# Design, Manufacturing, and Flight Testing of an Experimental Flying Wing UAV
## 5 Manufacturing Experimental Flying wing UAV
Figure 7: Main and secondary structural modules of flying wing UAV. right wing modules consist of numerous ribs and skins that together maintain the size and shape of the aircraft cross section and resist distributed aerodynamic pressure loads. The ribs are made of balsa wood and are placed inside the fuselage, left wing, and right wing. The ribs are produced through laser cutting in light of the manufacturing cost and time. When all ribs are produced, they are preassembled to ensure the shape and size of the cross section. Figure 8 shows an engineering drawing of the ribs and the preassembly of the ribs. The skin provides an impermeable surface for maintaining the air pressure distribution on the wing. It is made of composite materials, specifically, carbon fiber and epoxy resin composites that were fabricated using vacuum bagging and a hand lay-up method, to reduce the aircraft's structural weight. The mold and ribs must be produced before fabricating the skins. Composite materials and medium-density fiberboard (MDF) holds are cheaper than aluminum or steel molds and were therefore designed and fabricated to make the skins of the flying wing UAV. The molds of composite materials consisted of Styrofoam, glass fiber, and epoxy resin. First, the Styrofoam pieces were cut to predesigned sizes. Then, the glass fiber and epoxy resin were adhered to the Styrofoam pieces. It should be noted that epoxy resin, and not polyresin, is used; when poly resin adheres to Styrofoam pieces, it can damage or dissolve the Styrofoam. Figure 9 shows the predesigned size of the Styrofoam mold and the mold consisting of Styrofoam, glass fiber, and epoxy resin. Figure 10 shows the mold of the wing and the glass fiber and carbon fiber. Figure 8: (**a**) Engineering drawing of ribs and (**b**) preassembly of ribs. Figure 9: (**a**) Predesigned size of Styrofoam mold (fuselage) and (**b**) design size of mold consisting of Styrofoam, glass fiber, and epoxy resin (fuselage). After the molds made of the composite materials are completed, hand lay-up and vacuum bag molding methods are used to fabricate the main and secondary structural modules. The three main and two secondary modules are finally assembled to complete the flying wing UAV. The hand lay-up method is suitable for making a wide range of composite products. Its manufacturing equipment is inexpensive. However, skilled operators are required to achieve good production and quality using this method. In the study, carbon fiber, glass fiber, and epoxy resin are placed in an open mold and cured by exposure to air. This method is inexpensive and is suitable for manufacturing prototype products. In the vacuum bag molding method, the carbon fiber, glass fiber, and epoxy resin are placed in the bag to form the shape. Then, a pump is used to gradually create a vacuum in the bag. This approach removes air and eliminates excess resin, resulting in more favorable mechanical properties. Figure 11a shows the hand lay-up and open molding method. Figure 11b shows the vacuum bag molding method. Figure 12 shows the upper mold of the fuselage with ribs and the main structural modules (fuselage). Once the main and secondary structural modules are completed, they are assembled to form the experimental flying wing UAV. The skin is made of carbon fiber, glass fiber, and epoxy resin, and the  
Figure 11: (**a**) Hand lay-up and open molding method and (**b**) vacuum bag molding method. Figure 10: (**a**) Mold of the wing and (**b**) glass fiber and carbon fiber. ribs are made of balsa wood. The wingspan is 3.0 m, fuselage is 1.2 m, and structural weight is 6 kg. Figure 13 shows the main and secondary structural modules and the completed experimental flying wing UAV. Propulsion power is provided by an AXi 4130/20 kv305 electric brushless motor. Pixhawk is used as the flight control system. A polymer battery pack (\(2\times 5000\) mAh) with a total weight of 8.62 kg is also used.