A review of ice accretion on rotary-wing UAV propellers: scaling constraints, aerodynamic penalties, methodological challenges and mitigation strategies

Abstract Atmospheric icing poses a disproportionate hazard to rotary-wing unmanned aerial vehicles (RW-UAVs) because their small-chord, high-RPM propellers operate in a low-Reynolds-number regime where even modest ice roughness and accretion can trigger severe aerodynamic, energetic, and flight-dynamic penalties. This review synthesises the literature on ice accretion on RW-UAV propellers through a scale-aware framework that links collection physics, surface-water transport, morphology, performance degradation, methodological reliability and mitigation design. The central premise is that a scaling break arises when correlations developed for manned rotorcraft are transferred to small rotating propellers without additional validation. In this regime, elevated collection efficiency, heightened sensitivity to roughness-induced transition and rotation-driven radial redistribution of unfrozen water jointly alter ice morphology and its consequences. The review first examines similarity constraints governing Reynolds number, droplet inertia, freezing fraction, Weber number, surface roughness, advance ratio and tip Mach effects. It then traces how these mechanisms produce coupled penalties in thrust, torque, power demand, shedding transients and vehicle-level control authority, including rotor-to-rotor asymmetry and wake-interaction effects. Methodological validity is also assessed, showing how facility boundary conditions, cloud-calibration procedures, control-mode selection and uncertainty treatment shape reported penalty magnitudes. On this basis, a minimum reporting framework is proposed to improve cross-study comparability. Finally, passive, active and hybrid mitigation strategies are evaluated under the battery-capacity and mass constraints of small electric RW-UAVs. The review concludes that RW-UAV icing is not a downscaled analogue of manned rotorcraft icing but a distinct multi-physics and operational problem requiring scale-sensitive interpretation, standardised reporting, and energy-aware protection strategies.