An Enhanced Jig-Shape Approach to Lifting Propeller Design

The jig-shape approach decouples the design process of aeroelastic structures. During structural sizing, elastic deformations are subtracted from the initial shape to achieve a desirable flying shape under loads at one specific design point. However, due to nonlinear loads, stiffness, and deformations, there is a disparity between intended rigid and actual elastic propeller performance at off-design points. Propellers lifting air taxis or large cargo drones are particularly susceptible to such variances due to their slender design. This paper presents an enhanced jig-shape approach to minimize these discrepancies by inducing additional coupling effects counteracting elastic deformations. Beyond the traditional single-point predeflection analysis, the improved strategy employs geometric and structural modifications to mitigate errors at off-design points. Comparing the aeroelastic performance of propellers sized according to the traditional and the enhanced procedure illustrates the effectiveness of the modifications. The enhanced approach remains computationally efficient due to its decoupled nature. A novel finite beam element that accurately captures the relevant structural coupling effects of lifting propellers is derived. Applying unbalanced ply layups inducing extension–twist coupling is limited in effectiveness and increases weight. Modifying the coning angle of a straight blade affects loads and stresses but does not allow the adjustment of aeroelastic performance. Combining the coning angle with a swept planform enables the flexible correction of aeroelastic performance within limits at minimal weight increase.