Constraint-driven aero-structural twist optimization of 3D-Printed PETG low-Reynolds-number multirotor propellers

Abstract

Flexible fused-deposition-modelled propellers can lose endurance when deformation changes the designed incidence, while thin sections that appear aerodynamically superior may be structurally inadmissible. This study develops a constraint-driven aero-structural workflow for a 9.4 in two-bladed glycol-modified polyethylene terephthalate (PETG) multirotor propeller at a per-rotor hover thrust of 4.5 N. Six chord-twist and airfoil candidates were evaluated over 2-5 N using blade-element momentum theory (BEMT) and orthotropic finite-element analysis (FEA). Candidates were screened against a 40 MPa stress allowable and a 0.03R tip-deflection limit. The most efficient feasible blade was then refined by constrained stationwise twist redesign using local Reynolds number, inflow angle, and Cl/Cd information while retaining chord, airfoil schedule, diameter, root geometry, and section thickness. The final design was independently checked using steady RANS computational fluid dynamics (CFD) and pressure-mapped FEA. The aerodynamic-only winner failed the 0.03R deflection constraint, whereas the APC/E216 configuration satisfied both stress and stiffness requirements and was selected as the feasible baseline. Across 2-5 N, the local twist redesign reduced the required rotational speed by approximately 11% and increased the hover figure of merit by up to 4.6%. At the 4.5 N design point, outward load migration increased the torque arm while the lower rotational speed reduced combined stress by 24.2%. The associated reduction in centrifugal stiffening increased tip displacement by 45.5%, but the displacement remained within the prescribed limit. RANS-CFD and pressure-mapped FEA recovered the target thrust and confirmed structural feasibility. The results show that aerodynamic improvement cannot be separated from printed-blade stiffness. Twist-induced radial load redistribution can simultaneously improve hover efficiency, reduce centrifugal stress, and decrease centrifugal stiffening. The proposed tiered BEMT/FEA-to-CFD/FEA workflow therefore provides a physically traceable route for balancing aerodynamic performance and structural admissibility in printable low-Reynolds-number multirotor propellers.