From Simulation to Flight: Validation of the Racer Low-Drag Rotor Hub

The paper presents the successful drag reduction of the Racer demonstrator's rotor head through its innovative full fairing, based on a robust de-risking methodology leveraging 2D Robust Design Optimization (RDO) for airfoils, 3D CFD analysis with multiple fidelity levels, and experiments. We provide a unique end-to-end comparison across the full development cycle, correlating simulation predictions with both experimental and flight-test data. The fully faired architecture achieves a significant 42% reduction in rotor-hub form drag. At the full-vehicle level, flight tests confirm a 10% net drag reduction, including complex interactions with the airframe. This real-world measurement correlates highly with dynamic URANS predictions (11-12%), while effectively contextualizing the more optimistic 16% gains observed during static wind-tunnel and steady RANS evaluations. These findings provide a comprehensive validation of the low-drag fairing concept, offering valuable insights for the aerodynamic design of future high-speed rotorcraft.