Development of a Wind Tunnel Test Cell for Small Propellers with Application to the Plank Unmanned Aerial Vehicle

Abstract

The Plank unmanned aerial vehicle has been designed to be a test platform for an experimental bias angular moment flywheel designed by the NASA Guidance and Controls Branch. The baseline configuration of the aircraft is a flying wing with zero quarter-chord sweep. The benefits of this type of configuration include low structural weight and complexity and reduced drag compared to a standard wing-tail configuration. However, this type of configuration is inherently sensitive to pitch disturbances due to low pitch damping and moment of inertia. In order to remedy this sensitivity, NASA has proposed the use of a bias angular momentum flywheel with its rotational axis aligned with the z-axis of the aircraft. This momentum wheel will effectively stiffen the pitch axis of the aircraft by coupling it with the high damping, high moment of inertia roll axis. The aircraft was designed to be re-configurable allowing for a variety of flying qualities ranging from a well-behaved wing and aft tail configuration to the much more sensitive flying wing configuration. This range of flying qualities will allow for a more comprehensive performance evaluation of the momentum wheel system as well as contribute to risk mitigation during initial flight tests. An electric propulsion system has been chosen for this aircraft due its simple operation and low vibration characteristics. The AXi 5330/18 motor was chosen along with a Castle Creations Phoenix HV-110 electronic speed control. The system is powered by three FlightPower 5000 mAh 10s Evo Lite battery packs connected in parallel. A four-bladed propeller configuration was used in order to absorb the necessary power from the motor while still fitting between the tail booms of the aircraft. In order to experimentally evaluate the performance of the Plank propulsion system in the NCSU Subsonic Wind Tunnel, the Propeller Test Cell (PTC) was developed. The PTC consists of a strain gage based load cell that measures the thrust and torque generated by the propulsion system along with system operating conditions such as current, voltage, RPM, motor temperature, and battery consumption. The PTC was used to characterize the performance of three candidate propellers for the Plank aircraft: 16x10, 17x8, and 17x10. With this data, certain propulsion specific performance parameters of the aircraft were calculated including thrust and power available, rate of climb and climb angle, range, endurance, and take off performance. After analyzing the performance for each of the three propellers, the 17x8 propeller produced the most desired aircraft performance and was chosen to be paired with the AXi motor and the Plank aircraft.