Form of blade structure

A hollow shell corresponding to the defined blade envelope clearly provides a simple, efficient structure to resist flexural and torsional loads and some blade manufacturers adopt this form of construction (see Figure 7.1). However, in the case of small and medium size machines, where the out-of-plane loads dominate, there is greater benefit in concentrating skin material in the forward half of the blade, where the blade thickness is a maximum, so that it acts more efficiently in resisting out-of-plane bending moments (see Figures 7.2 and 7.3). The weakened areas of the

, Glass/Epoxy

, Glass/Epoxy

^ Aluminium screen for lightening protection \ Glass/Epoxy (unusual)

Polyurethane point

Figure 7.1 Wood/Epoxy Blade Construction Utilizing Full Blade Shell (Reproduced from Corbet (1991) by permission of the DT1 Renewable Energy R&D Programme)

Gel coat

Figure 7.2 Wood/Epoxy Blade Construction Utilizing Forward Half of Blade Shell (Reproduced from Corbet (1991) by permission of the DT1 Renewable Energy R&D Programme)

Gel coat

Figure 7.2 Wood/Epoxy Blade Construction Utilizing Forward Half of Blade Shell (Reproduced from Corbet (1991) by permission of the DT1 Renewable Energy R&D Programme)

Figure 7.3 Glass-fibre Blade Construction Using Blade Skins in Forward Portion of Blade Cross Section and Linking Shear Webs. (Reproduced from Corbet (1991), by permission of the DT1 Renewable Energy, R&D Programme)

shell towards the trailing edge are then typically stiffened by means of sandwich construction utilizing a PVC foam filling.

The hollow shell structure defined by the aerofoil section is not very efficient at resisting out-of-plane shear loads, so these are catered for by the inclusion of one or more shear webs oriented perpendicular to the blade chord. If the load-bearing structure is limited to a compact closed hollow section spar, consisting of two shear webs and the skin sections between them (see Figure 7.4), then a GFRP blade lends itself to semiautomatic lay-up on a rotating mandrel which can be withdrawn after curing.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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