Performance Evaluation of Airfoils at Low Reynolds Number for UAV Applications

Abstract

Unmanned Aerial Vehicles (UAVs) typically operate at low Reynolds numbers (Re), where aerodynamic characteristics differ significantly from those at higher Re values common in larger aircraft. This paper presents a comprehensive performance evaluation of various airfoils optimized for low Reynolds number conditions typical of small UAVs. The study investigates aerodynamic parameters such as lift coefficient (Cl), drag coefficient (Cd), lift-to-drag ratio (L/D), and stall behavior across Reynolds numbers ranging from 50,000 to 300,000. Both experimental wind tunnel tests and computational fluid dynamics (CFD) simulations were conducted on a selection of candidate airfoils including NACA 4412, Selig S1223, and Eppler 423. The results highlight the trade-offs between lift generation, drag minimization, and stall characteristics. Notably, the Selig S1223 demonstrated superior lift-to-drag ratios at Re ≈ 100,000, making it suitable for endurance-focused UAV missions, while the NACA 4412 showed better stall margin but higher drag. CFD results validated against wind tunnel data reveal critical flow separation and laminar-to-turbulent transition points influencing performance. The findings inform airfoil selection for UAV designers seeking to optimize flight efficiency, control, and stability under low Reynolds number conditions. This work contributes to advancing UAV aerodynamic design by providing detailed insights into airfoil behavior and guiding future airfoil development tailored to the unique challenges posed by low Re flight regimes.