The main function of the shell is to provide the aerodynamic shape of the blade. It also plays a part in stiffening and strengthening the spar, as the fiber orientation in the construction materials helps to resist torsion.
Blade shells are usually quite thin as the requirement for strength in shell structure is relatively low. However, in order to prevent large flat laminate areas from flexing - which could affect the aerodynamic shape and lead to buckling - certain areas are designed as a “sandwich” construction, with laminated skins and a core (typically low density rigid foam or balsa wood). As blade shells provide the finished surface of the blade they must resist harsh environmental conditions, for example in offshore wind farms. A composite shell has a streamlined aerodynamic design and provides excellent environmental resistance.
Hexcel has an optimized range of prepregs and other fiber-reinforced composites for shell construction including our surfacing prepreg that produces a fine surface ready for painting without the need for gel coat.