Bell has revealed an evolved design for its Nexus air taxi, with a new “4EX” version using fewer ducted fans and a longer wing than its predecessor, as well as being fully electrically powered.
The 4EX in the aircraft’s name represent the major design changes — “4” ducted fans, “E” for electric, and “X” for experimental. The original design, now referred to by Bell as the “6HX,” utilized six ducted fans and was envisioned as a hybrid-powered aircraft. Unveiled in the form of a full-scale mockup at CES 2020, which begins Jan. 6 in Las Vegas, Nevada, the 7,000-pound 4EX can carry four to five passengers up to 60 miles (95 kilometers) at a cruise speed of about 150 mph (240 km/h). While intended to be an electric aircraft, it has been designed to be propulsion agnostic, and a hybrid version would extend that range to beyond 150 miles. In terms of footprint, the 4EX will fit in the same 40-foot-by-40-foot box as the 6HX.
The evolution in design of the Nexus was dictated by market requirements, Bell CEO Mitch Snyder told media ahead of the aircraft’s unveiling. Bell had originally targeted range with its 6HX design, but it became clear that was one of two distinct and separating requirements for an urban mobility vehicle; the other being an aircraft that will serve cities as an intra-urban mobility provider.
“One vehicle was compromising the attributes of each, and so we went at it in a different direction,” said Snyder. “We looked at . . . what was coming from the market and what they wanted. And we were also able to progress our technology further and understand it and say, ‘You know what? I think we can build an all-electrical [aircraft].’”
The main driver in reducing the number of ducts was efficiency, said Scott Drennan, VP of innovation at Bell, with fewer ducts creating less drag. “And when you want to go to an all-electric vehicle, you need to get that efficiency in there,” he said.
The ducts have remained roughly the same size in terms of diameter — about eight feet — but are a little shallower on the 4EX than they were on the 6HX.
“There’s still work to be done around performance optimization in the duct, but we were confident enough to start showing a different chord length because of some of the data that we acquired [in testing],” said Drennan.
The move to all-electric also means a switch in propulsion partner, with the replacement for Safran (who had been working with Bell on the hybrid 6HX) to be announced shortly.
Building a safe aircraft is the main focus for the team, said Snyder. “With this form of transportation, we want to make it safe, we want to make it quiet, [and] we want to make it clean and green,” said Snyder. “And the most important thing here, besides the safety, is we want to make it affordable, [and] accessible to everyone.”
The exact level of safety Bell is targeting is one in a billion (10-9) for a catastrophic failure — which is the level of safety EASA recently identified in its certification standards for small VTOL aircraft.
“You can have a vehicle that’s 10-9 and still be affordable,” said Drennan. “Our vehicles will be at that level. They should be because of our history, [and] they should be because of the use of these — we’re talking about 2,000 hours per year, hundreds, maybe thousands of vehicles across these different areas — and when you start doing math, you want that number to be where it is.”
Bell will also continue to work on a systems integration lab (SIL) for the Nexus, following in the path of development established by Bell’s fly-by-wire 525 Relentless, V-280 tiltrotor, and 360 Invictus. The SIL combines the aircraft’s avionics, electrical and flight controls systems, tying together its hardware and systems to effectively create a non-flying “aircraft zero.”