Commercial

CityAirbus Prototype Unmanned Air Taxi to Take Flight in March

By Dan Parsons | February 28, 2019
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Artist rendering of the CityAirbus concept urban air taxi vehicle. (Airbus photo)

DONAUWORTH, Germany — CityAirbus, the namesake company’s prototype unmanned air taxi, should break contact with the ground sometime in March and then embark on a flight test campaign to incrementally expand the two-ton vehicle’s envelope and learn its capabilities.

Painted white, with a fuselage about the size of a light single engine helicopter, the aircraft now sits caddy corner in a large rolling-door workshop at the Airbus facility in Donauworth, Germany. The four ducts that surround each set of rotors are just high enough from the ground for a 5-foot-10 reporter to walk beneath them without bumping his head.

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The all-electric vehicle runs on four 800-volt batteries that power four sets of paired, counter-rotating props inside aerodynamic ducts fixed to the fuselage. It was designed for and dedicated to operating in urban environments. Each prop is 2.8 meters, or just over nine feet, in diameter and the ducts surround them.

“We have a vehicle which is able to carry up to four persons,” Marius Bebesel, Airbus head of urban air mobility, said during a tour of the lab here where CityAirbus is being built. “This was one of the main requirements we had in mind for CityAirbus, because we wanted to have a certain transport capacity because you need it to have the right business case.”

Other aircraft manufacturers looking to stake out a piece of the prophesied multi-billion-dollar urban air mobility market have included pilots in their designs, at least in the plans for initial fielding. Airbus is taking a “no-toy approach” that calls for rapid development and construction of an air vehicle to prove the concept. The company has not ruled out including a pilot on board an operational air taxi, but is perfecting the architecture and safety systems with the unmanned CityAirbus first, Bebesel said.

Artist rendering of the CityAirbus concept urban air taxi vehicle. (Airbus photo)

“We didn’t want to cheat ourselves,” he said. “We wanted to be strict on this one. This is why to be quick and to have proof of concept of such a vehicle, which can later be a product, we decided not to go with a pilot. It’s easier to operate it in the beginning as an unmanned vehicle.”

Airbus targeted a vehicle that was around 2 tons because it represents a sweet spot between carrying enough passengers to make the endeavor economically viable while keeping the aircraft relatively small to reduce noise.

The four carbon-fiber ducts weigh about 80kg, but are specially designed to provide additional lift. In hover, the ducts generate more than 400 kg of additional lift, Bebesel said.

Each fixed-pitch propeller is driven by its own direct-drive electric motor — there are two stacked in each of the four ducts. The vehicle is controlled by varying the rpm of each set of rotors.

“The approach is to be as efficient and compact as possible,” he added. “For this reason, we have chosen this sort-of coax configuration. … The basic principal is we want to keep it as simple and as safe as possible.”

Airbus is relying on redundancy — four batteries, stacked counter-rotating propellers, multiple power distribution boxes — as a safety net. Eight props is the minimum number that would still be safe enough to fly. In this configuration it can remain airborne with the loss of any one prop, but would struggle with the loss of two in the same duct, Bebesel said.

Artist rendering of the CityAirbus concept urban air taxi vehicle. (Airbus photo)

“We have the redundancy to cope with any kind of failure … on batteries, on distribution boxes, on the motor controls, on the motor itself,” he said.

When Rotor & Wing got a look at City Airbus in mid-January, engineers were tuning the flight control system. The company had already put the vehicle through at least four ground runs at that point. During that process, and while bolted to the ground, the aircraft was spooled up to about 600 rpm.  Another ground test was planned for that week that would ratchet the power up to 750 rpm.

“It is a vehicle where we have a big variation of rpm and we want to go step by step through the rpm levels until we have reached the nominal thrust,” he said.

Nominal thrust operational should require around 950 rpm and around 1,000 rpm should be good enough for takeoff.

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