At Airbus, we’re building the future of flight and we see electrification as being a key driver of this. We’ve identified key trends, opportunities, and challenges in bringing all electric and hybrid propulsion systems to aerospace.
Some of the key technologies in electric propulsion systems, such as electric machines (motors, generators), power electronics (converters, inverters, rectifiers), and battery systems, have seen their energy density, power density and recurring cost improve significantly over the past decade.
For example, just five years ago the lithium-ion batteries cost 600 $/kW-hr but today they cost 200 $/kW-hr and the electric motors had a power density of 2-3 kW/kg but we are now capable of 5-10 kW/kg with existing technology.
We believe these trends are set to continue as a result of growing cross-industry investment in electric technologies and targeted work that Airbus is doing with key partners, notably Siemens. Even using today’s technology, it is possible to foresee that batteries, which currently have an energy density of around 250 W-hr/kg, will improve over the next decade to around 1500 W-hr/kg.
With so much global investment going into battery technologies, it is likely that we will see some groundbreaking advances over the next 10-15 years.
Radically rethinking design
For Airbus, the pace of development in this area is truly exciting because it allows us to radically rethink the way we look at and design air vehicles.
The fact that electric motors are less costly and less heavy means they are potentially much easier to integrate into an aircraft, whether that is a completely new design or an older design that could now realise its potential.
For instance, it is much easier to hinge an electric cable than a rigid fuel pipe — along with the fact that from electromagnetic point of view an electric motor doesn’t care which orientation it is in — means tilt-wing VTOL aircraft start to become more interesting.
These aircraft types can have a similar take-off and landing performance to a helicopter but, because of the improved ratio between lift and drag during cruise, they can have a cruise speed and range equivalent to a fixed wing aircraft.
On larger commercial aircraft, boundary layer ingestion at the rear of the aircraft in order to reduce drag may start to look interesting if an electric motor is used instead of a gas turbine.
Additionally, distributed propulsion — where many electric propulsors are installed along the wing — could pave the way for the elimination of the vertical tail plane, with yaw control on the aircraft instead provided through differential thrust even in failure conditions.
Electric motors are also much quieter than their gas turbine or internal combustion engine counterparts. This could open the way for VTOL vehicles to be more integrated into Airbus’s urban air mobility solutions and possibly allow large commercial aircraft to extend their operations into the night.
Key current challenges
So the technology trends are promising in terms of how we think they will change the way we fly but there is still work to do.
For example, an aircraft’s capacity to conduct electricity is a vital property for electric propulsion but it gives us two interesting challenges with conflicting solutions.
The first is around electromagnetic interference, which occurs when the power in one cable causes interference in another cable or other equipment through induction, electrostatic coupling, or conduction. This is already a serious consideration on an aircraft, with rigorous design and installation methods to eliminate interference.
Two of the most common methods to solve this are segregation and shielding, which work well when in the range of hundreds of kilowatts. For the tens of megawatt range required for commercial aviation, however, lighter weight and lower cost solutions are needed and, at Airbus, a large amount of our research effort is focused on finding answers to this challenge — which is very specific to aerospace where there are such high power requirements in a single vehicle.
This is not, however, the only challenge related to high power in cables. Copper cables are approximately 99% efficient, which looks great because it is so close to 100%. However, once 20 megawatts is put through a cable, even with such high efficiency, about 200 kilowatts of heat comes off it — that’s equivalent to the power needed to heat 20 poorly insulated houses on a cold winter’s day.
Airbus is looking at innovative ways to use this heat; maybe, for instance, for the anti-ice function on the wing and engine nacelles, or for boundary layer heating that may reduce friction drag. It is, however, far from straight-forward. Also, to reuse the energy, we need to find ways to shield the cables and avoid the electromagnetic interference issues, while at the same time getting the heat to the places needed without shielding.
These kind of challenges highlight the need to think holistically about the way we design the entire aircraft and so solve some critical and conflicting requirements. To this end, we’re looking for the best and brightest to join our collaborative teams to help make the future of flight a reality. If you think that might be you, find out more about working with us.