# Simulation, Fabrication and Testing of UAV Composite Landing Gear
## 4 Conclusions  
The benefits of using a CAD system that can be coupled with various additive manufacturing technologies, such as the low production cost, the high design flexibility, or the ability to produce complex shapes without being constrained by manufacturing constraints, have made the use of these techniques more and more popular for UAV manufacturing, ranging from hobbies to military purposes. The lightweight and moderate dimensions of UAV components make it possible to use FFF-processed polymers for their manufacture, thus benefiting from all the above-mentioned advantages. The limited loads and moderate dimensions of the frames make those parts compatible with FFF-processed polymers. Figure 11: Microscopic analysis of the landing gear manufactured of PAHT CF15: (**a**) longitudinal section (100\(\times\)); (**b**) cross-section (100\(\times\)). Figure 12: Microscopic analysis of CFRP landing gear: (**a**) longitudinal section (100\(\times\)); (**b**) cross-section (100\(\times\)). In this paper, five landing gear models for an unmanned aircraft manufactured from different materials, three from carbon fiber and two from glass fiber, using the FFF process and molding process (for CFRP landing gear), are analyzed. All these components are made of filaments with short fibers (chopped fibers). Following the design of the landing gear and the analysis of the results obtained from the FEA analysis and the experimental tests to which the five models produced from various materials were subjected in order to establish the landing gear with the best mechanical strength as well, the following conclusions can be drawn: in the finite element analysis of the landing gear, performed in the Static Structural module of the ANSYS 2021 R2 software system, the conditions of the experimental tests (three-point bending) were respected, considering the dimensions and constraints of the testing machine. With the outputs of the von Mises equivalent stress distribution on the landing gear models were identified the areas where the equivalent stress presents the highest values. The load-displacement curves for the landing gears built of PLA GF, PP GF30, PET CF15, PAHT CF15 and CFRP were generated using the data gathered during the three-point bending tests. The mean values of the bending strength for all of the models tested at bending in three points were determined. After carrying out the three-point bending tests of the landing gear models and from the analysis with finite elements, it can be highlighted that the fracture of the analyzed gear models, in both cases, occurs in the lower skin area, roughly adjacent to the loading application area. Physical models were tested in three-point bending followed by microscopic analysis to detect manufacturing defects. Finally, a comparative study of the preliminary results obtained by simulation with the finite element analysis method and the experimental results obtained following the bending test of the landing gear models was carried out. The final conclusion reached after analyzing all of the results provided by both physical tests and computer simulations is that in the case of UAVs or drones, the landing gear can be manufactured using the FFF process, but in the case of a light airplane, a CFRP landing gear must be used. If the UAV's material allows for the fabrication of landing gear through additive manufacturing, the material must have the highest mechanical strength of the four materials studied, namely PET CF15. Conceptualization, C.L. and S.-M.Z. ; methodology, S.-M.Z., M.-A.P., L.-A.C. and I.S.P. ; software, G.-R.B. and C.L. ; validation, C.L. and V.-M.S. ; investigation, C.L., S.-M.Z., M.-A.P. and G.-R.B. ; writing--original draft preparation, C.L., G.-R.B., S.-M.Z., L.-A.C. and I.S.P. ; project administration, S.-M.Z. All authors have read and agreed to the published version of the manuscript. This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI--UEFISCDI, Project Number PN-III-P2-2.1-PED-2019-0739, within PNCDI III.