Introduction to Aircraft Structural Analysis (Elsevier Aerospace Engineering)

18.3 Torsion 533

18.3 Torsion................................................................................................

Generally,inthetorsionofcompositesections,theclosedportionisdominant,sinceitstorsionalstiffness
isfargreaterthanthatoftheattachedopensectionportionwhichmaythereforebefrequentlyignored
inthecalculationoftorsionalstiffness;shearstressesshould,however,becheckedinthispartofthe
section.

Example 18.2
FindtheangleoftwistperunitlengthinthewingwhosecrosssectionisshowninFig.18.4whenitis
subjectedtoatorqueof10kNm.Findalsothemaximumshearstressinthesection.G=25000N/mm^2.
Wall12(outer)=900mm.Nosecellarea=20000mm^2.
Itmaybeassumed,inasimplifiedapproach,thatthetorsionalrigidityGJofthecompletesectionis
thesumofthetorsionalrigiditiesoftheopenandclosedportions.Fortheclosedportion,thetorsional
rigidityis,fromEq.(17.4),

(GJ)cl=

4 A^2 G

∮

ds/t

=

4 × 200002 × 25000

( 900 + 300 )/1.5

whichgives

(GJ)cl= 5000 × 107 Nmm^2

ThetorsionalrigidityoftheopenportionisfoundusingEq.(17.11),thus

(GJ)op=G

∑st^3

3

=

25000 × 900 × 23

3

thatis,

(GJ)op= 6 × 107 Nmm^2

Fig.18.4

Wing section of Example 18.2.