From Airbus and Bell to Silicon Valley startups, everyone says they're building electric planes. How far off are they really?

The 1957 prediction hasn't actually gotten much closer

In the summer of 1957, an American teenager boarded a long-distance bus in Dallas, on his way to visit his father in Oklahoma City.

This was three months before the Soviet Union launched Sputnik 1, humanity's first artificial satellite, and a year before NBC started broadcasting in color.

Flying cars would be everywhere within ten years.

That was the conclusion the teenage Robert Sadler drew from the issue of Popular Mechanics he was reading on the bus. The July cover showed a flying car: no wheels, a red passenger pod in the middle of the body, four lift fans arranged front and back. In the lower left corner it said, Your Flying Car, 1967.

Sadler, then 12, fretted about it for weeks. He didn't have a driver's license yet, and he worried that by the time he grew up there would be no ground cars left to drive.

Sadler went on to serve in the Vietnam War, worked as a police officer, and became a novelist after he retired. In his first novel, Jamaica Moon, he gave that private turmoil of the summer of 1957 to a fictional character: I'll never get to drive a car.

Sixty years have passed. Humans have been to the moon, more than once. But flying cars never showed up — until recently.

At the TED conference in late April this year, Todd Reichert, head of aerodynamics at the startup Kitty Hawk, played a video on stage: a man dressed like an extreme-sports enthusiast straddled a "flying car" that looked like a cross between a DJI drone and a motorcycle, and took off.

Reichert said a rougher prototype would be available for people to ride within a few months, and a more polished product would go on sale before the end of the year.

Kitty Hawk's CEO is Sebastian Thrun, who used to run Google's self-driving car project. The money comes from Google co-founder Larry Page.

And Kitty Hawk is the least ambitious of this whole crowd of flying-vehicle companies.

The same week Reichert announced the flying plan, Uber held its flying-taxi summit in Dallas. There, Bell Helicopter — the giant behind the Huey, the Cobra and the Osprey — announced it would work with Uber on electric flying taxis.

Airbus announced a similar plan on its side, setting up a wholly owned subsidiary in Silicon Valley called A³, whose main goal is likewise a single-seat electric vertical take-off and landing aircraft. The project is called "Vahana" — Sanskrit for "vehicle of the gods."

Uber's and Airbus's plans are much the same: build an unmanned vertical take-off and landing aircraft that can pick up a passenger on its own and fly them to their destination. Arriving by 2020.

More ambitious still is Wright Electric, launched this year out of YC, Silicon Valley's biggest startup incubator. Within 20 years, it wants to deliver electrically powered regional airliners that can carry more than a hundred people.

Wright Electric; Kitty Hawk, the place where the Wright brothers test-flew the first airplane. You can read the ambition off the names.

Is 2017 really about to become "1967"?

The market wants electric planes, and it comes down to airline costs

What all these plans have in common is electric power, because motors and batteries are simple enough. In an "air taxi," they promise a smaller machine than a helicopter. In a regional airliner, they promise lower costs.

Today's aviation industry isn't worried about aircraft performance. The modern airliner is one of the best-value machines humans have ever built for moving people. Today's airliners have far more power than they need to get off the ground. The twin-engine airliners Boeing sells can still land safely after one engine shuts down.

And per passenger, they are far more efficient than a car engine.

Take Boeing's newest intercontinental airliner, the 787. The 787-8 holds more than 120,000 liters of fuel and flies more than 15,000 kilometers. On a three-class layout of 242 seats, each passenger burns only 0.03 liters of jet fuel per kilometer. In practice, many two-class 787-8s carry more than 300 people.

To match that, a sedan would have to be filled with four people — and it would still be much slower. Jet fuel costs about half what gasoline does, or less.

But that fuel bill is still too high. At the fiercely competitive US airlines, fuel now accounts for a third of all costs.

Airlines have already squeezed out everything they can, so they have moved on to adding seats and cutting service. Hence economy class that keeps getting tighter, food that keeps getting worse, and a free carry-on allowance that keeps shrinking.

Jet engines also still burn fossil fuel, and they put out large amounts of carbon dioxide in flight. In 2012, Europe brought aviation into the EU Emissions Trading System (ETS), requiring the airlines on any flight leaving from or arriving in Europe to pay for 15% of all the carbon dioxide they emitted over the year. The measure would have pushed the price of a single ticket up by at least 60 euros.

But big aviation countries including the US and China pushed back, arguing that the law did nothing to control emissions at the source — engine manufacturing, fuel and so on — and that charging the airlines was therefore unfair. From the autumn of 2013, the EU's carbon charge on airlines was suspended.

Suspended, but the direction has not changed.

The global air transport industry's carbon targets include raising fuel efficiency by 1.5% a year up to 2020; setting a cap on net emissions and reaching carbon-neutral growth before 2020; and cutting carbon emissions to half of 2005 levels by 2050. Boxed in like this, airlines' current fix is to replace jet fuel with biofuel extracted from things like waste cooking oil, saving energy and money at once.

But biofuel is not a complete answer, because the underlying problem is that carbon dioxide controls are tightening everywhere. Sooner or later, aviation will be a regulated-emissions industry too. Airlines may have no choice about it, but aircraft makers like Airbus and Boeing, for the sake of their own future and the industry's, have to find an alternative as well.

The hardest part of electric flight is power

Electricity is remaking the car industry, and the new companies getting into the flying business are trying to do the same thing.

That is also the hardest part.

What makes a modern airliner fly so efficiently is the two turbojet engines slung under the wings.

Ordinary airliners already run on jet engines, but not the kind that shoots out long flames when a fighter accelerates. More than 70% of an airliner engine's thrust comes not from the turbine's compression and combustion but from the fan being driven around the outer ring. Look at the engine head-on and you can see that spinning fan; it supplies most of the airplane's power.

Plenty of regional airliners, meanwhile, use turboprop engines — the most common being the ARJ series, Bombardier's Dash 8 series, and China's own Xinzhou regional aircraft.

Put simply, almost every airliner flying today makes its power by burning aviation fuel to spin a fan or a propeller.

That is what leaves room for the electric airplane, because electricity driving a motor can spin a fan too, and get a plane off the ground. In theory, take the turbofan engine on a Boeing or an Airbus, swap the core from a turbine to an electric motor, and as long as there is enough electricity to spin the fan at a similar speed, the plane will still fly.

The problem is that today's batteries are still too weak.

By Batterybro's calculation, a kilogram of the jet fuel used in jet aircraft holds 138 times the energy of the common 18650 power cell. The 18650 is a cylindrical lithium cell; a Tesla's battery is made up of more than 7,000 of them.

Clearly, putting electric motors on a 787 and flying 300 people from Beijing to New York is out of the question.

The fallback everyone reaches for is better aerodynamic design and a smaller airplane.

That is exactly what the startup Wright Electric is after. The YC-incubated company publishes a weekly report on who it has talked to, what work it has done, and what problems it has been studying.

In its report of April 23, 2017, Wright Electric set a battery target: 400 watt-hours per kilogram of energy density. That is a small fraction of jet fuel's energy density, but still far above the 250 watt-hours per kilogram of today's Tesla 18650 cells.

Lithium battery technology, meanwhile, is advancing slowly. Driven by phones, computers and electric cars, industrial lithium batteries have improved a good deal over the past 20 years. But from 1991 to 2011 their energy density only doubled, to roughly 200-300 watt-hours per kilogram, and that growth curve is now flattening.

Follow that curve, and even the minimum battery performance Wright Electric expects it can live with would require today's energy density to improve by at least 50%, and as much as 100%. At the current rate of progress, that is 20 years away, maybe more.

Another option is the fuel cell. In theory the fuel cell is an excellent source of power: a hydrogen or ethanol fuel cell can store its fuel in a conventional tank and travel a long way. Toyota's Mirai, a hydrogen fuel cell car, takes only a few minutes to fill its hydrogen tank and can go 700 kilometers.

But fuel cells cannot be used at scale on airliners right now. One reason is that the precious metals they need are scarce and the cost is too high. Another is that a large fuel cell reactor is not safe enough to put on an airplane.

The electric aircraft already flying aren't built to carry many people

Plenty of prototypes and experimental aircraft have already tried electric flight.

The Helios solar-powered prototype, developed by NASA with AeroVironment, is one of the most famous electric aircraft. The unmanned, remote-controlled plane was only 3.6 meters long, about the size of a Mercedes Smart, but its wingspan was enormous — more than 75 meters, wider than the 65-meter span of a Boeing 747. It looked like a flying ruler.

Helios's wing surfaces were covered in solar cells, with lithium batteries to store the surplus, and 14 two-horsepower electric motors to drive it. By design it could fly as high as 30,000 meters and stay up for months.

In 2001, Helios flew successfully, reaching 29,524 meters — a world record for a fixed-wing aircraft — and holding that altitude for more than 40 minutes. A normal airliner flies at around 9,000 meters. At 30,000 meters, Helios could get above all air currents, rain and other weather, in effect becoming a satellite inside the atmosphere, which was the whole point of the design.

In 2003, the improved second-generation prototype, its power system switched to a hydrogen fuel cell, broke apart on the take-off leg of a test flight because of the weather.

Some electric aircraft can of course carry people. In 2014, Airbus showed a small two-seater called the E-Fan at the Farnborough Airshow. Powered by lithium batteries, it had two 60-kilowatt electric motors behind the wings driving ducted fans, good for an hour in the air.

The E-Fan's demonstration flight at Farnborough went well. Airbus's plan called for some interesting touches on later versions of the E-Fan: powered landing-gear wheels, like a car's, that could get the plane up to about 60 kilometers per hour on the ground before the electric motors took over for take-off, saving power. Otherwise the propwash alone has to push the plane to take-off speed on the ground, which is the most energy-hungry stage of a flight.

Airbus's long-term plan for the E-Fan was to start with this two-seat, lithium-battery trainer and work up to a four-seat light aircraft with longer range and a kerosene fuel cell, with the eventual goal of a 90-seat electric regional airliner, fit for commercial service, sometime after 2020.

But progress on electric aircraft was too slow, and the E-Fan program was cancelled in April 2017. Airbus turned instead to conventional engines plus hybrid power — aircraft with electric wheels, for example.

One other electric aircraft went further still.

In July 2016, Solar Impulse 2, the solar aircraft project led by the Swiss explorers Bertrand Piccard and André Borschberg, completed a flight around the world: 558 hours in the air, split into 17 legs.

The plane was designed and built by the Solar Impulse team, with a wingspan of 71.9 meters. Its wings carried 11,628 flexible monocrystalline silicon solar cells covering 200 square meters. Those cells charged a total of 86 kilowatt-hours of lithium-ion batteries, which ran four motors of about 7 kilowatts each, without a break, day and night.

Solar Impulse 2 left Abu Dhabi in the UAE on March 9, 2015, and reached Muscat, Oman, 13 hours later. After a short stop it flew on to Ahmedabad, India. The route then took in Varanasi in India, Mandalay in Myanmar, Chongqing in China, Nagoya in Japan and Hawaii in the US, among other stops, before finally returning to Abu Dhabi. Most of the 17 legs came in under 20 hours, but a few ran for days: Nanjing to Nagoya took 44 hours, Nagoya to Hawaii 117 hours, Hawaii to California 62 hours.

The flight was broken into legs partly because the project wanted to travel the world promoting clean energy, but mainly because the aircraft weighed only 2.3 tons in all. It is closer to a powered glider, more easily pushed around by air currents, so the pilot had to stay at the controls for long stretches. On the 117-hour crossing of the Pacific — more than five days and nights — he had to fly to a peculiar schedule: two hours flying, 20 minutes' sleep.

In other words, the aircraft's power system could have kept it in the air indefinitely. Its control system wasn't good enough, and the pilot couldn't hold out that long.

There is a nice story about Solar Impulse 2. In the small hours of March 31, 2015, as it approached Chongqing Jiangbei Airport, it hit strong winds. The ground told pilot Bertrand Piccard that his groundspeed — the aircraft's absolute speed over the ground — was minus 20 kilometers per hour. The plane was moving slower than the wind.

Long-endurance solar-electric aircraft, NASA's Helios and Solar Impulse 2 included, all use a similar design. They are less airplanes than powered gliders.

Obviously, passengers who buy tickets will not accept that kind of speed.

In an earlier interview, Airbus's chief technology officer Paul Eremenko said that if there is a revolution in propulsion, future airliners will not look the way they do now; their shape could change a great deal.

If tomorrow's hybrid engines get small enough, he said, a single aircraft might carry many of them. The wing-and-fuselage structure planes use today could then give way to something like the Concorde's delta wing, or the blended wing-body shape of NASA's experimental X-48.

Airbus has already made a few attempts at changing what powers an airplane. This March it announced a partnership with Siemens to jointly develop hybrid-powered airliners.

Eremenko also said that a fully electric large commercial aircraft is limited by energy-storage technology — that is, batteries — and that it is too early to talk about seriously.

Air taxis that look like oversized drones are what the big companies want

A little closer at hand is the electric flying taxi.

In The Fifth Element, the New York of the future is a three-dimensional city: the classic yellow cab has become a flying craft, and the lanes of traffic have become different altitudes in the sky.

That is roughly the goal Uber set out at its flying-vehicle conference in late April. There, Uber said it would work with Bell Helicopter to jointly develop an automated transport system for commuting through the air over cities. In Uber's vision, the electric unmanned aircraft also replaces the car, but does not get around the way a car does.

Uber imagines that once flight technology and self-driving technology mature, rooftops downtown and residential neighborhoods in the suburbs will have landing pads with room for several electric aircraft, and a user will be able to summon a flying vehicle for a quick commute as easily as hailing a car on a phone today.

Airbus's plan is the same. At the 2017 Geneva Motor Show, Airbus displayed a prototype electric personal aircraft called Pop.Up.

This vehicle, billed as an electric car, is for now only a static display model, and its shape looks familiar: four ducted rotors in a square grid, with a passenger pod hanging below — for all the world a scaled-up DJI Phantom camera drone.

The design is very common. At CES 2016, the Chinese toy-drone maker EHang showed something much like it.

Some startups' prototype personal aircraft use a similar tilt-rotor design. Lilium Aviation, of Munich, Germany, test-flew its prototype successfully in April.

The aircraft is a two-seat, all-electric, vertical take-off and landing machine, powered by 36 small ducted fans on the wings and the front of the fuselage; the fans point down for take-off and swivel to face backward for level flight. Lilium Aviation claims a range of 300 kilometers and a top speed of 300 kilometers per hour.

But it looks unreliable too. Charles Eastlake, an aerodynamicist at Embry-Riddle Aeronautical University, says the claimed performance is overstated, because the batteries you can pack into a take-off weight of a mere 600 kilograms cannot fly a 450-horsepower aircraft for an hour. A Tesla Model S, with more than 900 kilograms of batteries, only manages 400 kilometers on the ground.

But this kind of design does look like the right direction for a flying car: vertical take-off and landing, no runway needed; a cabin that needn't be large, since seating 2 to 4 people like a sedan is enough; and no need for long range, because an urban commute is generally under 100 kilometers.

To get vertical take-off and landing and decent flying speed at the same time, the tilt-rotor design of the V-22 Osprey, developed jointly by Boeing and Bell Helicopter, is a better fit than DJI's.

The V-22 has two rotors. For take-off they point straight up and lift it vertically; then they rotate to face forward, and the aircraft flies like a fixed-wing plane, which performs better than a helicopter.

But this is not easy to pull off, because humans do not really understand what makes flight work. The widely repeated theory — that a plane flies because the upper and lower surfaces of the wing have different areas, so air flowing over them creates a pressure difference that lifts the plane — has been rejected by NASA's own research. The direct counter-example: a fighter jet can fly nose-down, a position in which the theory says the wing cannot generate lift at all.

So even though the aviation industry has verified how a great many different designs fly through exhaustive experiment, every new design still needs an enormous amount of testing, and real exposure to extreme conditions, before it can be called safe. That process still cannot be done entirely in a lab with computer simulation.

Because it was an entirely new field, developing the V-22 Osprey ran into serious trouble. From 1997, the Osprey prototype was found prone to a structural problem that dropped it into vortex ring state and crashed it. Three major accidents killed more than 20 soldiers and engineers. The fault was fixed later.

Soldiers dying in training, and aircraft killing people during test flights, are regrettable but foreseeable losses. Hailing a taxi is different.

Which is why manned aviation is regulated so strictly.

Especially in the scenario Uber and its peers imagine, with air taxis flying over cities, where an accident threatens pedestrians on the street and residents inside buildings. Put equipment like that into commercial service and the timetable is anyone's guess.

The US and China haven't even finished writing the law on commercial drones, never mind manned aircraft weighing several hundred kilograms at least.

Airbus has announced a 2020 target, but that is only for the first flight. Its CTO Paul Eremenko said in an interview that the Vahana electric personal aircraft in Airbus's plan would fly for the first time within two years, but that commercial service is a long way off.

The first electric aircraft to arrive will probably be a toy

Of this whole pile of companies, the one furthest along, and the one that looks most likely, is Kitty Hawk — a name with no less ambition than the rest. In 1900, the Wright brothers came to Kitty Hawk, North Carolina, and began testing powered gliders; in 1903, the Flyer I flew, becoming the first controllable powered aircraft in human history.

What this Kitty Hawk, the one Larry Page put money into, wants is simple: a big toy.

The prototype that has already flown is about the size of a motorcycle, carries one person, and gets its power from six rotors, but it can't go high — 2 to 3 meters off the ground. Its structure is actually simpler than a DJI drone's: apart from the rotors, which a computer keeps balanced, it has no radio control and no obstacle-avoidance radar. The rider sits on top and works a hand controller. It is a manually operated drone.

What Kitty Hawk is for is simple too — fun on a camping trip, that sort of thing. Nobody is really going to treat it as transport. Kitty Hawk says this big toy of theirs will go on sale by the end of 2017.

If all goes well, Kitty Hawk will end up somewhere alongside skydiving and paragliding: a thing people do so they can photograph it and post it to Moments. And that is probably as close as an electric aircraft will get to our daily lives.

As for landing at an airport on an electric regional airliner and then calling a flying Uber or Didi to get home — 2017 is not much closer to that world than 1957 was.

Images/Wikipedia