Introduction to Aircraft Structural Analysis (Elsevier Aerospace Engineering)

588 CHAPTER 22 Wings

Fig.22.1

Three-boom wing section.

Weshallreturntothesimplecaseofathree-boomwingsectionwhenweexaminethedistributions
ofdirectloadandshearflowsinwingribs.Meanwhile,weshallconsiderthebending,torsion,andshear
ofmulticellularwingsections.

22.2 Bending...............................................................................................

Bending moments at any section of a wing are usually produced by shear loads at other sections of
thewing.Thedirectstresssystemforsuchawingsection(Fig.22.2)isgivenbyeitherEq.(15.18)or
Eq.(15.19),inwhichthecoordinates(x,y)ofanypointinthecrosssectionandthesectionalproperties
arereferredtoaxesCxyinwhichtheoriginCcoincideswiththecentroidofthedirectstress-carrying
area.

Example 22.1
ThewingsectionshowninFig.22.3hasbeenidealizedsuchthattheboomscarryallthedirectstresses.
Ifthewingsectionissubjectedtoabendingmomentof300kNmappliedinaverticalplane,calculate
thedirectstressesinthebooms.

Boomareas:B 1 =B 6 =2580mm^2 B 2 =B 5 =3880mm^2 B 3 =B 4 =3230mm^2

Wenotethatthedistributionoftheboomareasissymmetricalaboutthehorizontalxaxis.Hence,
inEq.(15.18),Ixy=0.Further,Mx=300kNmandMy=0sothatEq.(15.18)reducesto

σz=

Mxy

Ixx

(i)