Lilium
Lilium

It’s a bird, it’s a plane, it’s…an Uber?

A prototype unmanned Volocopter two-seat air taxi made its first autonomous test flight in Dubai, UAE on September 25. The city hopes to have a low-altitude network of these air taxis in place in time for the World Expo there in 2020; and it plans to handle up to 25 percent of all its urban transport with the vehicles by 2030.

Both Dubai and Dallas are launch markets for the Elevate network that Uber unveiled last April. Its goal: to bring autonomous, small, electrically powered vertical-takeoff-and-landing craft (eVTOL) to densely populated urban areas and enable consumers to order them up on their smartphones—just as they summon a ground Uber taxi now. Proponents of the vehicles hope that fares will be around $1.32 per passenger mile—only a bit higher than what it costs to operate a car and about one-third of the price of operating a turbine helicopter. The vehicles would take off and land on rooftops and in parking lots and other confined spaces; seat two to four passengers; fly at altitudes up to 4,000 feet at 75 to 175 mph; and have an unrefueled range of up to 200 miles. For the economic model to work they would need to be mass-produced, relatively inexpensive—likely $250,000 or less—and simple to maintain.

Technologically, this endeavor promises to be as vexing as the NASA Apollo program that put men on the moon. That’s why Uber has hired a NASA scientist as the program’s director of aviation engineering. Mark Moore spent 32 years at the space agency, concentrating mainly on electric flight. He says the Uber Elevate vehicles will require “precise digital datalinks” onboard for real-time deconfliction data to be communicated between vehicles, to ensure they don’t collide.

A down-to-earth  look at flying cars

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A down-to-earth look at flying cars

Perhaps they’d be successful if we adjusted our expectations.

The amount of that deconfliction data could be substantial. Uber chief product officer Jeff Holden says the company’s modeling suggests a demand for up to 200,000 air trips per day in the demonstration cities. He adds that working with NASA and the FAA will be critical in developing the network. Uber is partnering with those governmental bodies to develop and test scheduling and separation methods to ensure safe flight. “We’re going to have a lot of these aircraft in the air,” Moore says. “NASA is going to be a tremendous partner to make this a reality.”

The goal of the Elevate network that Uber unveiled last April: to bring autonomous, small, electrically powered vertical-takeoff-and-landing craft to densely populated urban areas and enable consumers to order them up on their smartphones.

This new low-altitude frontier will be complex from a regulatory point of view, as the scheme needs to address many air traffic control and vehicle safety regulations and concerns. Dr. Jaiwon Shin, associate administrator for the aeronautics research mission directorate at NASA, says a likely urban air traffic control model for the network would follow along the lines of the UTM (Unmanned Aerial Systems Traffic Management) system currently being developed. He adds, however, that deployment of the Elevate network would likely test government regulators’ ability to work with industry expeditiously and that industry needs to be mindful of aviation safety requirements. “The FAA is learning that it has to move much faster—at the speed of innovation,” he emphasizes.

Uber first made the case for urban vertical flight last year in a widely distributed white paper entitled, “Fast-Forwarding to the Future of On-Demand Urban Air Transportation.” Benefits of the widespread deployment of such a system, according to the company, would include congestion reduction, time savings, and lower overall infrastructure costs compared with ground-based transportation. “This isn’t going to be easy,” admits Holden, “but this can be done sooner than later.”

Holden says the key to getting the network in place is “radically changing the type of aircraft we’re manufacturing here and doing it at mass scale.” Those aircraft would incorporate distributed electric power propulsion and fly-by-wire controls to improve speed, efficiency, redundancy, reliability, and safety while reducing noise and emissions. “Helicopters won’t work because of noise, cost and energy efficiency, and speed limitations,” Holden says.

To that end, Volocopter and several other manufacturers—including such major airframers as Bell Helicopter and Embraer—already are at work designing concept vehicles. Several, such as the Volocopter, have even flown.

Volocopter
Volocopter

Earlier this year, German start-up Lilium conducted a successful unmanned flight of its two-seat Eagle prototype eVTOL craft. The design features 36 low-vibration electric jet engines mounted to wings via 12 moveable flaps, which are pointed downward on takeoff and landing to facilitate vertical lift but gradually transition to a horizontal position to provide forward thrust. The engines are shielded to protect each other from the impact of uncontained failure. They have a small fan diameter and limited drag and feature a simple design of two bearings, one shaft, and simple rotors. The design of the aircraft makes it easily maneuverable during transition flight, a key advantage in an urban environment, says Lilium CEO Daniel Wiegand. “We can fly curves during climb and descent,” he says. The aircraft has a range of about 162 nautical miles and a top speed of 186 mph.

Last April, Aurora Flight Sciences—which Boeing recently announced it would acquire—flew a one-quarter-scale prototype vehicle based on the XV-24 aircraft that it is developing for the military. The Aurora design features separate propulsion systems for hover and cruise and uses eight distributed lift rotors mounted on booms and one main aft-mounted propulsor along with a main wing and three lifting surfaces. Once the aircraft transitions past the stall speed (40 mph) in cruise flight, the lift rotors shut down.

Airbus says subscale versions of its Vahana tiltwing eVTOL have already flown and that a full-scale version will be in the air by the end of 2017. The goal is for production aircraft to be fully autonomous and to be equipped with low-altitude ballistic recovery system parachutes.

Carter Aviation Technologies has partnered with Mooney to develop a four- to six-seat vehicle that uses Carter’s slowed rotor compound design and cruises at 175 mph. Carter CEO Jay Carter points out that the high-inertia main rotor is always turning and in effect functions as a main parachute while providing directional control all the way down to the ground in an emergency.

While Bell Helicopter hasn’t yet produced an eVTOL for public viewing, Scott Drennan, the airframer’s director of engineering innovation, says his company’s design would be robust enough to fly 2,000 hours per year; be “modular, adaptable, and scalable”; be able to use a variety of
powerplants; have both civil passenger and military logistics applications; and likely be certified under the FAA’s powered-lift category, a new section of the Federal Aviation Regulations developed for tiltrotors. Drennan’s boss, Michael Thacker, Bell’s executive vice president for technology and innovation, is more sanguine about the project, saying, “We’re working with Uber to make sure we can do it in a safe and appropriate manner.”

Workhorse
Workhorse

Clearly, designing and even flying a prototype eVTOL is the easy part of the equation; the bigchallenge is manufacturing one that can meet the mission and pass regulatory muster, says Patrick Conners, who is manager of manned aircraft for the Workhorse Group.

Workhorse has developed a variety of hybrid electric vehicles, including step vans and pickup trucks. In June, it unveiled its two-seat SureFly hybrid gas-electric VTOL concept at the Paris Air Show. SureFly has a maximum payload of 400 pounds, a range of 70 miles, and a cruising speed of 70 mph. The aircraft is powered by a fossil-fueled generator engine linked to a parallel bank of battery packs offering redundant power and eliminating the need for long battery recharging between flights. The electrical system powers motors linked to four propeller arms, each with two contra-rotating propellers. The batteries can power the motors if the generator fails. The airframe also has a ballistic parachute.

Workhorse plans to begin test flights this year and intends to achieve FAA certification in late 2019. However, in its current form, SureFly would not likely meet FAA certification requirements and Connors estimates the program would need at least $40 million to accomplish that goal and that a mass market needs to exist to justify the investment. “Our target price is $200,000,” he says. “We can make money if we sell 10,000 a year. Right now, in the U.S. only 1,200 helicopters are sold per year. If we sold only 50 of these per year we couldn’t get the price down to $200,000.”

Economics aside, daunting technological issues remain. Workhorse is still looking for a production engine that’s light and powerful enough to meet the performance goals of its hybrid design. Connors estimates that the company needs to find an engine that generates 300 horsepower and weighs only 200 pounds, and that means an internal-combustion rotary engine or a small turbine akin to what is found in auxiliary power units on corporate jets. “The challenge is getting it as light as possible and getting the most power,” Connors says. Workhorse has extensive experience with battery-powered vehicles, and Connors notes that current batteries are too heavy and take too long to charge to be practical for daily use in the eVTOL mission; emerging technology from major automakers such as Toyota may change that in the coming years, he adds, but for now, “hybrid is the way to go.”    

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