Silicon Valley technologists have become obsessed with transportation, from driverless cars and superfast trains to space travel. But their latest infatuation seems improbable even by those ambitious standards: flying cars.

Uber this week promised that it would start testing an aerial taxi service in Dubai and Dallas as soon as 2020.

“Just like artificial intelligence, flying cars have been promised for decades, but are arriving now,” Jeff Holden, Uber’s chief product officer, told a conference in Dallas organised by the car-booking app on Tuesday. “I actually hate that term [flying cars] but we have to live with it — the media loves it.”

As Uber continues to be roiled by negative headlines alleging sexism, theft of intellectual property and hyper-aggressive management, it might be easy to dismiss the idea as a flight of fancy designed to distract a hostile press. Yet Uber is not alone in pursuing this sci-fi fantasy.

Kitty Hawk, a start-up backed by Google co-founder Larry Page, this week unveiled a prototype of its “flyer” — a single-person ultralight aircraft powered by eight electric rotors, which it promised would go on sale “by the end of this year”. Sebastian Thrun, the founder of Google’s self-driving car programme who leads Kitty Hawk, said in a tweet on Wednesday that more than 1,000 flights had been successfully completed on its flyer to date.

Kitty Hawk is one of several private companies that have been quietly working for several years on so-called “vertical take-off and landing” (VTOL) vehicles. By one investor’s count, there are already more than 40 companies developing small VTOL aircraft that can run on batteries and do not require runways or conventional airports.

One such start-up, Lilium, recently completed a successful test flight of its all-electric air taxi. “We believe in a world where anybody can fly anywhere, anytime,” says Daniel Wiengand, co-founder and chief executive of Lilium, which was founded in Munich in 2015. “We want to democratise clean aerial on-demand transportation.”

At the other end of the corporate scale, aerospace giant Airbus has said its Vahana concept will take to the skies for testing later in 2017.

Jaiwon Shin, associate administrator for aeronautics research at Nasa, the US space agency, said it was a matter of “not if but when” such vehicles begin to swarm over American cities. “I truly believe that we are standing and looking at the dawn of a new era of aviation,” he told Uber’s Elevate conference in Dallas on Tuesday.

The technological breakthroughs powering this renewed enthusiasm are similar to those underpinning self-driving cars: the shift to electric propulsion, driven by improvements in battery technology, and advances in machine learning that enable machines to “see” and pilot themselves.

“The insanity now surrounding the driverless car community has spilled over [to aerospace] — in a good way,” says Missy Cummings, a former military pilot who is now a professor of mechanical engineering at Duke University. “I think the hype will help push these ideas ahead . . . The reality is all the pieces are in place.”

Another driver is the emergence of consumer drones. While much smaller and lighter, they are helping to drive down the cost of some components — just as the smartphone supply chain enabled the creation of products such as DJI’s Phantom quadcopters in the first place. One Chinese drone maker, Ehang, has already created a passenger vehicle it plans to test in Dubai this summer.

“If cheap drones are the peace dividend of the smartphone wars, self-flying cars are going to be the peace dividend of the drone wars,” says Jeremy Conrad, partner at hardware investor Lemnos Labs.

Paul Eremenko, Airbus’s chief technology officer, wants to accelerate the development and construction of flying demonstration vehicles. Exploring urban air mobility allows Airbus to test a number of emerging technologies including autonomy, electrification and inexpensive carbon composites. “At the convergence of all of those, we envision the possibility, and so we built the demonstrator to see if our view of technological convergence is right,” says Mr Eremenko, who Airbus poached from Google in 2015.

But he admits there is still much to do in terms of public acceptance and regulation before the skies are packed with flying cars. In a recent interview with the Financial Times, Mr Eremenko admitted that the flying car concept Airbus unveiled at the Geneva Auto Show in March was more about familiarising the public with the idea than trialling technology. “That’s not a real product — that’s the equivalent of a concept car,” he said. “Public acceptance, urban acceptance and regulatory acceptance are not there yet. We want to make people dream.”

One big problem in winning public acceptance is noise, even though electric engines promise to be much quieter than a traditional helicopter. Another challenge is regulatory uncertainty, from air traffic control to safety checks. Before achieving autonomy, these small aircraft will still need human pilots and it is unclear who will train or certify the thousands of pilots required to reach the scale Uber envisages.

The safety and long-term reliability of electric and VTOL vehicles is also unproven. More people have ridden a rocket into space than flown a battery-powered plane, according to an executive at Pipistrel, a pioneer of electric aircraft.

“The two biggest concerns I came away with as an investor are really the market risk and the regulatory risk,” says Michael Linse, co-founder of Levitate Capital, a new fund focused on VTOL companies. “Uber’s commitment to the industry helps mitigate those risks quite a bit.”

At Uber’s Dallas gathering, engineers, entrepreneurs and pilots who have dreamt for years about personal aerial vehicles could barely contain their glee at the extra momentum brought by the $62.5bn car-booking juggernaut. One engineer suggested that people might hail their flying cars with thought waves instead of a smartphone, while the creator of a steam-powered car in the 1970s put forward his design for a plane-helicopter hybrid that has been more than 20 years in development.

Claiming inspiration from Star Trek creator Gene Roddenberry, Pat Romano, the chief executive of electric-car charging network Chargepoint, said of his first meeting with Uber on the topic: “Before they could even get their questions out, I was like, ‘I’m in’.”

Chargepoint is one of several companies partnering with Uber to bring its vision of short-range urban aerial transport to life, alongside vehicle developers Aurora, Embraer, Pipistrel and Bell Helicopter.

Ivo Boscarol, the chief executive and founder of Pipistrel, promises small aircraft would be picking up passengers from their apartment windows within 20 years.

In the near term, Uber is being less ambitious. Its plan would see a citywide network of “vertiports”, allowing human-piloted aircraft to carry a handful of passengers an average of 25 miles, travelling at upwards of 150mph.

Uber believes that with enough volume, a 15-minute flight from San Francisco to San Jose would eventually cost no more than in its “X” ride-sharing service does today — about $1.32 per passenger mile. “It’s possible because we are radically changing the type of aircraft we are talking about here and we are doing it at mass scale. This is why Uber is running at this, as opposed to taking a careful, slow approach,” said Uber’s Mr Holden. “We are talking about volumes of [vehicle] production that go way beyond what aviation has ever done.”

Even though Uber has conquered the taxi industry and challenged the notion of car ownership, Prof Cummings suggests that traditional air transport companies need not be too worried about imminent disruption. Kitty Hawk’s flyer, for instance, is only designed for recreational use over fresh water, in uncongested areas.

“I have not seen any of these companies show any hint of a vehicle that is even close to being ready for passenger services,” she says. “There are still too many question marks in the air.”

Battery limits could ground flying cars
One of the key technical hurdles for getting flying taxis into the air is the batteries that power them, writes Leslie Hook.

Unlike electric cars, these flying vehicles will require a tremendous burst of power to achieve vertical lift-off, and this power burst means that there is less energy stored overall in the battery.

Uber itself acknowledged that batteries were a big barrier in an October white paper, where it described existing battery technologies as “insufficient”, adding that it expected batteries to become good enough within the next five years. However, at this week’s conference, Uber trimmed back its original goals for the speed and range of its flying taxis — two key measures that are highly dependent on batteries.

Batteries are extremely limiting for small aircraft because of their weight. For a small personal craft such as the Joby S2 electric VTOL aircraft, the 700-pound battery can represent nearly half the total weight of the entire vehicle.

The industry is divided over whether batteries or combustion engines will work best for flying cars. “The battery improvements are not going to happen nearly as fast as people believe,” says Paul Moller, head of Moller International, which is working on a flying car. “It is slow, it is very, very slow.”