# Simulation, Fabrication and Testing of UAV Composite Landing Gear
## 1 Introduction  
Given the current international situation, which has generated an unprecedented crisis in fossil fuels, to combat pollution, internal combustion vehicles have begun to be replaced, increasingly more, with electric vehicles [1, 2]. The automotive industry is the first that aligned with these requirements [3], but lately, there has been a growing interest in the aerospace industry as well [4], because the European air transportation system is of vital interest to the European economy [5, 6]. Under these circumstances, electric aircraft will become one of the major directions for aviation development. Over the last decade, the unmanned aerial vehicle (UAV) market has steadily increased. These systems are being used in a wide range of applications such as agriculture [7], communication, air quality monitoring, military reconnaissance and surveillance combat missions [8], civil engineering [9], couriers and sea surface optical wireless communications [10]. Due to its capacity for direct digital manufacturing of end products, additive manufacturing offers new avenues for design solutions that are otherwise challenging or impossible to achieve when using conventional manufacturing techniques [11]. Therefore, the evolution of additive manufacturing (AM) has been recognized as a key enabling technology in a wide range of applications, some of which include the aerospace [12], medical [13] and automotive industries [14, 15]. Composites are materials created by mixing two or more different components while maintaining the chemical integrity of each individual substance. [16]. Due to their gooddynamic characteristics and high mechanical properties, such as good strength/weight ratios, good stiffness and fatigue resistance or high corrosion resistance, the composite materials are frequently used for parts subjected to impact [17]. For these reasons, composite materials are increasingly used in the aerospace industry (civil aircraft or military aircraft), automotive, vessels, civil engineering, electrical engineering, arms industry or sporting goods industry [18]. At present, parts with complex geometric shapes can be manufactured without the need for a mold design, which significantly increases manufacturing costs. The solution to this problem is additive manufacturing, which is frequently used when aiming to quickly obtain a single part or a few parts. When manufacturing metal alloy parts, using the layer-by-layer manufacturing technique, the costs are still high, but not with plastic parts manufacturing, where the use of AM techniques has become very helpful, also from an economic point of view. Because of their good mechanical properties for the stress requirements of UAV components [19; 20; 21], thermoplastic materials such as styrene-butadiene acrylonitrile (ABS) and nylon have become some of the most commonly used materials in the production of 3D printed components for UAVs, manufactured through the fused filament fabrication (FFF) process [22; 23; 24]. The landing gear is an unmanned aerial vehicle's running system that supports the aircraft when it is not flying and can be used for both take-off and landing maneuvers to absorb horizontal and vertical loads. Because of the extremely high loads that appear when the aircraft is landing [25; 26], the aircraft equipment could be damaged if the high impact loads were transmitted directly to the fuselage of the UAV. That is why the primary requirements of landing gear are to absorb and dissipate the stresses caused by the impact of landing by reducing their impact on the aircraft fuselage [27]. In this situation, the landing gear design takes into account various requirements of strength, stability and stiffness. In this situation, when designing the landing gear, some requirements must be taken into account, such as strength, stiffness and stability [28]. Thus, very accurate analyses are required, to verify the impact resistance of the designed landing gear.