Sweden’s Heart Aerospace has radically redesigned its developmental ES-30 hybrid-electric regional aircraft, switching to an off-the-shelf propulsion system – a combination of stock turboprops and electric motors – and dropping distinctive features such as the strut-braced wing and large under-fuselage battery bay.
In addition, the company now says the first flight of its full-scale demonstrator aircraft, set for next year, will be uncrewed.
The newly-disclosed design revisions are the latest changes to the aircraft the Swedish start-up hopes to bring to market.
At its launch in September 2022, the ES-30 – itself a replacement for the abandoned full-electric 19-seat ES-19 – Heart said the aircraft would be driven by four electric motors powered by batteries stored in a large compartment mounted underneath the fuselage.
A turbogenerator in the rear fuselage was to serve as a range extender, pushing potential flight distances out from 108nm (200km) to 215nm with a full 30-passenger load. Range could even stretch to 430nm if only 25 passengers were carried.
Additional elelments such as a strut-braced wing with winglets also featured.
However, Heart has changed course, believing the new configuration, which it describes as having an “independent hybrid propulsion system”, offers a simpler, more cost-effective solution.
Underpinning the decision was the knowledge that the turbogenerator would only be used for a tiny fraction of the ES-30’s flights. “We don’t want to be spending all of our resources, all of our development, on that system,” says Heart co-founder and chief executive Anders Forslund.
Instead of the turbogenerator, hybridisation is achieved through a pair of small turboprop engines mounted outboard on the wing, while inboard will be a pair of large electric motors, sized to enable flights of up to 108nm on battery power alone.
While feathered during all-electric flights, the turboprops can be activated if the cruise phase needs to be extended, Heart says.
“The simplest way of doing it is to design a turboprop and design an electric aircraft and put [both powertrains] on the same wing,” adds Forslund.
It has yet to provide specifics but says the power output of the electric motors will be “not quite twice as large but in that ballpark”, he says.
“This is a really simple solution that we ran the numbers on extensively, we are really excited about it.”
Ditching the turbogenerator has freed up space in the rear fuselage, allowing the battery pack to take its place and removing the need for the sub-fuselage storage. This has twin benefits of reducing drag and improving crashworthiness, says Forslund.
Additionally, the move to the new propulsion system architecture meant that the wing-strut could be eliminated.
“When designing for the power constraints of the turboprop you end up being in a better place without the strut,” Forslund says.
However, the design changes do not alter any of the ES-30’s range or payload specifications, Heart stresses.
Heart has yet to disclose the suppliers for its powertrain, but Forslund says the thermal engines will be an off-the-shelf model “of a form factor that is commonly used”.
Using stock powerplants for propulsion rather than electrical generation also means that the “level of recertification required is very minimal,” he says.
While the ubiquitous Pratt & Whitney Canada PT6 would clearly offer one option, that engine class is a “competitive space” and Heart is “engaging with a few different suppliers”.
Heart had not disclosed the supply chain for its previous propulsion system: in its early days it had been developing its own electric motor, but it is unclear how far this had progressed. Additionally, the company in March 2023 said it was working with BAE Systems to define the battery system for the ES-30.
Development of the revised powertrain will be driven by a new R&D hub that Heart is setting up in Los Angeles, California under the leadership of newly-appointed chief technology officer Benjamin Stabler.
Heart is continuing to build a full-scale aircraft demonstrator at its Save airport headquarters near Gothenburg in Sweden but after its roll-out later this year it will be transferred by ship to Los Angeles ahead of its maiden sortie.
Although first flight is set for next year, Heart has yet to reveal where the milestone will take place, save that it will be in the USA.
But given that the maiden flight will be remotely-piloted it is, out of necessity, likely to occur somewhere “in a very unpopulated area”.
Having previously flown an uncrewed scaled demonstrator, Forslund thinks there is huge value in flying initially without a pilot on board.
“We are not trying to replace the conforming flight tests with pilots, we are just trying to put this as an early stage development tool,” he adds.
The location of the R&D hub has yet to be disclosed but Heart says it is in the “final stages” of selecting office and hangar space in the Los Angeles area.
Stabler, whose appointment is effective immediately, is also recruiting a team of aroudn 20 people to staff the facility.
Heart will retain its operation in Gothenburg and “remains headquartered in Europe, where it will pursue type certification in 2028”, it says.
“The team in Gothenburg will work closely with EASA and continue to mature the ES-30 program towards type certification in co-ordination with the US-based team.”
First flight of a more production-representative aircraft – with a pilot on board this time – is due in 2026.
Stabler joins Heart from Parallel Systems, a developer of automated, battery-electric rail freight vehicles, which he co-founded. He has previous experience hardware and software teams on SpaceX’s Crew Dragon programme.
In addition to the powertrain, the Los Angeles operation will develop “other key technologies” with a focus on “systems and vertical integration”.
Despite the company’s Nordic roots, the Swedish business is owned by Heart Aerospace Inc – a Delaware-registered company with premises in Palo Alto, California.
Building up that “local ecosystem” and “having boots on the ground in the US” will enable better engagement with regulators, key customers such as United Airlines, and policy makers, Forslund adds. A final assembly line in the USA is also likely, he says.
Stabler’s appointment as CTO will allow Forslund to transition from his interim technical leadership role to focus exclusively on his duties as chief executive.
“We have an exciting time ahead of us as we enter a new phase of hardware testing, and I’m thrilled that Ben is joining our team,” says Forslund, citing his “experience and passion for innovation”.
Heart has secured 250 orders for the ES-30, with options and purchase rights for another 120 aircraft. The company also holds letters of intent for a further 191 units.
