soaring¡¡birds¡¡did¡¡not¡¡exert¡¡any¡¡power¡¡in¡¡flying¡£
Writers¡¡and¡¡experimenters¡¡do¡¡not¡¡agree¡¡on¡¡the
question¡¡of¡¡the¡¡propulsive¡¡power£»¡¡or¡¡on¡¡the¡¡form
or¡¡shape¡¡of¡¡the¡¡wing¡¡which¡¡is¡¡most¡¡effective£»¡¡or
in¡¡the¡¡matter¡¡of¡¡the¡¡relation¡¡of¡¡surface¡¡to¡¡weight£»
nor¡¡do¡¡they¡¡agree¡¡in¡¡any¡¡particular¡¡as¡¡to¡¡the¡¡effect
and¡¡action¡¡of¡¡matter¡¡in¡¡the¡¡soaring¡¡principle¡£
Only¡¡a¡¡small¡¡percentage¡¡of¡¡flying¡¡creatures¡¡use
motionless¡¡wings¡¡as¡¡in¡¡soaring¡£¡¡By¡¡far£»¡¡the
greater¡¡majority¡¡use¡¡beating¡¡wings£»¡¡a¡¡method¡¡of
translation¡¡in¡¡air¡¡which¡¡has¡¡not¡¡met¡¡with¡¡success
in¡¡any¡¡attempts¡¡on¡¡the¡¡part¡¡of¡¡the¡¡inventor¡£
Nevertheless£»¡¡experimenting¡¡has¡¡proceeded¡¡on
lines¡¡which¡¡seek¡¡to¡¡recognize¡¡nature's¡¡form¡¡only£»
while¡¡avoiding¡¡the¡¡best¡¡known¡¡and¡¡most¡¡persistent
type¡£
SHAPE¡¡OF¡¡SUPPORTING¡¡SURFACES¡£When¡¡we¡¡examine
the¡¡prevailing¡¡type¡¡of¡¡supporting¡¡surfaces
we¡¡cannot¡¡fail¡¡to¡¡be¡¡impressed¡¡with¡¡one¡¡feature£»
namely£»¡¡the¡¡determination¡¡to¡¡insist¡¡on¡¡a¡¡broad
spread¡¡of¡¡plane¡¡surface£»¡¡in¡¡imitation¡¡of¡¡the¡¡bird
with¡¡outstretched¡¡wings¡£
THE¡¡TROUBLE¡¡ARISING¡¡FROM¡¡OUTSTRETCHED
WINGS¡£This¡¡form¡¡of¡¡construction¡¡is¡¡what¡¡brings
all¡¡the¡¡troubles¡¡in¡¡its¡¡train¡£¡¡The¡¡literature¡¡on
aviation¡¡is¡¡full¡¡of¡¡arguments¡¡on¡¡this¡¡subject£»¡¡all
declaring¡¡that¡¡a¡¡wide¡¡spread¡¡is¡¡essential£»¡¡because£»
birds¡¡fly¡¡that¡¡way¡£
These¡¡assertions¡¡are¡¡made¡¡notwithstanding¡¡the
fact¡¡that¡¡only¡¡a¡¡few¡¡years¡¡ago£»¡¡in¡¡the¡¡great¡¡exhibit
of¡¡aeroplanes¡¡in¡¡Paris£»¡¡many¡¡unique¡¡forms¡¡of¡¡machines
were¡¡shown£»¡¡all¡¡of¡¡them¡¡capable¡¡of¡¡flying£»
as¡¡proven¡¡by¡¡numerous¡¡experiments£»¡¡and¡¡among
them¡¡were¡¡a¡¡half¡¡dozen¡¡types¡¡whose¡¡length¡¡fore
and¡¡aft¡¡were¡¡much¡¡greater¡¡than¡¡transversely£»¡¡and
it¡¡was¡¡particularly¡¡noted¡¡that¡¡they¡¡had¡¡most¡¡wonderful
stability¡£
DENSITY¡¡OF¡¡THE¡¡ATMOSPHERE¡£Experts¡¡declare
that¡¡the¡¡density¡¡of¡¡the¡¡atmosphere¡¡varies¡¡throughout£»
that¡¡it¡¡has¡¡spots¡¡here¡¡and¡¡there¡¡which¡¡are£»
apparently£»¡¡like¡¡holes£»¡¡so¡¡that¡¡one¡¡side¡¡or¡¡the
other¡¡of¡¡the¡¡machine¡¡will£»¡¡unaccountably£»¡¡tilt£»¡¡and
sometimes¡¡the¡¡entire¡¡machine¡¡will¡¡suddenly¡¡drop
for¡¡many¡¡feet£»¡¡while¡¡in¡¡flight¡£
ELASTICITY¡¡OF¡¡THE¡¡AIR¡£Air¡¡is¡¡the¡¡most¡¡elastic
substance¡¡known¡£¡¡The¡¡particles¡¡constituting¡¡it
are¡¡constantly¡¡in¡¡motion¡£¡¡When¡¡heat¡¡or¡¡cold¡¡penetrate
the¡¡mass¡¡it¡¡does¡¡so£»¡¡in¡¡a¡¡general¡¡way£»¡¡so¡¡as
to¡¡permeate¡¡the¡¡entire¡¡body£»¡¡but¡¡the¡¡conductivity
of¡¡the¡¡atmospheric¡¡gases¡¡is¡¡such¡¡that¡¡the¡¡heat
does¡¡not¡¡reach¡¡all¡¡parts¡¡at¡¡the¡¡same¡¡time¡£
AIR¡¡HOLES¡£The¡¡result¡¡is¡¡that¡¡varying¡¡strata
of¡¡heat¡¡and¡¡cold¡¡seem¡¡to¡¡be¡¡superposed£»¡¡and¡¡also
distributed¡¡along¡¡the¡¡route¡¡taken¡¡by¡¡a¡¡machine£»
causing¡¡air¡¡currents¡¡which¡¡vary¡¡in¡¡direction¡¡and
intensity¡£¡¡When£»¡¡therefore£»¡¡a¡¡rapidly¡moving
machine¡¡passes¡¡through¡¡an¡¡atmosphere¡¡so¡¡disturbed£»
the¡¡surfaces¡¡of¡¡the¡¡planes¡¡strike¡¡a¡¡mass¡¡of
air¡¡moving£»¡¡we¡¡may¡¡say£»¡¡first¡¡toward¡¡the¡¡plane£»
and¡¡the¡¡next¡¡instant¡¡the¡¡current¡¡is¡¡reversed£»¡¡and
the¡¡machine¡¡drops£»¡¡because¡¡its¡¡support¡¡is¡¡temporarily
gone£»¡¡and¡¡the¡¡aviator¡¡experiences¡¡the¡¡sensation
of¡¡going¡¡into¡¡a¡¡¡¨hole¡£¡¨
RESPONSIBILITY¡¡FOR¡¡ACCIDENTS¡£These¡¡so¡called
¡¨holes¡¨¡¡are¡¡responsible¡¡for¡¡many¡¡accidents¡£¡¡The
outstretched¡¡wings£»¡¡many¡¡of¡¡them¡¡over¡¡forty¡¡feet
from¡¡tip¡¡to¡¡tip£»¡¡offer¡¡opportunities¡¡for¡¡a¡¡tilt¡¡at¡¡one
end¡¡or¡¡the¡¡other£»¡¡which¡¡has¡¡sent¡¡so¡¡many¡¡machines
to¡¡destruction¡£
The¡¡high¡¡center¡¡of¡¡gravity¡¡in¡¡all¡¡machines¡¡makes
the¡¡weight¡¡useless¡¡to¡¡counterbalance¡¡the¡¡rising
end¡¡or¡¡to¡¡hold¡¡up¡¡the¡¡depressed¡¡wing¡£
All¡¡aviators¡¡agree¡¡that¡¡these¡¡unequal¡¡areas¡¡of
density¡¡extend¡¡over¡¡small¡¡spaces£»¡¡and¡¡it¡¡is£»¡¡therefore£»
obvious¡¡that¡¡a¡¡machine¡¡which¡¡is¡¡of¡¡such¡¡a
structure¡¡that¡¡it¡¡moves¡¡through¡¡the¡¡air¡¡broadside
on£»¡¡will¡¡be¡¡more¡¡liable¡¡to¡¡meet¡¡these¡¡inequalities
than¡¡one¡¡which¡¡is¡¡narrow¡¡and¡¡does¡¡not¡¡take¡¡in¡¡such
a¡¡wide¡¡path¡£
Why£»¡¡therefore£»¡¡persist¡¡in¡¡making¡¡a¡¡form¡¡which£»
by¡¡its¡¡very¡¡nature£»¡¡invites¡¡danger£¿¡¡Because¡¡birds
fly¡¡that¡¡way£¡
THE¡¡TURNING¡¡MOVEMENT¡£This¡¡structural¡¡arrangement
accentuates¡¡the¡¡difficulty¡¡when¡¡the¡¡machine
turns¡£¡¡The¡¡air¡¡pressure¡¡against¡¡the¡¡wing
surface¡¡is¡¡dependent¡¡on¡¡the¡¡speed¡£¡¡The¡¡broad
outstretched¡¡surfaces¡¡compel¡¡the¡¡wing¡¡at¡¡the¡¡outer
side¡¡of¡¡the¡¡circle¡¡to¡¡travel¡¡faster¡¡than¡¡the¡¡inner
one¡£¡¡As¡¡a¡¡result£»¡¡the¡¡outer¡¡end¡¡of¡¡the¡¡aeroplane
is¡¡elevated¡£
CENTRIFUGAL¡¡ACTION¡£At¡¡the¡¡same¡¡time¡¡the
running¡¡gear£»¡¡and¡¡the¡¡frame¡¡which¡¡carries¡¡it¡¡and
supports¡¡the¡¡machine¡¡while¡¡at¡¡rest£»¡¡being¡¡below
the¡¡planes£»¡¡a¡¡centrifugal¡¡force¡¡is¡¡exerted£»¡¡when
turning¡¡a¡¡circle£»¡¡which¡¡tends¡¡to¡¡swing¡¡the¡¡wheels
and¡¡frame¡¡outwardly£»¡¡and¡¡thereby¡¡still¡¡further
elevating¡¡the¡¡outer¡¡end¡¡of¡¡the¡¡plane¡£
THE¡¡WARPING¡¡PLANES¡£The¡¡only¡¡remedy¡¡to
meet¡¡this¡¡condition¡¡is¡¡expressed¡¡in¡¡the¡¡mechanism
which¡¡wraps¡¡or¡¡twists¡¡the¡¡outer¡¡ends¡¡of¡¡the¡¡planes£»
as¡¡constructed¡¡in¡¡the¡¡Wright¡¡machine£»¡¡or¡¡the
ailerons£»¡¡or¡¡small¡¡wings¡¡at¡¡the¡¡rear¡¡margins¡¡of¡¡the
planes£»¡¡as¡¡illustrated¡¡by¡¡the¡¡Farman¡¡machine¡£
The¡¡object¡¡of¡¡this¡¡arrangement¡¡is¡¡to¡¡decrease¡¡the
angle¡¡of¡¡incidence¡¡at¡¡the¡¡rising¡¡end£»¡¡and¡¡increase
the¡¡angle¡¡at¡¡the¡¡depressed¡¡end£»¡¡and¡¡thus£»¡¡by¡¡manually¡
operated¡¡means¡¡keep¡¡the¡¡machine¡¡on¡¡an¡¡even
keel¡£
CHAPTER¡¡IV
FORE¡¡AND¡¡AFT¡¡CONTROL
THERE¡¡is¡¡no¡¡phase¡¡of¡¡the¡¡art¡¡of¡¡flying¡¡more¡¡important
than¡¡the¡¡fore¡¡and¡¡aft¡¡control¡¡of¡¡an¡¡airship¡£
Lateral¡¡stability¡¡is¡¡secondary¡¡to¡¡this¡¡feature£»¡¡for
reasons¡¡which¡¡will¡¡appear¡¡as¡¡we¡¡develop¡¡the
subject¡£
THE¡¡BIRD¡¡TYPE¡¡OF¡¡FORE¡¡AND¡¡AFT¡¡CONTROL¡£
Every¡¡aeroplane¡¡follows¡¡the¡¡type¡¡set¡¡by¡¡nature
in¡¡the¡¡particular¡¡that¡¡the¡¡body¡¡is¡¡caused¡¡to¡¡oscillate
on¡¡a¡¡vertical¡¡fore¡¡and¡¡aft¡¡plane¡¡while¡¡in
flight¡£¡¡The¡¡bird¡¡has¡¡one¡¡important¡¡advantage£»
however£»¡¡in¡¡structure¡£¡¡Its¡¡wing¡¡has¡¡a¡¡flexure¡¡at
the¡¡joint£»¡¡so¡¡that¡¡its¡¡body¡¡can¡¡so¡¡oscillate¡¡independently
of¡¡the¡¡angle¡¡of¡¡the¡¡wings¡£
The¡¡aeroplane¡¡has¡¡the¡¡wing¡¡firmly¡¡fixed¡¡to¡¡the
body£»¡¡hence¡¡the¡¡only¡¡way¡¡in¡¡which¡¡it¡¡is¡¡possible
to¡¡effect¡¡a¡¡change¡¡in¡¡the¡¡angle¡¡of¡¡the¡¡wing¡¡is¡¡by
changing¡¡the¡¡angle¡¡of¡¡the¡¡body¡£¡¡To¡¡be¡¡consistent
the¡¡aeroplane¡¡should¡¡be¡¡so¡¡constructed¡¡that¡¡the
angle¡¡of¡¡the¡¡supporting¡¡surfaces¡¡should¡¡be¡¡movable£»
and¡¡not¡¡controllable¡¡by¡¡the¡¡body¡£
The¡¡bird£»¡¡in¡¡initiating¡¡flight¡¡from¡¡a¡¡perch£»¡¡darts
downwardly£»¡¡and¡¡changes¡¡the¡¡angle¡¡of¡¡the¡¡body¡¡to
correspond¡¡with¡¡the¡¡direction¡¡of¡¡the¡¡flying¡¡start¡£
When¡¡it¡¡alights¡¡the¡¡body¡¡is¡¡thrown¡¡so¡¡that¡¡its
breast¡¡banks¡¡against¡¡the¡¡air£»¡¡but¡¡in¡¡ordinary¡¡flight
its¡¡wings¡¡only¡¡are¡¡used¡¡to¡¡change¡¡the¡¡angle¡¡of
flight¡£
ANGLE¡¡AND¡¡DIRECTION¡¡OF¡¡FLIGHT¡£In¡¡order¡¡to
become¡¡familiar¡¡with¡¡terms¡¡which¡¡will¡¡be¡¡frequently
used¡¡throughout¡¡the¡¡book£»¡¡care¡¡should¡¡be
taken¡¡to¡¡distinguish¡¡between¡¡the¡¡terms¡¡angle¡¡and
direction¡¡of¡¡flight¡£¡¡The¡¡former¡¡has¡¡reference¡¡to
the¡¡up¡¡and¡¡down¡¡movement¡¡of¡¡an¡¡aeroplane£»
whereas¡¡the¡¡latter¡¡is¡¡used¡¡to¡¡designate¡¡a¡¡turning
movement¡¡to¡¡the¡¡right¡¡or¡¡to¡¡the¡¡left¡£
WHY¡¡SHOULD¡¡THE¡¡ANGLE¡¡OF¡¡THE¡¡BODY¡¡CHANGE£¿
The¡¡first¡¡question¡¡that¡¡presents¡¡itself¡¡is£»¡¡why
should¡¡the¡¡angle¡¡of¡¡the¡¡aeroplane¡¡body¡¡change£¿
Why¡¡should¡¡it¡¡be¡¡made¡¡to¡¡dart¡¡up¡¡and¡¡down¡¡and
produce¡¡a¡¡sinuous¡¡motion£¿¡¡Why¡¡should¡¡its¡¡nose
tilt¡¡toward¡¡the¡¡earth£»¡¡when¡¡it¡¡is¡¡descending£»¡¡and
raise¡¡the¡¡forward¡¡part¡¡of¡¡the¡¡structure¡¡while¡¡ascending£¿
The¡¡ready¡¡answer¡¡on¡¡the¡¡part¡¡of¡¡the¡¡bird¡form
advocate¡¡is£»¡¡that¡¡nature¡¡has¡¡so¡¡designed¡¡a¡¡flying
structure¡£¡¡The¡¡argument¡¡is¡¡not¡¡consistent£»¡¡because
in¡¡this¡¡respect£»¡¡as¡¡in¡¡every¡¡other£»¡¡it¡¡is¡¡not
made¡¡to¡¡conform¡¡to¡¡the¡¡structure¡¡which¡¡they¡¡seek
to¡¡copy¡£
CHANGING¡¡ANGLE¡¡OF¡¡BODY¡¡NOT¡¡SAFE¡£Furthermore£»
there¡¡is¡¡not¡¡a¡¡single¡¡argument¡¡which¡¡can¡¡be
advanced¡¡in¡¡behalf¡¡of¡¡that¡¡method¡¡of¡¡building£»
which¡¡proves¡¡it¡¡to¡¡be¡¡correct¡£¡¡Contrariwise£»¡¡an
analysis¡¡of¡¡the¡¡flying¡¡movement¡¡will¡¡show¡¡that¡¡it¡¡is
the¡¡one¡¡feature¡¡which¡¡has¡¡militated¡¡against¡¡safety£»
and¡¡that¡¡machines¡¡will¡¡never¡¡be¡¡safe¡¡so¡¡long¡¡as
the¡¡angle¡¡of¡¡the¡¡body¡¡must¡¡be¡¡depended¡¡upon¡¡to
control¡¡the¡¡angle¡¡of¡¡flying¡£
_Fig¡£¡¡11a¡¡Monoplane¡¡in¡¡Flight¡£_
In¡¡Fig¡£¡¡11a¡¡three¡¡positions¡¡of¡¡a¡¡monoplane¡¡are
shown£»¡¡each¡¡in¡¡horizontal¡¡flight¡£¡¡Let¡¡us¡¡say¡¡that
the¡¡first¡¡figure¡¡A¡¡is¡¡going¡¡at¡¡40¡¡miles¡¡per¡¡hour£»
the¡¡second£»¡¡B£»¡¡at¡¡50£»¡¡and¡¡the¡¡third£»¡¡C£»¡¡at¡¡60¡¡miles¡£
The¡¡body¡¡in¡¡A¡¡is¡¡nearly¡¡horizontal£»¡¡the¡¡angle¡¡of
the¡¡plane¡¡D¡¡being¡¡such¡¡that£»¡¡with¡¡the¡¡tail¡¡E¡¡also
horizontal£»¡¡an¡¡even¡¡flight¡¡is¡¡maintained¡£
When¡¡the¡¡speed¡¡increases¡¡to¡¡50¡¡miles¡¡an¡¡hour£»
the¡¡angle¡¡of¡¡incidence¡¡in¡¡the¡¡plane¡¡D¡¡must¡¡be
decreased£»¡¡so¡¡that¡¡the¡¡rear¡¡end¡¡of¡¡the¡¡frame¡¡must
be¡¡raised£»¡¡which¡¡is¡¡done¡¡by¡¡giving¡¡the¡¡tail¡¡an¡¡angle
of¡¡incidence£»¡¡otherwise£»¡¡as¡¡the¡¡upper¡¡side¡¡of¡¡the
tail¡¡should¡¡meet¡¡the¡¡air¡¡it¡¡would¡¡drive¡¡the¡¡rear
end¡¡of¡¡the¡¡frame¡¡down£»¡¡and¡¡thus¡¡defeat¡¡the¡¡attempt
to¡¡elevate¡¡that¡¡part¡£
_Fig¡£¡¡12¡£¡¡Angles¡¡of¡¡Flight¡£_
As¡¡the¡¡speed¡¡increases¡¡ten¡¡miles¡¡more£»¡¡the¡¡tail
is¡¡swung¡¡down¡¡still¡¡further¡¡and¡¡the¡¡rear¡¡end¡¡of
the¡¡frame¡¡is¡¡now¡¡actually¡¡above¡¡the¡¡plane¡¡of¡¡flight¡£
In¡¡order£»¡¡now£»¡¡to¡¡change¡¡the¡¡angle¡¡of¡¡flight£»¡¡without
altering¡¡the¡¡speed¡¡of¡¡the¡¡machine£»¡¡the¡¡tail¡¡is
used¡¡to¡¡effect¡¡the¡¡control¡£
Examine¡¡the¡¡first¡¡diagram¡¡in¡¡Fig¡£¡¡12¡£¡¡This
shows¡¡the¡¡tail¡¡E¡¡still¡¡further¡¡depressed£»¡¡and¡¡the
air¡¡striking¡¡its¡¡lower¡¡side£»¡¡causes¡¡an¡¡upward¡¡movement
of¡¡the¡¡frame¡¡at¡¡that¡¡end£»¡¡which¡¡so¡¡much¡¡decreases
the¡¡angle¡¡of¡¡incidence¡¡that¡¡the¡¡aeroplane
darts¡¡downwardly¡£
In¡¡order¡¡to¡¡ascend£»¡¡the¡¡tail£»¡¡as¡¡shown¡¡in¡¡the¡¡second
diagram£»¡¡is¡¡elevated¡¡so¡¡as¡¡to¡¡depress¡¡the¡¡rear
end£»¡¡and¡¡now¡¡the¡¡sustaining¡¡surface¡¡shoots¡¡upwardly¡£
Suppose¡¡that¡¡in¡¡either¡¡of¡¡the¡¡positions¡¡1¡¡or¡¡2£»
thus¡¡described£»¡¡the¡¡aviator¡¡should¡¡lose¡¡control¡¡of
the¡¡mechanism£»¡¡or¡¡it¡¡should¡¡become¡¡deranged¡¡or
¡¨stick£»¡¨¡¡conditions¡¡which¡¡have¡¡existed¡¡in¡¡the¡¡history
of¡¡the¡¡art£»¡¡what¡¡is¡¡there¡¡to¡¡prevent¡¡an¡¡accident£¿
In¡¡the¡¡first¡¡case£»¡¡if¡¡there¡¡is¡¡room£»¡¡the¡¡machine
will¡¡loop¡¡the¡¡loop£»¡¡and¡¡in¡¡the¡¡second¡¡case¡¡the¡¡machine
will¡¡move¡¡upwardly¡¡until¡¡it¡¡is¡¡vertical£»¡¡and
then£»¡¡in¡¡all¡¡probability£»¡¡as¡¡its¡¡propelling¡¡power¡¡is
not¡¡sufficient¡¡to¡¡hold¡¡it¡¡in¡¡that¡¡position£»¡¡like¡¡a
helicopter£»¡¡and¡¡having¡¡absolutely¡¡no¡¡wing¡¡supporting
surface¡¡when¡¡in¡¡that¡¡position£»¡¡it¡¡will¡¡dart
down¡¡tail¡¡foremost¡£
A¡¡NON¡CHANGING¡¡BODY¡£We¡¡may¡¡contrast¡¡the
СÌáʾ£º°´ »Ø³µ [Enter] ¼ü ·µ»ØÊéÄ¿£¬°´ ¡û ¼ü ·µ»ØÉÏÒ»Ò³£¬ °´ ¡ú ¼ü ½øÈëÏÂÒ»Ò³¡£
ÔÞÒ»ÏÂ
Ìí¼ÓÊéÇ©¼ÓÈëÊé¼Ü