ABSTRACT
This section describes how a blade, whose outer contour is designed from aerodynamical considerations, is built to be sufficiently strong and stiff. In the past materials like wood, steel, aluminium, glass-fibre-reinforced plastics (GRPs) and carbon fibre reinforced plastics (CFRPs) have been used. The choice depends on many parameters such as strength, weight, stiffness, price and, very important for wind turbines, fatigue properties. The majority of wind turbine blades today are built using GRPs, and therefore a short description of a manufacturing process using this material is given. A negative mould for the upper part (suction side) and lower part (pressure side) of the blade is made. A thin film of so-called gelcoat is first laid in the moulds. The gelcoat gives a smooth white finish to the blades and therefore it is not necessary to paint the blades afterwards. Then a number of glass fibre mats are laid in. On each mat a layer of epoxy or polyester is rolled on to bind the mats into a hard matrix of fibres. The number of mats gives the thickness of the shell; typically a thin shell is made around the leading and trailing edges and a thick shell is made in the middle of the aerofoil. A section of such a blade is shown in Figure 11.1.
