the aeroplane speaks-第3部分

快捷操作: 按键盘上方向键 ← 或 → 可快速上下翻页 按键盘上的 Enter 键可回到本书目录页 按键盘上方向键 ↑ 可回到本页顶部! 如果本书没有阅读完，想下次继续接着阅读，可使用上方 "收藏到我的浏览器" 功能 和 "加入书签" 功能！


t　inefficient　way　of　securing　lift　compared　with　the　arrangement　of　an　inclined　surface　driven　by　a　propeller　revolving　about　a　horizontal　axis。


‘‘Then；　if　the　Pilot　is　green；　my　chance　will　come；''　said　the　Maximum　Angle　of　Incidence。　‘‘For　if　the　Angle　is　increased　over　the　Best　Climbing　Angle；　the　Drift　will　rush　up；　and　the　Speed；　and　with　it　the　Lift；　will；　when　my　Angle　is　reached；　drop　to　a　point　when　the　latter　will　be　no　more　than　the　Weight。　The　Margin　of　Lift　will　have　entirely　disappeared；　and　there　we　shall　be；　staggering　along　at　my　tremendous　angle；　and　only　just　maintaining　horizontal　flight。''

‘‘And　then　with　luck　I'll　get　my　chance；''　said　the　Drift。　‘‘If　he　is　a　bit　worse　than　green；　he'll　perhaps　still　further　increase　the　Angle。　Then　the　Drift；　largely　increasing；　the　Speed；　and　consequently　the　Lift；　will　become　still　less；　i。e。；　less　than　the　Weight；　and　thenwhat　price　pancakes；＇＇3＇＇　eh？''


＇＇3＇＇　Pancakes：　Pilot's　slang　for　stalling　an　aeroplane　and　dropping　like　a　pancake。


‘‘Thank　you；''　from　Efficiency；　‘‘that　was　all　most　informing。　And　now　will　you　tell　me；　please；　how　the　greatest　Speed　may　be　secured？''

‘‘Certainly；　now　it's　my　turn；''　piped　the　Minimum　Angle　of　Incidence。　‘‘By　means　of　the　Elevator；　the　Pilot　places　the　Aeroplane　at　my　small　Angle；　at　which　the　Lift　only　just　equals　the　Weight；　and；　also；　at　which　we　shall　make　greater　speed　with　no　more　Drift　than　before。　Then　we　get　our　greatest　Speed；　just　maintaining　horizontal　flight。''

‘‘Yes；　though　I'm　out　of　the　horizontal　and　thrusting　downwards；''　grumbled　the　Propeller；　‘‘and　that's　not　efficient；　though　I　suppose　it's　the　best　we　can　do　until　that　Inventor　fellow　finds　his　Mechanics。''

‘‘Thank　you　so　much；''　said　Efficiency。　‘‘I　think　I　have　now　at　any　rate　an　idea　of　the　Elementary　Principles　of　Flight；　and　I　don't　know　that　I　care　to　delve　much　deeper；　for　sums　always　give　me　a　headache；　but　isn't　there　something　about　Stability　and　Control？　Don't　you　think　I　ought　to　have　a　glimmering　of　them　too？''

‘‘Well；　I　should　smile；''　said　a　spruce　Spar；　who　had　come　all　the　way　from　America。　‘‘And　that；　as　the　Lecturer　says；　‘will　be　the　subject　of　our　next　lecture；'　so　be　here　again　to…morrow；　and　you　will　be　glad　to　hear　that　it　will　be　distinctly　more　lively　than　the　subject　we　have　covered　to…day。''



PART　II

THE　PRINCIPLES；　HAVING　SETTLED　THEIR　DIFFERENCES；　FINISH　THE　JOB

Another　day　had　passed；　and　the　Flight　Folk　had　again　gathered　together　and　were　awaiting　the　arrival　of　Efficiency　who；　as　usual；　was　rather　late　in　making　an　appearance。

The　crowd　was　larger　than　ever；　and　among　the　newcomers　some　of　the　most　important　were　the　three　Stabilities；　named　Directional；　Longitudinal；　and　Lateral；　with　their　assistants；　the　Rudder；　Elevator；　and　Ailerons。　There　was　Centrifugal　Force；　too；　who　would　not　sit　still　and　created　a　most　unfavourable　impression；　and　Keel…Surface；　　the　Dihedral　Angle；　and　several　other　lesser　fry。

‘‘Well；''　said　Centrifugal　Force；　‘‘I　wish　this　Efficiency　I've　heard　so　much　about　would　get　a　move　on。　Sitting　still　doesn't　agree　with　me　at　all。　Motion　I　believe　in。　There's　nothing　like　motionthe　more　the　better。''

‘‘We　are　entirely　opposed　to　that；''　objected　the　three　Stabilities；　all　in　a　breath。　‘‘Unless　it's　in　a　perfectly　straight　line　or　a　perfect　circle。　Nothing　but　perfectly　straight　lines　or；　upon　occasion；　perfect　circles　satisfy　us；　and　we　are　strongly　suspicious　of　your　tendencies。''

‘‘Well；　we　shall　see　what　we　shall　see；''　said　the　Force　darkly。　‘‘But　who　in　the　name　of　blue　sky　is　this？''

And　in　tripped　Efficiency；　in　a　beautifully　‘‘doped''　dress　of　the　latest　fashionable　shade　of　khaki…coloured　fabric；　a　perfectly　stream…lined　bonnet；　and　a　bewitching　little　Morane　parasol；＇＇4＇＇　smiling　as　usual；　and　airily　exclaiming；　‘‘I'm　so　sorry　I'm　late；　but　you　see　the　Designer's　such　a　funny　man。　He　objects　to　skin　friction；＇＇5＇＇　and　insisted　upon　me　changing　my　fabric　for　one　of　a　smoother　surface；　and　that　delayed　me。　Dear　me；　there　are　a　lot　more　of　us　to…day；　aren't　there？　I　think　I　had　better　meet　one　at　a　time。''　And　turning　to　Directional　Stability；　she　politely　asked　him　what　he　preferred　to　do。


＇＇4＇＇　Morane　parasol：　A　type　of　Morane　monoplane　in　which　the　lifting　surfaces　are　raised　above　the　pilot　in　order　to　afford　him　a　good　view　of　the　earth。

＇＇5＇＇　Skin　friction　is　that　part　of　the　drift　due　to　the　friction　of　the　air　with　roughnesses　upon　the　surface　of　the　aeroplane。


‘‘My　purpose　in　life；　miss；''　said　he；　‘‘is　to　keep　the　Aeroplane　on　its　course；　and　to　achieve　that　there　must　be；　in　effect；　more　Keel…Surface　behind　the　Vertical　Turning　Axis　than　there　is　in　front　of　it。''

Efficiency　looking　a　little　puzzled；　he　added：　‘‘Just　like　a　weathercock；　and　by　Keel…Surface　I　mean　everything　you　can　see　when　you　view　the　Aeroplane　from　the　side　of　itthe　sides　of　the　body；　struts；　wires；　etc。''

‘‘Oh；　now　I　begin　to　see　light；''　said　she：　‘‘but　just　exactly　how　does　it　work？''

‘‘I'll　answer　that；''　said　Momentum。　‘‘When　perhaps　by　a　gust　of　air　the　Aeroplane　is　blown　out　of　its　course　and　points　in　another　direction；　it　doesn't　immediately　fly　off　on　that　new　course。　I'm　so　strong　I　pull　it　off　the　new　course　to　a　certain　extent；　and　towards　the　direction　of　the　old　course。　And　so　it　travels；　as　long　as　my　strength　lasts；　in　a　more　or　less　sideways　position。''

‘‘Then；''　said　the　Keel…Surface；　‘‘I　get　a　pressure　of　air　all　on　one　side；　and　as　there　is；　in　effect；　most　of　me　towards　the　tail；　the　latter　gets　pressed　sideways；　and　the　Aeroplane　thus　tends　to　assume　its　first　position　and　course。''

‘‘I　see；''　said　Efficiency；　and；　daintily　holding　the　Chalk；　she　approached　the　Blackboard。　‘‘Is　this　what　you　mean？''

‘‘Yes；　that's　right　enough；''　said　the　Keel…Surface；　‘‘and　you　might　remember；　too；　that　I　always　make　the　Aeroplane　nose　into　the　gusts　rather　than　away　from　them。''

‘‘If　that　was　not　the　case；''　broke　in　Lateral　Stability；　and　affecting　the　fashionable　Flying　Corps　stammer；　‘‘it　would　be　a　h…h…h…o…r…rible　affair！　If　there　were　too　much　Keel…Surface　in　front；　then　that　gust　would　blow　the　Aeroplane　round　the　other　way　a　very　considerable　distance。　And　the　right…hand　Surface　being　on　the　outside　of　the　turn　would　have　more　speed；　and　consequently　more　Lift；　than　the　Surface　on　the　other　side。　That　means　a　greater　proportion　of　the　Lift　on　that　side；　and　before　you　could　say　Warp　to　the　Ailerons　over　the　Aeroplane　would　goprobable　result　a　bad　side…slip''

‘‘And　what　can　the　Pilot　do　to　save　such　a　situation　as　that？''　said　Efficiency。

‘‘Well；''　replied　Lateral　Stability；　‘‘he　will　try　to　turn　the　Aeroplane　sideways　and　back　to　an　even　keel　by　means　of　warping　the　Ailerons　or　little　wings　which　are　hinged　on　to　the　Wing…tips；　and　about　which　you　will　hear　more　later　on；　but　if　the　side…slip　is　very　bad　he　may　not　be　able　to　right　the　Aeroplane　by　means　of　the　Ailerons；　and　then　the　only　thing　for　him　to　do　is　to　use　the　Rudder　and　to　turn　the　nose　of　the　Aeroplane　down　and　head…on　to　the　direction　of　motion。　The　Aeroplane　will　then　be　meeting　the　air　in　the　direction　it　is　designed　to　do　so；　and　the　Surfaces　and　also　the　controls　（the　Rudder；　Ailerons；　and　Elevator）　will　be　working　efficiently；　but　its　attitude　relative　to　the　earth　will　probably　be　more　or　less　upside…down；　for　the　action　of　turning　the　Aeroplane's　nose　down　results；　as　you　will　see　by　the　illustration　B；　in　the　right　wing；　which　is　on　the　outside　of　the　circle。　travelling　through　the　air　with　greater　speed　than　the　left…hand　wing。　More　Speed　means　more　Lift；　so　that　results　in　overturning　the　Aeroplane　still　more；　but　now　it　is；　at　any　rate；　meeting　the　air　as　it　is　designed　to　meet　it；　and　everything　is　working　properly。　It　is　then　only　necessary　to　warp　the　Elevator；　as　shown　in　illustration　C；　in　order　to　bring　the　Aeroplane　into　a　proper　attitude　relative　to　the　earth。''

‘‘Ah！''　said　the　Rudder；　looking　wise；　‘‘it's　in　a　case　like　that　when　I　become　the　Elevator　and　the　Elevator　becomes　me。''

‘‘That's　absurd　nonsense；''　said　the　Blackboard；　‘‘due　to　looseness　of　thought　and　expression。''

‘‘Well；''　replied　the　Rudder；　‘‘when　'the　Aeroplane　is　in　position　A　and　I　am　used；　then　I　depress　or　ELEVATE　the　nose　of　the　machine；　and；　if　the　Elevator　is　used；　then　it　turns　the　Aeroplane　to　right　or　left；　which　is　normally　my　function。　Surely　our　roles　have　changed　one　with　the　other；　and　I'm　then　the　Elevator　and　the　Elevator　is　me！''

Said　Lateral　Stability　to　the　Rudder；　‘‘That's　altogether　the　wrong　way　of　looking　at　it；　though　I　admit''and　this　rather　sarcastically‘‘that　the　way　you　put　it　sounds　rather　fine　when　you　are　talking　of　your　experiences　in　the　air　to　those　‘interested　in　aviation'　but　knowing　little　about　it；　but　it　won't　go　down　here！　You　are　a　Controlling　Surface　designed　to　turn　the　Aeroplane　about　its　vertical　axis；　and　the　Elevator　is　a　Controlling　Surface　designed　to　turn　the　Aeroplane　about　its　lateral　axis。　Those　are　your　respective　jobs；　and　you　can't　possibly　change　them　about。　Such　talk　only　leads　to　confusion；　and　I　hope　we　shall　hear　no　more　of　it。''

‘‘Thanks；''　said　Efficiency　to　Lateral　Stability。　‘‘And　now；　please；　will　you　explain　your　duties？''

‘‘My　duty　is　to　keep　the　Aeroplane　horizontal　from　Wing…tip　to　Wing…tip。　First　of　all；　I　sometimes　arrange　with　the　Rigger　to　wash…out；　that　is　decrease；　the　Angle　of　Incidence　on　one　side　of　the　Aeroplane；　and　to　effect　the　reverse　condition；　if　it　is　not　too　much　trouble；　on　the　other　side。''

‘‘But；''　objected　Efficiency；　‘‘the　Lift　varies　with　the　Angle　of　Incidence；　and　surely　such　a　condition　will　result　in　one　side　of　the　Aeroplane　lifting　more　than　the　other　side？'

‘‘That's　all　right；''　said　the　Propeller；　‘‘it's　meant　to　off…set　the　tendency　of　the　Aeroplane　to　turn　over　sideways　in　the　opposite　direction　to　which　I　revolve。''

‘‘That's　quite　clear；　though　rather　unexpected；　but　how　do　you　counteract　the　effect　of　the　gusts　when　they　try　to　overturn　the　Aeroplane　sideways？''　said　she；　turning　to　Lateral　Stability　again。

‘‘Well；''　he　replied；　rather　miserably；　‘‘I'm　not　nearly　so　perfect　as　the　Longitudinal　and　Directional　Stabilities。　The　Dihedral　A