aeroplanes- 第26部分

Shellac　prevents　the　moist　atmosphere　from　affecting

them。



MATERIAL　FOR　PROPELLERS。Very　light　propellers

can　also　be　made　of　thin；　annealed　aluminum

sheets；　and　the　pins　in　that　case　will　serve　as

guides　to　enable　you　to　get　the　desired　pitch。

Fiber　board　may　also　be　used；　but　this　is　more

difficult　to　handle。



Another　good　material　is　celluloid　sheets；

which；　when　cut　into　proper　strips；　is　dipped　in

hot　water；　for　bending　purposes；　and　it　readily

retains　its　shape　when　cooled。



RUBBERSuitable　rubber　for　the　strips　are

readily　obtainable　in　the　market。　Experiment

will　soon　show　what　size　and　lengths　are　best

adapted　for　the　particular　type　of　propellers

which　you　succeed　in　making。



PROPELLER　SHAPE　AND　SIZE。A　good　proportion

of　propeller　is　shown　in　Fig。　89。　This　also

shows　the　form　and　manner　of　connecting　the

shaft。　The　latter　A　has　a　hook　B　on　one　end　to

which　the　rubber　may　be　attached；　and　its　other

end　is　flattened；　as　at　C；　and　secured　to　the　blade

by　two…pointed　brads　D；　clinched　on　the　other

side。



_Fig。　89。　Shape　and　Size。_



The　collar　E　is　soldered　on　the　shaft；　and　in

practice　the　shaft　is　placed　through　the　bearing

hole　at　the　end　of　the　frame　before　the　hook　is

bent。



SUPPORTING　SURFACES。The　supporting　surfaces

may　be　made　perfectly　flat；　although　in　this

particular　it　would　be　well　to　observe　the　rules

with　respect　to　the　camber　of　large　machines。







CHAPTER　XV



THE　AEROPLANE　IN　THE　GREAT　WAR





DURING　the　civil　war　the　Federal　forces　used

captive　balloons　for　the　purpose　of　discovering

the　positions　of　the　enemy。　They　were　of　great

service　at　that　time；　although　they　were　stationed

far　within　the　lines　to　prevent　hostile　guns　from

reaching　them。



BALLOON　OBSERVATIONS。Necessarily；　observations

from　balloons　were　and　are　imperfect。　It

was　found　to　be　very　unsatisfactory　during　the

Russian…Japanese　war；　because　the　angle　of　vision

is　very　low；　and；　furthermore；　at　such　distances　the

movements；　or　even　the　location　of　troops　is　not

observable；　except　under　the　most　favorable　conditions。



Balloon　observation　during　the　progress　of　a

battle　is　absolutely　useless；　because　the　smoke

from　the　firing　line　is；　necessarily；　between　the

balloon　and　the　enemy；　so　that　the　aerial　scout

has　no　opportunity　to　make　any　observations；　even

in　detached　portions　of　the　fighting　zone；　which

are　of　any　value　to　the　commanders。



CHANGED　CONDITIONS　OF　WARFARE。Since　our

great　war；　conditions　pertaining　to　guns　have　been

revolutionized。　Now　the　ranges　are　so　great　that

captive　balloons　would　have　to　be　located　far　in

the　rear；　and　at　such　a　great　distance　from　the

firing　line　that　even　the　best　field　glasses　would

be　useless。



The　science　of　war　has　also　evolved　another

condition。　Soldiers　are　no　longer　exposed　during

artillery　attacks。　Uniforms　are　made　to　imitate

natural　objects。　The　khaki　suits　were　designed

to　imitate　the　yellow　veldts　of　South　Africa；

the　gray…green　garments　of　the　German

forces　are　designed　to　simulate　the　green　fields

of　the　north。



THE　EFFORT　TO　CONCEAL　COMBATANTS。The

French　have　discarded　the　historic　red　trousers；

and　the　elimination　of　lace；　white　gloves；　and

other　telltale　insignias　of　the　officers；　have　been

dispensed　with　by　special　orders。



In　the　great　European　war　armies　have　burrowed

in　the　earth　along　battle　lines　hundreds　of

miles　in　length；　made　covered　trenches；　prepared

artificial　groves　to　conceal　batteries；　and　in　many

ingenious　ways　endeavored　to　make　the　battlefield

an　imitation　field　of　nature。



SMOKELESS　POWDER。While　smokeless　powder

has　been　utilized　to　still　further　hide　a　fighting

force；　it　has；　in　a　measure；　uncovered　itself；　as

the　battlefield　is　not　now；　as　in　olden　times；　overspread

with　masses　of　rolling　smoke。



Nevertheless；　over　every　battlefield　there　is　a

haze　which　can　be　penetrated　only　from　above；

hence　the　possibilities　of　utilizing　the　aeroplane

in　war　became　the　most　important　study　with　all

nations；　as　soon　as　flying　became　an　accomplished

fact。



INVENTIONS　TO　ATTACK　AERIAL　CRAFT。Before

any　nation　had　the　opportunity　to　make　an　actual

test　on　the　battlefield；　inventors　were　at　work　to

devise　a　means　whereby　an　aerial　foe　could　be

met。　In　a　measure　the　aerial　gun　has　been　successful；

but　months　of　war　has　shown　that　the

aeroplane　is　one　of　the　strongest　arms　of　the

service　in　actual　warfare。



It　was　assumed　prior　to　the　European　war　that

the　chief　function　of　the　aeroplane　would　be　the

dropping　of　bombs；that　is　for　service　in　attacking

a　foe。　Actual　practice　has　not　justified

this　theory。　In　some　places　the　appearance　of

the　aeroplane　has　caused　terror；　but　it　has　been

found　the　great　value　is　its　scouting　advantages。



FUNCTION　OF　THE　AEROPLANE　IN　WAR。While

bomb　throwing　may　in　the　future　be　perfected；

it　is　not　at　all　an　easy　problem　for　an　aviator　to

do　work　which　is　commensurate　with　the　risk

involved。　The　range　is　generally　too　great；　the

necessity　of　swift　movement　in　the　machine　too

speedy　to　assure　accuracy；　and　to　attack　a　foe　at

haphazard　points　can　never　be　effectual。　Even

the　slowly…moving　gas　fields；　like　the　Zeppelin；

cannot　deliver　bombs　with　any　degree　of　precision

or　accuracy。



BOMB…THROWING　TESTS。It　is　interesting；　however；

to　understand　how　an　aviator　knows　where

or　when　to　drop　the　bomb　from　a　swiftly…moving

machine。　Several　things　must　be　taken　into　consideration；

such　as　the　height　of　the　machine　from

the　earth；　its　speed；　and　the　parabolic　curve　that

the　bomb　will　take　on　its　flight　to　the　earth。



When　an　object　is　released　from　a　moving　machine

it　will　follow　the　machine　from　which　it　is

dropped；　gradually　receding　from　it；　as　it　descends；

so　that　the　machine　is　actually　beyond

the　place　where　the　bomb　strikes　the　earth；　due

to　the　retarding　motion　of　the　atmosphere　against

the　missile。



The　diagram　Fig。　90　will　aid　the　boy　in　grasping

the　situation。　A　is　the　airship；　B　the　path

of　its　flight；　a　the　course　of　the　bomb　after　it

leaves　the　airship；　and　D　the　earth。　The　question

is　how　to　determine　the　proper　movement

when　to　release　the　bomb。



METHOD　FOR　DETERMINING　MOVEMENT　OF　A

BOMB。Lieut。　Scott；　U。　S。　A。；　of　the　Coast　Survey

Artillery；　suggested　a　method　for　determining

these　questions。　It　was　necessary　to　ascertain；

first；　the　altitude　and　speed。　While　the　barometer

is　used　to　determine　altitudes；　it　is

obvious　that　speed　is　a　matter　much　more　difficult

to　ascertain；　owing　to　the　wind　movements；

which　in　all　cases　make　it　difficult　for　a　flier　to

determine；　even　with　instruments　which　have

been　devised　for　the　purpose。



_Fig。　90。　Course　of　a　Bomb。_



Instead；　therefore；　of　relying　on　the　barometer；

the　ship　is　equipped　with　a　telescope　which　may

be　instantly　set　at　an　angle　of　45　degrees；　or　vertically。



Thus；　Fig　91　shows　a　ship　A；　on　which　is

mounted　a　telescope　B；　at　an　angle　of　45　degrees。

The　observer　first　notes　the　object　along　the　line

of　45　degrees；　and　starts　the　time　of　this　observation

by　a　stop　watch。



The　telescope　is　then　turned　so　it　is　vertical；

as　at　C；　and　the　observer　watches　through　the

telescope　until　the　machine　passes　directly　over

the　object；　when　the　watch　is　stopped；　to　indicate

the　time　between　the　two　observations。



_Fig。　91。　Determining　Altitude　and　Speed。_



The　height　of　the　machine　along　the　line　D　is

thus　equal　to　the　line　E　from　B　to　C；　and　the　time

of　the　flight　from　B　to　a　being　thus　known；　as

well　as　the　height　of　the　machine；　the　observer

consults　specially…prepared　tables　which　show

just　what　kind　of　a　curve　the　bomb　will　make　at

that　height　and　speed。



All　that　is　necessary　now　is　to　set　the　sighter

of　the　telescope　at　the　angle　given　in　the　tables；

and　when　the　object　to　be　hit　appears　at　the　sight；

the　bomb　is　dropped。



THE　GREAT　EXTENT　OF　MODERN　BATTLE　LINES。

The　great　war　brought　into　the　field　such　stupendous

masses　of　men　that　the　battle　lines　have

extended　over　an　unbroken　front　of　over　200

miles。



In　the　battle　of　Waterloo；　about　140；000　men

were　engaged　on　both　sides；　and　the　battle　front

was　less　than　six　miles。　There　were；　thus　massed；

along　the　front；　over　20；000　men　every　mile　of

the　way；　or　10；000　on　each　side。



In　the　conflict　between　the　Allies　and　the　Germans

it　is　estimated　that　there　were　less　than

7500　along　each　mile。　It　was　predicted　in　the

earlier　stages　of　the　war　that　it　would　be　an　easy

matter　for　either　side　to　suddenly　mass　such　an

overwhelming　force　at　one　point　as　to　enable　the

attacking　party　to　go　through　the　opposing　force

like　a　wedge。



Such　tactics　were　often　employed　by　Napoleon

and　other　great　masters　of　war；　but　in　every　effort

where　it　has　been　attempted　in　the　present

conflict；　it　was　foi