Aircraft electrification: developing a strategy to facilitate greener air travel
Thu 18 July 2019 – The electrification of aircraft, or more electric aircraft, has been an ongoing research and development topic for the past few decades with focus on the electrification of non-propulsive systems of existing and near-future aircraft platforms. These include actuation systems, cabin pressurisation and air conditioning, wing de-icing, electric ground taxiing and electric power generation. Whilst ongoing, much is being developed to make these systems more reliable and lighter in weight. However, in the last few years there has been an acceleration of work into electrification of propulsion, writes Chris Gerada. This has been informed by advancements in electrification technologies such as automotive demonstrating technology feasibility, a greater realisation by stakeholders that electrification of propulsion is a fundamental ingredient in meeting future aviation emission targets and demand for alternative mobility modes.
Electrification of propulsion will impact aircraft platforms in the existing market as well as open opportunities for new platforms in new markets. Electrification of existing platforms is mainly driven by the need for reduced emissions. The technical challenges in doing this range from evolutionary to disruptive, depending on the level of powers and voltages needed.
A regional aircraft might be looking at powers in the megawatt (MW) range and a large aircraft in the tens of MWs. Achieving these requires overcoming significant technical challenges. Many key experts are currently looking into ways of improving current achievable power densities, efficiency and reliability properties.
The other benefit of the electrification of propulsion is greater design freedom brought about by the ability to distribute propulsors across the aircraft. As a result of this new development, we are seeing new aircraft design concepts for personal mobility and cargo, such as autonomous electric vertical take-off and landing (eVTOL) vehicles, to compete with taxis and other urban ground transportation methods.
Small platforms, such as those described above, have the advantage that the technology is relatively mature compared to high power electrical systems because it is translatable from automotive and existing aircraft electrification technologies. This has seen a myriad of technologically advanced concepts. Whilst there is much improvement to be made from the technological aspect, the key barriers to successful deployment are regulations, airspace management, public perception and successful business models to make them viable.
However, aircraft electrification, together with autonomy, has the potential to improve existing supply chains and create new aerospace market segments and supply chains. This is already evident from the significant R&D investment and activities from the more traditional aircraft industry, from other transportation sectors, especially automotive, and from the range of other mobility-service providers and start-ups.
From a technical development perspective there are significant challenges to develop new technologies, new manufacturing processes, establish new supply chains and new standards. These go hand-in-hand with challenges for testing and certification – there is a lack of infrastructure and facilities to test and demonstrate key electrical propulsion components, sub-systems and their integration into larger systems, especially at high power and voltage levels.
A number of focused and often proprietary facilities have and are being developed. An example is the test bench developed by Safran for eVTOL. Airbus’ E-Aircraft Systems Test House will offer the capability to test MW-level systems and Collins Aerospace Systems’ The Grid will also aim for MW-level power test systems, with Project 804 (hybridisation of a regional turboprop) being one of its first platforms to test.
The University of Nottingham is opening its Power Electronics and Machines Centre in 2020 to test and develop MW-class electrical machines and power electronics. The unique facility will be one of the first non-proprietary platforms able to support the development and testing of electrical machines and power electronics systems for all-electric and hybrid electric aircraft platforms. The UK Aerospace Research Consortium (UK-ARC) is also looking at establishing open, distributed test and development facilities capable of serving the needs of the aerospace industry in this new era of electrified aerospace.
There are technical challenges with eVTOLs but compared to larger aircraft platforms, the main bottlenecks for widespread adoption are regulatory, public perception and business challenges for this market segment. Success and predicted volumes are heavily reliant on investment by governments and city authorities in supporting regulatory frameworks as well as ground infrastructure and compatible mobility models.
These are, however, a clear disruptive technology to current helicopter developers and their supply chains. Many parallels can be drawn to the automotive sector. It is likely that the cargo segment of the market will be a first adopter, which will also help support perception with respect to the safety of these platforms.
For larger propulsive powers the technical challenges are more significant. They require electrical propulsion drive components that operate at significantly higher power densities and efficiencies compared to existing technologies and able to operate within high voltage distribution networks. New concepts for thermal management and aircraft integration are also required. Apart from the technological challenges, the skills pipeline is critical, especially in an environment where there is significant co-current demands on talent from the automotive industry.
In early July, the University of Nottingham’s Institute for Aerospace Technology ran an industry workshop on Solutions for Aircraft Electrification Leadership (SAEL), which aimed at developing a strategy for future electrified aircraft. The first of its kind, the two-day workshop brought together stakeholders from across the globe to collectively understand the key challenges, requirements and potential solutions for future aircraft electrification.
Around 30 experts from across the aviation sector attended including large, regional and small aircraft manufacturers, system integrators, engine manufacturers, electrical component and systems suppliers, propeller manufacturers, regulatory and certification bodies, technology institutes and universities. Workshop delegates came from the UK, Europe, USA and Japan and some of the key reflections are summarised below.
Firstly, some context for the discussions. Air travel is rapidly coming under the spotlight for its pollution footprint, with an airline making the top 10 list of Europe’s largest carbon emitters for the first time. The growth projections of passenger numbers mainly from emerging economies and the relatively slow progress towards electrification compared to other transport sectors have created a sense of determination within the aviation sector to decarbonise air travel.
Objectives from Europe’s Flightpath 2050, in line with the Paris Climate Agreement, are for safer, cleaner, quieter aviation. In order to achieve this, there is an urgency to transition from old to new technology, a move that will require overcoming significant hurdles, both technological and societal. From a technological perspective there are many aspects that require fundamental research, notably the development of electrical power systems which can operate at kilovolt levels; electrical machines and power converters capable of delivering megawatts at a fraction of the weight of state-of-the-art technologies; and batteries and alternative fuels that can store more energy.
From a societal point of view there is the question of safety and reliability. Existing aviation technology is mature and is consequently very reliable and safe due to the years of refinement it has undergone. Moving to new modes of aviation would require transition to emerging technologies that would not have the same levels of reliability and safety if they are to be deployed in a timely fashion to meet emission targets.
The objective of the SAEL workshop was to begin to unpick some of these challenges and to work towards identifying roadmaps to tackle and ultimately overcome these barriers. The workshop delegates were presented with a scenario in which they were required to work together to identify the steps required to electrify a 160-passenger aircraft for a journey from London to Paris. Undertaking this exercise immediately brought to the fore the necessity for close collaboration between all stakeholders.
During the exercise the major challenges were explored and strategies developed for how to tackle aspects such as energy storage and alternative fuels; energy conversion and distribution at high voltage; the nature of the infrastructure needed for aircraft electrification; overcoming current weight challenges in hybrid and all-electric propulsion (existing technologies are too heavy); and the significant technological hurdle of thermal management in electric aircraft, i.e. how to remove heat from electrical components and dispel it elsewhere.
Discussions then moved on to how future aircraft systems would develop their supply chains and the role of the safety and certification authorities in enabling aircraft electrification. The final part of the workshop focused on societal acceptance of electrified aviation and the necessity for public-private partnerships in order to achieve this. We concluded with the programming of regular meetings to push forward with the electrification agenda, establishing a roadmap for prioritisation of development and to act as a catalyst to lobby government and industrial bodies for critical research funding.
We are excited about the next stage of development and the opportunities it will create. As a leader on the development of electrified technologies for future aircraft platforms, the University of Nottingham is ideally placed to play its part. It has the highest level of participation in the flagship EU Clean Sky 2 aviation research programme of any other university involved, and is currently researching key underpinning technologies and developing technology demonstrators with key industrial players in the field.
The University recognises the capability, importance and challenges in this, and has prioritised – as well as investing in – the Propulsion Futures Beacon of Excellence, a multi-million pound flagship programme to develop core technologies for electrified aircraft propulsion.
Chris Gerada is Professor of Electrical Machines and Associate Pro-Vice-Chancellor (Industrial Strategy, Business Engagement and Impact) at the University of Nottingham, UK.