Introduction to Aircraft Structural Analysis (Elsevier Aerospace Engineering)

23.2 Fuselage Frames 625

23.2 FuselageFrames.....................................................................................

Wehavenotedthatfuselageframestransferloadstothefuselageshellandprovidecolumnsupportfor
thelongitudinalstringers.Theframesgenerallytaketheformofopenringssothattheinteriorofthe
fuselage is not obstructed. They are connected continuously around their peripheries to the fuselage
shellandarenotnecessarilycircularinformbutwillusuallybesymmetricalaboutaverticalaxis.
A fuselage frame is in equilibrium under the action of any external loads and the reaction shear
flowsfromthefuselageshell.Supposethatafuselageframehasaverticalaxisofsymmetryandcarries
averticalexternalloadW,asshowninFig.23.8(a)and(b).Thefuselageshell/stringersectionhasbeen
idealizedsuchthatthefuselageskiniseffectiveonlyinshear.Supposealsothattheshearforceinthe
fuselageimmediatelytotheleftoftheframeisSy,1andthattheshearforceinthefuselageimmediately
totherightoftheframeisSy,2;clearly,Sy,2=Sy,1−W.Sy,1,andSy,2generateshearflowdistributionsq 1
andq 2 ,respectively,inthefuselageskin,eachgivenbyEq.(21.1),inwhichSx,1=Sx,2=0,andIxy= 0
(Cyisanaxisofsymmetry).Theshearflowqftransmittedtotheperipheryoftheframeisequaltothe
algebraicsumofq 1 andq 2 ,thatis,

qf=q 1 −q 2

Thus,substitutingforq 1 andq 2 obtainedfromEq.(21.1)andnotingthatSy,2=Sy,1−W,wehave

qf=

−W

Ixx

∑n

r= 1

Bryr+qs,0

inwhichqs,0iscalculatedusingEq.(16.17),wheretheshearloadisWand

qb=

−W

Ixx

∑n

r= 1

Bryr

Fig.23.8

Loads on a fuselage frame.