11.3 Fabrication of Structural Components 361Fig.11.9
Wing ribs for the European Airbus (courtesy of British Aerospace).
undersurfaceofthewingandarefastenedtostiffenersandribflangesbyscrews,enablingthemtoresist
directandshearloads.Doorscoveringundercarriagewellsandweaponbaysareincapableofresisting
wingstressessothatprovisionmustbemadefortransferringtheloadsfromskin,flanges,andshear
webs around the cut out. This may be achieved by inserting strong bulkheads or increasing the spar
flangeareas,although,nomatterthemethodemployed,increasedcost,andweightresult.
The different structural requirements of aircraft designed for differing operational roles lead to a
variety of wing constructions. For instance, high-speed aircraft require relatively thin wing sections,
whichsupporthighwingloadings.Towithstandthecorrespondinglyhighsurfacepressuresandtoobtain
sufficient strength, much thicker skins are necessary. Wing panels are therefore frequently machined
integrally with stringers from solid slabs of material, as are the wing ribs. Figure 11.9 shows wing
ribsfortheEuropeanAirbusinwhichwebstiffeners,flangedlightnessholes,andskinattachmentlugs
havebeenintegrallymachinedfromsolid.Thisintegralmethodofconstructioninvolvesnonewdesign
principlesandhastheadvantagesofcombiningahighgradeofsurfacefinish,freefromirregularities,
with a more efficient use of material, since skin thicknesses are easily tapered to coincide with the
spanwisedecreaseinbendingstresses.
Analternativeformofconstructionisthesandwichpanel,whichcomprisesalighthoneycombor
corrugatedmetalcoresandwichedbetweentwoouterskinsofthestress-bearingsheet(seeFig.11.10).
The primary function of the core is to stabilize the outer skins, although it may be stress bearing
as well. Sandwich panels are capable of developing high stresses, have smooth internal and external