The measuring of contra rotating propellers with different diameters and design points

• Main Authors: Mixa, Jan, Luxa, Martin, Schmirler, Michal
• Format: Conference Proceeding
• Language: English
• Subjects: Aerodynamics; Aircraft; Automatic pilots; Contrarotating propellers; Design techniques; Diameters; Fluid mechanics; Horizontal flight; Measuring instruments; Mechanical engineering; Panel method (fluid dynamics); Position measurement; Power consumption; Power efficiency; Power management; Rotation; Static characteristics; Thrust; Unmanned aerial vehicles; Vertical orientation; Vertical takeoff aircraft
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/5.0122401

This paper is focused on measuring static characteristics of two coaxial contra rotating propellers (CRP). This particular measuring is a part of the complete design of the UAV VTOL tailsitter aircraft, which is developed at The Institute of Fluid Mechanics and Thermodynamics of the Faculty of Mechanical Engineering of the Czech Technical University. The measurement target is to verify correctness of the numerical design method used for measured propellers and then to find the data necessary for maximalization of the power efficiency of the designed UAV. The specificity of measured CRP is a different diameter of the propellers and a different design point. The bigger 22’’ propeller is designed to provide sufficient thrust for vertical take-off and landing. The smaller one, 16’’ propeller, is optimized for a horizontal flight with constant speed, however it contributes to achieve sufficient thrust in a vertical position as well. For the measurement of these propellers, a laboratory measuring device was designed and assembled. This device allows the propellers to be measured separately or together and the propellers can also be measured in an open space as well as integrated in the aircraft. In both cases the propellers take the same position in the space and therefore the same position relatively to each other. The first part of the measurement is focused on measuring static characteristics of each propeller separately. The measured data was compared with the design static characteristics calculated with 3D panel method, thus the accuracy of used numerical design method was determined. In the following part of the measurement, the propellers were integrated in the aircraft and all measurements were repeated. In this configuration it is possible to determine thrust losses caused by the aircraft body. Another important point of measurement is to determinate optimal propeller rpm ratio for the lowest possible power consumption and propeller rpm ratio when the final torque on a propeller axis is zero. This data is essential for subsequent tuning of the autopilot unit.