aeroplanes-第24章

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the　dry　places；　hence　evaporation　will　take　place

and　whenever　a　liquid　vaporizes　it　means　heat。



On　the　other　hand；　when　the　vapor　is　turning

to　a　liquid；　condensation　takes　place；　and　that

means　cooling。　If　the　air　should　be　of　the　same

degree　of　saturation　throughout；that　is；　have

the　same　amount　of　moisture　everywhere；　there

would　be　few　winds。　These　remarks　apply　to

conditions　which　exist　over　low　altitudes　all　over

the　earth。



But　at　high　altitudes　the　conditions　are　entirely

different。　As　we　ascend　the　air　becomes　rarer。

It　has　less　moisture；　because　a　wet　atmosphere；

being　heavier；　lies　nearer　the　surface　of　the　earth。

Being　rarer　the　action　of　sunlight　on　the　particles

is　less　intense。　Reflection　and　refraction　of　the

rays　acting　on　the　light　atmosphere　do　not　produce

such　a　powerful　effect　as　on　the　air　near　the

ground。



All　these　conditionsthe　contour　of　the　earth；

the　uneven　character　of　the　moisture　in　the　air；

the　inequalities　of　the　convection　currents；　and

the　unstable；　tenuous；　elastic　nature　of　the　atmosphere；

make　the　trials　of　the　aviator　a　hazardous

one；　and　it　has　brought　out　numerous　theories

connected　with　bird　flight。　One　of　these　assumes

that　the　bird；　by　means　of　its　finely　organized

sense；　is　able　to　detect　rising　air　currents；　and　it

selects　them　in　its　flight；　and　by　that　means　is　enabled

to　continue　in　flight　indefinitely；　by　soaring；

or　by　flapping　its　wings。



ASCENDING　CURRENTS。It　has　not　been　explained

how　it　happens　that　these　particular　〃ascending

currents〃　always　appear　directly　in　the　line　of

the　bird　flight；　or　why　it　is　that　when；　for　instance；

a　flock　of　wild　geese　which　always　fly　through

space　in　an　A…shaped　formation；　are　able　to　get

ascending　air　currents　over　the　wide　scope　of　space

they　cover。



ASPIRATE　CURRENTS。Some　years　ago；　in　making

experiments　with　the　outstretched　wings　of

one　of　the　large　soaring　birds；　a　French　sailor

was　surprised　to　experience　a　peculiar　pulling　motion；

when　the　bird's　wings　were　held　at　a　certain

angle；　so　that　the　air　actually　seemed　to　draw　it

into　the　teeth　of　the　current。



It　is　known　that　if　a　ball　is　suspended　by　a

string；　and　a　jet　of　air　is　directed　against　it；　in

a　particular　way；　the　ball　will　move　toward　the

jet；　instead　of　being　driven　away　from　it。　A　well

known　spraying　device；　called　the　〃ball　nozzle；〃

is　simply　a　ball　on　the　end　of　a　nozzle；　and　the

stream　of　water　issuing　is　not　effectual　to　drive

the　ball　away。



From　the　bird　incident　alluded　to；　a　new　theory

was　propounded；　namely；　that　birds　flew　because

of　the　aspirated　action　of　the　air；　and　the　wings

and　body　were　so　made　as　to　cause　the　moving　air

current　to　act　on　it；　and　draw　it　forwardly。



OUTSTRETCHED　WINGS。This　only　added　to　the

〃bird　wing〃　theory　a　new　argument　that　all　flying

things　must　have　outstretched　wings；　in　order

to　fly；　forgetting　that　the　ball；　which　has　no

outstretched　wings；　has　also　the　same　〃aspirate〃

movement　attributed　to　the　wings　of　the　bird。



The　foregoing　remarks　are　made　in　order　to　impress

on　the　novice　that　theories　do　not　make

flying　machines；　and　that　speculations；　or　analogies

of　what　we　see　all　about　us；　will　not　make　an

aviator。　A　flying　machine　is　a　question　of

dynamics；　just　as　surely　as　the　action　of　the　sun　on

the　air；　and　the　movements　of　the　currents；　and

the　knowledge　of　applying　those　forces　in　the　flying

machine　makes　the　aviator。



THE　STARTING　POINT。Before　the　uninitiated

should　attempt　to　even　mount　a　machine　he　should

know　what　it　is　composed　of；　and　how　it　is　made。

His　investigation　should　take　in　every　part　of　the

mechanism；　he　should　understand　about　the　plane

surface；　what　the　stresses　are　upon　its　surface；

what　is　the　duty　of　each　strut；　or　brace　or　wire

and　be　able　to　make　the　proper　repairs。



THE　VITAL　PART　OF　THE　MACHINE。The　motor；

the　life　of　the　machine　itself；　should　be　like　a

book　to　him。　It　is　not　required　that　he　should

know　all　the　theories　which　is　necessary　in　the

building；　as　to　the　many　features　which　go　to

make　up　a　scientifically…designed　motor；　but　he

must　know　how　and　why　it　works。　He　should　understand

the　cam　action；　whereby　the　valves　are

lifted　at　the　proper　time；　what　the　effect　of　the

spark　advance　means；　the　throttling　of　the　engine；

air　admission　and　supply；　the　regulation

of　the　carbureter；　its　mechanism　and　construction；

the　propeller　should　be　studied；　and　its　action

at　various　speeds。



STUDYING　THE　ACTION　OF　THE　MACHINE。Then

comes　the　study　on　the　seat　of　the　machine　itself。

It　will　be　a　novel　sensation。　Before　him　is　the

steering　wheel；　if　it　should　be　so　equipped。　Turning

it　to　the　right；　swings　the　vertical　tail　plane

so　the　machine　will　turn　to　the　right。　Certainly；

he　knows　that；　but　how　far　must　he　turn　the

wheel　to　give　it　a　certain　angle。



It　is　not　enough　to　know　that　a　lever　or　a　wheel

when　moved　a　certain　way　will　move　a　plane　a

definite　direction。　He　should　learn　to　know

instinctively；　how　FAR　a　movement　to　make　to　get

a　certain　result　in　the　plane　itself；　and　under　running

conditions；　as　well。



Suppose　we　have　an　automobile；　running　at　the

rate　of　ten　miles　an　hour；　and　the　chauffeur　turns

the　steering　wheel　ten　degrees。　He　can　do　so　with

perfect　safety；　but　let　the　machine　be　going　forty

miles　an　hour；　and　turn　the　wheel　ten　degrees；

and　it　may　mean　an　accident。　In　one　case　the

machine　is　moving　14　1/2　feet　a　second；　and　in　the

other　instance　58　feet。



If　the　airship　has　a　lever　for　controlling　the

angle　of　flight；　he　must　study　its　arrangement；

and　note　how　far　it　must　be　moved　to　assume

the　proper　elevating　angle。　Then　come　the　means

for　controlling　the　lateral　stability　of　the　machine。

All　these　features　should　be　considered　and　studied

over　and　over；　until　you　have　made　them　your

friends。



While　thus　engaged；　you　are　perfectly　sure　that

you　can　remember　and　act　on　a　set　of　complicated

movements。　You　imagine　that　you　are　skimming

over　the　ground；　and　your　sense　tells　you　that　you

have　sufficient　speed　to　effect　a　launching。　In

your　mind　the　critical　time　has　come。



ELEVATING　THE　MACHINE。Simply　give　the　elevator

lever　the　proper　angle；　sharp　and　quick　and

up　you　go。　As　the　machine　responds；　and　you　can

feel　the　cushioning　motion；　which　follows；　as　it　begins

to　ride　the　air；　you　are　aware　of　a　sensation

as　though　the　machine　were　about　to　turn　over

to　one　side；　you　think　of　the　lateral　control　at

once；　but　in　doing　so　forget　that　the　elevator　must

be　changed；　or　you　will　go　too　high。



You　forget　about　the　earth；　you　are　too　busy

thinking　about　several　things　which　seem　to　need

your　attention。　Yes；　there　are　a　variety　of　matters

which　will　crowd　upon　you；　each　of　which　require

two　things；　the　first　being　to　get　the　proper

lever；　and　the　second；　to　move　it　just　so　far。



In　the　early　days　of　aeroplaning；　when　accidents

came　thick　and　fast；　the　most　usual　explanation

which　came　from　the　pilot；　when　he　recovered；

was：　〃I　pushed　the　lever　too　far。〃



Hundreds　of　trial　machines　were　built；　when

man　learned　that　he　could　fly；　and　in　every　instance；

it　is　safe　to　say；　the　experimenter　made　the

most　strenuous　exertion　to　get　up　in　the　air　the

first　time　the　machine　was　put　on　the　trial　ground。



It　is　a　wonder　that　accidents　were　not　recorded

by　the　hundreds；　instead　of　by　the　comparatively

few　that　were　heard　from。　It　was　very　discouraging；

no　doubt；　that　the　machines　would　not　fly；

but　that　all　of　them；　if　they　had　sufficient　power；

would　fly；　there　can　be　no　doubt。



HOW　TO　PRACTICE。Absolute　familiarity　with

every　part　of　the　machine　and　conditions　is　the

first　thing。　The　machine　is　brought　out；　and　the

engine　tested；　the　machine　being　held　in　leash

while　this　is　done。　It　is　then　throttled　down　so

that　the　power　of　the　engine　will　be　less　than　i