aeroplanes-第16节

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projecting　frame。



_Fig。　53。　Plan　view。_



The　full　page　view；　Fig。　53；　represents　a　plan

view；　with　one　of　the　wings　cut　away；　showing　the

general　arrangement　of　the　frame；　and　the　three

wheels　required　for　support；　together　with　the

brace　bars　referred　to。



The　necessity　of　the　rear　end　elevation　will

now　be　referred　to。　The　tail　need　not；　necessarily；

be　located　at　a　point　on　a　horizontal　line

between　the　planes。　It　may　be　higher；　or　lower

than　the　planes；　but　it　should　not　be　in　a　position

to　touch　the　ground　when　the　machine　is　about

to　ascend。



_Fig。　54。　Alighting。_



The　angle　of　ascension　in　the　planes　need　not

exceed　25　degrees　so　the　frame　does　not　require

an　angle　of　more　than　17　degrees。　This　is　shown

in　Fig。　54；　where　the　machine　is　in　a　position

ready　to　take　the　air　at　that　angle；　leaving　ample

room　for　the　steering　rudder。



ACTION　IN　ALIGHTING。Also；　in　alighting；　the

machine　is　banked；　practically　in　the　same

position　thus　shown；　so　that　it　alights　on　the　rear

wheels　O。



The　motor　U　is　usually　mounted　so　its　shaft　is

midway　between　the　planes；　the　propeller　V　being

connected　directly　with　the　shaft；　and　being　behind

the　planes；　is　on　a　medial　line　with　the

machine。



The　control　planes　L；　M；　N；　are　all　connected　up

by　means　of　flexible　wires　with　the　aviator　at　the

set　W；　the　attachments　being　of　such　a　character

that　their　arrangement　will　readily　suggest　themselves

to　the　novice。



THE　MONOPLANE。From　a　spectacular　standpoint

a　monoplane　is　the　ideal　flying　machine。　It

is　graceful　in　outline；　and　from　the　fact　that　it

closely　approaches　the　form　of　the　natural　flyer；

seems　to　be　best　adapted　as　a　type；　compared　with

the　biplane。



THE　COMMON　FLY。So　many　birds　have　been

cited　in　support　of　the　various　flying　theories　that

the　house　fly；　as　an　example　has　been　disregarded。

We　are　prone　to　overlook　the　small　insect；　but　it

is；　nevertheless；　a　sample　which　is　just　as　potent

to　show　the　efficiency　of　wing　surface　as　the　condor

or　the　vulture。



The　fly　has　greater　mobility　than　any　other　flying

creature。　By　the　combined　action　of　its　legs

and　wings　it　can　spring　eighteen　inches　in　the

tenth　of　a　second；　and　when　in　flight　can　change

its　course　instantaneously。



If　a　sparrow　had　the　same　dexterity；　proportionally；

it　could　make　a　flight　of　800　feet　in　the

same　time。　The　posterior　legs　of　the　fly　are　the

same　length　as　its　body；　which　enable　it　to　spring

from　its　perch　with　amazing　facility。



_Fig。　55。　Common　Fly。　Outstretched　Wings。_



The　wing　surface；　proportioned　to　its　body　and

weight；　is　no　less　a　matter　for　wonder　and　consideration。



In　Fig。　55　is　shown　the　outlines　of　the　fly　with

outstretched　wings。　Fig。　56　represents　it　with

the　wing　folded；　and　Fig。　57　is　a　view　of　a　wing

with　the　relative　size　of　the　top　of　the　body　shown

in　dotted　lines。



_Fig。　56。　Common　Fly。　Folded　Wings。_



The　first　thing　that　must　attract　attention；　after

a　careful　study　is　the　relative　size　of　the　body

and　wing　surface。　Each　wing　is　slightly　smaller

than　the　upper　surface　of　the　body；　and　the　thickness

of　the　body　is　equal　to　each　wing　spread。



_Fig。　57。　Relative　size　of　wing　and　body。_



The　weight；　compared　with　sustaining　surface；

if　expressed　in　understandable　terms；　would　be

equal　to　sixty　pounds　for　every　square　foot　of　surface。



STREAM　LINES。The　next　observation　is；　that

what　are　called　stream　lines　do　not　exist　in　the　fly。

Its　head　is　as　large　in　cross　section　as　its　body；

with　the　slightest　suggestion　only；　of　a　pointed

end。　Its　wings　are　perfectly　flat；　forming　a　true

plane；　not　dished；　or　provided　with　a　cambre；　even；

that　upward　curve；　or　bulge　on　the　top　of　the　aeroplane

surface；　which　seems　to　possess　such　a　fascination

for　many　bird　flight　advocates。



It　will　also　be　observed　that　the　wing　connection

with　the　body　is　forward　of　the　line　A；　which

represents　the　point　at　which　the　body　will　balance

itself；　and　this　line　passes　through　the　wings

so　that　there　is　an　equal　amount　of　supporting

surface　fore　and　aft　of　the　line。



Again；　the　wing　attachment　is　at　the　upper　side

of　the　body；　and　the　vertical　dimension　of　the

body；　or　its　thickness；　is　equal　to　four…fifths　of　the

length　of　he　wing。



The　wing　socket　permits　a　motion　similar　to　a

universal　joint；　Fig。　55　showing　how　the　inner

end　of　the　wing　has　a　downward　bend　where　it

joins　the　back；　as　at　B。



THE　MONOPLANE　FORM。For　the　purpose　of

making　comparisons　the　illustrations　of　the　monoplane

show　a　machine　of　300　square　feet　of　surface；

which　necessitates　a　wing　spread　of　forty

feet　from　tip　to　tip；　so　that　the　general　dimensions

of　each　should　be　18　1/2　feet　by　8　1/2　feet　at　its

widest　point。



First　draw　a　square　forty　feet　each　way；　as　in

Fig。　58；　and　through　this　make　a　horizontal　line

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。