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Abstract
The purpose of this capstone project was to develop a method to optimize an airfoil and propeller for a multicopter operating in a low Reynolds number state. The capstone project is being submitted to meet the requirements for the Milwaukee School of Engineering's Master of Science in Engineering [MSE] program. Multicopters--also known as multirotors--are normally a type of Micro aerial vehicle [MAV]. The multicopter features two or more rotor blades; thus, a tricopter, quadcopter, hexacopter and octocopter refer to three-, four-, six-, and eight-rotor helicopters, respectively. MAVs are subject to different fluid flows as a result of operating at low Reynolds numbers, normally less than 300,000. This lowers the efficiencies in the propellers because of the higher drag forces on the airfoils. Optimization methods have been previously explored for large-scale propellers but as these larger propellers operate at a higher Reynolds number, the airfoils would not scale to an efficient small propeller. A few optimization methods have been developed for MAVs, but these have been for traditional airplane-style aircraft that have different design requirements. This study discusses methods to model the airfoils and the modified blade element momentum theory to optimize the propeller. The airfoil optimization is conducted with a combination of a MATLAB program for airfoil geometry and the use of Xfoil to provide the airfoil flight characteristics. Xfoil is a publicly licensed interactive design and analysis software tool that was first developed at the Massachusetts Institute of Technology. A second optimization is performed in MATLAB using the optimized airfoils to determine the best blade pitch, chord length, and blade taper for a propeller for each airfoil. Two of the top designs were modeled in Solidworks and then tested with computational fluid dynamics [CFD] software [Flow Simulation] to compare with the theoretical results from MATLAB. The results from the CFD software were imported into a finite element analysis [FEA] software package [Simulation] to verify the propeller would withstand the forces applied from the motor running at its maximum output to a factor of safety [FOS] no less than 1.5. Both of the propellers tested provided the required thrust during a near hovering state, while improving efficiency over the stock propeller.