aeroplanes and dirigibles of war-第8节

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being　as　steady　and　as　solid　as　a　boat's　deck。　　The　propellers

are　collapsible；　although　in　the　latest　craft　of　this　class　they

are　semi…rigid。



The　mechanical　equipment　is　also　interesting。　　There　are　two

propellers；　and　two　motors；　each　nominally　driving　one　propeller。　

But　should　one　motor　break　down；　or　motives　of　economy；　such　as

husbanding　of　fuel；　render　it　advisable　to　run　upon　one　engine；

then　the　two　propellers　may　be　driven　by　either　of　the　motors。



The　inventor　has　perfected　an　ingenious；　simple；　and　highly

efficient　coupling　device　to　attain　this　end；　but　to　ensure　that

the　propeller　output　is　of　the　maximum　efficiency　in　relation　to

the　engine；　the　pitch　of　the　propellers　may　be　altered　and　even

reversed　while　the　engine　is　running。　　When　one　motor　only　is

being　used；　the　pitch　is　lowered　until　the　propellers　revolve　at

the　speed　which　they　would　attain　if　both　engines　were　in

operation。　　This　adjustment　of　the　propeller　pitch　to　the　most

economical　engine　revolutions　is　a　distinctive　characteristic；

and　contributes　to　the　efficiency　and　reliability　of　the　Parseval

dirigible　to　a　very　pronounced　degree。



Steering　in　the　vertical　plane　is　also　carried　out　upon

distinctive　lines。　　There　are　no　planes　for　vertical　steering；

but　movement　is　accomplished　by　tilting　the　craft　and　thus

driving　the　gas　from　one　end　of　the　balloon　to　the　other。　　This

is　effected　by　the　manipulation　of　the　air…ballonets；　one　of

which　is　placed　at　the　prow　and　stem　of　the　gas　bag　respectively。　

If　it　is　desired　to　descend　the　gas　is　driven　from　the　forward　to

the　after　end　of　the　envelope；　merely　by　inflating　the　bow

ballonet　with　air　by　means　of　a　pump　placed　in　the　car。　　If

ascent　is　required；　the　after…ballonet　is　inflated；　thereby

driving　the　gas　to　the　forward　end　of　the　balloon；　the　buoyancy

of　which　is　thus　increased。　　The　outstanding　feature　of　the

〃Drachen…Balloon〃　is　incorporated　in　the　airship。　　This　is　the

automatic　operation　of　the　safety　valve　on　the　gas…bag　directly

by　the　air　ballonets。　　If　these　ballonets　empty　owing　to　the

pressure　of　the　gas　within　the　envelope；　a　rope　system　disposed

within　the　balloon　and　connecting　the　ballonets　and　the　gas…valve

at　the　top　is　stretched　taut；　thereby　opening　the　gas…valve。　　In

this　manner　the　gas…pressure　becomes　reduced　until　the　ballonets

are　enabled　to　exercise　their　intended　function。　　This　is　a

safety　precaution　of　inestimable　value。



The　Parseval　is　probably　the　easiest　dirigible　to　handle；

inasmuch　as　it　involves　no　more　skill　or　knowledge　than　that

required　for　an　ordinary　free　balloon。　　Its　movements　in　the

vertical　plane　are　not　dissimilar　to　those　of　　the　aeroplane；

inasmuch　as　ascent　and　descent　are　normally　conducted　in　a

〃screwing〃　manner；　the　only　exception　being　of　course　in　abrupt

descent　caused　by　the　ripping　of　the　emergency…valve。　　On　one

occasion；　it　is　stated；　one　of　the　latest　machines　of　this　type；

when　conducting　experimental　flights；　absolutely　refused　to

descend；　producing　infinite　amusement　both　among　the　crowd　and

those　on　board。



The　development　of　the　Parseval　is　directly　attributable　to　the

influence　and　intimate　interest　of　the　Kaiser；　and　undoubtedly

this　represents　the　wisest　step　he　ever　made　in　the　realm　of

aeronautics。　　It　certainly　has　enabled　the　German　military

machine　to　become　possessed　of　a　significant　fleet　of　what　may　be

described　as　a　really　efficient　and　reliable　type　of　dirigible。　

The　exact　number　of　military　Parsevals　in　commission　is　unknown；

but　there　are　several　classes　thereof；　in　the　nature　of　aerial

cruisers　and　vedettes。



The　largest　and　most　powerful　class　are　those　known　as　the　B

type；　measuring　about　240　feet　in　length　by　40　feet　maximum

diameter；　of　223；000　cubic　feet　capacity；　and　fitted　with　two

motorsand　two　propellers。　　This　vessel　carries　about　10

passengers；　can　climb　to　a　maximum　height　of　approximately　8；500

feet；　and　is　capable　of　remaining　in　the　air　for　twenty　hours

upon　a　single　fuel　charge。　　While　this　is　the　largest　and　most

serviceable　type　of　Parseval　designed　for　military　duties；　there

is　another；　the　A　class；　200　feet　in　length　with　accommodation

for　six　passengers　in　addition　to　the　crew　of　three；　which　is

capable　of　attaining　a　maximum　altitude　of　6；700　feet；　and　has　an

endurance　capacity　of　15　hours。　　This　class　also　is　fitted　with

twin　propellers　and　motors。　　In　addition　there　are　the　C　and

E　classes；　carrying　from　four　to　eight　passengers；　while　the

vedettes　are　represented　by　the　D　and　F　classes；　which　have　a

maximum　altitude　of　2；000　feet　and　can　remain　aloft　for　only　five

hours　upon　a　single　fuel　charge。　　These　smaller　vessels；　however；

have　the　advantage　of　requiring　only　one　or　two　men　to　handle

them。　　The　present　military　Parseval　dirigible　is　made　in　one　of

these　five　standardised　classes；　experience　having　established

their　efficiency　for　the　specified　military　services　for　which

they　are　built。　　In　point　of　speed　they　compare　favourably　with

the　latest　types　of　Zeppelin；　the　speeds　of　the　larger　types

ranging　from　32　to　48　miles　per　hour　with　a　motor　effort　of　360

to　400　horse…power。



So　far　as　the　French　airships　of　war　are　concerned；　the　fleet　is

somewhat　heterogeneous；　although　the　non…rigid　type　prevails。　

The　French　aerial　navy　is　represented　by　the　Bayard…Clement；

Astra；　Zodiac；　and　the　Government…built　machines。　　Although　the

rigid　type　never　has　met　with　favour　in　France；　there　is　yet　a

solitary　example　of　this　system　of　constructionthe　Spiess；

which　is　460　feet　in　length　by　47　feet　in　diameter　and　has　a

displacement　of　20　tons。　　The　semi…rigid　craft　are　represented

by　the　Lebaudy　type；　the　largest　of　which　measures　293　feet　in

length　by　51　feet　in　diameter；　and　has　a　displacement　of　10　tons。



One　may　feel　disposed　to　wonder　why　the　French　should　be

apparently　backward　in　this　form　of　aerial　craft；　but　this　may　be

explained　by　the　fact　that　the　era　of　experiment　had　not　been

concluded　at　the　time　war　was　declared；　with　the　result　that　it

has　been　somewhat　difficult　to　determine　which　type　would　meet

the　military　requirements　of　the　country　to　the　best　advantage。　

Moreover；　the　French　military　authorities　evinced　a　certain

disposition　to　relegate　the　dirigible　to　a　minor　position；

convinced　that　it　had　been　superseded　by　the　heavierthan…air

machine。　　Taken　on　the　whole；　the　French　airship　fleet　is

inferior　to　the　German　in　point　of　speed；　if　not　numerically；　but

this　deficiency　is　more　than　counterbalanced　by　the　skill　and

ability　of　the　men　manning　their　craft；　who　certainly　are

superior　to　their　contemporaries　in　Germany；　combined　with　the

proved　character　of　such　craft　as　are　in　service。



The　same　criticism　may　be　said　to　apply　to　Great　Britain。　　That

country　was　backward　in　matters　pertaining　to　the　airship；

because　its　experiments　were　carried　out　spasmodically　while

dependence　was　reposed　somewhat　too　much　upon　foreign　effort。　

The　British　airships　are　small　and　of　low　speed　comparatively

speaking。　　Here　again　it　was　the　advance　of　the　aeroplane　which

was　responsible　for　the　manifestation　of　a　somewhat　indifferent

if　not　lethargic　feeling　towards　the　airship。　　Undoubtedly　the

experiments　carried　out　in　Great　Britain　were　somewhat

disappointing。　　The　one　and　only　attempt　to　out…Zeppelin　the

Zeppelin　resulted　in　disaster　to　the　craft　before　she　took　to　the

air；　while　the　smaller　craft　carried　out　upon　far　less　ambitious

lines　were　not　inspiritingly　successful。　　Latterly　the　non…rigid

system　has　been　embraced　exclusively；　the　craft　being　virtually

mechanically　driven　balloons。　　They　have　proved　efficient　and

reliable　so　far　as　they　go；　but　it　is　the　personal　element　in

this　instance　also　which　has　contributed　so　materially　to　any

successes　achieved　with　them。



But　although　Great　Britain　and　France　apparently　lagged　behind

the　Germans；　appreciable　enterprise　was　manifested　in　another

direction。　　The　airship　was　not　absolutely　abandoned：　vigilance

was　maintained　for　a　superior　type　of　craft。　　It　was　an　instance

of　weighing　the　advantages　against　the　disadvantages　of　the

existing　types　and　then　evolving　for　a　design　which　should

possess　the　former　without　any　of　the　latter。　　This　end　appears

to　be　achieved　with　the　Astra　type　of　dirigible；　the　story　of　the

development　of　which　offers　an　interesting　chapter　in　the　annals

of　aeronautics。



In　all　lighter…than…air　machines　the　resistance　to　the　air

offered　by　the　suspension　ropes　is　considerable；　and　the

reduction　of　this　resistance　has　proved　one　of　the　most

perplexing　problems　in　the　evolution　of　the　dirigible。　　The　air

is　broken　up　in　such　a　manner　by　the　ropes　that　it　is　converted

into　a　brake　or　drag　with　the　inevitable　result　that　the　speed

undergoes　a　severe　diminution。　　A　full…rigged　airship　such　as　the

Parseval；　for　instance；　may　present　a　picturesque　appearance；　but

it　is　severe