• 25 Mar 2025 01:31 PM
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TVF 2025 Highlights AAM Progress and Challenges — Part 5: eVTOL Propulsion Developments

By Kenneth I. Swartz

This series is an expanded version of the article printed in the March/April 2025 issue of Vertiflite. Check out Part 1: Introduction, Part 2: AAM Perspectives, Part 3: Electric VTOL Leaders and Part 4: Small eVTOL Aircraft Developments.

The Vertical Flight Society’s TVF 2025 was held at Phoenix Convention Center on Feb. 4–6, 2025, including the 12th Electric VTOL symposium and the 11th Biennial Autonomous VTOL Technical Meeting. 

The TVF 2025 program featured presentations by two electric motor companies, three developers of hybrid-electric (heVTOL) propulsion systems and four companies developing hydrogen-electric VTOL (H2eVTOL) aircraft.

Unither Bioelectronics 

Unither Bioelectronics is a Canadian subsidiary developing a transplant organ delivery system company for its US-parent, United Therapeutics (UT), which is a biotechnology company developing novel, life-extending technologies for rare lung diseases, oncology and organ manufacturing.

The first battery-electric Robinson R44 was developed by Tier 1 Engineering, partially funded by UT, and flew in September 2016. Development continued and the third-generation e-R44 made a record cross-country flight in October 2022 (see “Tier 1 Engineering’s Electric e-R44 Makes First Cross-Country Flight,” Vertiflite, Nov/Dec 2022). 

Due to the limited range of battery-electric power, UT moved the electric-helicopter program to its Canadian subsidiary in 2023. In 2024, Unither Bioelectronics began ground running an electric R44 converted to run on a hydrogen (H2) PEM fuel cell powertrain at its headquarters in Bromont, Quebec (see “Unither Bioelectronics and Robinson Helicopter Partner on Hydrogen,” Vertiflite, Sept/Oct 2024).

UT has been in the news over the years as hospital transplant teams use its gene-edited pigs’ organs (i.e. UHeart, UKidney, UThymoKidney) for xenotransplantation in a living human as part of research trials. In early February, UT was one of two companies to receive US Food and Drug Agency (FDA) approval to conduct clinical trials transplanting genetically modified pig kidneys into human patients with kidney failure. 

As research and trials of these organs continue, Unither Bioelectronics has been building the foundation for a multifaceted zero-emissions organ delivery system that will utilize drones, hydrogen-electric helicopters, eVTOL and eCTOL aircraft, including the Beta A250 and C300.

Mikaël Cardinal, Vice President and Program Manager for Organ Delivery Systems, said his goal is to fly the hydrogen-electric proof-of-concept R44 Raven II in 2025 and develop a hydrogen-electric supplemental type certificate (STC) -conforming Robinson R66 in the 2026+ period. 

The maximum takeoff weight of the R66 is 200 lb (90 kg) more than the R44 — 2,700 lb (1,225 kg) versus 2,500 lb (1,135 kg). The five-seat R66 can also carry an additional passenger, and has a separate full-width, 18-ft³ (0.5-m³) baggage compartment, which — together with the space used for the R66’s 73.6-gallon (279-liter) fuel tank — UT believes could be used to install a hydrogen storage tank. 

Piasecki Aircraft Corp.

In early February, Piasecki Aircraft Corp (PiAC) completed the historic move of its headquarters from its long-time home on the shore of the Delaware River in Essington, Pennsylvania, to the Piasecki Heliplex in Coatesville, 35 miles (50 km) west. PiAC acquired the Heliplex from Sikorsky in 2023.

John Scott, program manager of Hydrogen Propulsion Technology at PiAC says his company is betting on hydrogen fuel cells to provide the energy required to power the PA-890 Pathfinder III slowed rotor winged compound helicopter.

The Safran Arriel turboshaft produces about 6,200 W/kg of power, he said, compared to batteries (380–400 W/ kg), hybrid-electric propulsion systems (4,525 W/kg) and hydrogen fuel cells (2,900 W/kg), but PiAC believes fuel cells will reach 4,500 W/kg by 2030.

One reason that Piasecki is optimistic about the outcome is its work with-high temperature proton exchange membrane (HTPEM) fuel cells, which offer the promise of being simpler, lighter and less expensive than low-temperature systems; HTPEMs produce higher specific power with the only moving parts being a fan and compressor (see “Hydrogen Begins to Take Off,” Vertiflite, July/Aug 2024).

Since 2019, PAC has received contract awards of $27.6M and air force Independent Research and Development (IRAD) investments of $9M to fuel cell development and integration working with ZeroAvia (which bought HyPoint in 2022).

Later this year, PiAC expects to fly its manned HAXEL (Hydrogen CoAxial Electric Lift) helicopter outfitted with four single power model (SPM) fuel cells, each of which produces 16 kW, augmented by batteries. 

The highly modified EDM Aerotec CoAX-2D co-axial helicopter will also be equipped with four 350-bar (35-MPa) tanks carrying 2.6-lb (1.2- kg) of hydrogen, and a 210-kW EMRAX eMotor 268. The demonstrator will also have a cockpit interface that Scott described as a “FADEC replacement” and will provide digital control of the electric motors and inverters, and monitor the fuel cell temperatures, compressor RPMs and other new technologies. 

PiAC’s AFWERX Strategic Funding Increase (STRATFI) contract has been underway for two years with the goal of developing a fuel cell (with 12 SPMs of 66 kW each) in a package that is about the same size as a helicopter engine. The unit is also split into left-hand and right-hand sides to provide redundancy across the compressors, SPMs and other components.

The unit has been sized to power the PA-890 and develop a family of H2 propulsion systems for eVTOL aircraft and can also be retrofitted into a number of turbine-powered helicopters, from the Robinson R66 to the Bell 505 and Airbus H145/UH-72 Lakota. 

PiAC is targeting the dual-use PA-680 to have significantly better performance than a conventional helicopter in terms of payload, range and speed, with up to a 50% lower direct operating cost (DOC) per flight hour. 

Looking ahead, Scott also believes that cryo-compressed hydrogen (CcH2) that uses cryogenic cooling and high pressure to store hydrogen is a promising option for aviation use since it allows for a lighter tank with less volume. 

MagLev Aero

In early February, Piasecki Aircraft Corp (PiAC) completed the historic move of its headquarters from its long-time home on the shore of the Delaware River in Essington, Pennsylvania, to the Piasecki Heliplex in Coatesville, 35 miles (50 km) west. PiAC acquired the Heliplex from Sikorsky in 2023.

When the founders of MagLev Aero Technologies started working on early eVTOL and drone projects in 2015, they quickly identified power and acoustic challenges with existing electric motors and set out to develop a quieter, more-efficient propulsion system with one of the applications a VTOL aircraft being developed for GoFly Prize competition. 

The result was the MagLev HyperDrive propulsion system, a tip-driven, shrouded-fan propulsion system that provides “more lift, range and speed for less power and noise” for vertical lift and cruise performance, said Ian Randall, CEO of MagLev Aero.

The company is applying the magnetic levitation concept used for trains with the “track” serving as a direct-drive rim motor to rotate the enclosed tips of the fan. The design contributes higher total thrust, disk loading and hover efficiency than with a ducted rotor or open fan, Randall said.

Randall says that the design provides higher thrust, disk loading and hover efficiency than with a ducted rotor or open fan, because the HyperDrive encloses the blade tips, preventing air leaks around the blade tips that cause tip vortices. The hub support and MagLev rim also enable the use of thinner blades to reduce drag, noise and required power and the rim provides increased torque per weight and air cooling.

MagLev claims that the ducted HyperDrive with thin blades generates 58% more hover lift efficiency (shp/lb or kg/kW) than traditional shaft-driven open rotors of equivalent size. 

In his presentation, Randall showed images of the flat profile MagLev tip-driven ducted fans incorporated in the 2019 Hyper-Delta concept aircraft, a 500–700-lb (227–318-kg) quad-fan cargo UAS, and a blended wing body (BWB) high-speed long-range VTOL with a hybrid-turbine propulsion system capable of transporting a 1,000-lb (450-kg) payload 650 miles (1,050 km) at a maximum speed of 350 kt (650 km/h). He then discussed the use of MagLev propulsion system in a high-speed VTOL aircraft equipped with a hydrogen fuel-cell system.

Evolito

When UK electric-motor maker YASA (which originally stood for Yokeless And Segmented Armature) was purchased by Mercedes in 2021, the aviation business was spun off to form Evolito; the new company opened offices across the street in Oxford. The two companies are developing axial flux motors and motor controls for their respective markets and a bi-directional intellectual property (IP) agreement ensures that their engineers will continue to learn from each other, said Matt Farides, Vice President of Business Development.

The Evolito product line includes the 6,000 rpm D250, which is targeted for geared battery-electric and hybrid applications, the D800 for multi-propeller hybrids and the D1700 for direct-drive applications. During TVF 2025, Evolito announced that the D250 had been selected as the propulsion system for the Flying Whales LCA60T large-capacity airship (see “Electric VTOL News,” pg. 58).

Farides said that one of the benefits of a liquid-cooled axial flux motor is that the torque can be doubled with only a 10% increase in engine size.

During TVF 2025, Evolito announced that the D250 had been selected as the propulsion system for Flying Whales LCA60T large capacity airship. Flying Whales is headquartered in Paris and plans to be a manufacturer and an operator. Airship final assembly lines are being established in Bordeaux, France, and in Quebec, which is also an investor.

Each 656-ft (200-m) long rigid airship will be powered by 32 D250 motors, which have a power density of 18.5 kW/kg, providing 240 kW of peak power while weighing only 28 lb (13 kg) each. In 2022, Flying Whales selected P&WC to provide a 1-MW turbo-generator based on the PT6 to power the airship, but in April 2023 announced it changed to Honeywell’s 1-MW generator.

VerdeGo

Eric Bartsch, CEO of VerdeGo Aero of Daytona Beach, Florida, began the session on hybrid-electric propulsion by describing the growing requirement for hybrid propulsion in both the AAM and defense sector. He provided a description of the company’s three hybrid-propulsion systems spanning the 185 kW to 1.5 WW range, with applications for eVTOL, eSTOL and eCTOL aircraft. A detailed look at the company and its hybrid-electric developments and products is found in the article “Here Come the Hybrids!” (pg. 32).

GE Aerospace

GE Aerospace has a long history of developing first-of-its-kind hybrid propulsion systems for flight and demonstrations, Darek Zatorski told the TVF attendees. The company is today working on a number of hybrid-electric powerplant to military applications. Active projects include the CFM RISE open rotor engine, NASA Electrified Powertrain Flight Demonstration (EPFD), NASA Hybrid Thermally Efficient Core (HyTEC), Sikorsky Hybrid-Electric [Experimental] (HEX), and the Army Research Lab’s Applied Research Collaborative Systematic Turboshaft Electrification Project (ARC-STEP).

The Electric Flightworthy Lightweight Integrated Thermally Enhanced powertrain System (eFLITES) program includes the T700-CT7 turboshaft with an electric machine for VTOL applications and a turbofan and electric machine for high-speed VTOL applications, with the electric machine and power electronics embodying a suite of GE-developed transformative technologies. 

RTX

RTX is developing a portfolio of propulsion systems to serve the general aviation, helicopter, business, regional and large commercial aircraft sectors, said Ray McFall, Emerging & Disruptive Capabilities Lead at Pratt & Whitney, a subsidiary of RTX Corporation (formerly Raytheon Technologies Corporation), which also includes Collins Aerospace.

McFall said four hybrid-electric propulsion “pillars” are being developed to serve these different aircraft market segments. 

The P&W and Collins Scalable Turboelectric Powertrain Technology (STEP-Tech) demonstrator completed its first engine run in East Hartford, Connecticut, in June 2023. STEP-Tech will produce 100–750 kW, and is intended for AAM aircraft, high-speed VTOL and BWB aircraft.

P&W Canada is modifying a De Havilland Dash 8-100 into a hybrid-electric flight demonstrator. One of the aircraft’s 1.4-MW (1,900-shp) PW120 turboprops is being replaced by a parallel-hybrid system consisting of a 1-MW (1,340 shp) gas turbine optimized for cruise efficiency and augmented by similar sized 1-MW battery-powered electric motor to provide extra power for takeoff and climb.

The Sustainable Water-Injecting Turbofan Comprising Hybrid-Electrics (SWITCH) project was announced by a P&W-led consortium in 2022 and supported by the European Union Clean Aviation Joint Undertaking (Clean Aviation) with the goal of achieving up to a 25% improvement in fuel efficiency and reduced CO2 emissions. 

The SWITCH design features a “mild parallel hybrid propulsion system,” a 0.5-MW electric machine driven by the engine core, a 1-MW electric machine on the low spool, and a 1-kV battery and distribution system. 

In July 2024, Airbus Helicopters announced it had selected RTX as a partner for the PioneerLab hybrid-electric demonstrator. The demonstrator is based on the twin-engine H145, with first flight expected in 2027 with the goal of achieving a 30% improvement in fuel efficiency with the new propulsion system and aerodynamic improvements. 

In place of the H145’s two Safran Helicopter Engines 894-shp (667-kW) Arriel 2E turboshaft engines, the research aircraft will be equipped with a P&WC 1,000-shp (735-kW) class PW210 engine derivative, linked through two Collins Aerospace 250-kW electric motors and controller to a common gearbox. The electric motors will be used to provide high torque for peak demand flight conditions, such as takeoff and landing. 

Bigger eVTOL

UK-based Sora Aviation presented details of its high-capacity 30-seat S-1 tandem-wing eVTOL aircraft with six tilting propellers. The hybrid-electric aircraft is targeted at the airport shuttle market, which is expected to account for about 50% of AAM operations, according to a Roland Berger study.

Sora was founded in February 2024. Company CEO Furqan (no second name) and CTO Malcolm Foster met at GKN Aerospace where they worked on various projects, including the large Skybus eVTOL concept. Foster retired as chief of preliminary design from Bell Helicopter in 2005.

High-volume helicopter airport shuttles once operated in London, Los Angeles, New York City and San Francisco. That’s the goal of the Sora S-1 design, which will use the same lithium-ion batteries as smaller air taxis; for short hops, batteries will only consume the same percentage of empty weight as on small aircraft. The company believes the Sora S-1 could replace five-seat eVTOL aircraft on high- volume routes, provide more baggage capacity and reduce vertiport congestion and community overflights.

Odys Aviation’s Laila UAS and nine- passenger Alta feature a large number of horizontally thrusting propellers with large drooping flaps that are used to vector the efflux downwards for hover and VTOL flight.

The first phase of the aircraft development, Odys CEO James Dorris explained, was to build eight subscale prototype aircraft and fly them over the past two years to validate the VTOL and cruise phases of flight, with a full transition achieved in the fourth quarter of 2024 using a battery-powered demonstrator.

The second phase is the maturation of the hybrid-electric Laila UAS, which is being developed as a product. The drone will have a speed of 125 mph (200 km/h), a 22-ft (6.7-m) wingspan, a 450-mile (725- km) range with a 65-lb (29.5-kg) payload, and 100-mile (160-km) range with a 130-lb (60-kg) payload. Odys has won 12 DoD contracts worth $10M.

The third phase is the development of the larger Alta, which is being designed to have a range of 750 miles (1,200 km), utilizing a hybrid-electric propulsion system, or a 200-mile (320-km) range using batteries alone.

Elroy Air’s new CEO Andrew Clare highlighted the company’s recent flight testing with its Chapparal C1 cargo demonstrator. Elroy was the first company ever to fly a turboshaft hybrid-electric VTOL aircraft in 2023 and has completed autonomous full transition testing of its subscale battery-electric VTOL test aircraft. The company will be conducting test flights of the Chaparral with customer Bristow in Norway later this year.

The Chaparral is optimized for middle- mile logistics. The production system is projected for an operating range of 300 miles (482 km) with a 300-lb (136-kg) cargo payload. As a hybrid system, it uses existing fueling infrastructure and provides long-range flight, allowing it to be deployed anywhere. The design featured autonomous flight and unattended cargo pickup and drop-off using customizable, swappable pods.

With and Without People 

Autonomy was also a theme in the invited plenary and eVTOL sessions. A plenary session had presentations by executives from Daedalean, Near Earth Autonomy and Wisk, talking about the past, present and future of the sensors, operations and artificial intelligence (AI) to reduce or eliminate the need for humans in the cockpits of aircraft, with or without passengers.

In the eVTOL track, another panel featured leaders from Daedalean, Rotor Technologies and Skyryse. The latter two are both using autonomy in Robinson R44 helicopters. With the slogan, “Big drones for tough jobs,” Rotor is taking pilots out of the aircraft altogether, while Skyryse is implementing its SkyOS autonomy to reduce pilot workload and improve safety (see “Rotorcraft News,” pg. 6).

Meanwhile, an Arizona AAM Stakeholders Panel discussed how humans will be impacted — positively and negatively — by AAM operations in their communities. Moderated by Taylor Alberstadt of Honeywell, the representatives of local organizations provided insights into the needs, wants and concerns of the public at large.

Summary

The annual TVF meeting is always a unique event. In addition to the robust technical program, this year focused on the range of autonomy for VTOL aircraft, and the invited talks in the Electric VTOL Symposium provided unique insights into the latest AAM developments from industry, academia and government leaders.

BAE Systems chaired a panel discussion with SURVICE Engineering and Malloy Aerospace to discuss the TRV-150 battery-electric VTOL UAS. This is the first logistics drone to enter service with the US miliary (see “SURVICE for Service,” Vertiflite, Sept/Oct 2023) and it has also been used by the UK military. Jonny Gilchrist, Head of US Business Development for the BAE Systems FalconWorks innovation unit highlighted the collegial environment at VFS events. “One of the things that drew us to wanting to come and speak … was reflecting over attending the last couple of years. It's the active sense of community to try and achieve common goals that actually plays out in reality here over the course of a couple of days.”

“Quite often in this space, you can see a lot of competition,” he continued. But at TVF, “there's never a negative competitive spirit to the event. It's never, ‘our system is better than yours.’ It's ‘here's what we're learning, here's what's important to us and what we've used to overcome things,’ and sharing that best practice with the community. And I think if we keep doing those things, that's going to benefit our end users in the military and it's going to benefit our day-to-day lives” in civil applications.

VFS is extremely grateful to our exhibitors and sponsors. Honeywell was the Diamond Sponsor and host, and BAE Systems was the Platinum Sponsor. Gold Sponsors were Bloomy, Boeing, Daedalean, Dassault Systèmes, Joby, Near Earth Autonomy, Piasecki Aircraft, SkyDrive, Toray, Unither Bioelectronics and Wisk. Silver Sponsors were Arizona Commerce Authority, Evolito, Phoenix Sky Harbor Airport, Pivotal and Stell Engineering.

Technical paper proceedings and invited presentation PDFs are available on the VFS online Vertical Flight Library. Video recordings are available for attendees, and several are public. Learn more at www.vtol.org/tvf2025.

Check out more resources on TVF 2025 and the other parts in this series!