。



When　it　is　first　set　in　motion　its　effective　pull

may　not　be　equal　to　four　pounds　for　each　horse

power；　due　to　the　slow　speed　of　the　propeller；　and

also　owing　to　the　great　angle　of　incidence　which

resists　the　forward　movement　of　the　ship。



INCREASE　OF　SPEED　ADDS　TO　RESISTANCE。Finally；

as　speed　increases；　the　angle　of　the　planes

decrease；　resistance　is　less；　and　up　to　a　certain

point　the　pull　of　the　propeller　increases；　but　beyond

that　the　vacuum　behind　the　blades　becomes

so　great　as　to　bring　down　the　pull；　and　there　is

thus　a　balance；a　sort　of　mutual　governing　motion

which；　together；　determine　the　ultimate　speed

of　the　aeroplane。



HOW　POWER　DECREASES　WITH　SPEED。If　now；

with　the　same　propeller；　the　speed　should　be

doubled；　the　ship　would　go　no　faster；　because　the

bite　of　the　propeller　on　the　air　would　be　ineffective；

hence　it　will　be　seen　that　it　is　not　the　amount

of　power　in　itself；　that　determines　the　speed；　but

the　shape　of　the　propeller；　which　must　be　so　made

that　it　will　be　most　effective　at　the　speed　required

for　the　ship。



While　that　is　true　when　speed　is　the　matter　of

greatest　importance；　it　is　not　the　case　where　it　is

desired　to　effect　a　launching。　In　that　case　the

propeller　must　be　made　so　that　its　greatest　pull

will　be　at　a　slow　speed。　This　means　a　wider

blade；　and　a　greater　pitch；　and　a　comparatively

greater　pull　at　a　slow　speed。



No　such　consideration　need　be　given　to　an　automobile。

The　constant　accretion　of　power　adds

to　its　speed。　In　flying　machines　the　aviator　must

always　consider　some　companion　factor　which

must　be　consulted。



HOW　TO　CALCULATE　THE　POWER　APPLIED。In　a

previous　chapter　reference　was　made　to　a　plane

at　an　angle　of　forty…five　degrees；　to　which　two

scales　were　attached；　one　to　get　its　horizontal　pull；

or　drift；　and　the　other　its　vertical　pull；　or　lift。



PULLING　AGAINST　AN　ANGLE。Let　us　take　the

same　example　in　our　aeroplane。　Assuming　that

it　weighs　900　pounds；　and　that　the　angle　of　the

planes　is　forty…five　degrees。　If　we　suppose　that

the　air　beneath　the　plane　is　a　solid；　and　frictionless；

and　a　pair　of　scales　should　draw　it　up　the　incline；

the　pull　in　doing　so　would　be　one…half　of　its

weight；　or　450　pounds。



It　must　be　obvious；　therefore；　that　its　force；　in

moving　downwardly；　along　the　surface　A；　Fig。　60；

would　be　450　pounds。



The　incline　thus　shown　has　thereon　a　weight　B；

mounted　on　wheels　a；　and　the　forwardly…projecting

cord　represents　the　power；　or　propeller　pull；

which　must；　therefore；　exert　a　force　of　450　pounds

to　keep　it　in　a　stationary　position　against　the　surface

A。



In　such　a　case　the　thrust　along　the　diagonal

line　E　would　be　900　pounds；　being　the　composition

of　the　two　forces　pul