By Bjorn Fehrm
November 29, 2017, © Leeham Co.: Airbus, Rolls-Royce and Siemens yesterday announced they will fly a hybrid-electric demonstrator by 2020, E-Fan X (Figure 1).
The aircraft, a BAe 146 four engine regional jet, will have one if its turbofans replaced by a Rolls-Royce/Siemens electric fan propulsor. The demonstrator is part of a technology program exploring the challenges around electric flight.
The E-Fan X program will fly a electric propulsor that is 30 times larger than Airbus’ first demonstrator, the E-Fan, which crossed the English channel in 2015 (Figure 2). The program brings the electric flight components into the domain where they can fit a regional airliner.
But it’s early days, showed by Airbus’ answer when I poked a bit deeper into the battery technology:
We have not yet designed the amount of energy storage we will put on board. There are many challenges which we expect to encounter during this project. Some of the key challenges we have are around the electromagnetic interference generated by a 2MW system, the end-to-end thermal management required on the electric motor, power electronics, the generator/gas turbine combination, and, of course, some electrical characteristics like corona effect and partial discharge.
The demonstrator programme will be investigating the best solutions, sometimes testing them in advance on the ground, and ultimately proving them in flight. The aim of the E-FAN X demonstrator is to pull the technology and pull the solutions which in some cases we don’t already have today. This is a change in the way we do research at Airbus and we expect it to accelerate technology development compared to the traditional approach.
This is refreshing. Instead of working on perfecting all these challenges in the labs, the trio puts together a flying demonstrator to try things out and learn.
The platform for the demonstrator is the only four-engine regional jet, the BAe 146. The starboard inboard 7klbf thrust Lycoming ALF502 turbofan is replaced with a 7klbf thrust Rolls-Royce AE3007 turbofan/nacelle, Figure 3.
The inboard AE3007 powerplant has its core replaced with a 2MW Siemens electric motor + inverter. Siemens also designs the 3kV DC power distribution system.
In the back of the fuselage, Rolls-Royce installs the core of the AE3007, now as the turboshaft AE2100. The Liberty T406 for the tilt-rotor V22 Osprey is the cores’ origin. The AE2100 turboshaft (Advanced Hercules) and AE3007 turbofan (Citation X, ERJ-145) are derivatives from the Osprey core. The air inlet for the AE2100 turboshaft on the demonstrator is visible in Figure 1 behind the wing.
The AE2100 is mated to a Rolls-Royce-designed 2.5MW generator with control electronics. This feeds the 3kV DC distribution system through its AC/DC converter.
Complementing the system is an Airbus supplied battery system. It occupies the forward and aft cargo holds and weighs two tonnes. It can deliver 2MW power by means of its DC/DC converter to the distribution network/propulsor; how long is not finally decided (and by it its kWh energy sizing).
The whole system is controlled and supervised by an Airbus-supplied E-supervisor system and cockpit monitors.
The Siemens motor and Rolls-Royce generator are non-superconducting (non-cryogenically cooled) designs. This means the power chain “AE2100 turbine to AE3007 fan” has efficiency losses above 15%.
There are enough challenges to master for such a demonstrator before chasing the last percent of efficiency losses would be our conclusion. Here are the challenges the partners have:
Finally, EASA, the European airworthiness authority, will take part in the program to develop certification criteria for electric airliners. Without adapted certification rules, electric flight will not take-off.
Note: For those interested in the technology and challenges for electric aircraft, read our 14 part series in my Friday Corners starting June 30. To find all parts, search for “electric aircraft” in our search box.