Analysis and Design of a Low Reynolds Propeller for Optimal Unmanned Aerial Vehicle (UAV) Flight

This paper presents a method for optimization of an airfoil and propeller for a small scale Unmanned Aerial Vehicle (UAV) operating in a low Reynolds number state. Operation at a low Reynolds number, generally less than 300,000, lowers the efficiency of the propeller due to greater drag forces on the airfoil. Most hovering-type small scale UAVs generate lift solely with the thrust created by the propellers, and their overall flight characteristics and performance are heavily influenced by propeller and motor efficiency. The method described in this paper generates and optimizes airfoils using the Class/Shape Function Transformation Technique (CST) for the airfoil geometry and a hybrid pattern and particle swarm optimizer to drive Xfoil as a panel method solver for lift and drag coefficients. It then uses a modified Blade Element Momentum Theory equation with a function minimum optimization to determine the propeller characteristics that provide the best figure of merit (FOM) for a hovering and rising thrust state from the optimized airfoils. The propellers are then modeled and analyzed using Computational Fluid Dynamics (CFD) to compare against the thrust and torque values obtained from the optimization program. The results from the CFD analysis indicate an increase of 18 percent in efficiency when compared to a similar stock propeller. Similar increases in efficiency results were obtained when the optimized propeller was manufactured and tested on a thrust stand against the stock propeller.