## 4 Composite Blade Manufacturing
The grits of the abrasive paper used are in ascending order as follows: 120, 180, 240, 320, 480, 600, and 1000 (note that the sanding for grits of 480 and above was conducted in the wet condition). Figure 6: Assembly of the printed mould 3D. (**a**) Printed sections 3D. (**b**) Assembly of the mould for the anti-torque blade. (**c**) Priming of the working area of the 3D-printed mould. (**d**) Three-dimensional printing of the blade core. (**e**) Cross-section of the anti-torque blade with an indication of materials and layout areas (dimensions in mm). As shown in Figure 8a, after 3D printing and assembly of the core, it is inserted into the mould for a final trial run for the geometry to be used further and to make the necessary adjustments. In order to control the position of the core inside the mould as precisely as possible, four centring studs are used (Figure 8b), which are arranged as follows: two at the distal end of the core and two at the proximal end of the core (Figure 8c). Once the core is made, the next step is to cut the layers of material that make up the anti-torque blade. The layers are cut according to the draping diagram. The draping diagram is usually specified in the design drawing of the part and specifies the type of layers (fibreglass, carbon fibre, Kevlar, etc.) found in the composition, the density of the layer per square metre (200 g, 300 g, 600 g, etc.) their size (cutting dimensions), the orientation or positioning of the layers on the part in relation to the main axis of the part, and the order in which they are laid down. Next, five successive layers of wax are applied to the surface of the two moulds to create a separating film between the composite blade and the 3D-printed mould. These wax layers are intended to make it easier to remove the blade from the 3D-printed mould after the polymerisation process is complete. The layers are applied sequentially with a strip of fabric at 15 to 20 min intervals between applications to allow the layers to adhere to the moulds and to each other. Layer cutting is performed by hand, using scissors specially designed for fabric-type products. This is how the layers are cut. The fibres that are part of the blade are as follows:  
1. Carbon fibre fabric 2 \(\times\) 2 twill 3K with a weight of 200 g/m\({}^{2}\)[58]: six layers are cut to form the blade shell and three layers are placed on the lower surface and three layers are placed on the upper surface;
2. Fibreglass fabric, with a weight of 200 g/m\({}^{2}\)[59], is cut as follows: * For the spar constituting the leading edge of the blade (Figure 9), about 75 layers are cut, ranging in width from 5.5 mm to 31 mm. The variation in layer width is necessary to form the specific shape of the leading edge. * Approximately 50 layers of varying widths between 5.5 mm and 40 mm were required for the spar constituting the trailing edge (Figure 10). Figure 8: Centring the core in the mould. (**a**) Distal end. (**b**) Proximal end. (**c**) Lower mould-positioning of the blade core. Figure 7: Digital model required for mould sanding: (**a**) upper mould template and (**b**) lower mould template. 3. Short fibres: * made of Kevlar: they are obtained by cutting a Kevlar fibre fabric with a weight of 300 g/m\({}^{2}\)[60]; * made of carbon: they are obtained by the same process as the fabric shown in Section 1 (carbon fibre fabric with a weight of 200 g/m\({}^{2}\)). Together, the short fibres form the monoblock section or the blade embedding section. The total volume of this section is 288.38 cm\({}^{3}\). The Kevlar to carbon ratio in this section is 50-50%. 4. The resin used is an epoxy resin--EL2 [61]--with AT30 fast hardener [62]. A total of 1000 g epoxy resin is used for the composite blade. The resin utilized in the manufacturing process of the anti-torque blade is divided into four batches. Epoxy resin is prepared on demand as needed for layup. The time elapsed between the first and last batch of resin is 100 min.