Introduction to Aircraft Structural Analysis (Elsevier Aerospace Engineering)

606 CHAPTER 22 Wings

Ifthewingstructurewerecontinuousandtheeffectsofrestrainedwarpingatthebuilt-inendignored,
theshearflowsintheskinpanelswouldbegivenbyEq.(17.1),thatis,

q=

T

2 A

=

10 × 106

2 × 200 × 800

=31.3N/mm

andtheflangeswouldbeunloaded.However,theremovalofthelowerskinpanelinbay②resultsin
atorsionallyweakchannelsectionforthelengthofbay②,whichmustinanycasestilltransmitthe
appliedtorquetobay①andsubsequentlytothewingsupportpoints.Althoughopensectionbeamsare
inherentlyweakintorsion(seeSection17.2),thechannelsectioninthiscaseisattachedatitsinboard
and outboard ends to torsionally stiff closed boxes so that, in effect, it is built-in at both ends. An
alternativeapproachistoassumethatthetorqueistransmittedacrossbay②bythedifferentialbending
ofthefrontandrearspars.ThebendingmomentineachsparisresistedbytheflangeloadsPasshown,
for the front spar, in Fig. 22.17(a). The shear loads in the front and rear spars form a couple at any
stationinbay②whichisequivalenttotheappliedtorque.Thus,fromFig.22.17(b),

800 S= 10 × 106 Nmm

thatis,

S=12500N

Theshearflowq 1 inFig.22.17(a)isgivenby

q 1 =

12500

200

=62.5N/mm

Fig.22.17

Differential bending of front spar.