flying machines-第23部分

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18。03　squared　X　0。00327　=　1。063　pounds　per　square　foot。



If　we　apply　Lilienthal's　co…efficients　for　an　angle　of

6　degrees　26'；　we　have　for　the　force　in　action：



Normal：　4。57　X　1。063　X　0。912　=　4。42　pounds。



Tangential：　4。57　X　1。063　X　0。074　=　…　0。359　pounds；

which　latter；　being　negative；　is　a　propelling　force。



Results　Astonish　Scientists。



Thus　we　have　a　bird　weighing　4。25　pounds　not　only

thoroughly　supported；　but　impelled　forward　by　a　force

of　0。359　pounds；　at　seventeen　miles　per　hour；　while　the

experiments　of　Professor　A。　F。　Zahm　showed　that　the

resistance　at　15。52　miles　per　hour　was　only　0。27　pounds；

　　　　　　　　　　　17　squared

or　0。27　X　…　=　0。324　pounds；　at　seventeen　miles　an

　　　　　　　　　　15。52　squared

hour。



These　are　astonishing　results　from　the　data　obtained；

and　they　lead　to　the　inquiry　whether　the　energy　of　the

rising　air　is　sufficient　to　make　up　the　losses　which　occur

by　reason　of　the　resistance　and　friction　of　the　bird's　body

and　wings；　which；　being　rounded；　do　not　encounter　air

pressures　in　proportion　to　their　maximum　cross…section。



We　have　no　accurate　data　upon　the　co…efficients　to　apply

and　estimates　made　by　myself　proved　to　be　much

smaller　than　the　0。27　pounds　resistance　measured　by

Professor　Zahm；　so　that　we　will　figure　with　the　latter

as　modified。　As　the　speed　is　seventeen　miles　per　hour；　or

24。93　feet　per　second；　we　have　for　the　work：



Work　done；　0。324　X　24。93　=　8。07　foot　pounds　per　second。



Endorsed　by　Prof。　Marvin。



Corresponding　energy　of　rising　air　is　not　sufficient　at

four　miles　per　hour。　This　amounts　to　but　2。10　foot　pounds

per　second；　but　if　we　assume　that　the　air　was　rising　at

the　rate　of　seven　miles　per　hour　（10。26　feet　per　second）；

at　which　the　pressure　with　the　Langley　coefficient　would

be　0。16　pounds　per　square　foot；　we　have　on　4。57　square

feet　for　energy　of　rising　air：　4。57　X　0。16　X　10。26　=　7。50

foot　pounds　per　second；　which　is　seen　to　be　still　a　little

too　small；　but　well　within　the　limits　of　error；　in　view　of

the　hollow　shape　of　the　bird's　wings；　which　receive

greater　pressure　than　the　flat　planes　experimented　upon

by　Langley。



These　computations　were　chiefly　made　in　January；

1899；　and　were　communicated　to　a　few　friends；　who　found

no　fallacy　in　them；　but　thought　that　few　aviators　would

understand　them　if　published。　They　were　then　submitted

to　Professor　C。　F。　Marvin　of　the　Weather　Bureau；　who

is　well　known　as　a　skillful　physicist　and　mathematician。

He　wrote　that　they　were；　theoretically；　entirely　sound

and　quantitatively；　probably；　as　accurate　as　the　present

state　of　the　measurements　of　wind　pressures　permitted。

The　writer　determined；　however；　to　withhold　publication

until　the　feat　of　soaring　flight　had　been　performed　by

man；　partly　because　he　believed　that；　to　ensure　safety；　it

would　be　necessary　that　the　machine　should　be　equipped

with　a　motor　in　order　to　supplement　any　deficiency　in

wind　force。



Conditions　Unfavorable　for　Wrights。



The　feat　would　have　been　attempted　in　1902　by　Wright

brothers　if　the　local　circumstances　had　been　more　favorable。

They　were　experimenting　on　〃Kill　Devil　Hill；〃

near　Kitty　Hawk；　N。　C。　This　sand　hill；　about　100　feet

high；　is　bordered　by　a　smooth　beach　on　the　side　whence

come　the　sea　breezes；　but　has　marshy　ground　at　the　back。

Wright　brothers　were　apprehensive　that　if　they　rose　on

the　ascending　current　of　air　at　the　front　and　began　to

circle　like　the　birds；　they　might　be　carried　by　the

descending　current　past　the　back　of　the　hill　and　land　in

the　marsh。　Their　gliding　machine　offered　no　greater

head　resistance　in　proportion　than　the　buzzard；　and　their　gliding

angles　of　descent　are　practically　as　favorable；　but

the　birds　performed　higher　up　in　the　air　than　they。



Langley's　Idea　of　Aviation。



Professor　Langley　said　in　concluding　his　paper　upon

〃The　Internal　Work　of　the　Wind〃：



〃The　final　application　of　these　principles　to　the　art　of

aerodromics　seems；　then；　to　be；　that　while　it　is　not　likely

that　the　perfected　aerodrome　will　ever　be　able　to　dispense

altogether　with　the　ability　to　rely　at　intervals　on

some　internal　source　of　power；　it　will　not　be　indispensable

that　this　aerodrome　of　the　future　shall；　in　order　to

go　any　distanceeven　to　circumnavigate　the　globe　without

alightingneed　to　carry　a　weight　of　fuel　which

would　enable　it　to　perform　this　journey　under　conditions

analogous　to　those　of　a　steamship；　but　that　the　fuel　and

weight　need　only　be　such　as　to　enable　it　to　take　care　of

itself　in　exceptional　moments　of　calm。〃



Now　that　dynamic　flying　machines　have　been　evolved

and　are　being　brought　under　control；　it　seems　to　be

worth　while　to　make　these　computations　and　the　succeeding

explanations　known；　so　that　some　bold　man　will

attempt　the　feat　of　soaring　like　a　bird。　The　theory

underlying　the　performance　in　a　rising　wind　is　not　new；

it　has　been　suggested　by　Penaud　and　others；　but　it　has

attracted　little　attention　because　the　exact　data　and　the

maneuvers　required　were　not　known　and　the　feat　had

not　yet　been　performed　by　a　man。　The　puzzle　has　always

been　to　account　for　the　observed　act　in　very　light

winds；　and　it　is　hoped　that　by　the　present　selection　of

the　most　difficult　case　to　explaini。　e。；　the　soaring　in　a

dead　horizontal　calmsomebody　will　attempt　the　exploit。



Requisites　for　Soaring　Flights。



The　following　are　deemed　to　be　the　requisites　and

maneuvers　to　master　the　secrets　of　soaring　flight：



1stDevelop　a　dynamic　flying　machine　weighing

about　one　pound　per　square　foot　of　area；　with　stable

equilibrium　and　under　perfect　control；　capable　of　gliding

by　gravity　at　angles　of　one　in　ten　（5　3/4　degrees）　in　still　air。



2nd。Select　locations　where　soaring　birds　abound　and

occasions　where　rising　trends　of　gentle　winds　are　frequent

and　to　be　relied　on。



3rd。Obtain　an　initial　velocity　of　at　least　25　feet　per

second　before　attempting　to　soar。



4th。So　locate　the　center　of　gravity　that　the　apparatus

shall　assume　a　negative　angle；　fore　and　aft；　of　about　3　degrees。



Calculations　show；　however；　that　sufficient　propelling

force　may　still　exist　at　0　degrees；　but　disappears　entirely　at

＋4　degrees。



5th。Circle　like　the　bird。　Simultaneously　with　the

steering；　incline　the　apparatus　to　the　side　toward　which

it　is　desired　to　turn；　so　that　the　centrifugal　force　shall

be　balanced　by　the　centripetal　force。　The　amount　of　the

required　inclination　depends　upon　the　speed　and　on　the

radius　of　the　circle　swept　over。



6th。Rise　spirally　like　the　bird。　Steer　with　the

horizontal　rudder；　so　as　to　descend　slightly　when　going

with　the　wind　and　to　ascend　when　going　against　the

wind。　The　bird　circles　over　one　spot　because　the　rising

trends　of　wind　are　generally　confined　to　small　areas　or

local　chimneys；　as　pointed　out　by　Sir　H。　Maxim　and

others。



7th。Once　altitude　is　gained；　progress　may　be　made

in　any　direction　by　gliding　downward　by　gravity。



The　bird's　flying　apparatus　and　skill　are　as　yet　infinitely

superior　to　those　of　man；　but　there　are　indications　that

within　a　few　years　the　latter　may　evolve　more　accurately

proportioned　apparatus　and　obtain　absolute　control　over

it。



It　is　hoped；　therefore；　that　if　there　be　found　no　radical

error　in　the　above　computations；　they　will　carry　the　conviction

that　soaring　flight　is　not　inaccessible　to　man；　as

it　promises　great　economies　of　motive　power　in　favorable

localities　of　rising　winds。



The　writer　will　be　grateful　to　experts　who　may　point

out　any　mistake　committed　in　data　or　calculations；　and

will　furnish　additional　information　to　any　aviator　who

may　wish　to　attempt　the　feat　of　soaring。







CHAPTER　XXI。



FLYING　MACHINES　VS。　BALLOONS。



While　wonderful　success　has　attended　the　development

of　the　dirigible　（steerable）　balloon　the　most　ardent

advocates　of　this　form　of　aerial　navigation　admit　that　it

has　serious　drawbacks。　Some　of　these　may　be　described

as　follows：



Expense　and　Other　Items。



Great　Initial　Expense。The　modern　dirigible　balloon

costs　a　fortune。　The　Zeppelin；　for　instance；　costs　more

than　100；000　（these　are　official　figures）。



Expense　of　Inflation。Gas　evaporates　rapidly；　and　a

balloon　must　be　re…inflated；　or　partially　re…inflated；　every

time　it　is　used。　The　Zeppelin　holds　460；000　cubic　feet

of　gas　which；　even　at　1　per　thousand；　would　cost　460。



Difficulty　of　Obtaining　Gas。If　a　balloon　suddenly

becomes　deflated；　by　accident　or　atmospheric　conditions；

far　from　a　source　of　gas　supply；　it　is　practically　worthless。

Gas　must　be　piped　to　it；　or　the　balloon　carted　to

the　gas　housean　expensive　proceeding　in　either　event。



Lack　of　Speed　and　Control。



Lack　of　Speed。Under　the　most　favorable　conditions

the　maximum　speed　of　a　balloon　is　30　miles　an　hour。

Its　great　bulk　makes　the　high　speed　attained　by　flying

machines　impossible。



Difficulty　of　Control。While　the　modern　dirigible　balloon　is

readily　handled　in　calm　or　light　winds；　its　bulk

makes　it　difficult　to　control　in　heavy　winds。



The　Element　of　Danger。Numerous　balloons　have

been　destroyed　by　lightning　and　similar　causes。　One　of

the　largest　of　the　Zeppelins　was　thus　lost　at　Stuttgart

in　1908。



Some　Balloon　Performances。



It　is　only　a　matter　of　fairness　to　state　that；　under

favorable　conditions；　some　very　creditable　records　have

been　made　with　modern　balloons；　viz：



November　23d；　1907；　the　French　dirigible　Patrie；　travelled

187　miles　in　6　hours　and　45　minutes　against　a

light　wind。　This　was　a　little　over　28　miles　an　hour。



The　Clement…Bayard；　another　French　machine；　sold

to　the　Russian　government；　made　a　trip　of　125　miles　at

a　rate　of　27　miles　an　hour。



Zeppelin　No。　3；　carrying　eight　passengers；　and　having

a　total　lifting　capacity　of　5；500　pounds　of　ballast　in

addition　to　passengers；　weight　of　equipment；　etc。；　was

tested　in　October；　1906；　an