Structural Design and Manufacturing of UAV Built with Rapid Prototyping Techniques

The Authors’ experience at the University of Bologna, started in 2000 with the design, assembly and test flight of a family of vehicles, ranging from maximum take-off mass of 30 Kg up to 65 Kg. The cost of the member of this UAV family dramatically increased with power and dimensions. Nevertheless, one of the requirements for the spreading of UAVs in civil market is the low cost of the whole system, and a reduction of the time-to-market. The conventional configurations and manufacturing technologies based on advanced composites, wood or aluminium alloys, require a lot of man-hour and wasting of materials, then a reduction of the product costs can be achieved replacing this technology with a less expensive one. Therefore, the authors propose the application of rapid prototyping (RP) techniques to Civil UAV design and manufacturing. The RP technique is based on the use of an hot-wire CNC cutting machine to manufacture the filling of the wing in polystyrene, which will be covered with standard glass fiber/epoxy composite material layers. A tailless configuration is selected to avoid the need of a mould for the fuselage and the resulting waste of man-hour for production. Two airfoil, together with the spar sections and internal payload vane can be interpolated to obtain a tapered wing. This paper briefly describes the configuration optimisation and focuses the attention on the structural design and manufacturing of the vehicle. After the cut of the polystyrene blocks with the hot-wire machine, a skin and spars in glass fiber were added to improve the resistance. Five parts are obtained in the cutting phase: the main and secondary spar, the filling of the wing, and the remaining upper and lower parts of the block. The spars can be reinforced with glass fabric and inserted back in the wing filling cuts; the airfoil shaped filling can be also used as a mould for the lamination of glass fiber/epoxy skins. The wasting upper and lower part of the block cut are used as a countermould to press the laminates over the airfoil filling. After the overall description of the procedure, the paper presents the structural analyses for the ply lamination and shows, with pictures and captions, the main phases of the UAV manufacturing. The final results are very promising, since the UAV airframe can be built in a short time with a very low final cost. Finally, the UAV airframe can be equipped with a small commercial autopilot system to achieve autonomous flight: earth and volcano monitoring, support to civil protection, meteorological researches and search missions are the final destination of this low cost expendable UAV.