Bell developing fan-driven electric anti-torque system

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.

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“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.

Bell Electrically Driven Anti-Torque EDAT
Bell has been flight testing its Electrically Distributed Anti-Torque system in Canada since May 2019. Bell Photo

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.

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“[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.”

19 thoughts on “Bell developing fan-driven electric anti-torque system

  1. I would like to see precision rapid rotation events. This is a very good idea and design change with lots of potential

  2. Entry level and small RC helis have been using electric motors for yaw control for as long as I can remember. Nice to see the big guys catching up.

  3. In this design, what would happen to tail rotor authority in the event of a total and complete loss of electrical power?

    1. Nothing any different than what would happen in a helo with a conventionally powered tail rotor in the event of a total and complete loss of mechanical power.

      1. isn’t the main rotor mecanically attached to the tail rotor and it would source energy from the main rotor inertia in case of autorotation?

        1. I guess it would be interesting to see how they do that, ‘cause normally you have the triple tachometer and few other electrical systems running while total electrical power loss. Anyway, I guess that an always off clutch system that engages only on power loss would make the trick.

  4. Glad to see that Bell is being innovative. Can Bell provide a percent improvement in performance, percent reduction in cost, and percent reduction of noise?

    Heliports/vertiports are essential to the use of helicopters and eVTOL aircraft. The single biggest obstacle in establishing heliports/vertiports is peoples’ objection to noise. We hope all aircraft manufacturers will make a concerted effort to reduce sound levels to the maximum extent practical. If they can reduce sound levels significantly, they will sell more aircraft.

    1. If so, first, when an emergency autorotation no ‘de torq’ needed because no main rotor powered…
      Secondly, if you has no electrical power, generally you have an emergency shed bus switch…

  5. I have TRIED a 3 tail electric rotor before and worked fine and add three other inventions to it. And greatly improved performance….

  6. i really *like* the notion that you do not need to counter torque *while sitting on ground. obviously, the design does not consider icing conditions on ground nor in the air. i understand that it is a fancy feature for future of electric driven crossovers. i also understand the benefits for autopilot enabled flight stabilisation.

  7. Tail rotor off when the main rotor is turning on the ground, such as during EMS, rescue and some tour/ski operations is a major leap in safety.

    1. Tlm is so correct about how much better safety for those around a chopper with idling engines and rotating rotor this potentially will be.

      Every year people get killed by tail rotors, and it doesn’t need to be big choppers, either!

      I have seen many almost fatal incidents as a heliguard onboard rigs and platforms. Take away the rotor and a lot is gained.

  8. EDAT has fixed pitch fans with variable speed. As the speed of helicopter increases, the vertical stabilizer will become more effective and reduce the anti-torque requirement. At some speed the vertical stabilizer becomes so effective that there will no requirement for the fans to produce the thrust. Once the fans are unloaded, with the fixed pitch fans/ variable speed, how its going to have the directional control, unless the fans can reverse the direction of rotation?

  9. If the tail blades don’t spin on the ground, then the second the heli lifts the skids it will spin like a frisbee until the anti torque fans get to speed, hense they will/must spin before liftoff.

    It’s a solution in search of a problem. Counter rotating mains, in addition to being able to fit in smaller spaces, is a much better solution than an over engineering, increasing power consumption, and unnecessary additional weight, not to mention the build and repair costs.

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