In a recent article I shared my thoughts about decarbonising General Aviation (GA) under the heading of “Futurology”, it was a medium-term prediction about the introduction of electrification to light aircraft, but it turns out that the future has already started to arrive in full force.
Shine Bright Like a Diamond
In August (2023), Diamond Aircraft successfully tested a fully-electric variant of their popular DA-40 single-engined propeller driven light aircraft, first announced in 2021.
Diamond’s fossil-fuel-powered Diamond Star and twin-engined Twin Star aircraft have dragged GA into the 21st century, with advanced composite material construction, comfortable glass cockpits and a sleek aerodynamic design which reduces fuel consumption. Diamond set out to fix the problems with traditional GA aircraft such as the Cessnas I’m familiar with, which suffer from poor in-cockpit visibility, high drag designs and more subtle problems such as large keel surfaces (tall, flat rear fuselage as an example) which makes them harder to control in cross-wind approaches.
Diamond Aircraft are clearly no strangers to innovation and the power plant is no exception, with Diamond introducing a diesel-powered DA-40 (the DA-40D), first flown in 2002.
Next came the diesel-powered, twin-engined DA-42 Twin Star, which was originally powered by a pair of Thielert ‘aerodiesel’ engines, but after Thielert went bust, Diamond began building their own via subsidiary, Austro Engine, in partnership with Mercedes-Benz. In fact, the DA-42’s engines are based on the engines found in the Mercedes A-Class.
In 2011, Diamond debuted the DA-36 e-Star at the Paris Airshow, demonstrating the first ever serial hybrid electric aircraft in collaboration with technology partners, EADS and Siemens. The e-Star is classified as a Touring Motor Glider (TMG), with a long and narrow (“high aspect ratio”) wing, suitable for long distance flight with low fuel consumption.
Fast forward to 2021 and Diamond announced the eDA-40, an all-electric version of the Diamond Star built in a joint venture with Electric Power Systems.
Compared to the smaller Pipistrel Velis Electro that I covered in the previous article, which only allowed 50 minutes of operation before a 1 hour recharge was required, the larger eDA-40 offers up to 90 minutes of flight time, with only a 20 minute recharge time.
One of those most interesting points in the eDA-40 video is that aircraft will be cloud-connected, allowing for better, automated monitoring of fleets, aircraft systems and pilots.
Diamond say that the eDA-40 will feed data into the Epicentre cloud, a hosted Oracle HCM (Human Capital Management) solution. This will enable automation of logging flight times and pilot resource allocation. Perhaps the days of having to write down the time you start and stop the engine (which is not the same event in an electric aircraft) and release and set the brakes are over.
Diamond also claim a 40% reduction in costs per hour, supporting my theory that electric aircraft won’t just help to reduce our environmental impact, but will also benefit our wallets.
The only snag to an all eDA-40 future is the price. A 20-year old fossil fuel burning DA-40 can still set you back £200,000! Compare that to the £50,000 that a 1970 Cessna 172 will cost you and the main barrier to electrified GA becomes clear.
Let’s look at some options we have to retrofit existing aircraft.
Hydrotreated Vegetable Oil
As discussed in the previous article on decarbonising GA, fuel is one area of intense innovation.
Hydrotreated Vegetable Oil or HVO, is a biofuel and a renewable, carbon-neutral source of “clean diesel”. Biofuels are carbon-neutral because when burned they only release the carbon into the atmosphere that the plants absorbed when they were growing. HVO is becoming popular amongst road transport organisations as it can significantly reduce carbon footprint without compromising performance.
HVO-based fuels can’t be used in just any engine, however. Diesel engines aren’t too choosy about their fuel and will run on used vegetable oil with minimal tweaks.
In aviation there are two main fuel types, Jet-A, used in jet aircraft and modern propeller aircraft engines, and Avgas, used in more traditional light aircraft. The Cessna 150s that I fly use Avgas, also known as 100LL (low lead). These engines need a little lead in their fuel to prevent knocking.
Jet A-fuelled piston engines are fairly unchoosy about their fuel as long as it resembles kerosene and will run on diesel just as well as Jet A. This makes Jet A engines a perfect candidate for running on HVO.
Continental, manufacturers of aviation powerplants, have been testing HVO in their CD-100 Jet-A engine with success.
In front of the pilots in a typical single-engine light aircraft, behind the ‘dashboard’, is a firewall separating the cabin from the engine. The CD-100 can be retro-fitted to Avgas powered aircraft with a “Firewall-Forward Kit”, making conversion as straightforward as an engine transplant can be.
But What About the Infrastructure?
When speaking to family and friends, the lack of electric charging infrastructure is holding back many from buying an electric vehicle. The same apprehension would be understandable in the aviation world.
In the UK this is being directly addressed by Aerovolt, an organisation building the world’s first airside charging network for electric aircraft.
In partnership with Octopus energy, and allowing payment with the Octopus Electroverse card, Aerovolt are rolling our chargers to 18 locations across the UK by the end of 2024.
It is still early days for electric aviation infrastructure, but Aerovolt are demonstrating that it is possible. The question is can it be done profitably. If Aerovolt and Octopus can show there is money to be made providing the charging network for electric aircraft, it is only a matter of time before other companies enter the market. This competition will help bring the costs for pilots and airfields down.
Hydrogen Fuel Cells
Hydrogen is another fuel source competing for the carbon-neutral aviation crown. Hydrogen fuel cells combine hydrogen (H2) with oxygen (O2) to create electrical power, with the only emission being H2O – water.
Stuttgart isn’t just the home of Mercedes-Benz but also H2Fly, an innovative aviation company building emission-free liquid hydrogen powered aircraft.
H2Fly is the leading member of an EU-funded consortium called Project HEAVEN, whose goal is “to design, develop and integrate the [world’s] first aircraft powertrain based on high power density fuel cell system and high energy density liquid hydrogen fuel system into an existing 2-4 seats aircraft for testing in flight operation”
Compared with gaseous hydrogen, cryogenically stored liquid hydrogen offers twice the range, with much less required volume for tanks.
H2Fly says the technology will scale well and has plans to build a 40-seat hydrogen powered transport aircraft.
Stuttgart will be the site of the world’s first Hydrogen Aviation Centre.
The UK is also innovating in hydrogen-electric aviation, led by ZeroAvia, a well-funded startup developing hydrogen powerplants.
ZeroAvia hopes to power a 9-19 seater transport aircraft by 2025 with their ZA600 500-700kWh continuous hydrogen electric engine, followed by powering a 30-40 seater aircraft capable of 800-900nm range in 2027 with the 2-5MWh ZA2000 engine.
ZeroAvia recently secured funding from Barclays, Airbus and Saudi Arabia’s NEOM.
Summary
The ideas and theories are now becoming reality.
The eternal pushback of ‘but infrastructure!’ is being answered. General Aviation airfields are being upgraded with Aerovolt smart electric charging units. Hydrogen fuel cells are showing signs of excellent scalability. Stuttgart Airport is leading the way for larger-scale H2 powered aircraft with their Hydrogen Aviation Centre.
Diamond Aircraft are offering EASA/FAA certified, fully-electric GA aircraft with excellent performance figures. H2Fly are aiming to launch commercial, regional aircraft powered by cryogenically stored liquid hydrogen powertrains this decade.
The cost of new electrified aircraft is steep, however, options such as retrofittable hydrotreated vegetable oil (HVO) piston engines mean traditional training aircraft aren’t going to be left behind. Continental’s CD-100 engine could not only extend the useful and practical life of classic Cessnas and Pipers but also significantly reduce the environmental impact of these planes.
I still believe that all-electric engines are the future, because – compared to hydrogen – they are very simple and the opportunity to dramatically lower the TCO of an aircraft over its lifetime, as well as reducing the complexity of operating the aircraft which will contribute to improved safety.
Hydrogen is complicated to store and handle due to its explosiveness and the general challenge of trying to contain the smallest molecular substance in the universe (like trying to trap air in a dog cage). Cryogenic storage is also complicated and requires additional energy. Personally, I still can’t help but think of the Hindenburg disaster whenever hydrogen fuel is mentioned. (Oh, the humanity).
HVO is promising, although it retains the same operational complexity as fossil fuels – constant watching of oil temperatures and pressures, mixture settings, etc. HVO becomes a problem when food becomes scarce. In a starving nation, it’s unlikely cereals will be used for biofuels rather than feeding the population. Starving nations are prone to revolution and overthrowing their leaders.
I was a bull on decarbonising aviation when I wrote my last article on the subject but seeing the real progress since, I am totally convinced that we are witnessing the first stages of significant decarbonisation of the aviation industry. Where food is plentiful (I’m looking at you, America) HVO is likely to be the easiest first step forward in GA, with synthetic aviation fuel (SAF) doing the same in air transport (airlines).
Full electrification of GA has been shown to be possible courtesy of Diamond, already a market leader, but the costs are high.
For GA, it seems to me that the best leap forward would come from combining all of the above – producing a retrofittable electric engine that can be easily bolted onto a classic Cessna’s firewall and batteries that can replace the fuel tanks in the wings giving at least 90 minutes of flying time with a sub-30 minute charging time.
I, for one, am not going to miss the Mixture lever, oil Ts and Ps, magneto checks, carb icing or the slippery feel of aviation-grade oil on my fingers.
Bring on the electrified future.