Thrust and Noise Experimental Assessment on Counter-Rotating Coaxial Rotors

Multirotors are gaining great importance in the layout of innovative and more agile mobility. In this framework, a possible solution to developing an aircraft complying with the stringent size requirements characterizing this type of application may be a coaxial rotor configuration. To exploit several possibilities linked to coaxial rotors, a scaled experimental model is designed to evaluate the performances of the counter-rotating propeller system, specifically regarding the distance between the two propellers. Both thrust and noise are considered as parameters of interest. Two brushless motors are deployed, whereas the propellers’ angular velocity, in terms of rounds per minute (rpm), is controlled by an external control system. Tests are conducted on both single isolated propellers as well as on the counter-rotating system: the two propellers and their respective motors are characterized regarding the thrust. Furthermore, a comparison with a numerical model is performed. Noise evaluation on the single propeller shows a motor contribution prevalence at a low rpm range (1140–1500 rpm) and a propeller prevalence for angular velocities higher than 1860 rpm. By varying the distances between the propellers, a sensitivity analysis is performed with the aim of identifying the optimum configuration, taking into account both noise and thrust performances.