Aerodynamic optimization method of propeller multi-design points and variable pitch angle strategy

The high-altitude solar powered Unmanned Aerial Vehicle（UAV）has a slow flight speed，low climb rate and long climb time in the take-off and climb stage，the propeller needs to provide large pull force to achieve fast climb. However，the low-altitude air density is high，and the propeller is in the state of low speed and high torque. At the altitude of 20 km，the air density is only 1/14 of the ground，requiring the propeller to be in a state of high speed and high efficiency. Due to the power limitation of the power system，fixed-pitch propellers cannot match these two states，so variable pitch technology is needed to realize the configuration of small pitch，low speed and large tension at low altitude，and large pitch，high speed and high efficiency at high altitude. This paper presents a method of aero- dynamic profile optimization for propeller with multiple design points and a strategy of variable pitch angle under mul- tiple operating conditions. The aerodynamic profile optimization model of propeller with multiple design points was es- tablished based on standard strip analysis，and the profile parameters of propeller were optimized，such as chord length and torsion angle distribution. A fast aerodynamic calculation model considering pitch angle variation is added to the model to realize the strategy of variable pitch angle under multiple working conditions. By comparing the aerody- namic performance of the propeller under fixed pitch and variable pitch，the results show that the efficiency of the pro- peller designed based on the aerodynamic shape optimization model of the propeller at multiple design points at high altitude is more than 80%，which is conducive to the long-term flight of the solar powered UAV. Considering the pro- peller with variable pitch optimization strategy，the maximum pulling force can be increased by 78. 42% in take-off climbing condition，which can provide a larger climbing rate，which is conducive to the solar powered UAV quickly fly- ing through the troposphere to reach the upper design point during take-off. © 2024 Chinese Society of Astronautics. All rights reserved.