Development and analysis of variable pitch propeller with aerodynamic stable blades

For small short/vertical takeoff and landing (S/VTOL) unmanned aerial vehicles, the propeller design should reach a compromise between S/VTOL and cruise. But the complexity cost of a variable-pitch propeller is too high to be applied to small propellers. To achieve the propeller pitch variability with minimum mechanic complexity and weight cost, an aerostable concept was used in the design of the blades. In this case, the propeller pitch was variable under the aerodynamic moment. First, the simulation method based on the computational fluid dynamics was validated by experiments of the NACA 5868-9 propeller and Gall’s biplane/winglet configuration. Second, the propeller design process for a four-blade aerostable propeller with high disk loading was presented. The design was based on the Blade Element Momentum Theory, with a section aerodynamic database modeled by an artificial neural network. To eliminate dynamic imbalance moment, a prebalance method based on the Parallel-Axis Theorem was established. Third, the thrust, power, and efficiency of the designed propeller was analyzed in both S/VTOL and cruise condition. The trim points of the blade were analyzed, and the pitch moment coefficient and the stability margin of the blade were discussed.