If you want to understand how electric power fits into the future of aviation, pay close attention to the progress of the E-Fan X, the hybrid-electric demonstrator launched by Airbus, Rolls-Royce and Siemens.
The E-Fan X replaces one of the four engines on the BAe 146 regional jet with a 2MW electric motor driven by an R-R AE2100 turboprop engine, with back-up battery power. It shares the E-Fan brand with Airbus-Siemens collaborations on an all-electric series of two- and four-seat aircraft, but little else.
The ambition of the E-Fan X is to introduce and experiment with a package of radical innovations that could, if they work, make hybrid-electric power a feasible alternative to a gas turbine alone for propulsion requirements significantly higher than its own 2MW (2,680hp)-class motor.
In that way, the E-Fan X is a more reliable guide to the future viability of electric power than, for example, air taxis, where airspace restrictions are the main barrier.
To challenge the gas turbine as the propulsion source for large aircraft, hybrid-electric systems face an entirely different set of technological challenges, including several so far unexplored in flight.
The gas turbine engine still seems an unlikely candidate for technological disruption. Some 80 years after engineers applied this machine to aviation, it remains among the most efficient means of practically producing energy for commercial use.
Jet-powered aircraft today typically use a gas turbine to directly drive a thrust-producing fan. Hybrid-electric aircraft designers propose to insert two more steps into the process, with a gas turbine driving a generator that powers a motor that drives a fan thruster. Those two extra steps add complexity and weight, the latter in particular remaining an aviation no-no.
There are more barriers for hybrid-electric aircraft to overcome. A 10MW electric motor needed to propel a large aircraft would overwhelm existing systems used to manage waste heat. It would also require high-voltage power lines – such as the E-Fan X’s 3,000V cables – that must be shielded from the Corona effect, in which the air around high-voltage lines at high altitudes turns into a conductive plasma and creates a severe risk of dangerous short circuits.
But that is, of course, the point of experimental aircraft. By launching the E-Fan X, Airbus, R-R and Siemens are now at the forefront of this fascinating new field of research.