Design and Thermal Modeling of a Semi-Passive, Low Power Ice Protection System for eVTOL

Atmospheric icing conditions adversely affect aircraft performance and safety. Electric vertical take off/landing (eVTOL) rotorcraft are typically not designed to fly in adverse weather and lack ice protection. Prior experiments have shown that ice accretion on rotor blades induces a large current draw due to increased drag. Without sufficient cooling, motors have been observed to burn out and have their controllers exceed temperatures of 200˚C (390˚F). Research has also shown that sizable internal flow rates can develop within hollow rotating blades. Combining these research efforts, this study presents the thermal modeling and design of a novel, semi-passive, low-power ice protection system (IPS). The ideal IPS uses centrifugal forces to extract heat dissipated from motor inefficiencies through a duct at the leading edge. First, wind tunnel testing is conducted to characterize the leading edge temperatures of a representative test section. Computational fluid dynamics (CFD) tools and software are then verified against the experimental results. Next, a closed-form solution is derived to estimate the internal mass flow rate due to centrifugal forces. Lastly, a parametric conjugate heat transfer (CHT) model is developed to predict the minimum temperatures and flow rates required to prevent ice accretion on a Joby S4 rotor blade. The results indicate that centrifugally-driven internal flows may be able to extract air, but the addition of a fan or external flow device can significantly lower the temperature required to deice the blades. In general, the smaller the supplied flow rates, the higher the required temperature will be for deicing. To meet the functional requirements of a semi-passive IPS, either the inlet flow rate or temperature should be maximized.