Piasecki and the Hydrogen-Powered Helicopter

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A well-known name in rotorcraft innovation prepares to do it again.

Trailblazer. Pioneer. Innovator. Not one of these words exaggerates the impact the Piasecki family has had on the helicopter industry since its beginnings in the late 1930s.

The Essington, Pennsylvania–based company’s history goes back to the development of the tandem helicopter—the foundation of today’s CH-47 Chinook—and has progressed through more than 25 vertical lift aircraft initiatives, including high-speed compound helicopters, hybrid heavy-lift helicopters, flying cars, and the world’s first fully autonomous man-rated helicopter.

Today, Piasecki Aircraft Corp. is pioneering an especially timely innovation: hydrogen-powered helicopters. With its multifaceted effort to bring the technology to market in the form of light helicopters and electric vertical takeoff and landing (eVTOL) vehicles, the company hopes to transform vertical flight once again by addressing some of its biggest constraints: high operating costs, noise, and growing public intolerance of transportation that carries a high carbon footprint.

The PA-890 eVTOL Compound Helicopter

Several high-profile start-ups have focused on battery-powered eVTOL aircraft, but the low energy density of batteries limits their application to small, short-range vehicles suitable for the urban air mobility market, with mission legs as short as 25 nm. Piasecki, meanwhile, has focused on developing a practical eVTOL aircraft to disrupt the turbine helicopter market: the PA-890 eVTOL hydrogen fuel cell–powered compound helicopter (pictured at the top of this article).

The PA-890 features:

• A design mission capability exceeding 200 nm plus IFR reserve
• A 50% reduction in operating cost per flight hour
• A significantly reduced acoustic signature
• Zero direct emissions.

Certifiable under FAA Part 27 standards, the aircraft couples the hover efficiency of a low disk loaded rotor with the forward-flight efficiency of a winged aircraft. The helicopter’s variable-incidence wing is designed to rotate up to 90 degrees to minimize download for efficient hovering. As the aircraft transitions to forward flight, the wing rotates to a horizontal position, providing lift to offload the rotor.

The 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 propulsion. With lift and thrust demands relieved, the rotor’s rpm is slowed. The net effect is increased range and reduced noise and vibration.

Why Power with Hydrogen?

The 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.

The 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. This led Piasecki to explore the potential of the third possibility, 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. The 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. The 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. “The 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 market—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 signature,” 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. The 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 outside of nuclear fuels.”

John Piasecki agrees. “Hydrogen is well on its way to becoming another major player in the fuel arena. I don’t know if it’s going to replace fossil fuels, but it’s going to be a big player.”

Universal Hydrogen has developed lightweight, ­aviation-grade modular hydrogen capsules that can be used to ship hydrogen to airports. The company formed a partnership in March with fuel-cell power-train developer H3 Dynamics to develop zero-emission propulsion systems for uncrewed aircraft, air taxis, and regional aircraft.

The Piasecki team believes hydrogen-powered eVTOL aircraft can add the most value initially in the existing light-helicopter market. Helicopter operators are always looking for ways to reduce operating costs, including maintenance, and this is one area where electric vehicles are expected to deliver benefits.

Maintenance schedules haven’t been established for electric motors and hydrogen fuel cells. But most of the systems’ inspection and refurbishment will be “more than an order of magnitude less demanding than with a turbine engine,” John Piasecki says. Some analysts predict that inspection intervals with hydro­gen propulsion will rise from 2,500 hours in the beginning to as long as 20,000 hours when the technology is fully mature and tested.

The CoAX 2D Coaxial Ultralight

As the company develops the PA-890, Piasecki is also working with the FAA on defining airworthiness certification criteria for hydrogen fuel cells. HyPoint will deliver five full-scale, 650 KWh hydrogen fuel cell systems for ground tests, flight testing, and for use in certification efforts. Piasecki Aircraft says it’s working on FAA certification criteria for the hydrogen fuel ­cell–powered PA-890 by 2023.

“Our main challenge will be in maturing the hydrogen fuel cell through a rigorous development program to educate ourselves and the FAA, using lessons learned to inform certification criteria, and developing a conforming design to take into production,” John says.

The firm plans to use the CoAX 2D coaxial ultralight helicopter from German developer edm aerotec GmbH as a test bed for a proof-of-concept demonstration of a scaled HTPEM hydrogen fuel cell. Piasecki aims to complete the first crewed helicopter flight powered by a hydrogen fuel cell with the CoAX 2D in 2023.

The CoAX 2D sports two counter-rotating rotors on a common shaft that counteract each other’s torque, providing highly efficient hover performance and eliminating the need for a tail rotor. The two-passenger helicopter weighs 1,320 lb., is powered by a 125 hp engine, and is certified by German airworthiness authorities as a light sport aircraft.

The HTPEM hydrogen fuel cell demonstrated on the CoAX 2D will reduce the risk for scaling up the technology for the PA-890. Modifications for the CoAX 2D will include removing the piston engine and replacing it with an electrical propulsion system while finding room for all the fuel cells and tanks.

While retrofitting an existing aircraft with hydrogen fuel cells will always present integration constraints, Piasecki will have more flexibility to optimize the results when designing the PA-890 to use hydrogen from the outset. Key design issues to be addressed are fuel cell integration, thermal management, tankage, and carriage and storage of hydrogen on board.

Meeting Market Demands

John Piasecki and his brother Fred, the company’s chairman and chief technology officer, are following in the footsteps of their father, Frank, who founded Piasecki Helicopter Corp. in the 1940s (see “Founding Father,” p. 44). In 1960, Boeing bought Piasecki Helicopter, which at that point went by the name Vertol Corp. Frank Piasecki continued on an independent path to research and develop advanced rotorcraft technology, founding Piasecki Aircraft Corp.

Today, John manages Piasecki Aircraft’s strategy, programs, and business aspects while Fred heads engineering development, fabrication, ground and flight testing, and airworthiness certification.

“[Our father] was always a forward-looking man, and he let the customer, or the need, drive the solution,” says John, who notes that the evolution of the hydrogen-powered helicopter is similar to that of the piston-powered helicopter.

“The development of the tandem helicopter was critical because it took what little power was available for the weight of a piston engine and made the most of it,” he says. “The efficiency of tandem rotors then opened the door for broader helicopter operations.

“Single-rotor helicopters were, in many respects, saved by the turbine engine, which provides ample power in a small weight budget. The problem is, turbine engines are expensive to operate, [which] has limited vertical lift to [more expensive] niche markets that can afford them,” John adds.

“Frank Piasecki would say that electrification and hydrogen fuel cell propulsion can address the fundamental issue of cost—that is, getting the cost of vertical flight down so more people can use it.”

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Founding Father

Frank Piasecki left his mark on the helicopter industry.

John and Fred Piasecki, the current leaders of Piasecki Aircraft Corp., like to say that Piasecki is an ideas company, with a legacy of more than 25 vertical flight aircraft developments. That tradition was begun by their father and company founder, Frank Piasecki, an engineer who pioneered helicopters during the industry’s infancy, developing innovations such as the tandem rotor that are in wide use today.

In 1943, Frank Piasecki developed the second helicopter to fly in the United States, the PV-2 single-seat, single-rotor helicopter, four years after Igor Sikorsky’s first flight in the VS-300. He was also the first to obtain a US helicopter pilot’s license without already having an airplane rating.

To promote the PV-2, Frank appeared in a short film, landing the helicopter on a golf course, at a gas station, and in other locations, displaying its novel ability to land practically anywhere. Developed as a technology demonstrator and never produced commercially, the PV-2 now resides at the Smithsonian Institution.

Frank’s accomplishments attracted the interest of the US Navy, and in 1945, the service awarded him a contract to design a large tandem-rotor, heavy-load helicopter. The result was the HRP-1, the “Flying Banana,” the first tandem-rotor helicopter and the first helicopter designed for the Navy. This aircraft and its derivatives were instrumental in pioneering vertical lift applications in the US military, including anti-submarine warfare, mine clearance, vertical envelopment with the Marine Corps, air assault and air ambulance for the US Army, and combat search and rescue for the US Air Force.

Piasecki’s tandem-rotor design formed the foundation of many present-day rotorcraft, including the CH-47 Chinook, cementing his helicopter legacy. A durable workhorse for both military and civilian missions, the CH-47 has a payload of approximately 14 tons.

In 1955, Frank left what was then called Piasecki Helicopter Corp. to form Piasecki Aircraft Corp. and concentrate on developing advanced VTOL systems. Piasecki Helicopter Corp., renamed Vertol, was then sold to Boeing.

Meanwhile, at Piasecki Aircraft Corp., Frank continued to advance vertical flight and, in 1958, developed the Airgeep flying car. At the same time, he flew the world’s first quadcopter drone, called the Sea Bat.

From 1961 to 1966, Frank developed the first shaft-driven, high-speed compound helicopter, the 16H-1 Pathfinder and 16H-1A Pathfinder II. In the 1970s and 1980s, he developed and flew the world’s largest VTOL aircraft, the PA-97 Helistat, a hybrid aircraft that incorporated a blimp and four helicopter rotors for super-heavy lift applications.

In his later years, Frank oversaw the resurgence of compound-helicopter technology with the successful test flight of the X-49A SpeedHawk compound aircraft, ushering in a period of VTOL innovation with the US Department of Defense’s Future Vertical Lift (FVL) program.

Before his death in 2008 at the age of 88, Frank received numerous awards, including the National Medal of Technology and Innovation and the Smithsonian National Air and Space Museum Lifetime Achievement Award.