formation¡¡of¡¡the¡¡plane£»¡¡have¡¡been¡¡considered¡¡in
all¡¡their¡¡aspects£»¡¡so¡¡that¡¡the¡¡art¡¡in¡¡this¡¡respect¡¡has
advanced¡¡with¡¡rapid¡¡strides¡£
NARROW¡¡PLATES¡¡MOST¡¡EFFECTIVE¡£It¡¡was
learned£»¡¡in¡¡the¡¡early¡¡stages¡¡of¡¡the¡¡development
by¡¡practical¡¡experiments£»¡¡that¡¡a¡¡narrow¡¡plane£»
fore¡¡and¡¡aft£»¡¡produces¡¡a¡¡greater¡¡lift¡¡than¡¡a¡¡wide
one£»¡¡so¡¡that£»¡¡assuming¡¡the¡¡plane¡¡has¡¡100¡¡square
feet¡¡of¡¡sustaining¡¡surface£»¡¡it¡¡is¡¡far¡¡better¡¡to¡¡make
the¡¡shape¡¡five¡¡feet¡¡by¡¡twenty¡¡than¡¡ten¡¡by¡¡ten¡£
However£»¡¡it¡¡must¡¡be¡¡observed£»¡¡that¡¡to¡¡use¡¡the
narrow¡¡blade¡¡effectively£»¡¡it¡¡must¡¡be¡¡projected
through¡¡the¡¡air¡¡with¡¡the¡¡long¡¡margin¡¡forwardly¡£
Its¡¡sustaining¡¡power¡¡per¡¡square¡¡foot¡¡of¡¡surface
is¡¡much¡¡less¡¡if¡¡forced¡¡through¡¡the¡¡air¡¡lengthwise¡£
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has¡¡proportionally¡¡a¡¡greater¡¡lift£»¡¡and¡¡this¡¡may
be¡¡more¡¡clearly¡¡understood¡¡by¡¡examining¡¡the
illustrations¡¡which¡¡show¡¡the¡¡movement¡¡of¡¡planes
through¡¡the¡¡air¡¡at¡¡appropriate¡¡angles¡£
_Fig¡£¡¡22¡£¡¡Stream¡¡lines¡¡along¡¡a¡¡plane¡£_
STREAM¡¡LINES¡¡ALONG¡¡A¡¡PLANE¡£In¡¡Fig¡£¡¡22£»¡¡A
is¡¡a¡¡flat¡¡plane£»¡¡which¡¡we¡¡will¡¡assume¡¡is¡¡10¡¡feet
from¡¡the¡¡front¡¡to¡¡the¡¡rear¡¡margin¡£¡¡For¡¡convenience
seven¡¡stream¡¡lines¡¡of¡¡air¡¡are¡¡shown£»
which¡¡contact¡¡with¡¡this¡¡inclined¡¡surface¡£¡¡The¡¡first
line¡¡1£»¡¡after¡¡the¡¡contact¡¡at¡¡the¡¡forward¡¡end£»¡¡is
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The¡¡second¡¡air¡¡stream¡¡2£»¡¡strikes¡¡the¡¡first¡¡stream£»
followed¡¡successively¡¡by¡¡the¡¡other¡¡streams£»¡¡3£»¡¡4£»
and¡¡so¡¡on£»¡¡each¡¡succeeding¡¡stream¡¡being¡¡compelled
to¡¡ride¡¡over£»¡¡or¡¡along¡¡on¡¡the¡¡preceding¡¡mass¡¡of
cushioned¡¡air£»¡¡the¡¡last¡¡lines£»¡¡near¡¡the¡¡lower¡¡end£»
being£»¡¡therefore£»¡¡at¡¡such¡¡angles£»¡¡and¡¡contacting
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but¡¡little¡¡lift¡¡in¡¡comparison¡¡with¡¡the¡¡1st£»
2d¡¡and¡¡3d¡¡stream¡¡lines¡£¡¡These¡¡stream¡¡lines¡¡are
taken¡¡by¡¡imagining¡¡that¡¡the¡¡air¡¡approaches¡¡and
contacts¡¡with¡¡the¡¡plane¡¡only¡¡along¡¡the¡¡lines¡¡indicated
in¡¡the¡¡sketch£»¡¡although¡¡they¡¡also¡¡in¡¡practice
are¡¡active¡¡against¡¡every¡¡part¡¡of¡¡the¡¡plane¡£
THE¡¡CENTER¡¡OF¡¡PRESSURE¡£In¡¡such¡¡a¡¡plane¡¡the
center¡¡of¡¡pressure¡¡is¡¡near¡¡its¡¡upper¡¡end£»¡¡probably
near¡¡the¡¡line¡¡3£»¡¡so¡¡that¡¡the¡¡greater¡¡portion¡¡of¡¡the
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line¡¡3¡£
AIR¡¡LINES¡¡ON¡¡THE¡¡UPPER¡¡SIDE¡¡OF¡¡THE¡¡PLANE¡£
Now£»¡¡another¡¡factor¡¡must¡¡be¡¡considered£»¡¡namely£»
the¡¡effect¡¡produced¡¡on¡¡the¡¡upper¡¡side¡¡of¡¡the¡¡plane£»
over¡¡which¡¡a¡¡rarefied¡¡area¡¡is¡¡formed¡¡at¡¡certain
points£»¡¡and£»¡¡in¡¡practice£»¡¡this¡¡also¡¡produces£»¡¡or
should¡¡be¡¡utilized¡¡to¡¡effect¡¡a¡¡lift¡£
RAREFIED¡¡AREA¡£What¡¡is¡¡called¡¡a¡¡rarefied¡¡area£»
has¡¡reference¡¡to¡¡a¡¡state¡¡or¡¡condition¡¡of¡¡the¡¡atmosphere
which¡¡has¡¡less¡¡than¡¡the¡¡normal¡¡pressure¡¡or
quantity¡¡of¡¡air¡£¡¡Thus£»¡¡the¡¡pressure¡¡at¡¡sea¡¡level£»
is¡¡about¡¡14¡¡3/4¡¡per¡¡square¡¡inch
As¡¡we¡¡ascend¡¡the¡¡pressure¡¡grows¡¡less£»¡¡and¡¡the
air¡¡is¡¡thus¡¡rarer£»¡¡or£»¡¡there¡¡is¡¡less¡¡of¡¡it¡£¡¡This¡¡is¡¡a
condition¡¡which¡¡is¡¡normally¡¡found¡¡in¡¡the¡¡atmosphere¡£
Several¡¡things¡¡tend¡¡to¡¡make¡¡a¡¡rarefied
condition¡£¡¡One¡¡is¡¡altitude£»¡¡to¡¡which¡¡we¡¡have¡¡just
referred¡£
Then¡¡heat¡¡will¡¡expand¡¡air£»¡¡making¡¡it¡¡less¡¡dense£»
or¡¡lighter£»¡¡so¡¡that¡¡it¡¡will¡¡move¡¡upwardly£»¡¡to¡¡be
replaced¡¡by¡¡a¡¡colder¡¡body¡¡of¡¡air¡£¡¡In¡¡aeronautics
neither¡¡of¡¡these¡¡conditions¡¡is¡¡of¡¡any¡¡importance
in¡¡considering¡¡the¡¡lifting¡¡power¡¡of¡¡aeroplane¡¡surfaces¡£
RAREFACTION¡¡PRODUCED¡¡BY¡¡MOTION¡£The¡¡third
rarefied¡¡condition¡¡is¡¡produced¡¡by¡¡motion£»¡¡and¡¡generally
the¡¡area¡¡is¡¡very¡¡limited¡¡when¡¡brought¡¡about
by¡¡this¡¡means¡£¡¡If£»¡¡for¡¡instance£»¡¡a¡¡plane¡¡is¡¡held
horizontally¡¡and¡¡allowed¡¡to¡¡fall¡¡toward¡¡the¡¡earth£»
it¡¡will¡¡be¡¡retarded¡¡by¡¡two¡¡forces£»¡¡namely£»¡¡compression
and¡¡rarefaction£»¡¡the¡¡former¡¡acting¡¡on¡¡the
under¡¡side¡¡of¡¡the¡¡plane£»¡¡and¡¡the¡¡latter¡¡on¡¡the¡¡upper
side¡£
Of¡¡the¡¡two¡¡rarefaction¡¡is¡¡the¡¡most¡¡effectual£»
and¡¡produces¡¡a¡¡greater¡¡effect¡¡than¡¡compression¡£
This¡¡may¡¡be¡¡proven¡¡by¡¡compressing¡¡air¡¡in¡¡a¡¡long
pipe£»¡¡and¡¡noting¡¡the¡¡difference¡¡in¡¡gauge¡¡pressure
between¡¡the¡¡ends£»¡¡and¡¡then¡¡using¡¡a¡¡suction¡¡pump
on¡¡the¡¡same¡¡pipe¡£
When¡¡a¡¡plane¡¡is¡¡forced¡¡through¡¡the¡¡air¡¡at¡¡any
angle£»¡¡a¡¡rarefied¡¡area¡¡is¡¡formed¡¡on¡¡the¡¡side¡¡which
is¡¡opposite¡¡the¡¡one¡¡having¡¡the¡¡positive¡¡angle¡¡of
incidence¡£
If¡¡the¡¡plane¡¡can¡¡be¡¡so¡¡formed¡¡as¡¡to¡¡make¡¡a¡¡large
and¡¡effective¡¡area¡¡it¡¡will¡¡add¡¡greatly¡¡to¡¡the¡¡value
of¡¡the¡¡sustaining¡¡surface¡£
Unfortunately£»¡¡the¡¡long¡¡fiat¡¡plane¡¡does¡¡not¡¡lend
any¡¡aid¡¡in¡¡this¡¡particular£»¡¡as¡¡the¡¡stream¡¡line¡¡flows
down¡¡along¡¡the¡¡top£»¡¡as¡¡shown¡¡in¡¡Fig¡£¡¡23£»¡¡without
being¡¡of¡¡any¡¡service¡£
_Fig¡£¡¡23¡£¡¡Air¡¡lines¡¡on¡¡the¡¡upper¡¡side¡¡of¡¡a¡¡Plane¡£_
THE¡¡CONCAVED¡¡PLANE¡£These¡¡considerations
led¡¡to¡¡the¡¡adoption¡¡of¡¡the¡¡concaved¡¡plane¡¡formation£»
and¡¡for¡¡purposes¡¡of¡¡comparison¡¡the¡¡diagram£»
Fig¡£¡¡24£»¡¡shows¡¡the¡¡plane¡¡B¡¡of¡¡the¡¡same¡¡length¡¡and
angle¡¡as¡¡the¡¡straight¡¡planes¡£
In¡¡examining¡¡the¡¡successive¡¡stream¡¡lines¡¡it¡¡will
be¡¡found¡¡that¡¡while¡¡the¡¡1st£»¡¡2d¡¡and¡¡3d¡¡lines¡¡have
a¡¡little¡¡less¡¡angle¡¡of¡¡impact¡¡than¡¡the¡¡corresponding
lines¡¡in¡¡the¡¡straight¡¡plane£»¡¡the¡¡last¡¡lines£»¡¡5£»¡¡6
and¡¡7£»¡¡have¡¡much¡¡greater¡¡angles£»¡¡so¡¡that¡¡only¡¡line
4¡¡strikes¡¡the¡¡plane¡¡at¡¡the¡¡same¡¡angle¡£
Such¡¡a¡¡plane¡¡structure¡¡would£»¡¡therefore£»¡¡have
its¡¡center¡¡of¡¡pressure¡¡somewhere¡¡between¡¡the
lines¡¡3¡¡and¡¡4£»¡¡and¡¡the¡¡lift¡¡being¡¡thus£»¡¡practically£»
uniform¡¡over¡¡the¡¡surface£»¡¡would¡¡be¡¡more¡¡effective¡£
THE¡¡CENTER¡¡OF¡¡PRESSURE¡£This¡¡is¡¡a¡¡term¡¡used
to¡¡indicate¡¡the¡¡place¡¡on¡¡the¡¡plane¡¡where¡¡the¡¡air
acts¡¡with¡¡the¡¡greatest¡¡force¡£¡¡It¡¡has¡¡reference¡¡to
a¡¡point¡¡between¡¡the¡¡front¡¡and¡¡rear¡¡margins¡¡only
of¡¡the¡¡plane¡£
_Fig¡£¡¡24¡£¡¡Air¡¡lines¡¡below¡¡a¡¡concaved¡¡Plane¡£_
UTILIZING¡¡THE¡¡RAREFIED¡¡AREA¡£This¡¡structure£»
however£»¡¡has¡¡another¡¡important¡¡advantage£»¡¡as¡¡it
utilizes¡¡the¡¡rarefied¡¡area¡¡which¡¡is¡¡produced£»¡¡and
which¡¡may¡¡be¡¡understood¡¡by¡¡reference¡¡to¡¡Fig¡£¡¡25¡£
The¡¡plane¡¡B£»¡¡with¡¡its¡¡upward¡¡curve£»¡¡and¡¡at¡¡the
same¡¡angle¡¡as¡¡the¡¡straight¡¡plane£»¡¡has¡¡its¡¡lower
end¡¡so¡¡curved£»¡¡with¡¡relation¡¡to¡¡the¡¡forward¡¡movement£»
that¡¡the¡¡air£»¡¡in¡¡rushing¡¡past¡¡the¡¡upper¡¡end£»
cannot¡¡follow¡¡the¡¡curve¡¡rapidly¡¡enough¡¡to¡¡maintain
the¡¡same¡¡density¡¡along¡¡C£»¡¡hence¡¡this¡¡exerts
an¡¡upward¡¡pull£»¡¡due¡¡to¡¡the¡¡rarefied¡¡area£»¡¡which
serves¡¡as¡¡a¡¡lifting¡¡force£»¡¡as¡¡well¡¡as¡¡the¡¡compressed
mass¡¡beneath¡¡the¡¡plane¡£
CHANGING¡¡CENTER¡¡OF¡¡PRESSURE¡£The¡¡center¡¡of
pressure¡¡is¡¡not¡¡constant¡£¡¡It¡¡changes¡¡with¡¡the
angle¡¡of¡¡the¡¡plane£»¡¡but¡¡the¡¡range¡¡is¡¡considerably
less¡¡on¡¡a¡¡concave¡¡surface¡¡than¡¡on¡¡a¡¡flat¡¡plane¡£
_Fig¡£¡¡25¡£¡¡Air¡¡lines¡¡above¡¡a¡¡convex¡¡Plane¡£_
In¡¡a¡¡plane¡¡disposed¡¡at¡¡a¡¡small¡¡angle£»¡¡A£»¡¡as¡¡in
Fig¡£¡¡26£»¡¡the¡¡center¡¡of¡¡pressure¡¡is¡¡nearer¡¡the¡¡forward
end¡¡of¡¡the¡¡plane¡¡than¡¡with¡¡a¡¡greater¡¡positive
angle¡¡of¡¡incidence£»¡¡as¡¡in¡¡Fig¡£¡¡27£»¡¡and¡¡when
the¡¡plane¡¡is¡¡in¡¡a¡¡normal¡¡flying¡¡angle£»¡¡it¡¡is¡¡at¡¡the
center£»¡¡or¡¡at¡¡a¡¡point¡¡midway¡¡between¡¡the¡¡margins¡£
PLANE¡¡MONSTROSITIES¡£Growing¡¡out¡¡of¡¡the¡¡idea
that¡¡the¡¡wing¡¡in¡¡nature¡¡must¡¡be¡¡faithfully¡¡copied£»
it¡¡is¡¡believed¡¡by¡¡many¡¡that¡¡a¡¡plane¡¡with¡¡a
pronounced¡¡thickness¡¡at¡¡its¡¡forward¡¡margin¡¡is¡¡one
of¡¡the¡¡secrets¡¡of¡¡bird¡¡flight¡£
Accordingly¡¡certain¡¡inventors¡¡have¡¡designed
types¡¡of¡¡wings¡¡which¡¡are¡¡shown¡¡in¡¡Figs¡£¡¡28¡¡and
29¡£
_Fig¡£¡¡28¡¡Changing¡¡centers¡¡of¡¡Pressures¡£_
_Fig¡¡29¡£¡¡Bird¡wing¡¡structures¡£_
Both¡¡of¡¡these¡¡types¡¡have¡¡pronounced¡¡bulges£»
designed¡¡to¡¡¡¨split¡¨¡¡the¡¡air£»¡¡forgetting£»¡¡apparently£»
that¡¡in¡¡other¡¡parts¡¡of¡¡the¡¡machine¡¡every¡¡effort¡¡is
made¡¡to¡¡prevent¡¡head¡¡resistance¡£
THE¡¡BIRD¡¡WING¡¡STRUCTURE¡£The¡¡advocates¡¡of
such¡¡construction¡¡maintain¡¡that¡¡the¡¡forward¡¡edge
of¡¡the¡¡plane¡¡must¡¡forcibly¡¡drive¡¡the¡¡air¡¡column
apart£»¡¡because¡¡the¡¡bird¡¡wing¡¡is¡¡so¡¡made£»¡¡and¡¡that
while¡¡it¡¡may¡¡not¡¡appear¡¡exactly¡¡logical£»¡¡still¡¡there
is¡¡something¡¡about¡¡it¡¡which¡¡seems¡¡to¡¡do¡¡the¡¡work£»
and¡¡for¡¡that¡¡reason¡¡it¡¡is¡¡largely¡¡adopted¡£
WHY¡¡THE¡¡BIRD'S¡¡WING¡¡HAS¡¡A¡¡PRONOUNCED
BULGE¡£Let¡¡us¡¡examine¡¡this¡¡claim¡£¡¡The¡¡bone
which¡¡supports¡¡the¡¡entire¡¡wing¡¡surface£»¡¡called¡¡the
£¨pectoral£©£»¡¡has¡¡a¡¡heavy¡¡duty¡¡to¡¡perform¡£¡¡It¡¡is¡¡so
constructed¡¡that¡¡it¡¡must¡¡withstand¡¡an¡¡extraordinary
torsional¡¡strain£»¡¡being¡¡located¡¡at¡¡the¡¡forward
portion¡¡of¡¡the¡¡wing¡¡surface¡£¡¡Torsion¡¡has
reference¡¡to¡¡a¡¡twisting¡¡motion¡£
In¡¡some¡¡cases£»¡¡as¡¡in¡¡the¡¡bat£»¡¡this¡¡primary¡¡bone
has¡¡an¡¡attachment¡¡to¡¡the¡¡rear¡¡of¡¡the¡¡main¡¡joint£»
where¡¡the¡¡rear¡¡margin¡¡of¡¡the¡¡wing¡¡is¡¡attached¡¡to
the¡¡leg¡¡of¡¡the¡¡animal£»¡¡thus¡¡giving¡¡it¡¡a¡¡support
and¡¡the¡¡main¡¡bone¡¡is£»¡¡therefore£»¡¡relieved¡¡of¡¡this
torsional¡¡stress¡£
THE¡¡BAT'S¡¡WING¡£An¡¡examination¡¡of¡¡the¡¡bat's
wing¡¡shows¡¡that¡¡the¡¡pectoral¡¡bone¡¡is¡¡very¡¡small
and¡¡thin£»¡¡thus¡¡proving¡¡that¡¡when¡¡the¡¡entire¡¡wing
support¡¡is¡¡thrown¡¡upon¡¡the¡¡primary¡¡bone¡¡it¡¡must
be¡¡large¡¡enough¡¡to¡¡enable¡¡it¡¡to¡¡carry¡¡out¡¡its¡¡functions¡£
It¡¡is¡¡certainly¡¡not¡¡so¡¡made¡¡because¡¡it¡¡is¡¡a
necessary¡¡shape¡¡which¡¡best¡¡adapts¡¡it¡¡for¡¡flying¡£
If¡¡such¡¡were¡¡the¡¡case¡¡then¡¡nature¡¡erred¡¡in¡¡the
case¡¡of¡¡the¡¡bat£»¡¡and¡¡it¡¡made¡¡a¡¡mistake¡¡in¡¡the
housefly's¡¡wing¡¡which¡¡has¡¡no¡¡such¡¡anterior¡¡enlargement
to¡¡assist¡¡£¨£¿£©¡¡it¡¡in¡¡flying¡£
AN¡¡ABNORMAL¡¡SHAPE¡£Another¡¡illustration¡¡is
shown¡¡in¡¡Fig¡£¡¡30£»¡¡which¡¡has¡¡a¡¡deep¡¡concave¡¡directly
behind¡¡the¡¡forward¡¡margin£»¡¡as¡¡at¡¡A£»¡¡so
that¡¡when¡¡the¡¡plane¡¡is¡¡at¡¡an¡¡angle¡¡of¡¡about¡¡22
degrees£»¡¡a¡¡horizontal¡¡line£»¡¡as¡¡B£»¡¡passing¡¡back¡¡from
the¡¡nose£»¡¡touches¡¡the¡¡incurved¡¡surface¡¡of¡¡the¡¡plane
at¡¡a¡¡point¡¡about¡¡one¡third¡¡of¡¡its¡¡measurement
back¡¡across¡¡the¡¡plane¡£
_Fig¡£¡¡30¡£¡¡One¡¡of¡¡the¡¡Monstrosities_
This¡¡form¡¡is¡¡an¡¡exact¡¡copy¡¡of¡¡the¡¡wing¡¡of¡¡an
actual¡¡bird£»¡¡but¡¡it¡¡belongs£»¡¡not¡¡to¡¡the¡¡soaring£»
but¡¡to¡¡the¡¡class¡¡which¡¡depends¡¡on¡¡flapping¡¡wings£»
and¡¡as¡¡such¡¡it¡¡cannot¡¡be¡¡understood¡¡why¡¡it¡¡should
be¡¡used¡¡for¡¡soaring¡¡machines£»¡¡as¡¡all¡¡aeroplanes
are¡£
The¡¡foregoing¡¡instances¡¡of¡¡construction¡¡are
cited¡¡to¡¡show¡¡how¡¡wildly¡¡the¡¡imagination¡¡will
roam¡¡when¡¡it¡¡follows¡¡wrong¡¡ideals¡£
THE¡¡TAIL¡¡AS¡¡A¡¡MONITOR¡£The¡¡tendency¡¡of¡¡the
center¡¡of¡¡pressure¡¡to¡¡change¡¡necessitates¡¡a¡¡correctional
means£»¡¡which¡¡is¡¡supplied¡¡in¡¡the¡¡tail¡¡of
the¡¡machine£»¡¡just¡¡as¡¡the¡¡tail¡¡of¡¡a¡¡kite¡¡serves¡¡to
hold¡¡it¡¡at¡¡a¡¡correct¡¡angle¡¡with¡¡respect¡¡to¡¡the¡¡wind
and¡¡the¡¡pull¡¡of¡¡the¡¡supporting¡¡string¡£
CHAPTER¡¡VII
ABNORMAL¡¡FLY
СÌáʾ£º°´ »Ø³µ [Enter] ¼ü ·µ»ØÊéÄ¿£¬°´ ¡û ¼ü ·µ»ØÉÏÒ»Ò³£¬ °´ ¡ú ¼ü ½øÈëÏÂÒ»Ò³¡£
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