aeroplanes-第19节

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！



of　the　squared　figure。　That　would　make

the　problem　as　follows：



　　　　　45　X　45　=　2025　/　200　=　10。125；　or；

　　　　　45　X　45　…　2025　X　。005　=　10。125。





Again；　twenty…five　miles　per　hour　would　be

25　X　25　=　625；　and　this　multiplied　by　。005　equals

2　pounds　pressure。



CONVERTING　HOURS　INTO　MINUTES。It　is　sometimes

confusing　to　think　of　miles　per　hour；　when

you　wish　to　express　it　in　minutes　or　seconds。　A

simple　rule；　which　is　not　absolutely　accurate；　but

is　correct　within　a　few　feet；　in　order　to　express

the　speed　in　feet　per　minute；　is　to　multiply　the

figure　indicating　the　miles　per　hour；　by　8　3/4。



To　illustrate：　If　the　wind　is　moving　at　the

rate　of　twenty　miles　an　hour；　it　will　travel　in　that

time　105；600　feet　（5280　X　20）。　As　there　are　sixty

minutes　in　an　hour；　105；600　divided　by　60；　equals

1760　feet　per　minute。　Instead　of　going　through

all　this　process　of　calculating　the　speed　per　minute；

remember　to　multiply　the　speed　in　miles　per

hour　by　90；　which　will　give　1800　feet。



This　is　a　little　more　then　two　per　cent。　above

the　correct　figure。　Again；　40　X　90　equals　3600。

As　the　correct　figure　is　3520；　a　little　mental　calculation

will　enable　you　to　correct　the　figures　so

as　to　get　it　within　a　few　feet。



CHANGING　SPEED　HOURS　TO　SECONDS。As　one…

sixtieth　of　the　speed　per　minute　will　represent　the

rate　of　movement　per　second；　it　is　a　comparatively

easy　matter　to　convert　the　time　from　speed　in

miles　per　hour　to　fraction　of　a　mile　traveled　in

a　second；　by　merely　taking　one…half　of　the　speed

in　miles；　and　adding　it；　which　will　very　nearly　express

the　true　number　of　feet。



As　examples；　take　the　following：　If　the　wind

is　traveling　20　miles　an　hour；　it　is　easy　to　take

one…half　of　20；　which　is　10；　and　add　it　to　20；　making

30；　as　the　number　of　feet　per　second。　If　the

wind　travels　50　miles　per　hour；　add　25；　making

75；　as　the　speed　per　second。



The　correct　speed　per　second　of　a　wind　traveling

20　miles　an　hour　is　a　little　over　29　feet。　At

50　miles　per　hour；　the　correct　figure　is　73　1/3　feet；

which　show　that　the　figures　under　this　rule　are

within　about　one　per　cent。　of　being　correct。



With　the　table　before　you　it　will　be　an　easy

matter；　by　observing　the　air　pressure　indicator；

to　determine　the　proper　speed　for　the　anemometer。

Suppose　it　shows　a　pressure　of　two　pounds；

which　will　indicate　a　speed　of　twenty　miles　an

hour。　You　have　thus　a　fixed　point　to　start　from。



PRESSURE　AS　THE　SQUARE　OF　THE　SPEED。Now

it　must　not　be　assumed　that　if　the　pressure　at

twenty　miles　an　hour　is　two　pounds；　that　forty

miles　an　hour　it　is　four　pounds。　The　pressure

is　as　the　square　of　the　speed。　This　may　be　explained

as　follows：　As　the　speed　of　the　wind

increases；　it　has　a　more　effective　push　against　an

object　than　its　rate　of　speed　indicates；　and　this

is　most　simply　expressed　by　saying　that　each　time

the　speed　is　doubled　the　pressure　is　four　times

greater。



As　an　example　of　this；　let　us　take　a　speed　of　ten

miles　an　hour；　which　means　a　pressure　of　one…

half　pound。　Double　this　speed；　and　we　have　20

miles。　Multiplying　one…half　pound　by　4；　the　result

is　2　pounds。　Again；　double　20；　which　means

40　miles；　and　multiplying　2　by　4；　the　result　is　8。

Doubling　forty　is　eighty　miles　an　hour；　and　again

multiplying　8　by　4；　we　have　32　as　the　pounds　pressure

at　a　speed　of　80　miles　an　hour。



The　anemometer；　however；　is　constant　in　its

speed。　If　the　pointer　should　turn　once　a　second

at　10　miles　an　hour；　it　would　turn　twice　at　20　miles

an　hour；　and　four　times　a　second　at　40　miles　an

hour。



GYROSCOPIC　BALANCE。Some　advance　has　been

made　in　the　use　of　the　gyroscope　for　the　purpose

of　giving　lateral　stability　to　an　aeroplane。　While

the　best　of　such　devices　is　at　best　a　makeshift；

it　is　well　to　understand　the　principle　on　which　they

operate；　and　to　get　an　understanding　how　they　are

applied。



THE　PRINCIPLE　INVOLVED。The　only　thing

known　about　the　gyroscope　is；　that　it　objects　to

changing　the　plane　of　its　rotation。　This　statement

must　be　taken　with　some　allowance；　however；

as；　when　left　free　to　move；　it　will　change　in

one　direction。



To　explain　this　without　being　too　technical；　examine

Fig。　63；　which　shows　a　gyroscopic　top；　one

end　of　the　rim　A；　which　supports　the　rotating

wheel　B；　having　a　projecting　finger　C；　that　is

mounted　on　a　pin…point　on　the　upper　end　of　the

pedestal　D。



_Fig。　63。　The　Gyroscope。_



When　the　wheel　B　is　set　in　rotation　it　will　maintain

itself　so　that　its　axis　E　is　horizontal；　or　at

any　other　angle　that　the　top　is　placed　in　when　the

wheel　is　spun。　If　it　is　set　so　the　axis　is　horizontal

the　wheel　B　will　rotate　on　a　vertical　plane；

and　it　forcibly　objects　to　any　attempt　to　make　it

turn　except　in　the　direction　indicated　by　the

curved　arrows　F。



The　wheel　B　will　cause　the　axis　E　to　swing

around　on　a　horizontal　plane；　and　this　turning

movement　is　always　in　a　certain　direction　in　relation

to　the　turn　of　the　wheel　B；　and　it　is　obvious；

therefore；　that　to　make　a　gyroscope　that

will　not　move；　or　swing　around　an　axis；　the　placing

of　two　such　wheels　side　by　side；　and　rotated

in　opposite　directions；　will　maintain　them　in　a

fixed　position；　this　can　also　be　accomplished　by

so　mounting　the　two　that　one　rotates　on　a　plane

at　right　angles　to　the　other。



_Fig。　64。　Application　of　the　Gyroscope。_



THE　APPLICATION　OF　THE　GYROSCOPE。Without

in　any　manner　showing　the　structural　details　of

the　device；　in　its　application　to　a　flying　machine；

except　in　so　far　as　it　may　be　necessary　to　explain

its　operation；　we　refer　to　Fig。　64；　which

assumes　that　A　represents　the　frame　of　the　aeroplane；

and　B　a　frame　for　holding　the　gyroscopic

wheel　C；　the　latter　being　mounted　so　it　rotates　on

a　horizontal　plane；　and　the　frame　B　being　hinged

fore　and　aft；　so　that　it　is　free　to　swing　to　the　right

or　to　the　left。



For　convenience　in　explaining　the　action；　the

planes　E　are　placed　at　right　angles　to　their　regular

positions；　F　being　the　forward　margin　of　the

plane；　and　G　the　rear　edge。　Wires　H　connect

the　ends　of　the　frame　B　with　the　respective

planes；　or　ailerons；　E；　and　another　wire　I　joins

the　downwardly…projecting　arms　of　the　two

ailerons；　so　that　motion　is　transmitted　to　both　at

the　same　time；　and　by　a　positive　motion　in　either

direction。



_Fig。　65。　Action　of　the　Gyroscope。_



In　the　second　figure；　65；　the　frame　of　the　aeroplane

is　shown　tilted　at　an　angle；　so　that　its　right

side　is　elevated。　As　the　gyroscopic　wheel　remains

level　it　causes　the　aileron　on　the　right　side　to

change　to　a　negative　angle；　while　at　the　same

time　giving　a　positive　angle　to　the　aileron　on　the

left　side；　which　would；　as　a　result；　depress　the

right　side；　and　bring　the　frame　of　the　machine

back　to　a　horizontal　position。



FORE　AND　AFT　GYROSCOPIC　CONTROL。It　is

obvious　that　the　same　application　of　this　force　may

be　applied　to　control　the　ship　fore　and　aft；　although

it　is　doubtful　whether　such　a　plan　would

have　any　advantages；　since　this　should　be　wholly

within　the　control　of　the　pilot。



Laterally　the　ship　should　not　be　out　of　balance；

fore　and　aft　this　is　a　necessity；　and　as　the　great

trouble　with　all　aeroplanes　is　to　control　them

laterally；　it　may　well　be　doubted　whether　it　would

add　anything　of　value　to　the　machine　by　having

an　automatic　fore　and　aft　control；　which　might；

in　emergencies；　counteract　the　personal　control　of

the　operator。



ANGLE　INDICATOR。In　flight　it　is　an　exceedingly

difficult　matter　for　the　pilot　to　give　an　accurate

idea　of　the　angle　of　the　planes。　If　the　air　is

calm　and　he　is　moving　over　a　certain　course；　and

knows；　from　experience；　what　his　speed　is；　he　may

be　able　to　judge　of　this　factor；　but　he　cannot　tell

what　changes　take　place　under　certain　conditions

during　the　flight。



For　this　purpose　a　simple　little　indicator　may

be　provided；　shown　in　Fig。　66；　which　is　merely　a

vertical　board　A；　with　a　pendulum　B；　swinging

fore　and　aft　from　a　pin　a　which　projects　out

from　the　board　a　short　distance　above　its　center。



The　upper　end　of　the　pendulum　has　a　heart…

shaped　wire　structure　D；　that　carries　a　sliding

weight　E。　Normally；　when　the　aeroplane　is　on

an　even　keel；　or　is　even　at　an　angle；　the　weight

E　rests　within　the　bottom　of　the　loop　D；　but

should　there　be　a　sudden　downward　lurch　or　a

quick　upward　inclination；　which　would　cause　the

pendulum　below　to　rapidly　swing　in　either

direction；　the　sliding　weight　E　would　at　once　move

forward　in　the　same　direction　that　the　pendulum

had　moved；　and　thus　counteract；　for　the　instant

only；　the　swing；　when　it　would　again　drop　back

into　its　central　position。



_Fig。　66。　Angle　Indicator。_



With　such　an　arrangement；　the　pendulum　would

hang　vertically　at　all　times；　and　the　pointer　below；

being　in　range　of　a　circle　with　degrees

indicated　thereon；　and　the　base　attached　to　the

frame