aeroplanes- 第4部分

normal　pressure。　A　pressure　of　this　kind

against　a　plane　is　where　the　wind　strikes　it　at

right　angles。　This　is　illustrated　in　Fig。　4；　in

which　the　plane　is　shown　with　the　wind　striking

it　squarely。



It　is　obvious　that　the　wind　will　exert　a　greater

force　against　a　plane　when　at　its　normal。　On　the

other　hand；　the　least　pressure　against　a　plane　is

when　it　is　in　a　horizontal　position；　because　then

the　wind　has　no　force　against　the　surfaces；　and

the　only　effect　on　the　drift　is　that　which　takes

place　when　the　wind　strikes　its　forward　edge。



_Fig。　4。　Normal　Air　Pressure_



_Fig。　5。　Edge　Resistance_





HEAD　RESISTANCE。Fig。　5　shows　such　a　plane；

the　only　resistance　being　the　thickness　of　the

plane　as　at　A。　This　is　called　head　resistance；

and　on　this　subject　there　has　been　much　controversy；

and　many　theories；　which　will　be　considered

under　the　proper　headings。



If　a　plane　is　placed　at　an　angle　of　45　degrees

the　lift　and　the　drift　are　the　same；　assumedly；　because；

if　we　were　to　measure　the　power　required

to　drive　it　forwardly；　it　would　be　found　to　equal

the　weight　necessary　to　lift　it。　That　is；　suppose

we　should　hold　a　plane　at　that　angle　with　a　heavy

wind　blowing　against　it；　and　attach　two　pairs　of

scales　to　the　plane；　both　would　show　the　same

pull。



_Fig。　6。　Measuring　Lift　and　Drift_



MEASURING　LIFT　AND　DRIFT。In　Fig。　6；　A　is　the

plane；　B　the　horizontal　line　which　attaches　the

plane　to　a　scale　C；　and　D　the　line　attaching　it　to

the　scale　E。　When　the　wind　is　of　sufficient　force

to　hold　up　the　plane；　the　scales　will　show　the　same

pull；　neglecting；　of　course；　the　weight　of　the

plane　itself。



PRESSURE　AT　DIFFERENT　ANGLES。What　every

one　wants　to　know；　and　a　subject　on　which　a

great　deal　of　experiment　and　time　have　been　expended；

is　to　determine　what　the　pressures　are　at

the　different　angles　between　the　horizontal；　and

laws　have　been　formulated　which　enable　the　pressures

to　be　calculated。



DIFFERENCE　BETWEEN　LIFT　AND　DRIFT　IN　MOTION。The

first　observation　is　directed　to　the　differences

that　exist　between　the　lift　and　drift；

when　the　plane　is　placed　at　an　angle　of　less　than

45　degrees。　A　machine　weighing　1000　pounds

has　always　the　same　lift。　Its　mass　does　not

change。　Remember；　now；　we　allude　to　its　mass；

or　density。



We　are　not　now　referring　to　weight；　because

that　must　be　taken　into　consideration；　in　the

problem。　As　heretofore　stated；　when　an　object

moves　horizontally；　it　has　less　weight　than　when

at　rest。　If　it　had　the　same　weight　it　would　not

move　forwardly；　but　come　to　rest。



When　in　motion；　therefore；　while　the　lift；　so

far　as　its　mass　is　concerned；　does　not　change；　the

drift　does　decrease；　or　the　forward　pull　is　less

than　when　at　45　degrees；　and　the　decrease　is　less

and　less　until　the　plane　assumes　a　horizontal　position；

where　it　is　absolutely　nil；　if　we　do　not　consider

head　resistance。



TABLES　OF　LIFT　AND　DRIFT。All　tables　of　Lift

and　Drift　consider　only　the　air　pressures。　They

do　not　take　into　account　the　fact　that　momentum

takes　an　important　part　in　the　translation　of　an

object；　like　a　flying　machine。



A　mass　of　material；　weighing　1000　pounds　while

at　rest；　sets　up　an　enormous　energy　when　moving

through　the　air　at　fifty；　seventy…five；　or　one　hundred

miles　an　hour。　At　the　latter　speed　the　movement

is　about　160　feet　per　second；　a　motion　which

is　nearly　sufficient　to　maintain　it　in　horizontal

flight；　independently　of　any　plane　surface。



Such　being　the　case；　why　take　into　account　only

the　angle　of　the　plane？　It　is　no　wonder　that

aviators　have　not　been　able　to　make　the　theoretical

considerations　and　the　practical　demonstrations

agree。



WHY　TABLES　OF　LIFT　AND　DRIFT　ARE　WRONG。

A　little　reflection　will　show　why　such　tables　are

wrong。　They　were　prepared　by　using　a　plane

surface　at　rest；　and　forcing　a　blast　of　air　against

the　plane　placed　at　different　angles；　and　for　determining

air　pressures；　this　is；　no　doubt；　correct。

But　it　does　not　represent　actual　flying　conditions。

It　does　not　show　the　conditions　existing

in　an　aeroplane　while　in　flight。



To　determine　this；　short　of　actual　experiments

with　a　machine　in　horizontal　translation；　is　impossible；

unless　it　is　done　by　taking　into　account

the　factor　due　to　momentum　and　the　element

attributable　to　the　lift　of　the　plane　itself　due　to　its

impact　against　the　atmosphere。



LANGLEY'S　LAW。The　law　enunciated　by

Langley　is；　that　the　greater　the　speed　the　less　the

power　required　to　propel　it。　Water　as　a　propelling

medium　has　over　seven　hundred　times

more　force　than　air。　A　vessel　having；　for　instance；

twenty　horse　power；　and　a　speed　of　ten

miles　per　hour；　would　require　four　times　that

power　to　drive　it　through　the　water　at　double　the

speed。　The　power　is　as　the　square　of　the　speed。



With　air　the　conditions　are　entirely　different。

The　boat　submergence　in　the　water　is　practically

the　same；　whether　going　ten　or　twenty　miles　an

hour。　The　head　resistance　is　the　same；　substantially；

at　all　times　in　the　case　of　the　boat；　with　the

flying　machine　the　resistance　of　its　sustaining

surfaces　decreases。



Without　going　into　a　too　technical　description

of　the　reasoning　which　led　to　the　discovery　of　the

law　of　air　pressures；　let　us　try　and　understand

it　by　examining　the　diagram；　Fig。　7。



A　represents　a　plane　at　an　angle　of　45　degrees；

moving　forwardly　into　the　atmosphere　in　the

direction　of　the　arrows　B。　The　measurement

across　the　plane　vertically；　along　the　line　B；

which　is　called　the　sine　of　the　angle；　represents

the　surface　impact　of　air　against　the　plane。



In　Fig。　8　the　plane　is　at　an　angle　of　27　degrees；

which　makes　the　distance　in　height　across　the　line

C　just　one…half　the　length　of　the　line　B　of　Fig。　7；

hence　the　surface　impact　of　the　air　is　one…half　that

of　Fig。　7；　and　the　drift　is　correspondingly　decreased。



_Fig。　7。　Equal　Lift　and　Drift　in　Flight。_



_Fig。　8。　Unequal　Lift　and　Drift。_





MOVING　PLANES　VS。　WINDS。In　this　way　Boisset；

Duchemin；　Langley；　and　others；　determined

the　comparative　drift；　and　those　results　have　been

largely　relied　upon　by　aviators；　and　assumed　to

be　correct　when　applied　to　flying　machines。



That　they　are　not　correct　has　been　proven　by

the　Wrights　and　others；　the　only　explanation　being

that　some　errors　had　been　made　in　the　calculations；

or　that　aviators　were　liable　to　commit　errors

in　observing　the　true　angle　of　the　planes

while　in　flight。



MOMENTUM　NOT　CONSIDERED。The　great　factor

of　momentum　has　been　entirely　ignored；　and　it　is

our　desire　to　press　the　important　point　on　those

who　begin　to　study　the　question　of　flying　machines。



THE　FLIGHT　OF　BIRDS。Volumes　have　been

written　concerning　observations　on　the　flight　of

birds。　The　marvel　has　been　why　do　soaring　birds

maintain　themselves　in　space　without　flapping

their　wings。　In　fact；　it　is　a　much　more　remarkable

thing　to　contemplate　why　birds　which　depend

on　flapping　wings　can　fly。



THE　DOWNWARD　BEAT。It　is　argued　that　the

downward　beat　of　the　wings　is　so　much　more

rapid　than　the　upward　motion；　that　it　gets　an　action

on　the　air　so　as　to　force　the　body　upwardly。

This　is　disposed　of　by　the　wing　motion　of　many

birds；　notoriously　the　crow；　whose　lazily…flapping

wings　can　be　readily　followed　by　the　eye；　and　the

difference　in　movement；　if　any；　is　not　perceptible。



THE　CONCAVED　WING。It　is　also　urged　that　the

concave　on　the　under　side　of　the　wing　gives　the

quality　of　lift。　Certain　kinds　of　beetles；　and　particularly

the　common　house　fly；　disprove　that　theory；

as　their　wings　are　perfectly　flat。



FEATHER　STRUCTURE　CONSIDERED。Then　the

feather　argument　is　advanced；　which　seeks　to

show　that　as　each　wing　is　made　up　of　a　plurality

of　feathers；　overlapping　each　other；　they　form　a

sort　of　a　valved　surface；　opening　so　as　to　permit

air　to　pass　through　them　during　the　period　of

their　upward　movement；　and　closing　up　as　the

wing　descends。



It　is　difficult　to　perform　this　experiment　with

wings；　so　as　to　show　such　an　individual　feather

movement。　It　is　certain　that　there　is　nothing　in

the　structure　of　the　wing　bone　and　the　feather

connection　which　points　to　any　individual　feather

movement；　and　our　observation　is；　that　each

feather　is　entirely　too　rigid　to　permit　of　such　an

opening　up　between　them。



It　is　obvious　that　the　wing　is　built　up　in　that

way　for　an　entirely　different　reason。　Soaring

birds；　which　do　not　depend　on　the　flapping　motion；

have　the　same　overlapping　feather　formation。



WEBBED　WINGS。Furthermore；　there　are　numerous

flying　creatures　which　do　not　have

feathered　wings；　but　web…like　structures；　or　like　the

house　fly；　in　one　continuous　and　unbroken

plane。



That　birds　which　fly　with　flapping　wings　derive

their　support　from　the　air；　is　undoubtedly　true；

and　that　the　lift　produced　is　due；　not　to　the　form；

or　shape；　or　area　of　the　wing；　is　also　beyond　question。

The　records　show　that　every　conceivable

type　of　outlined　structure　is　used　by　nature；　the

material　and　texture　of　the　wings　themselves　differ

to　such　a　degree　that　there　is　absolutely　no

similarity；　some　have　concaved　under　surfaces；

and　others　have　not；　some　fly　with　rapidly　beating

wings；　and　others　with　slow　and　measured

movements；　many　of　them　fly　with　equal　facility

without　flapping　movements；　and　the　proportions

of　weight　to　wing　surface　vary　to　such　an　extent

that　it　is　utterly　impossible　to　use　such　data　as　a

guide　in　calculating　what　the　proper　surface

should　be　for　a　correct　flying　machine。



THE　ANGLE　OF　MOVEMENT。How；　then；　it　may

be　asked；　do　they　get　their　support？　There　must

be　something；　in　all　this　variety　and　diversity　of

form；　of　motion；　and　of　characteristics；　which

supplies　the　true　answer。　The　answer　lies　in　the

angle　of　movement　of　every　wing　motion；　which

is　at　the　control　of