Because it’s just not practical to call multirotor flying machines “those multirotor thingies” we’ve come up with two terms to describe them, one for the machine itself and one for the market we imagine they will serve, such that we can imagine anything accurately in the midst of what’s clearly a revolution in aviation.
The machine label is EVTOL for electric vertical takeoff and landing, and the aspirational market segment is called, generically, urban mobility. This defines that imaginary world in which half the population of a city can potentially be whisked from one corner of the metro area to another in an autonomous, battery operated vehicle that’s quiet, cheap, free of emissions and actually exists. I’d say pick two because you can’t have all four, but it’s accurate to say you can’t have any at all for the time being.
The existing part is getting there, though, and this week I’ve been visiting Pipistrel, the creative Slovenian aircraft company that’s as far out front with this technology as anyone. They recently stood up a new division called Pipistrel Vertical Solutions and moved into a glitzy glass building in Ajdovscina, a charming little town in the Vipava valley about 16 kilometers east of the Italian border.
As we’ve reported, Pipistrel is one of several companies Uber Elevate has engaged to develop the vehicles that will fulfill the company’s vision of easily accessible, inexpensive three-dimensional urban transportation. Uber has in mind cityscape structures called Vertiports that would accommodate rooftop landings of EVTOLs, with elevators transporting passengers to the street level and perhaps to an Uber electric ride-share to the destination.
Pipistrel has a dog in this fight in the form of a proposed concept vehicle. It won’t be revealed until June 11 at Uber’s Elevate conference in Washington, so I can’t reveal even the minimal detail Pipistrel showed me during my visit. Four other companies are in the running for Uber’s business, including Aurora Flight Sciences, Bell, Embraer and Karem, an aerospace company that emerged from the drone segment, specifically the Predator. Of the five, Pipistrel has, by far, the most electric aircraft experience since it’s the only company delivering commercially viable manned electric flying machines. With its helicopter history, Bell is clearly out in front with vertical flight experience, although Embraer recently partnered with an Italian company to build and market its own business helicopters.
Uber wants to start flying demonstrations with these vehicles next year, with limited commercial service by 2023. There’s reason to doubt that timeline and further reason to doubt the validity of the underlying flight-based ride hailing concept, but, curiously, not the vehicles themselves. The technology in the form of batteries, reliable and powerful electric motors and autonomous control systems are right on the cusp of economic viability, says Pipistrel founder Ivo Boscarol.
Stipulating that the ride-share economics can be made to work, the largest barrier may not be the technology nor even FAA/EASA certification but what Pipistrel’s Tine Tomazic calls the related ecosystem, to include the infrastructure to support what Uber envisions as swarms of these vehicles. Tomazic said he was at a recent conference in which a city official poignantly observed that the entire urban mobility idea turns on what cities will allow these things to operate. Safety is an issue, of course, but in Europe and the U.S., noise may be the major driver. That alone has kept helicopters from gaining a useful foothold in intracity air taxi. If you’ve ever heard a multirotor drone fly, multiply that sound times five or 10 to imagine what a people-carrying version might sound like.
So all five companies, including Pipistrel, are hard are work developing ways to mitigate the racket. Interestingly, some of these, if all not all of them, may require something these vehicles don’t have an abundance of: power. Continuing energy density limitations of lithium ion batteries mean that the pure electric EVTOLs need all the amps they can get just to fly the basic mission, never mind schemes that might soak up more power to reduce the noise signature.
This has prompted more discussion about the hybrid or range-extender solution. In the EVTOL context, a hybrid is likely to be a serial design, in which an internal combustion engine drives a generator that can run the electric motors directly while also charging a smaller battery array than a pure electric aircraft would have. The tradeoff is weight against payload, complexity and reliability and emissions. Tomazic reminds us that combustion engines require fuel and cities with increasingly strict environmental regulations might not want liquid fuel hanging around the top of a five-story landing port in the middle of the downtown area. Maybe hydrogen? Maybe another discussion.
Pipistrel sees a dichotomy in the potential EVOTL market. A hybrid with a 300-mile-plus range for intercity transportation, possibly including cargo, and essentially the identical vehicle as a pure electric for the air taxi role. Right now, the range of such a thing pencils out to about 40 miles between charges, 60 at a stretch, but that taxes the all-important battery cycle life and the economics look less attractive if the batteries have to be replaced too often. Practical battery energy density now hovers at about 200 wH per kg and although it’s improving at the rate of 5% a year, it’s a long way from reaching capacities that would allow an EVTOL to fly all day and charge overnight.
Uber is leaning toward the pure-electric solution, but it’s hard to imagine they’ll stick with that. Given the range limitations, a mix of vehicles is likely. In addition to the weight penalty of the hybrid solution, there’s the challenge of what the hydrocarbon powerplant might be. Hydrogen isn’t on the table at the moment, but piston engines are and so are small turbines of the sort used for APUs now. These aren’t necessarily ideal because of the duty cycle is different and Tomazic says the foreseeable demand for potential hybrid aircraft is too small to ignite investment in new, purpose-made small turbines. It’s impossible to say when that disruption will occur, but it’s likely to eventually.
What’s the timeline likely to be here? No one knows that, either. Tomazic’s guess is that by 2028—about a decade from now—enough of these vehicles will be fielded to begin to notice them. But it’s doubtful that the role will be solely air taxi, if that market even potentiates at all.
While I was here, we toured Pipistrel’s new factory across the border in Gorizia, Italy, where I got my hands on a factory fresh Alpha Electro trainer, the only commercially viable such aircraft available. These airplanes are trickling down to the line at the rate of three to five a month, which is more than Ivo Boscarol thought the company would sell. The market is still a niche, but robust enough that Pipistrel is investing in a certified version with improved batteries. Global regulations have made it difficult to use the Electro for training, yet Pipistrel has sold about 60 nonetheless. Some flight schools are finding ways to employ them usefully.
The current version is much refined from the prototype I flew here in 2015. It’s much smoother, seems quieter and is generally just further down the developmental path. The battery monitoring system is prominent on the panel and there’s just no chance you’d miss knowing how much endurance remains. Right now, the Electro is reliably a 50-minute airplane with 20-minute reserve. Inside the cockpit, it’s not the quiet hum you might imagine from an electric motor because there is prop and slipstream noise. But no exhaust note, so with headsets off, you can converse normally. Its performance is virtually identical the Rotax-powered version, with the exception of the short endurance.
On the drive back to the offices in Slovenia, Ivo Boscarol told me one of those if-we-only-knew stories. He said when the Electro was first launched, the company had little idea how far they had to go to give it a strong commercial presence. While it’s not there yet, Pipistrel can at least say it’s further along than anyone else. Watch for a video on my factory visit in a couple of weeks.
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