Helikopter - Airbus kikker inn i krystallkulen - Air taxi - AW&ST

On-Demand Helicopter Experience Feeds Into Airbus Air Taxi Design Tony Osborne and Graham Warwick  Airbus is approaching urban air mobility from multiple directions, from gaining experience with on-demand helicopter service in gridlocked cities to designing vehicles optimized for the short-duration air taxi mission.  The helicopter service Voom is the first project to graduate from Airbus’ Silicon Valley incubator, A3, and has become a subsidiary of Airbus Helicopters. Voom began operations in April 2017, in Sao Paulo. With backing from Airbus Helicopters, the service soon will expand into Mexico City, which has similarly congested road traffic, but with the additional challenge for helicopter air taxis of hot-and-high operating conditions.  Since the online booking service began, using approved Part 135 helicopter operators and licensed heliports already in place in Sao Paulo, Voom says monthly growth has exceeded 200% in number of trips and 220% in riders. The service now makes “several dozen trips a day” between eight heliports, six in the city center and two at Sao Paulo’s domestic and international airports, says CEO Uma Subramanian. “And we have just scratched the surface.”  Voom on-demand helicopter service to expand into second city Ground testing under way for CityAirbus eVTOL demonstrator Crucially for Airbus’ urban air mobility initiative, “we are learning a lot about how people fly, where they want to go, and what they think about luggage,” she says. “That’s important to the next-generation vehicle and what operating costs should look like for future vehicles.”  Most electric vertical-takeoff-and-landing (eVTOL) air taxis are being designed for four passengers, but if they bring a lot of bags, “it could radically change the equation,” Subramanian says.  When booking with Voom, customers must say how much luggage they plan to bring, as it can require a larger helicopter, which drives up the cost. Some 60% of riders come with one or more checked bags, so Voom has paid one of its operators to add a luggage tray to its helicopter for airport routes.  Voom also is learning what routes customers want to travel. “It’s not just the airports. We have fairly regular business travelers who want to get from one end of town to the other,” Subramanian notes. “This is important to scaling the network in the future and to what we do [with larger helicopters] in quiet times.”  Airbus also is learning what passengers consider a fair price. “We have to think about vehicle design as a function of willingness to pay for an air transport service,” she says. If the goal is to offer lower operating costs per mile than a premium helicopter service, to increase usage, the questions are: “What is the delta, and what does the next-generation vehicle look like at that price?”

Already flying in Sao Paulo (pictured), Voom is to expand to Mexico City. Credit: Voom

What Airbus thinks that vehicle could look like is the four-seat CityAirbus eVTOL. At roughly 26 ft. (8 m) in length and width, this will be smaller than any helicopter Airbus produces and, while styled to resemble the twin-turbine H160, it will be a rather utilitarian aircraft. “It is not a sports car,” says Marius Bebesel, Airbus head of urban air mobility. “People will only spend 15-30 min. in this vehicle, so it will be more like a London taxi.”  Propulsion for the  4,850-lb. (2.2-metric-ton) demonstrator aircraft is provided by eight 100-kW Siemens SP200D motors, a total output more than twice what is needed to hover. “We are still learning. The motors are oversized, as are many of the systems onboard, so there is room for optimization,” Bebesel says. Safety is one driver for this conservative approach, with a high level of redundancy applied to major systems. If one motor shuts down, the other seven will more than take the strain without passengers noticing. Each of the eight motors drives fixed-pitch propellers, mounted in contra-rotating pairs with one inside the duct, the other raised just above it. The ducts increase performance but also are aerodynamically shaped to reduce drag in forward flight while providing some additional lift in cruise. The propeller shafts are the only mechanical parts on the aircraft, which will have a “big impact on operational costs,” Bebesel says. “We have an image of maintenance on this aircraft being done by one guy with a torque meter,” while the rest of the systems onboard will be self-monitoring. One key focus is on passenger comfort, particularly in the first seconds after takeoff as the CityAirbus transitions to forward flight. There is concern that a helicopter-like nose-down transition could be uncomfortable for some, so Airbus is working on maintaining level flight throughout the mission. The company is filing for a patent on technologies that could achieve this.

Safety and low noise are driving the design of the CityAirbus. Credit: Airbus

Because the CityAirbus is designed to operate in sensitive urban areas, engineers are studying how to keep noise levels low. Electric motors help, but using contra-rotating propellers in the ducts can result in unwanted noise from blade interactions, so tip speed is reduced to 395 fps (120 m/s) compared to the 690 fps in a traditional helicopter.  Behind the cabin, Airbus is suspending the four 100-kWh lithium-ion batteries on a rail that allows them to be moved to adjust the center of gravity during flight testing. Suspending them high in the fuselage also improves handling and flight characteristics, Bebesel says.  Airbus powered up a ground-test rig for the CityAirbus propulsion and flight control systems at the end of 2017 and is aiming to fly the demonstrator, unmanned, at the end of 2018. The first hop will take place in Donauworth, Germany, before testing is transferred to the nearby military airfield at Manching.  Once early testing is complete, the aircraft will be converted for manned flights. While initial commercial flights could be piloted, ultimately the CityAirbus would fly autonomously between preassigned stations. Passengers would walk under the ducted fans to enter the cabin, but as they are 6.4 ft. off the ground, only a handful would have to duck.  Props can be stopped within 2 sec., which should speed up turnaround times, allowing passengers to leave the vehicle moments after landing, unlike on a helicopter, where they might wait for rotor blades to stop turning before exiting.  Because the CityAirbus is carrying its 1,100-lb. (500-kg) energy source at all times, a key driver has been to keep weight low. The airframe itself is only about 10% of the vehicle’s empty weight. Motors and inverters feature separate liquid cooling systems, although Bebesel says production systems likely would have a more simplified approach. Artificial intelligence also would play a role, with the electrical systems calculating the temperature and charge status so it can be optimized for the upcoming flight.  Another lesson from Voom’s first 10 months of operations in Sao Paulo? “Weather can be a real problem. In January, we had to cancel 21 trips in 1.5 hr.,” Subramanian says. “We need to be thinking how weather factors in, and we need to design the vehicle to deliver a reliable product, even in inclement weather.”