Experimental analysis on the performance of small-scale UAV propellers with micro-structured surfaces

Ordered micro-structured surfaces have demonstrated many surface altering affects. Enhancing or decreasing friction characteristics, altering wetting characteristics, producing drag reduction and boundary layer effects. An experimental investigation into the performance of small-scale UAV propellers coated with micro-structured surfaces on the suction side of the blade is conducted. In order to characterize the performance of the propeller, a custom experimental setup featuring a motor-propeller system mounted directly to a 6-axis load cell on a steel tower with a speed sensor and external microphone are utilized. The DJI 9450 propeller is chosen as the stock blade on one of the most widely used drones in the world, the DJI Phantom III. The propeller is coated with cylindrical pillar structures at various pitches, heights, and diameters which are tested for force, torque and noise in several radial locations along the blade. Further testing is conducted on streamwise aligned ridges, and a comparison between converging and diverging tip cylindrical structures. Experimental results suggest that the most influential characteristic of the array is structure height and radial location on the blade. While structure diameter and center-to-center spacing has a secondary influence. Arrays with larger diameter, taller structures, and larger center-to-center spacings are shown to reduce performance consistently. The top performing structures are shown to have minor efficiency gains of around 3% at lower RPM while reducing performance above 5000 RPM compared to an uncoated control blade. Structures at the root of the blade do not contribute to noise attenuation but are shown to increase efficiency at lower RPM with minor degradation at higher RPM. Structures at the tip reduce broadband noise on the order of 5-10 dBA and can increase performance at low rotational velocities but severely degrade performance at higher rotational velocities. Earlier studies revealed that micro-structured coatings are effective at delaying laminar boundary layer separation. It is speculated that efficiency gains are minimal as a result of the DJI 9450 blade design minimizing boundary layer separation within its operation range. Thus, further investigation on flow visualization to determine the extent of boundary layer separation on a given propeller are necessary to effectively apply microstructure coatings for efficiency gains.

Embargo status: Restricted until 01/2024. To request the author grant access, click on the PDF link to the left.