flying machines-第30章

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buoyant　of　all　known　gases。　It　is　secured　commercially

by　treating　zinc　or　iron　with　dilute　sulphuric　or

hydrochloric　acid。　The　average　cost　may　be　safely　placed

at　10　per　1；000　feet　so　that；　to　inflate　a　balloon　of　the

size　of　the　Zeppelin；　holding　460；000　cubic　feet；　would

cost　4；600。



Proportions　of　Materials　Required。



In　making　hydrogen　gas　it　is　customary　to　allow　20

per　cent　for　loss　between　the　generation　and　the　introduction

of　the　gas　into　the　balloon。　Thus；　while　the

formula　calls　for　iron　28　times　heavier　than　the　weight

of　the　hydrogen　required；　and　acid　49　times　heavier；　the

real　quantities　are　20　per　cent　greater。　Hydrogen　weighs

about　0。09　ounce　to　the　cubic　foot。　Consequently　if　we

need　say　450；000　cubic　feet　of　gas　we　must　have　2；531。25

pounds　in　weight。　To　produce　this；　allowing　for　the　20

percent　loss；　we　must　have　35　times　its　weight　in　iron；

or　over　44　tons。　Of　acid　it　would　take　60　times　the

weight　of　the　gas；　or　nearly　76　tons。



In　Time　of　Emergency。



These　figures　are　appalling；　and　under　ordinary　conditions

would　be　prohibitive；　but　there　are　times　when

the　balloon　operator；　unable　to　obtain　water　or　coal　gas；

must　foot　the　bills。　In　military　maneuvers；　where　the

field　of　operation　is　fixed；　it　is　possible　to　furnish　supplies

of　hydrogen　gas　in　portable　cylinders；　but　on　long

trips　where　sudden　leakage　or　other　cause　makes　descent

in　an　unexpected　spot　unavoidable；　it　becomes　a　question

of　making　your　own　hydrogen　gas　or　deserting　the　balloon。

And　when　this　occurs　the　balloonist　is　up　against

another　serious　propositioncan　he　find　the　necessary

zinc　or　iron？　Can　he　get　the　acid？



Balloons　for　Commercial　Use。



Despite　all　this　the　balloon　has　its　uses。　If　there　is　to

be　such　a　thing　as　aerial　navigation　in　a　commercial

waythe　carrying　of　freight　and　passengersit　will

come　through　the　employment　of　such　monster　balloons

as　Count　Zeppelin　is　building。　But　even　then　the　carrying

capacity　must　of　necessity　be　limited。　The　latest

Zeppelin　creation；　a　monster　in　size；　is　450　feet　long；

and　42　1/2　feet　in　diameter。　The　dimensions　are　such　as

to　make　all　other　balloons　look　like　pigmies；　even　many

ocean…going　steamers　are　much　smaller；　and　yet　its　passenger

capacity　is　very　small。　On　its　36…hour　flight　in

May；　1909；　the　Zeppelin；　carried　only　eight　passengers。

The　speed；　however；　was　quite　respectable；　850　miles

being　covered　in　the　36　hours；　a　trifle　over　23　miles　an

hour。　The　reserve　buoyancy；　that　is　the　total　lifting

capacity　aside　from　the　weight　of　the　airship　and　its

equipment；　is　estimated　at　three　tons。







CHAPTER　XXII。



PROBLEMS　OF　AERIAL　FLIGHT。



In　a　lecture　before　the　Royal　Society　of　Arts；　reported

in　Engineering；　F。　W。　Lanchester　took　the　position　that

practical　flight　was　not　the　abstract　question　which　some

apparently　considered　it　to　be；　but　a　problem　in　locomotive

engineering。　The　flying　machine　was　a　locomotive

appliance；　designed　not　merely　to　lift　a　weight；

but　to　transport　it　elsewhere；　a　fact　which　should　be

sufficiently　obvious。　Nevertheless　one　of　the　leading　scientific

men　of　the　day　advocated　a　type　in　which　this；　the

main　function　of　the　flying　machine；　was　overlooked。

When　the　machine　was　considered　as　a　method　of　transport；

the　vertical　screw　type；　or　helicopter；　became　at

once　ridiculous。　It　had；　nevertheless；　many　advocates

who　had　some　vague　and　ill…defined　notion　of　subsequent

motion　through　the　air　after　the　weight　was　raised。



Helicopter　Type　Useless。



When　efficiency　of　transport　was　demanded；　the　helicopter

type　was　entirely　out　of　court。　Almost　all　of

its　advocates　neglected　the　effect　of　the　motion　of　the

machine　through　the　air　on　the　efficiency　of　the　vertical

screws。　They　either　assumed　that　the　motion　was

so　slow　as　not　to　matter；　or　that　a　patch　of　still　air

accompanied　the　machine　in　its　flight。　Only　one　form　of　this

type　had　any　possibility　of　success。　In　this　there　were

two　screws　running　on　inclined　axlesone　on　each　side

of　the　weight　to　be　lifted。　The　action　of　such　inclined

screw　was　curious；　and　in　a　previous　lecture　he　had

pointed　out　that　it　was　almost　exactly　the　same　as　that

of　a　bird's　wing。　In　high…speed　racing　craft　such　inclined

screws　were　of　necessity　often　used；　but　it　was

at　a　sacrifice　of　their　efficiency。　In　any　case　the　efficiency

of　the　inclined…screw　helicopter　could　not　compare

with　that　of　an　aeroplane；　and　that　type　might　be

dismissed　from　consideration　so　soon　as　efficiency　became

the　ruling　factor　of　the　design。



Must　Compete　With　Locomotive。



To　justify　itself　the　aeroplane　must　compete；　in　some

regard　or　other；　with　other　locomotive　appliances；　performing

one　or　more　of　the　purposes　of　locomotion　more

efficiently　than　existing　systems。　It　would　be　no　use

unless　able　to　stem　air　currents；　so　that　its　velocity　must

he　greater　than　that　of　the　worst　winds　liable　to　be　encountered。

To　illustrate　the　limitations　imposed　on　the

motion　of　an　aeroplane　by　wind　velocity；　Mr。　Lanchester

gave　the　diagrams　shown　in　Figs。　1　to　4。　The　circle

in　each　case　was；　he　said；　described　with　a　radius　equal

to　the　speed　of　the　aeroplane　in　still　air；　from　a　center

placed　〃down…wind〃　from　the　aeroplane　by　an　amount

equal　to　the　velocity　of　the　wind。



Fig。　1　therefore　represented　the　case　in　which　the

air　was　still；　and　in　this　case　the　aeroplane　represented

by　_A_　had　perfect　liberty　of　movement　in　any　direction



In　Fig。　2　the　velocity　of　the　wind　was　half　that　of　the

aeroplane；　and　the　latter　could　still　navigate　in　any

direction；　but　its　speed　against　the　wind　was　only　one…

third　of　its　speed　with　the　wind。



In　Fig。　3　the　velocity　of　the　wind　was　equal　to　that

of　the　aeroplane；　and　then　motion　against　the　wind　was

impossible；　but　it　could　move　to　any　point　of　the

circle；　but　not　to　any　point　lying　to　the　left　of　the　tangent

_A_　_B_。　Finally；　when　the　wind　had　a　greater

speed　than　the　aeroplane；　as　in　Fig。　4；　the　machine　could

move　only　in　directions　limited　by　the　tangents　_A_　_C_

and　_A_　_D_。



Matter　of　Fuel　Consumption。



Taking　the　case　in　which　the　wind　had　a　speed　equal

to　half　that　of　the　aeroplane；　Mr。　Lanchester　said　that

for　a　given　journey　out　and　home；　down　wind　and　back；

the　aeroplane　would　require　30　per　cent　more　fuel　than

if　the　trip　were　made　in　still　air；　while　if　the　journey

was　made　at　right　angles　to　the　direction　of　the　wind

the　fuel　needed　would　be　15　per　cent　more　than　in　a

calm。　This　30　per　cent　extra　was　quite　a　heavy　enough

addition　to　the　fuel；　and　to　secure　even　this　figure　it

was　necessary　that　the　aeroplane　should　have　a　speed　of

twice　that　of　the　maximum　wind　in　which　it　was　desired

to　operate　the　machine。　Again；　as　stated　in　the　last

lecture；　to　insure　the　automatic　stability　of　the　machine

it　was　necessary　that　the　aeroplane　speed　should　be

largely　in　excess　of　that　of　the　gusts　of　wind　liable　to

be　encountered。



Eccentricities　of　the　Wind。



There　was；　Mr。　Lanchester　said；　a　loose　connection

between　the　average　velocity　of　the　wind　and　the　maximum

speed　of　the　gusts。　When　the　average　speed　of

the　wind　was　40　miles　per　hour；　that　of　the　gusts　might

be　equal　or　more。　At　one　moment　there　might　be　a

calm　or　the　direction　of　the　wind　even　reversed；　followed；

the　next　moment；　by　a　violent　gust。　About　the　same

minimum　speed　was　desirable　for　security　against　gusts

as　was　demanded　by　other　considerations。　Sixty　miles

an　hour　was　the　least　figure　desirable　in　an　aeroplane；

and　this　should　be　exceeded　as　much　as　possible。　Actually；

the　Wright　machine　had　a　speed　of　38　miles　per

hour；　while　Farman's　Voisin　machine　flew　at　45　miles

per　hour。



Both　machines　were　extremely　sensitive　to　high　winds；

and　the　speaker；　in　spite　of　newspaper　reports　to　the

contrary；　had　never　seen　either　flown　in　more　than　a

gentle　breeze。　The　damping　ou