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Sunday, March 3, 2024

A New Air Taxi Model Takes Design Cues From a Far-Flying Bird

Air-taxi startup Beta Technologies debuted its new aircraft Friday with a dramatic helicopter airlift of the sleek white model across Lake Champlain from Burlington, Vermont, to Plattsburgh, New York. Code-named Alia, the electric vertical-takeoff-and-landing (eVTOL) airplane is the successor to Ava, a smaller prototype the company used to experiment with propulsion strategies and learn about the tricky aerodynamics of small, electrified, vertical-lift flight.

According to company founder Kyle Clark, Alia’s striking configuration and elegant shape owes a debt to the longest-migrating bird in the world, the Arctic tern. This includes a twin-tail assembly supported by angled trusses, dramatically arched wings, and arcing, tapered wingtips. The tern’s tail configuration and wing stance “proved a great baseline to start from,” Clark says.

For the tern, those features enable ultraefficient, long range flights. Beta hopes for similar performance. Its primary client, United Therapeutics, is developing man-made organs for human transplant and intends to use Beta’s aircraft as an efficient, environmentally friendly distribution system.

Beta didn’t release performance specifications, except to say that it aims to build a prototype that can fly 250 miles and charge in under an hour. Alia has a 50-foot wingspan, and will have a takeoff weight of 6,000 pounds—the prototype airlifted in Vermont on Friday weighed 3,800 pounds, having been stripped of batteries and other heavy components. The craft uses four horizontally mounted rotors for vertical lift and a single rear-facing propeller to boost speed in forward flight. The wide wings will generate lift for more efficient forward flight, instead of relying on the motors to do all of the work as in eVTOL aircraft that derive most of their lift from rotors. It will use existing battery technology and be deployed as part of an ecosystem that includes charging stations in urban centers, at hospitals, or in remote locations to extend the aircraft’s range.

Beyond transporting organs, Beta hopes to expand to commercial applications, cargo, and passenger-carrying air taxis. It is one of two companies, along with Joby Aviation, recently selected by the US Air Force to advance to the next stage of development in its Agility Prime eVTOL program.

The aircraft’s unusual shape will raise eyebrows, but its propulsion strategy is likely to raise even more—in the eVTOL aviation community, anyway. Many eVTOL developers use tilt-rotor systems in which multiple rotors point skyward for takeoff and landing then pitch forward for horizontal flight. Beta used that strategy for Ava, but it proved too complex for the engineers to want to deploy it in a production aircraft. “Our primary objective is to meet our first customer’s mission, reliable organ delivery when and where it’s needed,” Clark says. “We couldn’t have an aircraft that had any possibility of being grounded for repairs due to a complex system.”

Instead of tilt-rotors, Alia uses four fixed rotors on the top of the aircraft and a pusher-prop in the rear to speed forward flight. This strategy required the development of new, ultra-efficient rotors, but they could be optimized for just one job—vertical flight—rather than two. This simplicity will not only make the aircraft more reliable, Beta contends, but also easier to certify and more affordable, because it will have fewer parts, compared with tilt-rotor systems, and lower maintenance costs.

Because the rotors and pusher motor each have a single job, engineers can optimize their designs without worrying about tradeoffs, says propulsion engineer Herman Wiegman, who designed energy storage systems for GE Global Research before leaving to help form Beta in 2016. “We also brought the motor design and fabrication totally in-house, which enables us to completely customize the design to this application,” Wiegman says.

Similarly, Beta purchases its battery cells from well-known industrial suppliers, but designs and fabricates the packs in-house. The pack in Alia sits below the cabin, generating a low center of gravity that gives the airplane greater stability and resistance to gusts of wind or turbulence—something Wiegman says will also help future passengers acclimate themselves to smaller aircraft than they’re normally used to.

Beta hopes to begin testing the transition from vertical to forward flight in Plattsburgh sometime this summer. The aircraft has already been doing tethered hover tests and high-speed taxi tests, using landing gear in place of the skids planned for the final design. The idea, Clark says, is to understand its flight characteristics as a conventional airplane, then progress to gauging its performance as a helicopter, then finally as both combined. Beta is developing the flight-control system, avionics, and power management software to hone its performance to the point where it can reliably make both urgent transplant organ deliveries to hospitals and send passengers across towns or between cities.

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