Interview: ATI’s Mark Scully on innovations in aviation propulsion

As part of a series of articles exploring the propulsion technologies that will shape the future of key transport sectors The Engineer spoke to Mark Scully, head of technology, advanced systems & propulsion at the Aerospace Technology Institute about the innovations that will propel the aviation sector towards net zero.  

What propulsion innovations and technologies will help power your sector towards net zero?

The ATI’s focus on sustainability covers air vehicles, flight operations, manufacturing, ground operations, through-life support, and low-carbon-impact power sources.  Specifically, for propulsion we need to look at alternative energy/power sources to achieve the transition to net zero.

It is not a case of ‘one size fits all’. Technologies we are supporting include batteries for short range all-electric aircraft; liquid and gaseous hydrogen for short- and regional-range fuel cell-hybrid, gas turbine-hybrid or gas turbine powered aircraft; and drop-in sustainable alternative fuels derived from biomass-to-liquid or power-to-liquid approaches.

The priorities for future propulsion and power systems are to increase propulsive and energy efficiency, reduce emissions and reduce operational cost. That could come from configurations that include all-electric, series and parallel hybrid, geared turbofans (with options for variable pitch fans and/or hybridisation), and in the longer term the introduction of superconducting electric fan propulsors. It’s important we keep stimulating innovation across a range of configurations.

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Briefly describe some of your organisations own key activities in this area

The ATI is working closely with the sector on research initiatives to develop these future propulsion and power systems. Around half of the ATI’s R&T portfolio is focussed on future propulsion, including key demonstrator programmes. Examples of these are ACCEL – led by Rolls-Royce, with electric motor and controller manufacturer YASA and the aviation start- up Electroflight, a project to develop the world’s fastest all-electric aircraft; and ZeroAvia’s HyFlyer project – a research programme to develop a zero-emission powertrain solution based on hydrogen. The UK has a supply chain and an academic network that are both world class, and a key role of the ATI is to bring these together.

aviation propulsion
One project supported by ATI is Rolls-Royce’s ACCEL initiative, which is attempting to develop the world’s fastest electric aircraft

What are the key obstacles and challenges to developments in this area?

There are several technical challenges to delivering energy and power density to compete with conventional gas turbine propulsion systems which achieve power densities of around 10 kW/kg. The key building blocks for future propulsion systems are electrical machines, power electronics and fuel cells and current best-in-class power densities for each of these are of the order of 5 kW/kg and only 3 kW/kg for fuel cells. So further innovation will be required to deliver competitive future propulsion. In addition, a national network of research infrastructure is required to develop these future propulsion systems to represent sub-system, propulsion system and aircraft integration challenges in representative aerospace environments. The ATI is leading the sector to define the priorities for these new research infrastructure capabilities.

The key building blocks for future propulsion systems are electrical machines, power electronics and fuel cells

Ultimately, this is a global challenge that needs international cooperation. First movers will dictate the future direction, the standards and regulations, and so on. We want the UK to lead on this, and so it is important to support those who are innovating and leading the charge.

aviation propulsion
The ATI supported HyFlyer project recently saw the first flight of a commercial scale hydrogen-powered aircraft

What is your vision for the long term future of propulsion in your sector?

The ATI vision for propulsion focusses on three priority themes – these are the introduction of large ultra-high bypass ratio turbofan engines, all-electric battery and fuel-cell propulsion systems, and hybrid electric propulsion systems. These elements are set out in the ATI’s UK aerospace technology strategy, Accelerating Ambition, which has three overarching drivers on sustainability, mobility and competitiveness. The ATI’s strategic vision is further supported by the Future Flight Challenge, funded through the Industrial Strategy Challenge Fund (ISCF), which looks more widely at future air transport and services as a system of systems, new models of airspace management and anticipatory regulation, novel air vehicle demonstrators, ground infrastructure systems, new operating models for users and commercial operators of air services, and the engagement of critical regulatory authorities. Recently the ATI announced the launch of the FlyZero initiative, which will bring together 100 experts to kickstart work into zero emission aircraft technology in the UK. This will be delivered as a 12-month programme focusing on design challenges and market opportunities.

Mark Scully is head of technology, advanced systems & propulsion at the Aerospace Technology Institute.