## 2 Materials and Methods
### Drone Prototype and Collision Analysis  
This study examines the application of 3D printing technologies in manufacturing unmanned aerial vehicles (UAVs), with a specific focus on material selection and its impact on structural performance, particularly in terms of deformation energy absorption, evaluating the possibility of replacing expanded polyolefin (EPO). This foam-like polymer is typically used in UAV construction due to its low cost, ease of shaping, and lightweight properties. While EPO offers apparent advantages, it presents limitations in UAV design, particularly in terms of internal space utilization. Due to its foam structure, EPO occupies a significant portion of the fuselage, thereby reducing the available volume for critical payloads, such as sensors, cameras, batteries, or other mission-specific equipment. This limitation is especially relevant in UAV applications, where efficient transportation of cargo or equipment is crucial. To address this issue, this research proposes substituting EPO with additively manufactured polymeric materials, such as PLA or LW-PLA, which could provide comparable or enhanced mechanical performance while increasing the internal volume available for useful loads. Three models [39; 40; 41] were chosen due to their similar physical characteristics, particularly their wingspan and wing surface area, as well as their broad adoption within the UAV enthusiast community. All three are manufactured initially from EPO and share similar constraints related to payload space. After comparing the design features and practical constraints of the selected UAVs, the OPTERRA 2M WING [41] stood out as the most suitable candidate for further investigation and material substitution due to the possibility of isolating the front part of the fuselage, which is already formed as a separate, prototyping-ready fragment (Figure 3a). Its flying wing configuration simplified the structural geometry, making it more compatible with 3D printing processes. Additionally,  
Figure 1: The compression test specimens: (**a,b**) sliced model and internal fabrication pattern; (**c**) test setup; (**d**) test samples after the tests. Figure 2: The compression test results: (**a**) load–displacement diagrams; (**b**) normalized load–displacement diagrams. replacing its foam nose part with 3D-printed materials could significantly enhance the usable internal volume without compromising the flight performance. The potential to redesign and optimize the internal structure through additive manufacturing opens new avenues for increasing the payload capacity and improving the mechanical robustness of UAVs. The OPTERRA 2M WING (Figure 3b) is a flying-wing UAV renowned for its streamlined aerodynamic profile and large wingspan, which contribute to its inherent stability and flight efficiency. The manufacturer specifies the following drone characteristics [41]: wingspan = 1989 mm; fuselage length = 1036 mm; wing area = 6.66 \(\times\) 10\({}^{5}\) mm\({}^{2}\); flying weight = 1899 g; cruise speed = 64 km/h; and flying time = 30 min. Its center of gravity aligns with the dimples located just in front of the finger pockets on the bottom of the fuselage. This study presents a simplified analysis example, focusing on the front part of the drone fuselage (Figure 3a), while overlooking the support and installation details of the prototype. To evaluate the structural efficiency, the analysis scenario employs a theoretical drone collision energy, not as a design condition but as a comparative benchmark for assessing the performance of metastructural configurations. The analysis addresses the deformation energy released during the frontal collision of the drone. The calculations assume a rigid impact along with the manufacturer's specified flying weight, \(m\), and cruise speed, \(\upsilon\), as described above.