aeroplanes-第15章

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is　called　dihedral；　or　diedral。



_Fig。　35。　Dihedral　Angle。_



This　arrangement　in　monoplanes　does　away

with　the　necessity　of　warping　the　planes；　or

changing　them　while　in　flight。　If；　however；　the　angle

is　too　great；　the　wind　from　either　quarter　is　liable

to　raise　the　side　that　is　exposed。



THE　COMMON　KITE。While　the　Malay　kite　has

only　two　points　of　cord　attachment；　both　along

the　vertical　rib；　the　common　kite；　as　shown　in

Fig。　36；　has　a　four…point　connection；　to　which　the

flying　cord　is　attached。　Since　this　form　has　no

dihedral　angle；　it　is　necessary　to　supply　a　tail；

which　thus　serves　to　keep　it　in　equilibrium；　while

in　flight。



_Fig。　36。　Common　Kite。_



Various　modifications　have　grown　out　of　the

Malay　kite。　One　of　these　forms；　designed　by

Eddy；　is　exactly　like　the　Malay　structure；　but　instead

of　having　a　light　flexible　cross　piece；　it　is

bent　to　resemble　a　bow；　so　that　it　is　rigidly　held

in　a　bent　position；　instead　of　permitting　the　wind

to　give　it　the　dihedral　angle。



THE　BOW　KITE。Among　the　different　types　are

the　bow　kite；　Fig。　37；　and　the　sexagonal　structure；

Fig。　38；　the　latter　form　affording　an　especially

large　surface。



_Fig。　37。　Bow　Kite。…



_Fig。　38。　Hexagonal　Kite。_



THE　BOX　KITE。The　most　marked　improvement

in　the　form　of　kites　was　made　by　Hargreaves；

in　1885；　and　called　the　box　kite。　It　has　wonderful

stability；　and　its　use；　with　certain　modifications；

in　Weather　Bureau　experiments；　have　proven　its

value。



It　is　made　in　the　form　of　two　boxes；　A；　B；　open

at　the　ends；　which　are　secured　together　by　means

of　longitudinal　bars；　C；　that　extends　from　one　to

the　other；　so　that　they　are　held　apart　a　distance；

approximately；　equal　to　the　length　of　one　of　the

boxes。



_Fig。　39。　Hargreave　Kite。_



Their　fore　and　aft　stability　is　so　perfect　that

the　flying　cord　D　is　attached　at　one　point　only；

and　the　sides　of　the　boxes　provide　lateral　stability

to　a　marked　degree。



THE　VOISON　BIPLANE。This　kind　of　kite　furnished

the　suggestion　for　the　Voison　biplane；

which　was　one　of　the　earlier　productions　in　flying

machines。



Fig。　40　shows　a　perspective　of　the　Voison　plane；

which　has　vertical　planes　A；　A；　at　the　ends；　and

also　intermediate　curtains　B；　B。　This　was　found

to　be　remarkably　stable；　but　during　its　turning

movements；　or　in　high　winds；　was　not　satisfactory；

and　for　that　reason　was　finally　abandoned。



LATERAL　STABILITY　IN　KITES　NOT　CONCLUSIVE　AS

TO　PLANES。This　is　instanced　to　show　that　while

such　a　form　is　admirably　adapted　for　kite　purposes；

where　vertical　curtains　are　always　in　line

with　the　wind　movement；　and　the　structure　is　held

taut　by　a　cord；　the　lateral　effect；　when　used　on　a

machine　which　does　not　at　all　times　move　in　line

with　the　moving　air　current。　A　condition　is　thus

set　up　which　destroys　the　usefulness　of　the　box

kite　formation。



_Fig。　40。　Voison　Biplane。_



THE　SPEAR　KITE。This　is　a　novel　kite；　with

remarkable　steadiness　and　is　usually　made　with

the　wings　on　the　rear　end　larger　than　those　on

the　forward　end　（Fig。　41）；　as　thereby　the　cord

A　can　be　attached　to　the　spear　midway　between

the　two　sets　of　wings。



_Fig。　41。　Spear　Kite。_



THE　CELLULAR　KITE。Following　out　the　suggestion

of　the　Hargreaves　kite；　numerous　forms

embodying　the　principle　of　the　box　structure　were

made　and　put　on　the　market　before　the　aeroplane

became　a　reality。



_Fig。　42。　Cellular　Kite。_



A　structure　of　this　form　is　illustrated　in　Fig。

42。　Each　box；　as　A；　B；　has　therein　a　plurality　of

vertical　and　horizontal　partitions；　so　that　a　number

of　cells　are　provided；　the　two　cell…like　boxes

being　held　apart　by　a　bar　C；　axially　arranged。



This　type　is　remarkably　stable；　due　to　the　small

cells；　and　kites　of　this　kind　are　largely　used　for

making　scientific　experiments。



THE　TETRAHEDRAL　KITE。Prof。　Bell；　inventor

of　the　telephone；　gave　a　great　deal　of　study　to

kites；　which　resulted　in　the　tetrahedral　formation；

as　shown　in　Fig。　43。



_Fig。　43。　Tetrahedral　Kite。_



The　structure；　apparently；　is　somewhat　complicated；

but　an　examination　of　a　single　pair　of

blades；　as　shown　at　A；　shows　that　it　is　built　up　of

triangularly…formed　pieces；　and　that　the　openings

between　the　pieces　are　equal　to　the　latter；　thereby

providing　a　form　of　kite　which　possesses　equilibrium

to　a　great　degree。



It　has　never　been　tried　with　power；　and　it　is

doubtful　whether　it　would　be　successful　as　a　sustaining

surface　for　flying　machines；　for　the　same

reasons　that　caused　failure　with　the　box…like　formation

of　the　Voison　Machine。



THE　DELTOID。The　deltoid　is　the　simplest；　and

the　most　easily　constructed　of　all　the　kites。　It　is

usually　made　from　stiff　cardboard；　A…shaped　in

outline；　as　shown　in　Figs。　44　and　45；　and　bent　along

a　central　line；　as　at　A；　forming　two　wings；　each

of　which　is　a　right…angled　triangle。



_Fig。　44。　and　45。　Deltoid　Formation。_



The　peculiarity　of　this　formation　is；　that　it　has

remarkable　stability　when　used　as　a　kite；　with

either　end　foremost。　If　a　small　weight　is　placed

at　the　pointed　end；　and　it　is　projected　through　the

air；　it　will　fly　straight；　and　is　but　little　affected

by　cross　currents。



THE　DUNNE　FLYING　MACHINE。A　top　view　of

this　biplane　is　shown　in　Fig。　46。　The　A…shaped

disposition　of　the　planes；　gives　it　good　lateral

stability；　but　it　has　the　disadvantage　under　which

all　aeroplanes　labor；　that　the　entire　body　of　the

machine　must　move　on　a　fore　and　aft　vertical

plan　in　order　to　ascend　or　descend。



_Fig。　46。　The　Dunne　Bi…plane。_



This　is　a　true　deltoid　formation；　as　the　angle　of

incidence　of　the　planes　is　so　disposed　that　when

the　planes　are　horizontal　from　end　to　end；　the　inclination

is　such　as　to　make　it　similar　to　the　deltoid

kite　referred　to。



ROTATING　KITE。A　type　of　kite　unlike　the

others　illustrated　is　a　rotating　structure；　which

gives　great　stability；　due　to　the　gyroscopic　action

on　the　supporting　surfaces。



Fig。　47　shows　a　side　view　with　the　top　in　section。

The　supporting　surface　is　umbrella…shaped。

In　fact；　the　ordinary　umbrella　will　answer　if　not

dished　too　much。　An　angularly…bent　piece　of　wire

A；　provided　with　loops　B；　B；　at　the　ends；　serve　as

bearings　for　the　handle　of　the　umbrella。



At　the　bend　of　the　wire　loop　C；　the　cord　D　is

attached。　The　lower　side　of　the　umbrella　top　has

cup…shaped　pockets　E；　near　the　margin；　so　arranged

that　their　open　ends　project　in　the　same

direction；　and　the　wind　catching　them　rotates　the

circular　plane。



_Fig。　47。　Rotable　Umbrella　Kite。_



KITE　PRINCIPLES。A　careful　study　of　the　examples

here　given；　will　impress　the　novice　with

one　important　fact；　which；　in　its　effect　has　a　more

important　bearing　on　successful　flight；　than　all

the　bird　study　and　speculations　concerning　its

mysteries。



This　fact；　in　essence；　is；　that　the　angle　of　the

kite　is　the　great　factor　in　flight　next　to　the　power

necessary　to　hold　it。　Aside　from　this；　the

comparison　between　kites　and　aeroplanes　is　of　no

practical　value。



Disregarding　the　element　of　momentum；　the

drift　of　a　machine　against　a　wind；　is　the　same；

dynamically；　as　a　plane　at　rest　with　the　wind

moving　past　it。　But　there　is　this　pronounced

difference：　The　cord　which　supports　the　kite

holds　it　so　that　the　power　is　in　one　direction　only。



When　a　side　gust　of　wind　strikes　the　kite　it

is　moved　laterally；　in　sympathy　with　the　kite；

hence　the　problem　of　lateral　displacement　is　not

the　same　as　with　the　aeroplane。



LATERAL　STABILITY　IN　KITES。In　the　latter　the

power　is　definitely　fixed　with　relation　to　the　machine

itself；　and　if　we　should　assume　that　a　plane

with　a　power　on　it　sufficient　to　maintain　a　flight

of　40　miles　an　hour；　should　meet　a　wind　moving

at　the　same　speed；　the　machine　would　be　stationary

in　space。



Such　a　condition　would　be　the　same；　so　far　as

the　angles　of　the　planes