hovering. As the aircraft transitions to forward flight, the wing rotates to a horizontal position, providing lift to offload the rotor. Te propulsive efficiency of the aircraft is enhanced by a


swiveling tail rotor, which provides anti-torque and yaw control in hover and swivels 90 degrees for forward propul- sion. With lift and thrust demands relieved, the rotor’s rpm is slowed. Te net effect is increased range and reduced noise and vibration.


Why Power with Hydrogen? Te key design challenge in conceptualizing the PA-890 was how to power the aircraft electrically at an acceptable weight, volume, and cost. As part of the helicopter’s development, Piasecki evaluated three options: battery only, hybrid diesel– battery, and hydrogen fuel cell. While the simplicity of the battery-only approach was


attractive initially, detailed research into battery chemistries revealed that the projected energy density improvements of batteries aren’t being realized. Moreover, the high discharge and recharge rates required for VTOL operations significantly degraded battery life to the point that the operational cost was only marginally better than that of a turbine helicopter. Te hybrid diesel–battery alternative met performance


requirements and delivered a 25% reduction in cost relative to turbines but still retained a carbon footprint, albeit reduced. Tis led Piasecki to explore the potential of the third possi- bility, the hydrogen fuel cell. While low-temperature proton-exchange membrane


(LTPEM) hydrogen fuel cells have been in use for many years and are increasingly found in automotive applications, the powerplants suffer from weight, water-management, and cooling-system constraints that limit their specific power. To achieve the energy density and specific power levels


required for flight, Piasecki turned to HyPoint, a small start-up company developing turbo air-cooled high-temperature proton-exchange membrane (HTPEM) fuel cells specifically designed for aviation applications. Te cells’ higher operating temperature yields water vapor, via the reaction of hydrogen and oxygen, that is exhausted without the need for LTPEM’s heavy, complex water-management and cooling systems. In 2020, after initial feasibility studies were conducted,


Piasecki signed a collaborative agreement with HyPoint to develop aviation-grade HTPEM hydrogen fuel cell technology for the PA-890 and other applications. Te US Air Force is now co-investing with Piasecki in the development of this technology. Piasecki and HyPoint’s shared vision is a fuel cell with the


following key attributes: ■ A fivefold increase in energy density over today’s lithium-ion


batteries


■ A threefold increase in specific power over traditional LTPEM fuel cells


■ A 50% reduction in operating cost compared with turbine-powered helicopters. “While hybrid solutions were lower


risk, we decided to go with the hydrogen fuel cell because there’s a huge payoff for our customers,” says John Piasecki, president and CEO of Piasecki Aircraft. “Te fuel cell is less expensive to operate, it’s quieter, and it features zero carbon emissions. “If you look at the commercial market


and certain parts of the military mar- ket—like logistics and utility—you have the opportunity to provide the needed performance at 50% lower cost because the hydrogen fuel cell doesn’t have very many moving parts while providing zero emissions and a low acoustic sig- nature,” he says. “In addition, coupling hydrogen fuel cells with the winged compound’s variable-speed rotor design will enable the PA-890 to operate very quietly.” With space to seat eight people and


a large baggage compartment, the PA-890 will be able to fulfill various missions, including emergency medical services, high-value on-demand logistics, on- demand mobility, personnel air transport, and other applications. “We’re working closely with launch customers to make


sure the PA-890 addresses today’s helicopter operator’s needs for more affordable mission performance with a safe, reliable, supportable system,” says John. “I think, too, it’s fair to say that in the next 10 years the regulatory pressure to lower carbon emissions will only intensify. We plan to answer those demands.”


The Fuel of the Future? Introducing a new aviation fuel is another challenge facing the PA-890 team. Universal Hydrogen is one company that’s working on producing and shipping hydrogen to airports. Te start-up firm is led by former United Technologies senior VP and chief technology officer Paul Eremenko. Eremenko thinks hydrogen is the ideal propellant for


aviation. “Or expressed another way, aviation is the killer app for hydrogen,” he says. “It’s the most energetic propellant


SEPTEMBER 2022 ROTOR 41


The family legacy of rotorcraft innovation is being carried on by two of Frank Piasecki’s sons. John (top photo) is president and CEO of Piasecki Aircraft, while Fred is the company’s chairman and chief technology officer.


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