Testing Methods for Durable Leading Edge Ice Protection Coatings on Rotorcraft

Passive ice protection coatings have the potential to reduce or eliminate the size, weight and power burden of current active rotorcraft icing protection systems, with benefits for sustainability as well as operation of the vehicle. However, there is no broadly agreed-upon testing methodology for shedding and durability validation, and coatings that successfully combine ice-shedding with leading edge durability have yet to be implemented, due to conflicting requirements and extremely damaging effects of impact erosion on non-metallic surfaces. To address this challenge, testing is being conducted using the Adverse Environment Rotor Test Stand (AERTS) facility at Penn State University. The AERTS comprises a 10-ft. diameter climate controlled chamber with installed rotor stand designed to simulate aircraft icing conditions. Icing clouds are formed by super-cooled water droplets and can be controlled in terms of liquid water concentration, water droplet diameter, and temperature. Recent AERTS enhancements have added an in situ rain erosion feature allowing for alternating testing windows of icing and rain conditions. Using this setup, drag due to ice accumulation at the leading edge is tracked through change in motor current at fixed rotational speed. Motor current over icing cloud exposure time was initially measured with continuous shedding over 40 minutes between -16 and -5ºC. Surfaces tested include the bare metal leading edge, a commercial leading edge protection coating, and a developmental durable passive ice protection coating. Coatings were installed as 4-ft tapes along the span covering a 4-in chord centered at the leading edge. The developmental coating showed increased shed frequency compared to the bare metal and commercial coating. A 10 minute rain exposure was applied to the coatings and the icing test window repeated. Developmental coating shed frequency and motor current vs time were similar to pre-rain curves with outboard ice thicknesses post-test measured at ≤ 1/16- in.