A version of this article appears in the August 11/18 double issue of Aviation Week & Space Technology.
Autonomous technology, in the air and on the ground, is certain to be required if aviation is to break out of its niche and become a ubiquitous mode of transport. Whether it is easy-to-fly personal air vehicles, optionally piloted air taxis or single-pilot commuter transports, aviation will have to go beyond automation to enable wider public use of aircraft.
Visionaries like Mark Moore, an aerospace engineer at NASA Langley Research Center, look ahead to the “democratization” of air transport, where a mix of personal, air-taxi and other “thin-haul” air vehicles provide “on-demand” mobility for communities over distances of 50-500 mi. But he acknowledges there are technological, regulatory and societal challenges to the vision, which include airspace control, ease of use, safety, noise and enabling robust daily operations in all weathers.
An example is the Hopper electric vertical-takeoff-and-landing (VTOL) regional public transport concept developed by Stanford University and NASA. The baseline vehicle is a 30-passenger tandem-rotor helicopter with battery-electric, fuel-cell or hybrid-electric propulsion. The Hopper is designed for extreme short-haul flights—less than 100 nm—as an alternative to road and rail transport in congested metroplex areas. Electric propulsion is heavier, but energy usage is much lower than for turboshaft-powered aircraft.
The Joby S2 is a tilt-prop VTOL personal aircraft enabled by distributed electric propulsion. Credit: JOBY Aviation
Stanford has conducted simulations of Hopper operations in the neighboring San Francisco Bay Area, where population density and difficult geography make for long commutes. The simulations have looked at network operations carrying up to 30,000 passengers a day, which would require hundreds of Hopper vehicles making thousands of flights between dozens of vertiports connected to road and rail links. With three major airports in the area, this inevitably raises airspace management issues.
Simulations show that dynamic flightpath routing based on time of day could reduce potential conflicts with the background air traffic and limit controller workload by avoiding heavily used airspace. But enabling a Hopper-style public transport network will require a high level of automation on the ground and in the air. The vehicle would be single-pilot, with a potential for fully autonomous operation later. Vertiport operation, including charging or changing batteries, would be automated.
“Flying and VTOL are energy intensive transportation modes for short distances, and yet represent a potential way to bypass urban surface-transportation congestion,” says Larry Young, NASA principal investigator. Near-term battery technology, with 500-600 watt-hr./kg. energy density at reasonable power density, could make such short-range vehicles feasible within 10 years, he says, if airspace and infrastructure challenges can be overcome
Bay Area tech-industry commuters, albeit the wealthier ones, are also a target for Joby Aviation’s S2 electric VTOL two-seater. Slated to be available within a few years, the S2 is a near-term example of a personal aircraft enabled by electric propulsion. The design has 12 electrically driven propellers on the wing and tail that tilt for VTOL and fold in cruise, providing efficiency, redundancy and reduced noise.
Designed to fly at 200 mph., with a 200-mi. range, the estimated $200,000 S2 is five times faster point-to-point than a car and twice as fast as a Robinson R22 two-seat helicopter, says chief designer Alex Stoll. S2s use five times less energy than a car and 10 times less than a helicopter, he says. The operating cost is about $0.20/mi. compared with $0.60 for a car and $1.30 for an R22.
Moore says on-demand aviation could also work in Los Angeles, where an estimated 233,000 “hyper-commuters” travel 200 mi. or more a day to and from work, and in other metroplexes. The best place to start, he says, is by applying autonomy and electric propulsion to general aviation to improve safety, reduce noise and overcome today’s shortcomings in efficiency, emissions, ride quality, robustness and operating costs.
Autonomous technology could make flying easier and safer and reverse the long decline in the number of pilot’s licenses issued, says John Langford, president of autonomy specialist Aurora Flight Sciences. “Single-pilot is a key step along the way,” Langford says. “It would make air taxi commercially viable, flying single pilot with people on board and dead-heading unmanned.”