Electrified aircraft development demands propulsion systems with higher power-density motors, greater battery capacity, and more efficient power converters. At Ceramics Expo 2019, Deputy Director of Research and Engineering at NASA’s Glenn Research Center Dr. Ajay Misra presented a wish-list of technology advancements and capabilities necessary to realize a sky filled with electrified aircraft. While progress has been encouraging, much remains to be done to improve materials and manufacturing processes.
Misra cited a McKinsey & Co. report predicting demand by 2030 for 500 million package deliveries per year by unmanned aerial systems in 15 major U.S. cities and 750 million passenger trips annually by autonomous urban air mobility platforms – many powered electrically. Even if this is overly optimistic, Airbus, Siemens, and others are investigating concepts for short-haul travel by regional aircraft powered by hybrid-electric and turbo-electric systems. Current systems don’t have the juice to provide this vision of the future.
Presenting a roadmap for the next 15 years, Misra says the industry will require megawatt power levels with more than 98% efficiency instead of the 200kW and 95% efficiency that are now state of the art on the X-57. New manufacturing processes and advanced materials will be needed to get there. Misra’s list of manufacturing opportunities includes solid-state batteries, solid-oxide fuel cells with better than 60% thermal efficiency, thermal interface materials, high-temperature superconductors, and insulation that can withstand the thermal and electric loads of high-voltage power transmission systems.
Some necessary items will include boron nitride nanosheet insulators a few atomic layers thick; and polymer-ceramic composite insulation with high-thermal, low-electrical conductivity.
Among Misra’s wants are superconducting motors with more than 15kW/kg power density and small-diameter magnesium diboride coils to reduce current loss. Additive manufacturing (AM) can potentially double motor power density by embedding wires in structures and incorporating cooling channels to lower mass.
High-power-density power converters will require magnets and capacitors with increased temperature capacity and better thermal management (heat sinks) with advanced topology to integrate these technologies into a small form factor.
Small, non-flammable solid-state batteries with graphite, silicon, and silicon-carbide composite anodes, and complex oxide anodes with liquid electrolytes are needed, too. Challenges remain, though, such as manufacturing microstructures with layers less than 30µm thick without defects and producing bipolar stacks that will retain mechanical and chemical integrity.
New materials for cables will be needed to transmit megawatts of high-voltage power (more than 2,000V for superconducting motors, for example) without melting or degrading.
Scalability of all these technologies adds to the work of bringing them from the lab to full-rate production.
Doubtless, some of our readers are already tackling these problems, and may have progress to report by Ceramics Expo 2020 in Cleveland, Ohio, May 5-6, 2020. – Eric