Bell developing fan-driven electric anti-torque system

By Oliver Johnson | February 19, 2020

Bell has revealed a groundbreaking new electric anti-torque system in development for its commercial helicopter line, one that promises enhancements to safety and operating cost, as well as a reduction in noise compared to an aircraft with a conventional tail rotor.

The electrically distributed anti-torque (EDAT) system is composed of four small fans within a tail rotor shroud in an offset two-by-two pattern. Each of the rotors contains four blades, and they are powered by four separate motors, with the electrical energy provided through generators driven by the turbine engines.

“In a nutshell, we removed all of the conventional mechanical anti-torque components — which is gearboxes, driveshafts and tail rotor hub and blades — and replaced it with four electric motors and fans,” Eric Sinusas, program director of light aircraft at Bell, told Vertical. “They are fixed-pitch blades and they’re changing rpm constantly.”

The system has been installed on a Bell 429 demonstrator aircraft at Bell’s facility in Mirabel, Quebec, and began flight testing on May 23, 2019. Since then, the program has completed about 25 flight hours, with the aircraft gradually expanding its flight envelope.

Bell is not ready to share any performance figures, but Sinusas said the feedback from the customers that have seen the system in action has been positive.

“This is the first time anyone in the world ever done this, so the first step was just to make sure that it actually works — and yes it does work,” said Sinusas. “We’re still going to be optimizing it and refining it, but the product feedback in its current configuration has been very positive.”

The system’s anti-torque fans are controlled through pedals, as with yaw control in a traditional helicopter, but the link between the pedals and the motors is entirely electric “fly-by-wire” — all mechanical linkages and the control tubes of a conventional system have been removed. Other than the tail rotor and the control mechanisms, the demonstrator aircraft is unchanged to accommodate the system, using a conventional main rotor, engine, and airframe.

Sinusas said the driving force behind the EDAT system’s development was customer feedback.

“We were looking at what are the customers demanding for aircraft? . . . And safety is obviously always at the top of the list,” he said. “This [system] certainly meets those [requirements] and it has some interesting features that conventional rotors don’t with redundancy, and when the aircraft on the ground, the electric fans are not rotating at all.”

The redundancy is extensive, with the aircraft capable of still producing a level of anti-torque thrust even if three of the four fans become inoperable.

“What it provides — unlike any conventional helicopter out there today — is the ability to give the pilot some torque authority to get down safely,” said Sinusas.

The next driver was reduced operating cost, and while Bell is not currently sharing any figures, Sinusas said removing conventional components such as lubricated gearboxes and greased bearings, and moving to a more simplified electrical system, should help keep those costs down.

Thirdly, the design promises a reduction in noise levels.

“[Noise] hasn’t really been a top priority for helicopter industry for quite a while, but it’s quickly becoming a very important parameter,” said Sinusas.

The visual impact of the system is a blend of the familiar and the strange. It’s not as radical an anti-torque rethink as the tailboom fan-driven system proposed in Bell’s FCX-1 concept helicopter two years ago, or even MD’s NOTAR, which does away with the need for any type of tail rotor, but the sight of four smaller tail rotors instead of one may take a little getting used to.

And while the shrouding around the rotors certainly looks heftier than the simple vertical fin of a traditional tail rotor, Bell says the footprint is similar to that of shrouded tail rotors produced by other manufacturers (think the Fenestron on Airbus’s H145).

Sinusas said the focus of the program to date has been proof of concept rather than optimizing its performance, and the team is not working to a timeline for commercialization — at least not one that Bell is prepared to publicly disclose.

Both retrofit to existing products and incorporation into clean-sheet designs “would be an option” for the product when it does hit the market, said Sinusas, and he confirmed the technology is scalable to larger and smaller aircraft.

“It’s obviously been a secret project — we haven’t been public with it until now,” he said. “So it be interesting to see what feedback we do get.”