The development of electric aircraft is evolving rapidly, with over 300 companies worldwide reportedly developing aircraft.   And orders to purchase even ~ 100 electric aircraft have already been placed by well known companies, such as Cessna and United; even though many aircraft have not been certified for flight yet.  Electric propulsion has many well-known benefits including ~ 90-95% efficient drivetrains for battery-electric, ~ 60-70% efficient for fuel-cells, > 10x lower maintenance costs, ~3x lower purchase cost, and potential zero-emission using hydrogen fuel cells.  Also the structural design of aircraft including wing and body shapes can be changed significantly, and there is potential to develop new distance-height flight profiles, since the profiles do not have to be optimized for turbine engine specific propoerties.  The main drawback is a reduction of range with battery-electric; however designs for 4-10 passenger aircraft are reported capable of achieving 450 – 650 miles range, and fuel-cells and larger aircraft have existing/ potential for larger ranges > 1,000 miles; which can satisfy > 80-90% of existing markets. 

Some of the new challenges or electric aircraft, come especially from scaling up the electric drivetrains to ~100 MW or higher power levels, which also increases the size and heat loads of the electric power machines and distribution system.   The heat loads will increase exponentially from Ohm’s law Q_loss = R*I² as the aircraft current levels increase linearly as the aircraft propulsion power increases: P = I*V, and V ≤ ± 270 Volts is required to maintain safety from Corona discharge which occurs for V > 270 Volts.   And it is not a trivial matter to manage the very large heat loads that would occur, and also at low Delta temperatures for cooling.   The power density of existing electric drivetrains is typically ~ 1 kW/kg, and the ARPA-E ASCEND has determined the power density could increase only to ~ 2 kW/kg improving existing technology.  And it is needed to increase the density up to ~ 10 kW/kg to achieve most goals to reduce the electric propulsion.  

Superconducting power transmission and cryogenic machines have unique properties that can help overcome the challenges to achieve highest power density and energy efficiency.  Advantages include no ohmic losses, and utilizing ultra-small/light conductors which can enable practical solutions for lower transmission and system voltages.  Cryogenic machines utilizing superconducting wire have very high efficiency typically > 99.9% including cryo-cooling losses, and can operate at ultra-high current densities > 1000 A/mm².   This presentation provides the design and scaling of an electric power distribution system for 40-MW-class power, and compares different wire technologies including cryogenic metals, superconductors, and ‘conventional’ metals at ambient temperatures.   To effectively study how to optimize the weight and efficiency of electric aircraft designs, the mass and heat loss scaling laws of the components of the electric drivetrain are required for varying power/voltage /ampacity levels (0-20 kA) and power-wire distribution architectures, which is a focus of this work.  Electric power system components studied thus far include metal conductors (Cu-clad-Al (CCA), Al 99.999% ‘hyperconductor’), busbars, current leads, metal/superconducting T-joints, high temperature superconducting (HTS) Y,RE-Ba-Cu-O cables, and cryoflex tubing.   A weight and efficiency analysis of a 40 MW power drivetrain system will be provided, and material options for the power transmission cable will be compared.

Acknowledgments. This research was funded by the NASA University Learning Initiative (ULI) #80NSSC19M0125, the Air Force Research Laboratory/Aerospace Systems Directorate, and AFOSR LRIR #18RQCOR100, program manager Dr. Ken Goretta.

Keywords: electric aircraft, electric power distribution system, cryogenic, superconductivity