25 May 2023
Transformative Vertical Flight (TVF) 2022 was held Jan. 25–27, with some 375 participants in San Jose, California, and another 200 attendees online, in the first hybrid event organized by VFS. TVF2022 included both the 9th Annual Electric VTOL Symposium of invited talks and selected paper presentations in the biennial Aeromechanics for Advanced Vertical Flight Technical Meeting. More than 50 technical papers were presented in two tracks, covering aeromechanics, the Mars helicopter, electric vertical takeoff and landing (eVTOL) aircraft and urban air mobility (UAM). Industry and government plenary sessions and some 50 invited eVTOL talks were given by innovators in industry, government and academia.
Aeromechanics — Vertical Flight over Cities, Battlefields and Mars
Technical presentations addressed rotor noise from tandem rotor configurations, component load alleviation from individual blade control and other advances to improve rotorcraft performance and acceptance. A paper by NASA Langley researchers considered a UAM reference vehicle with six tilting ducted proprotors and concluded noise reduction may provide a compelling reason to use ducted thrusters.
NASA plenary speakers at TVF2022 David Hackenberg (NASA headquarters) and Jaakko Karras (NASA JPL), with Colin Theodore (NASA Ames), the TVF2022 General Meeting Chair. In addition, NASA’s Carl Russell was the Symposium Technical Chair, and the Army’s Buwana Jayaraman (at NASA Ames) was the Aeromechanics Meeting Technical Chair.
Besides captivating visions of UAM, the TVF meeting highlighted rotorcraft advances in other challenging domains. The proof-of-concept Mars Ingenuity helicopter now reconnoiters the red planet for the Perseverance rover. In a plenary keynote talk, Ingenuity chief engineer Jaakko Karras of NASA’s Joint Propulsion Laboratory (JPL) explained, “The rover team is now using our images to make decisions about where it’s going to drive. So, Ingenuity has, in a way, graduated to serving as a scout for the rover, which was the original vision and motivation for this type of technology.” By the time of the conference, the 4-lb (1.8-kg) helicopter with its rigid coaxial rotors had flown 18 times over legs to 2.4 miles (3,823 m) and logged 32 min 50 sec total flight time (see “Collaboration Powered Success of NASA’s Mars Helicopter,” Vertiflite, Jan/Feb 2022).
Atmospheric density on Mars is equivalent to that at about 100,000 ft (30.5 km) on Earth. Ingenuity in a vacuum chamber showed the 2,500 rpm direct-drive rotors could generate enough thrust to fly, but interplanetary latency demanded closed-loop autonomous control. “A human pilot, even an expert one, was not able to fly this vehicle,” said Karras. Density altitude also varies with Martian seasons. “With such a thin atmosphere, you don’t get much in the way of damping… which makes stable control quite difficult.” Flight control software in the little helicopter has been updated twice from Earth.
Supernal’s Diana Marina Cooper warned that the FAA must maintain its exclusive authority over aviation safety to avoid a dangerous patchwork of regulations across the US.
To fly amid integrated air defenses on Earth, the US Army’s Future Vertical Lift (FVL) ecosystem has to stay below 300 ft (91 m) according to Col. Jay Hopkins, FVL Cross-Functional Team chief of staff. The lower tier of the air domain makes networked communications difficult, but Hopkins said, “It’s that same clutter that allows you to be survivable against many of the threats… Rotary-wing aircraft are survivable in today’s environment.” Competitive prototypes of the Future Attack Reconnaissance Aircraft (FARA) were reported as being 70–80% complete at Bell and Sikorsky (see “FVL: Protected Across Domains,” pg. 26). “The mission systems are being wrung out with the competitive prototypes,” said Hopkins. The Future Long Range Assault Aircraft (FLRAA) is in competitive design and risk reduction (CDRR), and will introduce the modular open system approach (MOSA) ultimately spread across FVL crewed and uncrewed platforms. Both FARA and FLRAA aim for first units equipped (FUE) in 2030.
In contrast to the Mars helicopter, optionally piloted FARA and FLRAA put people in harm’s way. Hopkins offered, “The situational knowledge that a pilot and his or her co-pilot has cannot be replaced. That’s not to say that autonomy and AI [artificial intelligence] do not have a role in what we’re doing —we’ve proven that in spades with regards to cognitive offloading and the ability to do more with less — but we feel very strongly about the availability of the manned option on both of these platforms.” Hopkins added, “When all else fails, when the comms don’t work, when that sensor doesn’t work, our pilots are trained to have the tactical curiosity to continue the mission based on the commander’s intent in a manned platform. It’s not optional.”
Guy Kaplinsky, CEO and Co-Founder of NFT, Inc., stands with a display model of the company’s ASKA folding electric flying car.
Uncrewed FVL aircraft are also in development. The Future Unmanned Aircraft System (FUAS) is a runway-independent replacement for the Shadow UAS. Air Launched Effects (ALE) in small and large versions will be launched from FARA to give human crews stand-off safety. Hopkins said, “The two major platforms we’re looking at are not electric, but it’s not unlikely there will be an upgrade.” An abbreviated capabilities development document (A-CDD) signed in January 2022 described a scalable control interface for networked users to steer payloads and potentially fly the uncrewed systems.
Bypassed for continuing FARA and FLRAA development, Karem Aircraft continues optimum speed tiltrotor (OSTR) research with a single rotor tie-down (SRT) test program under the Army’s Joint Multi-Role Technology Demonstration (JMR TD) initiative. The conference was updated on promising SRT results with a stiff, light, variable-speed rotor 36 ft (11 m) in diameter and other integrated components. Karem also proposed military and commercial OSTR applications leveraging the added range, endurance, and fuel economy of an OSTR.
With more than 600 electric VTOL concepts now listed in the VFS World listed in the VFS World eVTOL Aircraft Directory (www.eVTOL.news) and hundreds of programs in active development, TVF2022 took a broad look at the interrelated pieces of the emerging eVTOL industry. A handful of transformative aircraft have begun feeding flight test data back into NASA simulations to model advanced air mobility (AAM). Joby Aviation is an AAM partner and has been making significant strides towards conducting certification testing (see “Pushing the Envelope: Joby Aviation in 2022,” Vertiflite, March/April 2022).
The ASKA flight simulator allowed attendees to experience the easy transition between drive and fly modes.
During a keynote plenary talk, NASA AAM integration manager Davis Hackenberg recognized the eVTOL progress but noted, “It’s not about the performance characteristics of the aircraft we’re seeing right now, although that’s going to be important to the long-term business cases. It’s really about the safety data that we’re starting to gather. I don’t think there’s an actual conforming prototype that’s on a certification basis flying, but we’re really, really close.”
The audience heard how NASA’s AAM National Campaign has teamed the eVTOL industry with airspace managers. The space agency has established UAM Maturity Levels (UMLs) ranging from UML 1 with today’s small uncrewed aircraft systems, through UML 2 with the first eVTOL aircraft, to UML 3 and 4 when complex operations manage hundreds of aircraft. Hackenberg said, “We’re going to need a lot more emphasis on what UML 3 and UML 4 are going to look like if we really want this industry to scale.”
He also acknowledged the value of skepticism. “Recently, I’ve begun to see more negative press about eVTOLs, people poking at the system: ‘How are the batteries going to work? How long is it going to take to get certification?’… I think we need as much of that as possible, so we can go out and defend what’s happening, so we can go out and show these things are going to be safe and put to bed some of those arguments.”
eVTOL Gets Real
eVTOL Symposium attendees heard updates on distributed electric propulsion, energy sources, air space management, and regulatory standards. Vertical Aerospace chief engineer Tim Williams reported 1,300 commitments for its VX4 air taxi due to fly for the first time this year. Volocopter Chief Technical Officer Dr. Arnaud Coville made the first announcement that the company’s VoloCity had flown the previous month, and told of plans to certify the multicopter by the end of 2023 — for short-range urban air mobility (UAM) services in early 2024. Elroy Air CEO Dave Merrill described its unveiled Chaparral C1 uncrewed cargo carrier that will enter commercial service in 2023, under the broader advanced air mobility (AAM) mission scope.
Merrill stated, “Elroy Air is a team of brilliant, kind, dedicated experts in aerospace, logistics and robotics all working together to improve the speed of express shipping.” The vision has drawn orders for 100 aircraft from humanitarian shipper AYR Logistics Limited and 150 more from regional carrier Mesa Airlines. Merrill said, “Our belief is that changing logistics and improving logistics will change the world in really profound ways.”
The Air Force has, so far, given 11 eVTOL developers Agility Prime contracts and access to government ranges and ground test facilities. AFWERX director Col. Nathan Diller noted, “Our approach has been one of risk reduction in a very collaborative manner.” Late last year, an Air Force pilot flew the Kitty Hawk Heaviside eVTOL vehicle via remote ground controller. Agility Prime representatives meet weekly with the FAA to consider flight standards, and an Air Force training effort aims to field some military eVTOL systems in 2023. AFWERX is now pursuing collaborative research, development, test and evaluation partnerships that can push eVTOL to speeds greater than 300 kt (555 km/h) and ranges more than 1,000 nm (1,850 km).
Helicopter maker Sikorsky Aircraft revealed no specific eVTOL plans, but the company’s Innovations strategy lead Jonathan Hartman said a decade of eVTOL technology maturation promises real products and offerings. “In my opinion, the value of vertical lift has never been higher… The ability to move from mechanical drivetrains to electrified trains really has the potential to change the way our customers use our products for their missions.” He added, “I do think it’s important to expand the concept of an ecosystem solution. That’s going to happen when customers realize both a time-saving as well as a stress-saving from using a vertical lift component.” Hartman later said, “Having fundamental trust in the behavior of the system is fundamentally important.”
Proposed European Union Aviation Safety Agency (EASA) Special Condition SC-VTOL-01 guidance enables Vertical Aerospace to trust that its all-electric air taxi will be 100 times safer than conventional helicopters, according to the VX4 chief engineer. Williams described its five-seat, eight-propeller, winged, vectored-thrust platform capable of 200 mph (157 kt or 322 km) cruise over 100 nm (185 km) range with existing battery technology. Small propellers with low tip speeds also promise a VTOL aircraft as much as 100 times (-20 dB) quieter than a helicopter. Vertical Aerospace bases its projections on the lessons learned from two multicopter demonstrators and extensive computer modeling. Williams announced that the first VX4 prototype is being assembled in the UK to fly in the first quarter of 2022. The company envisions a commercial vehicle flown by an on-board pilot. Williams said, “We think that autonomy is some ways away… probably not in this decade.”
Avports and Jaunt announced an alliance to incorporate the allelectric Jaunt Journey in airport operations.
Jaunt Air Mobility expects its Journey air taxi in service around 2026, and chief commercial officer Simon Briceno told the VFS audience that batteries are still the highest-risk system on eVTOL aircraft. His company’s slowed rotor compound (SRC) electric rotorcraft (see “Jaunt’s Journey,” Vertiflite, Sept/Oct 2021) uses a battery pack energy management system and flight control computers from BAE Systems. It offloads the slowed rotor with a fixed wing to transition from vertical takeoff to efficient cruising flight for higher speeds and lower energy consumption. Unlike most eVTOL designs, it can autorotate better than helicopters — thanks to its high-inertia rotor — or glide to a safe landing on its fixed wing with total loss of power. Four quiet scimitar propellers on the wing and airplane-like ailerons and elevators provide redundant control mechanisms.
Jaunt has partnered on Air Force Small Business Technology Transfer (STTR) contracts to study slowed-rotor acoustics and fast battery charging. The company also has an STTR effort underway to show the benefits of thermoplastic composites with automated layup, hot press forming and induction welding. Briceno said, “We’re going to be able to show a massive reduction in assembly time as well as a reduction in assembly cost by using this material as our primary structure.” The proposed Jaunt MAV55 uses the same technologies to address the AFWERX High-Speed VTOL Concept Challenge (see “Air Force Picks 11 Companies for High-Speed VTOL Program,” pg. 60).
Announcing an additional $450M of Boeing financial backing the week of the symposium, Wisk is now one of the best-funded eVTOL developers. The company’s vision puts several Cora self-flying air taxis aircraft under one multi-vehicle supervisor in a ground fleet management center, as the first step to fully autonomous operations. Vertiports will draw on an AAM service provider, an air navigation service provider and supplemental data providers. Wisk VP of Global Partnerships Dan Dalton reported the autonomous Cora had logged more than 1,500 test flights. The all-electric aircraft with 12 lift propellers and one pusher propeller is a candidate to fly from urban or suburban airports to city centers or to link commuter vertiports to downtown destinations. The company is now working on a larger eVTOL aircraft for the market — its so-called sixth-generation design, which has so far not been named.
Dr. Coville from Volocopter identified point-to-point UAM as the first and biggest eVTOL market for his company’s 18-rotor multicopter. “We have cities around the world that are approaching us to install urban air mobility,” he said. Paris and Singapore lead with plans to connect vertiports with railroads, and Coville noted, “Without this intermodal connectivity, the urban air mobility system may not be viable.” The eVTOL plans use current battery technology. In more than 1,000 demonstrator flights, the company has explored rotor cascade effects, rotor failures due to birdstrikes, battery fire hazards and noise.
Peter Vollheim and John Unghire show off the Transcend Aero Vy400 one-fifth-scale flight test demonstrator.
Coville said, “The noise of the aircraft pretty much gets drowned out by the noise of where you are.” The power system of the two-passenger VoloCity air taxi was sized to hover requirements to afford safety margins despite battery failures. The company’s more cruise-efficient inter-city VoloConnect lift-plus-cruise eVTOL will use lift propellers, two cruise fans and large tandem wings. Both concepts fly on swap-out battery packs recharged between missions. “We only make money when we fly,” noted Coville, “We can go down to a 10-minute turnaround time with this approach.” Battery capacity also declines with repeat cycles, and Coville noted, “The aircraft is aging with the battery. If you can remove the battery and put in a new battery, then you have a new aircraft and the full range when you need it.”
Craig Smith, product design leader for the Overair Butterfly told the VFS audience about his five-passenger air taxi with four tilting optimum-speed rotors, each 20-ft (6.1-m) diameter with independent blade control (IBC). The configuration minimizes disc loading for efficient hover and provides good control power to fight seasonal weather. According to Smith, “Hover actually sizes a lot of your capability — what your payload can be, your thermal system and the payload from your batteries.” Overair has begun ground-testing a full-scale rotor over a wide rpm range and put the complete propulsion system on a truck to feed test data back into computer simulations (see “Electric VTOL News,” pg. 62). The company is developing ground test articles to validate Butterfly aeromechanics and promises information later this year on flight testing.
A record 20 exhibitors discussed their products and capabilities with attendees during lunch and networking breaks.
Airbus UAM head of engineering Eric Ferreira da Silva gave an overview of the four-seat CityAirbus NextGen eVTOL air taxi. Building on flight testing with the Vahana tiltwing and CityAirbus shrouded fan demonstrators, the current concept with a fixed wing and eight propellers — six lifting propellers on the wings and two mounted at an angle at the rear to provide limited lift and cruise. The resulting configuration provides cruising speeds around 65 kt (120 km/h) and range up to 43 nm (80 km) with sound levels around 65 to 70 dBA, according to Airbus. Redundant propulsion and control systems give eVTOL new safety, but da Silva conceded non-traditional aircraft are complicated to fly. Industry is obliged to go to advanced fly-by-wire controls, “where the pilot is not like a pilot anymore, he’s an operator.” He acknowledged classic helicopters will remain the platforms of choice for heavier, longer-range vertical lift missions but stated, “This is not about a vehicle. This is about creating a service to society.”
The Hydrogen panel, L-R: Dave Edlund (Element 1), Thomas Jones (Plug Power), John Piasecki (Piasecki Aircraft) and Anubhav Datta (University of Maryland), chaired by Danielle McLean (Hy- Sky). Anita Sengupta (Hydroplane) joined virtually.
To give society same-day and next-day shipping everywhere, Elroy Air co-founder Dave Merrill said autonomous cargo aircraft can deliver goods five times faster than trucks. The new lift-plus-cruise Chaparral C1 is due to fly this year under an Agility Prime contract, and low-rate initial production aircraft should fly commercially in 2023. Merrill noted, “Because it takes off and lands vertically, it can serve exponentially more destinations, skipping airports altogether where needed.”
In contrast to short-range, all-electric aircraft, the uncrewed aircraft uses a conventional turboshaft and 150 kW generator to drive eight lift propellers for vertical takeoff and landing and four propulsors for cruise. The hybrid propulsion scheme increases mission range, recharges lithium batteries in flight and enables the autonomous cargo carrier to ground taxi and winch aboard interchangeable cargo containers at a logistics hub. The Chaparral C1 uses an ultra-wide-band beacon triangulation system to find its pods on the ground, an on-board datalink to maintain detect-and-avoid safety in flight, ADS-B Out for flight-following and lidar for safe navigation. Merrill said, “I actually think the airspace integration is where we’ll have the biggest challenges. How do you make sure that our existing aviation infrastructure can scale and make sure it’s safe?”
Regulate and Aviate
The VFS audience also heard perspectives on eVTOL standards, regulations and infrastructure, all aimed at safe operations in shared airspace. Tom Gunnarson, regulatory affairs lead at Wisk, talked about ASTM International initiatives to develop standards and means of compliance for eVTOL aircraft. The standards organization has five aviation sector committees backed by industry committees in composites and other eVTOL-related specialties. Work is underway on electric propulsion, energy storage systems, detect-and-avoid technology and other specialty areas. “When we talk about eVTOL, there are unique aspects compared to what we have to certify an aircraft in the General Aviation sector,” said Gunnarson. “We’re a little chicken-and-egg in some cases… There are gaps in the regulations.”
Steve Bradford, FAA Chief Scientist for Architecture and NextGen Airspace Development differentiated AAM from UAM. AAM outside cities requires no changes to existing rules and regulations. UAM in congested urban airspace requires defined corridors with pilots on board — or flying remotely — to dictate changes. With traditional air traffic control unscalable, UAM demands capacity management. Early plans confined UAM to corridors running from one vertiport to another. To reduce the impact on helicopters and other non-UAM aircraft, Concept 2.0 in development opens scalable corridors as needed but requires information exchange. “If you’re flying in a UAM environment, you have to have a fully integrated information environment,” said Bradford. “We really don’t think any particular operator will operate completely in UAM.” Wider, flatter corridors have less impact on the airspace, and the FAA and NASA plans corridor research in the Dallas/Fort Worth, Texas, area.
Christine DeJong Bernat, Director of Global Innovation and Policy for the General Aviation Manufacturers Association (GAMA), leads its Electric Propulsion and Innovation Committee (EPIC) of experts to look at safety and policy issues supporting eVTOL certification, operation and infrastructure. EPIC works with ASTM and SAE International on the standards for transformative vertical flight. Jonathan Archer, manager of aerospace standards business development and outreach at SAE International explained, “We work collectively with other organizations to bring the right expertise to bear when developing standards or defining a problem from which a standard may be developed.” SAE is also working with automotive and other experts to share data on battery charging stations, noise measurements, hydrogen fuel cells and material advances, including additive manufacturing and polymer matrix composites. “There’s no point in having materials that won’t support certification or be used in a higher production rate setting,” said Archer.
Making eVTOL aircraft in quantity assumes a powerful industrial base. Diana Marina Cooper, global head of policy and regulations at Supernal (previously the UAM Division of Hyundai Motor Group), reminded the VFS audience of the difference between traditional low-volume aircraft manufacturing and something closer to automotive-scale production for hundreds or thousands of eVTOL aircraft. Supernal’s team is exploring smart manufacturing processes and technologies that are used to build reliable cars at scale and plans to leverage those processes and technologies in the production of AAM.
Cooper also acknowledged the security issues facing eVTOL: “How do we think about security when there is no pilot on board, and passengers are just flying with one another?” The US Transportation Security Administration (TSA) recently initiated a working group that seeks to solve security challenges facing the AAM sector.
Supernal plans an innovation center in Washington, DC, to educate regulators, legislators and the public on the benefits that AAM will bring to communities, including sustainability, workforce development and accessibility. Cooper explained it is essential that the US Federal Aviation Administration (FAA) maintains its exclusive authority over aviation safety and to avoid a dangerous patchwork of regulations at the state and local levels that interfere with that authority.
Supernal is working with stakeholders on educational campaigns to build support for AAM. The broad effort seeks to harmonize airspace, develop zoning frameworks for vertiports, and serve as a tool to educate lawmakers on harmful bills that would hamper aviation safety and industry development. Legislatively appointed task forces were initiated last year to convene industry and government stakeholders to work on these issues in Arizona and Texas. These task forces will facilitate engagement between government, communities and industry in promoting policies that will help develop the AAM industry in an equitable manner, and to avoid the disparity of local regulations seen in the drone industry. For example, last year a bill was introduced in Texas that would have created a restrictive hodgepodge of airspace regulations throughout the state that differed from current and ongoing federal guidelines. The bill was not enacted due to broad industry opposition, but it serves as a good example of the need for industry and government collaboration when assessing the legislative and regulatory needs of AAM.
Yolanka Wulff, executive director of the Community Air Mobility Initiative (CAMI) described CAMI’s efforts with state and local decision makers and community planners to coordinate implementation of AAM. She reminded the VFS audience, “If we don’t have safety, we don’t have anything.” Wulff noted the growth of the AAM industry is technology-driven, and said, “It has not arisen from demand from local communities saying ‘build this transportation for us.’” She concluded, “There has to be broad public benefit.” Traditional aviation has not intersected with other forms of transportation in multi-modal systems. Wulff noted, “We haven’t solved any issues if we can transport people from Point A to Point B but there’s still a long time to their final destination.” CAMI is working with NASA on community planning, and conducting workshops with community partners to draft an AAM playbook for municipal planners.
TruWeather Solutions chief scientist Dr. Mounir Chrit cited an MIT study that acknowledged air weather prediction is a building block of advanced air mobility, but current weather data is not tailored to urban operations. Sudden changes in winds, for example, can increase UAM battery consumption and passenger cabin vibrations — and cause accidents. Under NASA contracts, TruWeather developed a lidar/radar-based wind-hazard location service able to support UAM in wet or dry conditions. The company’s RouteCast routing software develops flight plans based on optimal risk or best flight time.
Working for Watts
AAM envisions safe, economical aircraft harnessing radical distributed electric propulsion configurations and certified with all-new propulsion, control and structural technologies. Dr. Todd Quackenbush of computer modeling house Continuum Dynamics, Inc., (CDI) told the VFS meeting, “A lot of the vehicles face substantial modeling and design challenges.” He added, “There’s more to it than a splashy up-front presentation.” UAM is complicated by the highly disturbed air flow in dense urban environments where vortices bounce off buildings. This could give passengers an unfavorable ride experience and, if severe, pose safety hazards. CDI is working on flow field models for UAM environments, plus air vehicle and complementary safety-of-operations tools. Quackenbush observed, “In designing your aircraft, you have to design for your failure modes… What’s your plan for dealing with that failure?”
Ron Du Val, president of Advanced Rotorcraft Technology (ART), talked about real-time eVTOL simulation for comprehensive models that support real-world hardware and software testing. He explained, “First off, you need to deal with accurate modeling of the propeller. Then you need whole aircraft, including aeroelastic stability issues, stability and control issues with configuration changes in flight.” The modeling house built a hex-tiltrotor control simulation with pilot in the loop and is working to tie flight simulations into battery and power system models.
Aurora Flight Sciences’ Al Lawless, chair of the E-VTOL Flight Test Council (see “The E-VTOL Flight Test Council’s Pioneering Year,” Vertiflite, Nov/Dec 2021), considered the testing challenges of non-traditional aircraft with variable rpm controls and said, “They’re setting up vibration swamps. How do we testers deal with that?” The testing picture also has to include new air traffic ecosystems with different detect-and-avoid strategies, and it is complicated by the next level of cockpit automation where simplified vehicle operations may mean different levels of pilot qualification. The flight test council has worked with VFS, the Society of Flight Test Engineers, and regulators on means of compliance, simulator validation, cockpit inceptor conventions. Lawless confessed, “It’s a pretty overwhelming set of things we’re looking at here.”
After the panel on Workforce & Diversity, some of the attendees took part in this group photo to commemorate the moving experience.
Scott Drennan, advisor to the board of Electric Power Systems (EPS), provided an overview of battery power for electric flight and told the VFS audience that electrification of flight has to balance safety, cost, weight and infrastructure considerations. EPS now delivers battery power systems from their 2 MW-hr capacity factory and is working towards a GW-hr capacity factory. The compact, lightweight EPiC battery module from EPS incorporates containment, cooling and a battery management unit (BMU), and the company intends to provide energy as a service to aircraft manufacturers and operators. EPS battery systems are flying on eight different platforms and the EPiC module provides a pathway to more advanced systems and cell chemistries.
Jia Xu, senior director of strategy for UAM and UAS at Honeywell Aerospace, addressed integrated battery and hybrid-electric propulsion solutions. Without the benefit of constant forward flight for cooling airflows, eVTOL designs pose unique thermal challenges. Jia also noted, “Electric propulsion is no longer an isolated problem. It’s really an aero-propulsive control integration problem because the propulsors, whether by rpm control or torque control are also integral to the aircraft flight control system.” He added that integrating actuators, flight controls and motors is key to eVTOL success. “It’s one thing to build onesie-twosie demonstrators, but it’s something else to parse through the certification requirements and testing…” Honeywell has teamed with motor maker Denso Corp. in Japan to blend aviation assurance with automotive scale. A high-power-density axial flux motor adaptable to different eVTOL designs is due for testing in the first quarter of 2022 and flight tests in 2023.
A panel dedicated to hydrogen aviation heard from University of Maryland professor Anubhav Datta, who acknowledged, “It’s getting harder…to get more energy from batteries” due to diminishing returns in technology advancements. Fuel cell systems can provide more energy but fall short in specific power. Hybrid systems can be ideal, with fuel cells for cruise and batteries for hover. Datta called for a hydrogen eVTOL (H2eVTOL) demonstrator to establish the status of technology and to test the infrastructure and supply chain. He concluded, “eVTOL fuel cells have to be designed together with the aircraft, taking advantage of its unique attributes: low altitude, short storage, and high downwash.” Datta said the target is 1.0 kW/kg of net electrical power for the stack system including cooling and air, and a 5–15% weight-fraction hydrogen tank. The infrastructure barrier is common to cars and trucks and offers a major opportunity for cooperation between air and ground vehicles.
Anita Sengupta, CEO of hydrogen fuel cell powerplant developer Hydroplane, noted that aviation accounts for 2% of global carbon emissions, but emissions at altitude actually account for 3.5% of global warming. She used the backdrop to make a business case for aviation electrification where air vehicles with different weights and missions use batteries, hydrogen fuel cells and hybrid energy systems. Sengupta said fuel cells offer two to ten times better energy density than lithium batteries and three times the energy density of hydrocarbon fuels. Operating economics may be driven by the way the hydrogen is produced — cheap gray or blue hydrogen derived from processes that burn hydrocarbons, or costlier green hydrogen from electrolysis powered by renewables. Hydroplane has an Agility Prime contract aimed at fuel cells up to 1 MW. The Hydroplane Protium demonstrator, based on a Piper PA-28 Cherokee, is due to fly this year.
PlugPower has built a successful fuel cell business powering forklifts and pallet trucks round-the-clock without lengthy recharging. Thomas Jones, the company’s director of UAV/Aerospace Technology noted parallels with eVTOL operations. The company has formed a partnership with Airflow to develop a version of its electric short takeoff and landing (eSTOL) aircraft with hydrogen fuel cell propulsion.
The first hybrid VFS event found 375 attendees spaced out in San Jose and 200 more virtually from around the world.
Dave Edlund, CEO of Element 1 took hydrogen one step further with his proposal for using methanol to more easily transport hydrogen for applications such as fueling hydrogen aircraft. Inexpensive, commonly available methanol contains more recoverable hydrogen than an equivalent volume of liquid hydrogen. On-board generation technology would eliminate the need for high-pressure gas or cryogenic storage. Element 1 is a technology development and licensing company, and Edlund acknowledged that current hydrogen generator technology is heavy. “Very small aircraft are not going to be suited to this technology,” he said.
Piasecki Aircraft Corp. (PiAC) President John Piasecki told the VFS audience about the PA-890 hydrogen-powered electric rotorcraft. The historic helicopter maker has partnered with hydrogen fuel cell developer HyPoint to fly a slowed-rotor compound helicopter with a 200-nm (370-km) range. Hydrogen fuel cells have no published aviation standards for hydrogen tank crashworthiness and other issues, so PiAC is working with the FAA Center for Emerging Concepts and Innovation to develop a Special Condition requirement for the PA-890, with an eye to deploy and certify the helicopter by 2026.
Piasecki acknowledged promises of battery improvements have been over-optimistic. “I think a lot of people when they talk the economics of batteries, they are projecting-out.” He added, “Batteries have a lot of growth, but today simply don’t have the energy density.” Battery operating costs are also driven by cycle life, and battery eVTOL performance is lacking if the mission demands extended hover. Turboshaft-electric hybrids have good VTOL performance but retain a carbon footprint. Hydrogen hybrid-electric propulsion that uses batteries for peak hover power and recharges in cruising flight offers an attractive combination of clean performance, longer range, and reduced operating costs. Piasecki concluded, “Commercial helicopter operators, they are extremely cost-sensitive. You cannot convince them to take on new technology without a cost benefit.”
The Hydrogen panel was organized and chaired by Danielle McLean, CEO of Hy-Sky, LLC, who also serves as the VFS Advisor for Hydrogen.
McLean is also the VFS Advisor for Workforce & Diversity, and chaired a panel on that topic at the Symposium. Speakers included Hydroplane’s Sengupta, Wisk’s Chief People Office Rick Robinson, Los Angeles UAM Fellow Clint Harper of Urban Movement Lab, VFS Executive Director Mike Hirschberg and Women & Drones CEO Sharon Rossmark.
In addition to discussions of how AAM and rotorcraft employers were waging a “war for talent,” panelists also related some of their experiences and how the vertical flight community can help to provide a welcoming, inclusive environment for vertical flight. VFS also announced a number of efforts under its DiversiFlite program (see “Changing the Face of the AAM Industry,” pg. 52).
VFS has several additional eVTOL events this year. The 1st H2-Aero Symposium & Workshop will be held in Long Beach, California, March 29–31. The 16th Annual Electric Aircraft Symposium will be held as a hybrid event in Oshkosh, Wisconsin, on July 23–24, the weekend before the annual AirVenture air show. On Sept. 20–22, VFS plans to hold its 6th Workshop on eVTOL Infrastructure for UAM in Dayton, Ohio.
Next year, the 10th Annual Electric VTOL Symposium will be held in Mesa, Arizona, in conjunction with the 10th Biennial Autonomous VTOL Technical Meeting. The event, Jan. 24–26, 2023, is being hosted by the VFS Arizona Chapter.
Information on these and other events can be found at www.vtol.org/events.