Erosion Tolerant Passive Anti-icing Materials for UAM Rotor Blades

Weather-Tolerant Capability is considered essential in the expanding urban air mobility vehicle industry. Erosion effects of rain, dust, and sand on vehicle surfaces, especially rotor surfaces, have a considerable effect on operational and maintenance costs. Another crucial environmental condition that heavily impacts flight safety is ice accretion. This project addresses a novel erosion shield system incorporating ice-protective technology that can be applied directly to helicopter blades. The innovation is based on the concept of Super Elasticity in certain metals known as Shape Memory Alloys (or SMAs) that allow the material to elastically deform over 4% strain, making themvery durable and erosion resistant. The Phase I effort focused on the design of an SMA based erosion tape with natural durability qualities as well as the ability to change phase (strain) for anti-icing properties. Superior erosion resistance was demonstrated in the superelastic material Austenite phase. The material was also demonstrated to strain when activated by heat, and break the ice bond strength with a combination of surface strain and temperature, making this a very efficient electro-thermal de-ice mechanism. Its unique nature of high stress output rate and low power requirements is a promising material to meet the need for energy savings required for electric vertical take-off and landing (eVTOL) vehicles. Phase II will continue the development of an extremely efficient rotor blade de-icing actuator, with superior erosion resistance properties. Optimal actuator materials will be selected such that the SMA will self activate in the lower temp extremes, as well as be pulse activated electrically in a power assist mode, when the rotorcraft is in extreme icing environments. A final Proof of Concept demonstration will be perfromed at the Penn State AERTS Icing Faciity to evaluate SMA perfromance at representative temperature and cloud moisture (LWC) conditions. The proposed research supports NASA’s goal to develop “Weather-Tolerant Capability” technologies necessary for integrating next-generation Urban Air Mobility Vehicles into the National Airspace. Erosion effects of rain, dust, and sand on vehicle surfaces, especially the rotor surfaces, have a considerable effect on operational and maintenance costs. Another crucial environmental condition that heavily impacts flight safety is ice accretion. This proposal addresses a novel shape memory alloy (SMA) based erosion shield system with natural durability qualities as well as the ability to change phase (strain) for anti-icing properties. This innovation is possible due to the superelastic properties of SMA’s, making them extremely durable and erosion resistant. In addition, the highly conductive heating surface enables efficient heat transfer for anti-icing.  Its unique nature of high stress output rate and low power requirements is a promising material to meet the need for energy savings required for electric vertical take-off and landing vehicles. The overall objective is to develop an SMA rotorcraft erosion shield to work in icing as well as dust, sand, and rain erosion environments. SMA materials will be developed with unique properties needed for both superelasticity, as well as optimal heat/strain performance needed for deicing.  Both active and passive actuation modes will be evaluated.  SMA sheet materials will be fabricated for installation and test on a full-scale rotor blade.   Specific Phase II objectives include: Determine SMA alloy properties for desired erosion resistance and deicing performance. Through simulation and experiments, evaluate thermal and strain response of  SMA actuator to heat/shear the ice interface in direct tension or compression. Evaluate the SMA restraining mechanism reliability and dimensional stability. Demonstrate performance of erosion resistant SMA superelastic materials and compare to existing metal and other polymer coatings used on rotorcraft. Icing Tunnel POC Demonstration. Phase II deliverables will include a final demonstration on a representative UAM rotor blade over a range of environmental conditions at the Penn State AERTS Icing Faciity.

This proposal provides key technologies to support NASA’s  Advanced Air Mobility mission objective for reliable and safe operations of UAM vehicles during weather-related challenges. The market/application of these vehicles will be in urban and rural locations and be expected to have high use (life) in a broad range of weather conditions. An erosion shield with increased durability and built-in low-power ice protection capabilities gives it a significant market advantage over current rotor blade erosion systems. It is expected to have universal applications to new electric rotorcraft vehicles with limited available power. Other target applications include traditional helicopters and windmills.

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