The Engineer Q&A: Green skies ahead

Leading voices from across aviation share their thoughts on how the sector can decarbonise and what the future of air travel will look like.

Meet the panel

Mike Durham, Chief Technical Officer at Hybrid Air Vehicles

Riona Armesmith, Chief Technical Officer, Magnix

Dr Mark Bentall, Head of Technology Operations, Airbus

Sergey Kiselev, VP Europe, ZeroAvia

Describe your activity / key technology offering in this area and explain how it could be applied to low carbon flight?

RA: At Magnix, we are developing world leading electric propulsion systems for the commercial aviation market. We are agnostic of the power source or aircraft platform and our products are well suited to both retrofit of existing aircraft and to clean sheet aircraft designs.

SK: ZeroAvia is the leading innovator in zero emission propulsion for aviation, based at a growing facility at Cotswold Airport in Kemble and in Hollister, California. We are doing this by developing hydrogen-electric powertrains, which use low carbon hydrogen in a fuel cell system to generate electricity, which in turn is used to power aircraft without any emissions besides water vapour. While Sustainable Aviation Fuels (SAFs) are limited in availability and still generate harmful climate emissions, and current and expected battery technologies do not meet the weight-sensitive performance needs of aerospace, hydrogen-electric solutions are able to provide the energy density required to accelerate truly zero emission flight.

MB: At Airbus, our ambition is to put the first zero-emission aircraft into service by 2035. We strongly believe hydrogen propulsion will help us to deliver on this ambition, which is why we’re focusing our efforts on major technology development in this area. In addition, we’re committed to playing a leading role in the continued replacement of airline fleets with new fuel-efficient aircraft, as well as the increased use of SAF. Indeed, thanks to engine efficiencies and SAF, lower-carbon flying is already possible.

MD: Hybrid Air Vehicles Ltd is an innovative British aviation business offering one of the most exciting models of sustainable aviation in the world. Our new type of aircraft, Airlander will be able to deliver zero carbon aviation before 2030 and meet global challenges in mobility, logistics, and communications and surveillance.

Airlander is a new form of aviation, combining buoyant lift from helium with aerodynamic lift and vectored thrust. This creates significant efficiency over conventional aircraft and helicopters. It is designed to be low-carbon, efficient, and to operate from virtually any flat surface (including water) without the need for traditional transport infrastructure.

HAV's Airlander takes flight (Image: HAV)

Even with four combustion engines, Airlander 10 produces 75 per cent fewer emissions than other aircraft in a variety of roles. Work is currently ongoing with Collins Aerospace and the University of Nottingham to develop a 500kW electric motor suitable for Airlander. With this on board, a hybrid-electric Airlander will produce 90 per cent fewer emissions from 2025. An all-electric variant producing zero emissions will be available before the end of the decade.

What have you achieved so far?

SK: In September 2020, ZeroAvia successfully carried out the world’s first flight of a hydrogen-electric commercial-grade aircraft, with the hydrogen fuel cell being used in a flight of ZeroAvia’s 6-seat aircraft at Cranfield Airport. This was a part of HyFlyer I, a project supported by the ATI Programme and funded by Innovate UK, the Aerospace Technology Institute and the Department for Business, Energy and Industrial Strategy. This project saw ZeroAvia develop and integrate a full hydrogen-electric powertrain into a Piper Malibu aircraft, a model commonly used across the world.

At its Kemble site ZeroAvia is now actively developing HyFlyer II, also supported by the ATI Programme, which will scale up its zero emission technologies for a 19-seat Dornier 228 aircraft. The first milestone flights for this programme are expected in the coming months. Crucially, this will deliver a certified powertrain into commercial service by 2024, enabling regional flight operators to begin truly decarbonising their fleets for the first time.

MB: To accelerate hydrogen technology development, we recently launched our Zero-Emission Development Centres in Nantes and Bremen to build in-house expertise in cryogenic liquid hydrogen tanks, which will be essential to supply a future zero-emission aircraft with hydrogen as fuel. We’ll also launch ground testing on various hydrogen technology components in 2022. On SAF, we’re excited by progress on our 100 per cent SAF climate-impact projects. Preliminary results are very promising so far. Our objective is to achieve certification of 100 per cent SAF by 2030, and these projects will help us get there.

At Airbus, our ambition is to put the first zero-emission aircraft into service by 2035 Dr Mark Bentall, Head of Technology Operations, Airbus

MD: Hybrid Air Vehicles has spent nearly a decade developing Airlander in the UK through extensive R&D, establishing both civilian and defence applications. Unlike many of the low or zero emissions aircraft you see talked about, Airlander has flown as a full-scale prototype and is now ready for commercialisation and entry into service as a production aircraft. HAV also has clear interest from customers, including a number of deposit-paid reservations and aircraft covered by letters of intent.

A key moment for us this year was unveiling our mobility cabin interior concepts and city-to-city example routes, such as Liverpool to Belfast, Seattle to Vancouver, and Stockholm to Oslo. The great reaction from potential passengers, customers, and investors showcases that there is real appetite for alternatives that maintain our connections while reducing our footprint.

RA: In December 2019, operated by Harbour Air, we made the world’s first flight of an all-electric commercially-focused aircraft – the De Havilland “eBeaver” seaplane in Vancouver, Canada and we have been flying it with our 750HP electric propulsion unit (EPU) regularly ever since. Then in May of 2020, we started flying a magnified Cessna 208B Grand "eCaravan", the world’s biggest ever all-electric commercially focused aircraft. Towards the latter part of 2021 Magnix will power the Eviation Alice, a clean sheet design aircraft which has been developed to be electric from the ground up, as it takes its first flight with the next generation of our EPU technology.

Modified Cessna is the largest electric aircraft to take flight (Image: Magnix)

Looking forwards, Magnix will provide electric propulsion units for the world’s largest commercial electric aircraft, a hydrogen fuel cell powered retrofit of a De Havilland Canada DHC8-Q300, in partnership with Universal Hydrogen. From a certification perspective, we are today the only company in the world to have FAA CFR33 Special Conditions formally published for the certification of electric propulsion. This puts us on a roadmap for FAA certification in 2023.

What do you see as the key challenges/obstacles to decarbonising aviation and how are your working to overcome these challenges?

MB: The aviation industry is a global sector: we cannot move forward alone. This is why our top priority at Airbus is to collaborate closely with a network of partners to push the development of the various technologies and build the associated infrastructure to support their introduction and scale-up. We also need sustained investment in new-generation, cleaner technologies, including hybrid-electric engines, alternative fuels, and hydrogen-propulsion systems. This is vital to accelerate our route to net-zero, which will benefit airlines, passengers and societies worldwide.

RA: I believe the aerospace industry is at a pivotal point of transformation and not just from a viewpoint of decarbonisation. High density energy storage that is not derived from carbon is clearly one fundamental aspect of decarbonising aviation but it is not the only one. Technologies such as electric propulsion - which we have proven at Magnix - will enable a radical shift of the industry, where passengers are able to fly on smaller aircraft, on shorter point-to-point trips from local airfields because it is quieter, cleaner and more economically viable to do so. To decarbonise the industry, we will have to accept that the current model of flying large aircraft, long distances with many seats unfilled cannot be the model of the future. Therefore, I believe the challenge in changing mindsets and business models is greater than any technological challenge required to decarbonise aviation.

SK: Although hydrogen-electric solutions are well suited to the challenge of decarbonising flight, storing hydrogen on-board an aircraft to power longer distance flights requires innovative storage solutions that differ from the technologies and approaches used for existing jet fuels. As the distances hydrogen-electric powertrains are capable of flying increases, this includes the ability to store hydrogen as liquid hydrogen, which requires it to be cooled and maintained at very low temperatures. ZeroAvia is working with highly innovative companies to engineer the solutions to this challenge, including expertise from outside of the aerospace sector.

decarbonise aviation
Zeroavia’s Piper M-class six-seater aircraft to be used in HyFlyer flight tests (credit ZeroAvia)

Additionally, when we begin to deliver hydrogen-electric powertrains into service, operators will need to be able to fuel their aircraft at airports. Alongside our 6-seat aircraft, ZeroAvia also demonstrated the Hydrogen Airport Refuelling Ecosystem, a microcosm of the infrastructure needed, which included on-site electrolytic production of hydrogen, and mobile storage and aircraft fuelling. As a result of funding by an innovative Department for Transport programme in the UK, ZeroAvia is also investigating ‘LHARE’, which will do the same for liquid hydrogen.

MD: One of the biggest challenges to decarbonising aviation is the technology itself. Looking across the technologies we are familiar with today, it’s clear that the journey to achieving zero emissions is a long one. There are, however, many new technologies that are in varying stages of readiness, including Airlander. We believe that a variety of technologies will be necessary to decarbonise the whole sector and there are some quick wins available.

Take domestic routes, for example. Most domestic routes are served by aircraft designed for much longer routes, therefore utilising these aircraft inefficiently. Domestic routes are typically shorter range and lower passenger volume – which is ideally suited to new aircraft types like Airlander. Airlander can carry up to 100 passengers on routes up to 400km with a fraction of the emissions of other alternatives.

Airlander will be able to deliver zero carbon aviation before 2030 Mike Durham, Chief Technical Officer at Hybrid Air Vehicles

For longer haul routes, the industry will need to look to technologies like SAFs while we tackle the complex engineering challenges of making long-haul, zero-emissions flight possible. What’s important is that we can’t simply take one approach or another – we have to consider every available option to decarbonise aviation. Airlander has an important role to play and can start reducing emissions much more quickly than other technologies.

What does the future of low carbon flight look like?

MD: The future of aviation will be defined by different solutions that meet different needs and unlock different opportunities. Airlander is one part of that future ecosystem and there will be others – one size definitely doesn’t fit all.

SK: As a result of the fundamental energy density advantages of using low carbon hydrogen for hydrogen-electric propulsion, ZeroAvia believes this is the only viable, scalable way to tackle comprehensively aviation’s growing climate impacts. We plan to develop progressively larger powertrains that decarbonise greater proportions of the global fleet, meaning more and more flights will be truly zero emission. Other solutions such as SAFs will act as useful transitional technologies, particularly for the largest long-haul aircraft.

MB: At Airbus, we have been very clear there is no “silver-bullet” solution to decarbonising aviation. A mix of new energy pathways and fuels, including hydrogen and SAF, will be vital to achieving disruptive CO₂ reductions. In practice, SAF is likely to remain the best low-carbon solution for longer-haul travel, while hydrogen and electrification will likely be interesting for shorter-haul travel.

decarbonise aviation
Airbus ZEROe blended wingbody concept (Image: Airbus)

RA: I don’t believe there is a ‘one size fits all’ solution to low carbon flight because I believe the variety of air vehicles in future will be much greater than currently exists today. However, I am confident that increased electrification of aviation propulsion is inevitable, irrespective of whether the energy source is batteries, fuel cells, hydrogen or SAF.