Full-scale testing of a centrifugally powered pneumatic deicing system for helicopter rotor blades

A full-scale centrifugally powered pneumatic deicing system for helicopter blades was developed. The designed system makes use of the pressure differential created within a spinning rotor blade to deform a 0.03 in. (0.762 mm) thick metallic leading edge cap, producing the transverse shear stresses necessary to delaminate accreted ice. Two prototype designs were fabricated and parametrically tested. Both designs consist of a stainless steel leading edge cap tied to the blade surface via flexible stainless steel ribs. The leading edge section is sealed to the blade surface such that it can be pressurized, inflating and deflating as a microvalve is cycled between high and low pressure lines that run along the blade span. Both designs were fabricated and installed on a truncated 12 in. (0.3048 m.) span K-MAX blade section. Icing testing of the prototypes was conducted at The Pennsylvania State University Adverse Environment Rotor Test Stand. Input pressures representative of those produced by centrifugal pressures generated along a full-scale 24 ft. (7.3 m.) radius blade rotating at 270 RPM were provided to the prototypes via a pneumatic slip ring. Parametric testing of the two configurations demonstrated the superiority of one of the designs. The selected configuration was reproduced and installed on the outboard 8 ft. section of a full-scale 24 ft. (7.3 m.) K-MAX blade. Full-scale icing testing was conducted at Kaman's whirl tower during the month of February. A portable icing cloud generator capable of providing 40 minutes of continuous icing through 12 NASA Standard icing nozzles was developed to provide representative icing conditions. A second cloud generator providing uncontrolled water droplet sizes was also implemented due to power availability limitations to operate the portable icing cloud generation system. The full-scale system was tested at static air temperatures within the Federal Aviation Regulation (FAR) Part 25/29 icing envelope and was able to delaminate ice thicknesses as small as 0.08 in. (2.03 mm.) at 270 RPM.