the aeroplane speaks-第18部分

快捷操作: 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! 如果本书没有阅读完，想下次继续接着阅读，可使用上方 "收藏到我的浏览器" 功能 和 "加入书签" 功能！


top　of　the　strut；　and　then　tightening　ALL　the　wires　going　to　the　bottom　of　the　strut。

If　the　angle　is　too　small；　then　slacken　ALL　the　wires　going　to　the　bottom　of　the　strut；　and　tighten　ALL　the　wires　going　to　the　top　of　the　strut；　until　the　correct　adjustment　is　secured。

Never　attempt　to　adjust　the　angle　by　warping　the　main　spar。

The　set　measurement；　which　is　of　course　stated　in　the　aeroplane's　specifications；　should　be　accurate　to　1/16　inch。


LATERAL　DIHEDRAL　ANGLE。One　method　of　securing　this　is　as　follows；　and　this　method　will；　at　the　same　time；　secure　the　correct　angle　of　incidence：

The　strings；　drawn　very　tight；　must　be　taken　over　both　the　main　and　rear　spars　of　the　top　surface。　They　must　run　between　points　on　the　spars　just　inside　the　outer　struts。　The　set　measurement　（which　should　be　accurate　to　1/16　inch　or　less）　is　then　from　the　strings　down　to　four　points　on　the　main　and　rear　spars　of　the　centre…section　surface。　These　points　should　be　just　inside　the　four　centre…section　struts；　that　is　to　say；　as　far　as　possible　away　from　the　centre　of　the　centre…section。　Do　not　attempt　to　take　the　set　measurement　near　the　centre　of　the　centre…section。

The　strings　should　be　as　tight　as　possible；　and；　if　it　can　be　arranged；　the　best　way　to　accomplish　that　is　as　shown　in　the　above　illustration；　i。e。；　by　weighting　the　strings　down　to　the　spars　by　means　of　weights　and　tying　each　end　of　the　strings　to　a　strut。　This　will　give　a　tight　and　motionless　string。

However　carefully　the　above　adjustment　is　made；　there　is　sure　to　be　some　slight　error。　This　is　of　no　great　importance；　provided　it　is　divided　equally　between　the　left…　and　right…　hand　wings。　In　order　to　make　sure　of　this；　certain　check　measurements　should　be　taken　as　follows：

Each　bay　must　be　diagonally　measured；　and　such　measurements　must　be　the　same　to　within　1/16　inch　on　each　side　of　the　aeroplane。　As　a　rule　such　diagonal　measurements　are　taken　from　the　bottom　socket　of　one　strut　to　the　top　socket　of　another　strut；　but　this　is　bad　practice；　because　of　possible　inaccuracies　due　to　faulty　manufacture。

The　points　between　which　the　diagonal　measurements　are　taken　should　be　at　fixed　distances　from　the　butts　of　the　spars；　such　distances　being　the　same　on　each　side　of　the　aeroplane；　thus：


It　would　be　better　to　use　the　centre　line　of　the　aeroplane　rather　than　the　butts　of　the　spars。　It　is　not　practicable　to　do　so；　however；　as　the　centre　line　probably　runs　through　the　petrol　tanks；　etc。


THE　DIHEDRAL　BOARD。Another　method　of　securing　the　dihedral　angle；　and　also　the　angle　of　incidence；　is　by　means　of　the　dihedral　board。　It　is　a　light　handy　thing　to　use；　but　leads　to　many　errors；　and　should　not　be　used　unless　necessary。　The　reasons　are　as　follows：

The　dihedral　board　is　probably　not　true。　If　it　must　be　used；　then　it　should　be　very　carefully　tested　for　truth　before…　hand。　Another　reason　against　its　use　is　that　it　has　to　be　placed　on　the　spars　in　a　position　between　the　struts；　and　that　is　just　where　the　spars　may　have　a　little　permanent　set　up　or　down；　or　some　inaccuracy　of　surface　which　will；　of　course；　throw　out　the　accuracy　of　the　adjustment。　The　method　of　using　it　is　as　follows：

The　board　is　cut　to　the　same　angle　as　that　specified　for　the　upward　inclination　of　the　surface　towards　its　wing…　tips。　It　is　placed　on　the　spar　as　indicated　above；　and　it　is　provided　with　two　short　legs　to　raise　it　above　the　flanges　of　the　ribs　（which　cross　over　the　spars）；　as　they　may　vary　in　depth。　A　spirit…level　is　then　placed　on　the　board；　and　the　wires　must　be　adjusted　to　give　the　surface　such　an　inclination　as　to　result　in　the　bubble　being　in　the　centre　of　the　level。　This　operation　must　be　performed　in　respect　of　each　bay　both　front　and　rear。　The　bays　must　then　be　diagonally　measured　as　already　explained。


YET　ANOTHER　METHOD　of　finding　the　dihedral　angle；　and　at　the　same　time　the　angle　of　incidence；　is　as　follows：

A　horizontal　line　is　taken　from　underneath　the　butt　of　each　spar；　and　the　set　measurement　is　either　the　angle　it　makes　with　the　spar；　or　a　fixed　measurement　from　the　line　to　the　spar　taken　at　a　specified　distance　from　the　butt。　This　operation　must　be　performed　in　respect　of　both　main　and　rear　spars；　and　all　the　bays　must　be　measured　diagonally　afterwards。



Whichever　method　is　used；　be　sure　that　after　the　job　is　done　the　spars　are　perfectly　straight。


STAGGER。The　stagger　is　the　distance　the　top　surface　is　in　advance　of　the　bottom　surface　when　the　aeroplane　is　in　flying　position。　The　set　measurement　is　obtained　as　follows：

Plumb…lines　must　be　dropped　over　the　leading　edge　of　the　top　surface　wherever　struts　occur；　and　also　near　the　fuselage。　The　set　measurement　is　taken　from　the　front　of　the　lower　leading　edge　to　the　plumb…lines。　It　makes　a　difference　whether　the　measurement　is　taken　along　a　horizontal　line　（which　can　be　found　by　using　a　straight…edge　and　a　spirit…　level）　or　along　a　projection　of　the　chord。　The　line　along　which　the　measurement　should　be　taken　is　laid　down　in　the　aeroplane's　specifications。

If　a　mistake　is　made　and　the　measurement　taken　along　the　wrong　line；　it　may　result　in　a　difference　of　perhaps　1/4　will；　in　flight；　be　nose…heavy　or　tail…heavy。

After　the　adjustments　of　the　angles　of　incidence；　dihedral；　and　stagger　have　been　secured；　it　is　as　well　to　confirm　all　of　them；　as；　in　making　the　last　adjustment；　the　first　one　may　have　been　spoiled。


OVER…ALL　ADJUSTMENTS。The　following　over…all　check　measurements　should　now　be　taken。

The　straight　lines　AC　and　BC　should　be　equal　to　within　1/8　inch。　The　point　C　is　the　centre　of　the　propeller；　or；　in　the　case　of　a　‘‘pusher''　aeroplane；　the　centre　of　the　nacelle。　The　points　A　and　B　are　marked　on　the　main　spar；　and　must　in　each　case　be　the　same　distance　from　the　butt　of　the　spar。　The　rigger　should　not　attempt　to　make　A　and　B　merely　the　sockets　of　the　outer　struts；　as　they　may　not　have　been　placed　quite　accurately　by　the　manufacturer。　The　lines　AC　and　BC　must　be　taken　from　both　top　and　bottom　sparstwo　measurements　on　each　side　of　the　aeroplane。

The　two　measurements　FD　and　FE　should　be　equal　to　within　1/8　inch。　F　is　the　centre　of　the　fuselage　or　rudder…　post。　D　and　E　are　points　marked　on　both　top　and　bottom　rear　spars；　and　each　must　be　the　same　fixed　distance　from　the　butt　of　the　spar。　Two　measurements　on　each　side　of　the　aeroplane。

If　these　over…all　measurements　are　not　correct；　then　it　is　probably　due　to　some　of　the　drift　or　anti…drift　wires　being　too　tight　or　too　slack。　It　may　possibly　be　due　to　the　fuselage　being　out　of　truth；　but　of　course　the　rigger　should　have　made　quite　sure　that　the　fuselage　was　true　before　rigging　the　rest　of　the　machine。　Again；　it　may　be　due　to　the　internal　bracing　wires　within　the　lifting　surfaces　not　being　accurately　adjusted；　but　of　course　this　should　have　been　seen　to　before　covering　the　surfaces　with　fabric。


FUSELAGE。The　method　of　truing　the　fuselage　is　laid　down　in　the　aeroplane's　specifications。　After　it　has　been　adjusted　according　to　the　specified　directions；　it　should　then　be　arranged　on　trestles　in　such　a　way　as　to　make　about　three…　quarters　of　it　towards　the　tail　stick　out　unsupported。　In　this　way　it　will　assume　a　condition　as　near　as　possible　to　flying　conditions；　and　when　it　is　in　this　position　the　set　measurements　should　be　confirmed。　If　this　is　not　done　it　may　be　out　of　truth；　but　perhaps　appear　all　right　when　supported　by　trestles　at　both　ends；　as；　in　such　case；　its　weight　may　keep　it　true　as　long　as　it　is　resting　upon　the　trestles。


THE　TAIL…PLANE　（EMPENNAGE）。The　exact　angle　of　incidence　of　the　tail…plane　is　laid　down　in　the　aeroplane's　specifications。　It　is　necessary　to　make　sure　that　the　spars　are　horizontal　when　the　aeroplane　is　in　flying　position　and　the　tail　unsupported　as　explained　above　under　the　heading　of　Fuselage。　If　the　spars　are　tapered；　then　make　sure　that　their　centre　lines　are　horizontal。


UNDERCARRIAGE。The　undercarriage　must　be　very　carefully　aligned　as　laid　down　in　the　specifications。

1。　The　aeroplane　must　be　placed　in　its　flying　position　and　sufficiently　high　to　ensure　the　wheels　being　off　the　ground　when　rigged。　When　in　this　position　the　axle　must　be　hori…

nontal　and　the　bracing　wires　adjusted　to　secure　the　various　set　measurements　stated　in　the　specifications。

2。　Make　sure　that　the　struts　bed　well　down　into　their　sockets。

3。　Make　sure　that　the　shock　absorbers　are　of　equal　tension。　In　the　case　of　rubber　shock　absorbers；　both　the　number　of　turns　and　the　lengths　must　be　equal。


HOW　TO　DIAGNOSE　FAULTS　IN　FLIGHT；　STABILITY；　AND　CONTROL。


DIRECTIONAL　STABILITY　will　be　badly　affected　if　there　is　more　drift　（i。e。；　resistance）　on　one　side　of　the　aeroplane　than　there　is　on　the　other　side。　The　aeroplane　will　tend　to　turn　towards　the　side　having　the　most　drift。　This　may　be　caused　as　follows：

1。　The　angle　of　incidence　of　the　main　surface　or　the　tail　surface　may　be　wrong。　The　greater　the　angle　of　incidence；　the　greater　the　drift。　The　less　the　angle；　the　less　the　drift。

2。　If　the　alignment　of　the　fuselage；　fin　in　front　of　the　rudder；　the　struts　or　stream…line　wires；　or；　in　the　case　of　the　Maurice　Farman；　the　front　outriggers；　are　not　absolutely　correctthat　is　to　say；　if　they　are　turned　a　little　to　the　left　or　to　the　right　instead　of　being　in　line　with　the　direction　of　flightthen　they　will　act　as　a　rudder　and　cause　the　aeroplane　to　turn　off　its　course。

3。　If　any　part　of　the　surface　is　distorted；　it　will　cause　the　aeroplane　to　turn　off　its　course。　The　surface　is　cambered；　i。e。；　curved；　to　pass　through　the　air　with　the　least　possible　drift。　If；　owing　perhaps　to　the　leading　edge；　spars；　or　trailing　edge　becoming　bent；　the　curvature　is　spoiled；　that　will　result　in　changing　the　amount　of　drift　on　one　side　of　the　aeroplane；　which　will　then　have　a　tendency　to　turn　off　its　course。


LATERAL　INSTABILITY　（FLYING　ONE　WING　DOWN）。The　only　possible　reason　for　such　a　condition　is　a　difference　in　the　lifts　of　right　and　left　wings。　That　may　be　caused　as　follows：

1。　The　angle　of　incidence　may　be　wrong。　If　it　is　too　great；　it　will　produce　more　lift　than　on　the　other　side　of　the　aeroplane；　and　if　too　small；　it　will　produce　less　lift　than　on　the　other　sidethe　result　being　that；　in　either　case；　the　aeroplane　will　try