626 CHAPTER 23 Fuselage Frames and Wing Ribs
Themethodofdeterminingtheshearflowdistributionappliedtotheperipheryofafuselageframeis
identicaltothemethodofsolution(orthealternativemethod)ofExample21.2.
Havingdeterminedtheshearflowdistributionaroundtheperipheryoftheframe,theframeitself
maybeanalyzedfordistributionsofbendingmoment,shearforce,andnormalforce,asdescribedin
Section5.4.
23.3 WingRibs.............................................................................................
Wingribsperformsimilarfunctionstothoseperformedbyfuselageframes.Theymaintaintheshapeof
thewingsection,assistintransmittingexternalloadstothewingskin,andreducethecolumnlengthof
thestringers.Theirgeometry,however,isusuallydifferentinthattheyarefrequentlyofunsymmetrical
shapeandpossesswebswhicharecontinuousexceptforlightnessholesandopeningsforcontrolruns.
Wingribsaresubjectedtoloadingsystemswhicharesimilartothoseappliedtofuselageframes.
External loads applied in theplaneof therib produceachangein shear forcein thewing across the
rib; this induces reaction shear flows around its periphery. These are calculated using the methods
describedinChapters16and22.Toillustratethemethodofribanalysis,weshallusetheexampleofa
three-flangewingsectioninwhich,aswenotedinSection22.1,theshearflowdistributionisstatically
determinate.
Example 23.2
Calculatetheshearflowsinthewebpanelsandtheaxialloadsintheflangesofthewingribshownin
Fig.23.9.Assumethattheweboftheribiseffectiveonlyinshear,whiletheresistanceofthewingto
bendingmomentsisprovidedentirelybythethreeflanges1,2,and3.
Since the wing bending moments are resisted entirely by the flanges 1, 2, and 3, the shear flows
developedinthewingskinareconstantbetweentheflanges.UsingthemethoddescribedinSection22.1
forathree-flangewingsection,wehave,resolvingforceshorizontally,
600 q 12 − 600 q 23 =12000N (i)Fig.23.9
Wing rib of Example 23.2.