Electric Aircraft: Creativity in Flight


At the Electric Aircraft Symposium in Santa Rosa, California, on Saturday, I scribbled in my notebook a wry comment from Tine Tomazic of Pipistrel Aircraft, the innovative Slovenian company that’s an unabashed supporter—and maker—of electric airplanes. Tomazic said he hoped the era of electric conversions was coming to an end and he pointedly noted that he bothered to place a question mark in the title of his half-hour discussion about conversions.

His comment represented a watershed of sorts in that it has become clear—and probably always was—that converting conventional airframes to electric propulsion are merely technical exercises in the service of conceptual aspiration and not necessarily products with market legs. Pipistrel’s own recently introduced Alpha Electro may or may not cross that threshold. It is a converted gasoline model, but because it’s so light and so aerodynamically efficient, it may represent the very minimum in what an electric airplane can eventually be. We’ll know in a couple of years if it finds market viability in Europe, where noise and emissions drive purchase decisions in a way they don’t in the U.S., further reinforcing the notion that market tides outside North America are shaping electric aviation.

Further proof of that resides in the two big players who presented technical details of their projects at the symposium, Airbus and Siemens AG, the giant German electrical concern. As we reported, Airbus is planning a two-place trainer and a four-place personal aircraft for the U.S. general aviation market. The trainer is a battery-powered electric, the four-placer a hybrid drive. In the distant future is the ambitious E-Thrust project, a multi-engine regional airliner with as-yet-to-be-developed hybrid drive. In case you’re wondering, the hybrid’s theoretical advantage is that its energy conversion cycle can be more efficient than a turbine engine alone. It would use a smaller turbine than might otherwise be necessary for takeoff and climb; batteries supply the necessary burst energy for those phases of flight, while the airplane would cruise on a smaller, less thirsty engine. The efficiency equation may pencil out, but there are huge challenges in weight, complexity and certification to overcome, so in specific dollars (or Euros) per knot or seat-mile costs, we’re a decade from seeing where this is a slam dunk.

Siemens is just as bullish on hybrids and has already developed stunningly power-dense electric motors that address the thrust side of the equation ahead of proven solutions for the energy conversion side. Taken together, these two initiatives represent a clear trend toward the hybrid idea and when I asked Siemens’ Frank Anton where pure electrics—that is battery electrics—fit into the emerging market, he figured they’ll retain a niche foothold and I think he’s probably right. But the foothold doesn’t even exist yet. Pipistrel’s Alpha Electric hasn’t delivered any airplanes and won’t until later in the year.

When they do, we’ll find out if 90 minutes of endurance is a realistic number for flight schools, we’ll find out how customers like e-flight and we’ll find out how quick-change battery packs and fast charging perform in the real world. We may also find out if potential buyers are fence sitting, awaiting the magical high-endurance battery breakthrough.

If so, they’ll wait a while. As expected, much of the discussion at EAS focused on battery developments, but the general consensus seems to be that lithium-based technologies are simmering along with 7-percent improvements each year and I didn’t hear much that suggests a corner to be turned, at least one that’s in sight. Right now, 180 wh/kg batteries are available and by the time you account for connectors, containment and controls, it’s about 155 wh/kg, which is what Pipistrel specs for the Alpha Electro. In five years time or a little less, we might see 300 wh/kg. That’s obviously better, but it’s not clear to me that it’s transformational.

In one session, Yi Cui of Stanford and a company called Amprius threw up a slide charting the commercialization of various battery technologies. His timeline carries lithium, lead-acid and nickel metal hydride well past 2035, but other theoretical technologies such as sodium ion and zinc ion are best guesses for 2020 or beyond and the really hairy stuff like aluminum and magnesium-based energy storage are far beyond that. Cui’s company, Amprius, is working on silicon-based anodes for lithium cells. It’s unclear when that will be commercialized. Another company, ZAF Energy Systems, showed some data for nickel zinc and zinc air technology that it claims can deliver up 450 effective wh/kg. That’s a nice bump, but the company’s Zach Favors also conceded these are laboratory-demonstrated numbers and industrialization, as with many of these technologies, remains an unknown.

What is not an unknown is lithium-ion hazards. We sat through quite a few video snippets of smoking, flaming, melting and exploding batteries. The people in this industry are, if nothing else, cognizant of their limitations. Pipistrel’s Tomazic jokingly described the Alpha Electric’s battery pack as “664 little nightmares.” The NTSB’s Michael Bauer gave a nice dissection of the Boeing 787 battery fires, complete with more gruesome photos and lab-test conflagrations. Watching his talk, I couldn’t help but wonder that with all the rigor the FAA forces on manufacturers to certify fly-by-wire systems, how did they ever let these potentially deadly battery systems into commercial aircraft? The fact that they failed as soon and as frequently as they did indicates to me that the technology wasn’t ready. I think they’ve probably got it tamped down now, but it was a fortunate turn of events that prevented those fires from causing more havoc than they did. Airline passengers shouldn’t be beta testers.

And as dicey as an airliner battery fire is, think about the same thing in a spacecraft. NASA has and Eric Darcy of the Johnson Space Center described how the agency built ceramic containment barriers and foam so as to mitigate thermal runaways to a degree that the ISS filters could handle the smoke. “It is doable,” he said.

That’s good, because as experience has shown, lithium-ion batteries are BYOB with regard to fire; they supply their own fuel and oxygen and are all but impossible to extinguish. But there’s help coming there, too. We heard about research on non-organic, non-flammable electrolytes that may some day render lithium-ion no more hazardous than carbon cells, or at least less susceptible to runaway. Yi Cui discussed so-called “smart separators” that sense potential internal shorts that can drop the cell offline before it becomes dangerously anti-social.

The range of research and actual commercialization expressed at EAS shows just a glimpse into the intellectual energy being poured into electric everything, not just electric flight. It hardly represents everything going on out there, but judging by who was at this event, there’s plenty of seed money and interest available to commercialize these technologies. The likes of Cessna, Northrop Grumman, Boeing and Lockheed Martin are showing up at these conferences, which suggests they’re paying attention.

The larger question is will there be customers or customers sufficient to sustain businesses? One representative of a major OEM whose name you would readily know said, “not there yet.” I detected a definite emphasis on yet, a view that I share. I particularly resonate with the hybrid drive idea for it recognizes, as many pure-electric acolytes do not, that we’re still in the age of oil, but aircraft are uniquely inefficient users of that energy. If hybrids can help, I wouldn’t bet against them finding a market, just as Siemens’ Frank Anton predicts they will. But let’s not get too far ahead of ourselves. Show us some flying prototypes and actual flight data. From now until 2020 is going to be interesting.