Investigation of an ultrasonic ice protection system for helicopter rotor blades

A low-power, non-thermal, ultrasonic de-icing system is introduced as a potential substitute for helicopter rotor blade electro-thermal ice protection technology that is currently used. In this study, ultrasonic actuator disks excite isotropic plates that are representative of helicopter leading edge protection caps. The system generates delaminating ultrasonic transverse shear stresses at the interface of accreted ice, de-bonding thin ice layers (< 3 mm thick) as they form on the isotropic host structure. A finite element model of the proposed actuator and of the isotropic plates is used to guide the design of the prototypes. Several actuatorisotropic plate structures are fabricated and tested under freezer ice conditions. Test results demonstrate that 28.5 KHz radial resonance disk actuators create ultrasonic transverse shear stresses capable of instantaneously delaminating ice layers that accrete to the isotropic structures. At environment temperatures of -20°C, the system delaminates 2.5 mm thick ice layers with power input densities as low as 0.07 W/cm2 (0.5 W/in²). Wind tunnel icing tests were conducted to demonstrate the potential of the proposed ice protection technology under impact icing conditions. Continuous ultrasonic vibration prevented impact ice formation around the actuator location at an input power not exceeding 0.18 W/cm ² (1.2 W/in²). Ice shedding occurred on the isotropic plates at locations where transverse shear stresses were predicted to exceed the impact ice shear adhesion strength. Plate surface and leading edge ice shedding was observed as impact ice reached a critical thickness of approximately 1.2 mm on those areas.