Practical magic

It was during those five days and nights alone over the Pacific that Borschberg shaped his vision for that next step, according to Gregory Blatt, who handled marketing and communications for the record-setting endeavor.

“We always knew at Solar Impulse that there would be a ‘what next?’” said Blatt. “The ‘what next’ was really about how can we bring this, our expertise, our knowledge to the marketplace.”

Piloted alternately by Borschberg and Swiss compatriot Bertrand Piccard, the Solar Impulse 2 made history in 2016 when it became the first aircraft to circumnavigate the world powered only by electric motors and energy from the sun. The custom-built experimental aircraft had 17,248 solar cells, four 17.4-horsepower motors, and a wingspan of 236 feet—not exactly bound for your local T-hangar. But the Solar Impulse team believed in the efficiency, reliability, and quiet of electric propulsion in aviation, and realizing that promise would mean developing certified products. Borschberg, Blatt, and fellow Solar Impulse alum Sébastien Demont launched a new endeavor in 2017 with a goal of certifying electric propulsion systems
for aviation: H55.

This summer, the company is demonstrating its first application—an all-electric Bristell B23 Energic trainer—at flight schools across the United States, with hopes to deliver the EASA CS 23 certified version to schools in Europe by 2026.

Fly. Charge. Repeat.

Temperatures are in the mid-80s and rising this spring afternoon in central Florida. In the hangar at DeLand Municipal Airport’s (DED) Cloud Dancer Aviation, floor fans are aimed at the Energic after a charge between flights for investors and prospective customers. This is the second flight test airplane, still gathering data as the company builds the certification prototype in Sion, Switzerland. Florida is a crucible for hot-weather operations, but, as test pilot Markus Scherdel boots up the avionics, all the battery indicators are green.

BRM Aero Bristell’s line of all-metal two-seat aircraft is adaptable to a variety of powerplants, including several Rotax models and the Turbotech R90 turboprop (see “French Revolution,” April 2025 AOPA Pilot). Outfitting the B23 with H55’s electric propulsion system required minimal modifications to the airframe, Scherdel says, mainly swapping the wing tanks for batteries and replacing everything firewall forward.

Inside the cockpit, battery monitoring takes center stage in a simple VFR panel. A digital display shows the voltage of individual cells; the power of a battery is limited by the weakest cell, so the spread between the voltage of the highest- and lowest-voltage cells should be small, measured in millivolts. Other readouts of engine health track core temperature, coil temperature, and rotor temperature. If we see any signs of overheating in flight, Scherdel says the procedure is simple: reduce power and fly a bit faster. The batteries are controlled by a master switch, so we also can switch off one battery and fly on just the left or right to let the other one cool.

On the ramp, Scherdel talks through the startup sequence. The motor and motor controller are both liquid cooled, so we turn on the pump and auxiliary pump and check the flow sensor. The master motor switch has three settings: Off, Ready, and Fly. When it switches to Fly, the propeller starts turning to help others in the area understand the silent motor is armed. A running electric motor doesn’t need to turn the propeller, Scherdel explains, but rotating it takes hardly any power. Idling at 200 rpm, the power display shows 0 kW.

Company officials expect the production version of the Energic to have an endurance of one hour plus 10 minutes of reserves under European regulations that allow a lower energy reserve for local traffic pattern work. The propulsion system for this test airplane is slightly different, and U.S. regulations require 30 minutes of reserve; instead of six or seven laps around the pattern, H55 plans for just one landing for our flight during this American tour.

The battery monitors show 23 kWh per side, a full charge. Scherdel explains I can think of the power setting like fuel flow: A 40 to 45 kW cruise power setting with a 46 kWh battery gives about one hour of endurance. Once I set the power, the rpm might change but the controller will maintain that power setting independent of speed or altitude.

“That is also one of the beautiful things because it does not know any density altitude,” Scherdel says. The motor can deliver the full 95 kW takeoff power (about 130 horsepower) on a 100-degree day.

The throttle has no mechanical connection to the motor, so sliding the lever forward for taxi has the feeling of a flight simulator control. If the digital control were to fail, we’d control power via an override switch, which we test in lieu of an engine runup. From the standard throttle operation setting, we switch to the cruise setting of 45 kW, then the next position for maximum continuous power of 75 kW. That’s it. We’re ready for takeoff.

With one notch of flaps extended, I hold the brakes and advance the throttle to 95 kW on Runway 12. Rotation is at 55 knots, flaps up at 65 to 70, and then we climb to pattern altitude around 80 knots at a 10-degree pitch up.

It’s quiet. We’re wearing headsets to hear radio calls, but I lift the earpiece and hear mostly rushing air. When I pull the power back to 45 kW, the tone of propeller noise shifts slightly, but there’s little acoustic feedback as there would be from a piston engine. Scherdel says this can lead pilots to make too-large power adjustments because they don’t hear the change and make a larger adjustment; it’s important to monitor the numbers on the display.

At this setting, we’re flying at about 85 knots. The rush of student pilot traffic has subsided and I make a right three-sixty to get a feel for the airplane before rejoining the pattern. It’s here where I sense the appeal of the Bristell. The controls are responsive, and visibility is excellent through the canopy. With the extra weight of the batteries this model is about 200 pounds heavier than piston B23 models and 550 more than a light sport aircraft, and it’s only lightly bounced in the afternoon heat. If all goes to plan, this will be the first electric-powered airplane to be certified under CS-23, Europe’s Part 23 equivalent.

Back on downwind, I lower flaps at 75 knots and the nose rises. Final approach is normally 65 knots, but Scherdel advises 70 to add a gust factor. These are familiar trainer speeds, and with no fuel selector or mixture to manage, there’s not much to do now except land the airplane. The B23 is simple and easy to fly—appealing attributes for the training market. H55 says the Energic will have a one-to-one ratio of charging time to flight time: Fly an hour, charge an hour.

“So the idea is just like we went out and we took a lap around the pattern, students will do local pattern work,” he says. “They’ll come back, debrief while the airplane is charging, and then go back out again.” For cross-country work, they can switch to a combustion model.

Scherdel logs the data after the flight. Block time 22 minutes, eight minutes flight time, and six kilowatt hours. That leaves 40 kWh left in the “tank.”

No cheating

In the earliest days of electric aviation, electric vertical takeoff and landing aircraft developers made range predictions with a degree of magical thinking. Survivors in the electric propulsion space today take a more pragmatic view.

“Battery chemistry and battery density is what it is, where you can’t cheat with that, right?” said Blatt. “Everybody’s dealing with the same thing.”

Most of H55’s innovations are related to how the cells are configured, packaged, and monitored, including the software that monitors and manages the system and the way the information is presented to the pilot. Thermal management and fire prevention are critical.

“In an electric car, the rule of thumb is you need to contain a fire—meaning if your electric car has some thermal issues, some smoke coming out, you can get out. The exit strategy in an airplane is a little bit more complicated. So, it’s all about prevention.”

The system also has to be cost effective. Blatt said the $500,000 purchase price and hourly operating costs will be comparable to those of the Rotax 914 model, but advantages of the electric model over the lifetime of ownership include lower maintenance costs: no oil changes, the 100-hour inspection is a simple visual check, and most maintenance is on condition based on digital readouts. Money that would be spent on fuel instead goes to the next battery replacement, which will be better technology as battery density increases.

“You’re competing against the gas tank, right?” he says. “You’re not putting money in gas, you’re putting money in the technology.”

Blatt says batteries will be retired at 85 percent state of health, about 1,500 hours of use, when they’ll find second life applications in industries such as mining, oil platforms, or passenger boating. Some components, like circuits and electronics, will be recycled.

Into the future

H55 is focused on applications, like local flight training, where electric propulsion is practical with current battery technology. According to Blatt, 35 B23 Energics have been preordered in Europe, with EASA certification expected in 2026 and FAA the following year. The company also is developing the energy storage system for Pratt & Whitney Canada’s hybrid-electric de Havilland Dash 8 demonstrator and Harbour Air’s e-Beavers, and it will outfit CAE’s fleet of 80 Piper Archers with electric propulsion systems.

Borschberg said H55 decided to focus on the core technology for electric propulsion rather than designing for a specific airframe or solution: “There are a lot of potential solutions which are interesting, but you always need the battery and you always need an electric motor.”

Meanwhile, the Solar Impulse 2 is still flying, as an autonomous test vehicle for Oklahoma-based Skydweller Aero Inc. Borschberg, an accomplished pilot and engineer, said the goal of the Solar Impulse wasn’t to revolutionize aviation; it was to develop an ambassador for the potential use of renewable energy. He said his time in the airplane showed him advantages of electric propulsion such as reliability, lower noise and vibration, and efficiency—advantages he’s experienced while flying the B23 Energic.

“I guess if you fly electric, you don’t fly a combustion engine anymore,” Borschberg said. “For me, there’s no way back.”

[email protected]