Modeling and the Control Strategy of the Coaxial Contra-Rotating Propeller System

Abstract

AbstractThe counter-rotating propeller is a promising installation for fixed-wing unmanned aerial vehicles (UAVs) with a single engine, requiring high efficiency, high speed, and high thrust. The contra-rotating propeller comprises two propellers in the same axis but the opposite rotating direction to counter the torque effect and reuse the kinetic energy delivered in the forward propeller slipstream. Modeling the performance of the contra-rotating propeller with good accuracy in less run-time is still a challenging task in the design phase. An analytic Blade element momentum (BEM) model is derived in this presented study and then applied to model the counter-rotating propeller, reducing the model run time significantly compared to the conventional iterative BEM. Then the analytic BEM model for the counter-rotating propeller is validated by comparing it to the computational fluid dynamic (CFD) simulation results. Based on this validated model, the analyses on the effect of the rotational speed, freestream speed, forward and rear pitch angle on the counter-rotating propeller performance on the premise of torque balance are conducted. In the last part, a control strategy is proposed to schedule the rotational speed, forward and rear pitch angle. In this manner, the contra-rotating propeller can provide the target thrust while ensuring the highest efficiency and torque balance.KeywordsCounter-rotating propellerBlade element momentum theoryModelingControl strategy