Thrust Agility of Variable Pitch in Coaxial Rotor Pairs

Coaxial rotors offer design advantages for drones, in that they enable a smaller airframe while allowing for larger rotors. While larger rotors provide greater thrust and efficiency, they are not optimal for gust rejection, as their high inertia limits the rotor response frequency. Variable pitch propellers are a solution, decoupling the rotor response from the rotational inertia, but increase the complexity and mass of the system. This work looks at the agility advantages of a design compromise, using variable pitch only on the lower rotor of a coaxial pair. The results show that adapting variable-pitch lower rotor into coaxial configuration increased the overall stacked efficiency by 27%, and improved agility by 10.8% compared to the fixed-pitch, enhancing the overall coaxial performance.