Will you ever fly in an electric plane during your lifetime?
What if your plane could fly with 97% greater efficiency, less noise, and zero emissions?
For this video, We collaborated with a team of aerospace engineers, NASA scientists, and veteran pilots to sort through the current electric aircraft research and evaluate the most promising new technologies based on performance, practicality, and economics.
We’ll provide a comprehensive overview of electric airplane technology, discuss the benefits and challenges, and then rank the most revolutionary electric planes.
Electric aircraft are not a new idea. In fact, The first electric-powered flight predates the Wright brothers by 20 years, when, in 1883, Gaston and his brother Albert Tissandier fitted a 1.5 hp/1.1 kW electric motor to a dirigible airship. The brothers flew for just over an hour powered by their bichromate batteries, reaching a blazingly fast speed of… 7 MPH.
The first manned, electric, heavier-than-air flight had to wait another 90 years. Electric RC planes were becoming increasingly widespread in the 1960s, and it was an aeromodeller, Fred Militky, who converted the quirky Austrian Brditschka motor glider to run on Ni-Cad batteries and an 8kW Bosch motor. Its first flight in 1973 lasted for an enduring… 9 minutes.
By the end of the decade, a few solar powered aircraft had taken to the sky. The Gossamer Penguin was a variant on an experimental human-powered aircraft, weighing just 68lbs/31kg. Needing to keep the payload as light as possible, The test pilot was the designers 13 year-old son. Rumor has it, the boys mother was less than pleased with the father’s…pioneering spirit.
In recent years, the meteoric progress of vehicle electrification has many looking towards the skies wondering if aircraft will ever follow suit.
But does it even make sense to electrify planes, or is it just a…waste of energy?
Air travel produces 915 million tons of CO2 every year, accounting for 2.5% of global emissions and comprising 12% of total emissions from the transport sector. Not the biggest culprit under the sun, but it seems some forms of pollution have more impact than others.
Emissions at high altitude are more potent greenhouse contributors, and aircraft contrails have even been shown to have a significant extra warming effect by increasing cloud cover. Although the aviation industry boasts a reduction in CO2 per passenger-mile of over 50% since 1990, the unquenchable demand for passenger aviation is set to continue this rising trend.
As we speed into the electric future of transportation, the aerospace industry is trying to keep up, but they’re held back by the limitations of current technology, and the slow regulatory pace of this necessarily conservative sector.
Now, for the first time, There are green glimmers of electric-powered hope on the horizon, but if you look to the skies, you’re not likely to see them just yet, unless you’re Norweigan, and are watching this video a couple decades from now, because Norway recently required that all domestic flights go electric by 2040.
As well as being environmentally friendly, there are a several other potential benefits to electric power in aircraft.
Benefits and challenges of electric aircraft
Firstly, electric motors do not experience power loss from operating at high altitude. Combustion engines (excluding rockets) ingest air from the atmosphere to mix with fuel and burn. This air becomes increasingly thin at high altitudes meaning it contains less oxygen. This is a particular problem for piston and turboprop engines whose performance is significantly reduced.
We’ve all heard the maxim that electric cars require less maintenance, and the same can be said for aircraft. Combustion engines are inherently complex machines with thousands of moving parts, and routine maintenance can account for a high proportion of aircraft operating costs. Electric motors are fundamentally simple, and no part of the powertrain is exposed to the harsh environment of high temperature combustion.
Electric systems also don’t suffer from carburetor icing, contamination, or water in fuel tanks. Batteries are affected by the low temperatures at altitude, but providing heat is much easier than providing extra oxygen, and can be taken from the cooling systems as they dissipate excess heat from the powertrain.
Additionally, the various compact and cool running configurations of electrified aircraft allow designers more freedom for optimizations compared to conventionally powered craft. One NASA study estimated an improvement in efficiency of a modified electric aircraft of 4.8 times compared to an equivalent conventional format in the cruise condition.
Electric motors are also much quieter than jet and piston engines, so while propeller noise is still considerable, there’s enough noise reduction to permit flying where noise restrictions would typically constrain operation. This is not an insignificant detail, noise restrictions were the Concorde’s original Achilles’ heel, and the operation of small regional airports are frequently challenged by excessive noise.
Despite these advantages, electric aircraft have one major drawback that many believe is insurmountable…
We must contend with the fact that liquid fossil fuels offer a staggeringly high energy density compared to even the best batteries of today. In aviation, weight is of huge importance and directly impacts the range, endurance, takeoff performance and the stall speed of an aircraft. Compounding the problem of battery weight, heavy aircraft must be built with a sturdier airframe. Generally… designers wish to maximize the amount of payload that can be carried relative to the mass of the aircraft.
There’s also one huge aeronautical advantage of fuel people often overlook…It combusts.
Batteries do not observably decrease in weight as they are discharged. They’re just as heavy at the end of the flight as they were in the beginning. From the outset of the aircraft design process, fuel consumption is built into the calculations that determine the aircraft’s size and range. For long range aircraft, this increases the range by about 10-20%. Fuel burn also affects the mass of the aircraft structure since designers know that a landing aircraft will be lighter than its takeoff weight. For example, the landing gear and its attachment points don’t have to bear as much load.
Electric vs Combustion Comparisons
Modern automotive lithium-ion batteries can pack up to around 285 Wh/kg. That’s about 1 MJ/kg. Jet A1 fuel, by comparison, contains about 43 MJ/kg – more than 40 times the energy density per kilogram. This isn’t the whole story though: electric systems tend to be much more efficient than combustion engines. In an economic analysis of future electric commuter aircraft, Rolls-Royce quoted a report estimating a jet installation to be about 26% efficient compared to over 90% efficiency for an equivalent electric powertrain.
Heat engine efficiency is governed by the laws of thermodynamics. The inherent problem is that most of the energy created by burning fuel is wasted as heat, rather than converted to useful work.
Fundamentally, airplanes need to have a high power to weight ratio.
It’s hoped that battery technology will improve in the coming decades, and there are many exciting developments in the works to create much higher energy densities. Notably, the use of nanostructures within batteries appears promising, and a pan-European research team, are hoping to produce lithium sulphur batteries with an energy density of 500 Wh/kg (1.8MJ/kg). This battery chemistry is already employed by Airbus on their Zephyr solar UAV to power the aircraft through the night.
Practicality of Electric Aircraft
While Elon Musk might dream of supersonic electric flight, this is likely a long ways off.
The concorde required four jet engines each rated at 169 kiloNewtons (38,050 lb-force, or 17,230 kg-force) of thrust. Those four engines could generate enough thrust to lift a Boeing 737 into the air like a helicopter, just to give a sense of how much air resistance we’re up against.
While there have been some interesting research advances in electric plasma jet propulsion, for the moment we can’t easily achieve the high speed exhaust of a jet engine using electric power. Right now, Propellers are the most practical means for generating thrust from electric current, and our best shot at getting a serviceable electric aircraft into commercial operation.
We spoke to NASA, and it turns out they’re really into propellers…lots of propellers. Understanding the reasoning behind this strange configuration, is the key to grasping the benefits of electric aviation.
Electric aircraft of today
NASA X57 Maxwell
When you think about innovative flying machines, one name comes to mind. So it’s no surprise NASA is developing the experimental X-57 Maxwell to test the limits of electric aircraft propulsion.
Modified from a twin engine Tecnam P2006T, the final manned version of the X57 will feature a distributed electric propulsion system consisting of 14 electric motors mounted on the wings leading edge.
Distributed Electric Propulsion
what that means is we can design a wing that’s got only 40 percent the area of what a a typical wing would have required for this this sort of aircraft, we can make our wing very small and optimized for high speed very efficient flight and use the distributed propulsion system to augment lift when the aircraft is slowing down to land or or speeding up out of a takeoff and so we need to be able to spread them out in such a way that we we get that high lift effect blown across the the whole span of the wing
Spearheaded out of NASA’s Armstrong Flight Research Center, The two seater aircraft is hoping to achieve a 3.5 times aero-propulsive efficiency gain over its conventional counterpart, and will be capable of 100 miles of range at a cruising speed of 172 MPH. All with zero in-flight emissions.
Considering NASA is conducting battery research across other mission directorates, I was curious if they had any plans to incorporate experimental high energy density battery technologies in the X57. The answer might surprise you, but before we get into the battery system, you need to better understand the methodology behind NASA’s first X-plane in over two decades.
The project is a technology demonstrator. Meant to advance our understanding of how electric propulsion can improve cruise efficiency, and also provide certification data to establish commercial safety standards for the future of electric aviation.
We chose to modify an aircraft instead of building one from scratch in this case because we wanted to to get learning these lessons as quickly as we could and if we spent all of our time designing landing gear systems, and seat tracks and and instrument clusters then that would have been time taken away from from working on motors and batteries and high performance wings so that this approach for the project let us really focus in on the parts of the aircraft that we were trying to improve which are the the wing and the power system and and keep all the rest of the aircraft without having to spend too much time modifying it.
One of most significant innovations to the projects power system are the high lift motors. You can think of them, almost like flaps on an airplane.
The 12 fixed pitch propellers are only required at low speeds to reduce drag. Once up in a cruise regime, the high lift propellers fold conformally along the nacelles and the two wingtip motors take over. Putting the larger more powerful cruise propellers on the wingtips offers favorable vortex interactions and can provide up to a 5% reduction in drag.
The permanent-magnet synchronous motors were supplied by Joby Aviation, a california based aerospace company who are developing an electric vertical take off and landing air taxi of their own.
Designed For Redundancy
The cruise system there’s two 72 kw motors and they eventually end up on the mod four wing, out at the wingtips and each of those motors actually have two inverter systems driving them for for redundancy and so we’ve built the motors with with a split set of windings it’s actually two three phase motors intertwined on the on the same stator but are electrically isolated, and our and we have a dedicated inverter for each of those sets of windings and that goes all the way back to a dedicated transmission line a DC traction BUS that goes back to our battery system.
The redundancy speaks to the high standards and practical goals of the Aeronautics Research Mission directorate. For this reason, the X57 Maxwell aircraft will be powered by standard commercial lithium ion battery cells. The pack consists of 16 battery modules arranged into an aluminum honeycomb architecture designed to prevent thermal runaway. Battery safety is one of the principal challenges to electric aviation, and an area to which NASA has dedicated significant attention.
The battery pack will achieve a total power capacity of 47kWh at a weight of 860lb. for an energy density of 121 Wh/kg. Far below the theoretical 400+ W h/kg energy density of experimental Lithium Oxygen batteries currently being investigated by NASA.
we’ve got we’ve got battery experts at many of our centers including glenn research center and johnson space center that have helped the x-57 project but for x57 we really wanted to pick a an off-the-shelf commercial battery cell technology and not invest in an experimental technology there because putting the motors in strange places on our airplane is experimental enough for for one project.
NASA doesn’t like leaving much to chance. Because the final phase 4 version of the X57 will be piloted by a live human, all parts of the plane are subject to extensive testing. They even perform what’s known as “destructive inspection.” essentially tearing every component down to its most basic elements, Heaven forbid one weak magnet makes it into the planes 14 electric motors.
It may seem a bit obsessive, but this attention to detail is for good reason. Due to the nature of flight, and the grim consequences of gravity, electric aircraft have a much lower fault tolerance than ground based vehicles like cars.
The program should be worth the effort. The X57 Maxwell is expected to achieve a 30% reduction in total operating costs, but the future of electric aviation is not limited to experimental government projects, there are some fascinating flying machines already in commercial operation, and I got to fly one.
In the twilight skies of small town Ajdovnišča in 1980s Yugoslavia while private aviation was still illegal, dark silhouettes flitted about on clear evenings. The Slovenian locals spoke of bats, but these were just the powered hang-gliders and ultralights of Pipistrels enigmatic founder, Ivo Boscarol. Pipistrel, which means “bat” in the local dialect eventually transitioned from experimental power gliders to ultralight aircraft.
These curvaceous planes have gone on to set records: the first woman to cross the Atlantic and Pacific in a light sport aircraft, the first solo flight around the world in an ultralight, and now the first commercially viable and available electric aeroplane.
Their first electrified offering was a powered glider. Pipistrel already offered the Taurus in their lineup, the first self-launched glider in the microlight category, but electrified it with a pop out propeller to produce the Taurus electro. Motor gliders make the perfect platform for initial electrification efforts. The powered phase of flight only needs to get up to soaring altitude before the motor is cut and the pilot heads out in search of updrafts and thermals. This form factor is extremely light, and has very little drag which allows the use of small motors and batteries to meet the needs of the mission profile.
This means that the aircraft only needs a 4.75 kWh lithium polymer battery and the entire aircraft can have an empty weight as little as 675 lbs. With the three phase synchronous, permanent magnet motor rated to provide 40kW peak, or 30 kW continuously, the electric version actually outperforms the now-discontinued combustion engined option.
This electric Taurus demonstrated the technology was viable, and in 2011 the design was heavily modified to compete in the NASA Green Flight Challenge. The challenge was to fly 200 miles in less than 2 hours and achieve better than 200 passenger-miles per gallon. The custom built Taurus G4 NASA Racer was created by connecting two fuselages with a 16 foot (5 meters) long spar and mounting a 145-kilowatt brushless electric motor between the passenger pods. This design achieved 403 passenger-MPG at an average speed of 107mph, winning 1st place in the competition and taking home a prize of $1.35 million.
They didn’t waste much time drinking zganje (ooj-shgon-uh) and celebrating. From here, Pipistrel have continued their developments. The G4 was acknowledged to be a test bed for high power electrical systems on future commercial electric aircraft.
Most pilot training flights are less than an hour long, a mission profile that is well suited to the shorter endurance of current battery electric systems. Thus emerged the Alpha Electro, a variant on the conventionally powered Alpha which has seen widespread use as a flight trainer.
The lessons learned eventually led to the development of the Velis Electro, with a completely new electric powertrain. In 2020, The Velis became the first electric aircraft to be type certified by the EASA . This is no mean feat when incorporating new technology into an aircraft and this opens the door for commercial use. Working with the Slovenian electric motor specialists, Emrax and Emriso, they have developed their own aircraft motor, the Pipistrel E-811, and two 11 kwh battery packs. The full system is now liquid cooled rather than using air cooling as on the Siemens,of the Alpha Electro. This was an aerodynamically advantageous decision because the plane no longer needs to duct in additional air to cool the components.
The lightweight motor and its controllers are type certified separately for installation on other aircraft with a motor weight of 50 lbs, and a controller weight of 17.8 lbs. The custom-made battery packs are built up from cylindrical cells using a nickel-manganese-cobalt based lithium ion chemistry.
Pipistrel’s sights are set beyond trainers and gliders. They are working on both a hybrid and a fully electric version of their Panthera high-speed four-seater aircraft. They indicate that the cruising speed of the hybrid version will be about 20 knots slower than the piston engined version at around 204 mph 177KIAS. This will be at full generator output, and is comparable to the rated speed of the piston engine cruising at 55% power.
Pipistrel are demonstrating a sensible approach to electrification by merging new technology with existing airframes to produce certifiable, practical aircraft and have found the perfect niche to start with.
….But Maverick has needs.
The need, for speed. Well, strap in your safety harness, because one of the world’s largest aerospace companies are gearing up to break the electric flight speed record.
Rolls Royce have been at the forefront of aero engines for over 100 years and are no strangers to the record books. The Rolls Royce Eagle was the engine in the Vickers Vimy, the first aircraft to cross the Atlantic in 1919. But the ACCEL, an acronym for “Accelerating the Electrification of Flight” seems to hark back to the late 1920s when Supermarine were chasing down the Schneider Trophy for racing seaplanes. In those days, amphibians seemed to be the future of aircraft: you see, before WWII, long, well paved runways were about as rare as an honest politician. It was a Supermarine S.6B powered by a supercharged Rolls-Royce R engine that broke the world airspeed record in 1931, reaching a speed of 407.5 MPH. This race series was one of time period’s great drivers of airplane innovation. Most remarkably – the invention of engine cooling without radiators, by ducting coolant under the skin of the aircraft’s surface. Foreshadowing RR’s proclivity for novel solutions to high performance aeronautical challenges.
Following in the tradition of their racing heritage, Rolls Royce are building the ACCEL, a sleek race plane based on the airframe of the Sharp Nemesis NXT that’s capable of a blistering top speed.
The ACCEL is propelled by three lightweight axial electric motors driving a single three-blade propeller in a conventional sport class format.
The 82 lb / 37 kg YASA 750 R motors will deliver more than 500 horsepower to the Accel’s propeller. The Supermarine of days past had to make do with highly inefficient fixed pitch propellers, but the ACCEL’s electronically controlled variable pitch prop will allow the torque and motor speed to be tailored on the fly. The high power density axial motors operate at a lower RPM than a conventional plane, increasing stability and reducing noise.
The ACCEL’s high energy density pack has enough juice to fly 200 miles – from London to Paris on a single charge. Once again, it’s cooling that provides a significant challenge on such a power dense unit, this time the 750kW battery rather than a 2,800 Horsepower V12.
The 6000 battery cells are tightly packed to the fore of the pilot, and would melt your popsicle without a vigorous heat exchange campaign. Liquid cooling is used to transfer the heat into radiators ducted so smoothly into the fuselage that they’re almost invisible – look out for the NACA duct intakes just behind the propeller, a popular choice for a low drag duct entrance. Also notice the bulge under the batteries where the radiators and pumps are housed. That said, today’s engineers have much less heat to contend with than the intrepid technicians who worked on the Supermarine. With a system efficiency over 90%, we can expect that only 75kW (100hp) of power must be transferred out of the aircraft as heat loss. By comparison, it’s estimated that the Supermarine S6B had over 750kW (1000hp) of excess heat to dissipate from its powerful but inefficient engine – the same as the full power of the ACCEL’s powertrain. This allows the engineers to get away with a relatively small radiator unit which can be seen on the test rig, the IonBird, along with the large inverter and other power electronics that give a sense of scale to the crafts athleticism.
The record to beat stands at 213 mph (343 km/h) set by Siemens in 2017 in a modified Extra 300.
The ACCEL project is aiming for a top speed of over 300 MPH with their first aircraft, ‘the spirit of innovation’
Rolls Royce have since bought Siemens’ eAircraft unit. The broader purpose of the ACCEL project is to bring together electric power specialists and develop the technology and supply chains to suit future ventures.
As we’ve seen in the automotive world, with companies competing for bragging rights in souped up race cars, innovations learned on the track can translate into real world performance enhancements. The goal is for the optimizations made in high performance electric powertrain design to trickle down to broader commercial applications.
The racer is only the beginning of electric aviation for Rolls Royce and just one strand of their R&D efforts.
At the small end of their spectrum, Rolls Royce have developed an electric motor which can supplement the power of a conventional piston engine in a setup known as a ‘parallel hybrid’. In the HP3S, they have modified a Tecnam P2010 by exchanging its 180hp engine for a 140hp unit plus a 30kw electric motor to make up the difference. When choosing engines, it’s rarely the cruise condition that dictates its maximum size. Efficiency gains of 10-15% can be made by using a smaller engine at a more efficient power output, and battery electric power to supplement high energy flight modes.
Stepping up a level, Rolls Royce mated one of their most successful small turboshaft engines, the M250, to their generator in a test of high powered turbo-electric hybrid systems. A turbine drives a generator which drives the motor, without using batteries to the order of about 500kW to 1MW of power. This is representative of the needs of a 4000kg commuter aircraft for about 8 passengers.
Rolls Royce are paying close attention to the commuter aircraft market. In the all-electric format, Rolls-Royce have partnered with Tecnam to produce the 11 passenger P-Volt. Designed to serve medium range missions from cargo, to medevac, to commuter transportation, Norweigan carrier Wideroe are pushing to get passengers airborne in a P-Volt by 2026. Passengers like you and me.
Many new contenders are now entering the arena to try and meet this growing demand for electric passenger aircraft. One ambitious Israeli startup is building a futuristic full size passenger plane capable of astounding range, and it has the kind of space age looks you might expect when imagining the future of electric aviation.
Over half of all plane tickets sold today are for short regional flights, but most of these trips still use oversized jet planes that consume a lot of fuel, and often have empty seats.
In recent years the aviation industry has seen a rise in companies offering fractional ownership and on demand charters for private jets. But PJ’s are still prohibitively expensive for most people.
If you could build an electric plane from the ground up for these short trips, it wouldn’t just improve energy efficiency, but could potentially allow up to 80% cheaper airfare for you, the passenger.
And this is exactly what Eviation is attempting to do with the Alice, which is designated for use as an air taxi or business jet. By designing the aircraft around its novel power system, Eviation projects a staggeringly high performance with a range of 650 nautical miles and a cruising speed of 260 knots (299 mph) for its 9 passengers and two crew. The 920 kWh lithium ion battery at the heart of this aeroplane weighs 7,900 lbs / 3600 kg, about 60% of the aircraft’s maximum takeoff weight. Power is distributed between three 280 kw magnix electric motors cleverly arranged in a pusher configuration to reduce drag. A similar airplane has a lift to drag ratio of about 16:1, but the Alice, with its non-conventional V-tail arrangement achieves a ratio of about 25:1, a huge leap in efficiency.
The motor at the tip of this aircraft’s pointy tail provides what’s known as ‘boundary layer ingestion’. Around since the 1940s, this technique has been applied to ships and torpedoes alike.
Imagine dragging a spoon through honey. The sticky honey closest to the spoon drags along its surface, while honey farther away from the spoon remains stationary.
The same happens as aircraft travels through air. The layer of slower moving air close to the surface of the aircraft where the effects of viscosity are significant is called the boundary layer.
At the front of the aircraft, this boundary layer is very thin, But it gradually thickens as air passes over the length of the craft. Eventually it transitions into a turbulent layer where it becomes even thicker and has a large impact on drag.
The design of the Alice is an attempt to delay the transition of the laminar to turbulent as far aft on the surface as possible. With a propulsor ingesting this boundary layer, the rear propeller sees slower moving air which reduces the power required to maintain adequate thrust. This also sucks some of the drag-inducing boundary layer off of the aircraft’s skin, reenergizing the aircraft’s wake.
Then we have the outboard propellers. The Alice can alter the power input to the motors with great precision. This allows differential thrust to be used to supplement the control surfaces with a speed and sensitivity not possible with conventional engines. It’s even possible to spin the propellers in the opposite direction to the wingtip vortices and mitigate induced drag.
Wingtip vortices exist at a point where high-pressure air below the wings wants to swoosh around and fill in the low-pressure regions above the wings. This point at the wingtips is where the high-pressure and low-pressure regions meet. A wide variety of ‘wingtip devices’ installed on aircraft provide, some quite crudely, a solid fence to minimize air spill around the wing. Most of these devices are also designed to provide some sideways thrust which blows these vortices further outboard. This gives the aircraft a longer effective wingspan and higher aspect ratio. High aspect ratio wings generate less induced drag than stubby wings, which explains the long wings of gliders. The Alice cleverly uses its outboard propellers to generate a swirling vortex slipstream to match the strength of the wing vortices. This significantly reduces the induced drag, increasing efficiency, and range.
What this all means is that the Alice only costs about $200 per hour to operate, while a comparable turbo prop plane can cost $1200-$2000 per hour. Eviation has already received over 150 commercial orders at a price of $4 million a piece, and certification is expected to be completed by 2023.
Eviation’s motor supplier Magnix cut their teeth retrofitting existing aircraft with electric propulsion systems. Working in partnership with aerospace engineering firm AeroTEC, they actually built the largest electric commuter aircraft ever flown. The e-Caravan, a Cessna 208B Grand Caravan converted with a 750 horsepower motor, successfully completed a 30 minute flight in 2020. Incredibly, this hefty, Reagan era, high wing utility craft consumed less than 6 dollars worth of electricity during its maiden voyage.
Further back, Canada’s Harbour Air hit the news in 2019 with their claim to have operated the first commercial flight of an electric aircraft. The airline runs short flights connecting the pacific northwest with a fleet of seaplanes. Their longest route, Vancouver-Seattle is about 120 miles as the crow flies, an ideal electrification opportunity.
De Havilland Beavers are typically fitted with Pratt and Whitney Wasp Junior engines putting out 450 hp (336 kW). Teaming up with MagniX, the airline has converted one of its Beavers to full electric power and intends to electrify its whole fleet, projecting operational cost savings of 50-80%
Converting an existing airframe will make certification much smoother, but the Beaver was designed in the 1940s with a piston engine in mind from the outset.
Eviation demonstrates the potential to reinvent aerospace design by placing electrification at the forefront of their design thesis, not as an afterthought. With compact precision tuned electric motors, the future of passenger aircraft is streamlined, optimized, and will follow true form to function principles.
Short range commuter aircraft have their role, but what about airliners for longer journeys and mass transit? The major players have been exploring electrification for a while now, and they have created some radical designs.
Boeing has been working on its SUGAR Volt hybrid electric concept since 2006 in collaboration with NASA. The project has morphed into the Transonic Truss Braced Wing, a name that reflects the most obvious external design feature that permits the abnormally high aspect ratio wing. Normally wings are designed as cantilevers, meaning that they are unsupported outboard of the wing root. Although the strut represents extra mass and profile drag, this can be offset against the potential to reduce wing mass and enable the use of a very long wing to reduce induced drag. This concept is intended for 150-175 passengers. It seems that the main research effort is now going towards reducing fuel burn and increasing aerodynamic efficiency rather than attempting to incorporate electric propulsion, but this novel form factor is worth mentioning as an aviation advancement and future electrification candidate.
Airbus, meanwhile, have been working on their E-Fan concept since 2014, making the first electric crossing of the English Channel a year after launch. The twin engine all electric aircraft flew 46 miles / 74 km in 36 minutes.
The E-Fan 1.1 was an opening salvo. The 60kw two seater was the first variant of an electric ducted fan R&D initiative with plans to scale all the way up to a 100 seat regional jet. This project materialized as the E-FanX. A hybrid-electric flight demonstrator which swapped one of the four jet engines on a Avro RJ100 with a 2MW electric fan. In collaboration with Rolls-Royce and Siemens, the serial hybrid propulsion testbed utilized a 2.5 MW generator, and a 2 MW battery pack that weighed over 2 tons. 33 times more powerful than it’s petite predecessor. Unfortunately she never made it airborne. The project was grounded in 2020, but the myriad lessons learned will carry over to even more ambitious projects on Airbus’s quest for zero emission commercial flight. Let me introduce you to the elephant in the room.
So far we’ve focused mostly on Battery Electric, but there’s one very light gas, with heavy implications for the future of aviation.
In September of 2020 Airbus announced The ZEROe program with three conceptual designs, and they all run on hydrogen.
With respect to Aeronautics, hydrogen is interesting for a few reasons.
We can react hydrogen with oxygen in fuel cells to generate electricity. A fuel cell is an electrochemical cell that converts chemical energy into electricity through a pair of redox reactions.. Fuel cells are not as efficient as batteries; the theoretical maximum efficiency is 85%, but 50% is a more reasonable bet in real world applications. Although fuel cells are less efficient, batteries are staggeringly heavy for their energy capacity. Conversely, hydrogen is ridiculously light, which means that it has a very high specific energy, 142 MJ/kg – about three times higher than jet fuel. The drawback is that it takes up a lot of space. As a gas, it has just 5 MJ of energy per liter, but when liquefied its energy density doubles.
In the UK, ZeroAvia recently flew the world’s first hydrogen fuel cell powered electric flight. ‘HyFlyer’, a converted 6 seat Piper M completed a take-off, full traffic pattern, and landing running on Hydrogen alone. The 15 minute flight might not leave you in amazement, but this is no hobby project. Government backed ZeroAvia are aiming for a 200 seat 5000 nm range commercial airliner by 2040, and believe Hydrogen propulsion is the key to unlock sustainable aviation and reduce total trip costs by up to 50%.
Currently the overwhelming proportion of Hydrogen production is done by breaking down natural gas, an effective industrial method that kind of defeats the purpose because it emits CO2. This is called “grey hydrogen.” But you can also make hydrogen by using electricity to decompose water into oxygen and hydrogen gas. Leading natural gas executives argue that electrolysis is an exercise in futility, because the power has to come from somewhere, but this process can run clean if the electricity comes from renewable sources, like solar. This is called green hydrogen, and it’s a key component of ZeroAvia’s renewable vision.
Hydrogen propulsion is not without difficulties. Hydrocarbon fuels are quite convenient, particularly kerosene which is relatively difficult to ignite accidentally and liquid at ambient temperatures. Hydrogen, conversely, is gaseous at ambient temperature and violently flammable. Even though hydrogen is the lightest element on the periodic table, the high pressure tanks required for its storage can get quite hefty, especially when reinforced for crashworthiness. H2 molecules are so tiny they actually sneak between the atoms of storage tank materials and will leak slightly no matter how well contained. The hydrogen seeping into metals also causes embrittlement which can lead to fractures.
Fuel cells are not the only way to use hydrogen, it’s also possible to burn hydrogen in a conventional turbine engine to produce jet thrust. Airbus believes a combination of these two methods is their best chance to achieve an operational zero emission commercial aircraft by 2035.
All three Airbus ZeroE concepts use modified gas turbine engines, but they also incorporate hydrogen fuel cells to create electrical power, resulting in a highly efficient hybrid-electric propulsion system.
The first concept is a 200 passenger turbofan design, with a range over 2000 nm (2300 miles, 3704 km). The slightly shallower sweep of the wings indicates that this aircraft will be designed to travel a shade slower than the cruising speeds of equivalent airliners that tend to operate at around Mach 0.8.
The turboprop will have an expected range of 1000 nautical miles and carry 100 passengers. Airbus has also announced a distributed pod configuration. Each “pod” is its own independent fuel cell propulsion system and contains a propeller, electric motors, fuel cells, power electronics, Liquid hydrogen tank, cooling system, and a set of backup equipment. Designed to be modular and removable, these pods squeeze a lot of tech in a relatively compact package.
Lastly, the most radical of the designs: the blended-wing body. The idea is to reduce the skin-friction drag by reducing the wetted area of the aircraft, as well as minimizing ‘interference drag’ from transition areas we see on conventional aircraft. Such as those between the wing and fuselage, or around the tailplane. The blended wing also aims to ensure that no part of the aircraft is aerodynamically useless, since the entire body provides lift. Airbus estimate a 20% reduction in fuel burn with this aircraft type. Typically blended wings work best for large aircraft and this one certainly fits the bill. It’s expected to seat 200 passengers and fly over 2000 nm.
Hydrogen is not the only consumable fuel option for a hybrid system, petroleum based aviation fuels can work, as well as renewable biofuels, but hydrogen appears to be a versatile, low carbon, and potentially affordable contender.
And by the way, although Eviation opted for battery electric in the Alice, they did file a patent for a hydrogen after burner in 2018, so perhaps they haven’t written it off entirely.
Despite the lack of optimism for pure battery electric flight from the big names in aviation, Los Angeles based startup Wright Electric are working on a 186 seat battery electric airliner with a 500 km (310 mile) range. Slated for service with operational partner easyjet, they hope to run short haul routes like London-Paris by 2030. In an example of convergent evolution, Wright Electric have also independently arrived at distributed propulsion as the ideal thrust configuration. Their debut airliner, the Wright 1 will make use of about a dozen 1.5 MW electric motors spread across the span of the wing. Wright Electric presents a unique forward looking thesis, and appear to be positioning themselves strategically in anticipation of breakthrough advances in battery technology that can eventually extend the range to over 800 miles. (280km)
When looking at these large electric plane concepts, you may be thinking..that’s a lot of surface area, and it’s getting a lot of sun, especially when flying above the cloud layer.
Electric planes and solar panels seem like a match made in heaven. So, have you ever wondered about bolting solar panels on an electric plane? And why don’t all electric planes come equipped with solar panels for a sleek charge-on-the-go solution?
So far the constant theme has been the difficulties in attaining useful range and endurance. With the solar impulse project, Co-founders Bertrand Piccard and André Borschberg set their sights high on these targets, aiming for a complete circumnavigation using a fully electric plane powered only by solar energy.
I’ve always been really inspired by all the pioneers of aviation, this quest for innovation, this quest to push the limits. For me aviation is linked to pioneering spirit and exploration state of mind.
The original Solar Impulse was successful in achieving long range flying, taking off under its own power and storing enough energy to fly overnight. It crossed continents and proved that long range solar flight was possible, that such an aircraft was navigable, and offered a tangible demonstration that existing technology was adequate to achieve seemingly impossible goals.
this is something great when it’s electric you have your own source of energy to feed it you have the storage and you’re completely autonomous which you can never do if you have a thermal engine that has only 27 percent of efficiency and you have to refuel it all the time you’re always dependent on somebody else.
To make the around the world record attempt, the Solar Impulse 2 was designed with a similar layout. The wing is staggeringly long, spanning 236 feet 71.9m. That is more than seven times the wingspan of a Beechcraft Musketeer. This is partly to minimize induced drag, with a high aspect ratio of 19.7.
The large wing area means that the wing loading is only 8 kg/m2. Compare this to the 125 kg/m2 of the Beechcraft Baron which has a similar maximum take-off weight. Low wing loadings enable much slower flight without stalling, and the ability to fly slow allows the design of a highly efficient craft with low parasitic drag. During the circumnavigation, the cruising speed of the aircraft averaged just 47 mph 41 knots (76 km/h).
The wing’s large surface area provided plenty of real estate for Photovoltaic cells. The solar panels charged a lithium ion battery that would see the aircraft through the night. The pilot would also climb during the day and use up this extra height overnight, descending from 8500 m (27,890 ft)28 to 1500 m (4920 ft)5
The circumnavigation itself was as epic an adventure. It was divided into 17 legs, the longest taking over five days to cover the Pacific from Japan to Hawaii.
After 21 flying days, the aircraft made it back to its starting airfield in Abu Dhabi to claim the world record of the first unfuelled aerial circumnavigation.
After the flight, the work didn’t stop. The purpose of the circumnavigation was not so much to get into the record books as to demonstrate the future of electric flight, the possibilities of high efficiency engineering and encourage public discussion.
I would love to have electric airplanes either propelled with batteries or propelled with fuel cell and hydrogen and this will probably be for medium to short whole flights. For very very long-haul flights i think we have to envisage suborbital flying it means you you take off a bit like a rocket, you cut the engines of your airplane uh when you are on the top of the climb and then you just go parabolic suborbital and you can do half of the world in an hour and a half. You do Paris to Sydney, you do New York to Singapore, and with a big reduction of fuel consumption if you do that, so you see there is so many things to to be invented still.
If there’s one man who knows a thing or two about getting into outer space, it’s Elon Musk, so will Tesla or SpaceX ever build an electric plane?
Elon Musk’s Design
According to Elon it’s simple, you need to get high really fast! The higher the better.
Elon Musk proposes a vertical take off and landing, supersonic electric jet with gimbaled thrust that can change direction just like a rocket. He envisions a lightweight flying wing design, with high energy density batteries structurally integrated into the craft. He says the battery cells would need to be as light as possible, and have an energy density of at least 400 wh/kg with a high cycle life.
Because air is very thick at sea level, and air density decays exponentially, Elon argues the true benefits of electric aviation will be reaped in the low air resistance of high altitude, where you’ll go faster for the same amount of power.
To Elon, Electric Planes really start to make sense if you can ascend to a high enough altitude where you can cruise without using too much energy. He further posits that for electric aircraft efficiency, you want to have a high bypass ratio and move a large mass of air slowly with a large propeller, so you can reduce the velocity component of kinetic energy.
He argues that jet engines are inefficiently designed because they have to operate at a wide range of altitudes, and the key advantage of electric is that it’s not ingesting air. So it’s not effected by the low air density of high altitudes.
As for a Tesla Electric Aircraft, he’s not ruling it out entirely, but says he’s got a bit too much on his plate right now to tackle the friendly skies.
We are in the embryonic stages of electric aircraft.
With over 200 electric aircraft programs in development worldwide, this list was merely a sample of promising programs. Though currently limited by the weight-to-energy ratio of the batteries in an application where mass is mission critical, the industry stands positioned to make tremendous gains once a breakthrough in high-energy high-density battery technology is achieved. We will continue to see improvement in smaller limited range E-Aircraft, spurred on by efficiency advancements in motor and controller technology.
Meanwhile, we will see large and long-range aircraft adopt some form of hybrid power systems with existing combustion engines with hydrogen being a versatile and economical contender.
For long or high-speed flights, electric power is challenging but can certainly be used to offer a boost to smaller turbofans and it is quite possible.