Sky taxis: How to make them a reality
By Tom Risen|January 2018
Pioneers aim to bring urban air mobility to the masses
Piloting a modified Mooney M-20K plane at 275 kph has made it easy for Jon Rimanelli to travel to other cities, sometimes three times a week, to meet with clients for Nextronix, the electronics manufacturing firm he owns in the Detroit area. Seeing commuters stuck in the gridlock below gave Rimanelli a business idea. He contacted NASA to learn what he could about research toward personal air mobility services.
That was in 2010. Within a year, Rimanelli and a small team of experts were pitching local investors with their plan to put Detroit’s automobile-focused industrial base to work mass producing small aircraft that would fan out to landing sites near neighborhoods and ferry commuters to work.
How did things go? “There was zero interest,” Rimanelli recalls.
What a difference six years make. Inspired by consumer drones and Uber’s 2016 announcement that it aims to transport passengers in self-piloting aircraft, a cast of competing startups and established players are in discussion with NASA and the FAA about how to shepherd this proposed new class of aircraft into service. Hurdles abound, from social acceptance to safety certifications.
If things go as designers hope, commuters of the future will be whisked safely and affordably over highways and railways, likely in propeller-driven, electric-powered aircraft steered by autonomous software.
Unlike the situation with drones, designers are not starting largely from scratch. “The interest in drones has certainly made people realize this is possible,” says Rimanelli, who last year founded AirSpaceX, a 10-person air mobility company near Detroit.
Spinning off from drones
Rimanelli’s conceptual vehicle, a tilt-wing propeller aircraft called MOBi, must vie against at least 12 other designs in the nascent market, according to a list of new vertical flight concepts assembled by the American Helicopter Society. One is Vahana, a tandem tilt-wing full-scale demonstrator made by Airbus’ Silicon Valley arm, A3 [pronounced “A cubed”]. The company plans to fly the aircraft at its site in Pendleton, Oregon, in 2018. Then there is the eight-propeller aircraft conceived by Uber’s partner, Aurora Flight Sciences, now a Boeing subsidiary. Aurora flew a subscale version of the craft, which has not yet been named, in April at an airfield in California.
These and other designs capitalize on electric power, propeller technologies and software pioneered for consumer drones. Each would achieve the transition between vertical and horizontal flight by different methods, but all are eVTOLs, short for electric vertical takeoff and landing aircraft. Just as with many drones, multiple propellers would be driven with electricity from batteries.
It is early days for those pioneering this new breed of craft. While NASA has become more involved with drone makers in recent years, this time the agency wants to be proactive. In October, NASA hired the consulting firms Booz Allen Hamilton and Crown Consulting to complete a one-year study that will suggest how the agency could enhance its support for this new industry and how these aircraft might fit into society. The results of the study will be coordinated among different parts of NASA, says John Cavolowsky, the director of NASA’s Transformative Aeronautics Concepts Program.
NASA already sponsors some research specifically on the topic, and work in related areas, such as drone air traffic management and rotorcraft noise testing, will also benefit the personal transportation industry, says Cavolowsky.
Judging by interviews with Cavolowsky and others, the biggest questions facing the industry revolve around the interface of the technology with the prospective human customers. “We think we are getting much better at planning legal and regulatory approaches to urban air mobility,” Cavolowsky says. “Social acceptance is really very different,” he adds. “Just because there is a technology that can help doesn’t necessarily mean there is a market there to accept it.”
Would a passenger or passengers climb aboard an aircraft with no human at the controls? “Going to a fully automated passenger service for the uninitiated public is a pretty steep ask” in the short term, says John Hansman, a professor of aeronautics and astronautics at the Massachusetts Institute of Technology. Hansman predicts that during the span of years it will take the FAA to approve these aircraft, consumers will gradually adjust to the idea of self-flying taxis, because they will see publicity about the results of safety tests.
Hansman’s team at MIT is doing research for NASA on operational barriers for urban air mobility, including how to update air traffic control so fleets of air taxis can safely fly over the same city at once. “If a regulator were to approve autonomous passenger aircraft you could probably find someone who would be willing to fly in it,” he predicts. “At some point it will become socially acceptable because people will get used to automated cars and automated military aircraft.”
Giving consumers time to adjust appears to be a key factor, according to a survey published in July by New York-based market research firm YouGov. Two-thirds of Americans surveyed had not heard of unmanned eVTOLs, which the survey called “passenger drones,” and only 5 percent said they would feel safe flying in one. Two-thirds of respondents said they would expect FAA safety certification and precautions including parachutes, but 62 percent also said they would consider buying these unmanned passenger drones in the future.
The technologists I interviewed view autonomy as essential for making maximum use of the limited space aboard their proposed craft, which are typically about the size of a small helicopter. That said, the FAA told me that for the “urban transport market” it has received one application from a company for a type certificate, the document declaring a design’s airworthiness, and that application was for a “piloted VTOL airplane.” The FAA declined to name the company under its longstanding policy, but said the company has since shifted its focus to an unmanned aircraft.
As prominently as autonomy features in planning, it sometimes comes with caveats. Aurora, on its website, says its aircraft will fly initially with a safety pilot, but is designed for “fully autonomous operations.” A3, on its website, says it plans to employ “full automation and sense and avoid technology” so that many “air taxis” can be managed in the sky at one time.
Another challenge for social acceptance could be privacy, once fleets of eVTOLs are flying routinely overhead in cities and suburban areas, says NASA’s Cavolowsky.
These social acceptance considerations partly drive the aircraft designs. Not much can be done if passengers demand a human at the controls, but the noise of combustion engines and a helicopter rotor can be avoided by relying on electric power and multiple, small propellers.
This “distributed electric propulsion is a game changer,” says Diana Siegel, program manager of Aurora’s personal transportation eVTOL, which might someday be flown by the Uber Air service. In addition to creating a quieter aircraft, “it means our design freedom is much larger.”
Those designs must be matched to the needs of the market, though. For military applications, noise might be less of a concern and payload capacity a greater one. Siegel points to Aurora’s XV-24 Lightning Strike aircraft funded by DARPA and the U.S. Air Force. It takes off with ducted fans embedded in its tilt wing and canard. These ducted fans are hybrid electric, meaning their electric motors are powered by generators, which are in turn powered by a gas-turbine engine. The company built and flight-tested an unmanned, subscale, lithium battery-powered version in March at Webster Outlying Field in Maryland.
Siegel says an electrical design with multiple small propellers is better suited for air taxis than the ducted fans that are more powerful but heavy.
The advent of distributed electric propulsion, which for some applications could replace mechanical drive shafts, hydraulics and fuel lines, is welcomed by one prominent member of the rotorcraft industry.
“The history of aviation is littered with failed vertical takeoff craft,” says Mike Hirschberg, whose engineering background in vertical flight propulsion includes working in the U.S. Defense Department’s Joint Strike Fighter (F-35) Program Office and on several DARPA programs. “Many past designs for vertical takeoff craft failed because they relied on propellers turned by mechanically complex transmissions,” he says.
What avenues will these companies take to win FAA certification for their innovations? Hirschberg says there are two possible pathways. One would be Part 23 of the FAA’s Federal Aviation Regulations for small planes, which was revised in 2016 to create a less prescriptive and, it was hoped, less expensive process for certifying newly designed planes. Another would be Part 27, the regulations for small helicopters.
When he considers the regulatory and technology groundwork laid so far, Rimanelli ventures a bold prediction. Picture a chart showing demand: “Once we prove these aircraft to be safe and reliable, we will see hockey stick-rapid growth,” he says.
Related TopicsAircraft DesignCommercial AircraftUnmanned Systems
“If a regulator were to approve autonomous passenger aircraft you could probably find someone who would be willing to fly in it.”John Hansman, MIT professor of aeronautics and astronautics