Conceptual Design and Aerodynamic Analysis of Medium Altitude Long Endurance VTOL Fixed wing UAV

Abstract

This paper presents the conceptual design and multidisciplinary analysis of a Medium-Altitude Long-Endurance (MALE) Unmanned Aerial Vehicle (UAV) featuring a hybrid Vertical Take-Off and Landing (VTOL) and fixed-wing configuration. The design is driven by demanding mission requirements, including a 650 kg maximum take-off weight, a 100 kg payload capacity, a 200 km operational range, and an endurance of 10 hours at altitudes up to 7000 meters. The proposed twin-boom aircraft integrates an eight-rotor electric VTOL system for vertical flight and a conventional internal combustion engine (Rotax 914 ULF) for efficient forward cruise. The design process followed a systematic approach, beginning with initial sizing and weight estimation using empirical relations from Raymer's methodology, which established a baseline weight distribution. Constraint analysis identified the VTOL-to-cruise transition phase as the most critical, governing the thrust-to-weight ratio and wing loading. Aerodynamic design focused on the high-lift S1223 airfoil, with performance analyzed using XFLR5 and OpenVSP software to optimize the lift-to-drag ratio. Stability and control analysis were conducted to determine the optimal tail arm length of 3.85 meters, ensuring longitudinal and lateral stability, with the vertical stabilizer airfoil selection (NACA 0020) proving crucial for directional stability. Key results demonstrate a feasible design with an empty weight of 352 kg, a fuel weight of 185 kg, and a calculated cruise power requirement of 26 kW. The VTOL system requires a peak power of approximately 233 kW, met by eight 30 kW electric motors. The study concludes that the proposed VTOL fixed-wing UAV successfully balances the competing demands of vertical flight capability and long-endurance cruise performance. The insights and methodologies presented provide a robust foundation for future detailed design, prototyping, and flight testing of advanced hybrid UAVs.