Just as there are by now dozens of configurations floating around for proposed eVTOL aircraft — ducted fans, open rotors, wings, tilt-rotors, and more — multiple sources of electric power are being considered along the way, too. While batteries are still the front-runner, hybrid systems could have a place, as could conventional all-turbine systems.
But a new Boston-based startup that recently revealed itself has added yet another wrinkle to the electricity generation conversation. Alaka’i Technologies showed off its hydrogen-fuel-cell-powered Skai concept during a reveal at the Los Angeles offices of BMW Designworks, which penned the overall look of the five-passenger, six-rotor aircraft. Hydrogen has been a longtime interest for electric aviation researchers, but it has typically been a non-starter due to the cost of fuel cells and the challenges of sourcing the hydrogen when and where it’s needed.
But company co-founder Brian Morrison said his engineers and those of his as-yet-undisclosed partner have made breakthroughs in the fuel cell technology that will enable the aircraft to take flight sooner rather than later. If this proves true, the concept has much to recommend it. Hydrogen contains more than 200 times the energy of equivalent-weight batteries in its compressed state, enabling an eVTOL aircraft using it to achieve useful speeds and ranges, as well as practical payloads.
Morrison said Skai will be good for 118 miles per hour (190 kilometers per hour) with a 1,000-pound (450-kilogram) payload, and up to 400 miles (640 km) of range from a single fuel load. That fuel, of course, can be replenished in minutes, unlike current battery technology which can take several hours to top off the battery sizes being proposed for most air taxi configurations.
Bruce Holmes, a NASA veteran now serving on Alaka’i’s board, said the company made a variety of decisions meant to simplify the design of Skai and the resulting certification process. The rotors don’t articulate, for instance, and there are no fixed wings — both of which add complexity, he noted.
“Because of the simplicity here, we expect to be able to reach certification by the end of 2020,” Holmes said. The company will also start with military, search-and-rescue, and other industrial versions before pushing the passenger-carrying version through. Those conversations have already begun and have reportedly generated significant interest. That could allow the company to certify Skai faster for those applications while honing the technology for commercial certification.
The company is skipping subscale prototypes and starting its tests with a full-scale version. “There’s nothing really to be learned with subscale models,” Holmes explained. Ground runs and a low hover have already happened, and Alaka’i is now advancing through its rotor, motor, and control system tests before expanding the flight envelope any further. Meanwhile, team members with experience in aviation certification and automotive manufacturing — their preferred source of inspiration — are developing strategies for both to enable what they hope will be a smooth progression.
Though initially unit costs will be high and volumes low, Alaka’i hopes to eventually turn out 10,000 vehicles per year from the factory at a cost of around $200,000 each. “The big challenge there is bringing the supply chain along with you in these ambitious journeys,” Holmes said, explaining that suppliers have to be a part of the strategy from the very beginning. This will be especially true because the aircraft will be composite-built, as most other eVTOL aircraft will be, and manufacturing partner involvement has been critical in terms of developing a design that can be built practically and affordably.
As for the hydrogen component, the company didn’t disclose how much the fuel cells will cost or where they’ll come from. It did note during its reveal that there are multiple countries with developed hydrogen infrastructure, as well as multiple areas within the United States. Fuel will be delivered via tanker trucks to the landing spots for the aircraft, or Alaka’i will tap into pipelines where those are available. Ultimately, hydrogen won’t replace batteries so much as offer alternatives where it makes sense, the company seems to be arguing.
That approach seems sensible to Charles Eastlake, a professor emeritus of aerospace engineering at Embry-Riddle Aeronautical University. With decades of experience in electric propulsion, including hydrogen systems, his concerns focus on the handling and distribution of the fuel.
“It has a lot of advantages — it’s renewable, fairly easily made by electrolysis of water, and it burns clean. The oxidation process turns it back into water,” he explained. “But cities and safety regulatory bodies are not familiar with hydrogen. I can’t imagine a smooth approval process as a widespread network of airports seek permission to install refueling facilities for hydrogen-fueled airplanes.”