Lighter and more powerful electric motors, batteries that can store more energy, and more sophisticated aviation software are transforming small aircraft

By Tim Lee, Dec 2016, Cross-posted from Vox.  

There’s a couple of technologies that are maturing and converging” to make small, affordable airplanes feasible, says Brian German, an aerospace researcher at Georgia Tech.

German argues that lighter and more powerful electric motors, batteries that can store more energy, and more sophisticated aviation software could transform the market for small aircraft.

Indeed, several companies are already working on prototypes of car-size airplanes that could soon become cheap, safe, and versatile enough for ordinary people to use them regularly.

There’s a good chance you’ll rent them on demand from a company like Uber instead of buying one that parks in your driveway — a possibility Uber explored in a recent white paper. But a future where millions of people take short trips by air on a regular basis could be closer than you think.

a normal airplane needs a long runway to take off and land. Vertical takeoff and landing aircraft, by contrast, take off vertically like a helicopter, then switch to flying horizontally once they’re in the air. That allows them to take off and land in locations where conventional airplanes can’t.

VTOL airplanes are not a new technology — craft like the Harrier and the V-22 Osprey have been around since the 1960s. But these airplanes have never been very practical. They’re complex and expensive, and require pilots with specialized training to fly them.

But a shift from internal combustion engines to electric motors dramatically changes this equation. Electric motors can be much lighter, simpler, and cheaper than traditional aircraft engines powered by fossil fuels — and they’re getting lighter and more powerful every year. And that opens up a lot of new opportunities for airplane designers.

To see what the small, electric-powered aircraft of the future might look like, check out this image from a patent filing by Zee Aero, the Larry Page-funded startup. It shows a tiny personal airplane not much wider than a conventional parking space (you can get a sense of scale from this photograph of a man standing next to a prototype):

 Zee Aero, but there are lots of other prototypes under development.

It takes a lot more thrust for an aircraft to take off vertically than it does to keep the aircraft moving once it’s in the air. So Zee Aero’s design has eight vertical propellers that are used for takeoff, while there are just two in the back to provide horizontal thrust. Once the plane is soaring through the sky, the eight vertical propellers can be turned off to save power.

This kind of design wouldn’t work with conventional aircraft engines because 10 engines would be way too heavy. But electric motors can be made extremely small and light, allowing even a car-size vehicle to have 10 of them.

Of course, electric motors aren’t a new invention. But they’ve gradually gotten lighter and more powerful over time. Beyond that, it has taken rapid progress in two other areas to make VTOL vehicles practical: batteries and aviation software.

The big advantage of traditional airplane fuel is that it can pack a lot of energy into a small package, minimizing the amount of weight airplanes have to carry and allowing them to travel long distances without refueling.

“Right now, batteries that you could actually put in an airplane wouldn’t let you fly very far,” German says. “But you give it a few more years, and the writing’s on the wall that you will be able to make a very practical aircraft.”

Improvements in battery technology are a spillover benefit of innovations elsewhere in Silicon Valley. The burgeoning markets for laptops, smartphones, tablets, and electric cars have inspired companies to pour billions of dollars into better battery technology. As a result, the energy density of batteries has been improving steadily. And each time batteries improve, electric airplanes can be a little lighter and fly a little farther on a single charge.

German says battery technology isn’t quite there yet. He predicts the energy density of batteries will need to approximately double for small electric airplanes to really take off.

Batteries don’t improve as rapidly as computer chips, so it’s hard to say exactly how quickly batteries will improve. Tesla CEO Elon Musk, who is currently building a giant battery factory, has said that battery density typically improves by 5 to 8 percent per year, which implies that density could double in the next decade — though that could require finding new battery chemistries.

The other key breakthrough is better software. An airplane with 10 propellers is just too complex for a human pilot to manage effectively. But computer software can easily manage 10 propellers at once, supplying power to the propellers where the most thrust is needed.

And German says multi-propeller designs have significant safety advantages. “If you lose one, you still have some left,” he says. “You can design a lot of redundancy.”

The combination of smaller, more powerful electric motors, better batteries, and sophisticated software will open up dramatically new possibilities for aircraft design. I but there are lots of other prototypes under development.

The Volocopter looks a lot like a giant quadcopter drone — except that it has 18 propellers instead of the four you’ll find on a normal quadcopter.

Joby Aviation is working a two-seat airplane design that has 12 propellers for takeoff — four on the wings and four on the tail — that fold up once the aircraft is airborne, switching to four additional propellers optimized for horizontal flight:

 Joby Aviation

And of course, this is still a young field. If this technology does become mainstream, the successful design might look very different from these early prototypes.

Tiny electric airplanes could transform air travel

On its own, swapping conventional aircraft engines for electric motors could have significant benefits, reducing the cost of air travel and emissions per flight. But the bigger opportunity here is to make air travel practical in situations where no one would think to take an airplane today.

Back in October, Uber published a white paper describing its vision of the future small VTOL aircraft could make possible. Uber envisions a network of on-demand aircraft carrying passengers among many landing spots distributed throughout a metropolitan area. For example, right now it takes at least an hour to drive from San Jose, California, to San Francisco — and closer to two hours during rush hour. In contrast, Uber estimates, the same trip could take 15 minutes in a VTOL airplane.

Uber estimates that the trip would initially cost around $129, a cost that would fall to $43 within a few years and could eventually cost as little as $20. That compares favorably to the more than $100 it would cost to take a cab over the same route.

And because these aircraft can take off and land vertically, they wouldn’t require full-blown airports at each end. Vehicles could take off and land in small “vertiports” that could fit in a suburban parking lot or the top floor of an urban parking garage.  And naturally, Uber envisions an on-demand model where users book a flight with their smartphones minutes before arriving at a vertiport.

At first, VTOL aircraft are likely to have human pilots who steer the vehicles. Sophisticated software could control many routine aspects of the flight, allowing people to become pilots with less training than they require today.  In the long run, it will likely be possible to dispense with pilots altogether and have the aircraft fly themselves. This will not only save the cost of the pilot’s salary but will also reduce the vehicle’s weight and thereby further improve efficiency and lower costs.

That could lead to significant changes in traffic patterns. It could accelerate suburban sprawl, as affluent people buy land far from downtown and commute to work by air. Affordable short-range air travel could make it easier for city dwellers to take day and weekend trips to towns in the surrounding countryside.

In the long run, concerns about congestion and noise could create a bottleneck for widespread use of the technology. VTOL aircraft are likely to be significantly less noisy than a helicopter, but it would still be annoying to live next door to a vertiport with hundreds of flights taking off every hour. And even if the cost of operating a flying car gets cheap enough that middle-class people can afford it, there might simply not be enough space in the skies directly overhead major metropolitan areas to accommodate more than a fraction of the demand.

Obviously, we’re still several years away — at least — from commercial, on-demand flying car service. But we’re also well beyond the point of idle speculation. A number of startups have built working prototypes, and big companies like Uber have begun to study this market and consider how they might participate in it. So sometime in the next decade or two, expect to start seeing small, funny-looking airplanes buzzing around in the sky overhead