UAV Icing: Intercycle Ice Effects on Aerodynamic Performance

Abstract

Atmospheric in-flight icing poses a challenge to all aircraft including unmanned aerial vehicles (UAVs). Aircraft should avoid icing conditions unless they have ways of mitigating the negative effects of icing, e.g., if they are equipped with an ice protection system (IPS). When de-icing systems are used, a certain amount of ice is allowed to accumulate before it is removed. This intercycle ice deteriorates the aerodynamics by reducing the lift, adding mass, and increasing the drag. This study combines the energy that is required to compensate for the added drag of intercycle ice shapes with the energy required for a wing IPS and compares the energy needs for different IPS operations. Two different kinds of intercycle ice shapes are simulated numerically using FENSAP-ICE, one ice shape that would accrete on an unprotected wing and one ice shape that would accrete when using a parting strip, a continuously heated element at the leading edge. The results show that both intercycle ice shapes deteriorate the aerodynamic performance of the airfoil significantly compared to a clean airfoil. Additionally, the results show that the aerodynamics deteriorate fastest in the initial stages of ice accretion, likely caused by fast horn growth and a fast transition from laminar to turbulent flow. The aerodynamic performance is combined with energy requirements of electrothermal de-icing tests in an icing wind tunnel. The results show that de-icing with a parting strip is more energy-efficient than de-icing without a parting strip and anti-icing. In addition, it is found that the energy required for the IPS on a wing is significantly larger than the energy required to compensate for the added intercycle drag. Considering these results during the development and operation of an IPS will help to improve the range and endurance of UAVs in icing conditions.