On June 5, local time, test pilot Miguel Iturmendi flew the "Helios Horizon" electric aircraft into the sky at Zephyrhills Municipal Airport in Florida, USA, completing the first flight of the world's first manned fixed-wing aircraft powered by solid-state batteries, writing a historic page for the development of the electric aviation industry. This flight is not outstanding in terms of range and time. It is just a series of short-distance test flights to verify the weight and balance of the aircraft after replacing the battery. However, its symbolic significance is far greater than the technical performance itself.
Electric aviation has long been constrained by the physical properties of batteries. Traditional lithium-ion batteries currently widely used in electric vehicles rely on liquid electrolytes to conduct charge between electrodes. This structure has a natural upper limit in terms of energy that can be stored per unit mass, making it difficult to support commercially valuable aviation flights. In contrast, solid-state batteries replace liquid electrolytes with solid materials, making the cells more resistant to impacts, punctures and high temperatures, significantly reducing the risk of fires, and more importantly, significantly increasing the energy density per unit weight, opening up new imaginative space for electric aviation.
According to data disclosed by the project team, the energy density of the lithium-ion battery pack previously installed in "Helios Horizon" was about 260 Wh/kg, while the solid-state battery replaced this time reached 410 Wh/kg, an increase of about 60%. As the chief test pilot and company founder, Iturmendi said that as the technical roadmap further matures, this indicator is expected to increase by about 40% on the current basis in the next two years.
In terms of energy replenishment method, the battery pack of "Helios Horizon" can be charged through ordinary AC sockets without the need for special infrastructure. It also supports fast charging and can recharge the battery to about 80% in 15 minutes. Solar panels mounted on the aircraft's wings and a regeneration system that reverses the propellers during glide and descent to act as "wind turbines" can also recover energy during flight. "Regenerative flight can significantly extend the aircraft's range," Iturmendi said after the test flight.
"Helios Horizon" itself was modified from a Pippistrel Taurus powered glider. On this basis, the project team integrated a self-developed battery management system, a customized electric propulsion system, a thermal management control system and an extended wing structure with solar components. The aircraft has previously set a world altitude record for pure electric aircraft in its weight class, flying as high as 24,000 feet (approximately 7,315 meters). The team’s next goal is to hit the cruising altitude of 40,000 feet (approximately 12,192 meters) for commercial airliners. The relevant stratospheric flight plan is expected to begin later this year.
While Helios Horizon is temporarily leading the solid-state battery aviation race, it's not the only player. Chinese eVTOL manufacturer EHang has cooperated with Inx Energy to apply lithium metal solid-state batteries to the test of two EH216-S aircraft, and achieved a flight record with an energy density of 480 Wh/kg and a continuous battery power supply of 48 minutes. Battery giant CATL has demonstrated "condensed matter battery" technology with an energy density of about 500 Wh/kg, and said it has started testing related aviation applications. Airbus and Renault also signed a joint research and development agreement, with the goal of increasing battery energy density to about twice the current level around the 2030s to support the development of hybrid or all-electric passenger aircraft for medium-haul routes.
At present, most of the above-mentioned projects are still in the technical verification stage and are still a long way from obtaining airworthiness certification from aviation regulatory agencies. However, this real-life manned test flight of "Helios Horizon" is regarded by the industry as a step across a key node. It is fundamentally different from previous demonstrations that only stayed at the experimental platform or laboratory data level. If the energy density of solid-state batteries continues to increase in the coming years, as Iturmendi predicts, this seemingly mundane short-distance test flight is likely to be just the beginning of a new chapter in the history of electric aviation.