High-temperature superconducting (HTS) machines could enable development of all-electric aircraft with zero emissions, concludes a five-year study supported by NASA Glenn Research Center. Such an aircraft could use liquid hydrogen for cryogenic cooling and power generation and superconducting motors for propulsion and actuation.

In one candidate architecture, a cryogenically cooled HTS motor would replace the gas-turbine core of a high-bypass turbofan, producing an electrically driven ducted fan. The electrical power would be produced from the hydrogen through fuel cells or by burning it an high-speed turbogenerator. The aircraft's hydraulic system would be replaced by a hydrogen distribution scheme because superconducting linear motors would be used as power-by-wire actuators.

Using the conventional propulsion and electrical systems of a Boeing 737-200 for comparison, the paper study found that the heavier weight of all-electric powerplants was offset by reduced fuel needs due to greater efficiency. "The overall weight of the [propulsion] system...represents an increase of 60% compared to the original engine," says the study's authors, based at NASA Glenn, Georgia Institute of Technology and the joint Florida Agricultural and Mechanical University/Florida State University college of engineering.

Liquefied at the airport, the hydrogen would cool the superconducting motors driving the ducted fans to their -253e_SDgrC (-423e_SDgrF) operating temperature. The hydrogen would then flow on to cool the aircraft's power electronics and other sources of heat, eventually turning to a gaseous form and being burned in the turbogenerator's combustion chamber.

Glenn has also been developing non-superconducting cryogenic motors, which only need to be cooled to -196e_SDgrC, that could drive a ducted fan. As in the HTS study, these use hydrogen fuel that is warmed by acting as a sink for waste heat.

Read the full report on the Institute of Physics website

Source: Flight International