Measurement of Propeller Characteristics at a Negative Advance Ratio Using a Whirling Arm Facility

Although wind tunnels are the most popular aerodynamic measurement tool of today, whirling arms are another type of tool which is especially useful for the measurement at very low airspeed, including zero. The authors developed a modern whirling arm facility for the measurement of the characteristics of small-scale propellers. In this work, an experiment to measure the characteristics of APC SF 8x6 propeller at a negative advance ratio (from 0.0 to –0.8) is conducted. The rotation of the arm is controlled by a servo motor to maintain the steady rotational speed (i.e. axial airspeed of the propeller) against the thrust fluctuation of the propeller attached at the end of the arm. The very small standard error and standard deviation of the thrust and torque measurement demonstrate the developed system’s ability for precise aerodynamic measurement. In a certain range of advance ratio (from –0.4 to –0.8), remarkable fluctuation of thrust and torque was observed, which suggests the propeller was in a non-steady working condition such as vortex ring state.