flying machines-第7部分

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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。

In　this　connection　it　will　be　well　to　understand　the　velocity

of　the　wind；　and　what　it　means　as　shown　in　the

following　table：



Miles　per　hour　Feet　per　second　　　　　Pressure　per　sq。　foot

　　　　　10　　　　　　　　　　　　　　　　14。7　　　　　　　　　　　　　　　　　。492

　　　　　25　　　　　　　　　　　　　　　　36。7　　　　　　　　　　　　　　　　3。075

　　　　　50　　　　　　　　　　　　　　　　73。3　　　　　　　　　　　　　　　12。300

　　　　　100　　　　　　　　　　　　　　146。6　　　　　　　　　　　　　　　49。200



Pressure　of　wind　increases　in　proportion　to　the　square

of　the　velocity。　Thus　wind　at　10　miles　an　hour　has　four

times　the　pressure　of　wind　at　5　miles　an　hour。　The

greater　this　pressure　the　large　and　heavier　the　object

which　can　be　raised。　Any　boy　who　has　had　experience

in　flying　kites　can　testify　to　this；　High　winds；　however；

are　almost　invariably　gusty　and　uncertain　as　to　direction；

and　this　makes　them　dangerous　for　aviators。　It

is　also　a　self…evident　fact　that；　beyond　a　certain　stage；

the　harder　the　wind　blows　the　more　difficult　it　is　to

make　headway　against　it。



Launching　Device　for　Gliders。



On　page　195　will　be　found　a　diagram　of　the　various

parts　of　a　launcher　for　gliders；　designed　and　patented

by　Mr。　Octave　Chanute。　In　describing　this　invention

in　Aeronautics；　Mr。　Chanute　says：



〃In　practicing；　the　track；　preferably　portable；　is

generally　laid　in　the　direction　of　the　existing　wind　and

the　car；　preferably　a　light　platform…car；　is　placed　on　the

track。　The　truck　carrying　the　winding…drum　and　its　motor

is　placed　to　windward　a　suitable　distancesay　from

two　hundred　to　one　thousand　feetand　is　firmly　blocked

or　anchored　in　line　with　the　portable　track；　which　is

preferably　80　or　100　feet　in　length。　The　flying　or　gliding

machine　to　be　launched　with　its　operator　is　placed　on

the　platform…car　at　the　leeward　end　of　the　portable　track。

The　line；　which　is　preferably　a　flexible　combination

wire…and…cord　cable；　is　stretched　between　the　winding…

drum　on　the　track　and　detachably　secured　to　the　flying

or　gliding　machine；　preferably　by　means　of　a　trip…hoop；

or　else　held　in　the　hand　of　the　operator；　so　that　the

operator　may　readily　detach　the　same　from　the　flying…

machine　when　the　desired　height　is　attained。



How　Glider　Is　Started。



〃Then　upon　a　signal　given　by　the　operator　the　engineer

at　the　motor　puts　it　into　operation；　gradually　increasing

the　speed　until　the　line　is　wound　upon　the　drum

at　a　maximum　speed　of；　say；　thirty　miles　an　hour。　The

operator　of　the　flying…machine；　whether　he　stands　upright　and

carries　it　on　his　shoulders；　or　whether　he　sits

or　lies　down　prone　upon　it；　adjusts　the　aeroplane　or

carrying　surfaces　so　that　the　wind　shall　strike　them　on

the　top　and　press　downward　instead　of　upward　until

the　platform…car　under　action　of　the　winding…drum　and

line　attains　the　required　speed。



〃When　the　operator　judges　that　his　speed　is　sufficient；

and　this　depends　upon　the　velocity　of　the　wind　as　well

as　that　of　the　car　moving　against　the　wind；　he　quickly

cause