Airbus Evaluating Cryogenic Electric Propulsion For Commercial Aircraft

As Airbus evaluates liquid hydrogen as a possible route to zero-emission commercial aviation by the mid-2030s, it has begun a research program to explore the potential of cryogenically cooled electric propulsion for large civil aircraft.

The goal of the three-year Advanced Superconducting & Cryogenic Experimental Powertrain Demonstrator (Ascend) project is to determine through ground testing whether the technology has sufficient benefit to warrant flight demonstration in 2028.

“The objective is to demonstrate the potential and feasibility of cryogenic technology for electric propulsion,” said Ludovic Ybanez, Ascend project lead within the Airbus UpNext demonstrators unit. Cryogenic cooling can cut losses, reduce weight and increase efficiency in high-power electric systems.

“The question for us is how can we enable a high-power electric propulsion system for future aircraft, especially if we have liquid hydrogen onboard as a cold source?” Ybanez told the Emissions Free Transport Through Superconductivity virtual conference June 10.

“Airbus has launched a very ambitious program to assess and develop liquid hydrogen aircraft, either to burn hydrogen or to use hydrogen through fuel cells to generate electric power,” he said. “If we have liquid hydrogen onboard, how can we use this to improve the performance of the electrical system?”

There are two main options, Ybanez said. The first is to use cryogenic cooling to increase the performance of conventional electric systems, mainly by reducing losses, increasing current and reducing weight. “The second may be to use high-temperature superconducting technologies to push a breakthrough in propulsion, to dramatically reduce losses, reduce weight and increase efficiency at the aircraft level.” 

The first step was to assess the maturity of cryogenic technology in ground applications, particularly magnetic resonance imagers, particle accelerators and power transmission. The second step, Ybanez said, was to launch collaborative R&D projects with the main players in this technology, including the ASuMED superconducting motor demonstrator. The third step was to launch projects within Airbus to assess the feasibility of the overall system at the aircraft level.

“We think that some technologies are mature on the ground, like cables and current leads for cryogenic systems,” he said. A second family of technologies seems less mature, including superconducting electric motors and cold power electronics. 

“We saw some mature technologies, also potential at the technology level. The question now is can we adapt these technologies to aircraft requirements to give a strong recommendation on their use at the aircraft level to enable electric propulsion?”

At the component level, cryogenic and superconducting technologies can increase power density by a factor of 2-3, increase current and reduce voltage, improve power-train efficiency beyond 98% and enable new capabilities such as fault current limiters.

“The question is how can we assess the impact at the aircraft level? This is a difficult exercise,” Ybanez said. “The most favorable option would be to embed liquid hydrogen onboard. But what topology do we want to assess? What aircraft architecture would be interesting with these technologies?

Of the potential benefits, “the first two are probably game changers at the aircraft level,” he said. “The first is weight. It depends on the length of the cables, but we believe we can decrease weight by a factor of two to three depending on the topology.

“The second is voltage. Embedding high voltage into an aircraft is very difficult. If we can demonstrate we can reduce the losses, increase the current and reduce the voltage, we can increase the feasibility and interest in these technologies,” he said.

Where megawatt-scale propulsion systems using conventional electrics must operate at kilovolt levels to minimize currents and cable weight, Ascend is targeting 300-500 volts. “I hope we will be able to demonstrate 300 volts. That could be a game changer for electrification of aircraft,” Ybanez said. 

The goal of Ascend is to identify potential showstoppers and either evaluate how to overcome them or decide the technology is not mature enough for flight and stop the demonstration. “We need to integrate all the components and technology to be able to assess and confirm the potential,” he said.

Ascend will develop several “bricks” using ground technologies. First is a DC distribution network with cryogenically cooled current leads, 10-m-long superconducting cables and fault protectors. Second is a cold motor control unit with cryogenic power electronics. Third is the superconducting electric motor.

The 500-kW power train will use liquid hydrogen for cooling only, not as fuel. “For this first step we don’t want to use hydrogen directly, we just want to demonstrate we can master the technology to control temperature and be able to extract losses and show the potential at a system level.”

Testing of the demonstrator in Airbus’ E-Aircraft System house in Ottobrunn, Germany, is to be completed by the end of 2023. The results will be used to validate models of system bricks that then can be scaled from 100 kW to multi-megawatt power levels for use by Airbus in different aircraft studies.

If Phase 1 testing based on ground technologies is successful, Phase 2 from 2024 to mid-2025 would develop aircraft-specific technologies and the power train for a target aircraft. Phase 3 in 2026-28 would flight test the power train. “I really think this technology has a huge potential, and this is a very interesting opportunity to enable high-power electric flight,” Ybanez said.