Helios Horizon, a small US aerospace project seeking to demonstrate electric propulsion, aims to break a world altitude record for electric aircraft this summer and in 2025 to fly higher, into earth’s stratosphere.
Founder and test pilot Miguel Iturmendi – a veteran of well-known aerospace test programmes like the Perlan Project and Solar Impulse – laid out those goals on 13 January in Sarasota, Florida, where he and the project are based.
Iturmendi is seeking investments – modest sums by aerospace standards – to fund the project, which he views as an effort to prove the viability of electric propulsion for powering small fixed-wing aircraft.
“The goal is to be the first electric airplane that demonstrates a stratospheric flight,” says Iturmendi, who was born in Spain but has long lived in Sarasota.
“We want to demonstrate that electric aviation is doable… We want to inspire the next generation of scientists, engineers, technicians, mechanics, designers – to show that all of this is possible.”
Since launching the project in December 2021, Iturmendi made waves flying the team’s aircraft, called Helios Horizon, a modified all-electric Pipistrel Taurus Electro.
In stock form, the Taurus motor-glider is relegated to flying under roughly 10,000ft. But modifications allow the Helios Horizon – now a powered aircraft – to fly much higher. Last year, Iturmendi hit 16,000ft, setting an altitude record for electric aircraft weighing less than 500kg (1,102lb).
Iturmendi says he actually reached 20,000ft during another flight last year – but not for record-setting credit because a records official was not on hand – and used only 38% of the Taurus’s battery power doing so. The team flew from Minden-Tahoe airport in Nevada.
Iturmendi has worked for major aircraft manufacturers and test piloted several experimental aircraft. He has set records flying the solar-powered Solar Impulse 2 and has flown an electric demonstrator for SolarStratos. Both are Swiss projects. Iturmendi also flew the Perlan 2 high-altitude glider for the Airbus-backed Perlan Project.
He has since turned to the Helios Horizon project, which has been operating with volunteer staff and initial funding from Iturmendi and Wisconsin-based lead sponsor WindWalker. Iturmendi brought on Javier Merino, also a Spaniard living in Sarasota, to manage the project.
The team overhauled the Taurus, replacing its stock electric system with a new motor weighing 10kg and with 54kW (72hp) of continuous power. They gave it six 8.5kWh lithium-ion batteries, each weighing 32kg with cell-level energy density of 258 watt-hours per kilogram (Wh/kg). “Best in class anywhere”, Iturmendi says. They also installed a new motor controller, replaced the aircraft’s standard 168cm (66in)-wide propeller with a 224cm version, and modified the aircraft’s flight controls, elevators and wings, which span 18.3m.
“We got a lot more battery power,” Iturmendi says. “It’s harder to create thrust as we go higher because the air is thin.”
Thin high-altitude air also slows heat dissipation, meaning electric systems can become hot quickly and pose serious risk of overheating and fire – which is why Iturmendi wears a parachute during test flights. “Heat is what ends up making it not possible to keep climbing,” he says. “It’s hard to cool it, so you have to have active cooling systems.”
His crew developed a glycol-water system to keep the batteries, motor and controller within heat limits. They think the system can enable flights to 45,000-50,000ft.
The volunteer team has accomplished much with little. Friends and partners have helped with engineering. Tests have been completed using improvised components, including, at one point, a turkey fryer used as a test chamber.
Project supporter Pablo de Leon, a NASA researcher and chair of the University of North Dakota’s department of space studies, helped Iturmendi access the school’s altitude chamber, where they tested a pressure suit at a simulated 44,000ft. Iturmendi needs that suit because the Taurus is unpressurised.
The first phase of the Helios Horizon plan included last year’s flights and continues this year. It aims by April to fly the Taurus to 22,000ft, higher than any other multi-seat electric aircraft, and by June to hit 32,000ft, besting the current electric-aircraft altitude record, held by Solar Impulse, says Iturmendi. “We want to do this now, before summer.”
He thinks the project needs just $50,000 in additional funding to complete this year’s flights – a minuscule figure compared to the tens of millions of dollars larger players spend on electric-aircraft projects. “Fifty thousand [dollars] is not a lot for a project like this, but it’s huge for us,” he says.
Next will come phase two, which includes the planned 2025 flight into the stratosphere – an atmospheric layer beginning at slightly higher than 40,000ft depending on location and conditions.
“Our minimum goal is 44,000 feet, which will allow us to claim a stratospheric flight,” says Iturmendi, who estimates needing another $150,000 to make that happen. The future high-altitude test flights will also occur from Tahoe-Minden, or perhaps from Bishop airport in California.
If all goes to plan, the team will bring Helios Horizon back to Sarasota around mid-2024 to begin preparing for the stratospheric flight. It will give the aircraft new batteries, and a modified wing manufactured by a company in Holland.
At the same time, the Helios Horizon project is developing a “regenerative” power system – the propeller will act as a windmill, generating power during certain phases of flight – and it envisions eventually adding solar cells to much of the aircraft’s upper surface.
While numerous companies are developing small electric aircraft, most concepts are for electric vertical take-off and landing (eVTOLs) types – air taxis. But Iturmendi thinks his team’s work will prove electric propulsion is more feasible for powering small fixed-wing aircraft.
“Everybody’s looking at it wrong, because they’re looking just at eVTOL,” he says. “The key is to start with [light sport aircraft] and four seaters… Those are prime to be replaced by electric aviation.”
Iturmendi expects the next iteration of batteries will have energy density exceeding 300Wh/kg, up from about 250Wh/kg today and sufficient to power all-electric aircraft carrying about 20 passengers.
Though several companies developing electric regional aircraft aim to have their products flying in the coming years, Iturmendi thinks the technology will need more time to mature. “I just think the timeline is longer. The electrification of society is here to stay,” he says.
