the aeroplane speaks-第17部分

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l　the　camber　（curvature）　of　the　surface；　and　result　in　changing　both　the　lift　and　the　drift　at　that　part　of　the　surface。　Such　a　condition　will　cause　the　aeroplane　to　lose　its　directional　stability　and　also　to　fly　one　wing　down。

I　cannot　impress　this　matter　of　tension　upon　the　reader　too　strongly。　It　is　of　the　utmost　importance。　When　this；　and　also　accuracy　in　securing　the　various　adjustments；　has　been　learned；　one　is　on　the　way　to　becoming　a　good　rigger。

6。　Wire　Loops。Wire　is　often　bent　over　at　its　end　in　the　form　of　a　loop；　in　order　to　connect　with　a　turnbuckle　or　fitting。　These　loops；　even　when　made　as　perfectly　as　possible；　have　a　tendency　to　elongate；　thus　spoiling　the　adjustment　of　the　wires　Great　care　should　be　taken　to　minimize　this　as　far　as　possible。　The　rules　to　be　observed　are　as　follows：

（a）　The　size　of　the　loop　should　be　as　small　as　possible　within　reason。　By　that　I　mean　it　should　not　be　so　small　as　to　create　the　possibility　of　the　wire　breaking。


（b）　The　shape　of　the　loop　should　be　symmetrical。


（c）　It　should　have　well…defined　shoulders　in　order　to　prevent　the　ferrule　from　slipping　up。　At　the　same　time；　a　shoulder　should　not　have　an　angular　place。


（d）　When　the　loop　is　finished　it　should　be　undamaged；　and　it　should　not　be；　as　is　often　the　case；　badly　scored。


7。　Stranded　Wire　Cable。No　splice　should　be　served　with　twine　until　it　has　been　inspected　by　whoever　is　in　charge　of　the　workshop。　The　serving　may　cover　bad　work。

Should　a　strand　become　broken；　then　the　cable　should　be　replaced　at　once　by　another　one。

Control　cables　have　a　way　of　wearing　out　and　fraying　wherever　they　pass　round　pulleys。　Every　time　an　aeroplane　comes　down　from　flight　the　rigger　should　carefully　examine　the　cables；　especially　where　they　pass　round　pulleys。　If　he　finds　a　strand　broken；　he　should　replace　the　cable。

The　ailerons'　balance　cable　on　the　top　of　the　top　plane　is　often　forgotten；　since　it　is　necessary　to　fetch　a　high　pair　of　steps　in　order　to　examine　it。　Don't　slack　this；　or　some　gusty　day　the　pilot　may　unexpectedly　find　himself　minus　the　aileron　control。

CONTROLLING　SURFACES。The　greatest　care　should　be　exercised　in　rigging　the　aileron；　rudder；　and　elevator　properly；　for　the　pilot　entirely　depends　upon　them　in　managing　the　aeroplane。

The　ailerons　and　elevator　should　be　rigged　so　that；　when　the　aeroplane　is　in　flight；　they　are　in　a　fair　true　line　with　the　surface　in　front　and　to　which　they　are　hinged。

If　the　surface　to　which　they　are　hinged　is　not　a　lifting　surface；　then　they　should　be　rigged　to　be　in　a　fair　true　line　with　it　as　illustrated　above。

If　the　controlling　surface　is；　as　illustrated；　hinged　to　the　back　of　a　lifting　surface；　then　it　should　be　rigged　a　little　below　the　position　it　would　occupy　if　in　a　fair　true　line　with　the　surface　in　front。　This　is　because；　in　such　a　case；　it　is　set　at　an　angle　of　incidence。　This　angle　will；　during　flight；　cause　it　to　lift　a　little　above　the　position　in　which　it　has　been　rigged。　It　is　able　to　lift　owing　to　a　certain　amount　of　slack　in　the　control　wire　holding　itand　one　cannot　adjust　the　control　wire　to　have　no　slack；　because　that　would　cause　it　to　bind　against　the　pulleys　and　make　the　operation　of　it　too　hard　for　the　pilot。　It　is　therefore　necessary　to　rig　it　a　little　below　the　position　it　would　occupy　if　it　was　rigged　in　a　fair　true　line　with　the　surface　in　front。　Remember　that　this　only　applies　when　it　is　hinged　to　a　lifting　surface。　The　greater　the　angle　of　incidence　（and　therefore　the　lift）　of　the　surface　in　front；　then　the　more　the　controlling　surface　will　have　to　be　rigged　down。

As　a　general　rule　it　is　safe　to　rig　it　down　so　that　its　trailing

edge　is　1/2　to　3/4　inch　below　the　position　it　would　occupy　if　in　a　fair　line　with　the　surface　in　front；　or　about　1/2　inch　down　for　every　18　inches　of　chord　of　the　controlling　surface。

When　making　these　adjustments　the　pilot's　control　levers　should　be　in　their　neutral　positions。　It　is　not　sufficient　to　lash　them。　They　should　be　rigidly　blocked　into　position　with　wood　packing。

The　surfaces　must　not　be　distorted　in　any　way。　If　they　are　held　true　by　bracing　wires；　then　such　wires　must　be　carefully　adjusted。　If　they　are　distorted　and　there　are　no　bracing　wires　with　which　to　true　them；　then　some　of　the　internal　framework　will　probably　have　to　be　replaced。

The　controlling　surfaces　should　never　be　adjusted　with　a　view　to　altering　the　stability　of　the　aeroplane。　Nothing　can　be　accomplished　in　that　way。　The　only　result　will　be　to　spoil　the　control　of　the　aeroplane。


FABRIC…COVERED　SURFACES。First　of　all　make　sure　that　there　is　no　distortion　of　spars　or　ribs；　and　that　they　are　perfectly　sound。　Then　adjust　the　internal　bracing　wires　so　that　the　ribs　are　parallel　to　the　direction　of　flight。　The　ribs　usually　cause　the　fabric　to　make　a　ridge　where　they　occur；　and；　if　such　ridge　is　not　parallel　to　the　direction　of　flight；　it　will　produce　excessive　drift。　As　a　rule　the　ribs　are　at　right　angles　to　both　main　and　rear　spars。

The　tension　of　the　internal　bracing　wires　should　be　just　sufficient　to　give　rigidity　to　the　framework。　They　should　not　be　tensioned　above　that　unless　the　wires　are；　at　their　ends；　bent　to　form　loops。　In　that　case　a　little　extra　tension　may　be　given　to　offset　the　probable　elongation　of　the　loops。

The　turnbuckles　must　now　be　generously　greased；　and　served　round　with　adhesive　tape。　The　wires　must　be　rendered　perfectly　dry　and　clean；　and　then　painted　with　an　anti…rust　mixture。　The　woodwork　must　be　well　varnished。

If　it　is　necessary　to　bore　holes　in　the　spars　for　the　purpose　of　receiving；　for　instance；　socket　bolts；　then　their　places　should　be　marked　before　being　bored　and　their　positions　confirmed　by　whoever　is　in　charge　of　the　workshop。　All　is　now　ready　for　the　sail…maker　to　cover　the　surface　with　fabric。


ADJUSTMENT　OF　CONTROL　CABLES。The　adjustment　of　the　control　cables　is　quite　an　art；　and　upon　it　will　depend　to　a　large　degree　the　quick　and　easy　control　of　the　aeroplane　by　the　pilot。

The　method　is　as　follows：

After　having　rigged　the　controlling　surfaces；　and　as　far　as　possible　secured　the　correct　adjustment　of　the　control　cables；　then　remove　the　packing　which　has　kept　the　control　levers　rigid。　Then；　sitting　in　the　pilot's　seat；　move　the　control　levers　SMARTLY。　Tension　the　control　cables　so　that　when　the　levers　are　smartly　moved　there　is　no　perceptible　snatch　or　lag。　Be　careful　not　to　tension　the　cables　more　than　necessary　to　take　out　the　snatch。　If　tensioned　too　much　they　will　（1）　bind　round　the　pulleys　and　result　in　hard　work　for　the　pilot；　（2）　throw　dangerous　stresses　upon　the　controlling　surfaces；　which　are　of　rather　flimsy　construction；　and　（3）　cause　the　cables　to　fray　round　the　pulleys　quicker　than　would　otherwise　be　the　case。

Now；　after　having　tensioned　the　cables　sufficiently　to　take　out　the　snatch；　place　the　levers　in　their　neutral　positions；　and　move　them　to　and　fro　about　1/8　inch　either　side　of　such　positions。　If　the　adjustment　is　correct；　it　should　be　possible　to　see　the　controlling　surfaces　move。　If　they　do　not　move；　then　the　control　cables　are　too　slack。


FLYING　POSITION。Before　rigging　an　aeroplane　or　making　any　adjustments　it　is　necessary　to　place　it　in　what　is　known　as　its　‘‘flying　position。''　I　may　add　that　it　would　be　better　termed　its　‘‘rigging　position。''

In　the　case　of　an　aeroplane　fitted　with　a　stationary　engine　this　is　secured　by　packing　up　the　machine　so　that　the　engine　foundations　are　perfectly　horizontal　both　longitudinally　and　laterally。　This　position　is　found　by　placing　a　straight…edge　and　a　spirit…level　across　the　engine　foundations　（both　longitudinally　and　laterally）；　and　great　care　should　be　taken　to　see　that　the　bubble　is　exactly　in　the　centre　of　the　level。　The　slightest　error　will　assume　magnitude　towards　the　extremities　of　the　aeroplane。　Great　care　should　be　taken　to　block　up　the　aeroplane　rigidly。　In　case　it　gets　accidentally　disturbed　while　the　work　is　going　on；　it　is　well　to　constantly　verify　the　flying　position　by　running　the　straight…edge　and　spirit…level　over　the　engine　foundations。　The　straight…edge　should　be　carefully　tested　before　being　used；　as；　being　generally　made　of　wood；　it　will　not　remain　true　long。　Place　it　lightly　in　a　vice；　and　in　such　a　position　that　a　spirit…level　on　top　shows　the　bubble　exactly　in　the　centre。　Now　slowly　move　the　level　along　the　straight…edge；　and　the　bubble　should　remain　exactly　in　the　centre。　If　it　does　not　do　so；　then　the　straight…edge　is　not　true　and　must　be　corrected。　THIS　SHOULD　NEVER　BE　OMITTED。

In　the　case　of　aeroplanes　fitted　with　engines　of　the　rotary　type；　the　‘‘flying　position''　is　some　special　attitude　laid　down　in　the　aeroplane's　specifications；　and　great　care　should　be　taken　to　secure　accuracy。


ANGLE　OF　INCIDENCE。One　method　of　finding　the　angle　of　incidence　is　as　follows：

First　place　the　aeroplane　in　its　flying　position。　The　corner　of　the　straight…edge　must　be　placed　underneath　and　against　the　CENTRE　of　the　rear　spar；　and　held　in　a　horizontal　position　parallel　to　the　ribs。　This　is　secured　by　using　a　spirit…level。　The　set　measurement　will　then　be　from　the　top　of　the　straight…edge　to　the　centre　of　the　bottom　surface　of　the　main　spar；　or　it　may　be　from　the　top　of　the　straight…　edge　to　the　lowest　part　of　the　leading　edge。　Care　should　be　taken　to　measure　from　the　centre　of　the　spar　and　to　see　that　the　bubble　is　exactly　in　the　centre　of　the　level。　Remember　that　all　this　will　be　useless　if　the　aeroplane　has　not　been　placed　accurately　in　its　flying　position。

This　method　of　finding　the　angle　of　incidence　must　be　used　under　every　part　of　the　lower　surface　where　struts　occur。　It　should　not　be　used　between　the　struts；　because；　in　such　places；　the　spars　may　have　taken　a　slight　permanent　set　up　or　down；　not；　perhaps；　sufficiently　bad　to　make　any　material　difference　to　the　flying　of　the　machine；　but　quite　bad　enough　to　throw　out　the　angle　of　incidence；　which　cannot　be　corrected　at　such　a　place。

If　the　angle　is　wrong；　it　should　then　be　corrected　as　follows：

If　it　is　too　great；　then　the　rear　spar　must　be　warped　up　until　it　is　right；　and　this　is　done　by　slackening　ALL　the　wires　going　to　the　top　of　the　strut；　and　then　tightening　ALL　the　wires　going　to　the　bottom　of　the　strut。

If　the　angl