The latest would-be air taxi of the future has taken to the sky: Lilium’s new vertical-takeoff-and-landing prototype made its first flight on May 4, the Munich-based startup revealed today. Though Lilium says the gleaming five-seat electric can fly 186 miles in an hour, its first flight, like most such tests, was modest. Operated by remote control, it lifted off, hovered a few yards above the ground, and landed. The modest first outing that’s common for any new aircraft type. This followed months of extensive ground testing.
Lilium has been quiet since sowing a subscale, two-seat prototype two years ago, but it has one of the more interesting—and contested—technological approaches in this burgeoning field. The “Lilium Jet” uses 36 electric-powered ducted fans. Inside each, a small rotor ingests air from the front and pushes it out of the rear at higher speeds. They’re not technically jet engines (so the aircraft isn’t a “jet”). The lack of spinning blades improves efficiency, reduces noise, and eliminates the risk of turning passing birds into chop suey.
The motors are arranged in two rows of six on either side of the nose—embedded in a forward assembly known as a canard—and two rows of 12 in the rear wing. The aircraft would pitch the fan assemblies vertically for takeoff, then transition them 90 degrees for horizontal flight, with the aerodynamic wing and fuselage providing most of the lift at cruising speed. In this configuration, the aircraft would only need about 10 percent of the maximum thrust of the motors to maintain forward flight, a Lilium spokesperson says. Panoramic windows and gull-wing doors make for a flying experience that bears little resemblance to commercial aviation.
The Lilium does away with the sort of tools that conventional planes use to control their movement, including the vertical stabilizer, ailerons, or elevator. Instead, it relies on a flight-control computer that will angle the motors in different directions. The forward motors handle pitching the nose up and down. Those on the wing manage roll movements. The aircraft rotates on its axis in a hover by varying the speed of rotors, just as consumer quadcopter drones do.
Though the work of flight testing and certification remains—no easy feat—Lilium cofounder and CEO Daniel Wiegand aims to build an on-demand air taxi service in just a few years, with a network of launch and landing pads across a few cities to start, and a larger operational service by 2025. To start, humans will serve as pilots, but the company aims to drop them ASAP. Lilium says its autonomous technology is nearly ready and it’s just waiting for regulators to allow them to go robo. When that will happen is hard to predict and will vary by region, but analysts say Lilium should have three to five years to make sure the tech is as ready as it says.
As for the new aircraft itself, Lilium has dropped the off-the-shelf motors that powered its old prototype in favor of ones it designed. It’s made of aerospace-grade materials, as opposed to a variety of hand-built parts usually fashioned from prototyping techniques. Wiegand says the move from two seats in the prototype to five will help the fledgling system achieve efficiencies and economies of scale by providing transport to more passengers with each flight. The company is cagey with technical specs, but it says the battery is about the size of what you’d find in an electric car.
“In less than two years we have been able to design, build, and successfully fly an aircraft that will serve as our template for mass production,” Wiegand says.
Skeptics, though, have argued that Lilium’s decision to combine propulsion and control in one mechanism compromises the ability of either to function efficiently. “We don't believe that to be the case,” a company spokesperson said in an email, arguing that having 36 independently controlled engines offers finer control and improved redundancy. The aircraft also uses a triple-redundant flight-control computer and 12 independent flaps. Its shape allows for gliding in the event of a complete power failure, and it will carry a ballistic parachute just in case.
But among the many challenges facing the 200-plus companies in the quest for aeromobility, noise could be as high a hurdle as economics or safety. Vertical-lift aircraft have to move a lot of air to maneuver at low speed and hover, and that means making a serious racket—especially if you get a bunch in one urban area. Lilium says its ducted fans not only absorb and dampen the general noise of the aircraft, they also minimize the additional high-pitched whine that comes from using smaller blades. Overall, the company says, the design will allow the aircraft to “blend into the background of a typical urban scene.”
With the first flight now a memory, Lilium will run its aircraft through increasingly complex maneuvers, including the transition between vertical and horizontal flight, runs between cities, in inclement weather, and with a variety of degrees of automation. If all goes well, passengers will experience the flights in trials well ahead of the 2025 target for a fully operational service.
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