In the seven years since 100 invited visionaries gathered in Arlington, Virginia, for the first annual VFS Transformative Vertical Flight (TVF) Workshop, the dream of electric vertical takeoff and landing (eVTOL) aircraft has progressed from something perceived as a wild-eyed fantasy promoted by secretive companies to a diverse and full-fledged industry.
This remarkable transition formed the backdrop of the VFS Transformative Vertical Flight 2020 meeting in San Jose, California, in mid-January, which attracted almost 500 experts from more than a dozen countries for three integrated events: the Aeromechanics for Advanced Vertical Flight Technical Meeting, the 7th Annual eVTOL Symposium and the International Powered Lift Conference (IPLC).
When the VFS San Francisco Bay Area Chapter began holding biennial conferences in 1974, the focus was on helicopters and tiltrotors for civil and military applications. While this was still the focus of the technical papers for the Aeromechanics Meeting, the IPLC shifted its traditional focus from advanced rotorcraft and jet-lift, fixed-wing aircraft to eVTOL.
In the invited presentations of the eVTOL Symposium, VFS members and VIP speakers highlighted that Silicon Valley and other technology companies are also driving investment in vertical flight aircraft development and the urban air mobility (UAM) ecosystem.
Correspondingly, the scope of this year’s eVTOL symposium was much broader than in the past, with the addition of speakers on new topics such as aircraft manufacturing, supply chain, lightweight structures, crashworthiness, cargo delivery, military applications and investment opportunities, along with VFS’s traditional eVTOL focus on aircraft developments, technology, regulations, noise and infrastructure.
Big News for eVTOL
The VFS eVTOL Symposium is an annual opportunity for the vertical flight community to measure progress across the emerging eVTOL industry and associated ecosystem.
This year, the mood at the symposium was extremely positive, thanks to a series of public announcements and revelations over the preceding 30 days.
Leading the list, Joby Aviation of Santa Cruz, California, was identified as the seventh Uber Elevate vehicle partner on Dec. 20. On Jan. 7, the company announced a $590M Series C round funding — including $394M from lead investor Toyota Motor Corporation — and released the first photos of the Joby production prototype (see “The First Electric VTOL Unicorn: Joby Aviation,” Vertiflite, Mar/Apr 2020, pg. 48).
Joby founder and CEO JoeBen Bevirt was the keynote speaker at TVF 2020 and attendees had a unique opportunity to hear one of the eVTOL industry’s visionary leaders speak about his inspiration, his aspirations and the remarkable all-electric Joby air taxi. Bevirt and his team were active participants in the original VFS eVTOL symposiums, but as more companies launched eVTOL designs, Joby stopped sharing details of its aircraft development to protect its intellectual property.
The VFS 2020 plenary session was an opportunity to hear a range of vertical flight perspectives from government and industry. Brig. Gen. Wally Rugen, the director of the Army’s Future Vertical Lift (FVL) Cross Functional Team, gave the first presentation.
“We’ve done a lot of homework on what we call multi-domain operations and how we think we’re going to fight in a future battle. Rugen said there has been a big push to shave years off the “requirements … the contract and timeline” as it accelerates development of clean sheet VTOL designs “to really leap ahead and be able to compete on a future battlefield.”
Rugen noted that the five competitors submitted their FARA designs to the Army by Jan. 10. In the coming months, the Army will select two vendors — “again on budget and probably a little bit ahead of time” — to build competitive prototypes that will begin flying in late 2022. The final downselect is expected by the end of 2023, with initial operational capability in 2028 — this is still the plan, despite a Congressional cut of $34M for this year. The general ended his talk saying, “These forums are very valuable to us, and the Vertical Flight Society has been so helpful to FVL. We truly appreciate it.”
Asked about potential military use of eVTOL aircraft, Rugen said he hasn’t seen the specific power required in a battery yet that will support a military mission requiring the payload, range, maneuverability and agility for a combat scenario, but he sees a lot of spinoff potential “if eVTOL really takes off,” capitalizing on the potential for electric aircraft with very low acoustic signatures.
Dr. Rick Mange, chief engineer of the Lockheed Martin F-35, represented the jet-powered vertical lift community at TVF 2020. He said that the F-35 has “proven to be highly effective in combat,” with almost 500 airplanes — operating from 21 bases worldwide — which have accumulated more than 240,000 flight hours.
All three F-35 variants (A/B/C) share the same avionics system, which represents a significant share of F-35 development costs.
The short takeoff and vertical landing (STOVL) F-35B is roughly the same size and has similar aerodynamics to the F-35A, with F-35B’s lift fan and thrust lift system taking the place of fuel tanks on the F-35A. Mange explained that the ski jump takeoff utilized by British F-35Bs operating from the new Queen Elizabeth carriers can take off with more weight and less end-speed than needed for an unassisted horizontal launch, but the ski jump requirement drove landing gear design for the entire F-35B family.
Romanowski explained that with “a wide range of products that don’t meet any of the old paradigms … [the] line between a manned and unmanned system are so blurred right now.”
For example, Romanowski observed that new eVTOL aircraft are starting life as unmanned, remotely piloted vehicles — with the goal of testing the vehicles and systems to ensure they are safe for a human pilot to operate the aircraft. However, the long-term goal is to make these aircraft capable of flying without a pilot as autonomous systems mature.
Romanowski said that the FAR Part 23 rewrite of small airplane certification rules finalized in 2017 has been a huge enabler of innovation. For certification efforts to proceed smoothly, the FAA really wants “to talk to companies as early as possible before configurations are [finalized] — before technology has matured — to understand what are the strategies, what is [your] approach. And then we want to work with you on a plan — a clear path to certification.”
Uber Still Elevated
Mark Moore, Uber’s Engineering Director of Aviation, highlighted that, “Three years ago, we were here presenting [Uber Elevate’s] crazy white paper and the industry thought it was pretty audacious to be claiming what was going to happen over the next seven years. But guess what? We are right on target. We are executing exactly what we said in that initial white paper.”
Moore said, “we’re entering the next phase [of the eVTOL industry] where the automotive companies are taking us seriously and bringing the investment that’s required … to really make this happen … not just certification, but into full production.
“I predict within the next year and a half you will see, almost every major automotive company step into this industry in significant ways,” he continued. Uber is also having discussions with major aircraft leasing companies about what role they can play in making the aerial ridesharing industry a reality.
“We very much equate this urban aviation market to commercial airlines, just with much shorter trips and a large portion of commercial airliners are owned by lease companies,” said Moore. He added that it has raised “a very significant question of what is the residual value” of these aircraft when the first generation are replaced after five to seven years, and what secondary markets will exist to put these aircraft to use that would preserve their
Uber expects that some eVTOL manufacturers and their backers will put aircraft fleets on their “significant balance sheets” to receive “the equivalent of [a] power-by-the-hour … revenue stream that’s constantly coming in,” which will offset revenues from cyclical aerospace markets, he said.
Uber is also “spooling up a multimillion-dollar community engagement plan, which starts this year and carries through to our introduction to service in 2023.” Consequently, Moore now also has the job title of Uber’s Director of Elevate Strategy. Uber is supporting the VFS Workshop on eVTOL Infrastructure in March as a major sponsor (seewww.vtol.org/infrastructure).
Office of Science and Technology Policy
Col. Nathan Diller, US Air Force, Assistant Director of Aeronautics in the White House Office of Science and Technology Policy (OSTP) highlighted that the Trump Administration designated eVTOL aircraft as a national research and development funding priority for fiscal 2021.
Diller explained that the role of the OSTP is to “look across the innovation ecosystem … and find the ways to connect different pieces in order to accelerate our adoption of new technologies for America.”
He said the roles of government agencies like the FAA, NASA and the Department of Defense are pretty obvious, but OSTP also tries to identify other branches of government that can or should participate in “supercharging this ecosystem.”
For example, the OSTP recognizes the eVTOL industry has the ability to “energize a new workforce” and drive a “democratization of air travel” where new electric-powered aircraft dramatically reduce the cost of transportation by air.
Diller also noted that the Air Force issued an RFI seeking information on eVTOL technology in late 2019 and is seeking opportunities to partner with eVTOL developers on flight testing programs (see “US Air Force Moves to Boost eVTOL Development,” Vertiflite, Mar/Apr 2020, pg. 58).
Glenn Isbell, vice president for Rapid Prototyping & Manufacturing Innovation at Bell — and current VFS Chair of the Board — explained that the company recently shifted its eVTOL priorities from the hybrid-electric Nexus 6HX with six tilting, ducted fans to the all-electric Nexus 4EX revealed at CES featuring four ducted fans.
Bell will build and fly a Nexus 4EX concept demonstrator “to prove out some capabilities and technology to make sure that we’ve got everything exactly right” before it builds prototype aircraft for certification.
For Bell, the UAM ecosystem includes operational, manufacturing, certification and technology frameworks. This requires moving beyond an aircraft manufacturer to a Mobility-as-a-Service (MaaS) provider. To this end, Bell announced it is developing AerOS as an aerospace operating system to optimize the operation of large fleets of eVTOL aircraft on an individual “tail number” basis.
The Electric VTOL Symposium opened with a UAM ridesharing panel moderated by NASA’s Carl Russell, the symposium chair. The panel featured an international airline, a helicopter airline and two app-enabled helicopter service providers.
Kolin Schunck, research & intelligence analyst with the Lufthansa Innovation Hub gave a presentation — “Air Taxis: Hype or Gamechanger?” — that examined media coverage, venture capital investments and patent filings over the past decade and a half.
Schunck reported that the “tonality” of media coverage became positive in 2017, Joby Aviation became the first air taxi “unicorn,” and that the number of patent filings had really taken off, with a significant share (39%) filed by start-ups. He also reported the surprising revelation that General Electric has quietly become a significant filer of patents in the air taxi space.
Schunck said that air taxi companies have made a number of bold claims about what they expect to happen in the next five years, and it will be necessary to separate fact from fiction. Lufthansa has already committed to become “an airline forerunner in unmanned aerial services” and is developing a range of UAS hardware and software, flight operations, technical operations and value-added services to support these efforts. Lufthansa’s goal is to “own a share in every trip” and it is closely monitoring UAM developments from that perspective.
Danny Sitnam, president and CEO of Helijet International, has been operating a successful scheduled helicopter network on the Canadian west coast for 34 years. Success has required a lot of perseverance and an unbroken focus on its customers and communities, which have accepted public-use heliports as permanent infrastructure.
“We operate about 25 to 30 flights daily between downtown Vancouver/downtown Victoria. That’s about a 32-minute flight. About three-quarters of our flights are in hard IFR [instrument flight rules] operations most of the time. We very seldom are flying VFR because we’re trying to stay out of the VFR [visual flight rules] traffic airspace. This is a very congested airspace that we operate in; probably the third most congested airspace in North America,” said Sitnam.
Sitnam sees lots of opportunities to integrate eVTOL aircraft into Helijet’s route network, which currently serves three cities in British Columbia — Vancouver, Victoria and Nanaimo — but could be extended to serve Seattle, Washington, again.
Smaller eVTOL aircraft could feed passengers to Helijet’s “trunk” routes at hubs in Vancouver and potentially Seattle, but an IFR capable eVTOL aircraft is required to provide reliable service on a year-round basis.
Sitnam also sees an opportunity for a longer range eVTOL aircraft (such as the XTI Aircraft Trifan 600 or equivalent) that can fly Vancouver to Seattle non-stop, as well as longer air ambulance missions in British Columbia that today require the combination of both a Helijet S-76C+ and a King Air 350 to transfer a patient from a remote location to a hospital.
Blade and Uber Copter both offer app-enabled helicopter flights in New York City and other communities using helicopters contracted from local Part 135 charter operators.
Blade launched service in New York in 2014 and today has over 180,000 users on its booking platform. “We move more people in and out of city centers [by air] than anyone in the United States” using a network of 30 helicopter and seaplane operators, said Brandon Keene, Blade’s chief technology officer.
Blade changed the face of helicopter operations in New York City by helping to develop a new luxury leisure mission transporting people between Manhattan and the Hamptons at the east end of Long Island. A lot of their clients had never flown on a helicopter before.
The company has further expanded the market by offering a helicopter shuttle service from all three Manhattan heliports (West 30th Street, East 34th Street and Wall Street) and to all three New York City airports (LaGuardia, Kennedy and Newark) for $195 per seat. Blade has “really matured into what we think is a robust UAM operation that proves it can be done,” said Keene.
Blade also offers helicopter services in Miami, the San Francisco Bay area, Los Angeles and in November 2019 launched service in Mumbai, India.
“What we also see is a cohabitation phase in the initial rollout of eVTOL, with hopefully eVTOL’s operating side by side with a nextgeneration aircraft and current aircraft,” said Keene.
Uber Copter launched in New York in July 2019 contracting HeliFlite to operate helicopter flights between Manhattan and JFK International Airport with the goal of finetuning the operational and software engineering lessons required to implement aerial ridesharing with eVTOL aircraft as early as 2023, said Uber’s Luke Fischer.
Uber’s goal is to seamlessly integrate all the multimodal steps required in the app to pick up a person in Manhattan and get them to Terminal 4 at JFK, “but not just do that for one person, but do that for four people and drive up the utilization rate in aircraft,” said Fisher.
Graham Warwick, Executive Editor for Technology at Aviation Week magazine moderated the next Symposium panel, which included four eVTOL aircraft developers (other aircraft developers shared information on their aircraft in later sessions).
Opening the session, Warwick noted that, “It is an amazing opportunity to write about UAM because it is so much more than the vehicles, it is a complete ecosystem … We’ve never gone through this before where we are literally creating an end-to-end industry, product, whatever you want to call it. Everything else that’s out there evolved over decades. Air transport evolved over decades. This is something that we are seeing take shape in front of our very eyes.”
Nevertheless, he continued, “The vehicles are the sexiest bit of this industry [and] there are so many of them and they are so different from most of what we’ve seen before. Some of them are even credible.” The VFS World eVTOL Aircraft Directory now lists more than 250 eVTOL concepts at www.eVTOL.news.
Zach Lovering, vice president of urban air mobility systems at Airbus, oversaw the development of the Vahana tilt-wing technology demonstrator, which logged 138 test flights before it made its last flight on Nov. 14, 2019. Total flight time was just over 13 hours and the aircraft flew a total of 561 miles (903 km). The longest demonstrated flight was 30 miles (50 km) over 20 minutes at a cruise speed of 100 knots with the battery having a final state of charge of 30%.
The key objectives for the Vahana program were demonstrating the ability to fly a full-scale, autonomous eVTOL aircraft with sufficient performance to enable urban flights “to ensure our design fit within an existing market.”
Lovering said “the biggest challenge in eVTOL vehicle design [is] getting sufficient performance [range and speed in a multimodal environment] while meeting certification standards and [achieving] a low enough cost to have a viable market,” which comes down to performance, safety and cost. “It’s easy to design a vehicle when you sacrifice one or two [but] it’s very challenging to do all three,” he said.
Today, Airbus is spending a lot of time “looking at combining the business case with the technical side” of eVTOL development, he said. This includes studying the impact of total operating cost on passenger acceptance of eVTOL ticket prices. Willingness to pay for time saved is a key driver of market size and typically correlates with income. Low operating costs are essential to drive down the price of flights, so they can be attractive to a larger segment of the population.
Lovering said the ideal aircraft is also going to have to be very reliable with high availability, “which is going to push you to have a more robust aircraft with higher [poor] weather capabilities.” For example, headwinds will have a significant impact on eVTOL aircraft range. Airbus found that a shift to IFR from VFR will carry a significant penalty because this will require additional energy reserves, which will limit aircraft range.
Lovering said that batteries available for eVTOL aircraft today are at about 180 W-h/kg at the pack level. He said that the specific energy of batteries increased by 8% a year for the past decade, but “recently slowed down,” adding that, “there are some promising new batteries that … might unlock higher specific energies.”
He also said that other battery characteristics are equally important, such as charge rates and discharge rates, number of cycles available in a pack, and cost. “All of these things are really important factors when you design a battery pack,” said Lovering, adding that one of the interesting economic metrics eVTOL designers should study is “dollars per kilowatt hour per cycle.”
Piasecki Aircraft Corporation
John Piasecki, CEO of Piasecki Aircraft Corporation (PiAC) revealed details of the company’s PA890 all-electric Slowed Rotor Winged Compound helicopter program at TVF 2020.
Piasecki said the project began with a contract from a client who wanted to explore the feasibility of using an all-electric rotorcraft to fly transplant organs to hospitals in a way that was environmentally responsible (see “Electric VTOL for Organs on Demand,” Vertiflite, March/April 2019). This kicked off a “pretty rigorous evaluation of a lot of different rotorcraft configurations” that began with about two dozen models and a downselect process that narrowed the field to two worthwhile designs. These were a tiltrotor and a slowed-rotor winged compound configuration.
Piasecki said that the slowed-rotor winged compound configuration carried “an 8% increase in gross weight” penalty, but was selected in the final analysis because it offered a lower risk time to Part 27 Normal Category Rotorcraft certification; Piasecki’s presentation noted that the AW609 tiltrotor civil has been in development and certification for nearly 25 years.
“It’s not just a question of the configuration and the technology risk. It’s also a question of certification risk, time to get certified, money to get certified.”
After completing the initial design, PAC signed a launch customer agreement for the PA890. Piasecki noted that flying organs to hospitals is a longer-range mission than UAM flights.
The PA890 will be 40.12-ft (12.2-m) long and have a 40.26-ft (12.3-m) wingspan. The 44-ft (13.4-m) diameter three-blade, variablespeed rotor will allow the aircraft to hover and can be slowed down during forward flight by 70% to reduce drag, since the wing provides most of the lift in cruise.
The variable incidence wing, also known as a free wing, is able to seek a peak coefficient of lift throughout the flight regime, which helps to keep the design simple, said Piasecki. For example, in a hover the wing tilts upwards, which reduces the surface area in the rotor downwash.
A swiveling electric thruster mounted on the tail proves antitorque control in hover and propulsion in forward flight. Other technical features include a single-pilot IFR cockpit with dual controls, an integrated avionics suite, electromechanical actuators high-performance composite rotor blades, an electric power and propulsion system (EPPS), and a controllable rudder. A hybrid-electric engine may also be offered for greater range/payload.
Piasecki said that the PA890 will be twice as aerodynamically efficient as a helicopter (in terms of lift/drag), have lower energy costs and less complexity than a conventional helicopter. The design is also expected to have reduced loads and reduced vibration, as well as reduced failure rates, especially when vibration reduction is considered.
Piasecki also said that the noise from the lightly loaded variable-speed rotor (with gearbox) will be lower than a similar size conventional helicopter in both hover and forward flight. In fact, an acoustic analysis of the 6,900-lb (3,130-kg) gross weight PA890 by Continuum Dynamics, Inc., “shows sound levels near Uber targets, and equal to or better than [a] 36% lighter AS350 helicopter.”
The PA890 design draws heavily on PiAC’s decades of rotorcraft research and development work including the development of three previous compound helicopters. In the 1960s, PiAC developed and test-flew the five-seat P&WC PT6-powered Piasecki 16H-1 Pathfinder, and the larger eight-seat GE T-58-8 powered 16H-1A Pathfinder II — displayed at Forum 75 this past May —which achieved a top speed of 196 kt (362 km/h).
Then in the early 2000s, the concept was revised with a contract that saw PiAC develop the X-49 — a highly modified Sikorsky YSH-60F equipped with wings and tail-mounted vectored-thrust ducted propeller (VTDP) — which first flew on June 29, 2007. PiAC hopes to fly the X-49 again soon to serve as a full-scale flight demonstrator for the company’s Adaptive Digital Automated Pilotage Technology (ADAPT) flight control technology.
“I have to say that a lot of the focus of compound helicopters historically has been speed,” said Piasecki, but “in this case the design focus of compounding is really on efficiency because the amount of energy you have available in a battery is limited.”
To determine the potential market for the new rotorcraft, PiAC partnered with “one of the world’s largest helicopter operators” in a 12-month study of the emergency medical services market, which overlaps with organ delivery and medical logistics.
The study analyzed the flight and maintenance operations data for 50,000 air ambulance flights and determined that the operating costs of the PA890 would be 25% lower than a single-engine helicopter and 60% lower than a light-twin helicopter, assuming the same annual utilization rates, and offer even greater benefits if its lower operating costs stimulated increased annual utilization.
The market survey also established that the PA890 would be competitive for on-demand logistics, on-demand mobility and traditional light helicopter missions.
PA890 chief engineer Luigi Ricci-Moretti joined PiAC two years ago from Leonardo Helicopters where he had been (among many other things) chief engineer of Project Zero, the all-electric-powered, hybrid tiltrotor/fan-in-wing technology incubator. It was developed in secret in Italy and first hovered in 2011, but was only publicly revealed two years later (see “Project Zero — The exclusive story of AgustaWestland’s all-electric ‘technology incubator,’” Vertiflite, May/June 2013).
With a small, multi-disciplined development team, PiAC is now rapid prototyping an iron bird and technology demonstrator that will be used to validate the technology and “unlock the magnitude of investment required to get through a certification process” said Piasecki, while Ricci-Moretti assembles a host of industrial partners that are “very excited about the opportunity to really change the world.”
Jaunt Air Mobility
Jaunt Air Mobility first announced its formation to the public at last year’s Electric VTOL Symposium in Mesa, Arizona.
“Jaunt is still an embryonic company,” CEO Kaydon Stanzione told Vertiflite. “We were officially formed in April of 2019 and approximately two months later in June of 2019 we became an Uber air taxi partner, and over the last several months we’ve been inking partnerships with our Tier One players.”
The company was formed following the acquisition of the “slowed rotor/compound” technology developed by Carter Aviation. Some of this technology has now been incorporated into the design of Jaunt’s Reduced Rotor Operating Speed Aircraft (ROSA) eVTOL that will be able to operate as an electric helicopter, airplane and gyroplane in different phases of flight — which enhances overall safety, said Jaunt Chief Technology Officer Martin Peryea.
The high-energy ROSA system features rotor blades with tip weights that provide high rotational energy storage for autorotation, as well as stability during transition to wingborne flight, full fly-by-wire flight control system, a tilting pylon control for center of gravity balance (enabling indiscriminate passenger seating), four wingmounted propellers with dual propeller systems, and an advanced thermoplastic crashworthy structural design.
Jaunt’s market surveys suggest that passengers will be more comfortable getting into an all-electric aircraft that looks familiar, which favors an eVTOL aircraft with a large rotor as well as a wing.
Jaunt said the aircraft’s low disk-loading rotor provides a better glide ratio in autorotation than other eVTOL designs. It also has a wing, allowing the aircraft to glide and land like an airplane.
Jaunt contracted with Triumph Aerospace Structures to support Jaunt’s efforts to design, develop, certify and build a full-scale demonstration aircraft at Triumph’s manufacturing site in Red Oak, Texas, which has the capacity to produce aircraft in the large volumes Uber believes the market will require. BAE Systems is also collaborating with the company to explore the development of electric energy management systems for the aircraft.
Jaunt is targeting FAR Part 29 Transport Category Rotorcraft certification for the aircraft, including Category A performance — safe flight in the event of one motor inoperative during takeoff or landing — which Jaunt sees as a “key enabler and differentiator as other eVTOLs cannot meet this level of safety.”
Stanzione said in an interview that Jaunt plans to partner with a fleet operator to ensure it has tight control on aircraft utilization, pilot training and aircraft maintenance, “because this is all new.”
He explained, “This will probably take the form of a leasing model on the aircraft so that we retain the title to the aircraft and can control the inspections, the utilization, the quality control, as well as work with other organizations that provide power-by-hour maintenance and services.”
Designing for Crash Safety
Market barriers for the eVTOL vehicles include crashworthiness and occupant protection.
The crashworthiness panel moderated by Justin Littell from the NASA Langley Research Center discussed how the industry protects somebody in the event of a VTOL crash, including certification, vehicle technical details, public perception and costs.
Littell’s area of research includes conducting vehicle crash tests with the intent of achieving sufficient occupant protection in various scenarios. He pointed to the 2017 report compiled by the National Institute of Aerospace, “NASA Strategic Framework for On-Demand Air Mobility,” which estimated that by 2035 the market utilization of eVTOL aircraft could be flying 5.8 million flight hours per year.
Littell himself calculated about 14 million flight hours per year using Uber’s assumptions in their 2016 Elevate White Paper. As a benchmark, the National Transportation Safety Board (NTSB) stated that FAA Federal Aviation Regulations (FAR) Part 121 carriers (scheduled airlines) flew about 17 million flight hours in 2015.
The avenues to eVTOL certification include the current FAR Part 23, which relies on consensus standards (e.g. ATSM International, SAE International, etc.), as well as FAR Part 27 and 29, which have traditional standards related to occupant safety and crashworthy requirements. The difference, of course, is that Part 23 airplanes are designed for crash safety for horizontal impacts, while eVTOL aircraft will have a greater likelihood of impacting vertically, like rotorcraft.
NASA helicopter drop tests have shown that a fall from only 14 ft (4.3 m) — impacting at 30 ft/s (9.1 m/s) — has the capability of causing occupant injury if not protected.
Analysis of the crashworthiness of the NASA six-seat Lift + Cruise baseline aircraft showed that from 30 feet (9.1 m), an aircraft with a carbon fiber structure, non-energy-absorbing seats and no other energy-absorbing structure would exceed injury limits. In contrast, if the carbon airframe featured a carbon/Kevlar hybrid structure, with stroking seats and seat foam, and an energy attenuating subfloor, injury loads would be 20% below injury limits.
The range of mitigating systems includes ballistic parachute systems, energy absorbing airframe structures, energy absorbing landing gear, seat and restraint systems, and external energy absorbers, such as airbags.
Littell explained that most of these approaches have been tested by NASA, but he’d like to better understand how a ballistic parachute system would work for an eVTOL aircraft at low altitude or low speed.
Littell noted that one certification challenge is that “batteries located in the subfloor could potentially negate any occupant protection systems.” Safety standards have been developed in the automotive industry for vehicles utilizing lithium-ion batteries, but most aviation documents still refer to “fuel system crash resistance.”
The FAA’s Joseph Pellettiere said that the FAA has descriptions of load cases for seats for various-sized aircraft that can be applied to eVTOL aircraft development.
Uber’s Ryan Naru described the company’s layered safety approach that includes aircraft design, fleet operations and crashworthiness. Uber’s analysis of historical Part 135 operator data suggests that system failure was only responsible for 16% of fatal accidents between 2012 and 2016 and that 84% were attributable to operator error.
That’s why Uber is heavily focused on introducing new systems that reduce operator error rates in contrast to the approach taken by the European Union Aviation Safety Agency (EASA). As described in a previous Vertiflite Commentary (“EASA Publishes SC-VTOL,” Vertiflite, Sept/Oct 2019), EASA is requiring that even single-passenger air taxis would have to have even higher levels of aircraft reliability than a commercial airliner, which are designed to have only a one-in-a-billion chance of a catastrophic failure.
Bell’s Michael Smith highlighted that “designing crashworthiness into eVTOL aircraft protects not only occupants but ultimately public perception.” He explained that developers must design crashworthiness into an eVTOL, even though eVTOL crashworthiness certification requirements are not yet fully defined.
The Symposium also had insights from many other areas of development. This included manufacturing and lightweighting opportunities, a cargo delivery panel (see “Cargo eVTOL Matures,” Vertiflite, Mar/Apr 2020, pg. 54), systems developments — including subsystems, electrification and high-fidelity analysis and simulation tools — infrastructure, and the economics of investing in eVTOL.
Interestingly, Matt Pearson from Airspeeder relayed how automotive and aviation racing led to tremendous advances in safety for those industries. Airspeeder aims to replicate this with the world’s first electric VTOL races — with imagery that intentionally conjures visions of “Star Wars” pod racing.
The growing number of US government funding opportunities to support eVTOL/UAM developments was also detailed. NASA Armstrong Flight Research Center’s Starr Ginn is leading the NASA/FAA UAM Grand Challenge. Ginn explained that the goal of the Grand Challenge is to provide a proving ground where NASA, vehicle providers, airspace technology providers and the public can learn what it really requires to achieve urban air mobility. Not providing cash prizes, the Grand Challenge instead is intended to provide valuable knowledge for the organizations working to establish the certification requirements and standards needed for the market to move forward.
Col. Diller also presented on “Air Force Interest in TVF,” while Carmine Borelli, the Director of Unmanned Aerial & Ground Systems at Headquarters Marine Corps, discussed the possibilities for eVTOL to provide solutions for the Marines’ Unmanned Logistics Systems – Air (ULS-A), which is seeking early operational capabilities in 2023-25.
The final discussion was on the VFS/NASA TVF Working Groups, which were envisioned at the first TVF Workshop in 2014 and formalized at the third workshop in 2016. Each of the four TVF working groups is finalizing their summary reports. The NASA Aeronautics Research Institute (NARI) has been supporting the working groups since their inception, initially by the late NARI director, Mike Dudley, who was an organizer of and speaker at most of the Society’s paste eVTOL Symposiums. NASA has now launched a new initiative to form “UAM Ecosystem Working Groups,” which are also being supported by NARI.
The Future of Electric Vertical Flight
The sold-out Transformative Vertical Flight 2020 was a remarkable event when one considers that there are more vertical flight aircraft in development than at any time in history, with most of the newcomers featuring all-electric and hybrid-electric power plants. More significantly, a tremendous amount of engineering and technical talent has been employed to refine these new aircraft configurations and significantly expand the application of vertical flight in our daily lives.
The next opportunity for the vertical flight community to take a deep dive into eVTOL aircraft and UAM applications will be at the Society’s 76th Annual Forum & Technology Display in Montreal, Canada, on May 19-21, 2020. Forum 76 features a full day each of eVTOL technical papers and invited talks, as well as a day-long eVTOL Short Course.
The 8th Electric VTOL Symposium is planned to take place as part of the 9th Biennial Autonomous VTOL Technical Meeting in Mesa, Arizona, next January. As with each of the past eVTOL Symposiums, it too will surely sell out.
Additional articles in this issue describe other aspects of TVF 2020.
Technical papers from TVF 2020 are available for purchase in the VFS Vertical Flight Library: www.vtol.org/library
Invited presentations can also be downloaded for free by current VFS members in the VFS Vertical Flight Library: www.vtol.org/library
The TVF 2020 plenary sessions and the Electric VTOL Symposium discussions were video recorded, and can be viewed for free by current VFS members in the VFS Vertical Flight Video Library: www.vtol.org/videos
About the Author
Ken Swartz runs the agency Aeromedia Communications in Toronto, Canada. He specializes in aerospace market analysis and corporate communications. He’s worked in the regional airline, commercial helicopter and commercial aircraft manufacturing industries for 25+ years and has reported on vertical flight since 1978. In 2010, he received the Helicopter Association International’s “Communicator of the Year” award. He can be reached at firstname.lastname@example.org.
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Fairfax, Virginia, USA - 22031