Aerodynamics of Small Rotors in Hover and Forward Flight

A wind tunnel test of eleven two- and three-bladed small-scale rotors was conducted in an open-jet, lowspeed wind tunnel. The goal was to study the influence of number of blades, blade pitch and geometry on the hover performance. Two rotors were also studied in forward flight with varying rotational speeds, rotor tilt angles and flow velocities covering a wide range of operating conditions. The experimental results were used to develop a simple, empirical model of the studied rotor based on dimensionless quantities. The model can be used in the preliminary design of multicopters. The performance measurements were supplemented with optical background-oriented schlieren (BOS) measurements to visualize the blade tip vortices in the rotor wake in order to gain a better understanding of the flow state. Simulations with DLR’s free wake unsteady panel code (UPM) were carried out for comparison