Design Optimization of a Rotor Blade for a Variable Pitch Quadrotor Unmanned Air Vehicle

This paper describes design optimization of a rotor blade for variable pitch quadrotor unmanned air vehicle (UAV) to ensure optimal performance in hover and forward flight. In order to optimize the blade profile to maximize hover power loading, a modified Blade Element Theory based analysis is developed and validated using experimental measurements for sets of symmetric-untwisted rectangular blade and cambered-twisted variable chord blade. The blade twist and chord distribution is parametrized using fifth order polynomial functions and the BEMT analysis is coupled to Matlab optmization toolbox to maximize the power loading for an operational thrust of approximately 3N. It is observed that use of rotor blade with non-linear twist and non-linear chord variation results in significant improvement in hover performance for the variable pitch quadrotor UAV. The optimized blade profile and chord distribution with GOE-744 airfoil gives approximately 4% higher power loading than the COTS cambered and twisted blade and 17% higher power loading than the untwisted rectangular blade with symmetric airfoil. The forward flight performance of the optimized blades is compared with the baseline blades using a Blade Element Theory and Drees inflow model based trim analysis. It is observed that the optimized blade profile doesn't incur any significant penalty during forward flight due to high twist and its performance is similar to that of untwisted blade.