flying machines-第6部分

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weight　on　the　structure。　If　it　is　properly　put　together

it　will　remain　rigid　and　unyielding。　Should　it　sag　ever

so　slightly　the　tension　of　the　wires　must　be　increased

until　any　tendency　to　sag；　no　matter　how　slight　it　may

be；　is　overcome。



Putting　on　the　Cloth。



We　are　now　ready　to　put　on　the　cloth　covering　which

holds　the　air　and　makes　the　machine　buoyant。　The　kind

of　material　employed　is　of　small　account　so　long　as　it　is

light；　strong；　and　wind…proof；　or　nearly　so。　Some　aviators

use　what　is　called　rubberized　silk；　others　prefer

balloon　cloth。　Ordinary　muslin　of　good　quality；　treated

with　a　coat　of　light　varnish　after　it　is　in　place；　will　answer

all　the　purposes　of　the　amateur。



Cut　the　cloth　into　strips　a　little　over　4　feet　in　length。

As　you　have　20　feet　in　width　to　cover；　and　the　cloth　is

one　yard　wide；　you　will　need　seven　strips　for　each　plane；

so　as　to　allow　for　laps；　etc。　This　will　give　you　fourteen

strips。　Glue　the　end　of　each　strip　around　the　front

horizontal　beams　of　the　planes；　and　draw　each　strip　back；

over　the　ribs；　tacking　the　edges　to　the　ribs　as　you　go

along；　with　small　copper　or　brass　tacks。　In　doing　this

keep　the　cloth　smooth　and　stretched　tight。　Tacks　should

also　be　used　in　addition　to　the　glue；　to　hold　the　cloth　to

the　horizontal　beams。



Next；　give　the　cloth　a　coat　of　varnish　on　the　clear；　or

upper　side；　and　when　this　is　dry　your　glider　will　be

ready　for　use。



Reinforcing　the　Cloth。



While　not　absolutely　necessary　for　amateur　purposes；

reinforcement　of　the　cloth；　so　as　to　avoid　any　tendency

to　split　or　tear　out　from　wind…pressure；　is　desirable。　One

way　of　doing　this　is　to　tack　narrow　strips　of　some

heavier　material；　like　felt；　over　the　cloth　where　it　laps

on　the　ribs。　Another　is　to　sew　slips　or　pockets　in　the

cloth　itself　and　let　the　ribs　run　through　them。　Still　another

method　is　to　sew　2…inch　strips　（of　the　same　material

as　the　cover）　on　the　cloth；　placing　them　about　one

yard　apart；　but　having　them　come　in　the　center　of　each

piece　of　covering；　and　not　on　the　laps　where　the　various

pieces　are　joined。



Use　of　Armpieces。



Should　armpieces　be　desired；　aside　from　those　afforded

by　the　center　struts；　take　two　pieces　of　spruce；　3　feet

long；　by　1　x　1　3/4　inches；　and　bolt　them　to　the　front　and

rear　beams　of　the　lower　plane　about　14　inches　apart。

These　will　be　more　comfortable　than　using　the　struts；

as　the　operator　will　not　have　to　spread　his　arms　so

much。　In　using　the　struts　the　operator；　as　a　rule；　takes

hold　of　them　with　his　hands；　while　with　the　armpieces；

as　the　name　implies；　he　places　his　arms　over　them；　one

of　the　strips　coming　under　each　armpit。



Frequently　somebody　asks　why　the　ribs　should　be

curved。　The　answer　is　easy。　The　curvature　tends　to

direct　the　air　downward　toward　the　rear　and；　as　the　air

is　thus　forced　downward；　there　is　more　or　less　of　an　impact

which　assists　in　propelling　the　aeroplane　upwards。







CHAPTER　VI。



LEARNING　TO　FLY。



Don't　be　too　ambitious　at　the　start。　Go　slow；　and

avoid　unnecessary　risks。　At　its　best　there　is　an　element

of　danger　in　aviation　which　cannot　be　entirely　eliminated；　but　it

may　be　greatly　reduced　and　minimized　by

the　use　of　common　sense。



Theoretically；　the　proper　way　to　begin　a　glide　is　from

the　top　of　an　incline；　facing　against　the　wind；　so　that

the　machine　will　soar　until　the　attraction　of　gravitation

draws　it　gradually　to　the　ground。　This　is　the　manner　in

which　experienced　aviators　operate；　but　it　must　be　kept

in　mind　that　these　men　are　experts。　They　understand

air　currents；　know　how　to　control　the　action　and　direction

of　their　machines　by　shifting　the　position　of　their

bodies；　and　by　so　doing　avoid　accidents　which　would　be

unavoidable　by　a　novice。



Begin　on　Level　Ground。



Make　your　first　flights　on　level　ground；　having　a　couple

of　men　to　assist　you　in　getting　the　apparatus　under

headway。　Take　your　position　in　the　center　rectangle；

back　far　enough　to　give　the　forward　edges　of　the　glider

an　inclination　to　tilt　upward　very　slightly。　Now　start

and　run　forward　at　a　moderately　rapid　gait；　one　man　at

each　end　of　the　glider　assisting　you。　As　the　glider　cuts

into　the　air　the　wind　will　catch　under　the　uplifted　edges

of　the　curved　planes；　and　buoy　it　up　so　that　it　will　rise

in　the　air　and　take　you　with　it。　This　rise　will　not　be

great；　just　enough　to　keep　you　well　clear　of　the　ground。

Now　project　your　legs　a　little　to　the　front　so　as　to　shift

the　center　of　gravity　a　trifle　and　bring　the　edges　of　the

glider　on　an　exact　level　with　the　atmosphere。　This；　with

the　momentum　acquired　in　the　start；　will　keep　the　machine

moving　forward　for　some　distance。



Effect　of　Body　Movements。



When　the　weight　of　the　body　is　slightly　back　of　the

center　of　gravity　the　edges　of　the　advancing　planes　are

tilted　slightly　upward。　The　glider　in　this　position　acts

as　a　scoop；　taking　in　the　air　which；　in　turn；　lifts　it　off　the

ground。　When　a　certain　altitude　is　reachedthis　varies

with　the　force　of　the　windthe　tendency　to　a　forward

movement　is　lost　and　the　glider　comes　to　the　ground。

It　is　to　prolong　the　forward　movement　as　much　as　possible

that　the　operator　shifts　the　center　of　gravity　slightly；

bringing　the　apparatus　on　an　even　keel　as　it　were　by

lowering　the　advancing　edges。　This　done；　so　long　as

there　is　momentum　enough　to　keep　the　glider　moving；　it

will　remain　afloat。



If　you　shift　your　body　well　forward　it　will　bring　the

front　edges　of　the　glider　down；　and　elevate　the　rear　ones。

In　this　way　the　air　will　be　〃spilled〃　out　at　the　rear；　and；

having　lost　the　air　support　or　buoyancy；　the　glider　comes

down　to　the　ground。　A　few　flights　will　make　any　ordinary

man　proficient　in　the　control　of　his　apparatus　by　his

body　movements；　not　only　as　concerns　the　elevating　and

depressing　of　the　advancing　edges；　but　also　actual　steering。　You

will　quickly　learn；　for　instance；　that；　as　the

shifting　of　the　bodily　weight　backwards　and　forwards

affects　the　upward　and　downward　trend　of　the　planes；　so

a　movement　sidewaysto　the　left　or　the　rightaffects

the　direction　in　which　the　glider　travels。



Ascends　at　an　Angle。



In　ascending；　the　glider　and　flying　machine；　like　the

bird；　makes　an　angular；　not　a　vertical　flight。　Just　what

this　angle　of　ascension　may　be　is　difficult　to　determine。

It　is　probable　and　in　fact　altogether　likely；　that　it　varies

with　the　force　of　the　wind；　weight　of　the　rising　body；

power　of　propulsion；　etc。　This；　in　the　language　of　physicists；

is　the　angle　of　inclination；　and；　as　a　general　thing；

under　normal　conditions　（still　air）　should　be　put　down　as

about　one　in　ten；　or　5　3/4　degrees。　This　would　be　an　ideal

condition；　but　it　has　not；　as　vet　been　reached。　The　force

of　the　wind　affects　the　angle　considerably；　as　does　also

the　weight　and　velocity　of　the　apparatus。　In　general

practice　the　angle　varies　from　23　to　45　degrees。　At

more　than　45　degrees　the　supporting　effort　is　overcome

by　the　resistance　to　forward　motion。



Increasing　the　speed　or　propulsive　force；　tends　to

lessen　the　angle　at　which　the　machine　may　be　successfully

operated　because　it　reduces　the　wind　pressure。

Most　of　the　modern　flying　machines　are　operated　at　an

angle　of　23　degrees；　or　less。



Maintaining　an　Equilibrium。



Stable　equilibrium　is　one　of　the　main　essentials　to

successful　flight；　and　this　cannot　be　preserved　in　an

uncertain；　gusty　wind；　especially　by　an　amateur。　The

novice　should　not　attempt　a　glide　unless　the　conditions

are　just　right。　These　conditions　are：　A　clear；　level

space；　without　obstructions；　such　as　trees；　etc。；　and　a

steady　wind　of　not　exceeding　twelve　miles　an　hour。　Always

fly　against　the　wind。



When　a　reasonable　amount　of　proficiency　in　the　handling

of　the　machine　on　level　ground　has　been　acquired

the　field　of　practice　may　be　changed　to　some　gentle

slope。　In　starting　from　a　slope　it　will　be　found　easier

to　keep　the　machine　afloat；　but　the　experience　at　first　is

likely　to　be　very　disconcerting　to　a　man　of　less　than　iron

nerve。　As　the　glider　sails　away　from　the　top　of　the

slope　the　distance　between　him　and　the　ground　increases

rapidly　until　the　aviator　thinks　he　is　up　a　hundred　miles

in　the　air。　If　he　will　keep　cool；　manipulate　his　apparatus

so　as　to　preserve　its　equilibrium；　and　〃let　nature　take　its

course；〃　he　will　come　down　gradually　and　safely　to　the

ground　at　a　considerable　distance　from　the　starting　place。

This　is　one　advantage　of　starting　from　an　elevation

your　machine　will　go　further。



But；　if　the　aviator　becomes　〃rattled〃；　if　he　loses　control

of　his　machine；　serious　results；　including　a　bad　fall

with　risk　of　death；　are　almost　certain。　And　yet　this

practice　is　just　as　necessary　as　the　initial　lessons　on

level　ground。　When　judgment　is　used；　and　〃haste　made

slowly；〃　there　is　very　little　real　danger。　While　experimenting

with　gliders　the　Wrights　made　flights　innumerable

under　all　sorts　of　conditions　and　never　had　an　accident

of　any　kind。



Effects　of　Wind　Currents。



The　larger　the　machine　the　more　difficult　it　will　be　to

control　its　movements　in　the　air；　and　yet　enlargement　is

absolutely　necessary　as　weight；　in　the　form　of　motor；

rudder；　etc。；　is　added。



Air　currents　near　the　surface　of　the　ground　are　diverted

by　every　obstruction　unless　the　wind　is　blowing

hard　enough　to　remove　the　obstruction　entirely。　Take；

for　instance；　the　case　of　a　tree　or　shrub；　in　a　moderate

wind　of　from　ten　to　twelve　miles　an　hour。　As　the　wind

strikes　the　tree　it　divides；　part　going　to　one　side　and

part　going　to　the　other；　while　still　another　part　is　directed

upward　and　goes　over　the　top　of　the　obstruction。

This　makes　the　handling　of　a　glider　on　an　obstructed

field　difficult　and　uncertain。　To　handle　a　glider　successfully

the　place　of　operation　should　be　clear　and　the　wind

moderate　and　steady。　If　it　is　gusty　postpone　your　flight。