Customer concerns about helicopter noise pollution prompted Bell to begin working on its electrically distributed anti-torque (EDAT) system two years ago, said Eric Sinusas, the company’s program director for light aircraft. Bell officially acknowledged EDAT in February but has been operating it on a Bell 429 flying testbed since May 2019 and applied for a related patent in 2017. Bell plans to certify the system and put it into serial production.
Bell, which has been flight testing EDAT at its Mirabel, Quebec facility, teased it was working on an electrically-powered anti-torque system in 2017 when it unveiled a mock-up of its FCX concept helicopter. That design used electrically-driven vectored thrust in the tailboom to provide anti-torque.
EDAT is significantly different from that design. It reduces helicopter noise, augments power to the main rotor, and simplifies maintenance by replacing the tailrotor with a series of four ducted fans embedded in the vertical stabilizer. Power for the fans comes from a pair of liquid-cooled generators that distribute current to four separate air-cooled electric motors, one for each fan. The generators and the motors were provided by Safran Helicopter Engines, one of Bell’s announced partners on its Nexus eVTOL urban air taxi program. EDAT eliminates the need for tailrotor mechanical systems, including driveshafts and gearboxes. The fans are controlled via fly-by-wire, but the remainder of the helicopter’s controls remain the traditional hydromechanical system, Sinusas said.
In flight tests to date, EDAT has behaved similarly to a conventional tailrotor and the system has not resulted in any appreciable difference in cruising speed. Sinusas was not willing to share metrics with regard to any possible weight-saving or specific decibel level reduction from EDAT, but he did say that the system produced an appreciable difference in pitch that had the potential to be less irritating to the human ear.
“We are comfortable saying that the decibels are lower and we believe it's a significant reduction in noise as far as the pitch. [EDAT] produces a higher pitch, a higher frequency [than a conventional tail rotor]. Higher pitch tones tend to attenuate faster. The noises don’t travel quite as far,” Sinusas said.
Bell plans to continue work on the system and continue flight testing with an eye to serial production. “The next steps are to continue to expand the flight envelope and optimize the system. We’re going to try to get it certified and into production as soon as possible,” Sinusas said.
Sinusas declined to say on which product Bell plans to launch EDAT first as a production feature, but he cautioned not to make assumptions just because the company is testing it on its model 429 light twin. He said the impetus for flying EDAT on the 429 was that a test helicopter “was available.” And while some data derived from the EDAT flight-test program may indeed by helpful and migrated to Bell’s Nexus 4EX urban air taxi, which utilizes ducted fans for propulsion, he said the main thrust of EDAT was to provide technology to address customer noise concerns on conventional helicopters. “What drove this concept was our commercial customers telling us that noise was becoming increasingly important and that we needed to do something,” he said.