Ice testing of a centrifugally powered pneumatic deicing system for helicopter rotor blades

This paper presents a novel pneumatic approach to protect helicopter rotor blades from ice accretion. The system relies on centrifugally generated pressures to deform a 0.508-mm (0.02 inch)-thick titanium leading edge cap. The leading edge cap is protected by a 10-μm (390 μinch)-thick Ti-Al-N erosion-resistant coating. Beneath the titanium leading edge, six pneumatic diaphragms were installed. The diaphragms are normally deflated under vacuum against the surface of the blade and are inflated when ice accretion thickness reaches a critical value. The deformation of the leading edge introduces transverse shear stresses at the interface of the ice layer that exceed the ice adhesion strength of the material (868 kPa, 126 psi), promoting instantaneous ice debonding. Testing was conducted at The Pennsylvania State University Adverse Environment Rotor Test Stand Facility from October 2013 to February 2014. The applied input pressures to the system (±25.5 kPa, 3.7 psi) were representative of the pressures generated centrifugally by a medium-size helicopter rotor system. With these pressures, the maximum deformation of the leading edge was quantified to be 5 mm (0.2 inch). The aerodynamic performance degradation effects related to the leading edge deformation were quantified during low-speed (Re = 1 × 10⁶) wind tunnel testing. Results were compared to the aerodynamic performance degradation due to ice accretion. It was measured that the penalties related to the deployment of the pneumatic diaphragms were 35% lower than the aerodynamic drag penalty due to ice accretion. The lower aerodynamic penalty of deploying the proposed deicing concept with respect to that of the ice accretion case indicates that the system would not introduce any aerodynamic penalty while removing accreted ice. The system was tested under representative rotor icing conditions and at centrifugal loads that ranged from 110 to 516 ×g. The deicing successfully promoted instantaneous shedding of ice layers ranging from 1.5 to 5 mm (0.06-0.1 inch) in thickness for various icing conditions within 14 Code of Federal Regulations 25/29 Appendix C Icing Envelope.