It wasn’t so long ago that the suggestion of replacing piston engines with electric ones, in any vehicle, let alone aircraft, would be met with gentle smirks and sarcastic nods. But if you ask the question today, will aviation be electrified? Almost any industry executive will answer with a resounding and solemn, ‘yes’.
Today’s aircraft propulsion systems, broadly speaking, fit into one of the following categories: piston engines for short-range general aviation (GA), turboprops and small turbofans for regional and business aviation, and large turbofans for medium- and long-haul commercial air transport.
As the technology for electric propulsion continues to advance it is becoming clearer that there are no simple solutions. This is in fact one of the things that is most exciting, the vast range of ways in which these technologies can be applied, and must be applied for different markets and time frame demands. One size does not fit all.
The addition of electrification, whether this is fully electric propulsion systems or hybrid turboelectric systems, offers an array of options to increase power and efficiency in aircraft, as well as alter standard designs dramatically. This begs the question: what can we expect to happen in the aviation industry in the coming years?
Hybrid and electric propulsion systems can significantly reduce fuel consumption and noise of aircraft, but they require significant technological developments in energy storage, electrical distribution, power electronics and electric machines. Here are just a few of the exciting developments and key players propelling the electrification of aviation.
Airbus and Siemens
Airbus and Siemens plan to jointly develop prototypes for various propulsion systems with power classes ranging from a few 100 kW up to 10 or more megawatts. They hope to be able to produce electric based engines with sufficient power and efficiency “for short, local trips with aircraft below 100 seats, helicopters or UAVs up to classic short- and medium-range journeys,” by the early 2030s.
Currently there main focus is to prove beyond a shadow of doubt the feasibility of hybrid technologies in small aircraft by 2020.
One of the projects NASA are working on at the moment is the development of nano-electrofuel (NEF) flow batteries with rim-driven electric motors to produce a safe, clean and quiet propulsion systems for aircraft.
Liquid batteries aren’t a new idea, however, NASA believe they can perfect it, producing an estimated energy per density twice as high as a lithium ion battery, whilst making a completely renewable green battery source.
The idea would be to store charged nanoparticles suspended in electrolyte fluid at the airport. When refueling you simply replace the discharged (used) fluid from the plane with charged particle fluid, much like refueling with Jet fuel.
UBER and eVTOL
One of the main driving forces behind the development eVTOL (electric vehicle take-off and landing) vehicles is UBER, who are pushing hard on their idea of creating air taxis. What they are trying to do is create a real transportation solution by taking to the air with affordable electric vehicles, and developing skyports. This is seeming more and more distant as people come to understand the obstacles in the way.
The first is the short range of the vehicles. Whilst the technology is there to create an air taxi, it would likely have a range of no more than 25 miles. Compare that to even a small light sport aircraft which can get several hundred miles on a single tank.
Secondly, there are a number of regulations currently blocking their path, things like safety and noise, as well as a rule from the FAA that LSA must be powered by “a single, reciprocating engine.” This means that cheaper, easier to produce electric aircraft can’t be brought to market which is stymieing growth.
That being said, UBER have partnered up with some of the big names in the industry, including Pipestral, and Tesla, to name just two, and are confident that they will have made real headway against these obstacles by 2023. This then is certainly something to keep your eye on.
Also going hybrid is Terrafugia. Terrafugia’s Transition flying car, is set to enter production later next year. This is a road legal car that converts into a light aircraft. It now features hybrid electric power to the wheels for driving on the ground, while extra “boost” power will be available in flight from its lithium iron phosphate battery. Propeller power is provided by a fuel-injected Rotax 912iS piston engine.
There next development will be the TF-2 which is a detachable four man pod that attaches to a ground vehicle or to an aircraft. It will aim for type certification in 2023; a scale model is already flying, and a full-scale vehicle should begin flight test by the end of next year.
The truck manufacturer Workhorse Group have developed an utterly unique two-seat multicopter called the sure-fly. The aircraft, which will later have a piston engine to generate electrical power first flew at the end of April as an all-electric test vehicle. One to watch, they show the feasibility of fully electric powered vertical take off vehicles.
The E-Merlin PSA (Personal Sport Aircraft) from Aeromarine-LSA, is a single-seat aircraft fitting the experimental-amateur rules. It is powered by a Siemens electric engine. The batteries are housed in “drop tanks” under the wing that can be jettisoned in the unlikely event of an inflight fire. Plans for further developing the aircraft include streamlining pusher propellers on the rear of the pods, driven by electric motors, and replacing the Siemens motor in the nose with a small piston engine for cruise flight. The aircraft would take off as a trimotor and shut down the electrics on reaching cruise altitude.
Slovenia-based Pipistrel, a leading developer of light sport aircraft, are the first company to get a fully electric aircraft to market. They have already released the Alpha Electro LSA which is a two-seat trainer that fits European (though not the US specifications) for light sport aircraft rules and has an endurance of about 1 hour.
They also have the Taurus electro G2.The Taurus Electro applies the electric drive to a glider airframe, meaning battery capacity is not a limiting factor in performance/endurance.
On top of this they have developed a new solar-trailer that can recharge their aircraft when an electrical outlet isn’t available, providing 100% clean, renewable energy.
We are looking forward to see the future innovations from these companies!
The Benefits of Electrification
There are some obvious benefits to electrification. Cleaner energy and much quieter engines amongst them. On top of this electric motors work at around 90% efficiency compared to the 35% of a standard piston engine. However, the energy output is much smaller than a piston engine. So the larger the aircraft the less feasible a fully electric vehicles becomes with current battery technology.
Motor efficiency simply can’t compensate for the fact we can’t yet store enough energy, and we can’t recharge batteries fast enough.
Whilst the aforementioned NASA NEF battery running on charged nanoparticles might supply a solution to this, feasibly supplying an energy density up to twice as high a Lithium ion one, the technology is still a way off being viable for use in aircraft.
What really excites us though, is the change that electrification is having in the way it is allowing people to think about how aircraft are designed.
With an electric engine you suddenly have a huge range of possibility for the redesign of aircraft, like the Workhorse Groups multicopter – SureFly.
Suddenly, with electric engines you can divert power and move power around the aircraft in ways that couldn’t be done before and it’s opening up the industry to advancements that a decade ago we thought were impossible, and only five years ago left a lot of people very sceptical.
When are we likely to see fully electric or hybrid aircraft technology in commercial use?
Five years doesn’t seem like a long time, especially considering the slow moving bureaucracy that is the FAA, and technological advances that still need to come.
However, driving forces like Europe’s target to reduce carbon emission 75% by 2050, the continuous demand for more efficient aircraft, and UBERs desire to create an entirely new form of transport, means that huge amount of potential and possibility that these developing technologies are opening up are beginning even now to come into play.
By 2023 UBER are expecting some pretty major regulatory changes in the US and in Europe that will allow use of fully electric propulsion systems in light aircraft. Whilst I doubt there are going to be a lot of Terrafugia’s flying cars on the road, I would expect many more Pipestral vehicles in aircraft hangers as they are so much more cost efficient and practical for short flights.
The main hurdle though is going be the development of adequate battery technology that can begin to replace turbo engines. This is vital to making electric aircraft practical, and on top of this it will have huge ramifications outside of the industry. We will be watching the progress of this with eager eyes.
Image by Joe A. Kunzler
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