Aerospace Electrification: what are the challenges and opportunities?

The civil aviation sector is one of the fastest growing sources of carbon emissions as ever growing numbers of people travel by plane, and aircraft manufacturers are challenged to integrate new technologies at the pace required. On 10 December, the world’s first fully electric commercial aircraft flew for 15 minutes along the Fraser River near Vancouver international airport.

Aerospace manufacturers could benefit from the automotive industry’s established track record in hybrid and electric vehicles, and more advanced expertise in energy management, technology integration and virtual product development. With experience working for customers in the aerospace sector including component manufacturing, AS9100D certification, and decades developing, designing and integrating technology for all other transport sectors, Ricardo is well placed to advise the aerospace industry. Here Ricardo’s experts Julian Dunn, Cedric Rouaud and Huntly Thomas discuss the top five challenges and opportunities around a hybrid and electric approach for aerospace OEMs.

What are the main challenges?

"Air travel creates a particularly large carbon footprint, and reducing carbon dioxide is a big challenge for the aviation industry. Taking a hybrid or electric approach to aircraft poses specific technical challenges. Firstly, batteries are bigger and heavier than fuel. The energy density of aviation fuel is typically 43-48 MJ/kg, or approximately 40MJ/kg if fuel tanks and fuel handling are included. By comparison, in state of the art battery technology today, the energy density is around 1 – 1.1 MJ/kg with a 1.2-1.3MJ/kg roadmap anticipated for around 2025.

"Because of the energy required to move the aircraft over such long distances, given its size and weight, a lot of batteries are needed in each aircraft. With hydrocarbon fuels, the aircraft weight, and therefore the energy required, reduces as the fuel is consumed during the flight, whereas with electric vehicles, an aircraft has to carry the full weight of the battery for the whole flight.

"Thirdly, the aviation industry takes safety incredibly seriously. Given concerns about safety, particularly in the case of a thermal event in a battery pack, the safety standards for batteries in aircraft are even more stringent than for passenger cars.

"Fourthly, electrical components are not cooled at the same temperatures: a battery requires low temperatures whereas the electric motor and power electronics require mild temperatures. This is different from engines cooled at higher temperatures."

What progress has the aviation industry made in electrification so far?

"Two different approaches towards electrification have emerged. The first is the electrification of aircraft and carrying passengers in the usual way. An example of this is the Easyjet electric passenger jets which are expected to fly on some of the airline operator’s short-haul routes by 2027.

"The second is aircraft capable of vertical take off and landing, like the Airbus Vahana, which could be used to operate as ‘air taxis’ taking passengers on very short routes from a city to a nearby airport, through air quality controlled zones, such as from the Congestion Zone in Central London to Heathrow airport."

What technologies and expertise from the automotive industry can be successfully applied by aircraft manufacturers?

"There are six key technology applications:

• Optimising designs for low mass
• Thermal management for battery, electric motors and power electronics– for a battery, the conventional method is to air cool, but Ricardo proposes lightweight cooling solutions for cells and bus bars using advanced methods. For electric motor and power electronics, they are liquid cooled conventionally but Ricardo proposes high performance cooling methods which cool heat sources directly - using our experience in automotive research projects such as H2020 Ecochamps - and dielectric fluid cooling of the power circuit board and chips directly. The high performance cooling method is lightweight and has lower noise, vibration and harshness (NVH) than the conventional air cooling method using a large fan and blower
• Thermal design analysis tools for developing safe battery packs
• Advanced cell chemistry - to enable the selection of the right batteries for aircraft, not just bringing over batteries from the automotive sector
• Increasing the specific power of electrical components while still enabling cooling within temperature limits
• Development of cooling circuit architectures that are not common in conventional planes - coolant flowrate balancing, advanced control method for coolant pumps, valves and fans to minimise energy consumption"

What testing or safety cases are required?

"The aviation industry takes safety incredibly seriously, and given concerns about safety, particularly in the case of a thermal event, the safety standards for batteries in aircraft are even more stringent than for passenger cars. For aircraft, there are thermo-hydraulic functional tests with thermal surveys, heat balances, flowrate balances using thermocouples, pressure sensors, and flowrate meters. Using cell pad heaters, thermal runaway tests are triggered in one cell level or up to three cells being triggered at same time to assess the time it would take for a fire to start and then be contained within the battery enclosure."

What benefits could aerospace manufacturers gain from working with Ricardo?

"We have identified seven key benefits:

• Established track record in hybrid and electric vehicles – Ricardo has decades of experience integrating new technologies, garnered across the transport sector - automotive, commercial vehicles, off-highway, marine, rail, motorsport and motorcycle industries – in all regions globally, and this enables Ricardo to facilitate rapid progress for customers. In particular, Ricardo acts as a trusted technical partner for customers: expertise in hybrid and electric vehicles with capability across a whole range of propulsion technologies means that customers are receiving expert guidance in optimal technologies and solutions for their particular needs
• A systems engineering approach to hybrid and electric vehicles – Ricardo’s systems engineering approach comprises a number of technologies - including propulsion systems, energy storage, thermal management and virtual product development. We consider these technologies holistically for customer requirements including their challenge to respond to climate change, legislative strategy, end-customer expectations OEM product plans, maximise efficiency and drive down costs and then cascade the technologies based on functions and attributes to create an optimised solution.
• An example of this is the cooling system. We take an holistic approach to take into account all cooling requirements and also heating requirements (cold ambient at ground level but also in the air). Thanks to a system engineering approach, we can take into account all requirements and cascade them into targets for each subsystem In order to reduce the complexity and number of cooling systems and pumps, valves, fans, we use extensively thermal models and synergy approach. Coupling cooling circuits is possible during different operating conditions. It will enable reusing heat from one component to another but also store heat into components and cooling circuit for future use. The aim is to reduce the requirement for additional heat exchangers to even electrical heating sources.
• Driving cost out of electrification for manufacturers - Ricardo is a world-renowned expert in virtual product development, leveraging its proprietary software, enabling reduced testing and prototyping, without increasing risk, and accelerated product development, which would bring aircraft to market sooner.
  • Virtual product development, calibration and testing would enable aircraft manufacturers to be more agile and faster to market, while still maintaining the highest safety standards
  • Using a model based development approach and Model Predictive Control reduces time for control and validation development of the pump valves fans used to regulate temperatures
  • Through virtual engineering, we deliver more efficient automated processes, more accurate predictive analysis and real-time functionality, accelerated development timelines, and reduced risk through use of a digital twin as a predictive virtual physical model driving cost-savings throughout the entire development process
• Total cost of ownership – just as in the commercial vehicle sector where fleet costs are of paramount importance, electrification of a fleet of aircraft would cut fuel costs: one of the most significant costs for airline operators
• Lightweight inverters and emotors – Ricardo can deliver an integrated, optimised whole system
• Better packaging of the component and cooling methods
• Benefits for manufacturers and airline operators – if an airline operator can purchase electric aircraft from a manufacturer, it will enable them to operate different routes: for example, in low emission zones"