Electric Atmosphere

With innovations in sustainable fuels, airframe design, and safety, we may not recognize the machines that take us into the skies 20 years from now. Incredible resources are being poured into development of new technology at a rate not seen in 80 years—at least in the private sector. What’s surprising and inspiring is that much of the innovation shaping aviation across the board comes from the ground up—from general aviation—rather than trickling down from the airlines and military.

Pipistrel, one of these key ground-up innovators, experienced humble beginnings as a tiny hang glider manufacturer a few decades ago. It grew gradually and strategically from its original home in a garage serving hobbyists to winning consecutive competitions for flight design at NASA—and eventually scoring a $1.3 million grant from the agency 11 years ago.

Now, it’s part of Textron eAviation, and two years in, the company marked significant expansion in Africa, Canada, and the United States—including a deal with the U.S. Air Force—and a historic first piloted flight of liquid hydrogen powered electric aircraft. All of this innovation is impressive, and talking about it in sweeping terms rather overstates the obvious at this point.

But what does it mean for pilots—particularly those of us who inhabit the GA sphere? How will the advancements of companies like Pipistrel shape the practical realities of flying?

“It’s, to me, incredibly rewarding that now, some 15, almost 16, years after we started flying electrically, there’s genuine interest in the public domain for this field,” Tine Tomažič, Pipistrel’s director of engineering and programs, tells Plane & Pilot. “It’s interesting how people call it an ‘emerging field.’ To me, it seems like [we’ve been] doing it forever. 2007 was when we put together our first battery that flew. Looking back, it’s not something I would ever be willing to put in the hands of a customer, but it worked.”

The company has gone through generations of battery technology, applied to various airframe projects, since then.

“We’re probably still the one entity that has tried in flight tests, and put through to the product stage, more different electric aircraft than anyone else,” Tomažič says. “We’ve had gliders, trainers, record-setting aircraft, and even some hybrids involved in hydrogen flight through partnerships. So we’ve seen a lot.”

The Taurus Electro, a self-launching glider and the company’s first deployment airframe of choice in 2007, now flies with what Tomažič terms its third generation of battery performance and fourth generation of battery functionality. The liquid-cooled Velis Electro and its predecessor, the air-cooled Alpha, are also on their third generation of batteries. Timing and economics factor into when it’s feasible to introduce new technology waves, and Pipistrel was as affected by the COVID-19 pandemic as the rest of the industry.

“Pipistrel is continuously screening what’s happening on the battery technology front,” says Tomažič. “Through the years, we’ve equipped our laboratories, and we’ve essentially self-developed methodologies that allow us to screen what’s going on in the battery industry. We obtain samples of actual batteries from the makers and put them through their paces.”

Engineers then assess the electrical performance to answer questions such as whether a particular technology could improve the endurance of the Velis or affect the climb speed of the Taurus. They also consider the longevity of the battery, which is an economic driver.

“We look at the safety and the thermal aspects,” Tomažič says. “All of these are being assessed for essentially every new sample we can get our hands on. This catalog of cells is ever-growing. I think we are past 80 different cells in our catalogs. And we know all about how they would behave in terms of performance, safety, and longevity.

“That’s actually key because there’s no such thing as one single battery technology to find in a glider application or a motor plane application, let alone a hybrid powertrain… It is the battery that gives the aircraft its character.”

Airframe design, and aircraft purpose and mission, are inseparable from the technology that drives them. The necessary tradeoffs in battery technology development give new life to the old Bauhaus principle “form follows function.”

Pipistrel uses different battery chemistries for its products depending on the capabilities of each technology. Tomažič draws an analogy with sports to illustrate why one battery is not one-size-fits-all. You wouldn’t send a sprinter to run a marathon—or the other way around.

“There are nuances to that,” he says, “but you have to choose the best tool for the job. And when it comes to electric flight…what’s always hidden and perhaps not that easy to understand by an observer is how much the character of the aircraft can actually change because of what the battery can or cannot do.”

Tomažič points to a common misconception that you can produce viable electric flight products by swapping the powertrain, going from a fuel-powered airplane to an electric one for example. Some characteristics of electric drives make existing aircraft less than ideal for deploying electric platforms.

“Just like you may have seen with early electric cars where this exact thing was happening, they pulled out the big [engine] block and put in the battery and, I mean, how far did they drive? Yuck,” he says. “Now you see designs that were born to be electric, and they don’t have the feasibility of ever putting in a gasoline engine, and that makes the product really shine. I think the successful products will be those that are being prepared, or were prepared, with electrification in mind—or being developed only so that they are electric.

“We made an intentional choice with ourselves that we will just not design new aircraft if they are not at least hybrid-electric or all-electric, because we can appreciate how powerful the connection between the aircraft’s airframe and powertrain actually is. It’s a real marriage.”

This translates into tradeoffs in functionality, depending on what purpose comes to the fore.

“If you have a draggy airframe, it doesn’t matter if you have a super-efficient electric motor on the other side,” he says. “Everything somehow has to come in balance, and that’s what creates goodness. And this means that good electric aircraft will undoubtedly look and feel a little bit different from what you are used to seeing on your classic [Cessna] 172, your Piper, your Diamond, your Cirrus, etc. There is change coming because of electrification on the airframe look and feel side of things as well.”

One of those tradeoffs might be a more efficient, cost-effective battery charging cycle at the expense of range and endurance. Or the converse—better range might mean increased cost per flight hour and reduced efficiency. These options might look different depending on whether an aircraft is intended as a trainer or for GA cross-country missions in the U.S.

“Let’s say I want to improve charging speed. Maybe I will sacrifice a bit of cycle life,” says Tomažič. “For this reason, we are screening so many different battery technology candidates, so we can make an informed decision about where we will be introducing, let’s say, the increase of goodness, and Velis Electro is a good example. Between generations one and two of the batteries, what improved was the longevity, more cycles essentially obtained from the same battery, meaning every flight hour becomes significantly cheaper, and there is the opportunity to charge the battery faster—but the flight times are about the same.”

The next generation of battery might mean an increase in flight time, or it could mean further improving efficiency and cost.
“It’s all about how you strategically approach these things,” he says. “Every aviation maker, no matter large or small, continues to dream along the lines of faster, farther, bigger, more. We are not different.”

The endurance capabilities reflected in the Pipistrel aircraft are not at the leading edge of battery technologies, but instead are the best mix of affordability, safety, and practicality for the design, Tomažič points out.

The Velis Electro, designed to be operated alongside training aircraft that flight schools may already have, was not meant to replace a fleet and provide a platform that would fit an entire syllabus. Instead, Pipistrel designed it primarily as a cost-effective option for traffic pattern training with a low noise footprint.

“It is fantastic to see that people started asking questions like, ‘When can we fly longer?’ because this means that they started trusting the product as is,” says Tomažič. “We don’t get questions like, ‘When can we improve the reliability on this and that?’ or ‘This doesn’t work, or that doesn’t.’ It all works. The problematic child is endurance.

“I think range anxiety is a real thing when it comes to electric mobility: cars, electric bikes, scooters. Airplanes are no different, and I can appreciate this mindset. If you look at what the absolute majority of general aviation is doing, it kind of revolves around the three-hour mark, and that’s kind of sized according to what human bladders can take.”

Tomažič hints that a three-hour electric aircraft is possible in the future, “and if any company can do it, I want it to be us because we can leverage all that we’ve learned and build on top of these solutions…in a way that people will accept—and they will accept it when it’s quiet, practical, simple, and cheap.”

Range and endurance increase as technology advances, and Tomažič wonders if potential complications that come with new technologies will be acceptable to GA pilots. He points to the “modest but incredibly rewarding” truism of Pipistrel’s Taurus Electro and Velis Electro: Their environments are familiar for pilots.

“The technology has reached levels of maturity where you don’t have to be an engineer or an astronaut or some local neighborhood weirdo with funky hair because of having been electrocuted,” he says. “Electric aircraft fly just like everything else.”

Prudent or thrifty aviators may wonder if they could end up throwing away money on an aircraft that could become obsolete in a relatively short time. Our legacy aircraft have proven their reliability and staying power. What about these new birds?

Pipistrel designs its electric planes to be upgradeable over time, hoping to continue to lead the industry by ensuring new battery generations are compatible with its existing airframes, in addition to developing new platforms. And these upgrades don’t entirely correspond to engine upgrades and overhauls.

Tomažič asks the conventional aircraft owner to consider how often a craft becomes better in its lifetime.

“Pretty much never, right? Unless you throw a lot of financials on it,” he says. “Changing the avionics is kind of like the favorite cosmetic surgery of choice on a typical plane. But it doesn’t change its endurance. It doesn’t change its payload. It doesn’t change its performance. And with electric flight, all of these parameters continue to improve.

“The newest research we are applying to batteries goes in two directions, or almost two and a half directions. One of them is the more modest continuation of what we call wet energy chemistries, [or improvements in lithium-ion technologies].”

And then there are solid-state batteries, an emerging technology that replaces the liquid electrolyte insulation with a powder-like substance.

“That makes the aircraft’s battery potentially behave differently, and maybe safer as well,” he says. “But, in particular, it gives different packaging options to the battery. Now, batteries are…kind of luggage, in the sense of how they fly.”

He says Pipistrel is working on ways to better integrate batteries into airframes, exploring the possibilities of putting them into wing structures instead of the fuselage to offset the problem of bulk. Solid-state batteries are one potential solution.

“The most exotic battery research happens on what we call structural batteries,” Tomažič says. “Essentially [this means] putting batteries inside composite laminates so that the structure of the plane starts to get a dual function. Initial applications will not be for, let’s say, achieving propulsion, but the aircraft has many different electrical needs, including avionics.”

Pipistrel’s engineers are asking, what if there’s a better way to package batteries than as luggage? These new ideas take time to mature. For battery technology fielding, Tomažič asserts that there’s no such thing as year-over-year growth. A battery cell maker decides to start manufacturing a new chemistry, but with the decision-making time and production taken into account, it can be 40 years before particular batteries become cost-effective.

“There’s no such thing as me calling up to a supplier and saying, ‘Hey, can I get a 6 percent battery next year?’” he says. “The answer is probably not, but in three years’ time, we will have a new factory run on a new chemistry, and then the jump will be more noticeable.”

Tomažič suggests we can expect generational upgrades every three to five years or so.

“And this is what we’ve been achieving historically very successfully,” he says. “There will be a battery generational upgrade, anywhere between 10 and 30 percent improvement on a parameter that we choose. This might be endurance; it might be speed of charging; it might be longevity, like the reduction of the operational cost per hour. There’s no such thing as improving 30 percent across the board because all of these measurable battery parameters manifest themselves as different chemistry or different use of materials or different packaging. So there’s no free lunch.”

The potential changes on the horizon with the MOSAIC notice of proposed rulemaking may open doors for Pipistrel in terms of accessibility to more pilots in the U.S. Tomažič, who contributed to general aviation and light sport standards through ASTM as a company representative, believes MOSAIC will offer opportunities for pilots across a wide demographic—and open up those for OEMs and others in the industry.

“It is an enabler of electrification in the U.S., absolutely, so we are looking forward to our existing products like Velis Electro and Taurus Electro, which don’t meet the definition of what is a light sport aircraft today,” he says. “[But they] will be enabled in the U.S. skies sooner rather than later. We are all paying attention to when this rule actually is implemented, and we are working hand in hand with the FAA to…start implementing [these] aircraft into the field.”

So what technologies like those being developed by Pipistrel will offer a solution to GA pilots in the U.S.? Tomažič suggests aviators approach this with an open mind. You might find there’s more to like than you think.

While he acknowledges that there are many ways to draw comparisons between electric power, turbines, and normally aspirated gas-driven engines, Pipistrel’s certification status points to the fact that the technology, and electric flight in general, is mature today.

“It’s not only lower noise and less costly operation,” he says. “There is a significant opportunity to lower the cost of a typical flight hour by half just by introducing electric flight. But this comes at the expense of revisiting how we look at flying in particular from the lens of the aircraft size and its endurance in flight.”

Four-seat aircraft often carry only two persons aboard, and aircraft capable of longer endurance may be out for only an hour or two during training missions: arguably a waste of resources. For now at least, electric aircraft options are necessarily more specialized in their mission capabilities.

“Pilots will have to come to an understanding that there will be a bigger variety of tools,” Tomažič says. “But the good news is that these tools will continue to improve, so I think an electric aircraft will become a way better investment than ever before, because every time a new battery comes up, you’ll have an aircraft that’s better than ever before. And this is a direct opposite of what’s typically happening once you acquire an expensive asset.”

The technology interface available to the pilot provides real-time information that can improve flight planning and safety in all phases. The resulting simplicity reduces distractions. In a typical flight, “you have to create a mental picture that assembles fuel pressures, oil pressures, some temperatures, and you kind of say, oh, it looks all right,” Tomažič says. “An electric propulsion system with a display will just tell you this every split second. You don’t have to wonder. You have it right there in front of you.”

Mechanics can receive a wealth of information at a glance, or the touch of a button, as well. Operators and maintenance pros can access Pipistrel aircraft maintenance data and aircraft logs, and they don’t need specialized equipment—just a USB key and access to the website.

“They upload the data log, same as an attachment to an email, and the whole situation is portrayed to them,” Tomažič says. “Imagine a flight school that can revisit the complete behavior of the aircraft since its inception and look for exceedances or whether the students and instructors were using the aircraft in full accordance [with] how it should be used. If something happened, you have it right there…much less is hidden.

“For us, what matters a lot is that people understand the technology that they’re using and that they find it likable.”

You can’t ignore the pressures on the aviation industry to move toward decarbonization and sustainability. That leads Tomažič to wonder: Which aircraft will be the best pilot-makers or zero-emission passenger airliners of the future?

“It’s probably not the old-school trainers,” he says. “It’s probably something that is more in line technologically with the future transport needs. And this may be air taxis, or this may be the next zero-emission airliner. ... It’s not coming overnight, but pilot education also doesn’t happen overnight. So MOSAIC to me is an enabler of better pilots that are better suited for the challenges of tomorrow once these technologies make it all the way up into the airline world.”

Accident statistics show a depressing tendency for human factors to be at the heart of crashes: a pilot misreading a situation, getting confused, or some combination of forces converging at once to produce an ultimately wrong decision.

“The level of transparency that is catered by electric flight is kind of like using your mobile phone,” Tomažič says. “You know exactly how full your battery is. You can make decisions to stop using your TikTok [app] so that you preserve the battery for the important phone call at the end of the day. But you can do that because you know exactly where you stand.”

Pipistrel’s battery management systems (BMS)—sometimes referred to as hybrid management systems by the company to differentiate its technology from a more generic system that can enable and disable battery functionality—provide similar transparency and functionality in the air. The user interface goes beyond simple battery charge indications.

“What our systems are able to do is actually forecast what is happening with the battery and give clues into how much longer you can continue to use the battery before maintenance,” Tomažič says. “[The] Velis Electro, which has the same kind of a BMS system as the Taurus Electro…has a progress bar that goes from 100 percent when new to zero when it’s time to replace the battery. And this doesn’t mean zero, end-of-life criteria—it’s kind of like the TBO for the engine.

“Imagine a way that you would be able to forecast how your engine will perform based on compression of the pistons. Sometimes you do that as part of a yearly checkup. Our systems do this every single time you power them up…because they monitor every single thing that the battery is doing when it’s flying or charging. And because of our catalog of battery behavior…our battery management systems essentially contain the model of the anticipated behavior for every battery.”

If something is off, the system can flag it for the pilot. The information is provided visually and continuously during a given flight. Menu options allow for granular information to alert an owner to issues or aid in preflight planning. While you can visually inspect levels of the fuel tanks in an avgas-driven aircraft before flight, a battery looks the same and feels the same regardless of charge. So this kind of interface is vital.

Pipistrel, from glider to electric airplane, has worked to create affordable solutions for this and other elements. “You see it in our electric flight, cargo drone project, and many other places,” says Tomažič. “And Textron eAviation is able to propel this ideology through very fast-paced innovation because they are able to add resources that Pipistrel never had access to. I think we can all be very excited about the next [few] years, including gliders… As I said, I want to be the company that delivers the all-can-do, all-electric airplane in the future, because we can see how that is possible.

“I think we are at the moment in time where it’s a matter of ‘when,’ not a matter of ‘if.’”

Editor's note: This story originally appeared in the Jan/Feb 2024 issue of Plane & Pilot magazine.