In the five years since the Vertical Flight Society hosted its first “Transformative Vertical Flight Concepts Joint Workshop on Enabling New Flight Concepts through Novel Propulsion and Energy Architectures,” electric vertical takeoff and landing (eVTOL) aircraft have evolved from a wide-eyed futuristic concept into an emerging business within the global aerospace industry.
This transition was especially apparent in early 2019 when several first-to-market eVTOL aircraft developers unveiled mockups, flew prototypes, announced strategic partnerships, unveiled new owners or released market surveys.
These five aircraft programs are led by engineers and technical teams that are fully aware of the challenges of VTOL aircraft design and development, including certification for private, business aviation and commercial use by the US Federal Aviation Administration (FAA) and their international counterparts.
In fact, many of these eVTOL developers employ some of the original participants at the first VFS workshop in August 2014, while other attendees are now working for companies like Uber and plan to put the first eVTOL aircraft to work moving passengers by the early- to mid-2020s.
Research & Development
Historically, the aerospace industry has taken decades to develop successful new aircraft and air transportation modes in an evolutionary manner.
Most step-changes in military and commercial aircraft capabilities can be attributed to advances in aircraft engine technology.
For example, the development of the transformative Bell Boeing V-22 Osprey and Lockheed Martin F-35B Lightning II weapon systems were the culmination of decades of multi-billion dollar government and industry investments in disruptive technologies (including engines) designed to dramatically enhance military vertical flight capabilities.
In contrast, the timing of today’s eVTOL revolution is driven by the convergence of electric motors, batteries, hybrid-engine technology, control systems, low-cost design and manufacturing, autonomous systems and “green” technologies. This confluence of technology advances is being leveraged by innovations in the automotive, drone and aerospace industries.
Another distinction is that most of the eVTOL aircraft being developed today are company-funded programs (often supported by venture capital) being developed to aggressive timelines with a clear expectation of a positive financial return.
The innovative promotional and social media strategies of some eVTOL and urban air mobility (UAM) startups have stimulates frequent headlines about “flying cars,” although only a handful are in fact roadable aircraft.
The popular enthusiasm for urban aviation is nothing new. It occurred in the mid- to late-1940s when the first civilian helicopters first appeared on the scene, and arose again in the 1950s and ‘60s when NASA’s X-Plane program spawned numerous innovate new VTOL designs.
While some reports in the popular media may be off the mark, the idea that disruptive eVTOL aircraft will one day be more numerous than helicopters over most major cities is a widely accepted belief amongst most eVTOL developers and UAM advocates like Uber.
Ending several years of speculation regarding the configuration of its commercial eVTOL product, Bell unveiled a mockup of its Nexus on-demand mobility vehicle at CES 2019 on Jan. 7 (see “eVTOL Captures the Attention of CES”).
Last year, the Fort Worth, Texas-based company used a four-seat cabin to unveil the Bell Air Taxi “experience,” with “passengers” arriving up a simulated elevator opening onto the “skyport,” followed by an augmented reality flight across town, above the traffic.
This year, Bell completed the picture by showcasing a hybridelectric aircraft with six propellers, each housed in a tilting duct, three on each side of the aircraft cabin, with the middle set of ducts attached to 8 ft (2.4 m) wings that will provide significant lift in high-speed forward flight.
The debut of Bell Nexus highlights that the so-called “Electric VTOL Revolution” is gaining momentum. With its unique experience developing both helicopters and tiltrotor aircraft, Bell is combining its exceptional understanding of vertical flight technology with hybrid-electric power to create a disruptive new VTOL air taxi for everyday use.
Bell said one of the reasons it decided to unveil the Nexus at CES rather than an aerospace trade show was to build consumer awareness of eVTOL technology and help nurture its future acceptance as part of the urban landscape.
The Nexus is a 6,000 lb (2,725 kg)-class gross weight aircraft. The mockup was outfitted with “4+1” seating to accommodate a pilot and four passengers for an urban air taxi mission. Bell said the aircraft will have a top speed of 155 kt (288 km/h) and a range of 130 nm (241 km). The aircraft will fit in a 40 ft x 40 ft (12.2 m x 12.2 m) footprint, which means it can operate from the same sized helipad as a single-rotor Bell 407, which has a maximum internal gross weight of 5,250 lb (2,380 kg).
Bell said that the use of electrical power enables revolutionary configurations that can be much quieter and more environmentally friendly than conventional helicopters. Although batteries have much lower energy density than liquid fuel, the Nexus offsets this by cruising on an airplane wing — as well as lift generated by the six tilted ducts — for extended operational range.
“Bell ‘Nexus’ means the nexus of transport and technology, and of comfort and convenience,” said Michael Thacker, Executive Vice President of Technology and Innovation at Bell during the keynote address at the VFS 6th Annual eVTOL Symposium in Mesa, Arizona, in late January. “Nexus captures the longsought- after vision of quick air travel with a unique in-flight experience, keeping passengers connected to their lives and saving valuable time.”
Team Nexus members — consisting of Bell, Safran, Electric Power Systems (EPS), Thales, Moog and Garmin — are collaborating on Bell’s eVTOL aircraft and on-demand mobility solutions.
Safran is developing the hybrid propulsion and drive systems, EPS will provide the energy storage battery systems, Thales will provide the flight control computer hardware and software, Moog will develop the flight control actuation systems and Garmin will integrate the avionics and the vehicle management computer.
The Safran turboshaft-based hybrid propulsion and drive system provides the electrical power to the propellers. The unit consists of a turboshaft engine, a single gearbox and two generators. Last summer, Safran announced it had conducted the first ground test of a distributed propulsion system that featured four electric motors turning propellers for VTOL propulsion. Several operating modes were tested and validated during this first series of tests, with the electric motors powered only by batteries or by a combination of batteries and turbo-generator. The initial tests were conducted in July at the Safran Helicopter Engines test facility near Pau Pyrénées Airport, in southwestern France.
The turboshaft engine, which is housed on the aft fuselage above the cabin, provides additional power for vertical takeoffs and landings, as well as extended range, like a hybrid-electric automobile.
In September 2018, employees at the Bell factory in Mirabel, Quebec, assembled a complete Nexus ducted propeller for testing. The duct was then shipped to the National Research Council of Canada’s aerospace facility at Ottawa International Airport for propulsion and acoustics testing inside the NRC’s large 30 ft x 30 ft (9.1 m x 9.1 m) wind tunnel. The duct was also test outside.
There are six propeller blades and two control vanes per duct, according to the product briefing Thacker provided VFS members in Mesa. Each of the six electric motors has an integrated speed controller. The composite fuselage has a flat floor and 1-2-2 seating.
Bell said the battery pack will have 50 kWh of energy, 540 kW maximum discharge and have 200 Wh/kg lithium-manganesecobalt- oxide (NMC) cells. The aircraft V-tail configuration features fixed-horizontal and fixed-vertical stabilizers.
The design of the Nexus draws on Bell’s VTOL tiltrotor work on the XV-3, XV-15, V-22 and V-280 Valor, as well as the experimental X-22 VTOL X-Plane, which flew from 1966 to 1988. The Bell X-22 used four tilting ducted propellers, but the mechanical complexity of the four engines and 11 gearboxes and the high empty weight fraction were too limiting for the aircraft to be put into production.
The Nexus also features some of the technologies displayed on the Bell FCX-001 Concept Aircraft unveiled at Heli-Expo in March 2017, such as hybridized propulsion, advanced airframe design, virtual cockpit, enhanced cabin design, advanced landing gear and fly-bywire flight control technology.
The following month, Uber announced it had selected Bell as a partner to accelerate the eventual large-scale deployment of eVTOL air taxis for its Elevate network.
Thacker said that Bell is using four integrated frameworks to help define the Urban Air Mobility model: operational, regulatory, manufacturing and technology. “Through these frameworks developed with community, government and industry stakeholders, we are enabling innovative technologies, charting a path for regulatory support, and ultimately informing aircraft design and operating requirements.”
The operational framework will allow Bell to define the necessary functional requirements for on-demand urban air mobility. These include operational infrastructure, safety and acoustic considerations, and the critical need for a solution that is affordable for most people.
Thacker told the VFS audience that, “the operational framework encompasses a wide scope of activities including community engagement, fleet and air traffic management, ground infrastructure, vehicle to vehicle communication and separation, and very importantly, integration and interface with traditional aviation airspace and aircraft.”
Bell is also partnered with NASA on a System Integration and Operationalization project to develop system solutions to the airspace integration and operational control challenges.
“Bell’s top priority within the certification framework is working with the FAA, EASA [European Aviation Safety Agency] and other regulatory stakeholders to establish an integrated approach across vehicle, operational and air traffic requirements. We firmly believe that current aviation safety expectations should be met and even exceeded, but new vehicles and operational models may mitigate risks in new ways. A holistic regulatory approach will help provide clarity and clear paths to compliance and permission to operate for urban air mobility concepts,” added Thacker.
Beyond quality and safety, Bell’s manufacturing effort will focus on cost, weight and environmental impact.
“Expected volumes for on-demand mobility are well beyond traditional aviation, but also below typical automotive and drive a different mindset for fabrication and assembly,” said Thacker, adding that the shift from high-precision drive systems and gearboxes to electric motors and high power electrical distribution systems and batteries will change “our manufacturing scope, our support plans and our business model.”
Aurora Passenger Air Vehicle
On Jan. 22, Aurora Flight Sciences successfully completed the first unmanned hover flight of its autonomous passenger air vehicle (PAV) prototype in Manassas, Virginia. The two-seat aircraft is being developed for Boeing NeXt, which now leads the company’s urban air mobility efforts after Boeing completed its acquisition of Aurora Flight Sciences in November 2017.
Aurora’s entry into the urban air mobility market was first announced in April 2017 at the first Uber Elevate summit where it revealed that it had flown a quarter-scale model of its UAM aircraft. The new PAV design closely resembles this model and artists’ renderings released in April 2017. It features a sideby- side cockpit, a mid-fuselage wing, four two-bladed lifting propellers attached to outriggers on either side of the airframe, a five-bladed pusher propeller, and a horizontal stabilizer with twin vertical fins with rudders. Aurora did not release details of its electric propulsion system.
The PAV completed a controlled takeoff, hover and landing during the flight, which tested the vehicle’s autonomous functions and ground control systems. Future flights will test forward, wing-borne flight, as well as the transition phase between vertical and forward-flight modes. This transition phase is typically the most significant engineering challenge for any fixed-wing VTOL aircraft.
The prototype (serial number AU-083) was first registered by the FAA on May 2, 2018 as an Aurora Flight Science “Pegasus” and carries the N-number N83AU. The PAV prototype is designed for fully autonomous flight from takeoff to landing, with an operational range of up to 43 nm (80.47 km). Measuring 30 ft (9.14 m) long and 28 ft (8.53 m) wide, its advanced airframe integrates the propulsion and wing systems to achieve efficient hover and forward flight.
“In one year, we have progressed from a conceptual design to a flying prototype,” said Boeing Chief Technology Officer Greg Hyslop. “Boeing’s expertise and innovation have been critical in developing aviation as the world’s safest and most efficient form of transportation, and we will continue to lead with a safe, innovative and responsible approach to new mobility solutions.”
“This is what revolution looks like, and it’s because of autonomy,” said John Langford, president and chief executive officer of Aurora Flight Sciences. “Certifiable autonomy is going to make quiet, clean and safe urban air mobility possible.”
The development of the PAV draws on Aurora’s extensive work developing autonomous aircraft, including unmanned aircraft systems (UAS) and optionally-piloted fixed-wing and rotary-wing platforms, such as those based on their autonomous Diamond DA-42 light twin fixed-wing and Bell UH-1H Huey helicopter.
Aurora is developing a four-passenger PAV for the Uber mission and has other hybrid-electric VTOL technologies it can apply to the UAM market. In March 2016, Aurora Flight Sciences beat out three other competitors to win an $89.4M Defense Advanced Research Projects Agency (DARPA) contract to build and demonstrate the XV-24A LightningStrike concept, which Aurora said, at the time, was the first aircraft in history designed to demonstrate distributed hybrid-electric propulsion ducted fans; innovative synchronous electric-drive system; both tilt wing and canard for vertical takeoff and landing; and be high efficiency in both hover and high-speed forward flight. (See “Thinking Outside the Box…. Is Inside the Box at Aurora Flight Sciences,” Vertiflite, May/June 2018.)
Aurora flew a 20%-scale XV-24 subscale vehicle demonstrator (SVD) and teamed with partners Rolls-Royce and Honeywell for the full-scale aircraft, but technical issues caused cost overruns before it was completed. DARPA cancelled the development of the LightningStrike in April 2018, and Aurora announced that it had reached an agreement with DARPA, “to transition its X-Plane program technology to commercial applications, including expanding its research into commercial eVTOL systems.”
Joby Aviation S4
Joby Aviation, Inc. was among the first companies to embark on the development of VTOL aircraft incorporating distributed electric propulsion, after having begun developing electric motors in 2008. Company founder JoeBen Bevirt coined the term, “electric VTOL.”
Since presenting the four-seat Joby S4 at the 2nd Annual VFS “Transformative” eVTOL workshop in 2015 (available at www.vtol.org/TVF), Joby has revealed very little in public regarding the company’s very active eVTOL program. However, in February 2018, the company finally acknowledged that it has been testing the S4 from a secluded, private airfield on the California coast between Monterey and Santa Barbara.
The S4 demonstrator has been flying since early 2017 and the company is planning an advanced five-seat craft that will “fly at least 150 miles on a charge, and be 100 times quieter than conventional aircraft during takeoff and landing [i.e. a 20 dB noise reduction], and near-silent in flyover.”
At the 6th Annual eVTOL Symposium in Mesa, Joby Chief Test Pilot Justin Paines revealed that the S4 is being designed to achieve cruise-speeds of 200 mph (175 kt or 320 km/h).
A former Royal Air Force test pilot, Paines spent his military career flying the BAE Systems Harrier short takeoff and vertical landing (STOVL) fighter, including RAF Bedford’s Vectored-thrust Aircraft Advanced Control (VAAC) testbed, which played an important role developing the unified fly-by-wire flight control system. After great debate, the unified control system was selected for use on Lockheed Martin’s F-35B STOVL variant ordered by the USMC, the UK, Italy and Japan. Unified control makes it significantly easier for fighter pilots to land the Lightning II, particularly on rolling, pitching and heaving ship decks at sea.
Paines said that S4 also features a unified flight control to take advantage of simplified vehicle operations (SVO) regulatory approvals with “extremely simple” flight controls. The S4 will also have safety assurance in excess of FAA Part 23 and EASA CS-23 certification requirements.
No photos have ever been published of the S4 and no drawings except those presented the 2nd Annual VFS workshop more than three years ago. However, in January, small sections of Joby S4 appear for the first time in an Intel Capital video featuring Bevirt who acknowledges the role new investors — Intel Capital, JetBlue Technology Ventures and Toyota AI Ventures — are playing in the development of the S4 air taxi.
“Intel Capital has been incredible with the connections they have helped us with as we think about commercializing this,” said Bevirt. “Intel helped us push the cutting edge of autonomy, AI [artificial intelligence] and data science research. They brought those engineers in and mentored our engineers, brainstormed with our engineers and that has been really exciting.”
Bevirt said Intel’s policy team in Washington also helped him be well prepared when he testified before Congress in September 2018. He also noted that JetBlue is helping Joby “think about safety and global operations” and Toyota is helping Joby “think about how to reliably manufacturer tens of thousands of vehicles in scale.”
“Our dream at Joby Aviation is to save a billion people an hour a day, said Bevirt in the video, adding that, ”It’s a big audacious dream.”
Joby was honored at Forum 74 in May 2018 with Society’s Paul E. Haueter Award, “given for an outstanding technical contribution to the field of VTOL aircraft development other than a helicopter or an operational vertical flight aircraft.” Bevirt was honored, “for successfully demonstrating the world’s first high-speed multipassenger electric VTOL aircraft.”
XTI TriFan 600
In January, VFS released the first photos of the 65%-scale model (N665XT) of XTI Aircraft’s TriFan 600. The subscale model will be used to validate the design configuration in hover, transition and forward flight. Testing is scheduled to take place at the Deseret UAS test site near Tooele, Utah.
The TriFan 600 is a six-seat, hybrid-electric, fixed-wing airplane that uses three ducted fans to power the aircraft from vertical takeoff and landing to 340 kt (630 km/h) and a range of 650 nm (1,200 nm) for VTOL or 1,200 nm (2,200 km) when operating from a runway.
The full-size aircraft will have a wingspan of 37.7 ft (11.5 m) and a length of 38.7 ft (11.8 m). The two wing-mounted ducts will have single 6 ft (1.8 m) diameter propellers powered by two 350 hp (260 kW) electric motors and two 5 ft (1.5 m) diameter co-axial ducted propellers located in the aft fuselage with one motor for each propeller.
The TriFan 600 is one of the largest eVTOL aircraft in development, with the design combining the speed and range of a business jet or turboprop with the VTOL convenience of a helicopter.
A single 1,000 shp (745 kW)-class Honeywell HTS900 turboshaft engine will power three generators in the hybrid-electric propulsion system. The 65% scale model uses batteries only, with the battery pack made in-house by XTI. The electric motors and controllers are from MGM Compro, a company based in Zlín, the Czech Republic, that specializes in these components.
Jaunt Air Taxi
VFS announced at the 6th eVTOL Symposium that Jaunt Air Mobility has acquired the rights to the Carter Aviation Technologies Slowed-Rotor/Compound (SR/C) technology, including the Carter Air Taxi.
Since 1994, aeronautical engineer Jay Carter Jr. has designed, built and flown two compound gyroplanes that have coupled the speed, range and efficiency of an airplane with the vertical takeoff and landing capability of a helicopter.
Most of the Carter’s research has focused on developing a rotor that can be slowed in wing-born flight to reduce drag and achieve higher cruise speeds.
In April 2017, Mooney Aircraft announced that it had partnered with Carter to develop an eVTOL Air Taxi for the Uber Elevate mission, but Mooney soon dropped out of the Uber program, leaving Carter searching for a new partner.
At the VFS 74th Annual Forum in Phoenix, Carter revealed a further refinement of its Air Taxi concept featuring a fourpassenger cabin, a single powered rotor for vertical takeoff and landings, and four wing-mounted electric motors for forward flight.
The original CarterCopters were gyroplanes, but Jaunt is a singlerotor compound helicopter that incorporates a patented rotor system that enables both VTOL and high-speed flight.
One advantage of the Carter’s high-inertia, low-disk loading rotor is that the Air Taxi can autorotate like a conventional helicopter in an emergency.
Jaunt Air Mobility was founded in May 2018 to pursue the acquisition of Carter’s technology. The company was founded by Kaydon Stanzione, a former military flight test pilot and engineer, and former member of the VFS Board of Directors.
Stanzione is the founder of Praxis Technologies outside of Philadelphia, which has 30-years of experience in advanced technology development in various industries, including defense, aerospace, transportation, infrastructure and telecommunications.
Jaunt plans to flight test a modified airworthy SR/C in 2019, in two configurations: a hybrid version, followed by an eVTOL configuration. The power management system design and integration is being supplied by Portland, Oregon-based Volta Companies, makers of the electric-powered Volta Volaré and fourseat DaVinci aircraft.
The flight test data will help in developing the next generation of an all-electric SR/C in conformance with Uber’s Elevate urban air mobility requirements.
Additional features of the SR/C include design and power management flexibility to meet transportation challenges and fully integrated autonomous flight controls suitable to support FAA flight data acquisition studies.
Stanzione explained that “As lift is shared with the wing, the rotor disk loading and rpm continues to be reduced, and because it rotates at only around one-third the speed of a conventional helicopter, has a lower tip speed which significantly reduces noise and drag.”
As the Jaunt accelerates, the rotor lift and speed are reduced until approximately the aircraft hits 150 kt (280 km/h), where the wing is providing all the lift and the rotor is completely unloaded and free-spinning.
A tilting rotor mast is also incorporated, which maintains the fuselage at a level position in slow-speed flight, and then adjusts the aircraft attitude to achieve optimal flight performance. Anti-torque and high-speed cruise are provided by four wingmounted scimitar propellers. “The result enables Jaunt to achieve high cruise efficiencies at speeds in excess of two times that of a conventional helicopter while offering reduced noise, VTOL operations, and improved passenger comfort and safety,” Stanzione said.
Jaunt Air Mobility is now pursing venture capital funding in hopes that it can become the sixth airframe manufacturer developing an eVTOL aircraft for the Uber Elevate mission.
About the Author
Ken Swartz runs aerospace marketing communications agency Aeromedia Communications in Toronto, Canada. He specializes in contract public relations, freelance writing, and social media marketing for the aviation and aerospace industry. He has reported on the helicopter industry for 40 years. In 2010, he received the Helicopter Association International’s “Communicator of the Year” award. He can be reached at email@example.com.
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