# Design and Manufacture of Composite Landing Gear for a Light Unmanned Aerial Vehicle
## 1 Introduction  
Unmanned aerial vehicles (UAVs) have been used worldwide for industrial applications such as surveying objects and the ground using orthographic photos, volume calculations, digital height, and 3D models. Recent advances and challenges in road safety, traffic, and highway infrastructure management by using UAVs or through cooperation with ground unmanned vehicles can be found in [1, 2]. The integration of UAVs in smart cities is very challenging owing to issues and concerns related to safety, privacy, and ethical/legal use [3]. The false alarms of forest fires may be reduced by using the detection and monitoring system of UAVs [4]. In military applications, an unmanned combat aerial vehicle (UCAV) can carry aircraft ordnance such as missiles to perform drone strikes. For example, the X-47B has a wingspan of 18.9 m, a cruise range of 3889 km, and a maximum gross take-off weight of 20 t, and it can carry a payload of 2 t. The charging of UAVs may be solved by solar energy or wireless power. Another critical goal is to reduce the weight of UAVs. An efficient method to do so is to develop and use composite materials. Composite materials contain both fibers and resin and therefore show excellent characteristics including low density, high strength, anti-corrosion and anti-fatigue properties, and ease of construction and repair. Composite materials therefore find wide applications in aeronautical industries, medical fields, sports equipment, cars and boats, and construction industries. In particular, they are used in aerial vehicles to reduce the weight and thereby reduce fuel consumption. Furthermore, they show high endurance in space applications. Composite materials have a Young's modulus two times that of conventional metals and aluminum alloys with half the weight [5]. Newly developed composite materials are attracting commercial interest for applications in next-generation aircrafts. Composite structures are widely used in small UAV structures. Studies have reported on the challenges and advantages of composite materials when used for the design and fabrication of UAVs [6; 7]. In 2003, SP-Aerospace produced the first metal-based composite landing gear and evaluated it in terms of cost savings and weight reduction. The National Aerospace Laboratory (NLR) [8] evaluated the components of a composite landing gear and reported 20% weight reduction, 15% lower manufacturing costs, and reduced lead time. [PERSON] et al. conducted a finite element analysis using NASTRAN for the wing and landing gear of a composite drone air vehicle [9]. They applied forces of 5 g and \(-1.5\) g to the wing and 2 g to the main landing gear. They found that a 40-layer design of \([45/0/-45/90]_{\text{SS}}\) with 7.6-mm thickness is the optimal solution for the structure. To identify the possibility of other landing cases, vertical landing forces of 36, 120, and 240 N were performed and obtained the maximum stresses of 48, 129, and 911 MPa, respectively. The safety factor was 2, though the non-smooth shape of the landing gear results in stress concentration. [PERSON] presented a composite skid landing gear design for a helicopter in 2009 [10]. \([0/75/-75]_{\text{ss}}\) and \([0/45/-45]_{\text{ss}}\) designs for composite landing gears with 48 multilayers of mixed alloys were proposed. Fractures occurred at the alloy-composite interface when the helicopter was in service. The \([0/45/-45]_{\text{SS}}\) design showed less damage. [PERSON] et al. presented strategic design steps for the structural optimization of a UAV. An interactive parameterized method led to significant (>30%) airframe weight reduction between the initial coarse and the final optimized structural configurations [11]. The landing gear was not made of composite materials. Instead, A17075-T6 aluminum alloy was used with certain structural design changes to reduce the weight of the landing gear. The final optimal main landing gear shape had corners that may increase the stress concentration. [PERSON] et al.