Extending Aeroelastic-Informed Helicopter Rotor Blade Optimization to Include Vibration Reduction in Transitional Flight

Helicopter performance relies on well-designed rotor blades. This typically aims to improve two metrics: hover efficiency (Figure-of-Merit) and cruise efficiency (Lift-to-Drag ratio). This work extends a previous multi-objective optimization framework based on the University of Maryland's Aeromechanical Rotorcraft Analysis Code (UMARC-II) and Genetic Algorithm. That framework used aeroelastic analysis to design blades with non-linear twist, chord distributions, and spanwise airfoil selections, achieving significant aerodynamic gains within structural limits. In this study, we add vibration reduction as a third design objective. Helicopter vibrations peak during low-speed transitional flight, a regime dominated by unsteady aerodynamics that drives passenger discomfort and component fatigue. We calculate vibration index at low advance ratios and at the cruise speed and include it directly in the multi-objective optimization. The result is a tri-objective process that finds Pareto-optimal blade designs offering high Figure-of-Merit, high Lift-to-Drag ratio, and low vibratory hub loads. We also replace the linear inflow model used previously with the mid-fidelity Maryland Free Wake model, which accounts for vortex roll-up and wake distortion to give more accurate performance and load predictions. This extended framework generates blade designs that improve aerodynamic efficiency while reducing vibrations in both the critical transitional flight regime and at cruise speed.